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Sensory Receptors > Sensory Receptors > Flashcards

Sensory Receptors Flashcards

• Describe the structure of cutaneous receptors. • Explain the mechanisms of sensory transduction in the skin. • Explain the concept of frequency coding. • Describe the structure and function of the muscle spindle. • Explain the mechanisms of efferent control of spindle function. • Describe the role and mechanism of action of the Golgi tendon organ.

1
Q

What are sensory receptors

A
  • Nerve endings with non-neural structures

- Used to inform the CNS about any external or internal changes

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2
Q

What do we mean by the term sensory neurones are transducers?

A

They change any form of energy they receive into electrical impulse - frequency of Action Potentials

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3
Q

what is sensory modality?

A

The type of stimulus that activates a receptor

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4
Q

Name 5 different types of sensory modalities

A 
Temperature
Pressure
Pain
Light 
Touch
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5
Q

What is an adequate stimulus ?

A

The type of energy that normally activates a specific receptor

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6
Q

To how many stimuli does usually one sensory receptor respond to?

A

One

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7
Q

what are the different types of sensory receptors that there are? And what are their functions?

A
  1. Mechanoreceptors= They detect mechanical stimuli (i.e. pressure, temperature, pain, deformation, stretch), skin sensation of touch and pressure
  2. Proprioreceptors= Mechanoreceptors that acknowledge limb and body position and are located in muscles and joints.
  3. Nociceptors= Respond to painful stimuli, tissue damage and heat
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8
Q

What are the different types of potentials that adequate stimuli can produce and how?

A

By opening and closing ion channels.
Graded membrane potential change,
generated potential
Receptor potential

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9
Q

What is the adequate stimulus in the cutaneous mechano- and proprioreceptors?

A

Deformation of the membrane

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10
Q

How do adequate stimuli in mechano- and proprioreceptors stimulate the receptors?

A

Cause ion channels to open leading to local potential membrane change through stretch-sensitive ion channels

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11
Q

What does a stimulus do?

A

Triggers the movement of ions locally producing local potential membrane difference

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12
Q

What is the frequency coding of stimulus intensity?

A

The greater the stimulus,
the greater the intensity of the graded (receptor) potential and
the greater the frequency of the action potential produced

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13
Q

What is the stimulus intensity reflected by?

A

By the number of receptors activated spatially per unit area

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14
Q

What kind of stimuli do receptors on skin transduce?

A

Vibration,
temperature,
Texture
stretch

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15
Q

Name the 7 different receptors in the skin

A 
Merkel Receptors
Pacinian Corpuscle
Ruffini Corpuscle
Meissner's Corpuscle 
Proprioreceptors 
Free nerve ending on hair root
Nociceptor free nerve endings
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16
Q

Function of Merkel’s Receptors and Meissner’s Corpuscle

A

Merkel’s Receptors- Sense steady pressure and texture

Meissner’s Corpuscle- Respond to flutter and stroking movement

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17
Q

Function of Ruffini and Pacinian Corpuscle

A

Ruffini- Responds to skin stretch

Pacinian- Sense vibration

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18
Q

What do sensory nerves on the skin do?

A

Carry information to the spinal cord

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19
Q

What do the free nerve endings on the hair root and nociceptor do?

A

Root endings- Sense hair movement

Nociceptors- Respond to noxious stimuli (tissue damaging event)

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20
Q

What do we mean by the term adaptation?

A

The response changes while the stimulus remains the same

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21
Q

How does adaptation take place?

A
  • The stimulus causes a change in the local membrane potential
  • Threshold is reached and action potential is fired
  • While the stimulus is present at the same intensity
  • The generated potential declines
  • The action potential ceases
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22
Q

All receptors show the same degree of adaptation. True or false?

A

False

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23
Q

What are the different types of adapting receptors?

And two examples of each

A 
Rapidly/Moderating adapting receptors:
- Meissner's Corpuscle 
- Pacinian Corpuscle 
Slowly-adapting receptors:
- Merkel's receptors
- Ruffini's Corpuscle
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24
Q

What are the features of a rapidly/moderately adapting receptor?

A

Action potential when the stimulus is introduced
No action potential when stimulus is present
Action potential when stimulus is removed

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25
Q

What are the features of a slow-adapting receptor?

A

High frequency of action potentials when the stimulus is introduced.
The frequency of action potentials decreases as stimulus is present for a while.
After some time of the stimulus being present the lower frequency of action potentials is equal.

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26
Q

What is the structure of a Pacinian Corpuscle?

A 
Myelinated nerve tail
Naked nerve ending
Connective tissue layered with membrane lamellae 
Fluid between the layers of lamellae 
spongy onion
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27
Q

Activation of Pacinian Corpuscle

A
  1. Mechanical stimulus deforms the capsule
  2. Nerve ending stretches due to vertical force
  3. Sodium ion channels open and sodium ion moves into the nerve cell causing depolarisation
  4. Action potential is fired where the myelinated nerve starts.
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28
Q

Adaptation of Pacinian Corpuscle

A
  1. There is rapid redistribution of the fluid in the capsule laterally
  2. The vertical force causing the mechanical stretching of the end nerve is removed
  3. Sodium ion channels close
  4. Action Potential is lost
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29
Q

What do we mean by the on and off response of Pacinian Corpuscle?

A

Action Potential is fired once stimulus is introduced due to mechanical stretching of nerve ending
Action potential is lost during the stimulus action due to loss of vertical force
Action Potential fired when stimulus is removed due to vertical pressure in capsule.

30
Q

What happens if the Pacinian Corpuscle loses its lamellae?

A

No adaptation - continues producing generator and action potential

31
Q

What is a receptive field?

A

The specific area on a somatic neurone at which a stimulus needs to act in order to stimulate a specific receptor.

32
Q

What is an example of a receptive field?

A

Touch area on skin (pressure response)

33
Q

What does 2 point discrimination test measure?

A

The ability to distinguish two points apart on our skin

34
Q

On what does the two point discrimination test depend?

A

1) The receptive field size

2) neuronal convergence

35
Q

What does neuronal convergence mean?

A

When multiple presynaptic neurones input on a smaller number of postsynaptic neurones

36
Q

What are the characteristics of neural convergence?

A
  • Allow the summation of threshold subunits
  • Produces large receptive field
  • Initiate APs
  • Low acuity
37
Q

What does acuity mean?

A

The ability to locate a stimulus and differentiate it from other stimuli nearby on the skin

38
Q

How is high insensitivity produced?

A

Lots of convergence and large secondary receptive field

39
Q

What is the measurement for the two point discrimination test

A

Distance between two points on the skin that 2 points of stimulation are perceived rather than one.

40
Q

What is lateral inhibition?

A

The sharpening and cleaning up of sensory information

Only the important information is perceived.

41
Q

How is lateral inhibition carried out?

A
  1. The primary sensory receptors closest to the stimulation area is stimulated more than the neighbouring receptors.
  2. Pathway closest to the stimulus inhibits neighbours
  3. Inhibition of lateral receptors allows for a more precise localisation to the site of stimulation (ie. precise localisation of a single hair movement)
42
Q

What is the principle of lateral inhibition?

A

The degree of neurone response is proportional to the stimulus strength

43
Q

What is the purpose of lateral inhibition?

A

Enhancement of contrast between relevant and irrelevant information

44
Q

What are proprioreceptors made of?

A
  • Muscle spindles
  • Golgi Tendon Organs
  • Joint receptors
45
Q

What do muscle spindles do?

A
  • Control muscle length
  • Control rate of change of muscle length
  • Control reflexes
  • Control voluntary movements
46
Q

What is the function of the Golgi Tendon Organs?

A
  • Tension in tendons

- Tension in muscles

47
Q

What is the function of joint receptors?

A
  • Control tension on joints
  • Control the angle of joint movement
  • Control the rate of angular movement of the joint
48
Q

What are the 3 things that proprioceptors are used for?

A
  1. The Golgi tendon organ and the muscle spindles are used in the spinal cord reflex generation
  2. voluntary movement of muscles
  3. Provide exact limb and body position and direction of movement. - Kinaesthesia
49
Q

What is the most contractile part of muscle fibres made of?

A

Extrafusal fibres

50
Q

Where are the intrafusal fibres found?

A

Inside capsules

51
Q

In what direction relative to the muscle fibres are muscle spindles lying?

A

Parallel

52
Q

What are the two types of intrafusal fibres?

A
  • Nuclear bag fibres- bag shaped with nuclei contained within it
  • Nuclear chain fibres- nuclei lined up in a chain
53
Q

Structure of intrafusal fibres

A
  • Annulospiral endings: Ia afferent wraps around intrafusal fibres
  • made from central non-contractile elements and two contractile sarcomere areas on either side.
  • On the contractile ends γ- efferent neurones are attached
54
Q

How is muscle contraction stimulated?

A
  1. Afferent muscle becomes stimulated by stretch sensitive ion channels local generator potential.
  2. Action Potential is fired
  3. original length (F0) to new length F1
55
Q

What is the relationship between action potential and length of muscle spindles?

A
  • Action potential frequency is proportional to the length of muscle spindles.
  • The increased frequency of action potential during stretch is proportional to the velocity of stretch.
  • F1 (new resting length) is greater than F0 when the frequency of action potential is increased.
56
Q

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

A

Through the action of agonists and antagonists

57
Q

How is joint movement produced?

A

When the agonist contracts the antagonist relaxes and the joint moves

58
Q

How is the brain informed about joint position?

A

Through the action of spindle fibres and joint receptor information

59
Q

How is spindle affected when the agonist is contracted?

A

Contraction means stretch

Muscle spindle discharge increases

60
Q

How is spindle affected when the agonist is relaxed?

A

Relaxation means shortening

Muscle spindle discharge decreases

61
Q

How are tendons and Golgi Tendon organs connected?

A

Sensory nerve endings of GTOs are connected to bundles of tendons

62
Q

What is a feature of tendons?

A

Tendons are inelastic

63
Q

How is tendon stretching monitored produced?

A

The muscle contracts
Tension in tendon increases
Nerve ending of GTOs stretch
APs produced from the GTO

64
Q

In what type of fibres are action potentials produced in GTOs when tension in tendons increases?

A

1b afferent fibres

65
Q

How do GTOs lie relative to the extrafusal muscle fibres?

A

In series

66
Q

What happens when there is isometric contraction?

A

GTOs fire action potentials because the tension in tendons increases
Muscle length remains the same so no action potentials in la receptors

67
Q

What is the function of gamma motor neurons ?

A
  • When muscle fibres contract and shorten
  • gamma motor neurons cause muscle spindle to shorten as well
  • APs can be fired
  • Signals sent to the brain for muscle length
68
Q

What would happen if gamma motor neurons were not present?

A
  • Extrafusal fibres contract and shorten
  • Intrafusal fibres stay the same length
  • Muscles contract and shorten
  • Muscle spindles slack
  • No information send to the body about muscle length
  • Muscle movement is limited
69
Q

What does firing of intrafusal neurons cause?

A
  • Contracting ends to contract
  • Non-contracting central element to stretch
  • Restores tension in muscle spindle
70
Q

What is the α-γ coactivation?

A

When α motor neurones are activated extrafusal muscles contract
β motor neurones contract to cause intrafusal muscles t contract

71
Q

What is sensory neuronopahthy?

A
  • Autoimmune disease that caused loss of large myelinated fibres in sensory neurones of Dorsal Root Ganglion
  • Leads to loss of sense of body position and movement

Sensory Receptors (1 decks)

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