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Year 2 - Theme 1 > Physiology of the spinal cord > Flashcards

Physiology of the spinal cord Flashcards

1
Q

Physiological functions of the spinal cord

A
  • Initial processing of somatosensory input by the CNS

- Final processing of motor output by the CNS

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2
Q

What are spinal nerves

A
  • Highways of both somatosensory info traffic to the spinal cord(afferent pathways) and motor info traffic from the spinal cord to the muscles(efferent pathways)
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3
Q

Definition of sensation

A
  • Detection by receptors
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4
Q

Definition of perception

A
  • Interpretation by spinal cord and brain circuits
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5
Q

What are receptors

A
  • Receptors are neurons specialised in the transduction of energy generated by external stimuli
  • They are specific for a narrow range of input
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6
Q

Type of spatial resolution and convergence in cones and bipolar cells in retina

A
  • High spatial resolution

- Low convergence

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7
Q

Type of convergence in rods and bipolar cells in the retina

A
  • High convergence
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8
Q

What is the vestibulo-ocular reflex

A
  • Is a reflex, where activation of the vestibular system causes eye movement
  • This reflex functions to stabilize images on the retinas during head movement by producing eye movements in the direction opposite to head movement
  • High divergence
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9
Q

Two main kinds of primary(1st order) sensory receptors

A
  • look up lecture notes for picture
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10
Q

Types of receptors for touch, pressure and vibration

A
  • Mechanoreceptors
    (eg. Merkell’s cells, ruffini end-organs, pacinian corpuscles)
  • Bare nerve endings
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11
Q

Type of fibres in mechanoreceptors

A
  • A-beta
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12
Q

Type of fibres in bare nerve ending for fast pricking pain

A
  • A-delta
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13
Q

Features of A-delta fibres

A
  • Aδ fibers carry cold, pressure, and acute pain signals, and because they are thin (2 to 5 μm in diameter) and myelinated, they send impulses faster than unmyelinated C fibers, but more slowly than other, more thickly myelinated group
  • Medium diameter and speed
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14
Q

Features of A-beta fibres

A
  • Wide diameter

- Fast

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15
Q

Type of fibres in bare nerve endings for slow burning pain, itch

A
  • C-fibres
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16
Q

Features of C-fibres

A
  • Thin diameter

- Slow

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17
Q

Main feature of pacinian corpuscle

A
  • Specialised mechanoreceptor
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18
Q

What do pacinian corpuscles detect

A
  • They respond only to sudden disturbances and are especially sensitive to vibration.
  • The vibrational role may be used to detect surface texture, e.g., rough vs. smooth.
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19
Q

How do lamellar corpuscles function

A
  • Lamellar corpuscles sense stimuli due to the deformation of their lamellae, which press on the membrane of the sensory neuron and causes it to bend or stretch.
  • When the lamellae are deformed, due to either pressure or release of pressure, a generator potential is created as it physically deforms the plasma membrane of the receptive area of the neuron, making it “leak” Na+ ions
  • If this potential reaches a certain threshold, nerve impulses or action potentials are formed by pressure-sensitive sodium channels at the first node of Ranvier, the first node of the myelinated section of the neurite inside the capsule.
  • This impulse is now transferred along the axon with the use of sodium channels and sodium/potassium pumps in the axon membrane.
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20
Q

What is two-point discrimination

A
  • is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one.
  • It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is.
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21
Q

Where in the body is the density of mechanoreceptors much greater

A
  • Much greater on the hand and face than elsewhere, allowing the detection of stimuli at a much greater spatial resolution
22
Q

Why can lower limbs still receive impulses after cord transection

A
  • Presence of lower motor neurons
  • Lower motor neurons are collected in longitudinally organised columns
  • Each column contains the larger, alpha(thick axon, high conductance velocity), and smaller , gamma(thin axon, low conductance velocity), motor neurons to one muscle(or a few functionally similar muscles)
  • Each column extends through more than one segment of the cord
  • Each muscle receives motor fibers through more than one ventral root and spinal nerve
  • Destruction of a single ventral root or a single spinal nerve will not produce paralysis, only weakness(paresis)
23
Q

What does a motor unit refer to

A
  • A single alpha motor neuron and the muscle fibres it innervates
24
Q

What is proprioception

A
  • Self-detection
25
Q

What type of feedback do muscle spindles provide

A
  • Negative feedback regulation of muscle length(due to passive stretch)
26
Q

What type of feedback do golgi tendon organs provide

A
  • Negative feedback regulation of muscle tension(due to contraction)
27
Q

Example of when golgi tendon organs provide feedback

A
  • Clasp-knife reflex
28
Q

Example of when muscle spindles provide feedback

A
  • Knee-jerk reflex
29
Q

What are muscle spindles

A
  • Muscle spindles are small sensory organs that are enclosed within a capsule
  • Within a muscle spindle, there are several small, specialized muscle fibers known as intrafusal fibers
  • Intrafusal fibers have contractile proteins (thick and thin filaments) at either end, with a central region that is devoid of contractile proteins. The central region is wrapped by the sensory dendrites of the muscle spindle afferent.
30
Q

How do muscle spindles work

A
  • When the muscle lengthens and the muscle spindle is stretched, this opens mechanically-gated ion channels in the sensory dendrites, leading to a receptor potential that triggers action potentials in the muscle spindle afferent.
31
Q

What are intrafusal fibres innervated by

A
  • The intrafusal fibers are innervated by an efferent neuron known as the gamma motor neuron (MN).
32
Q

What are extrafusal fibres innervated by

A
  • The efferents that innervate extrafusal fibers are known as alpha motor neurons
33
Q

Role of gamma motor neuron

A
  • maintain muscle spindle sensitivity, regardless of muscle length
34
Q

What is alpha-gamma coactivation

A
  • When the extrafusal fibers have been stimulated to contract by alpha MN activation, the gamma MN is simultaneously excited.
  • This is known as alpha-gamma coactivation.
  • The gamma MN stimulates contraction in the two ends of the intrafusal fiber, readjusting its length and keeping the central region of the intrafusal fiber taut, which is necessary to keep the muscle spindle afferent responsive.
35
Q

How do afferent muscle spindle receptors cause inhibition of antagonist muscles

A
  • Ia afferents also excite motor neurons that innervate synergistic muscles, and inhibit motor neurons of the antagonist muscles
36
Q

Pathway for a monosynaptic reflex pathway

A
  • Disturbance(addition of liquid to glass)
  • Length change in muscle fibre
  • Spindle receptor detects change in muscle fibre length
  • Increase spindle afferent discharge onto alpha-motor neuron
  • Descending facilitation and inhibition effect on alpha-motor neuron
  • Alpha motor neuron alters muscle
37
Q

What type of pathway causes the flexion reflex

A
  • Polysynaptic reflex pathway
38
Q

Describe how the flexion reflex can be triggered

A
  • Stimulation of cutaneous pain receptors in the foot
  • Activation of spinal cord local circuits that withdraw(flex) the stimulated extremity and extend the other extremity to provide compensatory support
39
Q

How are motor neurons organised in the spinal cord

A
  • Motor neurons innervating axial(ie postural trunk muscles) are located most medially
  • whereas those innervating distal musculature(eg in the hands) are located most laterally
40
Q

What is the main thing that the homunculus shows

A
  • The amount of somatic sensory cortex devoted to the hands and face is much larger than the relative amount of body surface in these regions
41
Q

What is anterior cord syndrome

A
  • Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion(due to damage to lower motor neurons)
42
Q

Why is tactile discrimination and vibratory and proprioceptive sensations preserved in anterior cord syndrome

A
  • The posterior(dorsal) white columns on both sides are undamaged
43
Q

What does anterior cord syndrome cause

A
  • Bilateral spastic paralysis below the level of the lesion (due to loss of anterior descending tracts)
  • Bilateral loss of pain, temperature and light touch sensations below the level of the lesion (due to loss of anterior and lateral spinothalamic tracts).
44
Q

What is brown - sequard or cord hemisection syndrome

A
  • Ipsilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion(due to damage
45
Q

What does brown syndrome cause

A
  • Ipsilateral spastic paralysis below the level of lesion(due to loss of anterior descending tracts
  • Ipsilateral band of cutaneous anesthesia in the segment of the lesion(due to loss of dorsal root)
  • Ipsilateral loss of tactile discrimination and of vibratory and propriceptive sensations below the level of lesion(due to loss of ascending tracts in the dorsal white column on the side of the lesion
46
Q

Effect of brown syndrome on pain, temp and light touch detection

A
  • Contralateral loss of pain, temperature and light touch(due to loss of crossed lateral spinothalamic tracts on the side of the lesion)
47
Q

What remains intact in brown syndrome

A
  • Discriminative touch pathways traveling in the ascending tracts in the contralateral dorsal white column remain intact
48
Q

What is cord transection syndrome

A
  • Complete loss of sensation and voluntary movement below the level of the lesion
49
Q

Effect of cord transection syndrome

A
  • Bilateral lower motor neuron paralysis and muscular atrophy in the segment of the lesion
  • Bilateral spastic paralysis below the level of the lesion(due to loss of descending tracts)
50
Q

Effect of cord transection syndrome on sensations

A
  • Bilateral loss of all sensations below the level of the lesion(due to loss of ascending tracts)
51
Q

Effect of cord transection syndrome on bladder and bowel functions

A
  • No longer under voluntary control(due to loss of descending autonomic fibres)

Year 2 - Theme 1 (30 decks)

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