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Y1 Neuroscience and Mental Health > Peripheral Nervous System > Flashcards

Peripheral Nervous System Flashcards

1
Q

What are neural crest cells?

A

neural fold joins neural (CNS) and non neural component (skin), comprised of neural crest cells - cells can migrate into clusters and differentiate into the PNS (connecting skin and CNS)

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2
Q

What are sensory neurones

A

they are pseudounipolar, with a peripheral process that ends in dendrites in the skin and a soma in the middle. Central process is an axon to the CNS

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3
Q

What are the different types of sensory neurones?

A

A fibres: somatic myelinated
B fibres: visceral myelinated
C fibres: unmyelinated somatic/visceral pain afferents

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4
Q

What are ganglion?

A

Collection of sensory cell bodies

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5
Q

What does somatic nervous system do? What does it consist of?

A

Voluntary muscle control

Consists of upper and lower motor neurone

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6
Q

What is in the upper motor neurone?

A

exclusively CNS

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7
Q

What is the lower motor neurone?

A

Exclusively PNS - leads to skeletal muscle; can be activated without upper in a reflex

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8
Q

Where is a synapse found?

A

In cord or brain stem

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9
Q

What is a basal plate?

A

Ventral region of basal plate is site in developing spinal cord where motor neurones originate

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10
Q

Where are motor neurones found?

A

Motor units run cord to muscle, with each innervating several fibres but each fibre only innervated by one axon. Ventral root is where motor neurones emerge

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11
Q

What is the intervertebral foramen?

A

Gap between vertebra where mixed spinal nerves leave the cord

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12
Q

What is the rami?

A

Dorsal and ventral root emerge from cord and converge to mixed spinal nerves which then branch to form rami

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13
Q

What do posterior/dorsal ramus supply?

A

Back of body

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14
Q

What do anterior/ventral ramus supply?

A

Front and sides of body

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15
Q

How many PNS nerves are there?

A

12 cranial

31 spinal nerves (intervertebral foramen) to give 43 pairs

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16
Q

What is the autonomic NS?

A

3 neurones; autonomic ganglia contain synapses as well as cell bodies

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17
Q

What three neurones are found in the autonomic NS?

A

Hypothalamic nuclei - to brain stem nuclei (parasympathetic cranial)/spinal chord (sympathetic)/sacral region (parasympathetic sacral)
Preganglionic neurone - from brain/cord to autonomic ganglia - myelinated
Postganglionic neurone - from autonomic ganglia to visceral effectors - unmyelinated

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18
Q

What is special about vagus/sacral parasympathetic nerves?

A

No ganglia, so denoted as pre and post synaptic neurones

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19
Q

What neurones arise from the spinal cord’s basal plate? What are their structures?

A

Preganglionic sympathetic/presynaptic sacral neurones

multipolar myelinated B fibres

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20
Q

What neurones arise from neural crest, what are their structures?

A

Post ganglionic autonomic/postsynaptic and vagus/sacral parasympathetic neurones
multipolar unmyelinated C fibres

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21
Q

What cell produces myelin

A

Schwann cell, wrapping around axon clockwise to form successive layers

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22
Q

What is the major dense line

A

Plasma membrane of schwann cells where cytoplasm is condensed

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23
Q

What are the nodes of Ranvier?

A

Where saltatory conduction takes place

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24
Q

How many layers are in A fibres?

A

up to 100 layers

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25
How many layers are in C fibres?
still wrapped by one layer of schwann cell membrane
26
What is the propagation speed of A fibres
5-20 microns and myelinated therefore 130m/sec
27
What is the propagation speed of B fibres
2-3 microns and myelinated therefore 15m/sec
28
What is the propagation speed of C fibres
0.5-1 microns and unmyelinated therefore 2m/sec
29
What affects propagation speed?
Myelination | Diameter
30
What are the rootlets?
Areas of nerves closest to the cord, forming dorsal and ventral roots
31
What are the ramus?
Group of nerves following branching of mixed spinal nerves to supply either front or back of body
32
What are the paravertebral sympathetic chain ganglia?
Synapses with grey/white rami
33
What are cranial parasympathetic ganglia?
Four ganglia with synapses between pre/postganglionic neurones
34
What are the four cranial parasympathetic ganglia?
Ciliary Submandibular Otic Pterygopalatine
35
What are the paravertebral sympathetic chain ganglia?
Pre-ganglionic neurone exit ventral ramus and pass through white ramus into paravertebral chain and have three possible outcomes
36
What are the three possible outcomes of the paravertebral sympathetic chain ganglia?
- synapses to post-ganglionic neurone which exit via grey ramus to ventral root - pre-ganglionic fibre moves up/down 2 levels and then synapses - neurone passes through white ramus to splanchnic nerves and synapse to collateral ganglion, before post ganglionic neurone contines to organs
37
What are nerve plexuses?
Networks of ventral rami that exchange fibres to innervate limbs; do not form in thoracic region. Roots branch to cross and redistribute signals meaning each myotome or dermatome innervated by nerves from levels +/- 1 so a lesion at one root will not lead to full loss of sensation or paralysis
38
What are visceral afferents?
Not part of ANS, passing through splanchnic nerves and plexuses; nerve fibre from organ uses sympathetic nervous system to get to spinal dorsal root
39
Where are visceral afferents derived from?
Neural crest
40
How can you get referred pain at corresponding dermatomes
The visceral afferents use sympathetic collateral and paravertebral ganglia and white rami to get to dorsal root
41
How many spinal roots do peripheral nerves tend to have?
More than one
42
What is peripheral neuropathy?
Damage/disease to PNS nerves that may impair sensation, movement, gland or organ function
43
What are symptoms of peripheral neuropathy?
Sensory nerves: tingling, pain or numbness Motor: weakness to hands and feet Autonomic: heart rate or blood pressure changed
44
What is mononeuropathy?
When one nerve is affected and damaged/diseased
45
What is polyneuropathy?
When several nerves are damaged/diseased
46
What can cause peripheral neuropathy?
``` Metabolic toxic inflammatory traumatic genetic ```
47
What is the structure of an endoneurium?
Around each individial axon and comprised of loose collagen fibres. It is found in roots/rami
48
What is the structure of the perineurium?
``` Surrounds fascicles (bundles of axons) of nerve fibres, with greater collagen to give tensile strength. Found in roots and rami ```
49
What is the structure of the epineurium?
Around entire nerve, dense and collagenous with a blood supply and some fatty tissue Found in roots and rami
50
What is neuropraxia
Reversible conduction block, with selective demyelination of the sheath, yet endoneurium and axon intact. No axon discontinuity; recoverable axon compression
51
What is axonotmesis?
Demyelination and axon loss, with peri/epineurium still intact; still some continuity with degeneration occuring below and proximal to the site of injury
52
What is neurotmesis?
Most severe form of injury and damage to epineurium prevents growth; wallerian degeneration occurs distal to injury - support cells destroyed
53
What is the injury progression of nerve damage?
Nerve injured Phagocytes destroy axon sheath in chromatolysis/wallerian degeneration leaves a stump that sprouts and grows to muscle schwann cells proliferate around new sprout
54
What is an example of a postganglionic injury?
Neuroma - benign growth of nerve tissue (axon doesn't ifnd final position)
55
What is an example of a preganglionic injury?
Dorsal root avulsion will lead to nerve surviving as cell body keeps alive; motor and ventral roots degenerate as detached from cell body
56
What is electromyography?
Stick needle in muscle Ask patient to make slight movement causing AP approach to electrode that causes initial downward deflection Then up deflection reaches electrode, then another down Can be used to distinguish a myopathy and neuropathy
57
What does a denervated muscle look like on an electromyopathy?
Fibrillation and larger signal as other nerves will take over - reduced interference pattern
58
What does a myopathy look like on an electromyopathy?
Leads to fibrillation with smaller polyphasic units and a full interference pattern
59
What is a nerve conduction study?
Stimulate muscle with electrode Electrical field penetrates skin to activate nerve timing allows for conduction velocity to be calculated axonopathy affects amplitude demyelinating issue will affect velocity (proximal response delayed)
60
What is a somatosensory evoked potential?
Stimulation of a nerve eg median nerve by placing electrodes at various regions to evaluate the site of a CNS/PNS legion in somatosensory pathways - checking aplitudes and latency of response
61
What is a problem with the somatosensory evoked potential test?
Needs to average over many responses to negate noise as nerve responses have a naturally small amplitude
62
What are neural crest cells derived from?
Ectoderm gives rise to CNS (neural component) and skin (non-neural component);
63
What are sensory neurones derived from
neural crest cells

Y1 Neuroscience and Mental Health (10 decks)

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