Roles of Sensory Receptors

Question 1

What is a pacinian corpuscle?

Answer 1

A pressure sensor found in the skin

Question 2

What are sensory receptors?

Answer 2

Cells/sensory nerve endings that respond to a stimulus in the internal or external environment in an organism and can create action potentials.
Specialised cells that can detect changes in our surroundings, most are energy transducers that convert one form of energy to another.

Question 3

What is a transducer?

Answer 3

A cell that converts one form of energy into another - in this case to an electrical impulse.

Question 4

What is a stimulus?

Answer 4

A change in the environment, whether that’s a change in the energy level or the presence of a new chemical.

Question 5

If the stimulus is a change in light intensity. What is the sensory receptor and what is the energy change involved?

Answer 5

Light sensitive cells (rods and cones) in the retina.

Light to electrical.

Question 6

If the stimulus is a change in pressure of the skin. What is the sensory receptor and what is the energy change involved?

Answer 6

Pacinian corpuscles in the skin.

Movement to electrical

Question 7

If the stimulus is chemicals in the air. What is the sensory receptor and what is the energy change involved?

Answer 7

Olfactory cells in epithelium lining the nose.

These receptors detect the presence of a chemical and create an electrical nerve impulse.

Question 8

Describe the structure of a pacinian corpuscle.

Answer 8

The corpuscle is an oval-shaped structure that consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell.

Question 9

What happens to the pacinian corpuscle when pressure on the skin changes?

Answer 9

When pressure on the skin changes this deforms the rings of connective tissue, which push against the nerve ending.

Question 10

What happens when pressure on the skin is constant?

Answer 10

They stop responding as the pacinian corpuscle only responds to changes in in pressure.

Question 11

Cells associated with the nervous system have specialised channels in their membranes. What are they?

Answer 11

Sodium channels specific to sodium ions.

Potassium channels specific to potassium ions.

Question 12

What are the sodium channels sensitive to?

Answer 12

Small movements of the membrane.

Question 13

What does the sodium channel do if the membrane becomes deformed? What happens as a result?

Answer 13

The sodium ion channels open.

This allows sodium ions to diffuse into the cell, producing a generator potential (also called a receptor potential).

Question 14

What do sodium/potassium pumps do?

Answer 14

They actively pump sodium ions out of the cell and potassium ions into the cell.

Question 15

What is the number of sodium/potassium ions pumped in/out?

Answer 15

Three sodium ions are pumped out for every two potassium ions pumped in.

Question 16

What is the result of the ionic movements of sodium and potassium?

Answer 16

The cell is negatively charged inside compared with the outside. The negative potential is enhanced by the presence of negatively charged anions inside the cell.

Question 17

What is the membrane said to be when it is inactive?

Answer 17

Polarised. Negatively charged inside compared with the outside.

Question 18

How is a nerve impulse created?

Answer 18

By altering the permeability of the nerve cell membrane to sodium ions. This is achieved by opening the sodium ion channels. As the sodium ion channels open, the membrane permeability is increased and sodium ions can move across the cell membrane down their concentration gradient into the cell.

Question 19

What does the movement of sodium ions into the cell cause?

Answer 19

Creates a change in the potential difference (charge) across the membrane. Inside of the cell becomes less negative than the outside of the cell compared to normal. This is called depolarisation.

Question 20

What is depolarisation?

Answer 20

When the inside of the cell becomes less negatively charged than the outside of the cell compared to normal.

Question 21

What happens if a small stimulus is detected?

Answer 21

Only a small number of sodium channels will open.

Question 22

What happens if there is a large stimulus?

Answer 22

The larger the stimulus (change in energy levels of the environment) the more gated channels will open. If enough gated channels are open and enough sodium ions enter the cell, the potential difference across the membrane changes significantly and will create an action potential.