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My own anatomy > Body sensation - proprioception - reflexes > Flashcards

Body sensation - proprioception - reflexes Flashcards

1
Q

What are the functions of sensory receptors

A
  • Inform your brain about the internal and external environment
  • Are nerve endings (many have specialised non-neural nendings)
  • Convert different stimuli into frequency of action potentials
    They are transducers
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2
Q

What are the 3 types of sensory receptors

A

Mechanoreceptors
Proprioceptors
Nociceptors

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3
Q

Describe mechanoreceptors

A

Stimulated by mechanical stimuli - pressure, stretch, deformation - Give us skin sensation of touch and pressure

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4
Q

Describe proprioceptors

A

Are mechanoreceptors in joints and muscles which signal information about the body or limb position

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5
Q

What do nociceptors respond to?

A

Pain

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6
Q

Define ‘sensory modality’

A

The stimulus type that activates a particular receptor

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7
Q

Describe what is meant by an ‘adequate stimulus’

A

Is the form of energy to which a receptor normally responds

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8
Q

What does sensory receptor transduction involve?

A

The opening and closing of ion channels

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9
Q

What does an adequate stimulus cause?

A

A graded membrane potential change

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10
Q

What are graded membrane potential changes called when caused by an adequate simulus?

A

Receptor potentials or generator potentials

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11
Q

What is the name of an adequate stimulus in cutaneous mechanoreceptors and proprioceptors?

A

MEMBRANE DEFORMATION

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12
Q

What does membrane deformation activate?

A

Stretch sensitive ion channels

so ions flow across the membrane and change the membrane potential locally

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13
Q

When do action potentials start firing in cutaneous mechanoreceptors?

A

When depolarisation reaches the area with voltage gated ion channels (the first of o Ranvier)

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14
Q

What is frequency coding of stimulus intensity?

A

When a larger stimulus causes:

  • A larger receptor potential
  • A higher frequency of action potentials
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15
Q

What do Pacinian corpuscles sense?

A

Vibration and pressure

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16
Q

What do merkel receptors sense?

A

Steady pressure and texture

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17
Q

What do meissner’s corpuscle’s do?

A

They respond to flutter and stroking movements

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18
Q

What do Ruffini corpuscles respond to?

A

Stretches in the skin

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19
Q

Describe what is meant by adaptation in relation to mechanoreceptors

A

When they adapt to a maintained stimulus and only signal change - eg. the onset of stimulation

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20
Q

Describe the mechanism of adaptation in mechanoreceptors

A

Generator potential declines rapidly blow threshold and AP’s cease

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21
Q

What types of receptors are rapidly to moderately adapting

A

Pacinian corpuscles and meissner’s corupscles

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22
Q

What types of receptors are slowly adapting receptors?

A

Merkels discs and ruffini endings

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23
Q

What types of receptors do not adapt?

A

Nociceptors

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24
Q

Describe the structure of pacinian corpuscles

A

It comprises a myelinated nerve with a naked nerve ending
It is enclosed by a connective tissue capsule of layered membrane lamellae
Each layer is separated by fluid

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25
Q

Describe how the mechanism of a pacinian corpuscle

A

A mechanical stimulus deforms the capsule and the nerve ending
This stretches the nerve ending and opens ion channels
Na influx causes local depolarisation (receptor/generator potential)
AP’s are generated and fire where myelination begins (because regenerative Na channels cluster at nodes of ranvier)

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26
Q

How do pacinian corpuscles rapidly adapt?

A

Fluid rapidly redistributes within capsule lamellae, this spreads the stimulus impact out laterally - minimising downward deformation.
As stimulus is withdrawn - capsule lamellae spring back and fire AP again

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27
Q

What is the capsules effect on the sensory function of the pacinian corpuscle

A

It enhances sensory function

28
Q

What two things determine our ability to tell 2 points apart on the skin and by what test is this measured?

A
  1. Receptive field size
  2. Neuronal convergence
    Measured by the two point convergence test
29
Q

What are the 2 types of neuronal convergence - describe them?

A
  • Convergence
  • Divergence
    Convergence - sensory neurons converge on one 2ndary neuron
    Divergence - one sensory neuron diverges into many branches
30
Q

What does neuronal convergence allow for?

A

The simultaneous sub-threshold stimuli to sum at the secondary neuron forming a larger secondary receptive field

31
Q

Describe what is meant by ‘acuity’

A

The ability to locate a stimulus on the skin and differentiate it from another closeby
Low acuity is caused by high convergence

32
Q

What process allows us to locate stimulus so precisely

A

Lateral inhibition

33
Q

What are the 3 prorprioceptos?

A

Muscle spindles
Golgi tendon organs
Joint receptors

34
Q

What is the function of muscle spindles?

A

They monitor muscle length and the rate of change of muscle length
They also control reflexes and voluntary movements

35
Q

What is the function of golgi tendon organs?

A

Monitor tension on tendons

36
Q

What is the function of joint receptors?

A

Monitor joint angle, rate of angular movement and tension on the joint

37
Q

What type of muscle fibre are most skeletal muscle fibres?

A

Extrafusal

38
Q

What are Intrafusal muscle fibres? and where are they contained?

A

Muscle fibres which have their own sensory and motor innervation.
They are contained within a capsule and called MUSCLE SPINDLES

39
Q

Muscle spindles lie in ______ with muscle fibres

A

As DJ chorn says: PARALELL

40
Q

What are the two kinds of intrafusal muscle fibre?

A

Nuclear bag fibres - Bag shaped with nuclei collected together
Nuclear chain fibres - Nuclei lined up in a cha

41
Q

What is the function of Gamma motorneurons?

A

They innervate and cause contraction of the contractile ends of the intrafusal fibres

42
Q

What do the primary endings from type I afferent nerves form?

A

Annulospiral endings around the centre of intrafusal fibres

43
Q

What do secondary ending from type II afferent nerves form?

A

flower spray endings

44
Q

Does the central area of the muscle spindle contain contractile elements?

A

NO - dumbass

45
Q

What happens when Gamma motorneurons fire?

A

They contract the two ends of the muscle spindle and shorten. HOWEVER the central area does not contract - therefore it gets stretched out

46
Q

What do GTO’s monitor?

A

They are stretch receptors and hence monitor the stretch of a tendon. Muscles have to develop tension by contracting to stretch the tendons

47
Q

Do GTO’s lie in series or in parallel with muscle fibres?

A

Series

48
Q

Define isometric contraction

A

Same length - changing tension

49
Q

Define isotonic contraction

A

Changing length - same tension

50
Q

What is the result of alpha-gamma coactivation

A

Restores tension in the spindle and resets the sensitive of the central sensory part of the spindle to match a new muscle length

51
Q

What happens when alpha motorneurons are activated?

A

Contraction of muscle

52
Q

What type of reflex is found in all muscles?

A

Stretch reflex

53
Q

Give an example of a stretch reflex

A

Patellar tendon/knee jerk reflex

54
Q

Explain the mechanism of a stretch reflex

A
  • Knee jerk follows a sharp tap to an inelastic tendon
  • Force is transmitted to the muscle fibres (they are more elastic than tendons and so are more able to stretch)
  • Stretch activates 1a afferent sensory nerves in the muscle spindle
  • This increases the number of AP’s in 1a afferent sensory nerves projecting through the dorsal horn into the spinal cord
55
Q

What is a monosynaptic reflex

A

reflex that only contains one space for an action potential to travel between a sensory and motor neuron

56
Q

Describe reciprocal inhibition

A

Reciprocal inhibition describes the relaxation of muscles on one side of a joint to accommodate contraction on the other side.
aka; when agonist contracts antagonist relaxes

57
Q

Afferent Spindle firing travels up what colummns to what two structures?

A

Travels up the dorsal columns to the thalamus and the somatosensory cortex

58
Q

What is the effect of spindle afferent firing traveling up up the dorsal columns to the thalamus and the somatosensory cortex

A

To tell the brain about the length of muscles

59
Q

Describe what happens after the initial muscle stretch

A
  1. Afferent impulses fire from stretch receptor to spinal cord (dorsal root)
  2. Efferent impulses fire from the ventral horn to the alpha motor neurons, causing contraction of the stretched muscle that resists/reverses the stretch
  3. Efferent impulses to antagonist muscles are damped (reciprocal inhibition)
60
Q

What is the inverse stretch reflex caused by?

A

afferent nerve from the golgi tendon organs - which monitor muscle tension

61
Q

What happens to the golgi tendon organ when a muscle contracts/shortens

A

This pulls on the tendon and the sensory 1b afferent nerves from the GTO’s increase the firing of action potentials

62
Q

What 3 things does increased firing of action potentials from the GTO cause

A
  1. Activation of inhibitory interneurons to the agonist muscle and a decrease in contraction strength
  2. Activation of excitatory interneurons to antagonist muscles
  3. Information about muscle tension ascends in the dorsal columns to the somatosensory cortex
63
Q

What is the function of the ‘clasp-knife’ reflex? why does it happen?

A
  • Acts a protective mechanism to prevent muscle damage

- Happens because greatly increasing tension in tendon leads to a collapse of resistance

64
Q

Describe the function of the flexor reflex?

A

They withdraw part of the body away from the painful stimulus and in towards the body - so flex the affected part

65
Q

Describe the circuitry of the flexor relfex

A
  • Small diameter Aδ nocieptive fibres triggering pain enter spinal cord.
  • They branch and activate interneurons in several spinal segments above entry points
  • These activate α motorneurons controlling all the flexor muscles of the affected limb
66
Q

Describe how an upright posture is maintained during a flexor reflex?

A

The contralateral limb extends to bear the shift in body weight

My own anatomy (34 decks)

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