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Science for Medicine > Sensory Receptors 1 > Flashcards

Sensory Receptors 1 Flashcards

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1
Q

What are sensory receptors?

A

-Nerve endings, specialised non-neural structures

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2
Q

What do sensory receptors do?

A
  • They are transducers that convert different forms of energy into frequency of AP
  • Inform the CNS about the internal and external environment
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3
Q

Sensory modality

A

A type of stimulus activating a particular receptor e.g. touch, pressure, pain, temperature, light

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4
Q

Adequate stimulus

A

They type of energy a receptor normally responds to

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5
Q

What are sensory receptors sensitive to?

A

Highly sensitive to one specific energy form but can be activated by other intense stimuli

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6
Q

What are the types of sensory receptors?

A
  • Mechanoreceptors
  • Proprioceptors
  • Nociceptors
  • Thermoreceptors
  • Chemoreceptors
  • Photorececeptors
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7
Q

Mechanoreceptors

A
  • Stimulated by mechanical stimuli- pressure, stretch or deformation
  • Detect many stimuli- haring, balance, blood pressure and skin sensations of touch and pressure
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8
Q

Proprioceptors

A

Mechanoreceptors in joints and muscles that signal information related to body or limb position

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9
Q

Nociceptors

A

Response to painful stimuli- tissue damage and heat

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10
Q

Thermoreceptors

A

Detect cold and warmth

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11
Q

Chemoreceptors

A

Detect chemical changes e.g pH, pO2 and pCO2

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12
Q

Photoreceptors

A

Respond to particular wavelengths of light

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13
Q

What are cutaneous mechanoreceptors and proprioceptor good examples of?

A

The principles of peripheral sensory processing

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14
Q

What does transduction in all sensory receptors involve?

A

Opening and closing of ion channels

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15
Q

What does an adequate stimulus cause/

A

A graded membrane potential change called a receptor potential or a generator potential

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16
Q

Membrane deformation

A

The adequate stimulus in cutaneous mechanoreceptors and proprioceptors

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17
Q

What does membrane deformation activate?

A

Stretch sensitive ion channels causing ion flow across the membrane

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18
Q

What does a stimulus cause?

A

Local current to flow to where the membrane has voltage gated ion channels that generate action potentials

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19
Q

Where does the local current flow to in myelinated sensory neurons?

A

The start of myelination

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20
Q

Describe the receptor potential.

A

Graded to stimulus intensity

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21
Q

Frequency coding of stimulus intensity.

A

The larger the stimulus, the larger the receptor potential and the higher the frequency of AP in a sensory nerve

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22
Q

What also reflects the stimulus intensity?

A

The number of receptors activated

23
Q

What is the information a touch receptor in the skin responds to dependent on?

A

The properties of nerve endings and of accessory, non-neuronal structures

24
Q

What happens for some mechanoreceptors if the stimulus persists?

A

APs persist

25
Q

Adaption

A

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

26
Q

Why do some mechanoreceptors only signal at the onset of stimulus?

A
  • Stimulus is enough to cause an above threshold generator potential, which triggers APs
  • The generator potential declines rapidly and APs cease
  • They respond only to change or a novel event
27
Q

What do rapidly/ moderately adapting receptors include?

A
  • Pacinian corpuscles

- Meissners corpuscles

28
Q

What are examples of slow-adapting receptors?

A
  • Merkels discs

- Ruffini endings

29
Q

Why do nociceptors not adapt?

A

They are free nerve endings that detect painful stimuli and it is important to not ignore painful stimuli

30
Q

What is a pacinian corpuscle?

A

A myelinated nerve with a naked nerve ending, enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid

31
Q

How does the Pacinian corpuscle respond?

A
  • A mechanical stimulus deforms the capsule and nerve ending
  • Stretching the nerve ending opens ion channels
  • Na influence causes local depolarisation (generator potential)
  • APs are generated and fire at the myelinated nerve
32
Q

Describe adaption in the pacinian corpuscle?

A
  • Stimulus is on
  • Fluid redistribution in the capsule rapidly dissipates stimulus, removes mechanical stretch of nerve ending and the AP stops firing
  • Withdrawal of the stimulus means the capsule springs back and the AP starts firing again
33
Q

What happens if the lamellae is removed?

A

Much of the adaption is lost

34
Q

What happens when the capsule is removed?

A
  • Bare nerve ending loses much adaption

- Continues to produce a receptor/ generator potential

35
Q

What does the non-neural accessory structure do?

A

It is critical to how the sensory receptor works and in general enhances sensory function

36
Q

Receptive field

A

A somatic sensory neuron is activated by stimuli in a specific area e.g a touch-sensitive neuron in the skin responds to pressure within a defined receptive field

37
Q

What does our ability to tell 2 points on the skin apart depend on?

A
  • Receptive field size
  • Neuronal convergence
  • Determined by 2 point discrimination test
38
Q

hat do sensory neurons with neighbouring receptive fields exhibit?

A

Neuronal convergence= multi presynaptic neurons input on a smaller number of post-synaptic neurons

39
Q

What does convergence of primary sensory neurons allow?

A

Simultaneous sub-threshold to sum at the secondary neuron, forming a large secondary receptive field and initiating AP

40
Q

What does convergence and large secondary receptive field indicate/

A

A relatively insensitive area

41
Q

2 point discrimination test

A

Distance between points adjusted until just perceive 2 points rather than 1

42
Q

Where has a very small 2-point threshold?

A

Fingers and lips

43
Q

Where has a large 2 point threshold?

A

Back and limbs

44
Q

Acuity

A

The ability to locate a stimulus on the skin and differentiate it from another closeby

45
Q

How can we precisely determine the location of a stimulus?

A
  • Lateral inhibition
  • Information from afferent neurons with sensory receptors at edge of stimulus is strongly inhibited, compared with information from stimulus centre
46
Q

What does lateral inhibition do?

A

Enhances the contrast between relevant and irrelevant information

47
Q

Where does lateral inhibition occur/

A

In the spinal cord for cutaneous information

48
Q

Describe sensory signals in the brain.

A
  • All sensory information goes to the brain
  • Relayed through thalamus to somatosensory cortex
  • Cortical body map is distorted
  • Most sensitive areas occupy biggest cortical space
49
Q

Merkel receptors

A

Sense steady pressure and texture

50
Q

Meissners corpuscle

A

responds to flutter and stroking movements

51
Q

Pacinian corpuscle

A

Senses vibration

52
Q

Ruffini corpuscle

A

Responds to skin stretch

53
Q

Sensory nerves

A

Carry signals to spinal cord

54
Q

Free nerve endings of nociceptors

A

Responds to noxious stimuli

Science for Medicine (50 decks)

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