Topic 6

Question 1

What is a stimulus

Answer 1

A detectable change in the internal or external environment of an organism that leads to a response in the organism.

Question 2

How does the ability to respond to stimuli increase the chances of survival for an organism

Answer 2

To be able to detect and move away from harmful stimuli, such as predators and extremes of temperature or to detect and move towards a source of food clearly aid survival.

Question 3

How are stimuli detected

Answer 3

Receptors

Question 4

Outline receptors

Answer 4

-They are specific to one type of stimulus
-A coordinator formulates a suitable response to stimulus.

Question 5

Outline a coordinator

Answer 5

Formulates a suitable response to a stimulus. It may be at molecular level or involve a large organ such as the brain

Question 6

Outline effectors

Answer 6

A response is produced by an effector which may be at a molecular or involve the behaviour of a whole organism.

Question 7

What are the types of communication and their advantages

Answer 7

-Hormonal communication which occurs via chemicals and is a relatively slow process
-The nervous system has many different receptors and effectors linked to a central coordinator

Question 8

What is the simplest nervous response to a stimulus

Answer 8

A reflex arc

Question 9

What are the two major divisions of the nervous system

Answer 9

The central nervous system, made up of three brain and spinal cord
The peripheral nervous system, made up of pairs of nerves that originate from the brain or spinal cord

Question 10

Outline the subdivisions of the peripheral nervous system

Answer 10

-Sensory neurones: carry nerve impulses from receptors towards the central nervous system
-Motor neurones: carry nerve impulses away from the central nervous system to effectors

Question 11

Outline the motor nervous system divisions

Answer 11

-The voluntary nervous system: carries nerve impulses to body muscles and is under voluntary control
-The autonomic nervous system, which carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control

Question 12

Outline the spinal cord

Answer 12

A column of nervous tissue that runs along the back and lies inside the vertebral column for protection. It emerges at intervals along the spinal cord in pairs of nerves

Question 13

What is a reflex

Answer 13

An involuntary response to a sensory stimulus

Question 14

What is a reflex arc

Answer 14

The pathway of neurones involved in a reflex

Question 15

What is a spinal reflex

Answer 15

A reflex with one of the neurones in the spinal cord

Question 16

What is a spinal reflex

Answer 16

A reflex with one of the neurones in the spinal cord

Question 17

The main stages of a spinal reflex arc:

Answer 17

1. The stimulus
2. A receptor
3. A sensory neurone
4. A coordinator
5. A motor neurone
6. An effector
7. The response

Question 18

Give an example of a spinal reflex arc (heat)

Answer 18

1. heat from the hot object
2. temperature receptors generate nerve impulses in the sensory neurone
3. The sensory neurone passes nerve impulses to the spinal cord
4. A coordinator links the sensory neurone to the motor neurone in the spinal cord
5. Motor neurone carries nerve impulses from the spinal cord to a muscle in the upper arm
6. an effector the muscle is stimulated to contract
7. The hand is pulled away from the hot object

Question 19

Why are reflex arcs important

Answer 19

-Unconscious so the brain can carry out more complex responses. Some impulses are sent to the brain so it is informed of what is happening and sometimes override the reflex
-Protects the body from harm. They are effective from birth and do not have to be learnt.
-They are fast. because the neurone pathway is short with very few synapses
-The absence of any decision making process also means the action is rapid

Question 20

Outline features of all receptors

Answer 20

-Specific to a single type of stimulus
-Produces a generator potential by acting as a transducer: all stimuli involve a change in some form of energy. It is the role to convert the change in form of energy by the stimulus into a form (action potentials) that can be understood by the body
-They convert the energy of the stimulus into a nervous impulse known as a generator potential.

Question 21

Outline features of the pacinian corpuscle

Answer 21

-It responds only to mechanical pressure and no other stimuli
-Transduces the mechanical energy of the stimulus into a generator potential

Question 22

Where are pacinian corpuscles

Answer 22

-Occur deep in the skin and are most abundant on the fingers, soles of feet and external genitalia as well as joint, ligament and tendons
-In the centre of layers of tissue, each separated by a gel

Question 23

Outline the structure of the pacinian corpuscle

Answer 23

-The sensory neurone ending at the centre of the Pacinian corpuscle has a special type of sodium channel in its plasma membrane. This is called a stretch-mediated sodium channel

Question 24

Outline stretch-mediated sodium channels

Answer 24

Their permeability to sodium changes when they are deformed (e.g. by stretching)

Question 25

How do pacinian corpuscles function in resting state

Answer 25

The stretch-mediated sodium channels of the membrane around the neurone of a Pacinian Corpuscle are too narrow to allow sodium ions to pass along them and the neurone has a resting potential.

Question 26

What happens when pressure is applied to the Pacinian Corpuscle (4)

Answer 26

-It is deformed and the membrane around its neurone becomes stretched
-This stretching widens the sodium channels in the membrane and Na+ diffuses into the neurone
-The influx of Na+ changes the membrane potential producing a generator potential (depolarised)
-The generator potential in turn creates an action potential that passes along the neurone and then via other neurones, to the central nervous system