Nerves, Hormones, and Homeostasis

Topic 6.5

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.

Motor Neuron:

nodes of Ranvier

motor end plates

Motor neuron

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

Relay Neurons

Nerve Impulse(See supplemental info)

http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf

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

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

Increased body temperature·exercise or high environmental temps

Sensed by Thermoreceptors·in skin

Hypothalamus receives info·in brain

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

Sensory nerveMotor nerve

Homeostatic control of body temperature

Decreased body temperature·low environmental temps

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

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)

·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) β cells (beta) in pancreas produce insulin, a hormone2) insulin causes body cells to open protein channels and allow

glucose to diffuse into the cell by facilitated diffusion3) insulin causes the liver and muscle cells to convert

glucose to glycogen for storage

Diabetes

see supplemental info

Nerves, Hormones, and Homeostasis

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