Structure and function of the spinal cord

Question 1

Anatomy of the spinal cord

Answer 1

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

Question 2

Spinal nerves

Answer 2

Connect the periphery to the spinal cord

31 pairs formed by dorsal and ventral root

Question 3

Ventral root

Answer 3

Efferent fibres

Question 4

Dorsal root

Answer 4

Afferent fibres

Question 5

Inner core

Answer 5

Gray matter

Neuronal cell bodies

H shaped

Ventral, lateral and dorsal horn

Question 6

Outer

Answer 6

White matter

Myelinated axons

White columns/ tracts or funiculi

Question 7

Gray matter organisation

Answer 7

Dorsal horn: neurones receiving sensory input

Lateral horn: preganglionic sympathetic neurones

Ventral horn: motor neurones

Question 8

White matter organisation

Answer 8

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

Question 9

White matter organisation 2

Answer 9

Dorsal column: ascending reacts

Lateral column: descending and ascending tracts

Ventral column: mainly descending tracts

Question 10

Ascending tracts

Answer 10

Sensory

Proprioceptive
- information originating from inside the body

Exteroceptive
- information originating from outside the body

Question 11

Ascending tracts- anatomy

Answer 11

Three neurones in circuit

1. First order neurone: enters spinal cord via dorsal root
2. Second order neurone: ascends spinal cord or brainstem
3. Third order neurone:: projects to the cerebral cortex

Question 12

Dorsal column medial lemniscus pathway: First order neurones

Answer 12

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

Question 13

Topographical organisation of axons

Answer 13

Fasciculus gracilis terminates in nucleus gracilis
- information from lower limb

Fasciculus cuneates terminates in nucleus cuneatus
- information from upper limb

Question 14

Cauda equina

Answer 14

From dorsal ventral root of lower spinal nerves

Question 15

Cervical enlargement

Answer 15

Innervation to upper limb

Question 16

Lumbosacral enlargement

Answer 16

Innervation to lower limbs

Question 17

Dorsal column medial lemniscus pathway: Second order neurones

Answer 17

Cross in medulla and second to thalamus

- form medial lemniscus

Question 18

Dorsal column medial lemniscuis pathway: Third order neurones

Answer 18

Project from thalamus to somatosensory cortex

Question 19

Lesions on one side of spinal cord

Answer 19

Loss of tactile discrimination and proprioception on same side

Sensory ataxia

Test with Romberg’s sign

e.g. multiple sclerosis

Question 20

Sensory ataxia

Answer 20

Loss of coordination and balance without visual cues

Question 21

Romberg’s sign

Answer 21

Severe swaying on standing with eyes close/ feet together

Question 22

Spinothalamic tract

Answer 22

Pain, temperature and crude touch

Question 23

Spinothalamic: first order neurones

Answer 23

Enter dorsal horn and form tract of lissauer

Synapse in dorsal horn with second order neurones

Question 24

Spinothalamic: second order neurones

Answer 24

Cross in dorsal horn at each level

Ascend in anterolateral column to thalamus

Question 25

Spinothalamic: third order neurones

Answer 25

Project from thalmus to somatosensory cortex

Question 26

Damage to anterolateral column

Answer 26

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

Question 27

Spinocerebellar tracts

Answer 27

Unconscious muscle proprioception - for smooth motor coordination Two neurones only Four tracts Uncrossed

Question 28

Posterior spinocerebellar: first order neurones

Answer 28

Synapse in dorsal horn

Question 29

Posterior spinocerebellar: second order neurones

Answer 29

Ascend in lateral column to cerebllum

Question 30

SPinocerebellar: Lesions on one side of spinal cord

Answer 30

Uncoordinated lower limb muscular activity on same side

Question 31

Corticospinal tract

Answer 31

Great voluntary motor pathway 2 neurones in circuit 1. Upper motor neurone: from cerebral cortex to ventral horn 2. Lower motor neurone: from ventral horn to skeletal muscle

Question 32

Pyramidal tract

Answer 32

Primary motor cortex -> Posterior limb of internal capsule -> Cerebral peduncle -> Pons -> Pyramids of medulla -> Lateral/ anterior corticospinal tract

Question 33

Pyramids of decussation

Answer 33

80% cross- lateral corticospinal tract 20% on same side- anterior corticospinal tract

Question 34

topographical organisation in ventral horn of corticospinal tract

Answer 34

Medial- trunk Anterolateral- proximal limb segments Posterolateral- distal limb segments

Question 35

Motor neurone disease

Answer 35

Disruption of the corticospinal tract

Question 36

Upper motor neurone disease

Answer 36

Degeneration of upper motor neurones - spastic paralysis (increased muscle tone) - overactive tendon reflexes - no significant muscle atrophy e.g. following a stroke

Question 37

Lower motor neurone disease

Answer 37

Degeneration of lower motor neurones in ventral horn - flaccid paralysis (no muscle tone) - no tendon reflexes - muscle atrophy e.g. spinal muscular atrophy

Question 38

Amyotrophic lateral sclerosis

Answer 38

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

Question 39

Extrapyramidal tracts

Answer 39

Do not pass through the pyramids Descending tracts from basal ganglia, cerebellum and pons e.g. reticulospinal tract

Question 40

Reticulospinal tract

Answer 40

From reticular formation (pons) to spinal cord Regulates ventral horn motor activity/ reflexes Facilitates and inhibits lower motor neurones Important for posture and locomotion