Week 5 - Lecture 2- Alterations in Peripheral Nervous System Function Flashcards
Sensory receptors
specialised to respond to changes in environment (stimuli)
activation results in graded potentials that trigger nerve impulses
ganglia
ganglia contain cell bodies of neurones eg. dorsal root ganglia (sensory, somatic)
revise cranial nerves
pg. 8
spinal nerve functions
pg. 10
Dermatome
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
- receptor - site of stimulus action
- sensory neurone - transmits afferent impulses to CNS
- integration centre - either monosynaptic or polysynaptic region within CNS
- motor neurone conducts efferent impulses from integration centre to effector organ
- effector - muscle fibre or gland cell that responds to efferent impulses by contracting or secreting
reflex functional classifications
- 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
- when stretch activates muscle spindles, the associated sensory neurons transmit afferent impulses at high frequency to the spinal cord
- 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 brainstem
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.
19
Divisions of ANS
sympathetic
parasympathetic
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
- conserves energy and promotes sedentary activities
- decreased metabolic rate
- decreased HR, contractibility and blood pressure, vascular smooth muscle relaxation
- decreased RR, bronchial smooth muscle constriction
- increases mortility and blood flow in digestive tract, increased constriction of bladder and peristalsis of GI smooth muscle
- urination and defecation stimulation, relaxation of anal and bladder sphincter
- increases watery salivary and digestive glands secretion
Sympathetic division (7)
fight or flight
- heightened mental alertness
- increased metabolic rate
- reduced digestive and urinary functions (decreased constriction of bladder and peristalsis of GI smooth muscle, constriction of anal and bladder sphincter
- energy reserves activated
- increased respiratory rate and respiratory passageways dilate, bronchial smooth muscle relaxation
- increased heart rate, contractibility and BP, vascular smooth muscle constriction
- 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
neuropathy
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
- CNS oligodendrocytes (myelin sheet in CNS) bear growth inhibiting proteins that prevent CNS fibre regeneration
- 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
1.5mm/day
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
- 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
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
Polyneuropathy
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)
Ataxia
inability to coordinate muscle activity
Athetosis
involuntary movement of flexion and extension, pronation and supination of hands and toes and feet, slow writhing - type movements
Ballismus
jerking, swinging, sweeping motions of the proximal limbs
Bradykinesia/hypokinesia
decrease in spontaneity and movement
Chorea
irregular, spasmodic, involuntary movement of the limbs or fascial muscles, often accompanied by hypotonia
Cogwheel
resistance to movement: rigidity decreasing to stiffness after movement begins
Dystonia
abnormal tonicity, difficulty maintaining posture
Hyperkinesia
excessive motor activity
Tic
repeated, habitual muscle contractions : movements that can be voluntarily suppressed for short period only
Tremor
oscillating, repetitive movements of whole muscle; irregular, involuntary contractions of the opposing muscle
