Week 5 - Lecture 2- Alterations in Peripheral Nervous System Function Flashcards Preview

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Flashcards in Week 5 - Lecture 2- Alterations in Peripheral Nervous System Function Deck (43):

Sensory receptors

specialised to respond to changes in environment (stimuli)

activation results in graded potentials that trigger nerve impulses



ganglia contain cell bodies of neurones eg. dorsal root ganglia (sensory, somatic)


revise cranial nerves

pg. 8


spinal nerve functions

pg. 10



area of skin innervated by cutaneous branches of a single spinal nerve

-all spinal nerve except C1 participate in dermatomes

-extent of spinal cord injuries ascertained by affected dermatomes

- most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness

-local surgery : several spinal nerves must be blocked, anaesthetised


6 components of the spinal reflex arc

1. receptor - site of stimulus action
2. sensory neurone - transmits afferent impulses to CNS
3. integration centre - either monosynaptic or polysynaptic region within CNS
4. motor neurone conducts efferent impulses from integration centre to effector organ
5. effector - muscle fibre or gland cell that responds to efferent impulses by contracting or secreting


reflex functional classifications

1. somatic reflexes - activates skeletal muscle
2. autonomic (visceral) reflexes : activates visceral effectors (smooth or cardiac muscle or glands)


Spinal somatic reflexes

integration centre in spinal cord

effectors are skeletal muscle


Testing of somatic reflexes important clinically to assess condition of nervous system

if dysfunctional or absent - degeneration/pathology of specific nervous system regions
- to smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding
1. length of muscle
- from muscle spindles
2. amount of tension in muscle
- from tendon organs


stretch reflex

1. when stretch activates muscle spindles, the associated sensory neurons transmit afferent impulses at high frequency to the spinal cord
2. The sensory neurone synapse directly with alpha motor neurones, which excite extrafusal fibres of the stretched muscle
sensory fibres also synapse with interneurones that inhibit motor neurone controlling antagonistic muscles


information obtained

peripheral afferent neurone
peripheral muscle sensory response
dorsal root ganglia
dorsal and ventral horn
motor neurone
neuromuscular synapse
muscle fibre contractile response
selected spinal and cranial nerves


Somatic nervous system

operates under conscious control
controls skeletal muscles


autonomic nervous system

operates without conscious instruction (some conscious influence )
ANS controls visceral effectors : innervates smooth muscle and cardiac muscle, and glands
make adjustment to ensure optimal support for body activities
coordinate system functions
- CV, respiratory, digestive, urinary, reproductive


review pg.



Divisions of ANS

dual innervation- almost all visceral organs served by both divisions, but cause opposite effects

dynamic antagonism between two divisions maintains homeostasis


Role of parasympathetic division

promotes maintenance activists and conserves body energy (rest and digest)
- directs digestion, diuresis, defecation

in a person relaxing and reading after a meal
- BP is low
HR is low
RR is low
GI tract activity high
Pupils constricted ; lenses accommodated for close vision
- no danger to look out for


Role of sympathetic division

mobilises body during activity ; fight or flight system

exercise, excitement, emergency, embarrassment
- increased HR
-dry mouth
- cold, sweaty skin
-dilated pupils

during vigorous physical activity
- shunts blood to skeletal muscles and heart
-dilates bronchioles
-causes liver to release glucose


Parasympathetic division

rest and digest
1. conserves energy and promotes sedentary activities
2. decreased metabolic rate
3. decreased HR, contractibility and blood pressure, vascular smooth muscle relaxation
4. decreased RR, bronchial smooth muscle constriction
5. increases mortility and blood flow in digestive tract, increased constriction of bladder and peristalsis of GI smooth muscle
6. urination and defecation stimulation, relaxation of anal and bladder sphincter
7. increases watery salivary and digestive glands secretion


Sympathetic division (7)

fight or flight
1.heightened mental alertness
2. increased metabolic rate
3. reduced digestive and urinary functions (decreased constriction of bladder and peristalsis of GI smooth muscle, constriction of anal and bladder sphincter
4. energy reserves activated
5. increased respiratory rate and respiratory passageways dilate, bronchial smooth muscle relaxation
6. increased heart rate, contractibility and BP, vascular smooth muscle constriction
7. sweat glands activated


review 26

in lecture


difference between CNS and PNS

PNS has some regenerative capacity and reinnervation


MOIs to the PNS

significant injury to cell body or axon of the neurone : degeneration of axon and cell body
- cell death by necrosis: inflammatory responses : phagocytosis of cellular debris



axonal degeneration is due to damage to cell body


peripheral neuropathy

myelinopathy, axonopathy

distal axonopathy : injury affects cells in distal area of cell body
- regeneration is possible if body and proximal axon is not affected
-crushing injury : Wallerian degeneration


most CNS fibres never regenerate

1. CNS oligodendrocytes (myelin sheet in CNS) bear growth inhibiting proteins that prevent CNS fibre regeneration
2. astrocytes at injury site form scar tissue that blocks axonal regrowth


mature neurones are amitotic

if soma is damaged, neurone dies, another synapsed neurone may die too
if soma of damaged nerve is intact, peripheral axon may regenerated


If peripheral axon is damaged

axon fragments (Wallerian degeneration); spreads distally from injury (no nutrients delivered)
Macrophages clean dead axon; myelin sheath intact
axon filaments grow through regeneration tube
axon regenerates; new myelin sheath forms


Regeneration of nerve fibres in the PNS

greater distance between severed ends-less chance of regeneration
- tissue block growth
- axonal sprouts miss the regeneration tube
post-trauma axon growth never exactly matches prior condition
retraining of nerves to respond
- stimulus and response are coordinated


Traumatic Peripheral nerve injury

crushing/cutting of neurones
severed area of nerve degenerates (wallerian)
- stimulate inflammatory process

chromatolysis is induced in neurone

damage from traumatic injury manifests with sensory symptoms
- paraethesia
- pain

symptoms relates to the
- number of axons involved
-ability of axons to regenerate
- distance the fibre needs to regrow to restore communication
- short has better prognosis
- crushing injury has better prognosis


what is mononeuropathy

trauma limited to a single area (damage to a single nerve)

single nerve entrapment, compression (CTS)

sensory response can also result from scar tissue entrapping regenerating nerve



multiple axon involvement in nerve damage

secondary to disease processes : MS, diabetes mellitus, nutrient deficiencies, toxic agents

if ANS is involved, BP, bowel and bladder evacuation, erectile dysfunction


trauma may lead to oedema formation

oedema development in constricted space may lead to neuronal pressure injuries

repetitive use/over use leading to inflammation : CTS - pain and paraethesia
-change habit/technique/activity

trauma injury (compression, stretch, tear) during birth brachial plexus palsy, flaccid paralysis of the arm
- usually temporary, but neuroma may develop and significant impairment


Many injuries can lead to motor dysfunction

peripheral nerve injury (effector)
neuromuscular junction abnormalities (effector)
damage to skeletal muscle fibres (effector)
changes in muscle mass: atrophy/dystrophy may contribute to impaired responses (effector)
Spinal cord injury with damage to corticospinal/spinal nerve roots (integration)
impaired neurotransmitter responses in nervous tissue that control coordination and proprioception (integration)



inability to coordinate muscle activity



involuntary movement of flexion and extension, pronation and supination of hands and toes and feet, slow writhing - type movements



jerking, swinging, sweeping motions of the proximal limbs



decrease in spontaneity and movement



irregular, spasmodic, involuntary movement of the limbs or fascial muscles, often accompanied by hypotonia



resistance to movement: rigidity decreasing to stiffness after movement begins



abnormal tonicity, difficulty maintaining posture



excessive motor activity



repeated, habitual muscle contractions : movements that can be voluntarily suppressed for short period only



oscillating, repetitive movements of whole muscle; irregular, involuntary contractions of the opposing muscle