Transmission Of Nerve Impulses Along Axon - Resting, Depolarisation, Repolarisation

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Transmission of nerve impulses along axon involves the formation of action potentials. An action potential is divided into several phases which are resting phase, depolarisation phase and repolarisation phase.

Resting phase

During resting phase, the potential difference which exists across axon membrane at rest is called resting potential. The resting potential for human cell is about -70mV. Sodium potassium pumps actively pump three sodium ions out of the axon and pumps two potassium ions into the axoplasm, therefore more positive ions are pumped out that pump in.

Depolarisation phase

During depolarisation phase, sodium gates open, positively charged sodium ions diffuse into axon and the charge inside axon changes from negative to positive.

Repolarisation phase

During repolarisation phase, potassium gates open, positively charged potassium ions diffuse out from axon and the charge inside axon changes from positive to negative.

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Transmission Of Nerve Impulses Across Synapse - Neurotransmitter, Acetylcholine

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Neurones are not continuous there is a gap between neurones. The gap between axon of one neurone and the dendrites on the next neurone is called a synapse.

At an axon terminal, there are tiny vesicles filled with neurotransmitters which are chemical substances used by one neurone to signal another neurone. An example of neurotransmitter is acetylcholine.

Transmission of nerve impulses across synapse

When a nerve impulse reaches the axon terminal, vesicles containing neurotransmitters (acetylcholine) move towards presynaptic membrane. Vesicles fuse with the membrane, releasing neurotransmitters (acetylcholine) into synaptic cleft through exocytosis. Neurotransmitters (acetylcholine) diffuse across synapse and bind to the receptors at postsynaptic membrane. Some of the neurotransmitters (acetylcholine) are broken down by enzymes (acetylcholinesterase), taken up again by the axon terminal and recycled, or simply diffused away.
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Factors Affecting Rate Of Transpiration - Temperature, Humidity, Wind Speed, Light Intensity

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Transpiration is evaporation of water through stomatal openings in leaves. Factors affecting rate of transpiration are temperature, humidity, air movement and light intensity.

Effect of temperature on rate of transpiration

The higher the temperature, the higher the rate of transpiration. The hotter it is, the more water molecules evaporate.

Effect of humidity on rate of transpiration

The higher the humidity, the lower the rate of transpiration. The more saturated the air, the less evaporation can take place.

Effect of wind speed on rate of transpiration

The higher the wind speed the higher the rate of transpiration. The more water molecules are blown away, the more evaporation can take place.

Effect of light intensity on rate of transpiration

The higher the light intensity, the higher the rate of evaporation. The more stomata open during photosynthesis, the more water molecules evaporate.
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