lecture 7 physiology of the nervous system
TRANSCRIPT
Physiology of the
Nervous System
Lecture No. 7
The Nervous SystemThe Nervous System
•The nervous system coordinates The nervous system coordinates all body functions, enabling a all body functions, enabling a person to adapt to changes in person to adapt to changes in internal and external environmentinternal and external environment
•The nervous system is composed The nervous system is composed mainly of the nerve cells (neurons) mainly of the nerve cells (neurons) and supporting cells (neuroglia)and supporting cells (neuroglia)
The neuronThe neuron•This is the basic This is the basic
conducting cell of the conducting cell of the nervous systemnervous system
•Highly specialized but Highly specialized but cannot reproduce itselfcannot reproduce itself
•Main parts are the cell Main parts are the cell body (soma), the fibers: body (soma), the fibers: axon and dendrites.axon and dendrites.
The neuronThe neuron•The axon is a long process with The axon is a long process with
myelin sheath. This conducts myelin sheath. This conducts impulses away from the cell impulses away from the cell bodybody
•The dendrites are short, thick, The dendrites are short, thick, diffuse branching processes that diffuse branching processes that receive impulses and conduct receive impulses and conduct them towards the cell bodythem towards the cell body
The NEURONThe NEURON• The nervous The nervous
system is system is composed of composed of neuronsneurons, which , which produce and produce and conduct conduct electrochemicaelectrochemical impulses and l impulses and supporting supporting cells, which cells, which assist the assist the functions of functions of neurons. neurons.
The neurogliaThe neuroglia
•The supporting cellsThe supporting cells
•They supply nutrients to the They supply nutrients to the neurons and help maintain the neurons and help maintain the electrical potentialelectrical potential
•They also form part of the blood-They also form part of the blood-brain barrierbrain barrier
•They are made up of macroglia, They are made up of macroglia, microglia and ependymal cellsmicroglia and ependymal cells
The neurogliaThe neuroglia
•Oligodendrocytes produce Oligodendrocytes produce myelin sheath in the CNmyelin sheath in the CN
•Scwhann cells or lemmocytes Scwhann cells or lemmocytes produce myelin sheath in the produce myelin sheath in the peripheral NSperipheral NS
The Organization of the The Organization of the Nervous Nervous SystemSystem
•The nervous system is divided The nervous system is divided functionally and structurally into functionally and structurally into 2 parts2 parts
•1. Central Nervous System- the 1. Central Nervous System- the Brain and the spinal cordBrain and the spinal cord
•2. Peripheral Nervous System- the 2. Peripheral Nervous System- the cranial nerves and spinal nervescranial nerves and spinal nerves
The Organization of the The Organization of the nervous nervous SystemSystem
•The Peripheral Nervous System is The Peripheral Nervous System is further classified into THREE further classified into THREE Functional DivisionsFunctional Divisions
•1. The Somatic Nervous System- 1. The Somatic Nervous System- controls the skeletal musclescontrols the skeletal muscles
•2. The Autonomic Nervous System- 2. The Autonomic Nervous System- controls the visceral organscontrols the visceral organs
•3. The Enteric Nervous System- 3. The Enteric Nervous System- controls the functions of the GITcontrols the functions of the GIT
The Central Nervous SystemThe Central Nervous SystemComposed of the brainComposed of the brain
•The brain consists of the gross The brain consists of the gross structures: cerebrum, cerebellum, structures: cerebrum, cerebellum, brainstem and the diencephalon.brainstem and the diencephalon.
•Diencephalon- Thalamus. Diencephalon- Thalamus. Hypothalamus and pineal bodyHypothalamus and pineal body
•Brainstem- Pons, medulla and Brainstem- Pons, medulla and MidbrainMidbrain
Brain Brain
CortexCorpus callosumSeptum pellucidum
FornixThalamusHypothalamus
Optic chiasmaHypophysis
3rd ventricle
4th ventricleCerebellum
Brain stem
Spinal cord
The CerebrumThe Cerebrum
•This is the largest part of the brainThis is the largest part of the brain•Consists of right and left hemisphere Consists of right and left hemisphere
connected by the corpus callosumconnected by the corpus callosum•Each cerebral hemisphere is Each cerebral hemisphere is
composed of different lobes- frontal, composed of different lobes- frontal, temporal, parietal and occipitaltemporal, parietal and occipital
•Embedded in the cerebrum is the Embedded in the cerebrum is the BASAL gangliaBASAL ganglia
The Frontal Lobe of the The Frontal Lobe of the cerebrumcerebrum• Influences the Influences the personality of the personality of the personperson
• Also responsible for Also responsible for judgment, abstract judgment, abstract reasoning, social reasoning, social behavior, language behavior, language expression and expression and motor movement.motor movement.
The Temporal lobe of the The Temporal lobe of the CerebrumCerebrum• This part of the This part of the
cerebrum controls the cerebrum controls the hearing, language hearing, language comprehension, comprehension, storage and recall of storage and recall of memoriesmemories
• The LIMBIC system is The LIMBIC system is deeply located in the deeply located in the temporal lobe. This temporal lobe. This controls the basic controls the basic drives such as hunger, drives such as hunger, anger, emotion and anger, emotion and sexual drive.sexual drive.
The Parietal lobe of the The Parietal lobe of the cerebrumcerebrum• This is the principal This is the principal center for the center for the reception and reception and interpretation of interpretation of SensationSensation
• This part interprets This part interprets and integrates the and integrates the sensory inputs like sensory inputs like touch, temperature touch, temperature and painand pain
• It interprets size, It interprets size, shape, distance and shape, distance and texturetexture
The occipital lobe of the The occipital lobe of the cerebrumcerebrum
•This This functions functions mainly to mainly to interpret interpret visual visual stimulistimuli
Speech areas in the Speech areas in the cerebrumcerebrum
•1. Wernicke’s area- responsible 1. Wernicke’s area- responsible for the sensory reception of for the sensory reception of speech. speech.
•2.Broca’s Area- responsible for 2.Broca’s Area- responsible for the motor speechthe motor speech
The CerebellumThe Cerebellum•The second largest brain regionThe second largest brain region•Has also two hemispheresHas also two hemispheres•Functions to maintain muscle tone, Functions to maintain muscle tone,
coordinate muscle movement, posture coordinate muscle movement, posture and control balance/equilibriumand control balance/equilibrium
• If this is damaged, muscle tone If this is damaged, muscle tone decreases and fine motor movements decreases and fine motor movements become very clumsybecome very clumsy
The BrainstemThe Brainstem
•Lies inferior to the cerebrumLies inferior to the cerebrum
•Continuous with the cerebrum and Continuous with the cerebrum and the spinal cordthe spinal cord
• It is composed of the midbrain, the It is composed of the midbrain, the pons and the medulla oblongatapons and the medulla oblongata
•Functions: houses the center for Functions: houses the center for respiration and cardiovascular respiration and cardiovascular system system
The MidbrainThe Midbrain
•This connects with the This connects with the cerebrum cerebrum
•Contains numerous ascending Contains numerous ascending and descending tracts and and descending tracts and fibersfibers
The PonsThe Pons
•Connects the cerebellum with Connects the cerebellum with the cerebrumthe cerebrum
•Houses the respiratory center Houses the respiratory center and cardiovascular centerand cardiovascular center
•Exit points for cranial nerves 5, Exit points for cranial nerves 5, 6 and 76 and 7
The Medulla oblongataThe Medulla oblongata
•The most inferior portion of the The most inferior portion of the brainstembrainstem
•Serves as the center for autonomic Serves as the center for autonomic reflexes to maintain homeostasis, reflexes to maintain homeostasis, regulating respiratory vasomotor and regulating respiratory vasomotor and cardiac functionscardiac functions
•Serves as exit of cranial nerves Serves as exit of cranial nerves 9,10,11 and 129,10,11 and 12
The DiencephalonThe Diencephalon• The thalamus and the The thalamus and the
hypothalamushypothalamus
• The thalamus is the relay The thalamus is the relay station of all sensory station of all sensory stimuli towards the brainstimuli towards the brain
• The hypothalamus The hypothalamus controls body controls body temperature, appetite, temperature, appetite, water balance, pituitary water balance, pituitary secretions and sleep-wake secretions and sleep-wake cyclecycle
Brain circulation: The circle Brain circulation: The circle of Willisof Willis
The spinal cordThe spinal cord•A long cylindrical structure extending A long cylindrical structure extending
from the foramen magnum to the L1 from the foramen magnum to the L1 in adult, L3/L4 in pediain adult, L3/L4 in pedia
•In the cross section of the spinal cord, In the cross section of the spinal cord, we find the GRAY matter- contains we find the GRAY matter- contains neurons; and WHITE matter-consists of neurons; and WHITE matter-consists of nerve fibersnerve fibers
•There are 31 pairs of spinal nerves There are 31 pairs of spinal nerves that exit the spinal cordthat exit the spinal cord
The spinal cordThe spinal cord
•Each spinal nerve is formed by the Each spinal nerve is formed by the dorsal root (sensory) and the ventral dorsal root (sensory) and the ventral root (motor)root (motor)
•Cervical segments= 8 pairsCervical segments= 8 pairs•Thoracic segments=12 pairsThoracic segments=12 pairs•Lumbar= 5 pairsLumbar= 5 pairs•Sacral=5 pairsSacral=5 pairs•Coccygeal=1 pairCoccygeal=1 pair
The MeningesThe Meninges•These are 3 connective tissue layers These are 3 connective tissue layers
surrounding the brain and spinal cord.surrounding the brain and spinal cord.
•1. DURA MATER- the superficial, thickest 1. DURA MATER- the superficial, thickest layer. The area above the dura mater is layer. The area above the dura mater is called epidural spacecalled epidural space
•2. ARACHNOID- second layer, thin and wispy.2. ARACHNOID- second layer, thin and wispy.
•3. PIA MATER- the deepest layer, adhered to 3. PIA MATER- the deepest layer, adhered to the brain and spinal cord substancethe brain and spinal cord substance
The The MeningesMeninges• The space in between The space in between
the arachnoid and pia the arachnoid and pia mater is called the mater is called the arachnoid spacearachnoid space
• This arachnoid space This arachnoid space contains the cerebro-contains the cerebro-spinal fluid (CSF)spinal fluid (CSF)
• In this space, blood In this space, blood vessels are also foundvessels are also found
The VentriclesThe Ventricles
•These are CSF filled cavities in the These are CSF filled cavities in the brainbrain
•The lateral ventricle- found in the The lateral ventricle- found in the cerebrumcerebrum
•The third ventricle- in the center of The third ventricle- in the center of the thalamus and hypothalamusthe thalamus and hypothalamus
•The fourth ventricle- located at the The fourth ventricle- located at the base of the cerebellumbase of the cerebellum
The CSFThe CSF
•This is the fluid found inside the This is the fluid found inside the ventricles that bathe the brain and ventricles that bathe the brain and spinal cordspinal cord
•Function: provides protective cushion Function: provides protective cushion around the CNSaround the CNS
•Produced by the choroid plexus in the Produced by the choroid plexus in the ventriclesventricles
•Absorbed by the arachnoid granulationsAbsorbed by the arachnoid granulations
Tracing the CSF pathwayTracing the CSF pathway
•Lateral ventricleLateral ventricle Interventricular Interventricular foramen of Monroforamen of Monro Third ventricle Third ventricle Cerebral aqueduct of SylviusCerebral aqueduct of Sylvius fourth ventriclefourth ventricle exits trough the exits trough the median foramen of Magendie or the median foramen of Magendie or the lateral foramen of Lusckalateral foramen of Luscka Subarachnoid spaces in the cisterna Subarachnoid spaces in the cisterna magna, spinal cord magna, spinal cord subarachnoid subarachnoid space of the brainspace of the brain superior sagittal superior sagittal sinussinus
The cranial nervesThe cranial nerves
•Are 12 pairs of nerves that exit Are 12 pairs of nerves that exit the brainthe brain
•Can be classified asCan be classified as
•SensorySensory
•Motor mixed (sensory and motor)Motor mixed (sensory and motor)
The Autonomic Nervous The Autonomic Nervous SystemSystem
•The part of the peripheral nervous The part of the peripheral nervous system that innervates cardiac system that innervates cardiac muscles, smooth muscles and muscles, smooth muscles and glandsglands
•Functionally divided intoFunctionally divided into
•Sympathetic Nervous SystemSympathetic Nervous System
•Parasympathetic Nervous SystemParasympathetic Nervous System
The SYMPATHETIC The SYMPATHETIC systemsystem•Originates from the T1-L2/L3 Originates from the T1-L2/L3
segments of the spinal cord segments of the spinal cord (thoracolumbar)(thoracolumbar)
•Utilized by the body for FLIGHT and Utilized by the body for FLIGHT and FIGHT responseFIGHT response
•Neurotransmitter agents are Neurotransmitter agents are Epinephrine and Norepinephrine Epinephrine and Norepinephrine (coming from the adrenal gland)(coming from the adrenal gland)
•ADRENERGIC systemADRENERGIC system
Sympathetic nervous systemSympathetic nervous system
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
Pupils
Salivary glands
Heart
Bronchi of lungs
LiverStomach
Small intestines
Adrenal gland
KidneyLarge intestine
Rectum
Bladder
Genitals
Sympathetic responsesSympathetic responses• Increased:Increased:
– HRHR– RRRR– BPBP– Visual Acuity (Pupillary Dilation)Visual Acuity (Pupillary Dilation)– Smooth Muscle toneSmooth Muscle tone sphincters are sphincters are
contractedcontracted– VasoconstrictionVasoconstriction– MetabolismMetabolism ↑ glucose, ↑ fatty acids↑ glucose, ↑ fatty acids
Sympathetic responsesSympathetic responses
•DecreasedDecreased– PeristalsisPeristalsis– Salivary secretionsSalivary secretions
•EjaculationEjaculation
Parasympathetic SystemParasympathetic System
• CHOLINERGIC systemCHOLINERGIC system
• The vegetative systemThe vegetative system
• Feed and Breed responsesFeed and Breed responses
• Cranio-sacral locationCranio-sacral location
• Cranial nerves- 3, 7, 9, 10 and S2-Cranial nerves- 3, 7, 9, 10 and S2-S4S4
• Neurotransmitter is AcetylcholineNeurotransmitter is Acetylcholine
ParasympatheticParasympatheticnervous systemnervous system
Pupils
Salivary glands
Heart
Bronchi of lungs
LiverStomach
Small intestines
Large intestine
Rectum
Bladder
Genitals
ParasympatheticParasympathetic ResponsesResponses• IncreasedIncreased
– Gastric secretionsGastric secretions– Salivary secretionsSalivary secretions– peristalsisperistalsis
• Pupillary constrictionPupillary constriction
• DecreasedDecreased
• Smooth muscle toneSmooth muscle tone sphincters are relaxed sphincters are relaxed
• erectionerection
Nerve PhysiologyNerve Physiology•The nerve cells are excitable cellsThe nerve cells are excitable cells•Any stimulus will change the Any stimulus will change the
membrane potential and cause an membrane potential and cause an action potential to generateaction potential to generate impulse impulse transmission or action potentialtransmission or action potential
•The myelin sheath of the nerve cell is The myelin sheath of the nerve cell is responsible for the SALTATORY responsible for the SALTATORY conductionconduction increases the nerve increases the nerve transmissiontransmission
What is an action potential?What is an action potential?
• The synchronized opening and closing of The synchronized opening and closing of NaNa++ and K and K+ + gates result in the movement gates result in the movement of electrical charges that generates a of electrical charges that generates a nerve impulse or action potential.nerve impulse or action potential.
• Action potentials reach the end of each Action potentials reach the end of each neuron where these electrical signals are neuron where these electrical signals are either transmitted directly to the next cell either transmitted directly to the next cell in the sequence via gap junctions, or are in the sequence via gap junctions, or are responsible for activating the release of responsible for activating the release of specialized neurotransmitter chemicals.specialized neurotransmitter chemicals.
TerminologiesTerminologies• Action potential – another name for “spike” Action potential – another name for “spike”
potential or nerve impulsepotential or nerve impulse• Depolarization – upward oscilloscope deflection or Depolarization – upward oscilloscope deflection or
NaNa++ conductance is highest (hypopolarization) conductance is highest (hypopolarization)• All-or-None is when the action potential amplitude All-or-None is when the action potential amplitude
never variesnever varies• Repolarization – at this point, NaRepolarization – at this point, Na++ conductance is
falling rapidly and K+ conductance has peaked.• Absolute refractory period – time of depolarization Absolute refractory period – time of depolarization
(Na(Na++ gates open) gates open)• Relative refractory period – time of depolarization Relative refractory period – time of depolarization
(K(K+ gates open)• Hyperpolarization – downward oscilloscope Hyperpolarization – downward oscilloscope
deflection below restingdeflection below resting
ACTION POTENTIAL AT ACTION POTENTIAL AT SYNAPSESSYNAPSES
• Electrical synapses Electrical synapses between excitable between excitable cells allow ions to cells allow ions to pass directly from pass directly from one cell to one cell to another, and are another, and are much faster than much faster than chemical synapseschemical synapses
• An action potential at one node of Ranvier An action potential at one node of Ranvier causes inwards currents that move down causes inwards currents that move down the axon, depolarizing the membrane and the axon, depolarizing the membrane and stimulating a new action potential at the stimulating a new action potential at the next node of Ranvier.next node of Ranvier.
What is saltatory conduction?What is saltatory conduction?An action potential at one node of An action potential at one node of Ranvier causes inwards currents that Ranvier causes inwards currents that move down the action, depolarizing the move down the action, depolarizing the membrane and stimulating a new action membrane and stimulating a new action potential at the next node of Ranvier.potential at the next node of Ranvier.
The SYNAPSEThe SYNAPSE•This is the region where This is the region where
communication occurs between 2 communication occurs between 2 neurons or between a neuron and neurons or between a neuron and a target cella target cell
•A neurotransmitter is released A neurotransmitter is released from the nerve cell towards the from the nerve cell towards the other cell with receptorother cell with receptor
Reflex ArcReflex ArcThe reflex arc is a hard wired, unconscious rapid The reflex arc is a hard wired, unconscious rapid response to external stimulus involving spinal response to external stimulus involving spinal nerves and effector cell.nerves and effector cell.A reflex is an automatic, involuntary response of an A reflex is an automatic, involuntary response of an organism to a stimulus. organism to a stimulus. The entire nervous system is composed of The entire nervous system is composed of innumerable reflex arcs.innumerable reflex arcs.
REFLEXES IN MANREFLEXES IN MAN
Stretch reflexStretch reflex
Biceps reflex & Radial-ulnar Biceps reflex & Radial-ulnar reflexreflex
What is synaptic What is synaptic transmissiontransmission??
• Synaptic transmission is the process by Synaptic transmission is the process by which nerve cells communicate among which nerve cells communicate among themselves and with muscles and glands. themselves and with muscles and glands.
• The synapse is the anatomic site where The synapse is the anatomic site where this communication occurs. this communication occurs.
• Most synaptic transmission is carried out Most synaptic transmission is carried out by a chemical called a neurotransmitter.by a chemical called a neurotransmitter.
The neurotransmitter is The neurotransmitter is manufactured by the neuron and manufactured by the neuron and stored in vesicles at the axon stored in vesicles at the axon terminalsterminals
When the action potential reaches the When the action potential reaches the axon terminal, it causes the vesicles to axon terminal, it causes the vesicles to release the neurotransmitter molecules release the neurotransmitter molecules into the synaptic cleft.into the synaptic cleft.
The neurotransmitter diffuses The neurotransmitter diffuses across the cleft and binds to receptors across the cleft and binds to receptors on the post-synaptic cleft cell.on the post-synaptic cleft cell.
Then the activated receptors cause Then the activated receptors cause changes in the activity of the post-changes in the activity of the post-synaptic neuron.synaptic neuron.
The neurotransmitter molecules The neurotransmitter molecules are released from the receptors are released from the receptors and diffuse back into the synaptic and diffuse back into the synaptic cleft.cleft.
The neurotransmitter is The neurotransmitter is reabsorbed by the post synaptic reabsorbed by the post synaptic neuron. This process is known as neuron. This process is known as reuptake.reuptake.
NeurotransmittersNeurotransmitters
Physiology of VisionPhysiology of Vision• Light waves travel at a speed of 186,000 Light waves travel at a speed of 186,000
miles per second. Light is reflected into the miles per second. Light is reflected into the eyes by objects within the field of vision.eyes by objects within the field of vision.
• In order to achieve clear vision, light In order to achieve clear vision, light reflected from objects within the visual field reflected from objects within the visual field is focused in to the retina of both eyes. is focused in to the retina of both eyes.
• The processes involved in producing a clear The processes involved in producing a clear image are refraction of the light rays and image are refraction of the light rays and accommodation of the eyes. accommodation of the eyes.
The eye and the visual The eye and the visual pathwaypathway•Vision is made possible by the stimulation Vision is made possible by the stimulation
of the photoreceptor cells in the retinaof the photoreceptor cells in the retina
•Receptor cells are the RODS and CONESReceptor cells are the RODS and CONES
•The eye is made up of three layersThe eye is made up of three layers– Fibrous layer- sclerae and corneaFibrous layer- sclerae and cornea– Uvea- choroid and iris and ciliary bodiesUvea- choroid and iris and ciliary bodies– Nervous coat- retinaNervous coat- retina
Functions of the Parts of Functions of the Parts of the Eyethe Eye• Lens – refraction and focusingLens – refraction and focusing• Iris – regulated light entranceIris – regulated light entrance• Pupil – opening in the irisPupil – opening in the iris• Choroid – absorbs stray lightChoroid – absorbs stray light• Sclera – for protectionSclera – for protection• Cornea – refraction of lightCornea – refraction of light• Ciliary body – holds lens in placeCiliary body – holds lens in place• Retina – contains receptors (rods and cones)Retina – contains receptors (rods and cones)• Rods – for black and white visionRods – for black and white vision• Cones – for color visionCones – for color vision• Optic nerve – transmits impulseOptic nerve – transmits impulse• Ciliary muscle – for accommodationCiliary muscle – for accommodation
The optic nerveThe optic nerve
•This is the collection of fibers This is the collection of fibers from the cells in the retinafrom the cells in the retina
•It passes through the It passes through the brainstem as the optic chiasmbrainstem as the optic chiasm
• it will reach the occipital lobe it will reach the occipital lobe for visual interpretationfor visual interpretation
EMMETROPIAEMMETROPIA• Emmetropia is normal Emmetropia is normal
vision.vision.
• Parallel light rays Parallel light rays from distant objects from distant objects are in sharp focus on are in sharp focus on the retina when the the retina when the ciliary muscle is ciliary muscle is completely relaxed.completely relaxed.
• This means that the This means that the eye can see all eye can see all distant objects distant objects clearly, with its ciliary clearly, with its ciliary muscle relaxed, but muscle relaxed, but to focus objects at to focus objects at close range it must close range it must provide various provide various degrees of degrees of accommodation.accommodation.
MyopiaMyopia
• Myopia or nearsightedness results from Myopia or nearsightedness results from an axial length of the eye that is too an axial length of the eye that is too long for the refractive power of the eye. long for the refractive power of the eye.
• In this case, the focal point is in front of In this case, the focal point is in front of the retina, thus, distant objects cannot the retina, thus, distant objects cannot be focused on the retina.be focused on the retina.
• An object can be seen clearly if it is An object can be seen clearly if it is moved closer to the eye so that the moved closer to the eye so that the image forms in the retina.image forms in the retina.
• Hyperopia results Hyperopia results from an axial from an axial length of the eye length of the eye that is too short that is too short for the refractive for the refractive power of the eyepower of the eye. .
• In this case, In this case, distant objects distant objects cannot be focused cannot be focused clearly because clearly because the focal point is the focal point is at the back of the at the back of the retina. retina.
Astigmatism or Astigmatism or “ghost vision” is “ghost vision” is when both far and when both far and near objects near objects appear out of appear out of focus. This is focus. This is because of the because of the uneven diameter uneven diameter of the cornea of the cornea (oblong-shaped). (oblong-shaped). For light rays to For light rays to focus precisely on focus precisely on the retina, the the retina, the cornea usually cornea usually needs to be more needs to be more evenly round.evenly round.
Fovea & MaculaFovea & Macula• Fovea centralis Fovea centralis
is an oval, is an oval, yellowish area yellowish area with a with a depression depression where there are where there are only cone cells. only cone cells.
Size of the PupilsSize of the Pupils
• Pupil size influences accommodation by Pupil size influences accommodation by controlling the amount of light entering the controlling the amount of light entering the eye. In a bright light the pupils are eye. In a bright light the pupils are constricted. In a dim light they are dilated.constricted. In a dim light they are dilated.
• Contraction of the circular fibers constricts Contraction of the circular fibers constricts the pupil, and contraction of the radiating the pupil, and contraction of the radiating fibers dilate it. fibers dilate it.
• The size of the pupil is controlled by nerves The size of the pupil is controlled by nerves of the ANS. Sympathetic stimulation dilates of the ANS. Sympathetic stimulation dilates the pupils and parasympathetic stimulation the pupils and parasympathetic stimulation causes constriction.causes constriction.
What is Rhodopsin?What is Rhodopsin?• Rhodopsin or visualRhodopsin or visual
purplepurple is ais a photosensitive photosensitive pigment present only pigment present only in the rods. It is in the rods. It is bleached by bright bleached by bright light and when this light and when this occurs the rods can occurs the rods can not be stimulated. not be stimulated.
• Rhodopsin is quickly Rhodopsin is quickly reconstituted when an reconstituted when an adequate supply of adequate supply of Vit A is available.Vit A is available.
• The rate at which The rate at which dark adaptation takes dark adaptation takes place is dependent place is dependent upon the rate of upon the rate of reconstitution of reconstitution of rhodopsin.rhodopsin.
PHYSIOLOGY OF PHYSIOLOGY OF HEARINGHEARING
How are sounds heard?How are sounds heard?
• Sound waves cause movements of the Sound waves cause movements of the tympanic membrane and these movements tympanic membrane and these movements are both conveyed and amplified by the are both conveyed and amplified by the middle ear ossicles (malleus, incus, and middle ear ossicles (malleus, incus, and stapes). stapes).
• The vibrations transmitted to the ossicles The vibrations transmitted to the ossicles cause the foot plate of the stapes to vibrate cause the foot plate of the stapes to vibrate against the oval window thereby transmitting against the oval window thereby transmitting them to the inner ear. them to the inner ear.
• Thus air-borne sound waves are transferred to Thus air-borne sound waves are transferred to the fluid in the inner ear. the fluid in the inner ear.
The Vestibular apparatusThe Vestibular apparatus
•This is the part of the ear that This is the part of the ear that helps in equilibriumhelps in equilibrium
•Located in the inner earLocated in the inner ear
•The saccule and utricle control The saccule and utricle control LINEAR motionLINEAR motion
•The semicircular ducts control the The semicircular ducts control the Angular movement/ accelerationAngular movement/ acceleration
Physiology of SmellPhysiology of Smell• The sense of smell is The sense of smell is
perceived when perceived when odorous materials in the odorous materials in the air are carried into the air are carried into the nose and stimulate the nose and stimulate the olfactory cells.olfactory cells.
• Perception of odor Perception of odor decreases and decreases and eventually ceases due eventually ceases due to smell adaptationto smell adaptation
• The sense of smell may The sense of smell may affect the appetite affect the appetite
The Olfactory apparatusThe Olfactory apparatus•Stimulation from the olfactory Stimulation from the olfactory
nerves will reach the limbic nerves will reach the limbic system of the brainsystem of the brain
•Consists of the nose and the Consists of the nose and the olfactory nerveolfactory nerve
Primary Smell & Odor Primary Smell & Odor SystemSystem6 primary types of6 primary types of
smellsmell• FragrantFragrant• PutridPutrid• SpicySpicy• ResinousResinous• BurntBurnt• EtheralEtheral
7 Odor System7 Odor System CamphoraceousCamphoraceous MuskyMusky FloralFloral MintyMinty EtheralEtheral PungentPungent PutridPutrid
PHYSIOLOGY OF TASTEPHYSIOLOGY OF TASTE
The Gustatory apparatusThe Gustatory apparatus
•The receptor for taste are The receptor for taste are cells in the tongue group cells in the tongue group together called the taste together called the taste budsbuds
•They are numerous in the They are numerous in the vallate and fungiform vallate and fungiform papillaepapillae
The Gustatory apparatusThe Gustatory apparatus
Basic taste modalitiesBasic taste modalities•Sweet- tip of the tongueSweet- tip of the tongue•Salty- over the dorsum of the Salty- over the dorsum of the
tonguetongue•Sour- sides of the tongueSour- sides of the tongue•Bitter- back of the tongueBitter- back of the tongue
How are taste perceivedHow are taste perceived??
• Taste buds which consist of small bundles of Taste buds which consist of small bundles of cells and nerve endings of cranial nerves (VII, cells and nerve endings of cranial nerves (VII, IX and X).IX and X).
• The nerve cells are stimulated by chemical The nerve cells are stimulated by chemical substances in solution that enter the pores. substances in solution that enter the pores.
• The nerve impulses are transmitted to the The nerve impulses are transmitted to the thalamus then to the taste area in the thalamus then to the taste area in the cerebral cortex, one in each hemisphere, cerebral cortex, one in each hemisphere, where taste is perceived.where taste is perceived.
• 4 fundamental sensations of taste have been 4 fundamental sensations of taste have been described: sweet, sour, bitter and salty. described: sweet, sour, bitter and salty.
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• Quiz on Physiology of the Nervous Quiz on Physiology of the Nervous SystemSystem