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Neuroscience -part I > Ascending and Descending tracts > Flashcards

Ascending and Descending tracts Flashcards

1
Q

What is the spinal cord anatomy?

A
  • formed of bundles of nerve fibres which carry sensory information from the body to the brain and motor information from the brain to the body
  • Carries info from the brain which regulates the ANS for the control of the internal environment
  • Spinal cord starts superiorly at the distal end of the medulla
  • Ends at the conus medullaris ( lies at the level of the lumbar vertebral level 1/2)
  • The filum terminale extends from the end of the spinal cord to attach to the first coccygeal verterbra
  • The spinal cord terminates caudally at the L1-2 vertebral level
  • Lumbar and sacral roots have to travel some distance before reaching their respective intervertebral foramina
  • Cluster = cauda equina (tail of horse)
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2
Q

Where is the spinal cord housed?

A
  • In the vertebral colum (axial skeleton)
  • The bony framework to which the muscles and fasciae of the trunk and neck attach.
  • Conists of :
    • 7 cervical vertebrae
  • 12 thoracic vertebrae
  • 5 lumbar verterbrae
  • 5 fused sacral vertebrae
  • 3/4 coccygeal vertebrae
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3
Q

What is the cervical spine?

A
  • Large triangal vereterbral canal which contains the spinal cord with large numbers of ascending and descending neural tracts which carry information to and from the whole body
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4
Q

What is the Thoracic spine?

A
  • Smaller triangular vertebral canal
  • ## Contains the spinal cord with ascending and descending neural tracts which carry information to and from the trunk, pelvic region and lower limbs
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5
Q

What is the lumbar spine?

A
  • Contains the cauda equina with ascending and descending neural tracts which carry information to and from the pelvic region and lower limbs
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6
Q

What is the sacral spine?

A
  • Contains the cauda equina with neurons supplying the pelvic region and lower limbs
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7
Q

How does the spinal cord run?

A
  • runs in a protective but unyielding bony tunnel
  • about 12 mm thick (at largest point)
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8
Q

What are spinal nerves?

A
  • emerge from the intervertebral foramen (tight bony tunnel)
  • ## contain both somatic sensory and motor and autonomic nerves
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9
Q

What causes the compression of spinal nerves?

A
  • Disease processes such as osteoarthritis, or injurt affecting the facet joints, bony pedicles, intervertebral discs, vertebral bodies and/ or spinal ligaments
  • E.G. numbness, tingling (sensory), weakness , loss of use (motor)
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10
Q

What is the anatomical arrangement of the spinal cord and nerves?

A
  • Dorsal (posterior) root (Sensory- afferent- ascending)
  • Dorsal root ganglion (cell bodies of primary sensory neurons)
  • Dorsal (posterior) Ramus (mixed)
  • Ventral (Anterior) Ramus (mixed)
  • Ventral (anterior) Root (Motor- Efferent- descending)
  • Spinal roots are either motor or sensory
  • Spinal nerves and rami are mixed motor and sensory
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11
Q

What is a dermatome?

A
  • The area of skin that is supplied by the sensory nerve fibres of a particular spinal nerve
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12
Q

What are myotomes?

A
  • The motor axons of individual spinal nerves that tend to innervate anatomically and functionally related groups of skeletal muscles
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13
Q

What is the structure of the spinal nerves?

A
  • A sensory neuron, with a peripheral and central process, entering the spinal cord from the periphery i.e. carrying touch sensation from the index finger tip
  • A motor neuron exiting the spinal cord to go to the periphery, i.e exiting the spinal cord to go to the periphery- i.e carrying motor information to innervate the bicep muscle in the arm
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14
Q

What is the difference between the ascending and descending tracts?

A
  • Ascending (Sensory)- carry sensory information from the body to the higher centres (info about pain, touch, heat/cold etc)
  • Descending (Motor) - carry motor info from brain to the spinal cord (info to contract muscles in the arms and legs)
  • ## Found in the white matter surrounding the grey matter and are organised into tracts
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15
Q

What are the motor and descending (efferent pathways)?

A
  • Pyramadial tracts = lateral corticospinal tract, anterior corticospinal tract
  • Extrapyramdial tracts = rubrospinal tract, Reticulospinal , vestibulospinal tract
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16
Q

What are the sensory and ascending (afferent) pathways?

A
  • Dorsal column medial lemniscus system : - Gracile fasiculus, Cuneate fasciculus
  • Spinocerebelllar tracts : posterior spinocerebellar tract, anterior spinocerebellar tract
  • Anterolateral system : Lateral spinothalamic tract
  • Anterior spinothalamic tract
  • Spino-olivary fibres
17
Q

What are cell bodies and their procceses organised into?

A
  • ## Bundles (fasciculi) sharing similar functions
18
Q

What are the two main pathways of the descending motor spinal tracts?

A
  • Lateral and ventromedial pathways
  • Voluntary movemnt of distal musculature (fine control) - direct cortical control
  • Posture and locomotion - brainstem control
19
Q

What are the somatic motor pathways?

A
  • Motor efferent / descending
  • 2 (3) neurones
  • Brain to axon to synapses to Endings = motor end plate
20
Q

What is the corticospinal pathway?

A

2 (3) neurones in pathway
- Brain precentral gyrus motor cortex - cell body TO axon of UMN - Internal capsule, brain stem, corticospinal tract of spinal cord TO corticospinal pathways TO synapse in ventral horn TO axon of LMN TO Muscle (motor-end plates)

21
Q

What are corticospianl fibres?

A
  • They control the speed, direction and agility of movements- involved in rapid skilled movement
22
Q

Where do spinal nerves decussate?

A
  • Majority decussate in the caudal medulla (85-90%)
  • Some deussate at the level of the synapse in the spinal cord (10-15%)
  • Some remain ipsilateral - don’t decussate (i.e, some cranial nerves - corticobulbar)
  • Synapse directly with a lower motor neurone ,or with excitatory interneurone
23
Q

What is the lateral corticospinal tract and where does it decussate?

A
  • Main motor fibre tract in the spinal cord (90%)
  • Cell body in primary motor cortex
  • Axon decussate at pyramids (lower brainstem)
  • Upper motor neurone synapses with lower motor neurone in the ventral grey horn.
24
Q

What is the ventral corticospinal tract ?

A
  • Secondary motor fibre tract in the spinal cord (~10% of fibres)
  • Cell body in primary motor cortex
  • Axon do not decussate at pyramids
  • Upper motor neurone synapses with LMN in the ventral grey horn
25
Q

What is the motor homunculus?

A
  • The areas of the motor cortex where the cell bodies of these first order neurones supplying parts of the body lie in
26
Q

Describe the corticospinal tract from the cortex to the periphery through the central and peripheral nervous system.

A

The first order motor nerve fibres (upper motor neurones) run through the midbrain and at the medull athey cross over to the other side descend in the lateral white matter of the spinal cord

27
Q

What is the sciatic nerve?

A

A peripheral nerve which contains motor nerve fibres which supply some of the skeletal muscles of the leg

28
Q

Describe a conscious motor command from the cortex to the periphery through the central and peripheral nervous sytems?

A
  • Having crossed at the medulla, the descending motor fibres run down (descend) in the lateral white matter of the spinal cord
  • The upper motor nerve fibres will synapse with alpha, second order motor fibres (LMN) in the anteruor horn of the grey matter of the spinal cord
  • The second order motor nerve fibres exit the spinal cord in the ventral (Anterior ) spinal root, the anterior and posterior roots join to form the spinal nerve which exits and enters the vertebral column through the intervertebral foramen.
  • The motor fibres will run in the peripheral nerves to supply specific skeletal muscles associated with a specific level of the spinal cord
29
Q

What are the descending rubrospinal tracts ?

A
  • They influence flexor or extensor muscle tone
  • Rubrospinal - from red nucleus in brainstem (pons/ medulla) - CONTRALATERAL
  • Vestibulospinal - Ton vestibular nuclei in brain stem ( pons/ medulla ) - IPSILATERAL
  • Rubrospinal - mainly proximal limb and trunk muscles . Excite flexor LMN . INHIBIT extensor LMN

Vestibulospinal = antigravity
Excites extensor LMN . Inhibits flexor LMN.

  • Vestibulospinal = antigravity
30
Q

What are the ventral medial pathways ?

A
  • pontine (medial) and medullary ( lateral ) Retuculospinql tracts
  • Control posture of the trunk and antigravity muscles of the limbs
    Damage leads to exaggerated reflexes
    Pontine reticulospinal :
  • Enhances antigravity reflexes of spinal cord
    Helps maintain a standing position
  • What is the medullary reticulospinal?
  • Liberates antigravity muscles from reflex control ( dampens down spinal reflex to optimise muscle tone )

Activity in both tracts is controlled by descending signals from cortex
A fine balance is required between the two to maintain posture .

  • Liberates antigravity muscles from reflex control ( i.e. dampens form spinal reflex to optimise muscle tone)
  • Helps maintain a standing position
31
Q

Where can UMM lesions occur?

A
  • The cortex
  • Internal capsule
  • Corona Radiata
  • Descending tracts
  • Brainstem
  • Spinal Cord
32
Q

Where can LMN lesions occur ?

A
  • In the spinal cord ( LMN cell body level)
  • Spinal nerve
  • Cauda equina
  • Peripheral nerve damage ( radial nerve)
33
Q

What are some causes of MN lesions?

A
  • Stroke
  • MND
  • M sclerosis
  • CNS Tumour
  • Meningeal Tumour
  • Spinal tumour
  • Trauma
  • Penetrating injury
  • Fracture
  • Dislocation
  • Stenosis
  • Iv disc prolapse
34
Q

What can spinal cord hemisection lead to?

A
  • Cab lead to both UMN and LMN signs in different parts of the body
  • LMN at level of injury
  • UMM below injury
    Both upper and lower motor neurone damage
35
Q

What are the acsending ) sensory) spinal tracts?

A
  • Dorsal column (medial lemniscus ) and Lateral spinothalamic tract .

Neuroscience -part I (21 decks)

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