Structure and function of the spinal cord

Question 1

Spinal cord boundaries

Answer 1

Starts at C1 [atlas]
to
L1

Question 2

Spinal cord regions

Answer 2

Named according to the vertebrae which the spinal nerves leave:

Cervical [C1-8]- Thicker, supplying upper limb.
Thoracic [T1-12]
Lumbar [L1-5]- Thicker, supplying lower limb
Sacral [S1-5]
Lumbar cistern

Question 3

Lumbosacral enlargment

Answer 3

Thickening of the spinal cord at the lumbar-sacral region due to a large number of nerves supplying the lower limbs.

Question 4

Conus medullaris

Answer 4

Narrowing of the spinal cord at L1/L2.

- The pia mater still extends further down the spine.

Question 5

Terminal filum

Answer 5

Extension of the pia mater from the conus medullais, into the coccyx.

Internal part- pia mater
External part- dura

Question 6

Lumbar cistern

Answer 6

Subarachnoid space in the lower lumbal canal

• Contains cauda equina nerve roots.
• Contains terminal filum

Question 7

Cauda equina

Answer 7

A group of:
- Lumbar/sacral dorsal and ventral nerve roots

Contained in the lumbar cistern

Question 8

Surrounding of spinal cord

Answer 8

Spinal cord enclosed in vertebral canal.

Enclosed in meninges:

• Dura mater [meningeal]
• Arachnoid
• Pia

Question 9

Grey matter, spinal nerves

Answer 9

Contains neuronal cell bodies and associated glia.

Thickest in the cervical and lumbosacral region—> innervation to the limbs

Horns:
Ventral---->Motor [descending] neurones
Dorsal-----> Receives sensory input
Lateral---->Sympathetic preganglionic neurones
- Only in thoracic region

Interneurones also exist within each vertebral level.

Question 10

White matter, spinal nerves

Answer 10

Contains myelinated neuronal axons.

Tracts/Columns/ funiculi:
Dorsal—-> Sensory/ Ascending
Ventral—-> Motor/ descending
Lateral—-> Descending + Ascending.

Question 11

Proprioceptive and Exteroceptive

Answer 11

Proprioceptive:

• Information from within the body
• From joints, Golgi tendon organs, muscle spindles

Exteroceptive:

• Information from outside the body
• Pain, temperature, touch.

All communicated through the ascending tracts of the spinal cord.

Question 12

Ascending tract anatomy

Answer 12

1st order neurones
- Enter spinal cord at dorsal root

2nd order neurones
- Ascends spinal cord/ brainstem

3rd order
- Projects into cerebral cortex.

Question 13

Dorsal column medial-lemnisucus pathway

- Function

Answer 13

Ascending tract

• Fibres do not cross
• Longest axons in the body

Communicates fine touch/ tactile discrimination
- Cutaneous mechanoreceptors

Proprioception
- Positional information

Question 14

Dorsal column medial-lemnisucus pathway

Answer 14

1. Sensory neurone enters dorsal horn and ascend dorsal column on the SAME SIDE
   - Enters fasciculus gracile [medially]
   - Fasciculus cuneatus [laterally]
2. First order neurones synapse with 2nd order at the medulla.
   - F.gracile terminates at nucleus gracilis [Lower limb]
   - F.cuneatus terminates at nucleus cuneate [upper limb]

Crossing:
- Second order fibres cross medulla and ascend the thalamus as medial lemniscus [Reil’s ribbon]

3. 2nd order neurones in the thalamus synapse with third order neurones at the somatosensory cortex

Question 15

1st order neurones

- Dorsal column medial lemniscus pathway

Answer 15

Enters the dorsal horn and ascends the dorsal columns- on the same side.

• Fasciculus gracile [medially]
• Fasciculus cuneatus [Laterally]

Synapses with 2nd order neurones in the medulla

• DOES NOT CROSS

Question 16

2nd order neurones

- Dorsal column medial lemniscus pathway

Answer 16

Synapses with first order neurones in the medulla.
- Fasciculus gracile terminates—-> nucleus gracilis [lower limb]

• Fasciculus cuneatus terminates —-> nucleus cuneate [upper limb]

Neurones ascend to the thalamus

Question 17

3rd order neurones

- Dorsal column medial lemniscus pathway

Answer 17

Projects from the thalamus to the somatosensory cortex,

Question 18

Damage to the dorsal column medial lemniscus pathway

• Symptoms
• Sign
• Example

Answer 18

Lesion on one side of the spinal cord= sensory ataxia

Loss of tactile discrimination

Symptoms on the SAME side.

Sign:
Romberg’s sign

Example:
Multiple sclerosis

Question 19

Sensory ataxia

Answer 19

Loss of co-ordination and balance due to loss of sensory input

• Seen in damage to Dorsal column medial lemniscus pathway.
• Balance and co-ordination still there with visual cues

Question 20

Romberg’s sign

Answer 20

Clinical test used to diagnose sensory ataxia
- Seen in damage to the dorsal column medial lemniscus pathway

Individual sways off-balance when eyes are closed + feet apart.
- BUT can balance when eyes are opened.

Question 21

Spinothalmic tract

- Function

Answer 21

Ascending tract

Communicates pain, temperature, CRUDE touch
- Nociceptors [receptors that response to damaging/potentially damaging stimuli]

Question 22

Spinothalmic tract pathway

Answer 22

1. First order neurones enter dorsal horn—> Forms tract of Lissauer
   - Gives collateral branches at the tip that runs up 1/2 segments
   - Synapses in dorsal horn with 2nd order neurones.
2. 2nd order neurones cross in dorsal horn at each vertebral level
   - Ascends anterolateral column to thalamus
   - Lateral fibres= lower limb
   - Medial fibres= upper limb
3. Third order neurones project from thalamus to somatosensory cortex

Question 23

Spinothalmic tract pathway

- First order neurones

Answer 23

Enter dorsal horn and forms tract of Lissauer
- Gives off collateral branches to 1/2 segments

Synapses with 2nd order neurones in dorsal horn

Question 24

Spinothalmic tract pathway

- Second order neurones

Answer 24

Crosses at dorsal horn
- Ascends anterolateral column to the thalamus

Medial= upper limb fibres
Lateral- lower limb fibres

Question 25

Spinothalmic tract pathway | - Third order neurones

Answer 25

Projects from the thalamus to the somatosensory cortex.

Question 26

Damage to spinothalmic tract

Answer 26

Lesion on one side of the spinal cord gives rise to symptoms on the OTHER side - Loss of pain, temperature, crude touch. Compressing lesion= loss in lower limb first Inner, grey matter tumour= loss in upper limb first.

Question 27

Spinocerebellar tracts - Description - Function - Examples

Answer 27

Ascending tract - Communicates unconscious, muscle proprioception - Smooth, muscle co-ordination Only 2 neurones in circuit - 4 tracts altogether Fibres DO NOT CROSS Anterior and posterior spinocerebellar tracts - Proprioceptive information from the trunk and lower limbs

Question 28

Posterior spinocerebellar tract pathway

Answer 28

1. First order neurone synapses in dorsal horn 2. Second order neurone ascends lateral column ----> into cerebellum - Very quick axons [fastest sensory neurone in body]

Question 29

Anterior spinocerebellar tract pathway

Answer 29

1. First order neurone synapses at dorsal horn. 2. 2nd order neurone crosses dorsal horn then ascends the lateral column-----> cerebellum - Fibre crosses back at the cerebellum.

Question 30

Damage to post/ant spinocerebellar tract

Answer 30

Causes loss of co-ordination of lower limb on the same side | - Rarely affected in isolation

Question 31

Corticospinal tract

Answer 31

Voluntary motor pathway [descending tract] 2 neurones: 1. Fibres from the cerebral cortex synapse at ventral horn. 2. Fibres from ventral horn synapse at skeletal muscle

Question 32

Pyramidal tract

Answer 32

Part of the corticospinal tract 1. Fibres from primary motor cortex ----> posterior limb of internal capsule 2. Fibres from post. limb of internal capsule----> cerebral peduncle 3. Cerebral peduncle----> Pons 4. Pons ---> Medulla pyramids 5. Pyramids----> Lat/ anterior corticospinal tract-----> ventral horn etc

Question 33

Pyramidal decussation

Answer 33

In the pyramidal tract: 1. Lateral corticospinal tract crosses in the MEDULLA. [80% of tract] 2. Anterior tract is on the same side [20%] - cross at cervical region to supply neck muscle

Question 34

Topographical organisation in ventral horn of corticospinal tract

Answer 34

Medial horn- innervation of trunk Anterolateral- proximal limb Posterolateral- distal limb

Question 35

Upper motor neurone disease - Definition - Presentation - Example

Answer 35

Disruption of the corticospinal tract---> upper neurones Region affected - Above pyramid = opposite side - Below pyramid= same side Presentation - Spatic paralysis - Overactive tendon reflexes - No significant muscle atrophy Example: Following stoke

Question 36

Lower motor neurone disease - Definition - Presentation - Cause

Answer 36

Disruption of corticospinal tract----> lower neurones Presentation: - Flaccid paralysis - No tendon reflexes - Muscle atrophy Example: - Spinal muscular atrophy

Question 37

Spinal muscular atrophy

Answer 37

Lower motor neurone disease | - Mutation of SMN1 gene--->> codes for survival of motor neurone

Question 38

Amyotrophic lateral sclerosis [ALS]

Answer 38

Motor neurone disease that affects lower and upper neurones Presentation: - Progressive muscle weakness - Progressive muscle atrophy - Intact mind without control of body - Bulbar signs in later stage [speech, eating] Spasticity--> upper neurones affected Causes: Potential genetic mutation [SOD1 gene]

Question 39

Extrapyramidal tracts

Answer 39

Descending tracts - Do not pass through medullary pyramid Instead descend through: - Basal ganglia - Cerebellum - Pons Example - Reticulospinal tract

Question 40

Reticulospinal tract

Answer 40

Descending, extrapyramidal tract. - Locomotion and posture Reticular formation in pons-----> Ventral horn in spinal cord - Regulates its motor activity and reflexes - Facilitates/ inhibits lower motor neurones