Sensory Receptors

Question 1

What are the 3 types of sensory receptors?

Answer 1

Mechanoreceptors
Proprioceptors
Nociceptors

Question 2

What do mechanoreceptors respond to?

Answer 2

Mechanical stimuli such as pressure or stretch…can detect many stimuli

Question 3

Transduction in ALL sensory receptors involves …

Answer 3

Opening or closing of ion channels

Question 4

An adequate stimulus causes?

Answer 4

A graded membrane potential change called a receptor potential or a generator potential

Question 5

The adequete stimulus in mechanoreceptiors -Membrane deformation activates?

Answer 5

Stretch-sensitive ion channels causing ion flow across the membrane.

Question 6

The receptor potential is graded accounting to stimulus frequency. T or F

Answer 6

False - its graded according to stimulus intensity

Question 7

What is the frequency coding of stimulus intensity?

Answer 7

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

Question 8

What happens in some mechanoreceptors if stimulus persists?

Answer 8

Aps persist

Not ALL the time - e.g we don’t feel our clothes on our backs until we move them or take them off…

Question 9

What is adaptation in mechanoreceptors?

Answer 9

When they ADAPT to a maintained stimulus and only signal change

Question 10

Why do nociceptors not show adaptaion?

Answer 10

Important they don’t as we shouldn’t ignore pain

Question 11

What is the cutaneous Pacinian corpuscle?

Answer 11

The best understood mechanoreceptor

Its a myelinated nerve with a naked nerve ending which is enclosed in a connective tissue capsule of layered lamellae seperated by fluid inbetween

Question 12

How does the Pacinian corpuscle respond to stimulus?

Answer 12

A mechanical stimulus deforms the capsule and nerve ending

Nerve ending stretches which opens ion channels

Na+ influx causes local depolarisation – a generator potential

APs are generated and fire at the myelinated nerve

Question 13

How does the Pacinian corpuscle show adaptation?

Answer 13

After the initial response, the fluid in the capsule is redistributed which causes stimulus to dissipate, removing mechanical stretch of nerve ending stopping Aps firing.

When stimulus withdraws - capsule springs back and APs fire again

Question 14

What happens if the capsule is removed in the Pacinian corpuscle?

Answer 14

Adaptation is lost

Question 15

Somatic sensory neurons are activated by stimuli in a specific area..this is called?

Answer 15

The receptive field - e.g is touch only responds to area touched

Question 16

Does convergence of neurons increase or decrease the sensitivity of an area?

Answer 16

Decrease it

Question 17

So if you had convergence and a a large secondary receptive field..what do you have

Answer 17

An insensitive area

Question 18

What is acuity?

Answer 18

The ability to locate a stimulus on the skin and differentiate it from another close-by…

Question 19

High acuity means that two stimulus’s send how many signals to the brain?

Answer 19

Two

Question 20

Low acuity means that two stimulus’s send how many signals to the brain?

Answer 20

One - perceived as just one stimulus

Question 21

How can stimulus be so precise - for example with a pencil tip on the finger, how can we locate it so precisely?

Answer 21

Lateral inhibition - Information from afferent neurons with sensory receptors at edge of stimulus is strongly inhibited and

Question 22

What is the structure of the muscle spindle?

Answer 22

Made of intrafusal fibres and specialised motor and sensory innervation

The ends of these fibres contain sarcomeres and are contractile which are controlled by gamma motoneurones

Question 23

What is the function of the muscle spindle?

Answer 23

Monitor muscle length

As alpha motor neurones fire they cause contraction of extrafusal fibres causing muscle contraction -

Gamma motorneurons also fire on intrafusal fibres contracting the muscle spindels which restores tension and tells the brain to stop stretching in order to stop muscle ripping itself apart

Question 24

What is the adequete stimulus for the muscle spindle stretch receptors?

Answer 24

Muscle stretch

As the muscle lengthens, ion channels open and so the length is monitored

Question 25

How do we know what is happening regarding joint positioning?

Answer 25

Efferent control of spindle function

Question 26

What is efferent control of spindle function?

Answer 26

Agonist muscle contracts and the spindle contracts so output is decreased.

This causes the antagonistic muscle to lengthen and those muscle spindles increase their outflow of action potentials.

Question 27

What do the golgi tendon organs do?

Answer 27

Monitor muscle tension

Question 28

Mechanism of the golgi tendon organs?

Answer 28

The nerve endings are intermingled with the tendons at the ends of muscles.

They act as stretch receptors and monitor the stretch in tendons.

Since tendons are inelastic, the muscles must develop tension to stretch them to stop them ripping off of bone