Spinal Cord Flashcards
what does the spinal cord do
- the spinal cord connects the brain to the peripheral nervous system
describe the structure of the spinal cord
- 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.
where is the spinal cord to and from
- It extends from the level of the foramen magnum to the level of the L2 vertebra.
what do the spinal roots do
- It is these roots that carry information in and out of the cord exiting via the intervertebral foramen.
what does the dorsal root do
Dorsal roots transmit sensory information from the periphery to cells in the gray matter of the spinal cord.
what does the ventral root do
Ventral roots transmit motor and autonomic information from neurons in the spinal cord to the periphery.
what does the dorsal root ganglion do
- 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
what does the sympathetic chain ganglia do
- 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.
what happens when dorsal and ventral roots joint together
- they form a spinal nerve
how many spaniel nerves are there
There are 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 1 coccygeal) that supply all parts of the body except the head
what is the nervous supply of the head
supplied by cranial nerves
what happens and the level of cervical and lumbar
- the spinal nerve fibres intermingle with each other in the brachial and lumbosacral plexus to form peripheral spinal nerves that have multiple roles
what d spinal nerves consist of
- 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
what does each spinal nerve innervate
Each spinal nerve innervates in a specific skin region called a dermatome
describe the benefits of overlap at the boundaries of the dermatomes
- 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
how do you tell spinal cord cross sections apart from each other
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.
how to identify the grey and white matter
- 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
what are the two regions of the spinal cord
= grey matter
= white matter
white matter surrounds the…
gray matter in the spinal cord
what does white matter contain
- it contains the ascending and descending fibres to and from the brain int he dorsal, lateral and ventral funiculi
what does the grey matter contain
- cells and terminus of the primary afferents from the periphery
what can the grey matter be divided into
- dorsal horn - sensory perception
- ventral horn - motor neurones whose axons exit the cord via the ventral root and go towards the muscles
what happens to the dorsal and ventral horn at the thoracic and sacral levels
At thoracic and sacral levels, these 2 regions are separated by the intermediate zone, which contains the lateral horn
what does the lateral horn contain
containing the cell bodies of the sympathetic and parasympathetic preganglionic fibres - the autonomic system outflow
another word for ventral
anterior
another word for dorsal
posterior
what laminae are in the dorsal horn
6 laminae based on cell size
Describe what the 6 laminae receive information from in the dorsal horn
- 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
what are the laminae in the ventral horn
The ventral horn consists of laminae VII-IX (7-9)
describe the organisation of motor neurones within the ventral horn
- 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
what do ascending tract transmit
Ascending tracts transmit different types of sensation from the body - light touch, pain, pressure, temperature, and joint and muscle position sense
how many ascending tracts are there
3
each ascending tract has….
- different targets in the brain
- and a specific and consistent location within the white matter of the cord
describe the DCML
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).
describe the Spinothalamic
The second modality is pain and temperature, and includes the sensations of itch and tickle.
- This is transmitted by the spinothalamic tract pathway.
describe the spinocerebellar
- 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
how many descending tracts are there
1
describe the descending tract
- called the corticopsinal tract
- regulates the control of voluntary movements
what can damage to the spinal cord arise from
- trauma
- degenerative diseases
- ischaemia
- infectious
- toxic
- metabolic disorders
what the the 2 phases of cord damage
- primary damage
- secondary damage
describe primary damage
- results from cord compression, contusion, laceration or haemorrhage which occurs immediately on injury
describe secondary damage
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.
what are the clinical presentations of cord damage
- pain at the level of injury
- variable amount of sensorimotor loss below the level of the lesion
what is spinal shock
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
what happens in the acute phase of traumatic cord injury
- 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
what is tabes dorsalis
- 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
