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

Structure and function of the spinal cord Flashcards by aderonke adesanoye

Spinal cord boundaries

Starts at C1 [atlas]
to
L1

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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

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Lumbosacral enlargment

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

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Conus medullaris

Narrowing of the spinal cord at L1/L2.

- The pia mater still extends further down the spine.

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Terminal filum

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

Internal part- pia mater
External part- dura

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Lumbar cistern

Subarachnoid space in the lower lumbal canal

Contains cauda equina nerve roots.
Contains terminal filum

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Cauda equina

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

Contained in the lumbar cistern

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Surrounding of spinal cord

Spinal cord enclosed in vertebral canal.

Enclosed in meninges:

Dura mater [meningeal]
Arachnoid
Pia

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Grey matter, spinal nerves

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.

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White matter, spinal nerves

Contains myelinated neuronal axons.

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

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Proprioceptive and Exteroceptive

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.

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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.

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Dorsal column medial-lemnisucus pathway

- Function

Ascending tract

Fibres do not cross
Longest axons in the body

Communicates fine touch/ tactile discrimination
- Cutaneous mechanoreceptors

Proprioception
- Positional information

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Dorsal column medial-lemnisucus pathway

Sensory neurone enters dorsal horn and ascend dorsal column on the SAME SIDE
- Enters fasciculus gracile [medially]
- Fasciculus cuneatus [laterally]
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]

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

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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

DOES NOT CROSS

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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

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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.

Sign:
Romberg’s sign

Example:
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

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.
2nd order neurones cross in dorsal horn at each vertebral level
- Ascends anterolateral column to thalamus
- Lateral fibres= lower limb
- Medial fibres= upper limb
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 Fibres DO NOT CROSS 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

Corticospinal tract

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

Pyramidal tract

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

Pyramidal decussation

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

Topographical organisation in ventral horn of corticospinal tract

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

Upper motor neurone disease - Definition - Presentation - Example

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

Lower motor neurone disease - Definition - Presentation - Cause

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

Spinal muscular atrophy

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

Amyotrophic lateral sclerosis [ALS]

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]

Extrapyramidal tracts

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

Reticulospinal tract

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