Coordination and Response IGCSE

Cornea

Cornea

Transparent layer forming the front of the eye

Pupil

Dark circular opening in the centre of the eye which lets light through

Iris

Coloured ring of tissue which controls the amount of light entering the eye by changing the size of the pupil

Lens

Biconvex transparent body situated behind the iris that focuses light on the retina

Choroid

Dark pigmented vascular layer which stops light being reflected around the inside of the eye

Sclera

Tough outer coat of the eye

Retina

Light-sensitive layer at the back of the eye where light energy is transduced into the electrical energy of nerve impulses

Fovea

A small depression in the centre of the retina where a high concentration of cone cells can be found

Optic Nerve

Transmits impulses from sensory neurones in the retina to the brain

Ciliary muscles

Circular muscles that relax or contract to enable the lens to change shape for focussing

Suspensory ligaments

A series of fibres that hold the lens of the eye in place

Blind spot

The one area of the retina where an image cannot be formed as there are no rods or cones; this is where the optic nerve leaves the eye

Refraction

When light is bent. For example in the human eye at the air/cornea boundary and again at the lens

Circular muscles

Muscles found in the iris that contract in bright light and relax in dim light

Radial muscles

Muscles found in the iris that relax in bright light and contract in dim light

Pupil dilation

When the pupil of the eye becomes wider e.g. in response to dim light

Pupil constriction

When the pupil of the eye becomes smaller e.g. in response to bright light

Accommodation

The changes that take place in the eye which allow us to see objects at different distances

Stimulus

A change in an animal's surroundings

Response

A reaction to a change in one's surroundings

Central Nervous System (CNS)

Consists of the brain and spinal cord and is linked to sense organs by nerves

Reflex action

A rapid automatic (or involuntary) action in response to a stimulus that is not started by impulses from the brain

Reflex arc

The nerve pathway of a reflex e.g. stimulus > receptor > sensory neurone > CNS > relay neurone > motor neurone > effector > response

Sensory neurone

A neurone conducting impulses from receptors to the brain or spinal cord

Motor neurone

A neurone transmitting impulses from the brain or spinal cord to a muscle or gland

Synapse

A junction between two nerve cells

Neurotransmitter

A chemical substance released from a nerve cell, allowing an impulse to travel from a nerve cell to another nerve, muscle, organ or tissue

Hormone

Chemical messenger

Exocrine gland

A gland that secretes hormones through a tube or duct

Endocrine gland

Ductless gland that secretes hormones directly into the blood

Pituitary gland

Located at the base of the brain. It secretes a number of different hormones into the blood, including those that regulate reproduction.

Hypothalamus

A region of the brain that coordinates the activity of the pituitary gland

Pancreas

An endocrine and exocrine gland situated behind the stomach.

Glucagon

Produced in the pancreas and works to raise blood glucose levels

Insulin

Produced in the pancreas and works to lower blood glucose levels

Diabetes

A disease where the pancreas cannot make enough insulin to keep blood glucose levels constant, causing it to rise to high concentrations

Anti-diuretic hormone (ADH)

Produced by the pituitary gland and works to control the water content of blood

Testosterone

Produced in the testes, responsible for controlling the development of male secondary sexual characteristics

Progesterone

Produced in the ovaries and regulates the menstrual cycle

Oestrogen

Produced in the ovaries, responsible for controlling the development of female secondary sexual characteristics

Thyroxin

Produced by the thyroid gland and controls the body's metabolic rate

Nervous communication control

Works by fast travelling nerve impulses that act on individual cells. Responses are usually short-lived.

Endocrine communication control

Works by hormones travelling slowly in the bloodstream that have widespread effects on different organs. Responses are usually longer-lasting.

Homeostasis

Maintaining a constant internal environment.

Two examples of homeostasis

1. Control of body water content 2. Control of body temperature

Endotherms

Animals that keep their body temperature constant, despite changes in the temperature of their surroundings i.e. 'warm blooded'

Negative feedback

When a change in body condition is detected, and a process is initiated to return conditions to normal.

Thermoregulatory centre

Area of the hypothalamus that monitors core body temperature and acts as the body's thermostat.

Skin epidermis

Outer layer of skin that consists of dead cells that stop water loss and protect the body against invasion by microorganisms.

Skin hypodermis

Layer of skin that contains fatty tissue to insulate the body against heat loss and acts as a store of energy.

Skin dermis

Middle layer of skin containing sensory receptors, sweat glands, hair follicles and small blood vessels.

Hair erector muscles

Muscles attached to the base of each hair that can contract in cold conditions to pull the hairs upright. This traps a layer of air next to the skin insulating it.

Latent heat of vaporisation

The energy required to transform a liquid to a gas.

Vasodilation

A process where arterioles dilate to increase blood flow to the skin's surface. More heat is radiated from the skin helping to cool the body down in warm conditions.

Vasoconstriction

A process where arterioles constrict to reduce blood flow to the skin's surface. Less heat is radiated from the skin helping to prevent heat loss in cold conditions.

Sweating

A process where glands secrete liquid onto the surface of the skin. This liquid is evaporated using heat energy from the body, cooling the body down.

Shivering

A process where muscles contract and relax rapidly to generate heat in cold conditions

Body metabolism

Can be increased under the influence of adrenaline to generate heat.

Adrenaline

A hormone that can stimulate an increase in body metabolism.