Spinal Cord and Periphery Flashcards

1
Q

What is the cross sectional anatomy of the spinal cord?

A

Has a central grey matter and peripheral white matter

The grey matter has on each side a dorsal and a ventral horn

The axons of sensory fibres enter through the dorsal root in the dorsal horn of grey matter.

Motor neurons have their cell bodies in the ventral horn

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2
Q

What is motor neurone disease?

A

Group of diseases affecting the motor neuron in the spinal cord.
(this neuron is called the Lower Motor Neuron)

The neutron dies and as a result muscle supplied by it atrophies

Progressive, incurable disease

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3
Q

Describe the white matter of the spinal cord

A

White matter is made up of tracts (axons transmitting information between higher centres in the brain and peripheral nerves)

Tracts are pathways

Different tracts carry different bits of information. Ascending pathways are sensory, descending pathways are motor.

The white matter is arranged as 3 columns (posterior, lateral and anterior). Each column has in it various tracts

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4
Q

Explain ascending spinal tracts

A

Carries sensory information to the brain (cerebral cortex and cerebellum)

Pathways reaching conscious level have common characteristics:

  • There are 3 neurones between peripheral receptor and cortex)
  • –1st, 2nd and 3rd order neuron
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5
Q

Describe the general route of ascending spinal tract

A

Receptor

First order neuron

  • Dorsal route/ cranial nerve ganglion
  • Paraunipolar neuron

Grey matter of spinal cord or nucleus in medulla

2nd order neuron
-Crosses over to contralateral side in spinal cord or medulla

Nucleus in contralateral thalamus

3rd order neuron
-Contralateral parietal cortex

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6
Q

What does the posterior/ dorsal column nerves carry?

A

Sensory information for:

  • Fine touch
  • Tactile localisation
  • Vibration sense
  • Proprioception

Posterior column of right side = Touch, pressure, proprioception from right side of body

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7
Q

What is the lateral spinothalamic tract?

A

Pain and temperature from contralateral side

lateral spinothalamic tract of right side = pain and temperature from left side of body

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8
Q

Describe motor/ descending tracts of spinal cord

A

Originate in the cerebral cortex and brainstem

Are concerned with control of movement, muscle tone, spinal autonomic functions

Tracts coming from cerebral cortex have 2 neurons in their pathway

They decussate to the opposite side in the brainstem

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9
Q

What is the route of motor/ descending tracts of spinal cord?

A

Upper motor neuron in primary motor cortex

Pyramidal decussation in medulla

Lower motor neurone in spinal cord/ cranial nerve neclei

Neuromuscular junction

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10
Q

What is the corticospinal/ pyramidal tract?

A

Control of voluntary skilled movements.

Posterior limb of IC (blood supply MCA).

Corticobulbar fibres go to contralateral cranial nerve nucleii

Corticospinal fibres mostly cross in decussation of pyramids (lateral corticospinal tract)

(anterior corticospinal tract)

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11
Q

Describe upper motor neuron and lower motor neuron

A

The lower motor neuron (LMN) is responsible for muscle tone and reflexes.

If the upper motor neuron (UMN) is damaged with LMN intact, then reflexes and tone are exaggerated

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12
Q

Why would sensory info not reach the brain?

A

Not all sensory information needs to be sent to the brain for decisions to be made.

In certain instances where an immediate response in needed, the spinal cord or other lower centres themselves can take these decisions

The make up some of our reflexes

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13
Q

What are reflexes?

A

A reflex is an involuntary stereotyped pattern of response brought about by a sensory stimulus.

Many reflexes are mediated at the level of the spinal cord (spinal reflexes)

Anatomically they may be monosynaptic (e.g. stretch reflex) or polysynaptic (e.g. flexor reflex)

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14
Q

What is the stretch reflex (+ reciprocal innervation)?

A
  1. Tendon stretched
  2. Intrafusal muscle fibres stimulated
  3. Sensory neutron activated

4a. Monosynaptic reflex arc
4b. Polysynaptic reflex arc to inhibitory interneuron

  1. Muscle contraction
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15
Q

What is the stretch reflex for?

A

Important in control or muscle tone and posture

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16
Q

What is the flexor (+ crossed extensor) reflex?

A
  1. Pain stimulus
  2. Sensory neutron activated
  3. Polysynaptic reflex arc
    4a. Flexion and withdrawal from noxious stimulus
    4a. Crossed extensor response to contralateral limb (only in weight bearing limbs)
17
Q

Explain the effects of an upper motor neuron lesion

A

It is the lower motor neuron that was involved in both these reflexes

So a motor response was brought about (reflexively) without using the upper motor neuron

So even if the upper motor neuron is damaged, one still does have reflexes - which become EXAGGERATED

The muscle tone also increases -> leads to spasicity (as opposed to flaccidity)

i.e. with an upper motor lesion there is spastic paralysis with hyperreflexia

18
Q

What should you think about when dealing with neurological lesions?

A
  1. Cortical problems - speech
  2. Motor paralysis/weakness
    - Which side?
    - Is it spastic/flacid
    - What happens to reflexes?
  3. What about cranial nerve weakness?
    - Same or opposite side
  4. Sensory defects
    - Which side? for pain and temperature
    - Which side? for touch vibration etc
19
Q

What is Brown-Sequard Syndrome?

A

Herniated disc may cause
Hemisection of spinal cord left side

Pyramidal tract, spinothalamic tract, posterior column all abrupt on left side

20
Q

What would Brown-Sequard Syndrome of the left side cause?

A

Right sided loss of temperature and pain

Left sided paralysis (spastic)

Left sided loss of touch, vibration sense

Reflexes on left side exaggerated

21
Q

What is the basic organisation of ANS?

A

Autonomic nervous system refers to nerve cells within both cans and PNS concerned with innervation and control of visceral organs, smooth muscles and secretory glands.

It is not under voluntary control. Basic autonomic efferent pathway has 2 neurons in its pathway

22
Q

Describe the route of ANS

A

Cell body in brainstem/ spinal cord

Preganglionic neuron

Autonomic ganglion

Postganglionic neuron

Target organ

23
Q

How do sympathetic and parasympathetic outflow, preganglionic fibres and postganglionic fibres differ?

A

Outflow:

  • Symp = thoracolumbar
  • Para = craniosacral

Preganglionic fibres:

  • Symp = ganglia near spinal cord
  • Para = ganglia near target organ

Postganglionic fibres:

  • Symp = target every cell in the body
  • Para = target-> exocrine glands, heart, other selected organs