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Medical Pathophysiology > Week 5 - Lecture 2- Alterations in Peripheral Nervous System Function > Flashcards

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

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USMLE® Step 1 flashcards
1
Q

Sensory receptors

A

specialised to respond to changes in environment (stimuli)

activation results in graded potentials that trigger nerve impulses

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2
Q

ganglia

A

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

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3
Q

revise cranial nerves

A

pg. 8

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4
Q

spinal nerve functions

A

pg. 10

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5
Q

Dermatome

A

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
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6
Q

6 components of the spinal reflex arc

A
  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
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7
Q

reflex functional classifications

A
  1. somatic reflexes - activates skeletal muscle

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

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8
Q

Spinal somatic reflexes

A

integration centre in spinal cord

effectors are skeletal muscle

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9
Q

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

A

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
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10
Q

stretch reflex

A
  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
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11
Q

information obtained

A 
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
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12
Q

Somatic nervous system

A

operates under conscious control

controls skeletal muscles

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13
Q

autonomic nervous system

A

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

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14
Q

review pg.

A

19

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15
Q

Divisions of ANS

A

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

dynamic antagonism between two divisions maintains homeostasis

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16
Q

Role of parasympathetic division

A

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

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17
Q

Role of sympathetic division

A

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
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18
Q

Parasympathetic division

A

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
19
Q

Sympathetic division (7)

A

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
20
Q

review 26

A

in lecture

21
Q

difference between CNS and PNS

A

PNS has some regenerative capacity and reinnervation

22
Q

MOIs to the PNS

A

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

23
Q

neuropathy

A

axonal degeneration is due to damage to cell body

24
Q

peripheral neuropathy

A

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
25
Q

most CNS fibres never regenerate

A
  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
26
Q

mature neurones are amitotic

A

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

27
Q

If peripheral axon is damaged

A

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

28
Q

Regeneration of nerve fibres in the PNS

A

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

29
Q

Traumatic Peripheral nerve injury

A

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
30
Q

what is mononeuropathy

A

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

31
Q

Polyneuropathy

A

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

32
Q

trauma may lead to oedema formation

A

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
33
Q

Many injuries can lead to motor dysfunction

A

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)

34
Q

Ataxia

A

inability to coordinate muscle activity

35
Q

Athetosis

A

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

36
Q

Ballismus

A

jerking, swinging, sweeping motions of the proximal limbs

37
Q

Bradykinesia/hypokinesia

A

decrease in spontaneity and movement

38
Q

Chorea

A

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

39
Q

Cogwheel

A

resistance to movement: rigidity decreasing to stiffness after movement begins

40
Q

Dystonia

A

abnormal tonicity, difficulty maintaining posture

41
Q

Hyperkinesia

A

excessive motor activity

42
Q

Tic

A

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

43
Q

Tremor

A

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

Medical Pathophysiology (30 decks)

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