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Semester 2 Molecular Medicine > Reflexes > Flashcards

Reflexes Flashcards

1
Q

What is a reflex?

A

A specific, involuntary, unpremeditated, ‘built in’ response to an involuntary stimulus

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2
Q

What are the components of a spinal or motor reflex?

A

There is a sensory and an effector component

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3
Q

What is the sensory component in a spinal or motor reflex?

A

The sensory receptor

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4
Q

What is a monosynaptic reflex?

A

A reflex arc with one synapse, e.g. spinal or motor reflex such as the knee jerk reflex

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5
Q

What are the principle differences between axons?

A

Myelination and diameter

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6
Q

Describe the sensory component of the spinal/motor reflex

A
  • Axons are routed to the CNS inside nerves

* Single nerves can carry both sensory and motor axons and information can travel in 2 directions

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7
Q

Where do most sensory signals enter the spinal cord?

A

At the sensory route: dorsal/posterior root

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8
Q

What happens once the sensory signal has entered the spinal cord?

A

• Branches into 2:

  • One terminates immediately in the grey matter
  • One signals to a higher level
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9
Q

Describe the anterior motor neurones

A
  • Several thousand
  • 50-100% larger than most of the other neurones
  • Located in each segment of the anterior horns of the cord grey matter
  • Give rise to nerve fibres that leave the cord via the anterior roots and directly innervate the muscle fibres
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10
Q

What muscle fibres do the anterior motor neurones give rise to?

A
  • Alpha motor neurones

* Gamma motor neurones

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11
Q

Alpha motor neurones

A
  • Give rise to type A alpha motor nerve fibers averaging 14μm in diameter which branch after entering the muscle and innervating large skeletal muscle fibers
  • Stimulation of a single alpha nerve fibre can excite many skeletal muscle fibres e.g. motor unit
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12
Q

Gamma motor neurones

A
  • Much smaller than alpha motor neurones
  • Located in the spinal cord anterior horns
  • Transmit impulses through A gamma motor nerve fibres, averaging 5μm in diameter which go to intrafusal fibres and constitute the middle of the muscle spindle which helps to control basic muscle tone
  • There are approximately half the number of gamma as there are alpha
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13
Q

What are intrafusal fibres?

A

Small, specialised skeletal muscle fibres

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14
Q

Which type of motor neurone send impulses to the intrafusal fibres?

A

Gamma motor neurones

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15
Q

What are interneurones?

A
  • Small and highly excitable neurones which transmit impulses between neurones
  • 30 times as numerous as anterior motor neurones
  • Have many connections with each other but may also synapse directly with anterior motor neurones
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16
Q

Describe the activity of interneurones

A

• Often show spontaneous activity, capable of firing 1500 times per second

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17
Q

What provides sensory information from the muscles to the spinal cord?

A
  • Muscle spindles

* Golgi tendon organs

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18
Q

Describe how the muscle spindles feedback to the spinal cord

A
  • Sends information to the nervous system about muscle length or rate of change of length
  • Located throughout the muscle belly
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19
Q

Describe how the Golgi tendon organ feedbacks sensory info to the spinal cord

A
  • Transmits information about tendon tension or the rate of change of tension
  • Located in the muscle tendons
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20
Q

In muscle spindles, where do the sensory fibres originate?

A

In the central portion

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21
Q

What causes receptor excitation in the muscle spindle

A
  • Lengthening the whole muscles, stretching the mid portion of the spindle
  • Contraction of the end portions of the spindle’s intrafusal fibres, stretching the mid-portion of the spindle
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22
Q

What are the 2 types of sensory endings in the central receptor area in a muscle spindle?

A
  • Primary afferent: Type IA

* Secondary afferent: Type II

23
Q

What are the muscle fibre types in order of their conduction velocity/diameter from high to low? (conduction velocity classification)

A
  • A alpha
  • A beta
  • A gamma
  • A delta
  • B
  • C
24
Q

What are the muscle fibre types and their origin? (sensory function classification)

A
  • IA- muscle spindles
  • IB - Golgi tendon organs
  • II - muscle spindles; touch and pressure receptors
  • III - Pain and temperature receptors
  • IV - Pain and other receptors
25
Q

What is the origin of fibre type IA

A

Muscle spindles

26
Q

What is the origin of fibre type IB

A

Golgi tendon organ

27
Q

What is the origin of fibre type II

A

Muscle spindles; touch and pressure receptors

28
Q

What is the origin of fibre type III

A

Pain and temperature receptors

29
Q

What is the origin of fibre type IV

A

Pain and other receptors

30
Q

What are the 2 types of muscle spindle intrafusal fibres?

A
  • Nuclear bag

* Nuclear chain

31
Q

Describe nuclear bag fibres

A
  • 1-3 in each spindle
  • Several muscle fibre nuclei are congregated in expanded ‘bags’ in the central portion of the receptor area
  • Excites primary sensory nerve endings (Type IA)
32
Q

Describe nuclear chain fibres

A
  • 3-9 in each spindle
  • 1/2 the diameter of nuclear bag fibres
  • 1/2 the diameter of nuclear bag fibres
  • nuclei aligned in a chain throughout the receptor area
  • Excites both primary (IA) and secondary (II) sensory nerve endings
33
Q

Describe the response of sensory nerve fibres in a static response

A
  • Both the primary (IA) and secondary (II) endings

* Respond to the length of the receptor

34
Q

Describe the response of sensory nerve fibres in a dynamic response

A
  • Response of a primary ending (NOT SECONDARY)

* Respond to the rate of change of the receptor length

35
Q

What are the gamma motor nerves to muscle spindle?

A
  • Gamma-dynamic

* Gamma- static

36
Q

Gamma-d

A
  • Excite mainly the nuclear bag intrafusal fibres

* Dynamic response of the muscle spindle is enhanced but the static response is hardly affected

37
Q

Gamma-s

A
  • Excites mainly the nuclear chain intrafusal fibres

* Enhances the static response but has little influence on the dynamic response

38
Q

What is the muscle stretch reflex?

A
  • Basic circuit of the muscle spindle stretch reflex

* Monosynaptic pathway

39
Q

In terms of the muscle stretch reflex, what is the type IA proprioceptor nerve fibre?

A
  • A branch of fibre goes directly to the anterior horn of the cord grey matter
  • It then synapses with anterior motor neurones that send motor nerve fibres back to the same muscle from which the muscle spindle fibre originated
40
Q

What is the benefit of a monosynaptic reflex?

A

• Allows a reflex signal to return with the shortest possible delay back to the muscle after excitation of the spindle

41
Q

What is the role of the knee jerk reflex?

A

To maintain balance and posture

42
Q

What does a dynamic stretch reflex do?

A

• Opposes sudden changes in muscle length

43
Q

Which sensory endings are involved in the dynamic stretch reflex?

A

Primary (Type IA) sensory endings of the muscle spindles

44
Q

Describe a dynamic stretch reflex

A
  • Muscle is suddenly stretched or unstretched
  • Strong signal is transmitted to the spinal cord which causes and instantaneous strong reflex contraction of the same muscle from which the signal originated
  • Ends within a fraction of a second after the muscle has been stretched or unstretched to its new length
45
Q

Describe the static stretch reflex

A
  • Causes a degree of muscle contraction to remain reasonably constant
  • Elicited by continuous static receptor signals transmitted from the primary (Type IA) and secondary (Type II) endings
  • Follows and continues for prolonged periods
46
Q

What is the Golgi tendon organ?

A

An encapsulated sensory organ with muscle tendon fibres passing through
• Has 10-15 muscle fibres attached

47
Q

When does a Golgi tendon organ become stimulated/

A

When the small bundle of fibres connected to it is tensed by contracting or stretching the muscle

48
Q

Describe the Golgi Tendon Organ reflex

A
  • GTO stimulated but the increased tension in the connecting muscle
  • Signals are transmitted to the spinal cord
  • Causes reflex effects in the respective muscle
49
Q

What is the purpose of a Golgi Tendon Organ reflex?

A

• Prevents the development of too much tension on the muscle

50
Q

What happens when tension on a muscle becomes extreme?

A

• When tension on the muscle (and therefore tendon) becomes extreme, the inhibitory effect from GTO can be so great that it leads to a sudden reaction in the spinal cord that causes instantaneous relaxation of the entire muscle

51
Q

Rotatory nystagmus

A

eye movements driven by moving visual images

52
Q

Post Rotatory nystagmus

A

Eye movements driven by the moment of fluid in the semi circular canals of the inner ear

53
Q

What is the interpretation of movement within images on the retina used for?

A

To make postural adjustments to preserve balance

54
Q

Describe the baroreceptor reflex

A
  • Occurs via the medullary cardiovascular centre
  • Arterial baroreceptors respond to changes in pressure
  • Increased firing rate in response to increased pressure

Semester 2 Molecular Medicine (27 decks)

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