6.5 Nerves, Hormones, and Homeostasis
Terms in this set (12)
6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses.
The nervous system is divided into the central nervous system (CNS) and the peripheral nerve system (PNS);
CNS consisting of brain and spinal cord;
PNS consisting of motor and sensory nerves;
sensory neurons carry impulses to the CNS;
motor neurons carry impulses from the CNS;
6.5.2 Draw and label a diagram of the structure of a motor neuron.
Dendrites pick messages from another neuron.
Cell body contains the nucleus, cytoplasm, mitochondria and other organelles.
Axon ensures a speedy traveling of the nerve impulse to distant part of the body.
The nerve endings carry the message to the dendrites of the next neuron.
The myelin sheath is a lipid layer made by the Schwann cells) surrounding the axon that insulate the axon and helps in speeding up the nerve impulse.
Nodes of Ranvier are the intervals between the Schwann cells. The nerve impulse travels from node to node.
6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.
Neurons carry electrical impulses long distances in the body, using the axon.
Sensory neurons carry nerve impulses from sensory cells or receptors to the CNS.
Motor neurons carry impulses from the CNS to the muscle (effector).
Relay neurons carry impulses within the CNS, from one neuron to another.
6.5.4 Define resting potential and action potential (depolarization and repolarization).
Resting potential is the electrical potential across a plasma membrane when not propagating an impulse.
Action potential is the state of the cell membrane while conducting an impulse, meaning the rapid depolarization and repolarization of the cell membrane.is the state of the cell membrane while conducting an impulse.
6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron.
The nerve at rest
We have an imbalance of ions inside and outside of the plasma membranes.
The important ions are K+ and Na+.
K+ is more concentrated inside the cell (30X more) and therefore tends to diffuse out of the cell.
Na+ is more concentrated outside (10X more) of the cell and thus tends to diffuse into the cell, but at a lower rate.
Na+-K+ pumps embedded in the plasma membrane work against both ions' diffusion gradients in order to preserve the gradients and the membrane potential.
The inside of the cell is - charged due to Cl- and some proteins while the outside is + charged due to Na+.
The plasma membrane is said to be polarised (+ and - poles)
The resting potential is -70 mV.
When a nerve is stimulated the properties of the plasma membrane will change and Na+ - K+ channels will open.
Na+ will come inside the cell.
The inside of the cell will become more + and more or depolarised.
The outside of the cell will become -.
This is called the reverse polarisation.
At a certain point, you will have too many + charges inside the cell.
The K+ will begin to leave the cell.
This highly + charges inside the cell will start to decrease.
The plasma membrane potential goes back to his original level but the Na+ and K+ are not at the right place.
High concentration of Na+ inside the cell.
High concentration of K+ outside the cell.
To get the original setting, the Na+ - K+ pumps start working.
This restore the distribution of ions.
That period is called the refractory period or recovery period.
It means that a neuron is unable to respond to another stimulus.
6.5.6 Explain the principles of synaptic transmission.
Nerve impulse travels to end of presynaptic neuron
Na+ enter the axoplasm (cytoplasm of the neuron) through Na+ channels.
It releases a lot of Ca2+
The presence of Ca2+ causes vesicles of neurotransmitters to move to the pre-synaptic plasma membrane and burst.
The neurotransmitter coming out of the vesicles diffuses across the synaptic gap and binds to a specific receptor on the post-synaptic plasma membrane.
This junction between the neurotransmitter and the receptor will open channels allowing Na+ to enter the post-synaptic neuron causing the transmission of the nerve impulse through the post-synaptic neuron.
When this is completed, an enzyme will breakdown the neurotransmitter.
The broken parts of the neurotransmitter will be coming back into the pre-synaptic neuron.
In here, the neurotransmitter will be re-synthesised.
The Ca2+ is also removed and pumped back into the synaptic cleft.
The pre-synaptic neuron is ready for the next nerve impulse
6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood.
The system contains 'ductless glands' therefore they secrete hormones directly into the blood stream. Examples of these glands are Thyroid, Adrenal, and pituitary glads.
6.5.8 State what homeostasis involves
The endocrine systems and nervous system are both involved in homeostasis. Homeostasis involves maintaining the internal environment at a constant levels, and this includes blood ph, oxygen and carbon dioxide concentrations, blood glucose, body temperature and water balance.
6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.
Negative feedbacks contain a detector which measures the value of a feature to be controlled. This sends information to an effector, which then takes action. An example of that is a gland stopping excretion.
6.5.10 Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering.
1) Blood near the skin exchanges heat with the environment to preserve 37°C temperature.
2) Vasoconstriction (blood vessels become narrower) can decrease blood flow to the skin, preserving heat in the cold. Vasodilation (opposite of vasoconstriction) will cause an increase of blood flow close to the skin, so more heat will leave the body, cooling it down.
3) Sweating can cool the body as moisture on skin evaporates.
4) Shivering produces muscle heat.
6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and a and ß cells in the pancreatic islets.
1) Glucagon - released by A-cells in the pancreatic islets when blood sugar is low, it transforms stored glycogen into glucose that enters the blood stream.
2) Insulin - released by Beta cells in the pancreatic islets when blood sugar is high, it transforms glucose in blood to stored glycogen .
6.5.12 Distinguish between type I and type II diabetes.
Type I diabetes (early or juvenile onset):
Auto-immune disease in which the beta-cells pancreatic are destroyed. Unable to produce insulin. Responds well to regular injection of insulin probably manufactured as the genetically engineered humulin.
Type II diabetes (Adult onset):
Reduced sensitivity of the liver cells to insulin. Reduced number of receptors on the liver cell membrane.
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