Biology: Communication & Homeostasis

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Stimulus
Any change in the environment that causes a response.
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Response
A change in the behaviour or physiology of an organism as a result of a change in the environment.
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Homeostasis
The maintenance of the internal environment in a constant state despite external changes.
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Negative Feedback
A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis
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Positive Feedback
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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Neurotransmitter
A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.
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Cholinergic Synapses
Those that use acetylcholine as their transmitter substance.
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Synaptic Knob
A swelling at the end of the presynaptic neurone.
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Acetylcholinesterase
An enzyme in the synaptic cleft. It breaks down the transmitter substance acetylcholine.
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Summation
The way that several small potential changes can combine to produce one larger change in potential difference across the membrane.
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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 of the same magnitude, +40 mV.
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Polarised
A membrane that has a potential difference aross it. This is the resting potential.
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Depolarisation
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
A small depolarisation caused by sodium ions entering the cell.
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Action Potential
Achieved when the membrane is depolarised to a value of about +40 mV. It is an all-or-nothing response.
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Resting Potential
Potential difference or voltage across the neurone cell membrane while the neurone is at rest. It is about -60 mV inside the cell compared with the outside. Other cells may also maintain a resting potential that may change in certain circumstances.
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Voltage-gated Channels
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. In these channels the gates respond to changes in the p.d.across the membrane.
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Threshold Potential
A p.d. across the membrane of about -50 mV. If the depolarisation of the membrane does not reach the threshold potential then no action potential is created. If the depolarisation reaches the threshold potential then an action potential is created.
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Local Currents
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
Meaning '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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Hormones
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
A gland that secretes hormones directly into the blood. Endocrine glands have no ducts.
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Exocrine Gland
A gland that secretes molecules into a duct that carries the molecules to where they are used.
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Target Cells
Those that possess a specific receptor on their plasma 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
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
The hormone that transmits a signal around the body.
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Second Messenger
cAMP, which transmits a signal inside the cell.
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Pancreatic Duct
A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine.
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Islet of Langerhans
Small patches of tissue in the pancreas that have an endocrine function.
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Insulin
The hormone, released from the pancreas, that causes blood glucose levels to go down.
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Glucagon
The hormone that causes blood glucose levels to rise.
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Hepatocytes
Liver cells that are specialised to perform a range of metabolic functions.
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Diabetes Mellitus
A disease in which blood glucose concentrations cannot be controlled effectively.
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Hyperglycaemia
The state in which the blood glucose concentration is too high.
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Hypoglycaemia
The state in which the blood glucose concentration is too low.
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Genetically Engineered Bacteria
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
Unspecialised cells that have the potential to develop into any type of cell.
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Cell Metabolism
The result of all the chemical reactions taking place in the cytoplasm.
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Myogenic
Muscle tissue that can initiate its own contractions.
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Pacemaker
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
Found at the base of the brain. It is the region of the brain that coordinates the unconscious functions of the body such as breathing rate and heart rate. The accelerator and vagus nerve run from the medulla oblongata to the heart.
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Cardiovascular Centre
A region of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. It sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves.
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Other cards in this set

Card 2

Front

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

Back

Response

Card 3

Front

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

Back

Preview of the back of card 3

Card 4

Front

A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change. It is essential for homeostasis

Back

Preview of the back of card 4

Card 5

Front

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

Back

Preview of the back of card 5
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