Pg 8 10 12 Homeostasis and Feedback Loops

Pg. 8 #10 -12

Homeostasis and Feedback Loops

Definitions n Homeostasis – state of balance in the body n Stimulus- something in the environment that causes a change (can be internal) n Response – action of organism as a result of stimulus n Feedback mechanisms/loops – processes by which the body maintains levels – Usually uses nervous and hormonal cues to conduct processes

Steps in a Homeostatic process When a stimulus occurs, each of these steps must occur in order for a response to be initiated n 1) receptor must recognize stimulus n – Must be enough of a stimulus to surpass nervous threshold

Sensory Neuron n 2)sensory neuron must transmit message from the receptor, to a control center – Neuron = nerve cell – Most receptors are bundled together on individual neurons by region

Control center n 3)message is carried to a control center (usually in brain), where the message is interpreted, and the correct response is coordinated. – In the case of a reflex action, spinal chord is C. C.

Motor neuron n 4)Carries message from control center to effector organ dictating response

Effector organ n 5)Receives message and conducts actual response

Afferent vs. Efferent pathway Afferent pathway n Includes receptor and sensory neuron (aka afferent neuron) n Efferent pathway n Includes motor neuron (efferent neuron) and effector organ n

Positive Feedback loop n Process by which stimulus causes a response which will increase the stimulation n Ie. Oxytocin in childbirth n Rate constantly increases until action is complete n Least common

Graph of Positive Feedback n X-axis is time n Y-axis is hormone secreted

Negative Feedback loops Receptors detect change and initiate response that will counter that change n Tries to maintain a median n Ie. Blood glucose, temp, blood O 2/CO 2 levels n (draw graph from board into your notes) n

Example: Breathing Pattern n n Body is designed to detect blood p. H. Too high = too much CO 2 n n n Receptor = chemoreceptors in arteries Afferent neuron = vagus nerve C. C. = brain stem Efferent neuron = phrenic nerve Effector organ = intercostals and diaphragm n High p. H will trigger quicker breathing, lower p. H will slow it down (negative feedback)