3.6.1.2 Receptors (Unit 6 Responding to Environment)

Question 1

Give the location of osmoreceptors in the body of a mammal

Answer 1

hypothalamus

Question 2

When a person is dehydrated the water volume of an osmoreceptor falls - why?

Answer 2

1. Water potential of blood will decrease;
2. Water moves from osmoreceptor into blood by osmosis;

Question 3

What is the function of a receptor cell?

Answer 3

To detect stimuli

Question 4

The pressure receptors found in the skin are called…

Answer 4

Pacinian Corpuscles

Question 5

Pacinian corpuscles respond to which type of stimuli?

Answer 5

Mechanical pressure.

Question 6

Receptors cells are transducers. What is a transducer?

Answer 6

Something that converts one form of energy (e.g. light) into a form that can be understood by the body (e.g. an electrical impulse).

Question 7

In order to create an electrical impulse a receptor cell creates a…

Answer 7

generator potential.

Question 8

Where are pacinian corpuscles abundantly found?

Answer 8

In the skin of the fingers, genitals, hands, feet, ligaments and tendons.

Question 9

The cell membrane at the end of the sensory neurone found inside a pacinian corpuscle contains…

Answer 9

Stretch-mediated sodium ion channels

Question 10

What is a stretch-mediated sodium channel?

Answer 10

A sodium channel protein whose permeability to sodium ions increases when they are deformed.

Question 11

Describe how a generator potential is created by a pacinian corpuscle.

Answer 11

1. In the absence of pressure, stretch-mediated sodium channels in the membrane of the sensory nerve endings found the corpuscle are closed.
2. This maintains a resting potential difference in Na+ across the membrane (more outside than inside).
3. Pressure deforms the channel proteins, increasing permeability to Na+.
4. Na+ influx into cell causes a depolarisation to occur (more Na+ now inside than outside).
5. The depolarisation creates a generator potential which leads to a wave of depolarisations (action potentials) along the neurone.
6. This is called an electrical impulse.

Question 12

In which part of the eye are light receptor cells found?

Answer 12

The retina

Question 13

The 2 types of light receptor cells are called…

Answer 13

rod cells
cone cells

Question 14

Rod and cone cells are transducers. Explain.

Answer 14

They convert light energy into an electrical impulse.

Question 15

Rod cells are responsible for ____________ vision

Answer 15

black and white

Question 16

Why can rod cells only lead to images seen in black and white?

Answer 16

They cannot distinguish between different wavelengths of light.

Question 17

Does the eye contain more rod cells or cone cells?

Answer 17

Rod cells

Question 18

Rod cells are sensitive to _____ intensity light, cone cells are sensitive to _________ intensity light.

Answer 18

Rod cells are sensitive to LOW intensity light, cone cells are sensitive to HIGH intensity light.

Question 19

Why are many rod cells connected to a single sensory neurone?

Answer 19

1. To allow retinal convergence to occur.
2. The is a greater chance of the threshold value being exceeded to allow an action potential to occur along the sensory neurone. (note: you will need to study next topic to fully understand this).

Question 20

Which pigment, that breaks down in low intensity light, is found inside rod cells?

Answer 20

Rhodopsin

Question 21

Because each rod cell connects to multiple single sensory neurones the light from each neurone is not individually distinguishable. This means that rod cells can only produce…

Answer 21

LOW VISUAL ACUITY (low resolution)

Question 22

How many types of cone cell are there?

Answer 22

3

Question 23

Each of the three types of cone cell contain a specific group of pigments called…

Answer 23

iodopsins

Question 24

Does iodopsin break down in the presence of low or high intensity light?

Answer 24

high intensity

Question 25

Cone cells are connected to their own individual sensory neurone. True or False?

Answer 25

TRUE

Question 26

Because each cone cell connects to a single sensory neuron the light from each neurone is individually distinguishable. This means that cone cells can produce…

Answer 26

HIGH VISUAL ACUITY (high resolution)

Question 27

The lens of the eye focuses light at a central point in the retina called the…

Answer 27

fovea

Question 28

The outer periphery of the retina (not the fovea) contains _________ cells

Answer 28

Rod cells

Question 29

The fovea is where ________ cells are found because it receives the highest intensity of light.

Answer 29

Cone cells

Question 30

Describe how a pacinian corpuscle works

Answer 30

Pressure is applied and the lamella is deformed
Stretch mediated sodium ion channels open
Na+ diffuse into axon
Leading to depolarisation and action potential if threshold is exceeded

Question 31

Describe convergence in rod cells

Answer 31

Rods are found around the outside of the retina, away from the fovea
Light stimulus triggers depolarisation in the rod cells
Many rods converge and are connected to a single sensory neurone
Depolarisation undergoes (spatial) summation to trigger an action potential

In low light there is enough light to lead to action potential
However, this reduces visual acuity

Question 32

Describe acuity in cone cells

Answer 32

Cone cells are located in the fovea (behind the retina to maximise light stimulus)
Every cone cell is connected to a single sensory neurone (no convergence)
Each cone sends a single impulse to the brain
With high visual acuity

Three types of cones detect three different wavelengths of light