12.16.1 Sensory Systems: An Introduction

Question 1

Sensory Systems: An Introduction

Answer 1

• There are five major types of sensory receptors: thermoreceptors, electroreceptors, mechanoreceptors, chemoreceptors, and photoreceptors.
• Sensory receptors are cells that convert various stimuli into a change in the cell membrane, often by detection of the stimuli by membrane-bound proteins.
• The detection of stimuli by membrane-bound proteins results in the opening or closing of ion channels, causing changes in the membrane potential and firing of an action potential

Question 2

Thermoreception

Answer 2

• the perception of temperature changes. Thermoreceptors are temperature-sensitive membrane proteins on the surface of cells. At ambient temperatures sodium ions can freely pass through the ion channel. Temperature changes cause a conformation change of shape of the ion channel.
  This shape change blocks ions from passing through, thus polarizing the cell.

Question 3

Mechanoreceptors

Answer 3

• sensitive to pressure changes. At ambient pressure sodium ions can freely pass through the ion channel. As pressure is applied, the ion channel changes conformation preventing the movement of sodium ions across the membrane. Mechanoreceptors are found in places such as the ears and skin.

Question 4

electroreceptors

Answer 4

• are stimulated by changes in electrical potential. If one side of the membrane experiences ionic changes, the electroreceptor is stimulated.
• An example of electroreceptors is in the lateral lines of fishes such as sharks and catfish. They are able to detect weak changes in electrical potential. The lateral line allows the fish to detect the presence of objects and prey in the water.

Question 5

chemoreceptors

Answer 5

• able to detect the presence of specific molecules and ions. A chemical binding to a chemoreceptor causes a chain of reactions in a membrane-bound protein. This eventually effects the conformation of ion channels. Chemoreceptors are involved in smell and taste and can be found in the nasal membrane, tongue, and on the antennae of insects.

Question 6

Photoreceptionis

Answer 6

• the detection of light. When the membrane is at rest, ions can freely flow through the ion channel. Light
  detection involves the presence of the protein rhodopsin.
• Rhodopsin is a transmembrane protein composed of two subunits: opsin (not light sensitive) and retinal (light sensitive). There are two forms of retinal: cis-retinal and
  trans-retinal.
• When a photon hits cis-retinal, it turns to trans-retinal (the active form of rhodopsin). Once rhodopsin is activated, a sequence of events is triggered, which ultimately causes sodium channels to be shut. Once shut, the cell becomes polarized and an action potential is fired. This process is shown to the left

Question 7

True or false?

Trans-retinal is the active form of rhodopsin.

Answer 7

• true

Question 8

Which of the following places would a mechanoreceptor not be found?

Answer 8

• in the retinal wall

Question 9

True or false?

Mechanoreceptors are found on the surface of the tongue.

Answer 9

• true

Question 10

What is the function of a mechanoreceptor?

Answer 10

• to sense touch

Question 11

Which of the following statements regarding chemoreceptors is true?

Answer 11

• Chemoreceptors are neurons whose sodium channels open when a molecule binds to it.

Question 12

True or false?
The activation of rhodopsin causes sodium channels in the photoreceptors of the eye to open, triggering an action potential.

Answer 12

• false