help keep homeostasis

sensory nerve endings

desired output causes more desired output,

this is a cycle, or a cascade reaction... not an ideal way to regulate things like temp 

Positive feedback mechanisms control self-perpetuating events that can be out of control and do not require continuous adjustment. In positive feedback mechanisms, the original stimulus is promoted rather than negated. Positive feedback increases the deviation from an ideal normal value

desired output stops further output once setpoint is reached.

this is how we maintain homeostasis

Negative feedback mechanisms act like a thermostat in the home. As the temperature rises (deviation from the ideal normal value), the thermostat detects the change and triggers the air-conditioning to turn on and cool the house. Once the temperature reaches its thermostat setting (ideal normal value), the air conditioning turns off.

3 types of cells

(with respect to division)

constantly growing and dividing

eg blood cells, epithelial tissue

not growing or dividing ordinarily, but they have the capability if stimulated

eg. liver

permanent cells

cant divide,

if they are lost due to trauma you cannot replace them.

eg muscle and most neurons

wound healing

in the epidermis

in the epidermis, keratinocytes in basal layer grow and divide sideways(under the scab)

this takes about 5 days

granulation tissue forms,

capillaries with wbc's invade damaged area

macrophages

myofibroblast make collagen. this is what fils in the wound and then it shrinks and pulls skin together

total takes about 41 days

astrocytes, ependymal cells, microglia, oligodendrytes

schwann cells

typical nerve cell

(neuron)

neurons conduct a signal

they have a body, (soma) many dendrites, and an axon

CNS is brain and spinal cord

PNS is cranial and spinal nerves

info comes from receptors, to the CNS, info is processed, then s