Signals and messages

What is an all or nothing response?

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

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What is summation?

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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What is the main role of synapses?

To connect 2 neurones together so that a signal can be passed from one to the other.

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What may several presynaptic neurones do?

Several presynaptic neurones may converge to one postsynaptic neurone.

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What would this allow?

Would allow signals from different parts of the nervous system to create the same response which could be useful in danger.

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What may 1 presynaptic neurone do?

One presynaptic neurone may diverge to several postsynaptic neurones.

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What would this allow?

Would allow 1 signal to be transmitted to several parts of the nervous system. Useful in a reflex arc.

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What do synapses ensure about transmission?

Synapses ensure signals are transmitted in the correct direction.

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How do synapses ensure transmission in the correct direction?

Only the presynaptic knob contains vesicles of acetylcholine.

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What can synapses filter out?

Synapses can filter out unwanted low-level signals.If a low-level stimulus creates an action potential in the presynaptic neurone, it is unlikely to pass across a synapse to the next neurone as several vesicles of acetylcholine must be released.

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How can low-level signals be amplified?

Can be amplified by a process called summation.

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What happens if a low-level signal is persistent?

It will generate several successive action potentials in the presynaptic neurone.

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What will the release of many vesicles of acetylcholine over a short period of time enable?

Will enable the postsynaptic generator potentials to combine together to produce an action potential.

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When can summation also occur?

Summation can also occur when several presynaptic neurones each release small numbers of vesicles into one synapse.

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What may happen after repeated stimulation and what is this called?

A synapse may run out of vesicles containing the transmitter substance. Called acclimatisation.

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What is the synapse said to be and what does this mean in terms of responses?

Synapse is said to be fatigues. Means the nervous system no longer responds to the stimulus.

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What may this help to do?

May help to avoid overstimulation of an effector, which could damage it.

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What is the creation of specific pathways within the nervous system thought to be?

The creation of specific pathways thought to be the basis of conscious thought and memory.

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What does the brain do when it receives signals?

The brain perceives light when it receives signals from the light receptors in the eyes.

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What can it also perceive?

Can perceive sound when it receives signals from the ears.

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Describe what will happen when a stimulus is at higher intensity

When a stimulus is at higher intensity, the sensory receptor will produce more generator potentials.

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What will more generator potentials being produced cause?

Cause more frequent action potentials in the sensory neurone.

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What will happen when these action potentials arrive at a synapse?

They will cause more vesicles to be released.

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What will happen when more vesicles are released?

This creates a higher frequency of action potentials in the postsynaptic neurone.

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What can our brain determine?

Brain can determine the intensity of the stimulus from the frequency of signals arriving.

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What does a higher frequency of signals mean?

A higher frequency of signals means a more intense and stronger stimulus.

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What does it mean for a neurone to be myelinated?

The neurones are insulated by an individual myelin sheath.

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How is this sheath created?

Sheath is created by a series of separate cells called Schwann cells.

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Describe how Schwann cells are placed around the neurone

Schwann cells are wrapped around the neurone so the sheath actually consists of several layers of membrane and thin cytoplasm from the Schwann cell.

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What are present at intervals along the neurone?

Nodes of Ranvier are present at intervals along the neurone. Each node is very short.

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Describe non-myelinated neurones and Schwann cells

Non-myelinated neurones are still associated with Schwann cells, but several neurones may be enshrouded in 1 loosely wrapped Schwann cell.

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What does this mean?

This means that the action potential moves along the neurone in a wave in non-myelinated instead of jumping from node to node as seen in myelinated neurones.

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What is the advantage of myelination?

Myelinated neurones can transmit an action potential much more quickly than non-myelinated neurones can.

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Where do myelinated neurones carry signals from an to?

Carry signals from sensory receptors to the CNS and from the CNS to effectors.

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What does the increased speed of a myelinated neurone mean?

Increased speed means the signal reaches the end of the neurone much more quickly to enable a rapid response to a stimulus.

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Why is myelination not so important in coordinating body functions such as breathing and the action of the digestive system?

Non-myelinated neurones tend to be shorter and carry signals over a short distance.

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Signals and messages

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