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Neurosceince and mental health > PNS > Flashcards

PNS Flashcards

1
Q

Describe the divisions of the PNS

A

Sensory (afferent) divison

Motor (efferent) division

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2
Q

What can the motor (efferent) division of the CNS be split into

A

Autonomic nervous system

Somatic nervous system

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3
Q

Describe the key differences between the sympathetic and parasympathetic divisions of the autonomic nervous system

A

Parasympathetic
Conserves energy

Sympathetic
Mobilised body systems

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4
Q

Essentially, what is the PNS

A

A communicating centre which communicates between the body and CNS

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5
Q

What are the three germ cell layers

A

Ectoderm- CNS and skin
Mesoderm- muscles
Endoderm- GUT

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6
Q

Describe the neural crest

A

Non-Neural ectoderm-skin
Neural ectoderm- CNS
At junction- neural fold- neural crest cells- relay info between skin and CNS- migrate into various populations- - give rise to the PNS

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7
Q

By the end of development, where is the segmental arrangement of the nervous system (as determined by somites) retained

A

The spinal cord

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8
Q

List some lineages of neural crest cells

A 
Scwhann cells
Sensory neurones
Dorsal root ganglia
Chromaffin cells of the adrenal medulla
Melanocytes
Autonomic ganglia
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9
Q

Describe the basic structure of a sensory Neurone

A

Peripheral process:
From one half of cell body to sensory receptor along axon and dendrites between receptor and axon

Central process
Other half of cell body to CNS along axon via dendrites at end

Direction of conduction is from the Sensory receptor to the CNS

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10
Q

What is meant by the basal plate

A

motor neurones derived from the ventral region of the basal plate in the developing spinal cord

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11
Q

Describe the different types of sensory nerve fibres

A

A fibres: myelinated somatic
B fibres: myelinated visceral

C fibres: unmyelinated somatic and visceral pain afferents

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12
Q

Describe the different types of sensory receptors

A

Free nerve endings- pain
Encapsulated nerve ending (with connective tissue capsule)- e.g pacinian corpuscle- pressure
sensory cell- ear
cell with peripheral processes- smell (does not pass through sensory ganglia)

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13
Q

Where may the sensory ganglia be found

A

Sensory neurone cell bodies (somatic and autonomic) lie in ganglia associated with spinal dorsal roots or some cranial nerves

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14
Q

Summarise the somatic nervous system

A

Consists of efferent nerves responsible for stimulating muscle contraction
Basic route of nerve signals begins in the primary motor cortex
Can be voluntary or autonomic (reflexive)
Nerves terminate at the NMJ to produce the motor response

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15
Q

What are the different types of motor neurones

A

Upper motor neurones-Exclusive to the CNS- travel to the ventral horn via the pyramid tract (can also synapse in the brainstem)
Lower motor neurones- Innervate skeletal muscle fibres- the cell bodies of which arise in the spinal cord

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16
Q

Describe the embryology of the spinal cord

A

The neural tube contains neuroblast cells, its hollow centre (central cavity) becomes the spinal canal.
Neuroblasts adjacent to the canal divide and travel to the outer mantel- forming the neurones of the grey mater
These neuroblasts project nerve fibres that grow outwards into the marginal zone- forming the white mater of the spinal cord.

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17
Q

What happens to the neuroblasts in the grey mater

A

They form two discrete populations
A Doral alar plate and a ventral basal plate separates by a shallow groove (sulcus limitans).
Alar plate- interneurones and sensory neurones (from neural crest cells) of the dorsal horns
Basal plate- upper motor neurones of the ventral horn

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18
Q

What else may be found in the basal plate

A

Sympathetic and parasympathetic pre-ganglionic neurones

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19
Q

Describe motor neurones

A

Sensory neurone cell bodies (somatic and autonomic) lie in ganglia associated with spinal dorsal roots or some cranial nerves.
Each motor neurone that supplies a muscle is called a motor unit- will branch to innervate different muscle fibres (different motor neurones may innervate different muscle fibres of the same muscle)

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20
Q

How many PNS nerves are there

A

43 pairs of nerves
12 cranial nerves
31 spinal

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21
Q

What are the 12 cranial nerves

A 
Olfactory
Oculomotor
Trochlear
Abducens
Optic
Trigeminal
Facial
Vagus
Glossopharyngeal
Cranial Accessory 
Vestibulocochlear
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22
Q

Summarise the autonomic nervous system

A

Efferent nerves and ganglia, stimulating effectors outside our control (e.g., heart rate)

Consists of two divisions:
Sympathetic
Parasympathetic
3 neurones; autonomic ganglia contain synapses (as well as cell bodies)

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23
Q

Describe the different motor neurones of the ANS

A

1st . neuron from hypothalamic nuclei to brain stem nuclei (parasympathetic cranial) or spinal cord (sympathetic/parasympathetic sacral).

2nd . Neuron - preganglionic Neuron from brain stem nuclei/ or spinal cord to autonomic ganglia. (presynaptic neuron if from vagal nerve and Sacral parasympathetic nerves).

3rd. Neuron - postganglionic Neuron from autonomic ganglia to Visceral Effectors (postsynaptic neuron if associated with vagus nerve or sacral parasympathetic nerves).

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24
Q

What is important to remember about the vagal and sacral parasympathetic nerves

A

no ganglia, so denoted as pre and post synaptic neurones

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25
Q

List some visceral effectors of the ANS

A

Smooth muscle
Adipocytes
Glands
Cardiac Muscle

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26
Q

What are the anatomical divisions of the ANS

A

Sympathetic
T1-L2
Parasympathetic
S2-S4 and Cranial 10, 3,7,9

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27
Q

Where are the pre-ganglionic and pre-synaptic neurones of the ANS derived from

A

Basal plate and


Pre-ganglionic sympathetic motor neurones (T1 – L2)

- intermediolateral cell column
Pre-synaptic parasympathetic Sacral neurons (S2-4). 

Multipolar, myelinated 
B fibres

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28
Q

Where are the post-ganglionic and post-synaptic neurones of the ANS derived from

A

Derivatives of Neural Crest Cells.

Post-ganglionic Autonomic neurons (symp and parasymp)

Post-synaptic parasympathetic neurons (if associated with Vagus or sacral S2,3,4 parasympathetic)

Multipolar, unmylinated 
C fibres

29
Q

Summarise the functional components of the PNS

A

§ Somatic motor neurones have their soma in the CNS.

§ Autonomic motor neurones consist of a preganglionic and postganglionic motor neurone.

o There is an autonomic ganglion (with a synapse) in between the CNS and the effector

§ Sensory neurones have a ganglion in the middle ( NO SYNAPSE)

30
Q

What type of neurones are sensory neurones and motor neurones

A 
Sensory= pseudo unipolar 
Motor= unipolar (but technically multipolar)
31
Q

Describe the process of myelination

A

Myelin is formed by Schwann cells which wraps around the axon clockwise to form successive layers
Minor dense line: plasma membrane of Schwann cells
Major dense line: where cytoplasm of Schwann cells is condensed
Nodes of Ranvier: where saltatory conduction occurs
A-Fibre: up to 100 layers
C-Fibre: still wrapped by one layer of Schwann cell membrane

32
Q

Describe non-myelinated cells

A

Non-myelinated Cells – Axon diameter ~1m:
 Clothed in cytoplasm of Schwann cell (neurolemma).
 Several axons clothed per Schwann cell.
 Each axon only has a single layer of membrane and CANNOT facilitate Saltatory conduction
NOTE: Schwann cells are ALSO present on non-myelinated cells and they engulf multiple axons.

33
Q

What is the propagation speed of a nerve impulse related to

A

It is not related to the strength of the stimulus
Related to diameter (larger diameter, less resistance, greater speed of propagation)
Myelination (myelinated fibres conduct impulses faster, because of saltatory conduction)

34
Q

Describe the differences in the propagation speed of each type of sensory fibre

A

A Fibres: 5-20microns and myelinated therefore 130m/sec
B Fibres: 2-3microns and myelinated therefore 15m/sec
C Fibres: 0.5-1.5microns and unmyelinated therefore 2m/sec

35
Q

Describe the different types of A fibres

A

alpha- 13-20 microns, 80-120m/s
beta- 6-12 microns, 35-75 m/s
gamma- 1-5 microns, 5-35 m/s

36
Q

Describe the basic anatomy of the nervous system

A

Dorsal Root Ganglion: contains the cell bodies of sensory neurones entering the cord
Dorsal (Posterior) Horn: extends to edge of spine and receives inputs from sensory neurones
Ventral (Anterior) Horn: does not extend to edge of spine and contains the cell bodies of motor neurones that will exit the cord

Mixed spinal nerves: dorsal and ventral root nerves combine to form a mixed spinal nerve
Intravertebral foramen: space between vertebra where the mixed spinal nerve may emerge
Rami: the mixed spinal nerves branch to form rami upon exiting the cord
Dorsal (Posterior) Ramus: supplies the back of the body
Ventral (Anterior) Ramus: supplies the front and sides of the body

37
Q

Describe the cranial parasympathetic ganglia

A

four ganglia with synapses between pre/postganglionic neurones (ciliary, submandibular, otic and pterygopalatine)

38
Q

Describe the paravertebral sympathetic chain ganglia

A

pre-ganglionic neurone exits ventral ramus and passes through white ramus into paravertebral chain, with three possible outcomes:
Synapses to post-ganglionic neurone which exits via grey ramus to ventral root (sweat glands, piloerector muscles, blood vessels of skin and skeletal muscles).
Pre-ganglionic fibre moves up/down 2 levels and then synapses (iris, salivary glands, thoracic blood vessels, eosophagus)
Neurone passes through white ramus to splanchnic nerves and synapse to collateral ganglion, before post-ganglionic neurone continues to organs ( liver, spleen, stomach, intestines, kidneys, reproductive organs)

39
Q

Describe plexi

A

networks of successive ventral rami exchange fibres to innervate limbs (except in thoracic region), where roots branch to cross and redistribute signals so that each myo/dermatome is innervated by nerves +/- 1 level that the main ramus originates from - a lesion at one root will not lead to a full loss of sensation or paralysis

40
Q

What does the brachial plexus consist of

A

BRACHIAL PLEXUS
(UPPER LIMBS)

VENTRAL RAMI:
C5 TO T1 SPINAL NERVES

41
Q

What does the lumbosacral plexus consist of

A

LUMBOSACRAL PLEXUS
(LOWER LIMBS)

VENTRAL RAMI:
L2 – S2 SPINAL NERVES

42
Q

What is the skin described as

A

A continuous organ- dermatomes can overlap

43
Q

What is meant by a dermatome

A

Areas of skin supplied by a single sensory spinal nerve root. Skin is a continuous organ
Stacked along the thorax and abdomen; longitudinally along the limbs
Clinical significance: can determine the site of spinal damage by simple pin prick exam

44
Q

What is important to remember about visceral afferents

A

VISCERAL AFFERENTS ARE NOT A PART OF THE ANS BUT THEY PASS THROUGH THE SPLANCHNIC NERVES AND PLEXUXES, THE SYMPATHETIC COLLATERAL & PARAVERTEBRAL GANGLIA AND WHITE RAMI TO GET TO THE SPINAL DORSAL ROOT .

They use the sympathetic nervous system to get to the spinal dorsal root, but they are one continuous fibre

45
Q

Describe the phenomenon of referred pain

A

PHENOMENON OF REFERRED PAIN AT THE CORRESPONDING DERMATOME(S) OF THE SPINAL DORSAL ROOT(S)

46
Q

Describe the cutaneous distribution of peripheral nerves

A

Areas of skin supplied by a peripheral nerve that may be coming off a plexus.

Sensory Neurons of the peripheral nerve may come from more than one spinal nerve root

Clinical Significance: Identify which individual peripheral nerve is damaged by pin prick exam

47
Q

What is meant by a myotome

A

Muscles are discrete organs
Biceps supplied by more than one ventral root- nerve has two roots
Muscles that are supplied by a single motor spinal nerve root
Clinical significance: Testing for root level muscle weakness

48
Q

Describe the spinal levels which correspond to upper and lower limb innervation

A 
Head: Cranial and C2 
Neck: C3-C4 
Arms: C5-T1 
Torso: T1-L1 
Legs: L2-S4
49
Q

What is meant by peripheral neuropathies

A

Damage or disease affecting PNS nerves

May impair sensation, movement, gland or organ function

50
Q

Describe the different presentations of peripheral neuropathies

A 
Sensory nerves (sensation): cause tingling, pain, numbness 
Motor nerves (movement): cause weakness to hands and feet
Autonomic nerves (involuntary functions): cause changes in heart rate or blood pressure
51
Q

Summarise the causes of peripheral neuropathies

A

Has many causes
Mononeuropathy: refers to a single nerve being affected ( diabetic- oculomotor nerve)
Polyneuropathy: refers to several nerves being affected (Guillian- Barre syndrome- inflammatory)
Causes can be metabolic, toxic, inflammatory, traumatic, genetic
~30% of neuropathies are “idiopathic” - i.e. of unknown origin

52
Q

Describe the structure of a peripheral nerve

A

 The axons are in bundles called FASCICLES which are grouped together to form NERVES. blood vessels found between the fascicles

This structure is found from the spinal cord onwards
Connective tissues:

Endoneurium:
Around each individual neuron/axon
Loose collagen fibrils

Perineurium:
Around a fascicle (bundles of neurons/axons)
Gives main tensile strength to nerve

Epineurium: 
Around the entire nerve, 
Dense, collagenous
Blood supply
Some fatty tissue
53
Q

Why is the packaging of connective tissue important in nerves

A

 Some of the axons are very long and need to be able to cope with strain (e.g. bending of joints) so the packaging and connective tissue is very important.

54
Q

Describe neuropraxia

A

Slight compression in axon- recoverable. No axonal discontinuity
reversible conduction block
selective demyelination of the axon sheath
endoneurium and axon still intact - e.g., nerve compression
Class 1 injury

55
Q

Describe axonotmesis

A 
Class 2 injury 
Some disruption to axon
demyelination and axon loss 
epineurium and perineurium remain intact 
still some continuity within the nerve
degeneration occurs below and slightly proximal to the site of injury
Follows wallerian degeneration
axoplasmic disruption
56
Q

Describe neurotmesis

A

Class 3,4 and 5
most severe form of nerve injury
associated with complete nerve division and disruption
commonly seen after toxic or ischemic injuries
Damage to the epineurium (around the entire nerve) - no nerve growth
Damage to nerve structures
More severe= less chance of recovery
Wallernian degeneration

Axon disrupted, loss of tubules, support cells destroyed

57
Q

Describe regeneration of the nerve axon

A
  1. With the compression injury (forceps), the axoplasm is completely separated but the Endoneurium remains intact (important as a scaffold to build off).
  2. Once the compression has occurred, the part distal to the soma of the nerve degenerates.
  3. The macrophage influx clears the debris.
  4. The Schwann cells undergo mitosis and proliferate.
  5. Axonal sprouts grow from the proximal stump and there is competition between them to synapse with the target organ first.
  6. Once an axonal sprout synapses, the other axonal sprouts regress and the successful axonal sprout grows and is myelinated.
  7. End-result is an axon which looks similar to the original but the internode distance (between nodes of ranvier) is less than original (so conduction speed decreases).
58
Q

Describe post-ganglionic injury

A

e.g. Neuroma (axon doesn’t find final position)

59
Q

Describe pre-ganglionic nerve injury

A

dorsal root avulsion will lead to nerve surviving as cell body keeps alive; motor and ventral roots degenerate as detached from cell body

60
Q

What happens when a peripheral nerve is damaged

A

When a peripheral nerve is damaged:

The distal part of the nerve degenerates and macrophages phagocytose the axonal and myelin debris (Wallerian degeneration)

The proximal part of the axon and cell body usually survive but undergo metabolic changes (chromatolysis)

During regeneration Schwann cells proliferate to form a scaffold and axonal sprouts grow out from the proximal stump of the nerve into the distal stump

Successful regeneration mainly depends on how badly the axons and connective tissue sheaths are damaged and the distance from the target organ

Failure to reconnect leads to formation of a neuroma containing trapped axon

61
Q

What is meant by glove and stocking distribution

A

peripheral neuropathies Usually begins in distal parts of limbs (glove and stocking distribution)

62
Q

Describe some defects in nerve repair

A

 If the injury is close to the soma, the shock may kill the whole cell.
 If a compression injury occurs, the endometrial sheath is left intact, providing a scaffold to re-grow off but if the nerve is cut, the axonal sprouts have no guidance cues and so you ay have re-innervation of the wrong target.
o Clean cut = Surgeon can re-join in microsurgery.
o Mess cut = Nerve graft from the back of the calf.
 The damage could be so severe that the axonal sprouts have no guidance at all and form a tangled bundle called a neuroma  very painful and need to be surgically removed.

63
Q

What is meant by electromyography

A

Needle EMG: Diagnostic technique that distinguishes between myopathies (intrinsic to muscle) and muscle weakness due to nerve pathology (neurogenic). Looks at the waveforms of Motor Unit Action potentials.

64
Q

How do you perform an EMG

A

stick needle in muscle and ask patient to make slight movement, causing an AP; approach to electrode causes initial down deflection before up deflection when reaches the electrode, followed by another down deflection; can be used to distinguish myopathy and neuropathy

65
Q

Describe the EMG patterns of denervated muscle and myopathy

A

Denervated muscles: leads to fibrillation and larger signal as other nerves will take over; reduced interference pattern
Myopathy: leads to fibrillation with smaller polyphasic units and a full interference pattern

66
Q

What is meant by Nerve Conduction Study

A

Diagnostic technique for evaluating the speed of nerve impulses
nerve conduction velocity (NCV) in m/s
Amplitude of responses in mV.
Axonopathies (Amp), Demyelinating neuropathies (NCV)

67
Q

What happens in demyelination + Conduction Block (Guillian- barre syndrome)

A

Increased latency and reduced amplitude

68
Q

How do we perform a nerve conduction study

A

stimulate the muscle with electrode; electrical field penetrates skin to activate nerve; timing allows for conduction velocity to be calculated
CV= Distance/ proximal latency -distal latency (ms)

69
Q

Describe Somatosensory evoked potential

A

Evaluation of site of lesion (PNS or CNS) in somatosensory pathways by assessment of amplitude and latency of responses. Example, MS
Very small amplitude of NERVE responses (μV) therefore constant averaging over MANY responses is necessary to negate noise, compared to surface EMG (mV) looking at MUSCLE.

Neurosceince and mental health (18 decks)

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