Receptor Phsysiology

Question 1

Definition of a receptor?

Answer 1

Receptors are transducers (convert various forms of energy to action potentials, which is the currency of the nervous system).

Question 2

Receptors can be classified based on what? Discuss each of the classifications

Answer 2

1. Adequate stimulus (type of stimuli)
2. Location
3. Duration

Question 3

Receptors can either be specialised endings of neurons or a separate receptor cell. Describe how an action potential is generated in specialised nerve endings.

Answer 3

1. Stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential
2. Local current flow between depolarised receptor ending and adjacent region opens voltage gated Na+ channels
3. Na+ entry initiates action potential in afferent fibre that self propagates to CNS

Question 4

Receptors can either be specialised endings of neurons or a separate receptor cell. Describe how an action potential is generated in separate receptor cells.

Answer 4

1. Stimulus opens stimulus-sensitive channels, permitting net Na+ century that produces receptor potential
2. Local depolarisation opens voltage gated Ca+2 channels
3. Ca+2 entry triggers exocytosis of neurotransmitter
4. Neurotransmitter binding opens chemical gated receptor channels at afferent ending, permitting net Na+ entry
5. Resultant depolarisation opens voltage gated Na+ channels in adjacent region
6. Na+ entry initiates action potential in afferent fibre that self propagates to CNS

Question 5

What are the different types of mechanoreceptors? And what do each of these respond to?

Answer 5

1. Merkel’s disc - light sustained touch
2. Pacinian’s corpuscle - deep pressure and vibrations
3. Ruffini endings - deep pressure
4. Meisnner’s corpuscle - light fluttering touch
5. Hair receptors - movement and very gentle touch

Question 6

What is structure which pacinian corpuscles are covered with? What is the purpose of this structure?

Answer 6

Concentric lamella of connective tissue
- used for protection

Question 7

Define the following terms:
- sensory unit
- receptive field
- lateral inhibition

Answer 7

• sensory unit = a single sensory axon and all its dendrites
• receptive field of a sensory unit is the spatial distribution from which a stimulus produces a response in that unit
• lateral inhibition - info from neurons whose receptors are at the peripheral edge of the stimulus is inhibited, compared to information from the sensory neurons at the centre of a stimulus

Question 8

What is the Doctrine of specific energies by Muller?

Answer 8

When the nerve pathways from a particular sense organ are stimulated, the sensation evoked is that for which the receptor is specialised no matter how or where along the pathway the activity is initiated

Question 9

What is meant by the Law of Projection? And what phenomenon has this brought us to understand

Answer 9

If we stimulate a sensory pathway along its course to the sensory cortex, the conscious sensation produced is perceived to be from the location of receptors

Phantom limb pain - after amputation of a limb, individual is a still pain to feel pain in amputated region

Question 10

What is meant by rapidly and slow adapting receptors? Provide examples.

Answer 10

Rapidly adapting - respond maximally but briefly to stimuli and their response decreases if stimulus is still maintained
- light, pacinian and meissner

Slow adapting - receptors keep firing as long as stimulus is present
- muscle spindles, nociceptors, merkel cells and Ruffini endings