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

Question 1

Sensory receptors

Answer 1

specialised to respond to changes in environment (stimuli)

activation results in graded potentials that trigger nerve impulses

Question 2

ganglia

Answer 2

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

Question 3

revise cranial nerves

Answer 3

pg. 8

Question 4

spinal nerve functions

Answer 4

pg. 10

Question 5

Dermatome

Answer 5

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

Question 6

6 components of the spinal reflex arc

Answer 6

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

Question 7

reflex functional classifications

Answer 7

1. somatic reflexes - activates skeletal muscle

2. autonomic (visceral) reflexes : activates visceral effectors (smooth or cardiac muscle or glands)

Question 8

Spinal somatic reflexes

Answer 8

integration centre in spinal cord

effectors are skeletal muscle

Question 9

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

Answer 9

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

Question 10

stretch reflex

Answer 10

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

Question 11

information obtained

Answer 11

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 
brainstem

Question 12

Somatic nervous system

Answer 12

operates under conscious control

controls skeletal muscles

Question 13

autonomic nervous system

Answer 13

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

Question 14

review pg.

Answer 14

19

Question 15

Divisions of ANS

Answer 15

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

dynamic antagonism between two divisions maintains homeostasis

Question 16

Role of parasympathetic division

Answer 16

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

Question 17

Role of sympathetic division

Answer 17

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

Question 18

Parasympathetic division

Answer 18

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

Question 19

Sympathetic division (7)

Answer 19

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

Question 20

review 26

Answer 20

in lecture

Question 21

difference between CNS and PNS

Answer 21

PNS has some regenerative capacity and reinnervation

Question 22

MOIs to the PNS

Answer 22

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

Question 23

neuropathy

Answer 23

axonal degeneration is due to damage to cell body

Question 24

peripheral neuropathy

Answer 24

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

Question 25

most CNS fibres never regenerate

Answer 25

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

Question 26

mature neurones are amitotic

Answer 26

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

Question 27

If peripheral axon is damaged

Answer 27

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

Question 28

Regeneration of nerve fibres in the PNS

Answer 28

greater distance between severed ends-less chance of regeneration - tissue block growth - axonal sprouts miss the regeneration tube 1.5mm/day post-trauma axon growth never exactly matches prior condition retraining of nerves to respond - stimulus and response are coordinated

Question 29

Traumatic Peripheral nerve injury

Answer 29

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 - numbness - 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

Question 30

what is mononeuropathy

Answer 30

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

Question 31

Polyneuropathy

Answer 31

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

Question 32

trauma may lead to oedema formation

Answer 32

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 ```

Question 33

Many injuries can lead to motor dysfunction

Answer 33

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)

Question 34

Ataxia

Answer 34

inability to coordinate muscle activity

Question 35

Athetosis

Answer 35

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

Question 36

Ballismus

Answer 36

jerking, swinging, sweeping motions of the proximal limbs

Question 37

Bradykinesia/hypokinesia

Answer 37

decrease in spontaneity and movement

Question 38

Chorea

Answer 38

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

Question 39

Cogwheel

Answer 39

resistance to movement: rigidity decreasing to stiffness after movement begins

Question 40

Dystonia

Answer 40

abnormal tonicity, difficulty maintaining posture

Question 41

Hyperkinesia

Answer 41

excessive motor activity

Question 42

Tic

Answer 42

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

Question 43

Tremor

Answer 43

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