Spinal Cord

Question 1

what does the spinal cord do

Answer 1

• the spinal cord connects the brain to the peripheral nervous system

Question 2

describe the structure of the spinal cord

Answer 2

• It is located within the vertebral canal- this provides structure protection
• it is held in place by spinal roots, the denticulate ligaments and strands of pia mater
• The spinal cord is not segmented; rather the distribution of the spinal roots gives it a functional segregation.

Question 3

where is the spinal cord to and from

Answer 3

• It extends from the level of the foramen magnum to the level of the L2 vertebra.

Question 4

what do the spinal roots do

Answer 4

• It is these roots that carry information in and out of the cord exiting via the intervertebral foramen.

Question 5

what does the dorsal root do

Answer 5

Dorsal roots transmit sensory information from the periphery to cells in the gray matter of the spinal cord.

Question 6

what does the ventral root do

Answer 6

Ventral roots transmit motor and autonomic information from neurons in the spinal cord to the periphery.

Question 7

what does the dorsal root ganglion do

Answer 7

• these are along the dorsal root and are cell bodies

- inside the ganglia are the cell bodies of the receptor neurones that send processes out to the periphery and viscera

Question 8

what does the sympathetic chain ganglia do

Answer 8

• they have connections with the anterior ramus this allows efferent sympathetic outflow to reach different regions of the body
• They contain cell bodies of postganglionic neurons and are found on the T1-L3 spinal nerves.

Question 9

what happens when dorsal and ventral roots joint together

Answer 9

• they form a spinal nerve

Question 10

how many spaniel nerves are there

Answer 10

There are 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 1 coccygeal) that supply all parts of the body except the head

Question 11

what is the nervous supply of the head

Answer 11

supplied by cranial nerves

Question 12

what happens and the level of cervical and lumbar

Answer 12

• the spinal nerve fibres intermingle with each other in the brachial and lumbosacral plexus to form peripheral spinal nerves that have multiple roles

Question 13

what d spinal nerves consist of

Answer 13

• afferent fibres - these transfer information to the spinal cord from the skin, muscle joints and viscera
• efferent fibres - these derive from alpha and gamma motor neurones, post ganglion sympathetic neurons and in some nerves, preganglionic parasympathetic neurons

Question 14

what does each spinal nerve innervate

Answer 14

Each spinal nerve innervates in a specific skin region called a dermatome

Question 15

describe the benefits of overlap at the boundaries of the dermatomes

Answer 15

• acts as a damage insurance
• if 1 spinal nerve is damaged not all of the sensory information to that skin region will be lost as some is carried in nerves of the adjacent spinal nerves
• in order to get sensory or functional deficits more than 1 spinal nerve must be damaged

Question 16

how do you tell spinal cord cross sections apart from each other

Answer 16

Overall shape
- cervical sections are wide and squashed looking like an oval, they are larger than thoracic sections and lumbar and sacral are more circle shaped

Ventral Horn Enlargement

• At segments that control a limb, the motoneurons are large and numerous.
• This causes enlarged ventral horns in two places: the lower cervical sections (C5-C8) and the lumbar/sacral sections.
• If you see an enlargement, you just need to differentiate cervical from lumbar. This can be done by shape or by proportion of white matter

Amount of white matter relative to grey matter

• this decreases as you move down the cord
• in the white matter of the cervical cord you have all of the axons going to or from the entire body, more or less.
• In sacral cord, the white matter contains only those axons going to or from the last couple of dermatomes - all other axons have “exited” at higher levels. This is why sacral cord looks like it has so much gray matter - really, it has just lost all of the white.

Question 17

how to identify the grey and white matter

Answer 17

• wide, flat cord - lots of white matter
• ventral horn enlargements = cervical.
• Round cord, ventral horn enlargements = lumbar.
• Small round cord, almost no white matter = sacral.
• The remaining level, thoracic, - it has pointed tips, which stick out between the small dorsal and ventral horns. This extra cell column is called the intermediate horn, or the intermediolateral cell column. It is the source of all of the sympathetics in the body, and occurs only in thoracic sections.
• The cross-sectional area of white matter is largest at cervical levels because ascending and descending fibres to and from more caudal levels pass through the cervical funiculi and least at sacral level

Question 18

what are the two regions of the spinal cord

Answer 18

= grey matter

= white matter

Question 19

white matter surrounds the…

Answer 19

gray matter in the spinal cord

Question 20

what does white matter contain

Answer 20

• it contains the ascending and descending fibres to and from the brain int he dorsal, lateral and ventral funiculi

Question 21

what does the grey matter contain

Answer 21

• cells and terminus of the primary afferents from the periphery

Question 22

what can the grey matter be divided into

Answer 22

• dorsal horn - sensory perception

- ventral horn - motor neurones whose axons exit the cord via the ventral root and go towards the muscles

Question 23

what happens to the dorsal and ventral horn at the thoracic and sacral levels

Answer 23

At thoracic and sacral levels, these 2 regions are separated by the intermediate zone, which contains the lateral horn

Question 24

what does the lateral horn contain

Answer 24

containing the cell bodies of the sympathetic and parasympathetic preganglionic fibres - the autonomic system outflow

Question 25

another word for ventral

Answer 25

anterior

Question 26

another word for dorsal

Answer 26

posterior

Question 27

what laminae are in the dorsal horn

Answer 27

6 laminae based on cell size

Question 28

Describe what the 6 laminae receive information from in the dorsal horn

Answer 28

• Laminae I-II together are known as the superficial dorsal horn and they receive information from C and Ad fibres (nociceptors - “pain” fibres).
• Laminae III-VI receive input from Ab fibres (low threshold cutaneous receptors).
• A pale-staining area through which few myelinated fibres pass caps the dorsal horn: this is lamina II, the substantia gelatinosa

Question 29

what are the laminae in the ventral horn

Answer 29

The ventral horn consists of laminae VII-IX (7-9)

Question 30

describe the organisation of motor neurones within the ventral horn

Answer 30

• The motoneurons populations supplying different muscles are differentially organized within the ventral horn.
• Distal muscles are represented laterally
• proximal muscles are located more medially.
• Extensor muscle groups are located more ventrally within the ventral horn compared to flexor muscle motoneurons

Question 31

what do ascending tract transmit

Answer 31

Ascending tracts transmit different types of sensation from the body - light touch, pain, pressure, temperature, and joint and muscle position sense

Question 32

how many ascending tracts are there

Answer 32

3

Question 33

each ascending tract has….

Answer 33

• different targets in the brain

- and a specific and consistent location within the white matter of the cord

Question 34

describe the DCML

Answer 34

it includes touch, pressure, and vibration perception

• enables us to “read” braille letters, or describe the shape and texture of an object without seeing it.
• This is the dorsal column medial lemniscus pathway (containing the gracile & cuneate fasciculi).

Question 35

describe the Spinothalamic

Answer 35

The second modality is pain and temperature, and includes the sensations of itch and tickle.
- This is transmitted by the spinothalamic tract pathway.

Question 36

describe the spinocerebellar

Answer 36

• proprioception
• includes receptors for what happens below the body surface: muscle stretch, joint position, tendon tension
• This modality terminates in the cerebellum, which needs continuous feedback on what the muscles are doing
• This pathway is the spinocerebellar tract pathway

Question 37

how many descending tracts are there

Answer 37

1

Question 38

describe the descending tract

Answer 38

• called the corticopsinal tract

- regulates the control of voluntary movements

Question 39

what can damage to the spinal cord arise from

Answer 39

• trauma
• degenerative diseases
• ischaemia
• infectious
• toxic
• metabolic disorders

Question 40

what the the 2 phases of cord damage

Answer 40

• primary damage

- secondary damage

Question 41

describe primary damage

Answer 41

• results from cord compression, contusion, laceration or haemorrhage which occurs immediately on injury

Question 42

describe secondary damage

Answer 42

it is initiated by the trauma but occurs over a period of hours to days to months
- These mainly involve physiological alterations to trauma, hypoxia and ischaemia.

Question 43

what are the clinical presentations of cord damage

Answer 43

• pain at the level of injury

- variable amount of sensorimotor loss below the level of the lesion

Question 44

what is spinal shock

Answer 44

state of shock, or temporary loss of function in the spinal cord.

• All the functions and muscle reflexes below the level of the lesion are depressed or absent, giving the impression of flaccid paralysis of muscles and loss of sensation
• neurones gradually repair and the flaccid paralysis turn to spastic paresis
• first reflexes to reappear are flexion reflexes, after several months muscle tone and tendon reflexes may occur

Question 45

what happens in the acute phase of traumatic cord injury

Answer 45

• variable amounts of oedema, haemorrhaging, axonal swelling, ascending/descending tract disruption and foci of infarction
• over the next few weeks there is macrophage infiltration and a gradual removal of degenerative debris
• At the site of injury the grey matter becomes necrotic and may cavitate.
• later there is infiltration by fibroblasts and associated collagenous fibrosis occurs
• Frequently cavitation involves the ventral part of the dorsal columns, which is maximal at the site of injury but may extend a few segments rostral or caudal to the injury

Question 46

what is tabes dorsalis

Answer 46

• this is due to syphilitic infection that affects the large diameter fibres
• it results in a chronic inflammation of the dorsal roots and spinal ganglia
• the cells die result in degeneration of the axons within the dorsal columns