PNS Flashcards
what does the PNS include
everything except for the brain and spinal cord ie spinal and cranial nerves
what is the role of the PNS
it is the communication centre between the CNS and the body
2 main branches of the PNS
sensory and motor
2 branches of motor
autonomic and somatic
what does the somatic nervous system do
controls voluntary movement
skeletal muscle
what does the autonomic nervous system do
control involuntary responses
eg Bp and heart rate
branches to the autonomic nervous system
sympathetic and parasympathetic
describe the sympathetic nervous system
mobilises body systems
flight/fight responses
describe the parasympathetic action
conserves energy
rest and digest responses
what do sensory neurons do
carry information from sensory receptors in the skin and the viscera to the brain
which section is the cranial section
the head portion
what does the non-neuronal ectoderm give rise to in the development of neural crest cells
the skin
what does the neuronal ectoderm give rise to in the development of neural crest cells
cns
what does the neuronal fold give rise to in the development of neural crest cells
neuronal crest cells
they migrate - many lineages
between the skin and cns - relay information between them
what forms from neuronal crest cells
sensory neurons
and shwann cells
describe the structure of the sensory neuron
pseudounipolar
peripheral process - signal from skin/viscera to soma
central process to spinal cord
summarsie the structures of fibres A to C
a - myelinated somatic
b - myelinated visceral
c - unmyelinated somatic and visceral pain afferents
describe the structure of a fibres
free nerve endings
pseudounipolar
for pain
describe the structure of b fibres
encapsulated nerve endings
connective tissue capsule
pseudounipolar
pressure Pacinian corpuscle
describe the structure of c fibres
dipolar?
hearing hair cells in ear
describe the structure of d fibres
smell
cell body not in the ganglion
what does the motor division do
efferent
composed of motor neurons carry signal from CNS to effectors
describe the SNS
made of efferent nerves, important for muscle contraction
nerve signals begin in motor cortex
can be voluntary or automatic
nerves terminate at the NMJ to give a response
upper motor neurons in primary cortex are part of the CNS
lower motor neurons part of the PNS, cause response eg in reflex
neurons synapse with the brain stem and the spinal cord. lower motor neuron continue to skeletal muscle
development of the motor neurons
in lower part of the basal plate the lower motor neurons generate from the spinal cord itself
what is a motor unit
1 motor neuron innovates a range of muscle fibres
describe the peripheral processes of the sensory neurons
dorsal root
cell bodies in the dorsal root ganglion
describe the peripheral processes of the motor neurons
leave the spinal cord via the ventral root
where do the motor and sensory nerves go after their respective roots
mixed in the spinal nerve
the spinal nerve leaves through the invertebral foreman
spinal cord divide into posterior rami - ignal to skin on back, and ventral rami - feed front of body
paravertebral sympathetic chain ganglion goes into 2 rami
how many nerves are in the PNS
43 pairs
groups of spinal nerves
cervical plexus brachial plexus cervical enlargement intercostal nerves lumbar enlargement lumbar plexus sacral plexus cauda equina
describe the autonomic nervous system
efferent nerves and ganglia stimulating effectors out of our control
made of sympathetic and parasympathetic
composed of 3 neurons
describe the 3 neurons that make up the ANS
from hypothalamic nucleus (visceral motor nuclei) to brain stem nuclei/spinal cord
preganglionic neuron from spinal cord/brain stem to autonomic ganglia (pre synaptic if from vagal nerve/sacral parasympathetic nerves)
postganglionic from autonomic ganglia to visceral effectors (post synaptic if from vagal nerve/sacral parasympathetic nerves)
which nerves in the ANS are myelinated
preganglionic
describe the divisions of the ANS
nerves from T1 - L2 go to sympathetic chain
from here nerves go to the collateral ganglion or straight to organs
where do preganglionic or presynaptic neurons arise from
basal plate in spinal cord
difference between dorsal root ganglia and autonomic ganglion
dorsal exclusively contains cell bodies
autonomic ganglia has cell bodies and dendrites associated with synapses
how is the myelin sheath formed
from shwann cells that wrap around axon clockwise
features of the myelin sheath
major dense line (period line) - where the cytoplasm is condensed
minor dense line (intraperiod line) - plasma membrane
node of Ranvier allows saltatory conduction to take place
describe the myelination of C fibres
wrapped by 1 layer of the shwann cell and cytoplasm - neurilemma
many fibres are wrapped by the membrane of 1 neuron
describe A fibres
largest fibres 5-20microns - less resistance
myelinated
somatic - sensory and motor to skeletal muscle
fast transmission
130m/s
what is the propagation speed of a nerve impulse controlled by
size - larger = less resistance = faster
myelination - myelinated = saltatory conduction = faster
temperature
describe B fibres
medium size - 2-3microns
15m/s
myelinated
visceral - sensory and autonomic preganglionic
describe C fibres
smallest 0.5 - 1.5microns 2m/s unmyelinated sensory and autonomic motor pain
explain how rootlets, roots, rami and ganglia link
rootlets form dorsal and ventral roots which go into rami
how many cranial ganglia are there
4
name the 4 cranial ganglia
ciliary ganglion
otic ganglion
pterygopalatine ganglion
submandibular ganglion
describe the 3 sympathetic paravertebral and collateral pathways
preganglionic neuron goes through the ventral ramus
then either:
- through white ramus, synapse, postganglionic exits through the grey ramus to the spinal cord
- preganglionic move up/down the sympathetic trunk and synapse in the sympathetic ganglion
- pass through white ramus to splanchnic nerve and synapse later in the collateral ganglion
where does the collateral ganglion lead to
the liver, spleen, adrenal glands, stomach, intestines, kidneys, urinary bladder, reproductive organs
where do the nerves from the grey ramus go
sweat glands, piloerector muscles, bv of skin and skeletal muscles
where do nerves from the sympathetic ganglion go
iris salivary glands lungs heart thoracic oesophagus
what are nerve plexuses
networks of successive ventral rami that exchange fibres (crisscross and redistribute)
mainly innervate the limbs
lumbosacral and brachial plexus innervate the skin
thoracic ventral rami don’t form nerve plexuses
what innovates dermatomes
dorsal root of the spinal nerves
describe dermatomes
skin is continuous - can have overlap
area of skin supplied by single spinal nerve root
stacked along the thorax and abdomen
longitudinally along the limbs
clinical significance of dermatomes
can use pin prick test to determine the site of spinal damage
describe visceral afferents
not part of autonomic ns
nerve fibres from the organ - use sympathetic nervous system
pass through splanchnic nerves and plexuses, sympathetic collateral, and paravertebral ganglia and white rami to get to spinal dorsal root
describe the cutaneous distribution of peripheral nerves
area of skin supplied by a nerve that comes off a plexus (eg brachial and lumbosacral plexus to upper and lower limbs)
sensory neurons of the peripheral nerve may come from >1 spinal root eg lateral antebrachial cutaneous - C5-7
clinical significance of cutaneous distribution of peripheral nerves
identify which individual peripheral nerve is damaged by pin prick exam
describe myotomes
muscles that are supplied by single motor neuron root
ventral root
some muscles are supplied by >1 root
all muscle is supplied by the root of that nerve
describe peripheral neuropathies
damage/disease affecting PNS nerves
may impair sensation, movement gland or organ function
sensory nerves - tingling, pain and numbness
motor nerves - weakness to hands and feet
autonomic nerves - changes in heart rate or bp
describe monopathy
single nerve being affected
diabetic - ocular motor nerve - eye
describe polyneuropathy
several nerves are affected
gillian barre - inflammatory
causes of peripheral neuropathies
metabolic, toxic, inflammatory, traumatic, genetic, idiopathic
structure of nerve
Connective tissues:
endoneurium - around each individual neuron, loose collagen fibrils
perineurium - around a fascicle (bundles of neurons and axons) - give tensile strength made of collagen
[between fascicles - have bv]
epineurium - around the entire nerve, dense, collagenous, have a blood supply, some fatty tissue
where is the PNS nerve structure present
on everything beyond the spinal cord
describe neuropraxia
small compression axon can be repaired reversible conduction block selective demyelination of axon sheath endoneurium and axon still in tact
describe axonotmesis
demyelination and axon loss
epineurium and perineurium remain in tact
still some continuity with the nerve
degeneration below and proximal to the site of injury
describe neurotmesis
more sever injury - less likely for complete recovery
scaffold disrupted
associated with complete nerve division and disruption
seen after toxic/ischemic injuries
damage to endoneurium, perineurium and epineurium, around centre of nerve - no nerve growth (different degrees eg endo, endo and peri, endo and peri and epi)
describe axon regeneration
distal portion of axon is phagocytosed - remove myelin and axon - Wallerian degeneration
proximal end of nerve fibre regenerating into tube of shwann cells - stump from axon grow, try to reach tissues
shwann cell proliferate
what happens in a neuroma
axon doesn’t find final position
makes nerves there
what does avulsed mean
not in tact
what happens if there is avulsion in the ventral root and dorsal root
ventral: degeneration - it is not attached to the cell body
in dorsal cell body is attached so still intact
how do you do an EMG
put needle in muscle
what is the purpose of an EMG
distinguishes between myopathies and muscle weakness due to nerve pathology
what creates a larger response on the EMG
the fibre being closer to the electrode
ehat is myopathy
damage to the muscle fibre
what is the effect of myopathy on contractions
they are spontaneous
less frequent than in the nerves
signal is smaller
what is a nerve conduction study
a diagnostic technique for evaluating the speed of nerve impulses
Describe the NCS
involves the median nerve (in arm) electrodes are placed on the nerve create an electric field this stimulates the nerve the EMG is recorded at the surface
calculation for the conduction velocity
distance cm/(proximal latency - distal latency ms)
difference in latency between proximal and distal electrodes
proximal has a larger latency time
what can you measure in a NCS
NCV in m/s
amplitude of responses in mV
conditions you can see with a NCS
anoxopathies (from amplitude) and demyelinating neuropathies (from NCV)
what are axonal neuropathies
damage to the axons
result of axonal neuropathy
reduced amplitude
result of demyelination in NCS
proximal is delayed
result of demyelination and a conduction blocker in NCS
lower amplification
more delayed
Gillian Barre syndrome
what is a somatosensory evoked potential
evaluation of the site of a lesion in somatosensory pathways by assessment of amplitude and latency
why do you need to average many responses
the amplitude from the nerve responses is very small
so need averaging of 100 samples to get rid of noise
where do you put the electrodes in SEP
lower neck back of the neck cortex thalamus spinal area
how can you tell there is a lesion in SEP
there is a delay
alternative method to SEP to confirm a lesion
take a biopsy
which nerves don’t have ganglia
sacral and vagus
what type of nerve fibres are preganglionic and presynaptic
myelinated b fibres
multipolar
where do the postganglionic and synaptic fibres arise from
the crest cells
describe the postganglionic and synaptic fibres
multipolar
unmyelinated c fibres
what is the effect of a denervated muscle on an EMG
damaged nerve
surrounding nerves take over
larger signal there
fibrillation
