Sensory receptors

Question 1

What are sensory receptors?

Answer 1

Nerve endings often with specialised non-neural structures.
Transducers that convert forms of energy into APs.
Inform CNS about internal and external environment.

Question 2

What are Mechanoreceptors?

Answer 2

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

Question 3

What are Proprioreceptors?

Answer 3

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

Question 4

What are Nocireceptors?

Answer 4

Respond to painful stimuli - tissue damage and heat

Question 5

What are thermorecpetors?

Answer 5

Detect warmth and cold.

Question 6

What are chemoreceptors?

Answer 6

Detect chemical changes eg pH, pO2 and pCO2.

Question 7

What are photoreceptors?

Answer 7

Respond to particular wavelengths of light.

Question 8

What are the functions of cutaneous mechanoreceptors and proprioreceptors?

Answer 8

Process peripheral signals.

All transduction involves opening or closing of ion channels.

Question 9

What is the frequency of coding of stimulus intensity?

Answer 9

The larger the stimulus, the larger the receptor potential and the HIGHER THE FREQUENCY of APs in a sensory nerve.

Question 10

What is adaptation?

Answer 10

Some mechanoreceptors ADAPT to a maintained stimulus and only signal change. It responds only to a change or a novel event. E.g onset of a stimulus.

Question 11

What receptors do not adapt?

Answer 11

Nocireceptors because its important not to ignore a painful stimuli.

Question 12

What is a Pacinian corpuscle?

Answer 12

Mechanoreceptor.
Myelinated nerve with a naked nerve ending, enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid (onion).

Question 13

Describe how the Pacinian corpuscle responds?

Answer 13

1. A mechanical stimulus deforms the capsule and nerve ending.
2. This stretches the nerve ending and opens ion channels.
3. Na+ influx causes local depolarisation – a generator potential.
4. APs are generated and fire at the myelinated nerve.

Question 14

How does the pacinian corpuscle show rapid adaptation?

Answer 14

Fluid redistribution in the capsule – rapidly dissipates stimulus - removes mechanical stretch of nerve ending – APs stop firing.
Withdrawal of the stimulus - capsule springs back - AP fire again.

Question 15

What is a receptive field?

Answer 15

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

Question 16

What 2 factors determine our ability to tell 2 different ares of skin apart?

Answer 16

Receptor field size.

Neuronal Convergence.

Question 17

What is convergence?

Answer 17

Multiple presynaptic neurons input on a smaller number of post-synaptic neurones.

Question 18

What is the 2 point discrimination test?

Answer 18

Distance between points adjusted until you just perceive 2 points rather than one.

Question 19

What is acuity?

Answer 19

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

Question 20

What allows us to locate a stimulus precisely?

Answer 20

Lateral inhibition of surrounding sensory neurones increases the contrast between relevant and irrelevant information.

Question 21

What are some examples of proprioreceptors?

Answer 21

Muscle spindles – which monitor muscle length and rate of change of muscle length and so they control reflexes and voluntary movements.

Golgi tendon organs - monitor tension on tendons,
tension is produced by muscle contraction, so monitoring muscle tension.

Joint receptors - monitor joint angle, rate of angular movement and tension on the joint.

Question 22

What are the 3 main functions of Proprioreceptors?

Answer 22

Control voluntary movement.
Drive spinal cord reflexes.
Perceive limb and body position/movement in space.

Question 23

What are muscle spindles?

Answer 23

Capsulated intramural fibres with specialised sensory and motor innervation. They lie parallel to muscle fibres.

Question 24

What is then relevance of gamma innervation of muscle spindles?

Answer 24

If not present, then when muscle contracts, muscle spindle would be floppy and spindle discharges could stop.
The brain would not be informed about muscle length.
A lack of information flow to the brain about muscle length could prevent use of that muscle.