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Chapter 15:

Neural Integration I: Sensory Pathways and the Somatic Nervous System

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Neural Integration

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Afferent Division of the Nervous System

• Receptors• Sensory neurons• Sensory pathways

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Afferent Division

• Sensory receptors sensory pathway

1. Somatic Sensory info- Sensory cortex of cerebrum- Cerebellum

2. Visceral Sensory info- Reflex centers in brainstem- Reflex centers in diencephalon

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Sensory Receptors

• Specialized cells that monitor specific conditions in the body or external environment

• General Senses:– Temp, pain, touch, pressure, vibration,

proprioception– Simple receptors located anywhere on body

• Special Senses: – Are located in sense organs such as the eye or

ear– Olfaction, vision, gustation, hearing, equilibrium– Complex receptors located in specialized sense

organs

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Sensory Receptors

• Sensation – the sense info; action potentials– Taste, hearing, equilibrium, and vision

provided by specialized receptor cells– Communicate with sensory neurons across

chemical synapses

• Perception – conscious awareness of sensation

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Sensory Receptors

• Transduction – conversion of environmental stimulus into action potential by sensory receptor– Action potential:

• When stimulated, a receptor passes information to the CNS in the form of action potentials along the axon of a sensory neuron

– Receptors specific for particular type of stimulus

– Specificity is due to structure of receptor– Simplest receptors are dendrites (free

nerve endings), least specific

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Free Nerve Endings

• Branching tips of dendrites • Not protected by accessory

structures • Can be stimulated by many

different stimuli

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Sensory Receptors• Receptive field

– area monitored by single receptor (e.g. touch: arm vs. fingertip)

– Area is monitored by a single receptor cell– The larger the receptive field, the more

difficult it is to localize a stimulus

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Sensory Receptors

• Labeled line– Link between receptor and processing site

in CNS•Stimulation anywhere on labeled line will

produce the same perception (e.g. phantom limb)

• Stimulus -> receptor -> transduction -> action potential -> sensation ->-> CNS perception

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Sensory Pathways

• Deliver somatic and visceral sensory information to their final destinations inside the CNS using:– nerves– nuclei– tracts

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Sensory Receptors

1. Tonic Receptors:- Always active- Signal at different rate when stimulated- Monitor background levels

2. Phasic Receptors:- Activated by stimulus– Become active for a short time whenever

a change occurs- Monitor intensity and rate of change of

stimulus

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Sensory Receptors• Adaptation

– Reduced sensitivity to a constant stimulus1. Peripheral Adaptation:

- Reduction in receptor activity- Phasic fast adapting- Tonic slow or non adapting

- Remind you of an injury long after the initial damage has occurred

2. Central Adaptation:- Inhibition of nuclei along labeled line

- Not all pathways will adapt

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Four types of General Sensory Receptors

1. Pain: nociceptor2. Temperature: thermoreceptor3. Physical: mechanoreceptor4. Chemicals: chemoreceptors- All can be found in both somatic

(exteroceptors) and visceral (interoceptors) locations except:

- Proprioceptors (a mechanoreceptor) are somatic only - report the positions of skeletal muscles and

joints

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1. Pain Receptors: Nociceptors

• Detect Pain• Are common in the:

– superficial portions of the skin

– joint capsules– within the periosteum of

bones– around the walls of blood

vessels• Rare in deep tissue and

visceral organs• Consist of free nerve

endings with large receptor fields

Figure 15–2

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1. Pain Receptors: Nociceptors

• Mode of Action:1. Injured cells release arachidonic acid2. Arachidonic acid is converted into

prostaglandins by the interstitial enzyme cyclo-oxygenase

3. Prostaglandins activate nociceptors- Many pain medications like aspirin function

to inhibit cyclo-oxygenase

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1. Pain Receptors: Nociceptors

• Once transduced pain sensations are carried on either type A and type C fibers/axons:– Type A:

• Fast pain; stab or cut; triggers defensive reflexes

– Type C:• Slow pain; aching pain

• Tonic receptors with no peripheral adaptation

• Pain levels are modulated by endorphins which inhibit CNS function

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2. Thermoreceptors

• Detect temperature• Found in skin, skeletal muscle,

liver, and hypothalamus• Consist of free nerve endings• Phasic receptors that adapt easily

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3. Mechanoreceptors

**Detect membrane distortion Three receptor types:• Tactile Receptors• Proprioceptors• Baroreceptors

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3. Mechanoreceptors

1. Tactile Receptors- Detect touch, pressure and vibration on

skinA. Free nerve endings

- Detect touch on skin- Tonic receptors with small receptor fields

B. Root hair plexus nerve endings- Detect hair movement- Phasic receptors, adapt rapidly

C. Tactile discs/Merkel’s discs- Detect fine touch - Extremely sensitive- Whole cell tonic receptors

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3. Mechanoreceptors

1. Tactile ReceptorsD. Tactile corpuscles/Meissner’s corpuscles

- Detect fine touch and vibration- Larger receptor structure- Phasic receptors, adapt rapidly

E. Lamellated corpuscles/Pacinian corpuscles- Detect deep pressure- Larger multi-layer receptors- Phasic receptor, adapt rapidly

F. Ruffini corpuscles- Detect pressure and distortion- Large tonic receptors, no adaptation

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3. Mechanoreceptors

2. Proprioceptors:- Detect positions of joints and muscles- Tonic receptors, do not adapt, complexA. Muscle spindles

- Modified skeletal muscle cell- Monitor skeletal muscle length

B. Golgi tendon organs- Dendrites around collagen fibers at the

muscle-tendon junction- Monitor skeletal muscle tension

C. Joint capsule receptors- Monitor pressure, tension and movement in

the joint

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3. Mechanoreceptors

3. Baroreceptors- Detect pressure changes- Found in elastic tissue of blood vessels

and organs of digestive, reproductive and urinary tracts

- Consists of free nerve endings- Phasic receptors, adapt rapidly

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4. Chemoreceptors

• Detect change in concentration of specific chemicals or compounds– E.g. pH, CO2

• Found in respiratory centers of the brain and in large arteries

• Phasic receptors, adapt rapidly

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KEY CONCEPT

• Stimulation of a receptor produces action potentials along the axon of a sensory neuron

• The frequency and pattern of action potentials contains information about the strength, duration, and variation of the stimulus

• Your perception of the nature of that stimulus depends on the path it takes inside the CNS

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Somatic Sensory Pathways

• Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs

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Somatic Sensory Pathways• Consist of two or three neurons:1. First Order Neuron:

- Sensory neuron- Connects from receptor to CNS- Cell body is in dorsal root ganglion/cranial nerve

ganglion2. Second Order Neuron:

- Interneuron (stimulated by first order)- Located in spinal cord or brain stem- Subconscious processing of info

3. Third Order Neuron:- Located in thalamus- Relays info to primary somatosensory cortex of

cerebrum for conscious awareness (perception)

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• Only ~1% of somatic sensory info reaches cerebrum (major changes only, “background” in filtered)– LSD interferes with sensory

damping/filtering = sensory overload• All sensory info undergoes decussation

in spine before reaching target in CNS

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3 Major Somatic Sensory Pathways

Figure 15–4

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Posterior Column Pathway

• Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception

Figure 15–5a

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Visceral Sensory Pathways

• Interoceptors transmit info to solitary nucleus of medulla oblongata for relay to visceral centers in brainstem and diencephalon– No perception

• Two neurons: 1st and 2nd order

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Efferent Division

• Conscious and subconscious motor centers in brain -> motor pathways ->

1. Somatic Nervous System skeletal muscle

2. Autonomic Nervous System visceral effectors - Smooth and cardiac muscle, glands, and

adipose

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Somatic Nervous System• Motor control of skeletal muscle• Consists of two neurons:

1. Upper motor neuron- Has soma in CNS processing center:A. Primary motor cortex of cerebrum

- voluntary controlB. Cerebrum, diencephalon, and brain stem

- subconscious control:reflexC. Basal nuclei of cerebrum and cerebellum

- coordination, balance, fine tuning

2. Lower motor neuron- Soma in brain stem or spinal cord- Links to skeletal muscle motor unit

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Motor Homunculus

39Figure 15–5a, b

Sensory HomunculusFunctional map of the primary sensory cortex

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Processing in the Thalamus

• Determines whether you perceive a given sensation as fine touch, as pressure, or as vibration

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Motor Related Disorder

1. Parkinson’s Disease- Jittery movements: lack of fine tuning of

motor- Results from degeneration of dopamine

neurons of substantia nigra - Inhibits basal nuclei

- Overactive basal nuclei = “ticks”

2. Amylotrophic Lateral Sclerosis- Degeneration of motor neurons in CNS- Causes muscle atrophy and death

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Motor Related Disorder

3. Epilepsy- 1/25 people- Wide range in condition:

- Absence seizures (blank) to grand mal seizures (convulsions, unconscious)

- Uncontrolled/chaotic neuron activity in brain: blocks normal messages

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When the nociceptors in your hand are stimulated, what sensation do you perceive?

1. pain2. heat3. vibration4. pressure

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What would happen to you if the information from proprioceptors in

your legs were blocked from reaching the CNS?

1. no pain sensations from the legs

2. uncontrolled blood pressure in the legs

3. uncoordinated movements and inability to walk

4. no tactile sensations in the legs

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Chapter 16:

Neural Integration II: The Autonomic Nervous

System and Higher-Order Functions

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Autonomic Nervous System (ANS)

• Operates without conscious instruction

• Coordinates systems functions:– cardiovascular– respiratory– digestive– urinary– reproductive

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Autonomic Nervous System

• Motor control of visceral effectors• Involves three neurons:

1. Visceral motor nuclei in hypothalamus to autonomic nuclei in CNS

2. Autonomic nuclei to autonomic ganglia in PNS3. Autonomic ganglia to visceral effector

**Nuclei = in CNS, a center with a visible boundary

**Ganglia = in PNS, collection of somas together in one place

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Autonomic Nervous System

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• Two subdivisions1. Sympathetic: “fight or flight”2. Parasympathetic: “rest and digest”- Typically oppose each other on same

effector- Some effectors innervated by only one:

- Blood vessels/sweat glands –> sympathetic only- Smooth muscle of eye –> parasympathetic only

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Sympathetic Division

• Prepares body for heightened somatic activity

• Ganglia:1. Located near spinal cord2. Adrenal Medulla

- Center of adrenal gland (above kidney)- Releases epinephrine and norepinephrine

as hormones into blood to control effectors body wide at one (endocrine function)

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Sympathetic Division

• Sympathetic Activation Results– Increased alertness– Insensitivity to pain– Elevation in blood pressure, respiratory

rate– Elevation in muscle tone– Mobilization of energy reserves

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Sympathetic Division: Neurotransmitter

1. Preganglionic Neurons release acetycholine(cholinergic synapse) EPSP on ganglionic neuron- directly open ion channel- fast acting, short lived

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Sympathetic Division: Neurotransmitter

2. Ganglionic neurons/postganglionic fibers release norepinephine at effectors (adrenergic synapse)

- NE and E from adrenal medulla: hormones- Result depends on type of receptor:

1. Alpha1 and beta1 receptors:- excititory/stimulatory to effector

2. Alpha2 and beta2 receptors:- Inhibitory

**beta-blockers: block beta1 receptors

- G protein second messengers- Slow acting but long lasting

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Parasympathetic Division

• Stimulates visceral activity• Maintains homeostasis• Ganglia located in or near effector• Vagus nerve carries 75% of

parasympathetic innervations

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Parasympathetic Division

• Parasympathetic activations results:1. Constriction of pupils2. Secretion by digestive glands3. Secretion of hormones for nutrient uptake4. Sexual arousal5. Activation of digestive tract6. Defecation and urination7. Constriction of respiratory pathways8. Reduction in heart rate

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Parasympathetic Division:Neurotransmitters

• All release Ach: all cholinergic synapses

• Effects quick, localized, short-lived• Type of effect depends on receptor:

1. Nicotonic receptor- Excititory effect on target

2. Muscarinic receptor- Inhibitory or excititory, depends on target cell

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How many motor neurons are required to conduct an action

potential from the spinal cord to smooth muscles in the wall of the

intestine?

1. one2. two3. four4. six

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While out for a brisk walk, Julie is suddenly confronted by an angry dog.

Which division of the autonomic nervous system is responsible for the

physiological changes that occur in Julie as she turns and runs?

1. parasympathetic division2. somatic nervous system3. enteric nervous system4. sympathetic division

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On the basis of anatomy, how could you distinguish the sympathetic

division from the parasympathetic division of the autonomic nervous

system?

1. origin of preganglionic fibers

2. number of preganglionic fibers

3. placement of ganglia4. both 1 and 3 are correct

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How would a drug that stimulates acetylcholine receptors affect the

sympathetic nervous system?

1. complete shut-down of sympathetic activity

2. decreased sympathetic activity3. uncontrolled sympathetic

activity4. increased sympathetic activity

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An individual with high blood pressure is given a medication that blocks beta receptors. How could this medication help correct that

person’s condition?

1. aids sympathetic stimulation2. decreases blood volume3. prevents sympathetic

stimulation4. none of the above

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Which nerve is responsible for the parasympathetic innervation of the

lungs, heart, stomach, liver, pancreas, and parts of the small and

large intestines?

1. cranial nerve IX2. splanchic nerve3. vagus nerve4. pelvic nerve

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What effect would the loss of sympathetic tone have on blood

flow to a tissue?

1. Blood flow would decrease.2. Blood flow would be redirected

to heart, lungs and brain.3. Blood flow would increase.4. Blood flow would become

erratic.

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What physiological changes would you expect in a patient

who is about to undergo a root canal and is quite anxious about

the procedure?

1. change in motility of digestive tract

2. increased heart rate3. increased breathing rate4. all of the above

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Harry has a brain tumor that is interfering with the function of his hypothalamus.

Would you expect this tumor to interfere with autonomic function? Why or why not?

1. Yes; hypothalamus regulates ANS.

2. Yes; all brain tumors affect ANS functioning.

3. No; ANS has no connection to the hypothalamus.

4. No; ANS function is regulated by thalamus.

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Higher Order Functions

1. Involve cerebral cortex2. Involve both conscious and

subconscious processing3. Are not part of genetic wiring

(reflex): can be modifiede.g. memory and consciousness

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Memory

• Memory – storage and retrieval of info• Fact memories – specific bits of info• Skill memories – learned motor

behaviors• Short term memory (STM)

– primary/working memory– Rapid recall but short retention– Store 7-8 bits of info at one time– STM can be converted to long term

memory for more permanent storage

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Memory

• Memory consolidation: STMLTM– Performed by hippocampus– Depends on:

1. Emotional State2. Rehearsal 3. Association4. Automatic memory

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Memory

• Long term memory (LTM)– Infinite info– Can be stored for lifetime– Secondary memories:

• fade with time, can be difficult to recall much later

– Tertiary memories: • part of one’s consciousness (e.g. name)

– LTMs are broken into component parts to store in appropriate cerebral cortex• E.g. visual, olfactory, etc.

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Memory

• Mechanism of memory storage not clearly understood but involves:

1. New mRNA and protein synthesis in neurons involved

2. Change of shape of dendritic spines3. Change in size and number of synaptic

terminals4. Release of more neurotransmitter

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Memory

• Amnesia = loss of memory, due to disease or trama of hippocampus and amygdala

1. Retrograde Amnesia:- Lose memories of past events, - Remember now forward

2. Anterograde Amnesia- Unable to store new memories- Only remember past

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Consciousness

• Conscious: aware of external stimuli

• Unconscious: range of unawareness– Drowsy coma brain dead

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Sleep

• Sleep = partial unconsciousness from which a person can be aroused with stimuli

1. Deep Sleep- Relaxed state- Heart and respiratory rate decreased- Minimal activity in cerebral cortex

2. REM (rapid eye movement): sleep- active, dreaming state- Cerebral cortex as active/more active than in

conscious state- But little reaction to outside stimuli- Skeletal muscles inhibited

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Activity in Cerebral Cortex

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• Alternate between deep and REM sleep throughout sleep period

• Sleep required for life, but not clear why• Lack of sleep leads to serious disturbance in

mental function• During sleep protein synthesis in neurons

increases: sleep may be used to repair and recharge neural tissue

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Sleep Disorders

1. Narcolepsy- Condition where person lapses abruptly

into sleep for ~ 15 min- Usually follows pleasant event- Cause unknown- Sufferers show reduced levels of REM

sleep at night

2. Sleep apnea- Person stops breathing until hypoxia

(lack of O2) wakes them - Hypoxic wake response ability declines

with age or respiratory illness

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Arousal• Requires Reticular Activating System

(RAS)• RAS located in brainstem, provides

consciousness• Mechanism:

– Stimulation of RAS activation of cerebral cortex

– Positive feedback (reverberation) on RAS maintains consciousness after initial stimulus

– Over time RAS becomes less responsive = sleep feeling

• Internal clock in suprashiasmatic nucleus of hypothalamus – sets normal sleep-wake cycle

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Which of the following is not a characteristic of higher order

functions?

1. require cerebral cortex2. involve conscious and

unconscious processing3. part of the programmed

wiring of the brain4. subject to modification over

time

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After suffering a head injury in an automobile accident, David has difficulty comprehending what he hears or reads. This symptom might indicate damage to

which portion of his brain?

1. right temporal lobe of the cerebrum

2. left temporal lobe of the cerebrum

3. frontal lobe of the cerebrum4. left parietal lobe of the cerebrum

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As you recall facts while you take your A&P test, which type of

memory are you using?

1. long term memory2. skill memory3. memory consolidation4. short term memory

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You are asleep. What would happen to you if your reticular

activating system were suddenly stimulated?

1. You would wake up.2. You would experience a pleasant

dream.3. You would experience a

nightmare.4. You would experience muscular

contraction and cramping.

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Age Related Changes

• Decrease– Brain size and weight (cerebrum)– Number of neurons– Blood flow to brain (incr. chance of

stroke)– Number of synapses– Neurotransmitter production

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Age Related Changes

• Accumulation of deposits:A. Inside Cells

- lipofuscin: granular pigment- Neurofibrillary tangles: packed neurofibrils

B. Extracellular- plaques: collections of fibrillar proteins

entangling abnormal cell processes- Amyloid proteins: normal proteins misfolding

become sticky

* All forms of deposits affect processing and memory ability, motor speed, and sensory sensitivity

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Age Related Changes

• Increased disease:1. Alzheimer’s Disease

- Loss of higher order functions- Occurs in 15% over 65 years- Progressive, untreatable- Due to reduction of Ach levels and

accumulation of beta amyloid peptide- Plaques and tangles

- Current treatments block Ach breakdown

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Age Related Changes

2. Huntington’s Disease- genetic, middle age onset- Accumulation of huntington’s protein

kills neurons of basal ganglia and cerebral cortex ticks, cognitive dysfunction

- Progressive and fatal- On set death in ~ 15 years

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One of the problems associated with aging is difficulty in recalling things

or even a total loss of memory. What are some possible reasons for these

changes?

1. decreased blood flow to brain

2. formation of neurofibrillary tangles

3. reduction in brain weight4. all of the above

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SUMMARY

• Brain, spinal cord, and peripheral nerves continuously communicate with each other and with internal and external environments

• Information arrives via sensory receptors and ascends within afferent division, while motor commands descend and are distributed by efferent division

• Sensory receptor is a specialized cell or cell process that monitors specific conditions within body or in external environment:– arriving information is called a sensation– awareness of a sensation is a perception

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SUMMARY

• General senses are pain, temperature, physical distortion, and chemical detection:– receptors for these senses are distributed

throughout the body

• Special senses, located in specific sense organs, are structurally more complex

• Each receptor cell monitors a specific receptive field

• Transduction begins when a large enough stimulus changes the receptor potential reaching generator potential

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SUMMARY

• Tonic receptors are always active• Phasic receptors provide information about

intensity and rate of change of a stimulus• Adaptation is a reduction in sensitivity in

presence of a constant stimulus• Tonic receptors are slow-adapting receptors,

while phasic receptors are fast-adapting receptors

• 3 types of nociceptor found in the body provide information on extremes of pain:– temperature– mechanical damage– dissolved chemicals

• myelinated Type A fibers carry fast pain• Type C fibers carry slow pain

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SUMMARY

• Thermoreceptors are found in the dermis• Mechanoreceptors are sensitive to distortion of

their membranes and include:– tactile receptors, baroreceptors, proprioceptors

• 6 types of tactile receptors in the skin • 3 types of proprioceptors

• Chemoreceptors include carotid bodies and aortic bodies

• Sensory neurons that deliver sensations to CNS are referred to as first-order neurons:– synapse on second-order neurons in brain stem or

spinal cord– next neuron in this chain is a third-order neuron,

found in the thalamus

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SUMMARY

• Functions of the autonomic nervous system (ANS)

• Functions of CNS preganglionic neurons• The sympathetic division• Sympathetic activation• Function of neurotransmitters:

– acetylcholine (ACh) – norepinephrine (NE)– epinephrine (E)

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SUMMARY

• Sympathetic ganglionic neurons • Two types of sympathetic receptors:

– alpha receptors– beta receptors

• The parasympathetic division (food processing and energy absorption)

• Muscarinic and nicotinic receptors

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SUMMARY

• Memory: – short–term or long–term

• Memory consolidation• Consciousness, unconsciousness,

and sleep• Age-related changes in the

nervous system