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LCRS > Neuroscience 8 - PNS > Flashcards

Neuroscience 8 - PNS Flashcards

1
Q

Describe the structure of a sensory neuron.

A
  • Pseudounipolar
  • One long dendrite, cell body in the middle, then a long axon
  • May be type A, B or C
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2
Q

List the types of sensory neuron.

A
  • Free nerve endings (pain receptor neurons)

- Encapsulated nerve endings in the pacinian corpuscle

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3
Q

Describe the structure of the somatic nervous system

A
  • Consists of efferent nerves responsible for stimulating muscle contraction
  • The basic route of nerve signals begins in the primary motor cortex
  • Voluntary or automatic
  • Nerves terminate at the NMJ
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4
Q

Describe the pathway through the ventral and dorsal horns

A
  • Sensory input enters the dorsal horn of the spinal chord through the dorsal root, which passes through the dorsal root ganglion
  • Motor nerves enter the ventral root to muscles.
  • Motor and sensory neurons mix in the mixed spinal nerve
  • The mixed spinal nerve splits into the anterior and posterior ramus
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5
Q

How many pairs of PNS nerves are there?

A

12 cranial nerves

31 spinal nerves

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6
Q

Briefly describe the structure of the autonomic nervous system

A
  • Efferent nerves and ganglia stimulate effectors outside our control
  • Parasympathetic/sympathetic
  • 1st neuron is from hypothalamic nuclei to brain stem/spinal cord
  • 2nd neuron (preganglionic) to the autonomic ganglia
  • 3rd neuron postganglionic to the visceral effectors
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7
Q

What are the types of nerve fiber?

A
  • A fibers
  • B fibres
  • C fibres
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8
Q

Describe the structure and location of A nerve fibers.

A
  • Largest diameter
  • Thick myelin sheath
  • Somatic (sensory and motor neurones to skeletal muscle)
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9
Q

Describe the structure and location of B nerve fibers.

A
  • Medium
  • Myelinated
  • Visceral (sensory and autonomic preganglionic)
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10
Q

Describe the structure and location of C nerve fibres.

A
  • Unmyelinated, smallest diameter

- Sensory and autonomic motor neurones.

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11
Q

Which factors affect conduction speed?

A
  • Myelination
  • Larger fibres conduct faster due to the increased size and reduced resistance.
  • Temperature
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12
Q

What is a nerve plexus?

A
  • A network of nerve fibres originating from different levels associated with an organ
  • Formed from merging of anterior rami of the spinal cord and blood vessels
  • Mainly innervate the limbs
  • Thoracic ventral rami don’t form nerve plexuses
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13
Q

What is a dermatome?

A
  • An area of skin supplied by a single sensory spinal nerve root.
  • Stacked along the thorax and the abdomen, longitudinally across the limbs
  • Used to assess spinal damage with a skin prick test
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14
Q

What are visceral afferents?

A
  • They pass through the spanchnic nerves and plexuses

- This is to get to the spinal dorsal root - they are not a part of the ANS

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15
Q

What is a myotome?

A
  • Muscles supplied by a single motor spinal nerve root
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16
Q

What is the clinical significance of myotomes?

A

They allow testing for root level muscle weakness.

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17
Q

What is a peripheral neuropathy?

A

Damage or disease affecting the PNS nerves

18
Q

What symptoms will you get if you have damage to the sensory nerves?

A

Tingling, pain and numbness due to loss of sensation

19
Q

What symptoms will you get if there is damage to the motor nerves?

A

Weakness to the hands and feet

20
Q

What symptoms will you have if there is damage to the autonomic nerves?

A

Changes in heart rate/blood pressure

21
Q

What are the two types of neuropathy?

A
  • Mononeuropathy is where a single nerve is affected

- Polyneuropathy is where several nerves are affected

22
Q

What are the causes of neuropathies?

A
  • Metabolic
  • Toxic
  • Inflammatory
  • Traumatic
  • Genetic
  • Idiopathic
23
Q

Describe the structure of a PNS nerve.

A
  • Endoneurium is around each neuron/axon
  • Perineurium is around a fascicle (a bundle of neurones/axons)
  • Epineurium is around the entire nerve
24
Q

What is the perineuriums function?

A

It gives the nerve its main tensile strength

25
Q

What us the composition of the epineurium?

A
  • Dense collagenous
  • Good blood supply
  • Some fatty tissue
26
Q

What is neuropraxis?

A
  • A reversible block in conduction due to selective demyelination of the axon sheath
  • The endoneureum and axon is still intact
  • Often due to nerve compression
27
Q

What is axontmesis?

A
  • 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
28
Q

What is neurotmesis?

A
  • The most severe form of nerve injury
  • Associated with complete nerve division and disruption
  • Commonly seen after toxic or ischemic injuries
  • There is damage to the epineurium (around the entire nerve), so no nerve growth
29
Q

What is wallerian degeneration?

A
  • A process that occurs when a nerve fiber is cut or crushed and the part of the axon distal to the injury degenerates.
  • This is also known as anterograde or orthograde
30
Q

What is chromatolysis?

A

Dissolution of the nisl bodies in the cell body of a neuron

31
Q

What are the uses of EMG in diagnosis?

A

It is used to distinguish between myopathies and muscle weakness due to nerve pathology

32
Q

What is a nerve conduction study?

A
  • A diagnostic technique where the speed of impulses is evaluated
  • Assesses the peripheral nerves only
33
Q

What is somatosensory evoked potential (SEP)?

A
  • The site of a lesion is evaluated by assessment of amplitude and latency of responses
  • Peripheral and central pathways
  • Used in MS diagnosis
34
Q

What spinal level innervates the upper limbs?

A
  • The brachial plexus innervates the upper limbs (C5 to C8 and T1)
  • Cervical nerves
35
Q

Which section of the spinal cord innervates the lower limbs?

A

The lumbar nerves

36
Q

True or false: A peripheral nerve may contain myelinated or unmyelinated fibres but not both

A

TRUE

37
Q

What is the name for the supporting cells of the dorsal root ganglia?

A

Satellite cells

38
Q

Describe how the mixed spinal nerve divides

A
  • Dorsal ramus
  • Ventral ramus
  • Grey and white ramus communicans
39
Q

What is the ventral ramus?

A

Contains nerves that serve ventral parts of the trunk and upper/lower limbs (somatic and visceral sensory and motor information)

40
Q

What is the dorsal ramus?

A

Contains nerves that supply dorsal portions of the trunk (visceral/somatic motor and somatic sensory information to and from skin/muscles of back)

41
Q

What are the white and grey ramus communicans?

A
  • Convey autonomic signals of the sympathetic nervous system, communicating the spinal nerve and sympathetic trunk
  • Gray ramus carry postganglionic nerve fibres from ganglia to their destination (and pregnaglionic that don’t synapse)
  • White ramus carries preganglionic nerve fibres from the spinal cord to paravertebral ganglia
  • Different colours due to differences in myelination
42
Q

What is the difference between a ramus and a root?

A
  • Rootlets combine to form roots

- Roots combine to form the spinal nerve, then split again to form rami

LCRS (24 decks)

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