Structure and function of the spinal cord Flashcards
Anatomy of the spinal cord
Sits within vertebral column- well protected
Surrounded by meninges
Divided into 4 regions
- cervical (C1-8)
- thoracic (T1-12)
- lumbar (L1-5)
- sacral (S1-5)
- lumbar cistern
Spinal nerves
Connect the periphery to the spinal cord
31 pairs formed by dorsal and ventral root
Ventral root
Efferent fibres
Dorsal root
Afferent fibres
Inner core
Gray matter
Neuronal cell bodies
H shaped
Ventral, lateral and dorsal horn
Outer
White matter
Myelinated axons
White columns/ tracts or funiculi
Gray matter organisation
Dorsal horn: neurones receiving sensory input
Lateral horn: preganglionic sympathetic neurones
Ventral horn: motor neurones
White matter organisation
Contains tracts
Long ascending tracts carry afferent impulses within to centres within the brain
Long descending tracts carry efferent impulses from centres within the brain
White matter organisation 2
Dorsal column: ascending reacts
Lateral column: descending and ascending tracts
Ventral column: mainly descending tracts
Ascending tracts
Sensory
Proprioceptive
- information originating from inside the body
Exteroceptive
- information originating from outside the body
Ascending tracts- anatomy
Three neurones in circuit
- First order neurone: enters spinal cord via dorsal root
- Second order neurone: ascends spinal cord or brainstem
- Third order neurone:: projects to the cerebral cortex
Dorsal column medial lemniscus pathway: First order neurones
Enter spinal cord and ascend dorsal column on same side within the:
- fasciculus gracilis
- fasciculus cuneatus
Fibres ascend dorsal column uncrossed
Longest neurones in body
Topographical organisation of axons
Fasciculus gracilis terminates in nucleus gracilis
- information from lower limb
Fasciculus cuneates terminates in nucleus cuneatus
- information from upper limb
Cauda equina
From dorsal ventral root of lower spinal nerves
Cervical enlargement
Innervation to upper limb
Lumbosacral enlargement
Innervation to lower limbs
Dorsal column medial lemniscus pathway: Second order neurones
Cross in medulla and second to thalamus
- form medial lemniscus
Dorsal column medial lemniscuis pathway: Third order neurones
Project from thalamus to somatosensory cortex
Lesions on one side of spinal cord
Loss of tactile discrimination and proprioception on same side
Sensory ataxia
Test with Romberg’s sign
e.g. multiple sclerosis
Sensory ataxia
Loss of coordination and balance without visual cues
Romberg’s sign
Severe swaying on standing with eyes close/ feet together
Spinothalamic tract
Pain, temperature and crude touch
Spinothalamic: first order neurones
Enter dorsal horn and form tract of lissauer
Synapse in dorsal horn with second order neurones
Spinothalamic: second order neurones
Cross in dorsal horn at each level
Ascend in anterolateral column to thalamus
Spinothalamic: third order neurones
Project from thalmus to somatosensory cortex
Damage to anterolateral column
Lesions on one side of spinal cord
- loss of pain, temperature and crude touch on opposite side
Outside compression of cord
- loss of lower limb pain first
Inside grey matter tumour
- loss of upper limb pain first
Spinocerebellar tracts
Unconscious muscle proprioception
- for smooth motor coordination
Two neurones only
Four tracts
Uncrossed
Posterior spinocerebellar: first order neurones
Synapse in dorsal horn
Posterior spinocerebellar: second order neurones
Ascend in lateral column to cerebllum
SPinocerebellar: Lesions on one side of spinal cord
Uncoordinated lower limb muscular activity on same side
Corticospinal tract
Great voluntary motor pathway
2 neurones in circuit
- Upper motor neurone: from cerebral cortex to ventral horn
- Lower motor neurone: from ventral horn to skeletal muscle
Pyramidal tract
Primary motor cortex ->
Posterior limb of internal capsule ->
Cerebral peduncle ->
Pons ->
Pyramids of medulla ->
Lateral/ anterior corticospinal tract
Pyramids of decussation
80% cross- lateral corticospinal tract
20% on same side- anterior corticospinal tract
topographical organisation in ventral horn of corticospinal tract
Medial- trunk
Anterolateral- proximal limb segments
Posterolateral- distal limb segments
Motor neurone disease
Disruption of the corticospinal tract
Upper motor neurone disease
Degeneration of upper motor neurones
- spastic paralysis (increased muscle tone)
- overactive tendon reflexes
- no significant muscle atrophy
e.g. following a stroke
Lower motor neurone disease
Degeneration of lower motor neurones in ventral horn
- flaccid paralysis (no muscle tone)
- no tendon reflexes
- muscle atrophy
e.g. spinal muscular atrophy
Amyotrophic lateral sclerosis
Selectively affects lower and upper motor neurones
Progressive muscle weakness and atrophy but mind intact
Symptoms initially in limbs or bulbar signs
Spasticity present when upper motor neurones affected
Short life span
Extrapyramidal tracts
Do not pass through the pyramids
Descending tracts from basal ganglia, cerebellum and pons
e.g. reticulospinal tract
Reticulospinal tract
From reticular formation (pons) to spinal cord
Regulates ventral horn motor activity/ reflexes
Facilitates and inhibits lower motor neurones
Important for posture and locomotion
