The Nervous System
6.5 Nerves, Hormones, and Homeostasis 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. The Neuron is composed of 3 main parts: 1.Dendrites 2.Cell body (Nucleus and Cytoplasm) 3.Axon
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. 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 Nervous System
Typically, sodiumpotassium 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 sodiumpotassium pump. 7.Resting potential is restored.
The Nervous System
Steps of Synaptic Transmission 1.Nerve impulse reaches the
7. The nerve impulse is
terminal end of the pre-
then propagated along
synaptic neuron.
the post-synaptic neuron.
2.Depolarization causes
8. Enzymes in the synaptic
voltage-gated calcium
gap then break down the
channels to open and Ca+2
NT. The products of this
rushes in.
break down are taken up by the pre-synaptic
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. 6. Sodium channels open, causing Na+ to enter, leading to depolarization of the post-synaptic neuron, and an action potential is initiated.
neuron by active transport.
The Endocrine System
The endocrine system consists of glands that release hormones that are transported in the blood.
When a stimulus is received
Homeostasis involves
and processed, hormones are
maintaining the internal
secreted into the blood via
environment between limits,
ducts. They are carried to the
including blood pH, carbon
target tissue—the place of
dioxide concentration, blood
action. The action of the
glucose concentration, body
hormone changes conditions
temperature and water
of the tissue. This change is
balance.
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.
The Endocrine System
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. 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.
http://www.youtube.com/watch?v=x4PPZCLnVkA http://www.youtube.com/watch?v=WVrlHH14q3o http://ibguides.com/biology/notes/nerves-and-hormones