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NSB > Physiology of the Spinal Cord > Flashcards

Physiology of the Spinal Cord Flashcards

1
Q

4 physiological functions of the spinal cord:

A
  • acts as a conduit between the brain
    and the rest of the body
  • initial processing of somatosensory
    input to the CNS
  • final processing of motor output from
    the CNS
  • can act without brain signals; reflex
    activity
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2
Q

Sensation definition:

A

the detection of a stimulus by a receptor

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3
Q

Perception definition:

A

the interpretation of that stimulus by the brain with existing emotions and memories

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4
Q

Sensory Receptors:
- are
- two types

A
  • specialised endings of the peripheral
    process of the sensory neuron
  • mechanoreceptors (pressure or
    distortion)
  • nociceptors: chemical, thermal,
    mechanical
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5
Q

Mechanoreceptors in skin:

A
  • hair follicle receptors
  • merkell’s receptor
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6
Q

Receptors Mediating Tactile Senses:

A

insert diagram

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7
Q

All somatosensory processing receptors are located in the

A

dermis
epidermis = dead skin = no sensory fibers

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8
Q

Pancinian Corpuscle:

A
  • distortion due to pressure = stimulus
  • causes all or nothing action potential
  • depolarisation of dorsal root ganglion
  • deep pressure, fast vibration
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9
Q

What are C fibre pains?

A

slow pain, might have a delay
slow phase

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10
Q

Mechanosensory (proprioception/vibration/light touch): ascend in dorsal columns on the

A

same side to ssynapse with second order neuron in medulla

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11
Q

Pain & temperature: synapse at level of entry with second order neuron which

A

crosses midline and ascends in lateral spinothalamic tract

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12
Q

Sensory information is integrated at all levels of the nervous system;

A

excitatory and inhibitory modulation

whether stimulus is passes to brain

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13
Q

Descending pathways can modulate sensory input:

A

green and red are descending trunks
different neurotransmitters modulate the transmission at spinal level

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14
Q

Mechanisms of sensory stimulus discrimination:

A
  • different receptor types allow
    differentiation between different
    sensations
  • spatial distribution of receptors
  • windows of response intensity
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15
Q

Spatial Distribution of Receptors:

A
  • two point discrimination to measure
    variation in the sensitivity of tractile
    discrimination as a function of location
    on the body surface
  • the higher the density of the
    mechanoreceptors,
    the smaller the distance at which two
    tactile stimuli can be discriminated

eg higher density of mechanoreceptors on the
hand and face, allowing the detection of
stimuli at a much greater spatial resolution

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16
Q

Motor Processing:

A

descending pathway, short dendrons, long axons, decussation at brain level

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17
Q

Ventral horn of the cord has anterior motor neurons: give rise to nerve fibers innervating muscles:

A
  • alpha motor neurons
  • gamma motor neurons
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18
Q

What is a motor unit?

A

a motor neuron and the muscle fibres it synapses with

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19
Q

Merkell’s receptor:
- type of receptor
- what sensory information

A
  • mechanoreceptor
  • touch and pressure; low threshold
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20
Q

Meissner’s Corpuscle:
- type of receptor
- what sensory information

A
  • mechanoreceptors
  • texture, slow vibration
  • just under the epidermis
21
Q

Painless burns

A

can be deeper than dermis

22
Q

Ruffini’s Ending:
- type of receptor
- what sensory information

A
  • mechanoreceptor
  • skin stretch
  • superior dermis
23
Q

Mechanisms of Sensory Stimulus Discrimination:

A

insert diagram

24
Q

How are lower motor neurons collected?

A

longitudinally in organised columns

25
Q

No muscle is innervated by a single spinal cord level:

A

each column of lower motor neurons extend through more than one segmented

each muscle receives motor fibers through more than one ventral root

hence damage to a single nerve will not cause complete paralysis

26
Q

Renshaw Cells:

A

groups of cells sitting close to motor neurons

inhibitory to motor neurons

affected by descending pathways through the spinocerebellar tract

lateral inhibition of lower motor neurons; preventing innervation of muscles that are not needed

27
Q

Can more than one muscle be innervated by the same spinal nerve root?

Link with lateral inhibition.

A

more than one muscle can be innervated by the same spinal nerve root

lateral inhibition via renshaw cells prevents for example 2 muscles moving when not needed

28
Q

Effect of lateral inhibition on signals?

A

Lateral inhibition sharpens or focusses signals

29
Q

2 types of reflex integration:

A
  • simple reflex
  • complex polysynaptic reflex causes
    bilateral withdrawal

both occur solely in the spinal cord

30
Q

Muscle Sensory Organs: Mechanoreceptors:

A
  • detect proprioception = forces
    generated within the body
  • sensory nerve fibers
  • muscle spindles
  • golgi tendon organs
  • continuous feedback; integrate
    between several muscles
  • control muscle at conscious and
    unconscious levels: spinal cord,
    cerebellum, cerebral cortex
31
Q

What do Muscle Spindles do?

A

Muscle sensory organs found in bodies of muscle, which respond to muscle length

32
Q

What do Golgi Tendon Organs do?

A

Muscle sensory organs found in bodies of muscle, which respond to tension of muscle

33
Q

Muscle Spindles:
- are
- when are impulses created

A
  • sensory fibers stimulated by stretch
  • spindles emit impulses continually!!!
  • with stretch = impulses increase
  • with contraction = impulses decrease
34
Q

Muscle Spindles:
- dynamic response

A

a sudden increase in length, causes impulses to suddenly increase

35
Q

Muscle Spindles:
- gradual increase

A

impulses increase proportionally to the stretch

36
Q

Muscle Spindles:
- static response

A

impulses continue after stretch

37
Q

What is shown in the diagram below?

A

Muscle spindle

38
Q

Monosynaptic Pathway:

A

interaction of sensory and motor nerves at a spinal cord level: simple circuit

39
Q

Knee Jerk Reflex:

A
  • dynamic stretch reflex
  • sudden stretch leads to strong reflex
    contraction
  • static stretch reflex, leads to weaker,
    more prolonged phase
  • due to muscle spindles
40
Q

Golgi Tendon Organ:
- is
- does
- effect
- function

A
  • sensory receptor through which muscle
    tendon fibers pass
  • detects muscle tension
  • effect is inhibitory
  • protects against excess tension due to
    prolonged contraction of muscle
41
Q

What is show below?

A

Golgi Tendon Organ

42
Q

Clasp Knife Reflex:

A
  • golgi tendon organ responds to
    tension, not passive stretch
  • activation inhibits the alpha motor
    neuron
  • leads to reduction in activity in the
    same muscle
  • sometimes called the inverse stretch
    reflex
43
Q

What is the reflex circuitry for the contraction of muscle below?

A
  • bicep contract, triceps relax to flex
    elbow to maintain distance
  • stretch of muscle leads to lengthening
    of muscle spindle
  • activates the alpha motor neuron to
    contract the muscle
  • negative feedback loop regulates
    muscle length
  • desired length set by descending
    pathways; circuits do not exist in
    isolation
44
Q

The flexor reflex is a monosynaptic or polysynaptic reflex pathway?

A

Polysynaptic

45
Q

Flexor Reflex:

A
  • pain leads to flexion of muscle
  • allows muscle withdrawal
  • other circuits are also activated to
    inhibit antagonistic muscles
  • effects on opposite side of the body:
    crossed extensor reflex
46
Q

Knee Jerk Reflex can assess how senstive the

A

stretch reflexes are

47
Q

If a reflex is reduced, then which motor neurons are afffected?

A

lower motor neurons

48
Q

If a reflex is exaggerated, then which motor neurons are affected?

A

upper motor neurons

NSB (50 decks)

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