Session 3 - Somatic Sensations and Sensory Pathways

Question 1

Give five general senses

Answer 1

o	Somatic
	Tactile (touch, pressure, vibration)
	Thermal
	Pain
	Proprioception
o	Visceral
	Internal organs)

Question 2

Give five special senses

Answer 2

o	Smell
o	Taste
o	Vision
o	Hearing
o	Balance

Question 3

Give four stimulus modalities

Answer 3

Light, touch, temperature and chemical change

Question 4

What are stimulus qualities?

Answer 4

A subdivision of stimulus modalities

Question 5

How specific are sensory receptors?

Answer 5

Specific to stimulus modalities

Question 6

Outline the process of sensory transduction

Answer 6

1. Stimulus evokes change in permeability to ions of the receptor membrane
2. Movement of ions across membrane
3. Triggers action potential
4. Action potentials propagate into the CNS

Question 7

What are tonic receptors?

Answer 7

Slowly adapting tonic receptors which may keep firing as long as the stimulus lasts

Question 8

Give two places where tonic receptors found

Answer 8

Joint receptors

Pain receptors

Question 9

What are phasic receptors?

Answer 9

Rapidly adapting phasic receptors respond maximally and briefly to a stimulus

Question 10

Give an example of a phasic receptor

Answer 10

o Touch receptors

E.g. you don’t feel your clothes touching you until they are moved

Question 11

What is signal strength determined by?

Answer 11

Signal strength is determined by rate of action potential firing (Frequency coding).
(Stronger stimuli also activate neighbouring cells, but to a lesser degree).

Question 12

What is sensory acuity?

Answer 12

Sensory acuity is the precision by which a stimulus can be located,

Question 13

Give three factors which determine sensory acuity

Answer 13

o Lateral Inhibition in the CNS
o Two Point Discrimination
o Synaptic Convergence and Divergence

Question 14

What is lateral inhibition?

Answer 14

A stimulus causes a response in one receptor maximally and, to a lesser extent, in neighbouring receptors. If solely excitatory neurons link the inputs, the signal becomes blurred.
However, if inhibitory interneurons are introduced, then the cells that are not maximally stimulated will cease to fire. This sharpens sensory acuity.

Question 15

What is two point discrimination?

Answer 15

Minimal interstimulus distances required to perceive two simultaneously applied skin indentations. E.g. bend a paperclip so it has two points about 1cm apart, close your eyes and touch it on your forearm. It only feels like there is one point.

Question 16

What is two point discrimination of fingers

Answer 16

2mm

Question 17

What is two point discrimination in the forearm?

Answer 17

40mm

Question 18

Give two factors which determine two point discrimination?

Answer 18

o Density of sensory receptors (3-4x greater in fingertips than rest of hand)
o Size of neuronal receptive fields (1-2mm in fingertips, 5-10mm in palm)

Question 19

What is synaptic convergence?

Answer 19

The convergence of several 1st order neurones onto a single 2nd order neurone. Convergence decreases acuity.

Question 20

What is synaptic divergence?

Answer 20

The divergence of a single 1st order neurone onto several 2nd order neurones.
Divergence amplifies the signal.

Question 21

What is a receptive field?

Answer 21

The receptive field of a sensory neurone is the area where stimulus will alter the firing of that neurone. Receptive fields vary in size and density, and overlap with neighbouring receptive fields.