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Semester 2 BMA 1912 > Sem 2 Module 2 - The Spinal Cord > Flashcards

Sem 2 Module 2 - The Spinal Cord Flashcards

1
Q

What is in the Spinal Cord?

A
  • Is composed of interneurons
  • Receives and directs incoming sensory information to procession centres in the brain
  • Receives and relays motor output from the brain
  • Initiates spinal reflexes
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2
Q

What is the gross anatomy of the Spinal Cord?

A
  • Approximately 42cm long and 14mm wide
  • Extends from foramen magnum to L2 in adults and L4 in infants
  • Terminates in a cone shaped structure —> conus medullaris
    - filum terminale —> a strand of fibrous tissue that extends from the conus medullaris and anchors the spinal cord to the coccyx
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3
Q

What are the spinal nerves?

A

Spinal nerves are:

  • Short nerves
  • Contain both sensory and motor axons (mixed nerves)
  • Connect to the spinal cord at one end and branch to form peripheral nerves at the other
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4
Q

How do the spinal nerves attach

A

Spinal nerves attach to the spinal cord by paired nerve roots —-> dorsal and ventral roots

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5
Q

What is the Ventral root?

A

Contains the axons of motor neurons (issue motor commands to effector gland and muscles)

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6
Q

What is the dorsal root?

A

Contains the axons of sensory neurons (relays sensory input from receptors to the spinal cord)

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7
Q

How is the spinal cord protected?

A

The spinal cord is protected by the vertebral column, cerebrospinal fluid and the spinal meninges

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8
Q

What are the spinal meninges?

A
  • Are continuous with the brain meninges
  • Include the dura, arachnoid and pia mater
  • Contain CSF within the subarachnoid space
  • Provide stability and protection for the spinal cord
  • Contain blood vessels that deliver oxygen and nutrients to cord tissue
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9
Q

What is a lumbar puncture (spinal tap)?

A
  • Involves the insertion of a needle into the subarachnoid space beyond the L3

This procedure:

  • Does not damage spinal cord
  • Used to withdraw CSF for diagnostic testing
  • Used to administer medications
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10
Q

What are the spinal meninges separated by?

A

Epidural space

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11
Q

What is the epidural space?

A
  • Filled with adipose tissue and blood vessels
  • Site of anaesthetic injection
  • Aare secured to the spinal cord by denticulate ligaments
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12
Q

The spinal cord consists of grey and white matter and is divided into left and right halves by two grooves - what are they?

A

Anterior (ventral) median fissure

Posterior (dorsal) median sulcus

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13
Q

What is grey matter?

A
  • Composed of the cell bodies and dendrite of neurons, unmyelinated axons and neuroglia
  • Varies in size and shape down the spinal cord
  • Surrounds the central canal
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14
Q

The grey matter is organised into grey horns - what are they?

A
  • Posterior (dorsal) grey horns
  • Lateral grey horns (thoracic & lumbar regions only)
  • Anterior (ventral) grey horns
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15
Q

What are the cell bodies of neurons within the grey matter are organised into functional groups called?

A

Nuclei

- Sensory nuclei and motor nuclei

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16
Q

What are sensory nuclei?

A

Contain the cell bodies of spinal cord interneurons

- Receives and integrate sensory information entering the spinal cord

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17
Q

What are motor nuclei?

A

Contain the cell bodies of motor neurons

  • Receive and relay motor output generated by the brain
  • Generate motor output that mediates spinal reflexes
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18
Q

What is white matter?

A
  • Superficial to grey matter (opposite to the brain)

- Composed of myelinated (mainly) and unmyelinated axons

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19
Q

What are the white columns that white matter is organised into?

A
  • Posterior (dorsal) white columns
  • Lateral white columns
  • Anterior (ventral) white columns

Anterior white commissure —-> site of axon cross over

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20
Q

The axons within the white mater are functionally organised into spinal tracts - what do these tracts relay?

A

Relay information between spinal cord segments or, between the spinal cord and brain

  • Ascending tracts —> relay sensory information
  • Descending tracts —> relay motor information

Often reveal their origin, destination and spinal cord location in their name:
e.g. lateral spinothalamic tract

  • Origin = spine
  • Destination = thalamus
  • Tract location = lateral white column
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21
Q

What are neural pathways?

A

Spinal cord tracts belong to neural pathways that connect the body periphery to the brain

These pathways:

  • Consist of 2-3 neurons
  • Usually decussate within the spinal cord or brainstem
  • Are paired symmetrically on each side of the spinal cord and brain
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22
Q

What are Somatosensory pathways?

A

Sensory pathways of the somatic nervous system convey sensory information, from receptors to the brain, through a chain of three successive neurons:

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23
Q

What are these neurons?

A
  • First-order neuron
  • Second-order neuron
  • Third-order neuron
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24
Q

What are first-order neurons?

A

First-order neurons (sensory neurons):
Conduct sensory input from receptors to the spinal cord.
- The cell body resides in a dorsal root ganglion
- The axon enters the spinal cord via a dorsal root and synapses with a second-order neuron within the sensory nuclei

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25
Q

What are second-order neurons?

A

Second-order neurons (interneurons):
Conduct sensory input to the thalamus or cerebellum
- The cell body resides in the sensory nuclei of the posterior grey horns
- The axon travels in a specific spinal cord tract

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26
Q

What are third-order neurons?

A

Third-order neurons (interneurons):
Conduct sensory input from thalamus to a specific brain destination
e.g. primary somatosensory cortex

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27
Q

What are the major somatosensory pathways?

A
  1. Posterior column pathway (dorsal column-medial lemniscal pathways)
  2. Anterolateral pathway
  3. Spinocerebellar pathway
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28
Q

What is the posterior column pathway?

A
  • Begins at a peripheral receptor
  • Involves the fasciculus gracilis and fasciculus cuneatus spinal cord tracts (within the posterior white columns)
  • Ends within the primary somatosensory cortex
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29
Q

What does the posterior column pathway relay?

A

Sensations of:

  • Fine touch
  • Pressure
  • Vibration
  • Proprioception
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30
Q

What is the Anterolateral pathway?

A
  • Begins at a peripheral receptor
    Involves
    - Anterior spinothalamic tracts –> relay crude touch, pressure tickle and itch sensations (within anterior white column
    - Lateral spinothalamic tracts –> relay pain and temperature sensations (within lateral white column)

Ends with the primary somatosensory cortex

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31
Q

What is the Spinocerebellar pathway?

A
  • Begins at proprioceptors in skeletal muscles, tendons and joints
    Involves the:
    - Anterior Spinocerebellar tracts
    - Posterior Spinocerebellar tracts
    - Within the lateral white columns
    Ends within the cerebellum
    Relays sensation of proprioception
32
Q

What do motor pathways do?

A

Motor pathways convey motor output from the brain to skeletal muscles via a chain of two successive neurons:

  • Upper motor neurons (pyramid neurons)
  • Lower motor neurons
33
Q

What are Upper motor neurons (interneurons)?

A

Conduct motor output from the primary motor cortex to the spinal cord:

     - Cell bodies located in primary motor cortex 
     - Axons travel in a specific spinal tract and synapse with lower motor neurons in the motor nuclei of the anterior grey horns
34
Q

What are Lower motor neurons?

A

Conduct motor output from the spinal cord to skeletal muscles:

   - Cell bodies located in the anterior grey horns (motor nuclei) 
   - Axons exit the spinal cord via ventral root and travel to skeletal muscles
35
Q

What are the two main somatic motor pathways?

A
  1. Lateral corticospinal pathway

2. Anterior corticospinal pathway

36
Q

What is the lateral corticospinal pathway?

A
  • Begins in the primary motor cortex
  • Upper motor neurons travel in the lateral corticospinal tract
  • Ends at the skeletal muscle sot he limbs
  • Relays motor output that controls voluntary skeletal muscles contractions
37
Q

What is the Anterior corticospinal pathway?

A
  • Begins in the primary motor cortex
  • Upper motor neurons travel in the anterior corticospinal tract
  • Ends at the skeletal muscles of the axial skeleton (neck and trunk), pectoral and pelvic girdles
  • Relays motor output that controls voluntary skeletal muscles contractions
38
Q

What are the spinal reflexes?

A

The spinal cord mediates somatic reflexes

  • Sensory information is processed, and a reflex response generated, within the spinal cord
  • Lower motor neurons relay the motor output to effector skeletal muscle
39
Q

What are somatic reflexes?

A
  • Rapid, involuntary motor responses generated by the spinal cord in response to a stimulus
  • Can be modified by the primary motor cortex
40
Q

What can somatic reflexes be used to assess the condition of?

A
  • Lower motor neurons
  • Spinal cord
  • Primary motor cortex
  • Corticospinal tracts
41
Q

What is the general structure of a neuron?

A

The axons (fibres), blood and lymphatic vessels that comprise nerves are enclosed by three connective tissue layers.

42
Q

What are the three connective tissue layers?

A
  • Epineurium
  • Perineurium
  • Endoneurium
43
Q

What is the epineurium tissue layer?

A

Tough fibrous outer layer that encloses entire nerve

44
Q

What is the Perineurium tissue layer?

A

Middle layer that surrounds bundles of axons called fascicles

45
Q

What is the Endoneurium tissue layer?

A

Innermost layer that surrounds each individual axon

46
Q

Nerves can be classified as?

A
  • Sensory nerves
  • Motor nerves
  • Mixed nerves
  • Cranial nerves (12 pairs)
  • Spinal nerves
47
Q

What do sensory nerves contain?

A

Contain the axons of sensory neurons

48
Q

What do motor neurons contain?

A

Contain the axons of motor neurons

49
Q

What do mixed nerves contain?

A

Contain both sensory and motor axons

50
Q

Where do cranial nerves arise from?

A

Arise from the brain to innervate the head and neck, visceral organs

51
Q

Where do spinal nerves arise from?

A

Arise from the spinal cord and branch into peripheral nerves that innervate all body areas except some head and neck regions

52
Q

What are the spinal nerves interconnected called?

A

After emerging from the vertebral column, most spinal nerves (not thoracic) branch and interconnect to form nerve networks called nerve plexuses

53
Q

What are the four main plexuses?

A
  1. Cervical plexus
  2. Brachial plexus
  3. Lumbar plexus
  4. Sacral plexus
54
Q

What is the cervical plexus?

A
  • Arises from spinal nerves C1 to C5
  • Provides sensory innervation from the:
    - Skin of the head (posterior), neck and shoulders
    - Phrenic nerve
  • Provides motor innervation to:
    - Neck and shoulder muscles
    - Phrenic nerve
  • Main nerve —-> Phrenic nerve
55
Q

What is the Brachial plexus?

A
  • Arises from spinal nerves C4 to T1
  • Provides sensory innervation from the skin of the:
    - Shoulders
    - Arms
    - Hands
  • Provides motor innervation to:
    - Shoulder muscles
    - Arm muscles
    - Hand muscles
  • Main nerve —-> Axillary, Musculocutaneous, Median, Radial, Ulnar
56
Q

What is the Lumbar plexus?

A
  • Arises from spinal nerves L1 to L4
  • Provides sensory innervation from the skin of the:
    - Lower abdomen
    - Hips
    - Anterior & medial thigh, leg & foot
  • Provides motor innervation to:
    - Abdominal wall muscles
    - Hip muscles
    - Medial & anterior thigh muscles
  • Main nerve—> femoral nerve
57
Q

What is the sacral plexus?

A
  • Arises from spinal nerves L4 to S4
  • Provides sensory innervation from the skin of the:
    - Buttocks
    - Posterior thigh
    - Leg & foot
  • Provides motor innervation to:
    - Gluteal muscles
    - Posterior thigh muscles
    - Leg & foot muscles
  • Main nerve—> Sciatic nerve
58
Q

What is a Dermatome?

A

An area of skin innervated by the sensory fibres of a single spinal nerve

59
Q

What are dermatomes useful for?

A

Clinically, dermatomes are useful in identifying spinal nerve damage and locating spinal cord injuries

- Spinal cord and spinal nerve injuries can result in a loss of sensation from the dermatome they innervate 
- Painful rash and blisters may also appear in affected dermatome  e. g. shingles ----> herpes zoster virus 
- Attacks the sensory neurons of a spinal nerve ---> painful rash and blisters appear in corresponding dermatome
60
Q

What are cranial nerves?

A
  • 12 pairs of nerves that originate directly from the brain (forebrain and brainstem)
  • Innervate structures of the head and neck, and visceral organs
  • Can be classified as sensory nerves, motor nerves or mixed nerves
  • Named according to the structures they innervate or their functions
  • Numbered using Roman numerals
61
Q

I

1

A

Olfactory

62
Q

II

2

A

Optic

63
Q

III

3

A

Oculomotor

64
Q

IV

4

A

Trochlear

65
Q

V

5

A

Trigeminal

66
Q

VI

6

A

Abducens

67
Q

VII

7

A

Facial

68
Q

VIII

8

A

Vestibuloccoclear

69
Q

IX

9

A

Glossopharyngeal

70
Q

X

10

A

Vagus

71
Q

XI

11

A

Accessory

72
Q

XII

12

A

Hypoglossal

73
Q

What is different about the Vagus nerve (CN X)?

A
  • Only cranial nerve to extend beyond head/neck region
    Motor innervation
  • Parasympathetic motor to visceral organs —-> heart, lungs, abdominal organs
  • Somatic motor to pharynx and larynx

Sensory innervation

  • Thoracic & abdominal viscera
  • Baroreceptors
  • Chemoreceptors
  • Taste buds
  • Proprioceptors (larynx and pharynx)
74
Q

What are cranial nerve reflexes?

A
  • Are rapid, involuntary motor responses generated by the brain in response to a stimulus
    e. g. - Pupillary light response
    - Auditory reflex
75
Q

What happens in nerve repair?

A

If damaged, the sensory and motor axons within a peripheral nerve can regenerate providing:

  • The cell body remains intact
  • Schwann cells that produce myelin remain active
  • Severed axon endings are closed together

In general axon regrowth never matches what existed pre-trauma

76
Q

What are cranial nerves?

A
  • Arise from the brain (mainly brainstem)
  • Most extend into the periphery to supply sensory and motor innervation to the skin, muscles and gland of the head and neck
  • Vagus nerve innervates thorax and abdomen
  • Mediate cranial reflex responses

Semester 2 BMA 1912 (5 decks)

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