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Foundations of Medicine > Sensory Receptors > Flashcards

Sensory Receptors Flashcards

1
Q

What are cutaneous receptors?

A

Type of sensory receptor found in the skin.

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2
Q

What are examples of cutaneous receptors?

A

Mechanoreceptors, nociceptors, and thermoreceptors.

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3
Q

Where are cutaneous receptors found?

A

Cutaneous receptors are found at the distal ends of the primary sensory axon; they act as dendrites

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4
Q

What are nociceptors?

A

Respond to painful stimuli - heat and tissue damage

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5
Q

What do sensory receptors do?

A

Convert different stimuli into frequency of action potentials so they are transducers

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6
Q

What are mechanoreceptors?

A

They are primarily involved in recognizing different mechanical stimuli. Example is the touch receptor in the skin.

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7
Q

What are proprioceptos?

A

Mechanoreceptors in joints and muscles that signal information about body or limb possition

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8
Q

Define sesnsory modality

A

The stimnulus type that activates a particular receptor eg touch, pressure, joint angle, pain

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9
Q

Define adequete stimulus

A

Form of energy which a receptor normally responds to

Sensory receptors are highly sensitive to one specific energy form

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10
Q

What can an adequete stimulus cause?

A

A graded membrane potential change (only a few mV)

This is called a receptor potential or geenrator potential

This is called a receptor potential or geenrator potential

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11
Q

What is the adequate stimulus in cutaneous mechanoreceptors and proprioceptors?

A

Membrane defromarion which activates stretch-sensitive ion channels so ions flow across the membrane and change the membrane potential locally

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12
Q

How is a receptor potential graded?

A

By stimulus intensity

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13
Q

What does a stimulus trigger?

A

Ions to flow through the membrane locally

When depolarisation reaches the area with voltage gated ion channells (the first node of Ranvier) - action potentials start firing

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14
Q

What do the lowest and highest stimuli intensity produce?

A

Lowest - no action potential
Highest - most action potential

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15
Q

What does a larger stimulus cause in a sensory nerve?

A

A large receptor potential and a higher frequency of action potentials - this is called frequency coding of stimulus integrity

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16
Q

What is frequency coding?

A

As the intensity of a stimulus increases, the frequency or rate of action potentials, or “spike firing”, increases

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17
Q

What is sensory transduction?

A

The translation of the sensory stimulus into neuronal activity

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18
Q

What causes sensory transduction?

A

Either membrane hyperpolarization or membrane depolarization.

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19
Q

What are chemoreceptors?

A

Special nerve cells or receptors that sense changes in the chemical composition of the blood.

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20
Q

What are exteroreceptors?

A

The organs responsible for detecting information from outside the body – the traditional five senses.

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21
Q

What are enteroreceptors?

A

Any receptor that responds to stimuli inside the body

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22
Q

What are the receptors in the skin for touch?

A

Merkel receptors
Meissner’s corps
Pacinian corpuscle
Ruffini corpuscle

Skin also contains sensory nerves to carry signals to spinal cord

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23
Q

What do merkel receptors sense?

A

Steady pressure and texture

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24
Q

What do meissener’s corpuscle’s sense?

A

Responsible for transmitting the sensations of fine, discriminative touch and vibration.

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25
Q

What do pacinian corpuscles sense?

A

Vibraitons

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26
Q

What do ruffini corpuscles sense?

A

Streches in skin

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27
Q

What do free nerve endings of the skin respond to?

A

Noxinous stimuli

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28
Q

What is a noxious stimuli?

A

A stimulus strong enough to threaten the body’s integrity (i.e. cause damage to tissue).

29
Q

What is the pacinian corpuscle?

A

Sensory receptors for vibration and deep pressure and are essential for proprioception

30
Q

What does a pacinian corpuscle consist of?

A

A myelinated with a naked nerve ending.

It is enclosed by a connective tissue capsule of layerd membrane lamellae.

Each layer is seperated by fluid.

31
Q

How does the pacinian corpuscle respond?

A
  1. A mechanical stimulus deforms the capsule and the nerve ending
  2. This stretches the nerve ending and opens ion chanels
  3. **Na+ influx causes local depolarisation - a receptor/generator potential **
  4. APs are generated and fire where myelination begins (because regenerative Na+ channels cluster at nodes of Raniver)
32
Q

What is adaptation?

A

Some mechanoreceptors adapt to a maintained stimulus and only signal change - eg the onset of stimulaiton

32
Q

Adaptation steps

A
  1. Stimulus causes an above threshold generator potential this triggers APs
  2. Generator potential declines rapidly below threshold and APs cease
  3. Mechanoreceptor only signals the onset of a stimulus
  4. Responds only to a change or a novel event

Different receptos show different extents of adaptation.

33
Q

What happens to the pacinian corpsucle when the stimulus is withdrawn?

A

Capsule springs back - more action potentials

34
Q

What type of structure is the pacinian corpsucle?

A

Non-neural accessory structure

35
Q

What is the receptive field?

A

The area that a stimuli will activate a sensory neurone

36
Q

What is the receptive field?

A

The area that a stimuli will activate a sensory neurone

37
Q

What does the ability to tell apart two points on the skin depend on?

A

The size of the receptive field and neuronal convergence

38
Q

What is meant by convergence?

A

When multiple presynaptic neurones synapse with fewer post synaptic neurones

39
Q

What does convergence allow?

A

Allows sub threshold stimuli to sum at the secondary neurone forming and initiating action potentials

40
Q

How can we locate a stimulus so precisely?

A

Lateral inhibition of sensory neurones that are at the edge of the stimulus

41
Q

What are proprioceptors?

A

Mechanoreceptors that signal body or limb position

42
Q

Give three examples of proprioceptors

A

Muscle Spindles
Golgi tendon organs
Joint receptors

43
Q

What do proprioceptors do?

A
  1. Control voluntary movements
  2. Generate spinal reflex movements
  3. Perceive limb and body position and movement in space
44
Q

What is the funciton of muscle spindles?

A

Monitor the muscle length and rate of change of muscle length

45
Q

What do golgi tendon organs do?

A

The golgi tendon organ is the sense organ that tells how much tension the muscle is exerting. If there is too much muscle tension the golgi tendon organ will inhibit the muscle from creating any force (via a reflex arc), th

46
Q

What do joint receptors do?

A

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

47
Q

What do muscle spindles do in relation to stretch?

A

Functionally, muscle spindles are stretch detectors, i.e. they sense how much and how fast a muscle is lengthened or shortened.

Accordingly, when a muscle is stretched, this change in length is transmitted to the spindles and their intrafusal fibers which are subsequently similarly stretched.

48
Q

What are muscle spindles sensitive to?

A

Muscle spindles are sensitive to changes in velocity and are innervated bytype 1a nerve fibers.

49
Q

What do type 1A nerve fibres do?

A

These afferent nerve fibers conduct the impulse directly to the spinal cord, where they are immediately conducted via interneurons to alpha motor neurons, which stimulate muscle contraction.

50
Q

How does spindle information contribute to the perception of body position and movement?

A
  • Joint movement is organised by groups of muscles working in opposition ie agonists and antagonists (biceps and triceps)
  • When agonist contracts, antagonist relaxes and the joint nerve moves
51
Q

What is the role of the Golgi tendon?

A

If there is too much muscle tension the golgi tendon organ will inhibit the muscle from creating any force (via a reflex arc), thus protecting the you from injuring itself.

52
Q

Which proprioceptors are involved with sending sensory information for spinal cord reflexes?

A

Golgi tendon organs and muscle spindles

53
Q

What is a muscle spindle?

A

Intrafusal fibres with special sensory and motor innervation contained within a capsule, they lie in parallel with extrafusal muscle fibres

54
Q

What are the two types of intrafusal fibre?

A

Nuclear bag fibres - bag shaped, nuclei are all grouped together

Nuclear chain fibres - nuclei are lined up in a chain

55
Q

What is contained at the ends of the muscle spindle?

A

Sacromeres

56
Q

What do sacromeres do?

A

Each sarcomere is composed of two main protein filaments—actin and myosin—which are the active structures responsible for muscular contraction.

57
Q

What is a sacromere?

A

A sarcomere is the basic contractile unit of muscle fiber.

58
Q

What do gamma motoneurones innervate?

A

Innervate ends of intrafusal fibres which contract

59
Q

What do alpha motoneurones innervate?

A

The extrafusal muscle fibres, they are larger than gamma motoneurones

60
Q

How are regenerative action potentials in the muscle spindles created?

A

Muscle stretch stimulates the stretch receptors, stretch sensitive ion channel opens causing local generator potential - causing regenerative action potentials

61
Q

Stretch receptors can monitor the rate of change of muscle length, how is this done?

A

The rate of action potential formation reflects the velocity of change of muscle length

62
Q

How is muscle length determined by the muscle stretch receptors?

A

The resting rate of action potential formation at one muscle length will be different to the resting rate of action potential formation at another length

63
Q

How can spindle discharge be increased?

A

Stretching the agonist

64
Q

Describe the structure of the golgi tendon organ

A

Each Golgi tendon organ consists of small bundles of tendon fibers enclosed in a layered capsule with dendrites (fine branches of neurons) coiling between and around the fibers

65
Q

How are golgi tendon organs activated?

A

Contraction of the muscle, passive stretch doesn’t affect them much

66
Q

Are GTO’s in series or parallel with the muscle?

A

Series

67
Q

Which proprioceptors are activated during isometric contraction?

A

Only GTO’s since tension is increased but length of the muscle is kept constant

68
Q

What is the purpose of gamma motor neurones?

A

Makes the intrafusal muscle contract in time with the extrafusal muscle, this restores sensitivity of the central part of the intrafusal fibres at a new muscle length - maintains spindle sensitivity

Foundations of Medicine (56 decks)

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