B10: The Human Nervous System

Question 1

What is Homeostasis?

Answer 1

The maintenance of steady conditions. The ability of the body to maintain a constant internal environment, eg temperature and blood glucose concentration.

Question 2

What are the 3 main things that homeostasis controls?

Answer 2

blood glucose concentration
body temperature
water levels

Question 3

What composes the nervous system?

Answer 3

the
central nervous system– the brain and spinal cord

the peripheral nervous system – nerve cells that carry information to or from the CNS

Question 4

What are the three main parts of a control system?

Answer 4

Cells called
receptors, which detect stimuli (changes in the environment).
The coordination centre, such as the brain, spinal cord , which receives and processes information from receptors around the body.

Effectors bring about responses, which restore optimum levels, such as core body temperature and blood glucose levels. Effectors include muscles and glands, and so responses can include muscle contractions or hormone release.

Question 5

What are neurones?

Answer 5

Nerve cells. They carry an electrical message or impulse when stimulated.

Question 6

What are the features of a neurone?

Answer 6

A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.
Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.

Question 7

Show a diagram on how the nervous system work

Answer 7

Stimulus → receptor → coordinator(CNS) → effector → response

Question 8

What are receptors?

Answer 8

Receptors are groups of specialised cells. They detect a change in the environment (stimulus) and stimulate electrical impulses in response. Sense organs contain groups of receptors that respond to specific stimuli.

Question 9

What are effectors?

Answer 9

Effectors include muscles and glands - that produce a specific response to a detected stimulus.

For example:

a muscle contracting to move an arm

Question 10

What is a reflex arc?

Answer 10

Automatic and rapid response to a stimulus.

Question 11

Explain the reflex arc

Answer 11

Receptor in the skin detects a stimulus (the change in temperature).
Sensory neurone sends electrical impulses to relay neurone, which are located in the spinal cord. They connect sensory neurones to motor neurones.
Motor neurone sends electrical impulses to an effector.
Effector produces a response (muscle contracts to move hand away).

Question 12

What happens at the synapse (the junction of 2 neurones)

Answer 12

An electrical impulse travels along the first axon.
This triggers the nerve-ending of a neurone to release chemical messengers called
neurotransmitters
.
These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the second neurone.
The receptor molecules on the second neurone bind only to the specificneurotransmitters released from the first neurone. This stimulates the second neurone to transmit the electrical impulse.

Question 13

Why are reflexes important?

Answer 13

They enable you to avoid damage and danger because they happen
very fast.
They control many vital bodily functions, such as breathing, without
need for conscious thought.

Question 14

Why is it important that reflexes don’t reach the conscious parts of your brain?

Answer 14

This would slow process down, making it less effective at preventing
damage. It would be very difficult to consciously control all bodily
functions and still be able to do anything else.

Question 15

Ruler Drop Test Required Practicals:

Answer 15

Ruler drop test
Work with a partner.
Person A holds out their hand with a gap between their thumb and first finger.
Person B holds the ruler with the zero at the top of person A’s thumb
Person B drops the ruler without telling Person A and they must catch it.
The number level with the top of person A’s thumb is recorded in a suitable table. Repeat this ten times.
Swap places, and record another ten attempts.
You can use the conversion table to help convert your ruler measurements into reaction time or just record the catch distance in cm.
You could also investigate it with different factors.

Question 16

What is the Brain?

Answer 16

The organ of the central nervous system of mammals where vital functions are coordinated

Question 17

What are the 4 main areas of the brain?

Answer 17

The cerebrum (the outer layer is called the cerebral cortex), which is split into two hemispheres and is highly folded. It controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory.
The cerebellum, which controls balance, co-ordination of movement and muscular activity.
The medulla, which controls unconscious activities such as heart rate and breathing rate,
The hypothalamus
, which is the regulating centre for temperature and water balance within the body.

Question 18

Describe 2 ways where in which scientists can find out about the functions of the different parts of the brain.

Answer 18

*Studying people with brain damage
* Electrically stimulating parts of the brain
* MRI scans
more information:
studying people with brain damage allows scientists to match
changes of behavior or memory to the damaged area of the
brain
* this allows scientists predict what function the area normally
carries out.
* scientists can electrically stimulate specific areas of the exposed
brain
* and observe the effect this has on the patient’s behavior.
* MRI scans produce images of brain activity or damage within
live patients,
* This can be linked to observed behaviors.

Question 19

What is electrical stimulation?

Answer 19

Scientists have stimulated different parts of the brain with a weak electrical current and asked patients to describe what they experienced. If the motor area is stimulated, the patient makes an involuntary movement. If the visual area is stimulated, they may see a flash of colour. EEGs (Electroencephalograms) can be created and studied, to observe the electrical activity in the brain.

Question 20

What is MRI?

Answer 20

Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans, use strong magnetic fields and radio waves to show details of brain structure and function. Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out.

Question 21

How is the eye structured?

Answer 21

Cornea Refracts light - bends it as it enters the eye
Iris Controls how much light enters the pupil
Lens Further refracts light to focus it onto the retina
Retina Contains the light receptors
Optic nerve Carries impulses between the eye and the brain
Sclera-Tough white outer layer of the eye. It helps protect the eye from injury

Question 22

What are the receptors in the retina?

Answer 22

Light passes through the eyeball to the retina. There are two main types of light receptors - rods and cones. Rods are more sensitive to light than cones so they are useful for seeing in dim light. There are three different types of cone cells which produce colour vision.

Question 23

What is Myopia?

Answer 23

Someone with short-sight can see near objects clearly, but cannot focus properly on distant objects.

Short sight is caused by one of the following:

The eyeball being elongated - so that the distance between the lens and the retina is too great.
The lens being too thick and curved - so that light is focused in front of the retina.

Question 24

What is hyperopia?

Answer 24

Someone who is long-sighted can see distant objects clearly, but they cannot focus properly on near objects.

Long-sightedness is caused by one of the following:

the eyeball being too short - so the distance between the lens and retina is too small
a loss of elasticity in the lens - meaning it cannot become thick enough to focus (which is often age-related)
As a result, the lens focuses light behind the retina instead of onto it. Long-sightedness is corrected by putting a convex lens in front of the eye.

Question 25

What are the 3 alternatives to wearing glasses?

Answer 25

Contact lenses – work by being in ‘contact’ with your eye. They float on the surface of the cornea. They work like spectacle lenses, by focusing and refracting the light.

Laser surgery – reshapes the cornea surgically. Common for myopia but can be used for some hyperopia conditions.
Replacement lens – implanting artificial lenses is a recent development, and can placed in front of the original lens, through a small cut in the cornea, to correct an eye defect.

Question 26

What is accomodation?

Answer 26

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

To focus on a near object – the lens becomes thicker, this allows the light rays to refract (bend) more strongly.

To focus on a distant object – the lens is pulled thin, this allows the light rays to refract slightly.