Sensory Receptors

Question 1

Cutaneous receptors

Answer 1

Found in the dermis or epidermis. The nerve endings are protected by a capsule. The stimulus needed to trigger an AP causes a membrane deformation which activates stretch sensitive ion channels. These channels can be found in the distal tip of the affruent axon, or in specialised sensory cells that then release a neurotransmitter creating a generator potential in the axons dendrites.

Question 2

Mechanism of sensory transduction in the skin

Answer 2

A stimulus causes a membrane deformation which opens/closes stretch sensitive ion channels leading to a receptor potential and an AP

Question 3

Frequency coding

Answer 3

A bigger stimulus causes a greater receptor potential leading to a higher frequency of APs. A high frequency equals a high stimulus intensity.

Question 4

Muscle spindle

Answer 4

It monitors muscle length ans the rate at which it changes. Skeletal muscle is made up of extrafusal and intrafusal fibres. A muscle spindle is the intrafusal fibres plus the motor/sensory innervation.
They have contractile ends called sarcomeres and are controlled by gamma motorneurones.
Stimulus is the muscle stretch.
Function is to convey length info to the CNS.

Question 5

Efferent control of spindle function

Answer 5

An agonist muscle contracts so the spindle contracts, AP output decreases, the antagonistic muscle lengthens and AP outflow increases.
All of this information allows you to know exactly what is happening around a joint.

Question 6

Golgi tendon organ

Answer 6

It monitors muscle tension by acting as stretch receptors in tendons. Since tendons are elastic, the muscles must develop tension to stretch them. The nerve endings are intermingled with tendons at the ends of muscles.