coordination in animal (i) nervous coordinationmlwk/al_powerpoint_public/al... · web viewf stimuli...

Animal Coordination (I) Nervous Coordination P.1

Coordination in Animal (I) Nervous Coordination

he ability to respond to changes in the environment, known as irritability or sensitivity, is a characteristic of all living organisms.T

Irritability in plants is less easy to demonstrate. The generally faster responses of animals reflect the need to move about seeking f____. Moving through the environment necessitates a system for the rapid co-_________ of movements, as well as a means of det_______ and res_______ to the changes that the animal will be subjected to as a result of its movement.

Animals are able to respond to changes in their in_______ environment (inside their bodies) as well as changes in the ex_______ environment. Such responses form an integral part of hom_________.

Any change in the environment that evokes a response on the part of an organism is called a st______. Light, gravity, temperature, pressure, and various chemical substances are the main types of stimulus to which organisms respond. In order to respond to a stimulus an organism must possess:

R_________ to detect the stimulus, e.g. eyes, muscle stretch receptors, E_________ to bring about the response, e.g. muscles, glands, a c___________ system- to link together receptors and effectors.

Q. Label the diagram with the following: Synapse, CNS, Peripheral nerves, Environmental change, Sensory neurons, Association neurones (s), Motor neurone, Negative feedback, Response

A schematic diagram showing the general working principle of the nervous system

In animals co-ordination is brought about by the ne_____ system, or by chemical messengers called h________, or both

The nervous system does not simply provide a pathway for the passage of information from the receptors to the effectors. It also f_____ out non-essential information, draws together / int______ information from different receptors, make dec______ and puts into effect the appropriate response, and in more advanced nervous systems, stores in_________ and retrieves this stored information when required to play a part in the 'decision making' process.

The main parts of the vertebrate nervous system are as follows: The c________ nervous system (CNS)- comprising the brain and spinal cord; P__________ nerves are cable-like structures that l____ the CNS to all parts of the body.

Receptor

Effector


I) Neurones

Nervous system is composed of n_______; cells specialised to convey information. The three basic types of neurones:

Sensory or afferent neurones convey impulses from r________ to the central nervous system; Motor or efferent neurones convey information from the CNS to e________; Association neurones form part of the CNS and l_____ sensory and motor neurones.

The nucleus is contained in the cell body or s____. A number of thin cytoplasmic fibres extend out from the soma. Two types of fibre may be distinguished, a____ and den_____.

Axons are usually long (in large animals they may be several metre long), and rarely branched, except at their termination. They carry impulses a from cell bodies

Dendrites are shorter (they rarely exceed 1mm) and much-branched. They carry impulses to cell bodies

The soma is concerned with controlling and maintaining the cell and its meta_______,

Many hundreds, or even thousands, of axons together are surrounded by a common connective tissue sheath to form a n . Nerves themselves do not contain cell bodies; these are restricted to the CNS and to swellings of nerves called gan____.

Some neurones are surrounded by S cells which form sheath-like wrappings called m sheath around axons.

The sheath wrapped around the axon so tightly that there is little or no cytoplasm found between the layers of membrane—so the m____ sheath becomes effectively layers of li___ wrapping around the a___.

A single Schwann cell forms the wrapping for up to 2mm of axon. The gap between adjacent Schwann cells, where the axon is exposed, is called the n of R . The myelin sheath increases the s of nerve impulse conduction; it may also act as an i n layer .

nerve fibre

nucleus of Schwann cell

myelin sheath - Folds of Schwann cell cell membrane wrapping a nerve fibre


Structure of a Neurone

Three Types of neurons

Complete the table to distinguish the three basic types of neuronsSensory neurone Interneurone /

Association neuroneMotor neurone

Connection

Function

Position of soma / cell body

A NERVE IS A BUNDLE OF NERVE FIBRES THE CELL BODY / SOMA OF A NEURONE


II) Membrane Potentials

The conduction of a nerve impulse along a neurone is accompanied by chem and el________ changes at the neurone m . When at rest, that is not conducting a nerve impulse, the neurone membrane is pol______; the outside is positively charged and the inside is n charged.

This polarisation creates a p__________ difference across the membrane. This varies in magnitude between 30 and 100 millivolts (mV) according to the type of neurone, and to the species. Because this potential difference is characteristic of the nerve at rest it is known as the r potential.

Membrane potentials are not restricted to neurones. Most cells (including plants) maintain a membrane potential of about 10 mV. In sensory cells, neurones and muscle cells this value ch______ with the activity of the cells and hence they are known as ex cit_____ cells . #All living cells show a similar potential difference across the membrane, known as the membrane potential, but in these cells this is constant and so they are known as non-excitable cells.

A) RESTING MEMBRANE POTENTIAL

The axoplasm inside the axon has a high concentration of p (K + ) ions and a low concentration of s (Na + ) ions , in contrast to the fluid outside the axon which has a low concentration of K+ ions and a high concentration of Na+ ions.

Ion Extracellular concentration Intracellular concentration

K+ 20 400Na+ 460 50

A- (Organic anions) 0 370Ionic concentrations of extracellular and intracellular fluids in squid axon. (in mmol kg-1

H2O)

These electrochemical gr are maintained by the a transport of ions against their


electrochemical gradients by c______ pumps.

These constantly active carrier mechanisms (cation pumps) are driven by energy supplied by and couple the removal of Na + ions from the axon with the uptake of K + ions .

The active movement of these ions is opposed by the passive d (facilitated) of the ions.

These ions constantly pass down their e______________ gradients at a rate determined by the p er of the axon membrane to the ion.

K + ions have an ionic mobility and membrane permeability which is 20X greater than that of Na+

ions, therefore K+ l_____ from the axon is greater than Na+ g ain .

This leads to a net loss of ____ ions from the axon, and the production of a n charge within the axon. The value of the resting potential is largely determined by the K+ electro___________ g________.

The resting potential is maintained by :

the differential concentration and mobility of ions across the axon membrane,

the selective permeability of the membrane to the ions

and the action of a cation pump.

Subsequent changes in the permeability of the membrane of excitable cells to K+ and Na+ ions lead to changes in the potential difference across the membrane and the formation of an a______ potential in the axon.


B) ACTION POTENTIAL

The experimental stimulation of an axon by an electrical impulse, results in a change in the potential across the axon membrane from a negative inside value of about -70 mV to a p inside value of about +40 mV.

This pol change is called an action potential or spike and appears on the cathode ray oscilloscope.

An action potential is generated by a sudden momentary increase in the p_________ of the axon membrane to Na + ions .

The increase in sodium conductance causes sudden inf of Na + & increases the number of positive ions inside the axon and reduces the membrane potential from its resting value of -70 mV to +40 mV. The change in membrane potential is called de .

Sodium conductance and depolarisation influence each other by p feedback, that is an increase in one factor reinforces an increase in the other, and this produces the steep r______ phase of the action potential.

At the peak of the action potential, sodium conductance declines and about 0.5 ms after the initial depolarisation, potassium con increases and K+ ions d______ out of the axon.

As K + ions diffuse outwards the internal positive charge is replaced by a negative charge. This re_____________ of the membrane is shown by the fa____ phase of the action potential 'spike' and results in the membrane potential resuming its original level.


From the above account it can be seen that whilst the resting potential is determined largely by free diffusion of _____________ ions, the action potential is determined largely by the momentary influx of ___________ ions into the axon.


Fig. Diagrams to show the relationships between (a) the membrane potential, (b) ionic conductance and (c) the potential distribution across the axon membrane during production of an action potential

Q. Give two reasons why there is a sudden influx of Na+ ions into the axon following an increase in Na+ permeability of the axon membrane.

Q. lf the permeability of the axon membrane to Na+ ions and K+ ions increased simul-taneously what effect would this have on the action potential?

The graph below shows the effect of Na+ ions on the production of action potentials in squid axons.

Intracellular microelectrodes recorded action potentials from axons bathed in different concentrations of isotonic sea water. The results are shown in the figure.

Q. Which action potentials correspond with axons placed in normal sea water, one-half sea water and one-third sea water?

Q. Explain the effect of these solutions on the action potentials.

C) FEATURES OF ACTION POTENTIAL

a) Stimulus strength and nerve impulse conduction ( All-or Nothing response )

a. Do stimulus voltages 1 and 2 elicit an action potential ? Explain the response shown.

b. How is the response to stimulus 3 different from that to stimulus 2 ?

c. What is the difference in the responses to 4, 5, 6 compared with the response to 3 ?

d. On the basis of the evidence shown here, formulate a statement about the response of an axon to gradually increasing strengths of stimulus.

ALL-or-Nothing response :

Below a certain strength, called the th level, a stimulus will not produce an action potential. Above the threshold level the mag______ (voltage) of the action potential is independent of stimulus


strength, i.e. double or triple the threshold level of stimulus will elicit an action potential the s_____ size as that from the threshold level.

Because the stimulus either causes a f___ strength action potential or n____ at all, the action potential is described as an a -or-n response.

b) Transmission of nerve impulses along the nerve fibre

A nerve impulse passes along an axon as a w of de accompanied by a wave of neg along the surface of the axon.

Action potentials are prop , that is s___-generated, along the axon by the effects of ions entering the axon.

This creates an area of positive charge and a flow of current is set up in a l circuit between this dep____ area and the pol_____ resting region immediately ahead.

The current flow in the local circuit re_____ the membrane potential in the resting region and this depolarisation produces an increase in sodium p and the development of an all-or-nothing a potential in this region.

Action potentials are propagated along the axon without change in am______ and are capable of being transmitted over an infinite distance, that is, they are non-decrem________. The reason for this is that the production of an action potential at each point along the axon is a self-generating event resulting from a change in the local con________ of ions.

c) Speed of conduction

Q. Transmission speeds vary from one nerve fibre to another. Study the figure below:

a. What effect does an increase in axon diameter have on speed of conduction?

b. For cat fibres of fairly similar diameter, which conduct most rapidly, myelinated or unmyelinated fibres?

c. Suggest a reason why a conduction velocity of at least 10ms-1 can occur in a frog nerve fibre of 6.5 m diameter, whilst a squid fibre conducting at the same rate has a diameter of 250 m.

d. Suggest a reason, connected with the animal's physiology, for the differences in conduction speeds of myelinated fibres of frog and cat.

In non-myelinated axons, typical in invertebrates, the velocity of the propagated action potential is related to the d of the axon. The smaller the diameter the greater the res________. In the case of fine axons (< 0.1 mm) the high resistance of the axoplasm has an effect on the spread of current and reduces the length of the local circuits so that only the region of the membrane immediately in front of the action potential is involved in the local circuit. These axons conduct impulses at about 0.5 m s-1. Gi____ axons, typical of many annelids, arthropods and molluscs, have a diameter of approximately 1mm and conduct impulses at velocities up to 100 ms-1, which are ideal for conducting information vital for sur______.


Q. Explain, in terms of the resistance of the axoplasm and local circuits, why giant axons conduct impulses at greater velocities than fine axons.

In vertebrates, the majority of neurones have an outer covering of m____ derived from the spirally wound S______ cell. Myelin is a fatty material with a high electrical resistance and acts as an electrical in________ in the same way as the plastic covering of electrical wiring.

The resistance of the myelin sheath is very high but where breaks in the myelin sheath occur, as at the nodes of R , the resistance between the axoplasm and the extracellular fluid is l_____.

It is only at these points that l c are set up and current flows across the axon membrane generating the next action potential. This means, in effect, that the action potential 'j ' from node to nod e ( ~ 1mm apart ) and passes along the myelinated axon faster than the series of smaller local currents in a non-myelinated axon. This type of conduction is called sal_______ and can lead to conduction velocities of up to 120 ms-1 .

Q. How do the structural features of neurones affect the conduction speed of a nerve impulse.

Tem__________ has an effect on the rate of conduction of nerve impulses and as temperature rises to about 40 °C the rate of conduction increases.

Reference Reading : Multiple sclerosis

In a disease called Multiple sclerosis (MS), gradual degradation of the myelin sheath takes place leaving areas of bare, demyelinated axons which cannot conduct impulses. MS attacks the nerves of the CNS, peripheral nerves are unaffected.

The most commonly affected areas include the optic nerve, cerebellum and cervical spinal cord. The symptoms include weakness of the limbs, ‘pin and needle’ and numbness, damage to the optic nerve can lead to blurring of vision and pain in the eyes.

At present there is no cure for MS, treatment is mainly supportive in the form of pain-killers and physiotherapy. MS is one of the most common diseases of the CNS in Europe and yet the cause is still unknown, it is uncommon in tropical countries. About 1 in 10 MS suffers end up in a wheelchair.

d) Coding of nervous information


Nerve impulses pass through the nervous system as propagated, all-or-nothing action potentials with a fi amplitude.

Information cannot therefore be passed as an amplitude code and is passed instead as a fre________ code.

The frequency of nerve impulses is directly related to the st of the stimulus giving rise to the impulses.

Fig. Impulses recorded from a pressure receptor on the human hand. A rod of one mm diameter was pressed onto the skin with the force indicated on each record

III) SYNAPTIC TRANSMISSION- COMMUNICATION % NEURONES

The point where one neurone makes contact with another is called a sy . Actually, the cells do not actually meet, a narrow gap, the synaptic c , separates the two membranes. N euromus cular junction is a special form of synapse between a neurone and a m_____.

Reference: Electrical transmission The depolarisation arriving at the synapse depolarises the post synaptic membrane and in so doing triggers an action potential in the post synaptic neurone. This occurs at special synapses, called tight junctions because the synaptic cleft is extremely narrow, usually less than 10 nm across. Such junctions occur in coelenterate nerve nets, and in parts of the CNS of more advanced animals, including vertebrates.

A) STRUCTURE OF THE CHEMICAL SYNAPSES

They consist of a bulbous expansion of a nerve term called a synaptic k lying closely to the membrane of a dendrite of the next nerve cell.

The cytoplasm of the synaptic knob contains m__________ , smooth endoplasmic r________ and numerous synaptic v .

The membrane of the synaptic knob forms the p___________ membrane; that of the dendrite is the p membrane. These are separated by a gap, the synaptic c , of 20 nm.

Postsynaptic membrane contains re sites for the transmitter substances and numerous ch , normally closed, for the movement of ions into the postsynaptic neurones.

Synaptic vesicles hold t substances #

In the synaptic knob transmitter substance is 'packaged' into ve____ and waiting for release.

The two main transmitter substances are ac (ACh) and nor . Neurones releasing acetylcholine are _______nergic neurones and those releasing noradrenaline are called adren_______ neurones.


An average motor neurone may have as many as 15 000 synapses

B) MECHANISMS OF SYNAPTIC TRANSMISSION

The possible events that occur after an electrical impulse reaches the synaptic knob.1 Arrival of the nerve impulse at the synaptic knob causes de_________ of the pre-synaptic

membrane. This opens Ca2+ ch_____ in the pre-synaptic membrane; Ca2+ flows into the terminal.

2 Brief increase in Ca2+ levels leads to f_____ of synaptic v______ with the p__-synaptic membrane.

3 Transmitter substance, such as acetylcholine (about 1000 molecules per vesicle), is released from vesicles by ex_______, diffuses across the synaptic cl___ and binds to the special re_____, a membrane protein found on the p___-synaptic membrane.

4 Conformational change of the receptor protein causes the opening of i__ ch_____ in the post-synaptic membrane.

5 This channel is open for about one ms and allows flow of i___ down the concentration g_______.

6 This ion flow results in changes in the membrane p_______ (either depolarize or hyperpolarize). The voltage change may last for up to 5ms. The voltage change is known as a Post-synaptic P______. It may trigger the passage of an im______ in the post-s_______ fibre.

7 The transmitter substance, ac________, is very rapidly broken down by the enzyme ____________sterase, situated on the p____-synaptic membrane, and reabsorbed into the synaptic knob to be recycled into acetylcholine by in the vesicles.


a) Excitatory and Inhibitory Synapses :

At Excitatory synapses, i -specific channels open up allowing + ions to enter and + ions to leave down their respective concentration gradients. This leads to a partial d in the postsynaptic membrane. The depolarising response is known as an E postsynaptic potential (EPSP). The amplitude of EPSPs changes in steps, suggesting that transmitter substance is released in 'packets' rather than individual molecules. Each 'step' is thought to correspond to the release of certain amount of transmitter substance from one synaptic vesicle.

At Inhibitory synapses the release of transmitter substance increases the permeability of the postsynaptic membrane by opening up ion-specific channels to + ions .

As the ions move down their concentration gradients they produce a h polarisation of the membrane known as an inhibitory postsynaptic potential (IPSP).

# Transmitter substances are neither inherently excitatory nor inhibitory. For example, acetylcholine has an excitatory effect at most neuromuscular junctions and synapses, but has an inhibitory effect on neuromuscular junctions in cardiac muscle and visceral muscle.

It seems that it is the molecular properties of the re________ that determine which ions enter the postsynaptic cell, which in turn determines the corresponding changes in postsynaptic potentials.

Q. Action potentials are ‘ALL or nothing event’, whereas EPSP is not--it is graded in amplitude. Explain this in terms of the difference in properties of ‘the ion channels’ between the axon membrane and postsynaptic membrane.


Refererce only : How Practice and Learning work?

Summation at synapses

A single EPSP is normally unable to produce sufficient depolarisation to reach the threshold required to propagate an action potential in the postsynaptic neurones. The depolarising effect of the EPSPs is additive, a phenomenon known as summation.

Temporal summation (in time) occurs when action potentials arrive at the same synapse in close enough succession to ensure that the depolarising effects of the preceding action potentials have not worn off. The EPSP can thus be built up to the level where it initiates an action potential. In such cases a nerve impulse will only be generated in the post synaptic neurone if the stimulus which initiated the nerve impulse is strong enough to produce a fairly high frequency of action potentials.

Spatial summation (in space) occurs when action potentials arriving at separate synapses on the same post synaptic neurone at the same time, release enough transmitter to initiate an action potential.

Most neurones receive both stimulatory & inhibitory inputs from thousands of other neurons. It seems that not only EPSPs & IPSPs summate, but also EPSPs summate with IPSPs. If the stimulatory effect of EPSPs dominate the membrane potential enough to reach the threshold, the neurone will fire, and vice versa.

Facilitation

Even, partially depolarized neurone are facilitated, that is, more easily excited by successive depolarization events, because they are already nearer to the threshold. A synapse is said to be facilitated when the arrival of one action potential, while not itself triggering an impulse, leaves a residual effect which makes it easier for subsequent action potentials to initiate an action potential in the post synaptic cell.

E) Neuromuscular junction

The neuromuscular junction is a specialised form of synapse found between the nerve terminals of a motor neurones and the muscle fibres.

Each muscle fibre has a specialised region, the motor e -p , where the axon of the motor neurones divides and forms non-my branches on the sar

The sarcolemma, has many deep folds called junctional folds.

The cytoplasm of the motor neurones axon terminal on stimulation releases ac .

Changes in the structure of receptor sites on the sarcolemma increase the pe of the sarcolemma to Na+ and K+ ions and a local de___________ known as e -p p (EPP) is produced.

A sufficiently large EPP would lead to a propagated a potential spreading along the sarcolemma and down into the fibre via the membranous __-system. This results in the initiation of muscular con .


Q. What’s the significance of the junctional fold ?

Q. Why should the motor nerves form non-myelinated branches ?

Q. What is the importance of the T system in the initiation of muscular contraction ?

F) Functions of synapses and neuromuscular junctions

The primary function of neuronal synapses and neuromuscular junctions within the vertebrate nervous system is the transmission of information between receptor and effector. Several other significant functional features arise out of the structure and organisation of these sites of chemical secretion.

Unidirectionality The release of transmitter substance at the presynaptic membrane, and the location of receptor sites on the postsynaptic membrane, ensure that nerve impulses pass in one____ direction along a given pathway. This gives precision to the nervous system.

Adaptation or accommodation The amount of transmitter substance released by a synapse steadily f___ off in response to constant stimulation until the supply of transmitter substance is ex and the synapse is described as fatigued. Further information passing along this pathway is inhibited and the ad_____ significance of fatigue is the prevention of damage to an effector due to overstimulation. Adaptation in sensory neurone f____ off background stimulus that are not ch______ and allow the brain to fo___ on more information more important for survival; similar adaptation also occurs at the level of the receptor.

Integration A post_______ neurones may receive impulses from a large number of ex__________ and in_________ presynaptic neurones. This is known as synaptic con ______ and the postsynaptic neurones is able to summate the stimuli from all the presynaptic neurones.

This spatial summation enables int_________ of stimuli from a variety of sources and the production of a co-ordinated response. Facilitation occurs at some synapses and this involves each stimulus leaving the synapse more resp______ to the next stimulus.


Discrimination Temporal summation at synapses enables weak background stimuli to be filtered out before it reaches the brain. For example, information from receptors in the skin, the eyes and ears receive constant stimuli from the environment which has little immediate importance. Only changes in intensity of stimuli are significant to the nervous system and these increase the frequency of stimuli and pass across the synapse and evoke a response.

Reference Reading: The effect of drugs and poisons on synaptic transmission

Many drugs and poisons exert their effects by interfering with the mechanism of synaptic transmission. There are several different ways in which they can do this.

1. By preventing the release of transmitter substance. Botulinum toxin produced by the bacterium Clostridium botulinum, the causative agent of a mercifully rare form of food poisoning, produces paralysis by preventing the release of acetylcholine from the pre-synaptic terminals of motor neurones. This toxin is one of the most poisonous substances known to man. It has been calculated that 250 g would be sufficient to wipe out the entire world population.

2. By preventing the transmitter from combining with the receptor. Curare, it is the poison used by South American Indians on their arrow tips. Curare is obtained from the skin of the some of the most colourful rainforest frog. As the combination of curare and receptor does not lead to the setting up of an end-plate potential, muscle paralysis results.

3. By inactivating the enzyme that breaks down the transmitter. A number of organophosphorus compounds, originally developed as nerve gases for use in wartime and now used as insecticides, inactivate the enzyme that breaks down acetylcholine (acetylcholinesterase). Such substances greatly prolong the end-plate potential and may initiate a series of action potentials in muscle fibres which give rise to uncontrollable muscle spasms.

There are many different neurotransmitters responsible for information exchange across synapses. Most of the psychoactive drugs available in society today, such as ecstasy ( ), cannabis ( ) and cocaine ( ), cause their effects by interfering with the synaptic transmission of one of these-messengers. Those drugs which amplify the process of synaptic transmission are called excitatory or agonistic drugs, -whlist those which inhibit synaptic transmission are known as inhibitory or antagonistic drugs.

Narcotics such as heroin ( ) and morphine ( ) mimic the actions of the neurotransmitters known as endorphins, binding to their specific receptors and blocking sensations of pain. Nicotine similarly mimics natural transmitters.

The presence of caffeine in the body raises cell metabolism leading to the release of more neurotransmitters. Amphetamines cause increased release of noradrenaline by interfering with storage mechanisms. This leads to excessive activation of neurones and extra information is transmitted around the brain. A user will feel highly aroused but may also suffer damage to organs including the heart.

Some drugs affect the body by interacting with natural neurotransmitters. The benzodiazepine tranquillizers, such as Valium ( ), increase the effect of the inhibitory transmitter GABA in the brain resulting in less transfer of information between neurones. In contrast phencyclidine, the active -. ingredient in magic mushrooms, interacts with excitatory transmitters in the brain and inappropriate information is passed between neurones leading to hallucinations.

It is important to remember that neurotransmitters are rapidly absorbed or broken down. Cocaine causes noradrenaline to 'linger' in the synapse producing effects similar to those from amphetamines:

Table of chemical substances affecting the synapse and neuromuscular junction in mammalsSubstance Site of action Function

tetanus toxin presynaptic membrane

prevents release of inhibiting transmitter substance

botulinum toxin presynaptic membrane

prevents release of acetylcholine

organophosphorus weedkillers and insecticides (and nerve gas used in chemical warfare)

postsynaptic membrane

inactivates acetylcholinesterase and blocks action of acetylcholine prevents breakdown of acetylcholine

curare (poison used in arrow of South American tribes)

postsynaptic membrane

chemically resemble acetylcholine, it competes with the transmitter for the receptor sites at neuromuscular junctions


IV) NERVE PATHWAYS

Most behaviour is brought about by the passage of im______ from receptors to the CNS, and then from the CNS to an effector. The number of neurones in such a pathway varies enormously according to the number of receptors and effectors engaged in the response, and to the degree of difficulty involved in deciding the appropriate response. Where the so-called 'higher' or 'decision-making' centres of the brain are involved, the pathway tends to become very complex, and may involve many tens of thousands of neurones.

The simplest pathways are those involved in simple r_____ actions. A reflex is defined as an unl______, aut______ response to a stimulus. Examples include the es_____ responses of many invertebrates, and in man, the knee j___, the with_______ of the hand or foot from a painful stimulus (the flexion reflex), and the control of h_____ beat and br_______ rate.

A) PLAN OF A REFLEX ARC

The nerve pathway responsible for bringing about a reflex action is called a reflex a__. At its simplest, the reflex arc involves only two neurones a s______ neurone and a m_____ neurone which make synaptic contact in the CNS. Nerve impulses triggered by the stimulus pass along the sensory neurone and then along the motor neurone to the ef______ that brings about the response.

More common is the reflex arc consisting of three neurones, with an as_______ neurone / interneurone between the sensory and motor neurone. eg. withdrawal of hand from a painful stimulus.

Reflex actions perform a very important function, in that they provide a means of carrying out vital p_________ and hom________ reactions au___________, without involving the h_____, 'decision-making' centres; in so doing, they give in______ responses and also f___ these centres to deal with more complex problems.

Neurones in reflex arcs synapse with longitudinally-running neurons which pass to the brain:


Impulses pass to the c cortex resulting in s in the finger (by which time the hand is already being withdrawn due to the impulses conducted via the sh reflex arc).

It is also possible to repress this reflex by an exertion of w power . E.g. It is possible to touch and hold something very hot. This indicates that the motor neurone involved can receive impulses from the brain which over the reflex impulses.

The fibres that connect the different areas of the cord with one another, and with the brain, run in as_________ and des________ tracts located in the w_____ matter of the nerve cord.

More complex reflexes, such as the one controlling breathing rate, require more complex circuitry, involving several receptors and effectors, whose activities are generally co-ordinated by special centres in the b .

Some examples of cranial and spinal reflexesType of reflex

Nature of reflex Reflex center

Physiological significance

Sucking reflex

Sucking action of mouth when lips of young babies come in contact with objects

Brain(medulla)

S_____ milk from mother's breasts

Salivation reflex

Production of saliva with stimulation of food- smell, taste, etc

Brain(medulla)

Facilitating d______ and s________ of food

Peristaltic reflex

Peristalsis of gut when the gut is distended

Brain(medulla)

Facilitating d______, absorption and e______

Cornea reflex

Closing of eyelids when the cornea is stimulated

Brain(medulla)

Protecting the e____ from injury

Breathing reflex

Regulate rate of inspiration and expiration

Brain(medulla)

Adapting g___ exchange to body need


Heartbeat reflex

Regulate rate of heart beating Brain(medulla)

Adapting r____ of blood flow to body need

Vascular reflex

Constriction and dilation of arterioles Brain(medulla)

Maintaining normal blood p________

Withdrawal reflex

Withdrawal of arms or legs when prickled by sharp objects

Spinal cord

P__________ the hands and feet from mechanical injury

Bladder reflex

Relaxation of bladder sphincters when the urinary bladder is distended (babies)

Spinal cord

Removal of u_____

Anal reflex ex

Relaxation of anal sphincters when the rectum is distended (babies)

Spinal cord

Removal of f_______

Ejaculation reflex

Ejaculation of semen when sexually stimulated

Spinal cord

Essential process of r___________

Knee jerk reflex

Kicking up of the leg when the tendon below the patella is tapped

Spinal cord

Part of a st_____ reflex of skeletal muscle in the maintenance of p_____and b_______

Postural reflex

Contraction of appropriate skeletal muscles

Spinal cord

Preventing from toppling down and to maintain a bal______ p_______

B) CONDITIONED REFLEX

Pavlov in 1910 demonstrated another kind of reflex in mammals, the con________ reflex. He noticed that hungry dogs salivate( ) when presented with food( ), this being an innate reflex.

He then observed that dogs salivate when exposed to a secondary stimulus, a ringing bell( ), at the same time as the primary stimulus, food.

Pavlov discovered that in time the dogs learned to associate the ringing bell( ) with food and salivated( ) when a bell was rung even though food( ) was not present.

Pavlov's classical experiments on conditioned reflex

Step 1Food in mouth(unconditioned stimulus)

Salivation(unconditioned response)

Step 2Food in mouth(unconditioned stimulus)

+Ringing of bell(conditioned stimulus)

Salivation (unconditioned response)

Step 3Ringing of bell(conditioned stimulus)

Salivation(conditioned response)

A conditioned reflex is acquired through:

the rep_____ pairing of an unrelated stimulus (conditioned stimulus-CS) with a natural stimulus (unconditioned stimulus-UCS) that elicits an automatic response(unconditioned response-UCR).

In time, the animal became conditioned, that is, an association has been made between CS and Salivation(UCR).

When the animal is presented with CS only, it responds to give an conditioned response-CR It is a kind of reflex behaviour that can be a_______ / l_______.

Q.Conditioning is also common in animal behaviour. Birds learn to avoid eating certain insects that are distasteful. These insects advertise their distastefulness with certain colored markings to prevent being eaten by birds. There are some other insects which are not distasteful but evolved to take advantage of this by mimicry.


Complete the table below to explain about how insects employ mimicry to avoid being eaten by birds.

Step 1 Sight of warning markings( )

Avoid eating( )

Step 2( )

+( ) ( )

Step 3( ) ( )

If the conditioned stimulus is presented repeatedly without the unconditioned stimulus, the conditioned reflex eventually dies out. This process is called extin_____. However, if the conditioned reflex is reinforced from time to time by p____ the conditioned and unconditioned stimuli, the conditioned reflex persists indefinitely.

Q. What would happen if the not-distasteful species outcompete the distasteful species?

The essential feature of the conditioned reflex is the formation of a new functional connection in the brain. In Pavlov's experiment, for example, salivation in response to bell ringing, indicates that a fun______ con______ has been developed between au______ pathways and auto_____ centres controlling salivation. In other words, the dog had l_____ that it would be fed when the bell was rung.

Learning is an ad______ behaviour in response to a certain stimulus. The initial learning and development of a skill depends upon vol______ actions. But once the skill is adapted, it becomes a conditioned reflex. Examples include toilet training, walking, cycling, etc.

Thus conditioned reflexes form the basis of learning. Much of the behaviour of animals and humans is due to conditioned reflexes. The building up of proper conditioned reflexes is of utmost importance in the training of c_______. Conditioned reflexes are similar to simple (unconditioned) reflexes in that both are im______ responses to appropriate stimuli without involvement of the de_____- making processes of the cerebral cortex. However, removal of the cerebral cortex was known to cause loss of conditioned response.

Comparison between simple reflex, conditioned reflex and voluntary action

Simple reflex Conditioned reflex Voluntary action

Innate, instinctive behaviour

Ac_____ through learning process Acquired through l______ process

Number limited / innate Number in_________ with learning Number increasing with learning

Controlled by the medulla or spinal cord

Establishment requiring the cerebral cortex

Controlled by cerebral cortex

Response stopsimmediately after theremoval of stimulus

Response dim_____ / extincts after repeated application of conditioned stimulus without unconditioned stimulus

No definite asso_______ between stimulus and response

Response relatively constant or invariable(same stimulus triggers same response)

Response highly var_____, reinf_____ by repeated pairing of con_____ stimuli and uncon______ stimuli

Highly var_____, dec____ making depends on individual pref_______

Adaptability limited Adaptability prec___ and perfect Adaptable to most com___ situations through think___ and dec___ mak___

Homework : Look carefully into television advertisement tonight. Note how many describe the true nature of the product to be sold and how many associate it with something attractive but possibly quite unrelated to the product?


V) Organization of the Mammalian Nervous System

There are two principal divisions of the nervous system the cent___ nervous system, comprising the brain and spinal cord, and the peri______ nervous system, comprising the cr____ and sp___ nerves.

A) THE PERIPHERAL NERVOUS SYSTEM

a) The Spinal NervesIn man there are thirty one pairs of spinal nerves, one pair per body segment. They carry fibres to and from a__ parts of the body, except for the head which is innervated by the c_____ nerves. Each nerve has two separate connections with the spinal cord, a d and a v root. The dorsal root carries s fibres, while the ventral root carries motor fibres. The roots unite to form the spinal nerve which is a m nerve, carrying both sensory and motor fibres.

b) The Cranial NervesThere are twelve pairs of cranial nerves in man. They arise from the ventral surface of the brain, and pass to various receptors and effectors in the head, except for the vagus, the wandering nerve, which gives off branches to the heart and gut. Some cranial nerves are mixed, while others are either sensory or motor.

B) THE VISCERAL AND SOMATIC DIVISIONS OF THE PNS

The peripheral nervous system is divided into two functionally distinct parts, the som system and the vis system. The former is chiefly concerned with detecting and responding to ext____ stimuli, while the latter is concerned with detecting and responding to int____ stimuli.

Some of the visceral system's receptors are located in the brain, for example, the chemo_______


involved in breathing control. Effectors innervated by the visceral system are not generally under con_____ control , unlike the effectors of the somatic system. Some visceral reflexes are mediated by the spinal cord alone, but the majority are controlled by centres in the me and hy________.The entire visceral system is sometimes called the au system.

C) THE AUTONOMIC NERVOUS SYSTEM

Autonomic means 'self-governing': this refers to the n feedback control mechanisms which govern in_________ control of internal body organs

The autonomic nervous system is involved in such vital r as the control of heart rate and blood pr_______, the per_______ movements of the gut, and the secretion of sw___ and sal___.

The autonomic system has two sub-divisions, the sy division and the p sympathetic division. In both systems, impulses pass from the CNS to effectors via two m____ neurones .

The two divisions differ in the transmitter substance they release from their synaptic terminals; sympathetic neurones are adrenergic while parasympathetic neurones are chol_______.They also differ in the position of the ganglia where the two motor neurones synapse. The parasympathetic ganglia are situated on, or very near, the effectors so that the post-ganglionic fibres are very sh___, whereas the sympathetic ganglia lie close to spinal cord so that the post-ganglionic fibres are relatively l____.

The sympathetic division of the ANS has a more widespread effect than the parasympathetic division because a single sympathetic preganglionic neuron synapses with 20 or more postganglionic neurons whereas the preganglionic neuron in parasympathetic synapses with just around five postganglionic neurons.


The two divisions have an__________ or opposite effects. So that, while one nerve stimulates a particular organ, the other inhibits it.

In general, the sympathetic system tends prepares the body for action (f_____-or-f______ response)

Parasympathetic division generally c____ the body, increases digestive activity.

Autonomic regulation involves constant interplay of balance between s__________ and p____________ activities.

The brains___ and the hypo_______are the locations of major centres for autonomic activities

Antagonistic effects of Sympathetic and Parasympathetic system

Sympathetic Parasympathetic

dilates pupil constricts pupil

suppresses secretion of salivary gland

stimulates secretion of salivary gland

dilates bronchioles constricts bronchioles

accelerates heart slows heart

constricts arteries dilates arteries

slows peristalsis accelerates peristalsis

contraction of anal and bladder sphincter muscles

relaxation of anal and bladder sphincter muscles

relaxation of blood vessels (vasodilation)

contraction of blood vessels (vasoconstriction)

Increases sweat secretioncontracts hair erector musclescauses secretion of adrenalin


D) THE CENTRAL NERVOUS SYSTEM (CNS)

The central nervous system is a co-ordinating centre. It receives impulses from all the body's re______ via sensory or afferent neurones, and sends impulses to all the ef______ via motor or efferent neurones.

The entire CNS is covered by a system of membranes, the men____ consisting of three layers. They protect the brain tissues from m_________ inj_____.

Between them is a space packed with a network of fibrous tissue and is filled with c_____-s____ fluid, and serves a cush_____, pro______ function, as well as nou_____ the underlying nervous tissue.

a) The spinal cord

The spinal cord stretches from the base of the brain to the end of the backbone. It is enclosed and protected by the ver______. The nerve cord is composed of w____ and g____ matter. The grey matter contains cell b____ and nonmy______ fibres. The white matter owes its lighter colour to the fatty white sheaths of my_______ fibres.

The spinal cord has two main functions: it connects the sp____ nerves to the brain, and it is a co-_________ centre, mediating re_____ such as the knee jerk.

b) The brain

1) Anatomy of the Vertebrate Brain

The brain tissue encloses several ventricles filled with cerebro-spinal fluid. This fluid is derived from the b_____, it distributes nut and ox to the tissues of the brain and spinal cord. Ciliated cells lining the vesicles, maintain the cir________ of the fluid.

In the mammalian brain, the cer_______ is enormously expended. The outer surface of which consists of a thin layer of grey matter known as the cerebral c_____. The latter is the dominant brain area in mammals, directing and co-ordinating all vol , and some in voluntary activities . In man, the cerebral cortex is so large that it


covers many of the other brain regions.

The brain, like the spinal cord, is composed of white and grey matter.

The area of grey matter, known as centres or nuclei, comprise groups of cell b_____ making syn_____ with incoming or outgoing, fibres, and with one another.

These centres range in size from tiny clusters of cells, to the whole of the cerebral cortex, which contains some 109 cells.

The w____ matter consists of bundles or tracts of fibres that link the centres with one another, and with the body's effectors and receptors.

2) Brain Regions and their Functions in a Mammal

i) Medulla oblongata

This region connects the sp___ cord with the rest of the brain and as might be expected, contains tracts of nerve f____ passing to the brain from the nerve cord, and vice versa. It also contains the cell bodies of the last five cranial nerves, and a number of important r_____ centres. The medulla controls some basic vital functions such as regulation of h____ beat, b_____ pressure, ven_______ rate, and important reflexes such as swa______, vom____, snee_____ and cou_____.

ii) Cerebellum

The cerebellum is responsible for co__________ movement, m____ activities, learning and rem_________ of physical sk___ and for some cognitive abilities. The cerebellum controls movement by collecting sen____ nerve in___, such as l___ position, bal____ information and vi____, and synthesising them together to control movement by sending nerve transmissions down motor nerve out___.

The learning of physical tasks is done by tr___ and error and then stored into cerebellar memory. This is the reason that we never forget certain skills such as riding a bike.

The cerebellum is divided into two hemispheres. The surface of each hemisphere is made up of grey matter surrounding a large mass of white matter.

Some of symptoms associated with damage to the cerebellum or the nervous tracts leading to it are:

difficulty in coordinating movements tremors loss of balance and vertigo muscle weakness loss of coordination of the muscles

controlling speech loss of postural tone.

http://www.mult-sclerosis.org/muscleweakness.html

http://www.mult-sclerosis.org/vertigo.html

http://www.mult-sclerosis.org/intentiontremor.html

http://www.mult-sclerosis.org/whitematter.html

http://www.mult-sclerosis.org/greymatter.html

http://www.mult-sclerosis.org/greymatter.html


iii) Hypothalamus

Regulate internal state of body to maintain con______ necessary for life i.e. homeostasis. Hypothalamus involves in homeostasis in three ways:

initiate or surpress behaviours such as e_____ or dr_______ that affect internal body conditions regulates pit______ gland, exerts control over end______ system, which in turn adjusts many

internal conditions such as s___ and w____ balance in blood control of autonomic system, which influences factors such as b_____ pressure and body

t_____________.

iv)The cerebrum and the cerebral cortex

The cerebrum is the newest (evolutionarily) and largest part of the brain as a whole. It is here that things like per_______, imag_______, th______, jud_____, and de_____ occur.

The outer layer of the cerebrum, the cerebral cortex, is the centre that controls all vo , and some involuntary, activities in mammals. It receives information from all the somatic re_______, and can transmit information to all the vol______ (skeletal) muscles.

It is primarily a thin layer of g___ matter -- usually six neurons thick, in fact -- on top of a larger collection of white matter pathways. The thin layer is heavily conv______. This layer includes about 10 billion neurons, with about 50 trillion synapses!

The fibres that carry this information cr___ over, so that the left cerebral hemisphere co-ordinates the activities of the r_____ hand side of the body and vice versa.The cerebrum is divided into four areas called lobes. The furthest forward is the frontal lobe. It seems to be particularly important: This lobe is responsible for vol______ movement and planning and is thought to be the most significant lobe for pers_____ and int_________.


At the back portion of the frontal lobe is an area called the mot___ cortex. In studies with brain surgery patients, stimulating areas of the motor cortex with tiny electrical probes caused mov______. It has been possible for researchers to actually map out the motor cortex quite precisely.

Behind the frontal lobe is the parietal lobe (from a Latin word meaning wall). It includes an area called the somato_______ cortex. Again, doctors stimulating points of this area found their patients describing sen_______ of being touched at various parts of their bodies. Just like the motor cortex, the somatosensory cortex can be mapped.

At the side of the head is the temporal lobe. The special area of the temporal lobe is the aud_____ cortex. This area is intimately connected with the ears and specializes in h______.

At the back of the head is the occipital lobe. At the very back of the occipital lobe is the vi_____ cortex, which receives information from the eyes and specializes, of course, in v____. The areas of the lobes that are not specialized are called ass_______ cortex. Besides connecting the various sensory and motor cortices, this is also thought to be where our tho____ processes occur and many of our mem____ are ultimately stored.

Reference reading : The left and right Hemispheres

The Hemispheres

If you look at the brain from the top, it becomes immediately obvious that it is split in two from front to back. There are, in fact, two hemispheres, almost as if we have two brains in our heads instead of just one. These two halves are intimately linked together with an arch of white matter called the corpus callosum.

Researchers have discovered that the two halves do have some specialization. It is the left hemisphere that relates to the right side of the body (generally), and the right hemisphere that relates to the left side of the body.

Also, it is the left hemisphere that usually has language, and seems to be primarily responsible for similar systems such as math and logic.

The right hemisphere has more to do with things like spatial orientation, face recognition, and body image. It also seems to govern our ability to appreciate art and music.


Some of the most interesting work done concerning the two hemispheres was done by Roger Sperry. He worked with people who had had a pretty serious operation to control their epilepsy. It seems that, in some cases, severe epilepsy could be nearly eliminated by cutting the corpus callosum. In a sense, these people really did have two brains (or cerebrums, to be accurate)!

For example, Sperry found that if he put something in the right hand of one of these people after they had their operation, they could say what it was. But if he put it in their left hand, they could not. This is easy to understand: The feeling of the thing in the right hand goes to the left hemisphere and, since that's the side with language, the person could say what it was. The feeling of the thing in the left hand, though, went to the right hemisphere, which can't do much talking. The eyes are hooked up to the hemispheres in a somewhat complicated way: The right hand side of each retina (which sees things to the left of a focus point) goes to the right hemisphere, and the left hand side of each retina (which see things to the right) goes to the left hemisphere.

What this means is that, if you have someone stare at a focus point and briefly show them something on the left, it is the right hemisphere that receives the information. If you show them something on the right, it is the left hemisphere that receives the information.

Sperry would flash things on a projection screen and ask the patients to either say what they saw or pick what they saw with one hand or the other from a box full of things. So, if he showed a ball on the left side of the screen and a pencil on the right, the person would say "pencil" (using the left hemisphere's speech centers) but pick a ball from the box with his or her left hand (using the right hemisphere)!

There were many interesting things that came out of his research. E.g. it turns out that, though the left hemisphere has speech, it is pretty bad at drawing. The right hemisphere, controlling the left hand, could still draw quite well.

With one young woman, he flashed a picture of a naked man on the right side of the screen. She blushed and giggled, but when asked, couldn't say why. Of course, only the right hemisphere had seen the picture, and the left hemisphere had not!

Fortunately for these people, these situations don't come up much in ordinary life, so they didn't feel terribly confused most of the time. Most of us, of course, have an intact corpus callosum, and the two halves of our brains are in constant communication. Reference: www.ship.edu/~cgboeree/ genpsycerebrum.html

END

http://www.ship.edu/~cgboeree/genpsycerebrum.html

coordination in animal (i) nervous coordinationmlwk/al_powerpoint_public/al... · web viewf stimuli...

Documents