Communication and Homeostasis

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Stimulus
An environmental change - either internal or external - that elicits a response
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Response
A change in behaviour or physiology as a result of change in the environment
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Homeostasis
The maintenance of the internal environment within narrow parameters despite changes in the external environment
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Negative Feedback
When a condition deviates from a set point, a response is brought about to reverse the change, returning the condition to its set point
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Stimulus-response pathway
The standard stimulus response pathway = Stimulus-------->Receptors-------->Communication pathway------->Effector-------->Response
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Positive feedback
If a condition deviates from the set point, a response is brought about that increases the original change moving the condition further away from its set point. IT IS NOT HOMEOSTASIS
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Endotherm
Organisms that can regulate their body temperature internally.
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Ectotherm
Organisms that rely on external factors to regulate body temperature
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Cell Signalling
The communication between cells. One cell receives a signal that is detected by the second. This second cell then responds to the signal of the first.
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Nervous System
The signal is transported through nerve cells. The signal crosses the synapse junction and can be conducted very quickly enabling rapid response
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Endocrine System
The signal is carried in the form of hormones which are transported in the blood. These chemical messengers are recognized by specific target cells
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Transducer
Something that can convert one form of energy into another
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Sensory Receptor
Found at the end of a sensory neurone and pick up environemental stimuli
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Pacinian Corpuscle
Pressure receptos in the skin. Can detect touch.
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Proprioreceptors
Can detect the length of muscle receptors and so can detect movement
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Neurone
A single nerve cell
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Dendrite
Conducts the signal towards the cell body
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Axon
Conducts the cell signal away from the cell body
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Dorsal Root Ganglia
Found outside the central nervous system and houses the cell body of the sensory neurone
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Motor Neurone
The cell body is found in the central nervous system. It has a short dendron and a very long axon. Carries the signal to the effector
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Sensory Neurone
Cell body is found in the dorsal root ganglia. Usually have a long dendron and a short axon.
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Relay Neurone
Forms a junction between sensory neurones and motor neurones. These are very short nerve cells.
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Perineurium
Each nerve consists of multiple neurones. The axons are usually clustered together in bundles surrounded by this protective covering.
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Reflex Arc
A pathway along which impulses are carried from receptor to effector without consious thought
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Resting Potential
When the neurone is at rest. The membrane is said to be polarised and the potential differance is around -60mv
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Polarised
The cell membrane is said to be polarised when the the inside of the cell is maintained at a negative potential compared to the outside
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Sodium/potassium Pump
This exchange pump pumps three sodium ions out of the cell for every two potassium ions it pumps in. This maintains the potential differance of -60mv across the membrane.
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Anions
Large negatively charge ions that are inside the axon. This also decreases the potential inside the nerve cell and works to maintain the potential difference across the membrane.
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Action potential
When the cell temporarily becomes more positive inside compared to out. There is an exchange of ions and the signal is fired.
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Local Current
When an action potential occurs at one point in the cell, it disrupts the balance of ions established by the sodium/potassium pump. This circuit is established between the depolarised region and the resting areas on either side.
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Refractory period
After an action potential has occured there is a period of time where the neurone cannot fire again. This is because the membrane is hyperpolarised the inside of the cell more negative than it should be.
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Threshold Potential
the potential differance across the membrane is -50mv At this voltage the voltage gated sodium ion channels will open and an action potential will occur
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Depolarisation
Where the inside of the cell becomes less negative compared to the outside
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All or nothing principle
If the threshold potential is crossed then an action potential will occur. The potential differance will either increase to +40 mv or not reach -50 mv
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Repolarisation
The period of time after an action potential where the sodium ion channels close and the potassium ion channels open. This returns the inside of the cell to its more negative state.
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Hyperpolarised
Where the inside of the cell is more negative than it should be. Means that the neurone cannot fire again until the potential difference has been restored.
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Myelin Sheath
Is an insulating layer formed by very thin elongated Schwann cells that wrap around the axon of neurones. It provides electrical insulation and speeds up the rate of transmission.
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Nodes of Ranvier
The gaps in the myelin sheath.
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Saltatory Conduction
The local current is established at the nodes of ranvier. Ion exchange cannot occur through the myelin sheath so action potentials can only occur at the nodes of ranvier. The impulse appears to jump
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Synapse
The junction between neurones
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Cholinergic Synapse
A synapse that uses the neurotransmitter acetylcholine
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Neurotransmitter
A chemical that is released as a result of action potential in the presynaptic neurone. It crosses the synaptic cleft, binding to specific receptors and triggering an influx of sodium ions resulting in an action potential in the post synaptic neurone
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Acetylcholinesterase
The enzyme in a cholinergic synapse that breaks down the acetylcholine preventing the neurone from firing continuously.
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Summation
The term that refers to the way that several small potential changes can produce one larger change in potential difference across the membrane
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Temporal summation
Several consecutive action potentials in the presynaptic neurone are needed to generate an action potential in the post synaptic neurone
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Spatial Summation
Several presynaptic neurones are needed to generate an action potential in the post synaptic neurone.
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Other cards in this set

Card 2

Front

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

Back

Response

Card 3

Front

The maintenance of the internal environment within narrow parameters despite changes in the external environment

Back

Preview of the back of card 3

Card 4

Front

When a condition deviates from a set point, a response is brought about to reverse the change, returning the condition to its set point

Back

Preview of the back of card 4

Card 5

Front

The standard stimulus response pathway = Stimulus-------->Receptors-------->Communication pathway------->Effector-------->Response

Back

Preview of the back of card 5
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