The Nervous System is made up of the Central Nervous System (CNS) and Peripheral Nervous System (PNS), and is made up of cells called neurons that carry electrical impulses.

Nerve impulses are conducted from receptors to the Central Nervous System by sensory neurons. They are then conducted within the CNS by relay neurons and conducted from the CNS to effectors by motor neurons.

6.5Nerves, Hormones, and Homeostasis

The Neuron is composed of 3 main parts: 1.Dendrites2.Cell body (Nucleus and Cytoplasm)3.Axon

The

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Resting potential is the electrical potential across the plasma membrane of a cell that is not conducting an impulse.

Action potential is the reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it. (depolarization and repolarization).

The

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Typically, sodium-potassium pumps maintain equilibrium inside and outside of the cell.

1.When an impulse passes along a nerve, resting potential rises above the threshold level.

2.Voltage gated sodium channels open and sodium ions rush into the cell.

3. The net positive charge inside of the cell leads to depolarization.

4. Voltage gated potassium channels open and potassium ions rush out of the cell.

5.After potassium rushes out, the cell now has a net negative charge, and this results in repolarization.

6.The concentration gradient is restored by the sodium-potassium pump.

7.Resting potential is restored.

The

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System 1.Nerve impulse reaches the

terminal end of the pre-synaptic neuron.

2.Depolarization causes voltage-gated calcium channels to open and Ca+2

rushes in.

3.Ca+2 causes synaptic vesicles to move to the membrane and fuse.

4.Neurotransmitters (NTs) that were stored in the synaptic vesicle now diffuse across the synaptic gap.

5.Neurotransmitters bind with post-synaptic receptors. Neurotransmitters are specific to their receptor.

Steps of Synaptic Transmission

7. The nerve impulse is then propagated along the post-synaptic neuron.

8. Enzymes in the synaptic gap then break down the NT. The products of this break down are taken up by the pre-synaptic neuron by active transport.

6. Sodium channels open, causing Na+ to enter, leading to depolarization of the post-synaptic neuron, and an action potential is initiated.

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The endocrine system consists of glands that release hormones that are transported in the blood.

Homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

When a stimulus is received and processed, hormones are secreted into the blood via ducts. They are carried to the target tissue—the place of action. The action of the hormone changes conditions of the tissue. This change is monitored through feedback mechanisms. Most hormonal change results in negative feedback, which means that any change from a set point results in an opposite change.

When internal body temperature changes past a set point, negative feedback takes place. When the body is

too hot, arterioles dilate, sweat glands open, and body hairs lie lie flat. When the body is too cold, arterioles constrict, sweat glands close, body hairs stand up, and muscles spasm, causing shivering.

Type I Diabetes- Onset early, usually in childhood- Beta cells don’t produce enough insulin- Diet by itself cannot be used to control the condition. Insulin injections are needed to control glucose levels.

Type II Diabetes- Onset usually late, after childhood- Target cells become insensitive to insulin.- Insulin injections not typically needed.

Blood glucose concentration is regulated similarly to the way body temperature is regulated. When blood glucose levels are too high, beta cells in the pancreas produce insulin, which converts glucose to glycogen so that it can be stored in the cytoplasm of cells. When blood glucose levels are too low, alpha cells produce glucagon, which stimulates cells to convert glycogen back into glucose so that it is released into the blood.

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