Body Sensation

Question 1

What are some properties of sensory receptors?

Answer 1

Transducers (converts stimuli into APs).
Highly sensitive to one specific energy form (but can be activated by other intense stimuli).

Question 2

Define sensory modality.

Answer 2

The stimulus type that activates a particular receptor.

Question 3

Describe the three main receptors.

Answer 3

Mechanoreceptors - stimulated by mechanical stimuli.
Proprioceptors - mechanoreceptors in joints and muscles.
Nociceptors - responds to painful stimuli.

Question 4

Describe the process of forming APs.

Answer 4

1. An adequate stimulus causes a generator potential (membrane deformation).
2. Ions flow across the membrane and the local membrane potential changes.
3. APs fire when depolarisation reaches an area with VGCs (the first node of Ranvier).

Question 5

Describe the frequency coding of stimulus intensity.

Answer 5

A larger stimulus - a larger receptor potential and a higher frequency of APs.

Question 6

Describe how adaptive receptors work.

Answer 6

When a GP dips below the threshold: APs stop.
Mechanoreceptors only signal the onset of a stimulus, responding only to changes.

Question 7

Give examples of adapting receptors.

Answer 7

Fast - Pacinian corpuscles.
Slow - Merkel’s discs.

Question 8

Why are nociceptors non-adaptive?

Answer 8

It is important not to ignore painful stimuli.

Question 9

Describe the Pacinian corpuscle.

Answer 9

A mechanoreceptor is enclosed by a CT capsule of layered membrane lamellae.
Each layer is separated by fluid.

Question 10

Describe the process of forming APs in Pacinian corpsucles.

Answer 10

1. A mechanical stimulus deforms the capsule.
2. Nerve ending stretches, ion channels open.
3. Na+ influx causes local depolarisation. A generator potential occurs.
4. APs are generated and fire where myelination begins. Na+ channels cluster at nodes of Ranvier.

Question 11

How are PCs adaptive?

Answer 11

Fluid redistributes within capsule lamellae. This spreads the stimulus impact out and minimises deformation. APs stop.

Question 12

What happens when the stimulus is withdrawn from a PC?

Answer 12

Lamellae spring back. Another AP fires.

Question 13

What happens if the PC capsule is removed?

Answer 13

Adaptation cannot occur.
The capsule enhances sensory function.

Question 14

Define the receptive field.

Answer 14

A somatic sensory neuron is activated by stimuli in a specific area.

Question 15

What is the two point discrimination test?
What does it depend on?

Answer 15

Measures the ability to tell 2 points apart on the skin.
Depends on receptive field size and neuronal convergence.

Question 16

Define acuity.

Answer 16

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

Question 17

What causes low acuity?

Answer 17

High convergence.

Question 18

Define neuronal convergence.

Answer 18

Simultaneous sub-threshold stimuli sum at a secondary neuron (primary to secondary receptive field). This initiates APs.
Lots of convergence and a large secondary receptive field indicates a relatively insensitive area.

Question 19

Describe lateral inhibition.

Answer 19

Receptors at the edge of a stimulus are more inhibited than receptors at the centre.
This enhances the contrast between relevant and irrelevant information.

Question 20

How is sensory information dealt with?

Answer 20

Brain via the spinal cord.
Thalamus, then the somatosensory cortex, where there is a distorted body map.
The most sensitive areas innervate the largest cortical space.