Topic 14 (coordination and response)

Question 1

What is stimuli?

Answer 1

A stimulus (plural: stimuli ) is any change in the environment that causes an organism to react.

Question 2

What is the role of the nervous system in humans?

Answer 2

The nervous system regulates bodily functions and activities, and coordinates the body’s responses to stimuli.

Question 3

What does the nervous system consist of?

Answer 3

It consists of the brain, spinal cord, spinal nerves and sense organs. The sense organs
*help the body to adjust rapidly to any changes in the environment;
*enable the various body parts to coordinate with one another quickly.

Question 4

What are the components of the human nervous system?

Answer 4

The human
nervous system is made up of
*the central nervous system (CNS), which is the brain and spinal cord.
*the peripheral nervous system (PNS), which is the cranial nerves and spinal nerves.

Question 5

What other components are part of the human nervous system?

Answer 5

1) Receptors
2) Nerves
3) Nerve impulses

Question 6

What are neurones?

Answer 6

Nerves cells that send electrical impulses and chemical signals to and from the brain.

Question 7

What is a synapse?

Answer 7

*Synapse is the tiny junction between two neurons.
*Nerve impulses cannot directly cross from one neuron to another neuron due to the synapse.
Nerve impulses are transmitted across a synapse by chemical released by the neuron.

Question 8

How is an impulse transmitted across a synapse?

Answer 8

The swelling at the end of the sensory neuron is called the
synaptic knob . The space between two neurons
is the synaptic gap

Question 9

How does the nervous system process information?

Answer 9

Sensations
*When the receptors under the skin are stimulated, nerve impulses are produced and transmitted to the
brain. The brain interprets these impulses, and gives us a sensation of the stimulus.

Question 10

What is a voluntary action?

Answer 10

A voluntary action is a deliberate action, which means it happens under conscious control.

Question 11

What is a reflex action?

Answer 11

A reflex action is an immediate response to a specific stimulus without conscious control. Reflex actions are
rapid and automatic, and are examples of involuntary actions

Question 12

What are the two types of reflex actions?

Answer 12

The brain and the spinal cord are reflex centers. Reflex actions are classified as follows:
(a) Cranial reflexes (controlled by the
brain involuntarily).
(b) Spinal reflexes (controlled by the
spinal cord).

Question 13

What is a reflex arc?

Answer 13

A reflex arc is the shortest pathway for nerve impulses to travel from receptor to effector in a reflex action.

Question 14

How is a reflex action different from a voluntary action?

Answer 14

Reflex action:
It happens automatically, not under conscious control.
It is immediate or quick.
A specific stimulus is required.
Impulses are produced by the receptor.

Voluntary action:
It happens under conscious control.
It is slower than a reflex action.
A specific stimulus is not required.
Impulses are produced in the brain.

Question 15

What are sense organs?

Answer 15

Receptors or sense organs which receive stimuli from the environment and inform your body of changes. Those are the eye, nose, ear, tongue, and skin.

Question 16

What is the structure of the human eye?

Answer 16

Upper lid, tear gland, eyelashes, lower lid, conjunctiva, iris, and pupil.
*The eye is the sense organ responsible for sight.

Question 17

What is the internal structure of the eye?

Answer 17

Slide 20

Question 18

What are the two types of photoreceptors?

Answer 18

Cones:
*Cones enable us to see colors in bright light . There
are three different kinds of cone red, blue and green.
Rods:
Rods
*Rods enable us to see in dim light, but only in
black and white . Rods are sensitive to dim light.

Question 19

What is the pupil reflex?

Answer 19

The right amount of light must enter the eye in order for a person to see clearly. The size of the pupil determines
how much light enters the eye.
The pupil reflex is a reflex action.

Question 20

How does the iris control the amount of light entering the eye? (in bright light)

Answer 20

In bright light:
*The circular muscles of the iris contract.
*The radial muscles of the iris relax.
*The pupil constricts to reduce the amount of light entering the eye.

Question 21

How does the iris control the amount of light entering the eye? (in dim light)

Answer 21

*The radial muscles of the iris contract.
*The circular muscles of the iris relax.
*The pupil dilates to increase the amount of light entering the eye.

Question 22

How does the reflex arc in the pupil reflex work?

Answer 22

1) Light ray enters the eye.
2) The receptors in the retina are stimulated.
3) The sensory neuron in the optic nerve transmits impulses to the brain.
4) The impulses are then transmitted from the relay neuron to the motor neuron.
5) Motor neuron transmits the impulses from the brain to the iris.
6) The iris (effector) receives the impulses.

Question 23

How is image formed on the retina of the eye?

Answer 23

*The light rays are refracted through the cornea and the aqueous humour onto the the lens.
*The lens causes further refraction and the rays are brought to a focus on the retina.
*The image on the retina stimulates either the rods or the cones, depending on the intensity of the light.

Question 24

What is focusing or accommodation?

Answer 24

Focusing or accommodation is the adjustment of the lens of the eye, so that clear images of objects at
different distances are formed on the retina.

Question 25

What happens when the eye focuses on a distant object?

Answer 25

*Ciliary muscles relax, pulling on the suspensory ligaments.
*The suspensory ligaments become taut, pulling on the edge of the lens.
*The lens becomes thinner and less convex, increasing the focal length.
*Light rays from the distant object are sharply focused on the retina. Photoreceptors are stimulated.
*Nerve impulses are produced via the optic nerve to the brain.
*The brain interprets the impulses and the person sees the distant object.

Question 26

What happens when the eye focuses on a near object?

Answer 26

*Ciliary muscles contract, relaxing their pull on the suspensory ligaments.
*The suspensory ligaments slacken, relaxing their pull on the lens.
*The lens becomes thicker and more convex, decreasing it’s focal length.
*Light rays from the near object are sharply focused on the retina. Photoreceptors are stimulated.
*Nerve impulses are produced via the optic nerve to the brain.
*The brain interprets the impulses and the person sees the near object.