Biology

Stimulus

is any change in the environment that causes a response.

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Response

is a change in behavior or physiology as a result of a change in the environment.

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Homeostasis

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

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Negative feedback

is a process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained.

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Positive Feedback

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

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Ectotherm

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

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Endotherm

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

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Generator potential

is a small depolarisation caused by sodium ions entering the cell.

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Action Potential

is achieved when the membrane is depolarised to a value of about +40mV. It is a all or nothing response.

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Resting potential

is the potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60mV inside the cell compared with the outside.

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Voltage-gated channels

are channels in the cell membrane that allow the passage of charged particles or ions. They have a mechanism called a gate which can open and close the channel.

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Threshold potential

is a potential difference across the membrane of about -50mV. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created.

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Action Potential

is a depolarisation of the cell membrane so that the inside is more positive than the outside, with a potential difference across the membrane of +40mV.

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Local curents

are 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 of higher concentration.

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Saltatory

conduction means jumping conduction. It refers to the way that the action potential appears to jump from one node of Ranvier to the next.

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Neurotransmitter

is a chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.

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Cholinergic synapses

are those that use acetylcholine as their transmitter substance.

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Synaptic knob

is a swelling at the end of the presynaptic neurone.

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Acetylcholinesterase

is an enzyme in the synaptic cleft. It breaks down the transmitter substance acetylcholine.

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All or nothing

refers to the fact that a neurone either conducts an action potential or it does not. All action potentials are the same magnitude, +40mV.

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Summation

is a term that refers to the way that several small potential changes can combine to produce one larger change in potential difference across the membrane.

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Hormones

are molecules that are releases 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

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

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Exocrine gland

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

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Target cells

are those that possess a specific receptor on their plasma membrane. The shape of the hormone molecule. Many similar cells together form a tissue.

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Adenyl cyclase

is 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

is the hormone that transmits a signal around the body.

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Second Messenger

is cAMP, which transmits a signal inside the cell.

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Pancreatic duct

is a tube that collects all the secretions from the exocrine cells int he pancreas and carries the fluid to the small intestine.

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Islets of Langerhans

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

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Insulin

is the hormone, released from the pancreas, that causes blood glucose levels to go down.

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Glucagon

is the hormone that causes blood glucose levels to rise.

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Hepatocytes

are liver cells. They are specialised to perform a range of metabolic functions.

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Diabetes mellitus

is a disease in which blood glucose concentrations cannot be controlled effectively.

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Hyperglycaemia

is the state in which the blood glucose concentration is too high.

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Hypoglycaemia

is the state in which the blood glucose concentration is too low.

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Genetically engineered

bacteria are those in which the DNA has been altered. In this case a gene coding for human insulin has been inserted into the DNA of the bacteria.

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Stem Cells

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

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Cell metabolism

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

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Myogenic

muscle tissue can initiate its contractions.

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Pacemaker

is a region of tissue in the right atrium wall that can generate an impulse and initiates the contraction of the chambers.

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Medulla oblongata

is found at the base of the brain. It is the region of brain that coordinates that unconscious functions of the body such as breathing rate and heart rate.

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Cardiovascular centre

is a specific region of the medulla oblongata that recieves sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure.

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Biology

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