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202: Theme 2, Sensory inputs and motor outputs > Structure and function of the spinal cord > Flashcards

Structure and function of the spinal cord Flashcards

1
Q

Spinal cord boundaries

A

Starts at C1 [atlas]
to
L1

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2
Q

Spinal cord regions

A

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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3
Q

Lumbosacral enlargment

A

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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4
Q

Conus medullaris

A

Narrowing of the spinal cord at L1/L2.

- The pia mater still extends further down the spine.

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5
Q

Terminal filum

A

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

Internal part- pia mater
External part- dura

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6
Q

Lumbar cistern

A

Subarachnoid space in the lower lumbal canal

  • Contains cauda equina nerve roots.
  • Contains terminal filum
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7
Q

Cauda equina

A

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

Contained in the lumbar cistern

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8
Q

Surrounding of spinal cord

A

Spinal cord enclosed in vertebral canal.

Enclosed in meninges:

  • Dura mater [meningeal]
  • Arachnoid
  • Pia
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9
Q

Grey matter, spinal nerves

A

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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10
Q

White matter, spinal nerves

A

Contains myelinated neuronal axons.

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

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11
Q

Proprioceptive and Exteroceptive

A

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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12
Q

Ascending tract anatomy

A

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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13
Q

Dorsal column medial-lemnisucus pathway

- Function

A

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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14
Q

Dorsal column medial-lemnisucus pathway

A
  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]

  1. 2nd order neurones in the thalamus synapse with third order neurones at the somatosensory cortex
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15
Q

1st order neurones

- Dorsal column medial lemniscus pathway

A

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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16
Q

2nd order neurones

- Dorsal column medial lemniscus pathway

A

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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17
Q

3rd order neurones

- Dorsal column medial lemniscus pathway

A

Projects from the thalamus to the somatosensory cortex,

18
Q

Damage to the dorsal column medial lemniscus pathway

  • Symptoms
  • Sign
  • Example
A

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

19
Q

Sensory ataxia

A

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
20
Q

Romberg’s sign

A

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.

21
Q

Spinothalmic tract

- Function

A

Ascending tract

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

22
Q

Spinothalmic tract pathway

A
  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
23
Q

Spinothalmic tract pathway

- First order neurones

A

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

Synapses with 2nd order neurones in dorsal horn

24
Q

Spinothalmic tract pathway

- Second order neurones

A

Crosses at dorsal horn
- Ascends anterolateral column to the thalamus

Medial= upper limb fibres
Lateral- lower limb fibres

25
Q

Spinothalmic tract pathway

- Third order neurones

A

Projects from the thalamus to the somatosensory cortex.

26
Q

Damage to spinothalmic tract

A

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.

27
Q

Spinocerebellar tracts

  • Description
  • Function
  • Examples
A

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

28
Q

Posterior spinocerebellar tract pathway

A
  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]
29
Q

Anterior spinocerebellar tract pathway

A
  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.
30
Q

Damage to post/ant spinocerebellar tract

A

Causes loss of co-ordination of lower limb on the same side

- Rarely affected in isolation

31
Q

Corticospinal tract

A

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
32
Q

Pyramidal tract

A

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
33
Q

Pyramidal decussation

A

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
34
Q

Topographical organisation in ventral horn of corticospinal tract

A

Medial horn- innervation of trunk

Anterolateral- proximal limb

Posterolateral- distal limb

35
Q

Upper motor neurone disease

  • Definition
  • Presentation
  • Example
A

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

36
Q

Lower motor neurone disease

  • Definition
  • Presentation
  • Cause
A

Disruption of corticospinal tract—-> lower neurones

Presentation:

  • Flaccid paralysis
  • No tendon reflexes
  • Muscle atrophy

Example:
- Spinal muscular atrophy

37
Q

Spinal muscular atrophy

A

Lower motor neurone disease

- Mutation of SMN1 gene—» codes for survival of motor neurone

38
Q

Amyotrophic lateral sclerosis [ALS]

A

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]

39
Q

Extrapyramidal tracts

A

Descending tracts
- Do not pass through medullary pyramid

Instead descend through:

  • Basal ganglia
  • Cerebellum
  • Pons

Example
- Reticulospinal tract

40
Q

Reticulospinal tract

A

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

202: Theme 2, Sensory inputs and motor outputs (13 decks)

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