Nerves, Hormones, and Homeostasis

1. Nerves, Hormones, and Homeostasis Topic 6.5

2. The vertebrate nervous system has two main divisions: ·Central Nervous System (CNS): consists of the brain and spinal cord. ·Peripheral Nervous System (PNS): consists of all the nerves and their branches that enter and leave the brain and spinal cord.

3. Motor Neuron:

4. Motor neuron motor end plates nodes of Ranvier

5. Nerves are made up of 3 types of neurons (nerve cells): ·Sensory neurons: bring information to the CNS from receptors ·Relay neurons: conduct nerve impulses within the CNS ·Motor neurons: carry response information to the muscles

7. Relay Neurons

8. Nerve Impulse (See supplemental info) http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf

9. Homeostasis ·Human body usually stays within certain limits for many physiological variables - blood pH - CO2 concentration - body temp - blood glucose concen. - water balance w/in tissues ·Each variable has an expected value or set point - ie Body temp = 98.6 ℉ or 37 ℃ ·Fluctuations above and below are inevitable

10. Negative feedback mechanisms ·physiological changes that bring a value back closer to a set point ·nervous system and endocrine system work together to ensure homeostatis house example

11. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

12. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

13. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

14. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

15. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

16. Homeostatic control of body temperature Sensed by Thermoreceptors ·in skin Increased body temperature ·exercise or high environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated cooling mechanisms ·increased activity of sweat glands leads to evaporative cooling effect of perspiration ·dilation of arterioles in skin, fills capillaries with blood, allows heat to radiate out of skin

17. Sensed by Thermoreceptors ·in skin Decreased body temperature ·low environmental temps Hypothalamus receives info ·in brain Sensory nerve Motor nerve Activated warming mechanisms ·stimulates skeletal muscles to shiver, generating body heat ·constriction of arterioles in skin so blood is diverted to deeper tissues and less heat is lost

18. Control of Blood Glucose Concentration ·Although other sugars exist in the blood, it is glucose that is most important and is monitored in order to maintain homeostasis ·Levels rise after meals and are usually lowest in the morning before breakfast ·If levels drop too low, hypoglycemia develops - symptoms include lethargy, impaired mental function and irritability ·If levels are too high, hyperglycemia develops - symptoms include diabetes and its associated problems (eye, kidney, and nerve damage)

19. ·Glucose levels are monitored by cells in the pancreas ·If blood glucose drops to a dangerous level: 1) α cells (alpha) in pancreas produce glucagon, a hormone 2) glucagon activates liver and muscle cells to convert glycogen to glucose (glycogenolysis) and thus raise blood sugar ·If blood levels of blood sugar rise (either due to a meal or as a result of glycogen conversion) 1) βcells (beta) in pancreas produce insulin, a hormone 2) insulin causes body cells to open protein channels and allow glucose to diffuse into the cell by facilitated diffusion 3) insulin causes the liver and muscle cells to convert glucose to glycogen for storage

21. Diabetes see supplemental info