1. Topic 6: Human Health and Physiology
6.5 Nerves, Hormones and Homeostasis

2. The Nervous System Bit
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.(1)
6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron.(3).
6.5.2 Draw and label a diagram of the structure of a motor neuron.(1)
6.5.6 Explain the principles of synaptic transmission.(3)
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.(1)
6.5.4 Define resting potential and action potential (depolarization and repolarization).(1).

3. The Hormones and Homeostasis Bit
6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood.(1)
Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in
the pancreatic islets.(3)
6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.(3)
Distinguish between type I and type II diabetes. (2)
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.(3).

4. 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 carry rapid electrical impulses.
Nervous system is divided into
Central nervous system
Brain and spinal cord
Peripheral nervous system
The other nerves
Peripheral nerves are called neurons
They transport messages in the form of electrical impulses to specific sites
This is done very quickly by local depolarization of the cell membrane of the neuron.

5. 6.5.2 – Draw and label a diagram of the structure of a motor neuron.
A motor neuron - nerve cell which transmits impulses from the brain to a muscle or gland.

6. 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.
Reflex arc – a neural pathway that allows a quick reaction.
Pain receptor sends out an impulse (2)
Ex–a person puts his or her finger on a sharp object (1)
The impulse is carried to the CNS by a sensory neuron (3)
Inside the spinal cord the impulse is passed to a relay neuron (4)
The impulse travels from the CNS to the muscle by the motor neuron. (6)

7. 6.5.4 – Define resting potential and action potential (depolarization and repolarization)
the electrical potential (measured in millivolts, mV) across a cell membrane when not sending an impulse.
The resting potential is maintained by the active transport of Na+ outside the neuron.
Action potential
the localized reversal (depolarization) and then restoration (repolarization) of the electrical potential (mV)
measured across the membrane of a neuron as the impulse is passes along it.

8. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.

9. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
Resting potential
At rest, there is a potential difference between the outside of an axon membrane and the inside
-70 mV, this means that the outside of the cell is positive compared to the inside.
Concentrations of Na+ is higher outside when K+ concentrations are higher inside the axon.
Both have a charge of +1 so this doesn’t affect the potential difference
The Resting Potential is maintained by:
It is the distribution of Cl-.
The situation is also maintained by a selectively permeable membrane. Na+/K+ pumps (3 Na+ out for every 2 K+ in)

10. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
The Action Potential
Information travels down a neuron as an action potential
An action potential is generated by a stimulus of a receptor and from an action potential of another neuron

11. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
Step 1: Depolarization
First, the Na+ pores suddenly open
Because of the high concentration outside the cell, Na+ diffuses into the cell
Also the electrical forces will cause sodium to go from positively charged environment to negatively charged environment
Influx of positive ions reduces the potential difference – called depolarization
When the potential difference is above zero, The Na+ is only driven by diffusion forces (high to low conc. grad.)
The inside of the axon is now more positive than the outside and the Na+ move into a more positively charged area

12. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
Step 2: Repolarization
When the value reaches +40 mV, the Na+ pores close and the K+ pores open.
K+ moves through the potassium channels out of the axon. The forces are both diffusion and electrical
As a result the potential difference will begin to decrease (repolarization)
When it falls bellow zero, K+ is only driven out by diffusion forces
K+ channels will shut when the potential reaches approximately -70 mV
The potential is restored but the Na+ and K+ are in the wrong place.
Active transport will restore them to original positions.

13. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
Step 3: Repolarization
Repolarization is called the refractory period
Divided into two states
Absolute refractory state (1 msec)
Relative refractory state (up to 10 msec)
During the absolute refractory state, no new impulses are possible
During the relative refractory state, the potential is below the resting potential (-70 mV) and a stronger stimulus is necessary to generate an action potential
The refractory period is followed by the Na/K pump which returns the ions to their original sides of the membrane

14. 6.5.5 – Explain how a nerve impulse passes along a non-myelinated neuron.
The Threshold Potential
An action potential is not generated by every impulse
A threshold needs to be reached
Depolarization must reach -40 to -50 mV.
If not, the impulse fades out
This is called the “all or nothing response”

15. 6.5.6 Explain the principles of synaptic transmissions
Synapse – the small space between the pre-synaptic motor end plate and post synaptic membrane. There are electrical and chemical synapses.
Electrical Synapses
Membranes of two neurons may be very close together
The have very small pores called “gap junctions”
An impulse can travel from one membrane to another causing an action potential (electrically)
Electrical synapses are faster than chemical synapses

16. 6.5.6 Explain the principles of synaptic transmissions
Chemical Synapses
At non-electrical synapses, the impulse cannot “jump” from one neuron to the next.
It needs chemicals messengers (called neurotransmitters) to carry the impulse

17. 6.5.6 Explain the principles of synaptic transmissions
Chemical Synapses
How it works…
At the synapse, when an action potential arrives it causes a change in the membrane permeability for Ca2+ (1)
The result…Ca2+ flows into the synaptic knob
This causes vesicles containing neurotransmitters to move to the plasma membrane (2)
The vesicles fuse with the membrane and release the neurotransmitters (exocytosis) into the synaptic cleft (3)

18. 6.5.6 Explain the principles of synaptic transmissions
Chemical Synapses
How it works…(continued)
The transmitters diffuse across the synaptic cleft and attach to receptors on the post-synaptic membrane (4)
The receptor site changes its configuration and opens Na+ channels
The influx of Na+ initiates an action potential
Enzymes in the cleft breakdown the neurotransmitters and the Na+ channels close (5)
Synaptic transmissions can also be inhibitory:
The receptor site changes it configuration and opens K+ and Cl- channels
K+ moves out and Cl- moves in, which increases the distance from the threshold value (inside becomes more negative)

19. The Hormones and Homeostasis Bit
6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood.(1)
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.(3).
6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood, pH, CO2 concentration, blood glucose concentration, body temperature and water balance
Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in
the pancreatic islets.(3)
6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.(3)
Distinguish between type I and type II diabetes. (2)

20. 6.5.7 State that the endocrine system consists of glands that release hormones that are transported by the blood
The endocrine system - made up of endocrine glands that secrete hormones into the blood Hormones pass a cell and causes a reaction/response only if it has a receptor that the hormone recognizes – these cells are called “target cells”

21. 6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood, pH, CO2 concentration, blood glucose concentration, body temperature and water balance
Homeostasis – is the maintenance of the internal environment (within reasonable limits) despite fluctuations in the external environment
Internal environment – blood and tissue
Non-biological example – regulating the temperature in your home
Biological examples
pH – narrow limits (about 7.4) Blood plasma has buffers to help avoid large fluctuations
O2 and CO2 concentrations are maintained by chemoreceptors on the walls of certain blood vessels

22. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms
Negative feedback – the control process by maintaining homeostasis in such a way that an increase (or decrease) in the “situation” is always reversed. When body temperature becomes too high, the body will do everything to decrease your body temperature. Negative feedback requires sensors to measure the current situation and the sensors pass the information to a “coordinator” which knows the desired (normal) value

23. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms

24. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms

25. 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.
Remember, one of the things that the blood carries is heat. The body of mammals and birds have thermoreceptors in the skin and in the heat center of the hypothalamus of the brain. This allows the organism to monitor external and internal environmental conditions.
If an organism is too hot, it can reduce its temperature by:
1. vasodilation
2. sweating 3. decreased metabolism
4. behavior
If an organism is too cold, it can increase its temperature by:
1. vasoconstriction
2. shivering 3. increased metabolism
4. fluffing of hair

26. 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.
I’m Too Hot!
Vasodilation
Blood vessels (called arterioles) relax and become wider(dilate) in areas near the skin. This is called vasodilation.
Blood flows to the skin and the skin increases in temperature.
The heat is radiated to the environment and the body is cooled.

27. 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.
Sweating
When water changes phase from liquid to gas it requires energy
This energy is taken from the body and as a result the body is cooled.
Panting has the same effect.
Decreased metabolism
many biological reactions produce heat as a by- product
By decreasing metabolism you can decrease body temperature
Behavioral adaptations
bathing,
hiding from the sun (returning to burrow)
remove top layer of earth and lie on cool soil

28. 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.
I’m Too Cold!
Vasoconstriction
Blood vessels (called arterioles) constrict and become narrower in areas near the skin. This is called vasoconstriction.
Blood flow does not reach the skin surface
The heat is conserved in the body.

29. 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.
Shivering
repeated muscle contractions will produce heat
Increased metabolism
As mentioned before, biological reactions produce heat as a by-product
The hypothalamus senses a decrease in body temperature and stimulates the pituitary gland to produce TSH (thyroid stimulating hormone)
TSH travels in the blood stream to the thyroid gland and stimulates the thyroid gland to make TH (thyroid hormone).
Nearly every cell in the body is a target cell for TH. The thyroid hormone binds to the receptor causing the cell to increase its metabolic rate.
As a result, heat is produced.

30. 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.
Fluffing of hair or feathers
increases the thickness of the insulating layer of air (B)
Also, the contraction of the hair muscles will generate heat (A)
Behavior
Reptiles lay in the sun to increase body temperature

31. Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.
Blood glucose levels are monitored by cells in the pancreas by chemoreceptors
The pancreas is both an exocrine and endocrine gland
The endocrine cells are clustered together in groups called the islets of Langerhans.
The islets of Langerhans is where the α and β cells are located.
Islets of Langerhans

32. Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.
The digestion and absorption part
Carbohydrates are broken down into glucose in the month and later the small intestines by amylase
Glucose (and other monosaccharides) are absorbed are absorbed in the small intestines and used for cellular respiration.
If not completely used, It can be converted to glycogen and stored in the liver and muscle cells

33. Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.
If blood glucose levels are too high (1.)
the β cells in the islets of Langerhans will secrete insulin.
It is secreted into the blood and carried to all parts of the body.
The presence of insulin causes the muscles to absorb more glucose and the muscle cells and hepatocytes convert glucose into glycogen.
Also, all the cells in your body have receptors for insulin. When insulin binds to these cells, it sends a signal to tell the cell to uptake glucose from the blood.
The result…glucose levels decrease.

34. Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.
If blood glucose levels are to low (2.)
the α cells secrete glucagon.
The target cells for glucagon are the liver cells (hepatocytes) and muscle cells.
Glucagon binds to receptors on the muscle cells and the hepatocytes.
The cells respond to the glucagon by converting the stored glycogen in the cell to glucose and releasing it into the blood.

35. 6.5.12 Distinguish between type I and type II diabetes
Type I (Early Onset)
Type II (Late Onset)
Epidemiology
Cause
Treatment
combination of insufficient amounts of insulin are produced and the cells are less sensitive to insulin because the insulin receptors are deficient in target cells
no insulin or insufficient levels are produced by the β cells
an antibody is produced that attacks the β cells and/or insulin (Type I diabetes is and autoimmune disease)
obesity, increase in age and family history
inject insulin daily or pancreas transplantation
reduce the amount of carbohydrates ingested, weight loss, insulin injections and medication