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Coordination AQA Unit 5 Biology

Frihah Parvaiz

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Hormonal System Nervous System

Communication by hormones Communication by nerve impulses

Transmission is by the blood system Transmission is by neurones

Transmission and response is usually relatively slow Transmission and response is very rapid

Response is often long lasting Response is short lived

Response is widespread Response is localised

Hormones travel to whole body but only target cells

respond

Nerve impulses travel to specific parts of the body

Effect may be permanent and irreversible Effect is temporary and reversible

Mammalian are that stimulate their target cells via

blood This results in slow, long-lasting and

Nerve cells electrical impulses along their length. They stimulate target cells by secreting

chemical neurotransmitters directly on to them. This results in rapid, short-lived and localised

The hormonal system consists of glands (group of cells that are specialised to secrete a useful

substance, eg pancreas secretes insulin) and hormones

Hormones diffuse directly into the blood then they are taken around the body by the circulatory

system. Each hormone will only bind to receptors in the target cell.

Hormones arent released directly onto their cells, but instead have to travel through the blood

to get there; meaning the response time is much slower. However they arent broken down as

quickly as neurotransmitters so the effects can last for much longer. They response may be

widespread as they are transported all over the body.

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CHEMICAL MEDIATORS... ...are released from cells and only affect cells in immediate vicinity.

Usually released by injured cells.

Ssecretion causes blood vessels around the area to dilate

(inflammation)

Histamine

Produced by mast cells in response to injury

Increases permeability of capillaries nearby to allow more immune system cells

to move out of the blood to the infected area

Prostaglandins

Produced by most cells in response to inflammation, fever, blood clotting

Cause warmth, pain and redness around the injured area.

Hormones

They have a few differences to hormones

Chemical mediators are secreted from cells all over the body not just glands

Target cells are nearby (stimulate a local response)

They have to travel a shorter distance so produce a quicker response

Histamine and are local chemical

some mammalian cells and affect only cells in their immediate vicinity.

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In flowering plants, specific growth factors diffuse from growing regions other They regulate growth

in to directional stimuli. role of indoleacetic acid in controlling tropisms in flowering

The auxin causes increased

growth in the lower side

of the shoot causing

upwards curvature

(negative gravitropism).

The auxin causes

decreased growth in

the lower side of the

root causing

downwards curvature

(positive gravitropism).

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The structure of a myelinated motor

Myelinated motor neurone

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The of a resting potential in terms of differential permeability,

electrochemical gradients and the of sodium

Distribution of ions at resting potential

When there is no nerve impulse the membrane potential of an axon

is called resting potential. The inside of the axon is -70Mv. Due to

this difference in charge between the inside and outside of the

axon we say that it is polarised. The sodium- potassium pump

moves sodium out of the neurone but the membrane is

impermeable to sodium ions so they cannot move back in, creating

a sodium ion electrochemical gradient. Potassium ions move into

the axon via the sodium potassium pump however the membrane is

permeable to potassium ions so they diffuse back out through

potassium ion channels. This makes the outside of the cell positively

charged compared to the inside.

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The term action potential and

resting potential can be misleading

because the movement of sodium ions

inwards during the action potential is

due to diffusion and resting potential is

maintained by active transport.

The action potential

in permeability lead to and the

generation of an action potential. The all-or-nothing

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The nature and of the refractory period in producing impulses.

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:

oo

o

Factors affecting th

e of

myelination

ax

on diam

eter;

The

of an action potential along

and

axons, resulting in nerve

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Candidates should be able to explain

unidirectionality

temporal and spatial summation inhibition.

The detailed structure of a and of a neuromuscular

Structure of a synapse

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Summation Temporal Summation Temporal summation occurs when

two or more action potentials (nerve impulses) arrive in

rapid succession along a single pre-synaptic neurone.

Spatial Summation Spatial summation occurs when two or

more separate inputs arrive almost simultaneously from

different pre-synaptic neurones. The individual pre-

synaptic potentials add together.

Summation is the method of signal transduction between neurons, which determines whether or not

an action potential will be triggered by the summation (adding together) of postsynaptic potentials.

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The sequence of events involved in transmission across a cholinergic synapse and across a neuromuscular junction.

Mechanism of transmission across a cholinergic synapse

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Drug Effect Examples 1. Mimic a neurotransmitter

stimulate a synapse

levodopa

2. Stimulate the release of a neurotransmitter

stimulate a synapse

cocaine, caffeine

3. Open a neuroreceptor channel

stimulate a synapse

alcohol, marijuana,

3. Block a neuroreceptor channel

stimulate a synapse

salbutamol atropine, curare,

5. Inhibit the breakdown enzyme

stimulate a synapse

DTT

When provided with information, candidates should be able to predict

explain the effects of specific drugs on a

Recall of the and mode of action of individual drugs not be

Some drugs affect synaptic transmission; 1. They are same shape as neurotransmitters so they

mimic action of receptors 2. Block block receptors so they cant be activated 3. Inhibit enzymes that break down neurontrasmitters

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Coord

ination