Neuroscience 1b – Spinal Cord Dysfunction
Anil Chopra
1. Draw a diagram of a cross-section through the spinal cord, labelling the main
areas of grey matter and main ascending and descending tracts.
2. Define the function of the cells in the dorsal, ventral and intermediate horns of the
spinal cord.
3. Distinguish between the terms nerve, root and ramus in relation to the spinal cord.
4. Explain the relationship between spinal and vertebral levels and its clinical
significance.
5. Define the cervical and lumbar enlargements and state the spinal segments
involved in them.
6. Describe the meningeal layers of the spinal cord and explain how they differ from
those of the brain.
7. State at what level a lumbar puncture is usually performed and explain why. Why
is it hazardous to perform lumbar puncture in the presence of raised intracranial
pressure?
8. Explain the sensory and/or motor deficits which would follow:
a. complete section at mid-thoracic level
b. complete section at mid-cervical level
c. complete section at C2 level
d. hemi section at mid-thoracic level
9. Demonstrate in diagrams the course of the following main ascending and
descending tracts through the CNS and define their function:
a. corticospinal tract
b. corticobulbar tract
c. spinothalamic tract
d. dorsal columns-medial lemniscus
e. reticulospinal tract
f. vestibulospinal tract
Spinal Cord: Grey matter (cell bodies) surrounded by white matter (axons).
Dorsal Horns: receive sensory information from spinal nerves and dorsal roots. This
is then either taken to the brain for processing, or used in a reflex.
Ventral Horns: contain the axons of the motor neurons used in muscle contraction
via the ventral roots and spinal nerves.
White matter: contains shorter axons which connect the different segments of the
spinal cord, and longer pathways which run to and from the brain.
Nerve is the nerve fibre coming from a single cell body
The root, ventral or dorsal is the nerve root in which a nerve is contained when it
leaves the spinal column, dorsal roots contain afferent sensory fibres, the ventral roots
contain efferent motor fibres. Roots contain more than one nerve
A ramus is a smaller structure which a nerve divides into. Therefore near a target a
nerve, originating from a single cell body can divide into a number of rami to
innervate different targets
Each vertebral level gives of a pair of spinal nerves below the inferior border, except
C1-7 which are above the superior border. Therefore there are 31 pairs of spinal
nerves (29 vertebrae – C1-7, T1-T12, L1 – L5, S1-5, 1 Coccyx) and the coccygeal
nerve above the coccyx
Number of
Number of spinal Relationship of nerve to
vertebrae
nerves
vertebra
7
8
Above, except C8
Cervical
12
12
Below
Thoracic
5
5
Below
Lumbar
5
5
Below
Sacral
1 fused (4 unfused)
1
Below
Coccyx
30
31
Total
The level of injury to the vertebral column will therefore predict the neuronal damage
that occurs. Generally the higher the injury, the more severe the disability
To perform a lumbar puncture, a needle is inserted between vertebrae L4 and L5. This
is because the spinal cord stops but there is still CSF in the meningeal column. It
should never be performed in the presence of raised intracranial pressure because it
may lead to herniation of the cerebral hemispheres through the foramen magnum.
Meninges




CSF in Sub-arachnoid space similar to that of the brain.
Dentate ligaments in the pia mater extend to the dura which stabilise the spinal
cord holding it in place.
The filum terminale connects the inferior end of the spinal cord to the coccygeal
vertebrae.
The lumbar cistern (Subarachnoid space below the end of the spinal cord) contains
the lumbar and sacral spinal roots.
Factors that Affect Severity of Spinal Lesion
• Loss of neural tissue
• Vertical level
• Transverse plane
It is important to note how the tracts of the white matter are affected. Generally, the
higher the lesion, the greater the disability.
Important Points:
- Phrenic nerve C3-C5 (diaphragm innervation)
- Lumbosacral level (loss of bowel and bladder control).
- Mid-thoracic (paraplegia – unable to use lower limbs as well as bowel and bladder)
- Cervical (quadriplegia)
Damage of the spinal cord can lead to both positive and negative effects:


“Negative” effects can include paralysis, anaesthesia.
“Positive” Effect of Spinal cord Injury can lead to spacicity. Hyper-reflexia
can also result. They may not occur until after spinal shock subsides.
CNS tracts cannot regenerate.
Descending Tract
Ascending Tract
As a general rule in the white matter ascending sensory tracts from the dorsal horns
run in the periphery, and descending motor tracts run centrally
Different sensory inputs innervate different laminae of the central grey matter, e.g.
skin terminates in laminae I-IV
Lateral Corticospinal Tract
Dorsal Columns
Spinothalamic Tract
3 Factors: Loss of neural tissue
Vertical Level
Transverse plane
o Complete section at mid-thoracic level
o Complete section at mid-cervical level: Quadriplegia: no-use of all 4limbs.
o Complete section at C2 level: Breathing problems.
o Hemi section at mid-thoracic level
Main ascending and descending tracts through the CNS Corticospinal tract
o Corticobulbar tract
o Spinothalamic tract
o Dorsal columns-medial leminiscus
o Reticulospinal tract
o Vestibulospinal tract
Ascending
 The major difference between the main ascending sensory tracts is that fine touch
information in the dorsal column tract is conveyed on the same side as it enters,
whereas pain, temperature and crude touch via the spinothalamic tract is portrayed
on the opposite side
 The point at which the tract crosses to the contralateral side is known as the
decussation
 Sensory tracts are both arranged segmentally, i.e. the fibres from the same level
run together in the tract
The Dorsal Column Pathway
 One function is to re-arrange the input from dermatomes of the primary sensory
fibres into the grossly distorted map of the body surface seen in the primary
sensory cortex – the sensory homunculus
 It segregates information into modality-specific pathways for touch, hair
movement, pressure and joint rotation
 Contains feedback mechanisms to gate the amount of incoming information to the
cortex
 Decussation occurs in the medulla
 The functions are carried out in the areas where the pathway is interrupted by
synapses – medulla, thalamus, cortex
 The primary sensory neurons synapse in the dorsal column nuclei:
 Gracile nucleus – leg and lower trunk
 Cuneate nucleus – arm and upper trunk
 Trigeminal nucleus – face via the trigeminal nerve (V)
 Thalamic nucleus = contralateral ventroposterolateral nucleus (VPL) for
cuneate and gracile fibres, and in the contralateral ventroposteromedial nucleus
(VPM) for trigeminal inputs
 Travels through the medial lemniscus
 VPL and VPM project to the cortex via thalamocortical radiations
The Spinothalamic Tract:
 Carries pain, crude touch and thermal information
 Pain is also carried in the spinoreticular and spinomesencephalic tracts
 Noxious and thermal information carried into the dorsal horn via fast myelinated
Aδ fibres (sharp, stabbing pain), and slower un-myelinated C fibres (dull,
nagging pain and thermal information)
 Aδ fibres terminate in laminae I and V, the axons decussate and ascend in the
anterolateral white matter forming the spinothalamic tract
 C fibres terminate in lamina II and use interneurons to influence the firing of
dorsal spinothalamic cells
 Spinothalamic fibres join the medial leminiscus in the medulla and project to the
thalamus
 The thalamic termination of the tract is in the ventroposterior nuclei and
intralaminar nuclei, from which there is a relay to the cortex
 Nociceptive afferents from face carried in the trigeminal (V) nerve to the
trigeminal nucleus, then they cross over the medulla to join the other inputs in the
thalamus
The Dorsal Column Pathway
The Spinothalamic
Tract
The Spinocerebellar Tract:
 Deals with proprioceptive information and is divided into 2 parts
 The dorsal spinocerebellar tract is formed by the axons of cell bodies in the base of
the dorsal horn (Clarke’s column) running from T1 – L2. It conveys information
about body movement from the trunk and lower limbs to the cerebellum via the
inferior cerebellar peduncle. The same kind of information from the upper limb is
transferred via the external cuneate nucleus located laterally in the medulla
 The ventral spinocerebellar tract receives its inputs from cell bodies in lamina VII
(the spinal interneuron layer). This primarily sends inhibitory interneuron signals to
the cerebellum via the superior cerebellar peduncle
Descending:
The Corticospinal Tract:
»
Also known as the pyramidal tract is the major controller of skeletal muscle
activity
It has two branches:
» The decussating lateral tract controls precision movements of the limbs,
innervating lateral motor neuron pools
» The uncrossed anterior tract controls the less precise movements of the trunk,
innervating medial motor neuron pools
The fibres that influence motor neurons innervating muscles in the head, e.g. tongue and
facial muscles run in the corticobulbar tracts at the appropriate cranial nerve nuclei.
 The somatotopic (specific arrangement) arrangement of the descending motor
fibres from the cortex includes the head in the cerebral peduncles (narrow
structure, acts as support or connection), but not at the level of decussation in the
medulla
 The tract carries signals for highly skilled movements and so is highly
somatotopic and there are very few collaterals so the excitation from one fibre is
not transmitted to another
 There are also fibres which regulate
spinal reflexes in the tract and
feedback to the dorsal horn sensory
circuits from the sensory cortex
The corticospinal and
corticobulbar tracts
Other descending tracts:
 Mainly involved in autonomic and
involuntary control of muscles
 Largely
deal with axial and
proximal muscles which control
posture
 Tectospinal tract deals with head
and neck posture
 Vestibulospinal tract is involved in
keeping the head balanced on the
shoulders as the body moves
through space to turn the head
 The reticulospinal tract controls
posture and helps control crude
imprecise movements. The reticular
formation describes a diffuse
network of cells in the brainstem
which receives information from a
large part of the central nervous
system and is involved in the control
of many of the body’s automatic
processes.
The
pontine
reticulospinal tract projects to
neurons innervating axial muscles.
The medullary reticulospinal tract
projects to neurons innervating
distal muscles.