Control and Coordination Cheat Sheet

Definitions

Stimulus

A change in the environment that can be detected by an organism and brings about a response.

Response

The reaction of an organism to a stimulus.

Neuron

The structural and functional unit of the nervous system that carries electrical impulses.

Dendrites

Short branched parts of a neuron that receive impulses and pass them to the cell body.

Axon

The long part of a neuron that carries impulses away from the cell body.

Synapse

The tiny gap between two neurons across which a nerve impulse is transmitted by chemicals.

Reflex action

A sudden, automatic response to a stimulus without conscious thought.

Reflex arc

The pathway taken by a nerve impulse in a reflex action: receptor → sensory neuron → spinal cord → motor neuron → effector.

Cerebrum

The largest part of the forebrain; the seat of thinking, memory, learning and voluntary action.

Cerebellum

The part of the hindbrain that maintains posture and balance and controls precise movements.

Medulla

The part of the hindbrain that controls involuntary actions such as heartbeat, breathing and blood pressure.

Hormone

A chemical messenger secreted by an endocrine gland that controls a specific body function.

Tropism

A growth movement of a plant part in response to a stimulus.

Phototropism

Movement of a plant part in response to light; shoots grow towards light (positive).

Geotropism

Movement of a plant part in response to gravity; roots grow downwards (positive).

Auxin

A plant hormone that promotes cell elongation and is responsible for phototropism.

Gibberellin

A plant hormone that helps in the growth of the stem.

Cytokinin

A plant hormone that promotes cell division.

Abscisic acid

A plant hormone that inhibits growth and causes wilting and dormancy of seeds and buds.

Insulin

A hormone secreted by the pancreas that controls the level of sugar in the blood.

Feedback mechanism

A system in which the level of a substance controls the secretion of the hormone that regulates it.

Key Points

• Nervous tissue is made of neurons; an impulse travels from dendrites to the cell body and along the axon.
• A synapse is crossed by chemicals released at the end of the axon, so the impulse passes from one neuron to the next.
• In a reflex action the impulse is routed through the spinal cord without involving the brain, so the response is very fast.
• The brain is protected by the skull and the spinal cord by the vertebral column; cerebrospinal fluid gives further cushioning.
• Parts of the brain: forebrain (cerebrum — thinking and memory), midbrain (control of reflex movements) and hindbrain (cerebellum for balance, medulla for heartbeat and breathing).
• Hormones are secreted by endocrine glands, which have no ducts, and are carried by the blood to the target organ.
• Pituitary — growth hormone; thyroid — thyroxine; pancreas — insulin; adrenal — adrenaline; testes — testosterone; ovaries — oestrogen.
• Thyroxine regulates carbohydrate, protein and fat metabolism; it needs iodine, and its deficiency causes goitre.
• Adrenaline prepares the body for emergencies by increasing heartbeat and breathing.
• Deficiency of insulin causes diabetes; the hormone level is kept steady by a feedback mechanism.