Structure and function of the spinal cord Flashcards Preview

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Spinal cord boundaries

Starts at C1 [atlas]


Spinal cord regions

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


Lumbosacral enlargment

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


Conus medullaris

Narrowing of the spinal cord at L1/L2.
- The pia mater still extends further down the spine.


Terminal filum

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

Internal part- pia mater
External part- dura


Lumbar cistern

Subarachnoid space in the lower lumbal canal
- Contains cauda equina nerve roots.
- Contains terminal filum


Cauda equina

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

Contained in the lumbar cistern


Surrounding of spinal cord

Spinal cord enclosed in vertebral canal.

Enclosed in meninges:
- Dura mater [meningeal]
- Arachnoid
- Pia


Grey matter, spinal nerves

Contains neuronal cell bodies and associated glia.

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

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

Interneurones also exist within each vertebral level.


White matter, spinal nerves

Contains myelinated neuronal axons.

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


Proprioceptive and Exteroceptive

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

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

All communicated through the ascending tracts of the spinal cord.


Ascending tract anatomy

1st order neurones
- Enter spinal cord at dorsal root

2nd order neurones
- Ascends spinal cord/ brainstem

3rd order
- Projects into cerebral cortex.


Dorsal column medial-lemnisucus pathway
- Function

Ascending tract
- Fibres do not cross
- Longest axons in the body

Communicates fine touch/ tactile discrimination
- Cutaneous mechanoreceptors

- Positional information


Dorsal column medial-lemnisucus pathway

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]

- 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


1st order neurones
- Dorsal column medial lemniscus pathway

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



2nd order neurones
- Dorsal column medial lemniscus pathway

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


3rd order neurones
- Dorsal column medial lemniscus pathway

Projects from the thalamus to the somatosensory cortex,


Damage to the dorsal column medial lemniscus pathway
- Symptoms
- Sign
- Example

Lesion on one side of the spinal cord= sensory ataxia

Loss of tactile discrimination

Symptoms on the SAME side.

Romberg's sign

Multiple sclerosis


Sensory ataxia

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


Romberg's sign

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.


Spinothalmic tract
- Function

Ascending tract

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


Spinothalmic tract pathway

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


Spinothalmic tract pathway
- First order neurones

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

Synapses with 2nd order neurones in dorsal horn


Spinothalmic tract pathway
- Second order neurones

Crosses at dorsal horn
- Ascends anterolateral column to the thalamus

Medial= upper limb fibres
Lateral- lower limb fibres


Spinothalmic tract pathway
- Third order neurones

Projects from the thalamus to the somatosensory cortex.


Damage to spinothalmic tract

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.


Spinocerebellar tracts
- Description
- Function
- Examples

Ascending tract
- Communicates unconscious, muscle proprioception
- Smooth, muscle co-ordination

Only 2 neurones in circuit
- 4 tracts altogether


Anterior and posterior spinocerebellar tracts
- Proprioceptive information from the trunk and lower limbs


Posterior spinocerebellar tract pathway

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]


Anterior spinocerebellar tract pathway

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.


Damage to post/ant spinocerebellar tract

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