Communication & Homeostasis - Definitions

Front 1

Stimulus

Back 1

Any change in the environment that causes a response.

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Response

Back 2

A change in behaviour or physiology as a result of a change in the environment.

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Homeostasis

Back 3

The maintenance of the internal environment in a constant state despite external changes.

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Negative Feedback

Back 4

Brings about a reversal of any change in conditions. Ensures an optimum steady state can be maintained, as the internal environment is maintained and returned to its original conditions after any change.

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Positive Feedback

Back 5

A process that increases any change detected by receptors. It tends to be harmful and does not lead to homeostasis.

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Ectotherm

Back 6

An organism that relies on external sources of heat to regulate its body temperature.

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Endotherm

Back 7

An organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain its body temperature.

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Polarised Membrane

Back 8

Has a potential difference across it. The resting potential.

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Depolarisation

Back 9

The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.

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Generator Potential

Back 10

A small depolarisation caused by sodium ions entering the cell.

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Action Potential

Back 11

When the membrane is depolarised to a value of about +40 mV. An all-or-nothing response. In the event leading up to an action potential, the membrane depolarises and reaches a threshold level, then lots of sodium ions enter the axon and an action potential is reached. Can be transmitted along the axon/dendron plasma membrane.

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Resting Potential

Back 12

The potential difference or voltage across the neurone cell membrane while the neurone is at rest. About -60mV inside the cell compared with the outside. Other cells may also maintain a resting potential that might change under certain circumstances.

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Voltage-gated Channels

Back 13

Channels in the cell membrane that allow the passage of charged particles or ions. Have a mechanism called a gate which can open and close the channel. In these channels, the gates respond to changes in the potential difference across the membrane.

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Local Currents

Back 14

The movements of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region or higher concentration.

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Saltatory Conduction

Back 15

‘Jumping conduction’. The way that the action potential appears to jump from one node of Ranvier to the next.

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Neurotransmitter

Back 16

(Transmitter substance). A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.

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Cholinergic Synapses

Back 17

Those that use acetylcholine as their transmitter substance.

Front 18

Synaptic Knob

Back 18

The swelling at the end of the presynaptic neurone.

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Acetylcholinesterase

Back 19

An enzyme in the synaptic cleft. Breaks down the transmitter substance acetylcholine.

Front 20

All or Nothing

Back 20

A neurone either conducts an action potential or does not. All action potentials are of the same magnitude, +40mV

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Summation

Back 21

The way that several small potential changes can combine to produce one larger change in potential difference across the membrane.

Front 22

Hormones

Back 22

Molecules that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue.

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Endocrine gland

Back 23

A gland that secretes hormones directly into the blood. Endocrine glands have no ducts.

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Exocrine gland

Back 24

A gland that secretes molecules into a duct that carries the molecules to where they are used.

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Target cells

Back 25

Those that possess a specific receptor on their plasma (cell surface) membrane. The shape of the receptor is complementary to the shape of the hormone molecule. Many similar cells together form a tissue.

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Adenyl cyclase

Back 26

An enzyme associated with the receptor for many hormones, including adrenaline. It is found on the inside of the cell surface membrane.

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First Messenger

Back 27

The hormone that transmits a signal around the body.

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Second Messenger

Back 28

cAMP, which transmits a signal inside the cell.

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Pancreatic Duct

Back 29

A tube that collects all secretions from exocrine cells in the pancreas and carries the fluid to the small intestine.

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Islets of Langerhans

Back 30

Small patches of tissue in the pancreas that have an endocrine function.

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α cells

Back 31

Found in islets of Langerhans. Secrete the hormone glucagon.

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β cells

Back 32

Found in islets of Langerhans. Secrete the hormone insulin.

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Insulin

Back 33

The hormone, released from the pancreas, which causes blood glucose levels to go down.

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Glucagon

Back 34

The hormone that causes blood glucose levels to rise.

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Hepatocytes

Back 35

Liver cells specialised to perform a range of metabolic functions.

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Diabetes Mellitus

Back 36

A disease in which blood glucose concentrations cannot be controlled effectively.

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Hyperglycaemia

Back 37

The blood glucose concentration is too high (hyper = above, glyc = glucose, aemia = blood).

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Hypoglycaemia

Back 38

The blood glucose concentration is too low (hypo = under).

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Genetically Engineered Bacteria

Back 39

The DNA has been altered.

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Stem Cells

Back 40

Unspecialised cells that have the potential to develop into any type of cell.

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Cell Metabolism

Back 41

The result of all the chemical reactions taking place in the cytoplasm.

Front 42

Myogenic

Back 42

Muscle tissue can initiate its own contractions.

Front 43

Pacemaker

Back 43

Region of tissue in the right atrium that can generate an impulse and initiates the chamber contraction.

Front 44

Medulla Oblongata

Back 44

Found at the base of the brain. Coordinates the unconscious functions of the body.

Front 45

Cardiovascular Centre

Back 45

A part of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. Sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves.