Sensory Receptors

Question 1

What are sensory receptors?

Answer 1

• Nerve endings, often with specialised non-neural structures
• Transducers which convert different forms of energy into the frequency of action potentials
• They inform the CNS about the external and internal environment.

Question 2

What is meant by sensory modality?

Answer 2

This is the type of stimulus that acts on a particular receptor

Question 3

What is adequate stimulus?

Answer 3

This is the form of energy to which a receptor generally responds.

Question 4

What are the 6 main types of sensory receptor?

Answer 4

1. Mechanoreceptors
2. Proprioceptors
3. Nociceptors
4. Thermoreceptors
5. Chemoreceptors
6. Photoreceptors

Question 5

What are mechanoreceptors?

Answer 5

Receptors stimulated by mechanical stimuli (e.g. pressure, stretch or deformation)

Question 6

What are proprioceptors?

Answer 6

Mechanoreceptors within joints and muscle which signal information about body and limb position.

Question 7

What are nociceptors?

Answer 7

Receptors which respond to painful stimuli (e.g. heat and tissue damage)

Question 8

What is meant by the receptor/ generator potential?

Answer 8

Graded potential formed by the opening of ion channels due to adequate stimulus.
If it reaches a threshold, it will cause the formation of an action potential.

Question 9

What is adequate stimulus for cutaneous mechanoreceptors and proprioceptors?

Answer 9

Membrane deformation

Question 10

What is meant by accessory structures on receptors?

Answer 10

Non-neural structures to which they are attached.
In cutaneous receptors, these structures play a large part in determining what sort of stimulus a receptor will respond to.

Question 11

What are Pacinian Corpuscles?

Answer 11

Receptors attached to hair follicles. Sense Vibrations

Question 12

What are Merkel’s receptors?

Answer 12

Receptors which sense steady pressure and texture.

Question 13

What are Meissner’s Corpuscles?

Answer 13

Receptors which sense fluttering and stroking movements.

Question 14

What are Ruffini Corpuscle’s?

Answer 14

Receptors which detect stretching of skin

Question 15

Describe the process of adaptation for mechanoreceptors.

Answer 15

Initially, a mechanical stimulus is of large enough intensity to cause a generator potential above stimulus, generating an action potential.
Stimulus intensity remains constant but generator potential declines and, once it drops below threshold, action potentials stop firing.

Question 16

What type of receptors do not adapt?

Answer 16

Nociceptors

Question 17

Describe the structure of the Pacinian Corpuscle?

Answer 17

Myelinated axon with naked nerve ending, surrounded by a capsule of connective tissue, layered into lamella which are separated by fluid.

Question 18

Describe the mechanism of action potential formation in the Pacinian Corpuscle.

Answer 18

Mechanical stimulus deforms the capsule of layer lamella and so deforms the nerve ending.
Stretching of the nerve ending opens ion channels.#
Sodium ions diffuse into the nerve ending, causing local depolarisation- generator potential.
This generator potential strength is proportional to stimulus intensity.
If generator potential reaches threshold, action potential fires in myelinated axon.

Question 19

What is meant by neuronal convergence?

Answer 19

Multiple pre-synaptic neurons synapsing with a single post synaptic neuron.

Question 20

What is meant by acuity?

Answer 20

The ability to differentiate one stimulus from another in close range.

Question 21

What is the function of muscle spindle?

Answer 21

Monitor muscle length and rate of change of muscle length.

Question 22

What is the function of Golgi tendon organs?

Answer 22

To measure tension on tendons

Question 23

What produces tension on tendons?

Answer 23

Muscle contraction

Question 24

What type of neurons innervate intrafusal muscle fibres?

Answer 24

Gamma motor neurons

Question 25

What type of neurons innervate extrafusal muscle fibres?

Answer 25

Alpha motor neurons

Question 26

Give one advantage of convergence of primary sensory neurons onto secondary neurons.

Answer 26

Allows summation of sub- threshold potentials, forming an action potential in the secondary neuron.

Question 27

Give one disadvantage of convergence of primary sensory neurons onto secondary neurons.

Answer 27

Creates a larger sensory receptor field and so a relatively insensitive area. It makes it hard to distinguish one point of stimulus from another (low acuity)

Question 28

What is the difference between how muscle spindle and golgi tendon organs operate in respect to muscle position?

Answer 28

Muscle spindle operates in parallel to the muscle fibre.

Golgi Tendon organ operates in series to the muscle fibre.

Question 29

What re the two types of intrafusal fibres?

Answer 29

Nuclear bag fibres

Nuclear chain fibres

Question 30

How does the spindle fibre contract?

Answer 30

Only the ends of intrafusal fibres contain contractile sarcomeres.
Gamma motor neurons innervate these ends of the intrafusal fibres
Muscle contraction causes gamma motor neurons to activate contraction of spindle fibres to match muscle length.