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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Types Of Neurones - Sensory Neurone, Relay Neurone, Motor Neurone

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Neurone or nerve cell is classified into three types which are sensory neurone (afferent neurone), relay neurone (interneurone) and motor neurone (efferent neurone).

Sensory neurone / Afferent neurone

Sensory neurone also known as afferent neurone, transmits nerve impulses from receptor to central nervous system (CNS) which consists of brain and spinal cord.

Relay neurone / Interneurone

Relay neurone also known as interneurone, transmits nerve impulses from sensory neurone to motor neurone. Relay neurone is found within the central nervous system (CNS).

Motor neurone / Efferent neurone

Motor neurone also known as efferent neurone, transmits nerve impulses from central nervous system (CNS) which consists of brain and spinal cord, to effectors which are either muscles or glands. In response to impulses, muscles contract and glands secrete.
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Neurone Structures And Functions - Cell Body, Axon, Myelin Sheath, Dendrites

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A neurone is the most basic functional unit of nervous system. A neurone consists of dendrites, dendrones, cell body, axon, myelin sheath and nodes of Ranvier.

Dendrites

Dendrites form connections with other neurones and transmit nerve impulses towards the cell body.

Dendrones

Dendrones transmit nerve impulses from dendrites to the cell body.

Cell body

Cell body which contains nucleus, controls the activities of the neurone.

Axon

Axon transmits nerve impulses away from the cell body.

Myelin sheath and nodes of Ranvier

Myelin sheath protects the axon from injuries; and together with nodes of Ranvier, they speed up the rate of transmission of impulses.
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Differences Between Nervous And Endocrine Systems

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Complexity

Nervous system is more structurally complex whereas endocrine system is less structurally complex.

Structure

Nervous system involves systems of neurones which branch throughout body whereas endocrine system involves endocrine glands which secrete hormones into the bloodstream and are carried to target organs.

Communication

In nervous system, neurones conduct electrical signals directly to and from specific targets whereas in endocrine system, hormones circulate throughout whole body in bloodstream.

Response time

In nervous system, transmission of nerve impulses is fast whereas in endocrine system, it may takes minutes, hours or days for hormones to be produced, carried in bloodstream to target organs and for responses to occur.
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Parts Of Human Brain - Cerebrum, Cerebellum, Medulla Oblongata

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The human brain consists of three main parts which are cerebrum, cerebellum and medulla oblongata.

Cerebrum

Cerebrum is divided into left and right hemispheres and each hemisphere is further divided into four lobes which are frontal, parietal, occipital and temporal lobes. Cerebrum controls voluntary actions, actions which can be controlled by our own will, such as walking, reading, speaking and others.

Cerebellum

Cerebellum coordinates muscular movement and maintains body posture and balance.

Medulla oblongata

Medulla oblongata controls involuntary actions, actions which cannot be controlled by our own will, such as heartbeat, homeostasis, peristalsis and others.
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Regulation Of Body Temperature - Thermoregulation

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Regulation of body temperature or thermoregulation is a negative feedback mechanism which aims at maintaining constant body temperature. Optimum body temperature for human is 370C.

Thermoregulation in hot condition

In hot condition, sweat glands increase sweating, superficial blood capillaries undergo vasodilation, erector muscles relax thus lower the hair, and endocrine glands decrease metabolic rate. These activities increase heat loss and decrease heat gain to maintain the optimum body temperature.

Thermoregulation in cold condition

In cold condition, sweat glands decrease sweating, superficial blood capillaries undergo vasoconstriction, erector muscles contract thus raise the hair, endocrine glands increase metabolic rate, and skeletal muscles contract involuntarily hence shivering. These activities decrease heat loss and increase heat gain to maintain the optimum body temperature.
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Regulation Of Blood Sugar Level - Insulin, Glucagon

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Regulation of blood sugar or glucose level is a negative feedback mechanism which aims at maintaining normal blood glucose level. Two hormones, insulin and glucagon are involved in regulation of blood glucose level. Insulin stimulates liver cells to convert glucose to glycogen whereas glucagon stimulates liver cells to break down glycogen to glucose.

Increase in blood glucose level

After a meal, blood glucose level increases, pancreas secretes more insulin, liver cells convert glucose to glycogen for storage and body cells increase glucose uptake for respiration. These activities decrease blood glucose level to normal.

Decrease in blood glucose level

During fasting or exercise, blood glucose level decreases, pancreas secretes more glucagon, liver cells break down glycogen to glucose and body cells decrease glucose uptake for respiration. These activities increase blood glucose level to normal.
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