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Medicine Year 1 Semester 1 - Part 2 > Spinal Nerves, Dermatomes and Myotomes > Flashcards

Spinal Nerves, Dermatomes and Myotomes Flashcards

1
Q

What does gray matter contain ?

A

Contains neuronal cell bodies within the horns.

Receives sensory information from the periphery and sends motor stimuli to the periphery.

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2
Q

What does white matter contain ?

A

Myelinated and un-myelinated nerve fibres.

Conduction of information inside the nervous system.

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3
Q

Describe the horns of the gray matter

A

Dorsal (posterior) horns : inter-neurons, sensory neurons

Lateral horns : visceral (autonomic) motor neurons

Ventral (anterior) horns : somatic motor neurons

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4
Q

Where are lateral horns found ?

A

Lateral horns are only found in thoracic and upper lumbar regions.

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5
Q

Function of visceral motor neurons

A

Innervate smooth muscles and glands

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6
Q

What divides the spinal cord ?

A

Posterior median sulcus - found at dorsal horn side
Anterior median fissure - found at ventral horn side

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7
Q

How many spinal nerves are there ?

A

31

8 Cervical
12 Thoracic
5 Lumbar
5 Sacral
1 Coccygeal

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8
Q

Where do the spinal nerves emerge from ?

A

The C1 nerve passes between the occipital bone and the atlas.

The C2-L5 spinal nerves emerge through their own intervertebral foramen.

S1-S4 from anterior and posterior sacral foramina.

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9
Q

Describe the ventral root

A

Contains :

Anterior root
Ventral root
Motor root

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10
Q

Describe the dorsal root

A

Contains :

Posterior root
Dorsal root
Sensory root

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11
Q

What does the ventral horn contain ?

A

Somatic neuron
(lower motor) in ventral horn

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12
Q

What does the lateral horn contain ?

A

Visceral motor (preganglionic sympathetic) neuron
in lateral horn

Found between T1 and L2

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13
Q

What does the dorsal root ganglion contain ?

A

Contains 1st order sensory pseudo-unipolar neuron

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14
Q

Difference between root and rami

A

Roots are pure
Rami are mixed

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15
Q

What are rootlets ?

A

Rootlets contain axons of one type of neuron (either motor or sensory, irrespective of somatic or visceral)

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16
Q

Describe formation of spinal nerves

A

Rootlets
Roots (dorsal and ventral - posterior and anterior)
Spinal nerve
Dorsal ramus and Ventral ramus

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17
Q

Describe the dorsal ramus

A

Posterior branch
Dorsal ramus
Motor and Sensory neurons

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18
Q

What do the dorsal rami of the thoracic spinal nerves carry ?

A

Motor fibres to erector spinae (back muscle)

Sensory fibres from the skin of the back and from vertebral joints.

Sympathetic neurons to blood vessels and sweat glands of the skin of the back.

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19
Q

What do the ventral rami of the thoracic spinal nerves carry ?

A

Motor fibres to intercostal muscles

Sensory fibres from the thoracic skin and parietal pleura and vertebral joints.

Sympathetics fibers to blood vessels and sweat glands of the skin.

T1 also contributes to a nerve plexus. (brachial)

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20
Q

What is the function of the motor fibres of the dorsal ramus ?

A

Innervate the deep muscles of the back

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21
Q

What is the function of the sensory fibres of the dorsal ramus ?

A

Innervate the skin of the back

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22
Q

Describe the ventral ramus

A

Anterior branch
Ventral ramus
Motor and Sensory neurons

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23
Q

Ventral ramus vs Dorsal Ramus

A

They both carry motor and sensory information.

Ventral ramus is thicker.

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24
Q

What are nerve plexuses ?

A

Ventral rami of spinal nerves may join with others to form nerve plexuses.

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25
Q

What do adjacent rami communicate to form ?

A

Large plexuses e.g. :

  • Cervical plexus : C1-4
  • Brachial plexus : C5-T1
  • Lumbar plexus : L1-4
  • Sacral plexus : L4-S4
26
Q

What is different about the nerves of the thoracic region ?

A

The nerves of the thoracic region remain distinct from each other.

They are continuous with the intercostal nerves.

27
Q

What do the nerves of the plexuses and intercostal nerves provide ?

A

Sensory innervation to the :

  • upper and lower limbs
  • ventral abdominal wall
  • thoracic wall
28
Q

What is reflex ?

A

Reflex is a rapid, involuntary motor response to a stimulus.

29
Q

What is a reflex arc ?

A

Receptor
Sensory neuron
Integration centre
Motor neuron
Effector organ

30
Q

Function of the spinal reflex

A

Somatic spinal reflexes provide information on integrity of the reflex pathway and degree of excitability of the spinal cord.

31
Q

Describe the development of somites

A

Around day 20 of gastrulation, in the occipital region, paraxial mesoderm becomes segmented and organises into somites.

32
Q

What do somites differentiate into ?

A

(new somites appear in a cranio-caudal sequence)

Sclerotome
Myotome
Dermatome

33
Q

Describe the formation of sclerotome

A

Cells in the ventral and medial walls of the somite shift their position to surround the neural tube and notochord.

They form sclerotome which forms the vertebrae and ribs.

34
Q

What does sclerotome form ?

A

Vertebrae and ribs

Each vertebral body is derived from 2 adjacent somites.

35
Q

Describe the formation of dermatome (dermatomyotome)

A

Cells at the dorsomedial and ventrolateral edges of the upper region of the somite, form precursors and muscle cells, whereas cells from these 2 groups form the dermatome.

36
Q

What is dermatome ?

A

Dermatome is an area of skin innervated by a single spinal segment.

37
Q

What does the dermatome give rise to ?

A

The dermis.

38
Q

What does the dorsal root ganglia contain ?

A

The cell bodies of somatic sensory neurons are located in the dorsal root ganglia, which develop from neural crest.

39
Q

What is a dermatomyotome ?

A

Myotome + Dermatome

40
Q

What does a dermatomyotome give rise to ?

A

Dermatomyotome of each somite gives rise to skeletal muscle and dermis of skin.

41
Q

What does dermatome contain ?

A

Axons of sensory neurons that innervate a defined area of skin.

42
Q

What does myotome contain ?

A

Axons of motor neurons that innervate a group of muscles arising form the same somite.

i.e. they share the same function

43
Q

What is myotome ?

A

Dorsomedial muscle cells

A group of muscles innervated by the same spinal nerve.

44
Q

What do dorsomedial muscle cells give rise to ?

A

Intrinsic back muscles

45
Q

What do ventrolateral muscle cells give rise to ?

A

All other trunk and limb muscles.

46
Q

What does myotome give rise to ?

A

Skeletal muscle.

The cell bodies of motor neurons that will supply this myotome are located anteriorly in the neural tube.

Axons of motor neurons (to become spinal nerves later) from the spinal cord segment adjacent to their corresponding somite follow the dermatomyotome.

47
Q

Myotome examination

A

Most muscles of the body are innervated by more than one spinal cord level.

Selected joint movements are used to test myotomes.

48
Q

What causes shingles ?

A

Varicella / Herpes Zoster virus

After initial infection (chickenpox) the virus lies dormant in a dorsal root ganglion.

The virus can be reactivated in later life causing shingles.

49
Q

C4

A

Tip of shoulder

50
Q

C6

A

Thumb

51
Q

C7

A

Middle finger

52
Q

C8

A

Little finger

53
Q

T10

A

Umbilicus

54
Q

L5

A

Big toe

55
Q

Why do you need to perform a lumbar puncture ?

A

Sample CSF for blood or organisms

Measure the pressure of CSF

Injection of anaesthetics
Injection of medications

56
Q

Why is it safest to carry out lumbar puncture from the lumbar cistern ?

A

Spinal cord ends at L1/2

Subarachnoid space (dural sac) extends to S2

Cauda equina is unlikely to be damaged.

57
Q

What is the supracristal plane ?

A

A plane (line) between the superior most points of iliac crests

Crossing L4 spinous process and L4/5 intervertebral disc.

58
Q

Clinical Relevance of Lumbar puncture

A

Contraindicated (not used) in patients with raised intracranial pressure. (as may cause harm)

Can lead to coning (herniation of the brain)

59
Q

Layers of the back

A

Skin
Superficial fascia
Supraspinous ligament
Interspinous ligament
Ligamentum flavus
Extradural space
Dura mater
Arachnoid mater
Subarachnoid space
Pia mater

60
Q

Paresthesia

A

Altered sensation (pins and needles)

61
Q

What is the function of the L5 root ?

A

One of the roots that provides motor innervation to the anterolateral muscles of the calf.

Altered motor function and tendon reflexes.

62
Q

Where are sympathetic neurons found ?

A

T1-L2 segments, although the axes of these neurons are found in all spinal nerves.

Medicine Year 1 Semester 1 - Part 2 (37 decks)

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