THE HUMAN NERVOUS SYSTEM

Question 1

What is homeostasis?

Answer 1

The regulation of the internal conditions of the cells to maintain optimum conditions for functioning, in response to internal and external changes.

Question 2

What internal conditions are controlled by homeostasis?

Answer 2

Body temperature
The water content of the body
Blood glucose concentration.

Question 3

How does the body detect and respond to changes in the body?

Answer 3

Automatic control systems, including nervous responses in your nervous system and chemical responses in your hormone system.

Question 4

What are receptors?

Answer 4

Cells that detect changes in the internal or external environment. These changes are known as stimuli. Receptors may be part of the nervous or hormonal control systems of the body.

Question 5

What are coordination centres?

Answer 5

Areas that receive and process the the information from receptors. They send out signals and coordinate the response from the body. They include the brain, which acts as a coordination centre for both the nervous system and parts of the hormonal system, the spinal cord, and some organs such as the pancreas.

Question 6

What are effectors?

Answer 6

Muscles or glands that being about response to the stimulus that has been received. These responses restore conditions in the body to the optimum levels.

Question 7

What are sense organs?

Answer 7

Eyes and skin are examples.

Question 8

How does the nervous system works?

Answer 8

When a sensory detector detects a stimulus, the information is sent as an electrical impulse that passes along the neurones. These are usually found in bundles of hundreds or thousands of neurones known as nerves.
The impulse travels along the neurone until it reaches the central nervous system. The CNS is made up of the brain and spinal cord.
The cells that carry impulses from your sense organ to your CNS are called sensory neurones.

Question 9

What are motor neurones?

Answer 9

The brain coordinates a response to the information and the motor neurones carry information from the CNS to the rest of your body.

Question 10

Why are the effectors?

Answer 10

They respond to the signals. They may be muscles or glands.

Question 11

What does the receptor do?

Answer 11

Sends an impulse along a sensory neurone, carrying information about a change in the environment to the coordinator (CNS). Once all the incoming information has been processed, the coordinator sends impulses down motor neurones. These motor impulses stimulate the effectors to bring about the response needed in an particular situation.

Question 12

What are reflexes?

Answer 12

Automatic responses. They are rapid and don’t involve the conscious part of your brain.

Question 13

What are reflexes for?

Answer 13

Avoiding danger or harm because they happen so fast.

Take care of your bodies basic functions such as breathing.

Question 14

How do simple reflex actions work?

Answer 14

Involve three types of neurone
Sensory
Motor
Relay -

Question 15

What are relay neurones?

Answer 15

These connect a sensory neurone and a motor neurone, and are found in the CNS.

Question 16

Explain the pathway of the reflex arc.

Answer 16

An electrical impulse passes from the receptor along the sensory neurone to the CNS. It then passes along a relay neurone (usually in the spinal cord) and straight back along the motor neurone. From there, the impulse arrives at the effectors organ. The effector organ will be a muscle or a gland. This pathway is called the reflex arc.

Question 17

What are synapses?

Answer 17

These are junctions between the neurones which form physical gaps between the neurones. The electrical impulses travelling along your neurones have to cross these synapses.

Question 18

What happens when you touch an object? REFLEX ARC

Answer 18

A receptor in your skin is stimulated. An electrical impulse from a receptor passes along a sensory neurone to the CNS. In case the spinal cord.

Question 19

What happens when an impulse from the sensory neurone arrives at the synapse with a relay neurone? REFLEX ARC

Answer 19

A chemical is released. The chemical diffuses across the synapse to the relay neurone where it sets off a new electrical impulse travelling down the motor neurone to the effector.

Question 20

What happens when the impulse reaches the effector organ? REFLEX ARC

Answer 20

It is stimulated to respond.

Question 21

What is the coordinator in a reflex action?

Answer 21

Relay neurone either in the spinal cord or the unconscious areas of the brain.

An impulse also traveled up the spinal cord to the conscious areas of you brain. You know about the reflex action, but only after it has happened.

Question 22

What is the cerebral cortex?

Answer 22

Concerned with consciousness, intelligence, memory and language.

Question 23

What is the cerebellum?

Answer 23

Mainly concerned with coordinating muscular activity and balance.

Question 24

What is the medulla?

Answer 24

Concerned with unconscious activities such as controlling the heartbeat, the movement of the gut, and breathing.

Question 25

How can scientists electrically stimulate parts of the brain?

Answer 25

If scientists expose the brain by removing the top of the skull, they can stimulate different areas and see what effect this has. As there are no sensory nerve endings in the brain, brain sergers is usually done on conscious patients. People can experience hunger, fear, anger or thirst simply because relevant areas of their brain have been stimulated.

Question 26

How can MRI scans be used on the brain?

Answer 26

Taking images of the brain in living people. A magnetic resonance imaging (MRI) scan will show exactly which area of the brain is affected by eg a stroke.
This enables scientists to link loss of a certain function such as speech or control of movement on one side of the body, with damage to a particular region of the body.

The most recent MRI scanners can take images as someone carries out a simple task.

Question 27

Why is it difficult to investigate the brain?

Answer 27

Many different neurones in different areas.

Range of different chemicals released in the synapses in the brain.

Question 28

What is the eye?

Answer 28

A sense organ containing many receptors that are sensitive to light.

Question 29

Where are the light sensitive cells found in the eye?

Answer 29

Arranged together inside the back of the eye in a special light sensitive layer known as the retina.

Question 30

What is the sclera?

Answer 30

White outer layer of the eye. Relatively strong so the eyeball is not easy to damage.

Question 31

What is the cornea?

Answer 31

Transparent area at the front of the eyeball. This lets light into the eye. The curved surface of the cornea is important for changing the direction of the light rays coming into the eye, making sure that as they enter the eye they are focussed on the retina.

Question 32

What is the iris?

Answer 32

Muscular and it controls the size of the pupil. It is a hole through which light enters the eye.
It is made of muscles that contract and relax to change the size of the pupil and do control the amount of light reaching the retina.

Question 33

What happens to the iris in dim light?

Answer 33

Enlarged the pupil so as much light as possible can be let in.

CIRCULAR MUSCLES RELAX
RADIAL MUSCLES CONTRACT
PUPIL DILATES.

Question 34

What happens to the iris in bright light?

Answer 34

The iris makes the pupil very small. The prevents too much light from damaging the delicate, light sensitive cells.

CIRCULAR MUSCLES CONTRACT
RADIAL MUSCLES RELAX
PUPIL CONSTRICTS

Question 35

What is the lens?

Answer 35

Once through the pupil, might passes through a clear disc - the lens. It ‘fine tunes’ the focussing of the light rays, changing their direction to produce a clear image on the retina.

Question 36

What holds the lens in place?

Answer 36

Suspensory ligaments and the ciliary muscles.

Question 37

How is the image sent to the brain from the eye?

Answer 37

When light hits the retina, the light-sensitive cells are stimulated. They send impulses to the brain along sensory neurones in the optic nerve. When the brain receives these messages it interprets them as a visual image.

Question 38

How does the eye focus the light?

Answer 38

The light gets focussed by the process of refraction, where light changes direction as it passes through the eye.

The cornea and the jelly in the eyeball change the direction of the light rays onto the retina, but they also refract it the same amount.

The shape of the lens can be changed by contraction or relaxation of the ciliary muscles. This changes the amount the lens refracts the light.

Question 39

What happens to they eye when focussing on distant objects?

Answer 39

Lens less convex (flatter)
Ciliary muscles relax
Suspensory ligaments pulled tight
lens 'flat' and relatively thin
Only refracts light slightly so they are focussed on the retina. This is because the light that reaches your eyes from distant objects is travelling in almost parallel rays.

Question 40

What happens to they eye when focussing on a nearby object?

Answer 40

Lens more convex (rounded)
Ciliary muscles contract
Suspensory ligaments slack. 
Lens more rounded and relatively thick.
The lens is thicker and curved so it refracts light rays more strongly so that they are focussed on the retina.

Question 41

What is accommodation?

Answer 41

The process of changing the shape of the lens to focus on near or distant objects.

Question 42

What is myopia?

Answer 42

Short sightedness

You can see close objects in clear focus, but distant objects look blurred.
This is because the light is focussed in front of the retina.
May be due to a lens that is too curved or a long eyeball.

Question 43

How is myopia treated?

Answer 43

Wear glasses with a concave lens that spread out the light from distant object before it reaches the eye. This means that the thicker lens can bring it into perfect focus on the retina.

Question 44

What is hyperopia?

Answer 44

Long sightedness

You can focus clearly on distant objects but close objects appear blurred. This may be dur to a lens that is too flat and thin, or due to a particularly short eyeball.
As a result the lens cannot refract the rays strongly enough and the light is focussed behind the retina.

Question 45

How is hyperopia corrected?

Answer 45

Convex lens. They bring the rays together more before they reach the eye itself. So, the rays are brought into perfect focus.

Question 46

What is laser eye surgery?

Answer 46

Used to treat myopia by reducing the thickness of the cornea so it refracts less strongly. This means that the lens now focusses distant light on the retina instead of in front of it.

To treat hyperopia lasers are used to change the curve of the cornea so it refracts light from close objects more effectively.

Can only be done on adults whose eyes have become stable.

Question 47

What are replacement lenses?

Answer 47

Add another lens inside the eye to correct the visual defect permanently.
Two techniques;
the permanent contact lens is implanted into the eye and the natural lens left in place.
Or, the faulty lens is replaced by an artificial lens.

Risks - damage to the retina, cataracts developing if the natural lens remains in place, and infections.