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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, often with specialised non-neural structures.

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2
Q

How are sensory receptors transducers?

A

They convert different forms of energy into frequency of action potentials.

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3
Q

What information do they feed to the CNS?

A

Inform CNS about internal and external environments.

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4
Q

What is a sensory modality?

A

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

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5
Q

What is an adequate stimulus?

A

The type of energy a receptor normally responds to.

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6
Q

Sensory receptors are highly sensitive to one specific energy form, but what else may activate them?

A

They can activated by other intense stimuli.

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7
Q

What are mechanoreceptors?

A

They’re stimulated by mechanical stimuli - pressure, stretch, or deformation. Detect many stimuli - hearing, balance, blood pressure and skin sensations of touch and pressure.

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8
Q

What are proprioceptors?

A

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

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9
Q

What are nociceptors?

A

They respond to painful stimuli - tissue damage and heat.

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10
Q

What do thermoreceptors detect?

A

Cold and warmth.

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11
Q

What do chemoreceptors detect?

A

Chemical changes, e.g. pH, pO2, pCO2.

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12
Q

What do photoreceptors do?

A

Respond to particular wavelengths of light.

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13
Q

What are cutaneous mechanoreceptors and proprioceptors 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 or closing of ion channels.

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15
Q

What will an adequate stimulus cause?

A

A graded membrane potential change called a receptor potential or a generator potential (mV).

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16
Q

What is the adequate stimulus in cutaneous mechanoreceptors and proprioceptors?

A

Membrane deformation.

This activates stretch-sensitive ion channels causing ion flow across the membrane.

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17
Q

Is the receptor potential graded?

A

The receptor potential is graded to stimulus intensity.

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18
Q

A stimulus causes local current to flow where?

A

To where the membrane has voltage-gated ion channels that generate action potentials.

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19
Q

In myelinated sensory neurones, where would this be?

A

The start of myelination (before).

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20
Q

What frequency of action potentials will the lowest stimulus intensity and the highest stimulus intensity produce?

A

Lowest - no action potentials.

Highest - most action potentials produced (high frequency).

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21
Q

Describe frequency coding of stimulus intensity.

A

The larger the stimulus, the larger the receptor potential and the higher the frequency of action potentials in a sensory nerve.

22
Q

Aside from frequency coding of stimulus intensity, what else may convey stimulus intensity?

A

The number of receptors activated (for instance per unit area spatially).

23
Q

Skin is packed with different receptors for touch, what does the information they transmit depend on?

A

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

24
Q

What do Meissner’s corpuscles sense?

A

Flutter and stroking movements.

25
Q

What do Pacinian corpuscles sense?

A

Vibration.

26
Q

What do Merkel receptors sense?

A

Steady pressure and texture.

27
Q

What do the free nerve endings of hair roots sense?

A

Hair movement.

28
Q

What do the free nerve endings of nociceptors respond to?

A

Noxious stimuli (tissue damage/pain).

29
Q

If the stimulus persists, will the action potentials persist?

A

Only in some mechanoreceptors.

30
Q

What is adaptation in mechanoreceptors?

A

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

31
Q

Explain how adaptation in mechanoreceptors comes about.

A
  • Stimulus is enough to cause an above threshold generator potential - AP triggered.
  • Generator potential declines rapidly and APs cease.
  • So only responds to onset of stimulus (a change or novel event).
32
Q

What are the two types of adaptation that can be exhibited in sensory receptors and give examples of receptors in each?

A
  • Rapidly/moderately-adapting receptors (e.g. Pacinian corpuscles and Meissner’s corpuscles).
  • Slowly adapting receptors (e.g. Merkle’s discs and Ruffini endings).
33
Q

What do Ruffini corpuscles respond to?

A

Skin stretch.

34
Q

What kind of sensory receptor will not adapt and why?

A

Nociceptors are free nerve endings that detect painful stimuli that are too important to ignore.

35
Q

Describe the structure of a Pacinian corpuscle.

A

A myelinated nerve with naked nerve ending, enclosed by a connective tissue capsule of layer membrane lamellae separated by fluid (like an onion).

36
Q

How does the Pacinian corpuscle respond to mechanical stimuli (vibration)?

A
  • Mechanical stimulus deforms capsule and nerve ending.
  • Stretching the nerve ending opens ion channels.
  • Sodium ion influx causes local depolarisation - generator potential.
  • APs generated and fire at myelinated nerve.
37
Q

How does the Pacinian corpuscle show rapid adaptation?

A

Fluid redistribution in the capsule rapidly dissipates stimulus and removes mechanical stretch of nerve ending, so APs stop firing.

38
Q

What will withdrawal of the stimulus in Pacinian corpuscles do?

A

Causes capsule to spring back - APs fire again. This allows it to detect on and off phase of the mechanical stimuli.

39
Q

In a Pacinian corpuscle what may cause adaptation to be lost? Why is this?

A

If the lamellae is removed.

Bare nerve endings lose much of adaptation and continue to produce receptor potentials.

So non-neural accessory structure is critical to how this sensory receptor works - enhancing sensory function.

40
Q

Sensory receptors possess receptive fields, what are these?

A

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

41
Q

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

A

Receptive field size and neuronal convergence.

(It is determined by a two point discrimination test).

42
Q

What do sensory neurones with neighbouring receptive fields exhibit?

A

Neuronal convergence.

43
Q

What is neuronal convergence and what does it allow?

A

It is multiple presynaptic neurones input on a smaller number of post-synaptic neurones.

Convergence of primary sensory neurones allow simultaneous sub-threshold stimuli to sum at the secondary neurone, forming a large secondary receptive field and initiating APs.

44
Q

What would indicate a relatively insensitive area?

A

Convergence and a large secondary receptive field.

45
Q

Describe the 2-point discrimination test.

A

Distance between points adjusted until just perceive two points rather than one.

46
Q

What is acuity?

A

The ability to locate stimulus on the skin and differentiate it from another close by.

47
Q

What is lateral inhibition?

A

When the information from afferent neurones with sensory receptors at the edge of stimulus are strongly inhibited, compared with information from stimulus centre.

48
Q

Why is lateral inhibition important?

A

It enhances the contrast between relevant and irrelevant information.

It is a major mechanism for sharpening up or cleaning up sensory information.

49
Q

Where does lateral inhibition happen for cutaneous information?

A

Spinal cord.

50
Q

What is a major component in pathways with high precision information?

A

Lateral inhibition.

Allows precise localisation to single skin hair movement.

51
Q

What does the sensory information travel?

A

To brain, relayed through thalamus to somatosensory cortex, cortical body map is distorted.

Most sensitive areas occupy biggest cortical space.

Science for Medicine (3 decks)

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