Pg. 8 #10-12Pg. 8 #10-12

Homeostasis and Homeostasis and Feedback LoopsFeedback Loops

DefinitionsDefinitions

Homeostasis – state of balance in the bodyHomeostasis – state of balance in the body

Stimulus- something in the environment that Stimulus- something in the environment that causes a change (can be internal)causes a change (can be internal)

Response – action of organism as a result of Response – action of organism as a result of stimulusstimulus

Feedback mechanisms/loops – processes by Feedback mechanisms/loops – processes by which the body maintains levelswhich the body maintains levels– Usually uses nervous and hormonal cues to conduct Usually uses nervous and hormonal cues to conduct

processesprocesses

Steps in a Homeostatic Steps in a Homeostatic processprocess

When a stimulus When a stimulus occurs, each of occurs, each of these steps must these steps must occur in order for a occur in order for a response to be response to be initiatedinitiated

1) receptor must 1) receptor must recognize stimulusrecognize stimulus– Must be enough of a Must be enough of a

stimulus to surpass stimulus to surpass nervous thresholdnervous threshold

Sensory NeuronSensory Neuron

2)sensory neuron 2)sensory neuron must transmit must transmit message from the message from the receptor, to a receptor, to a control centercontrol center– Neuron = nerve cellNeuron = nerve cell– Most receptors are Most receptors are

bundled together bundled together on individual on individual neurons by regionneurons by region

Control centerControl center

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

action, spinal chord is action, spinal chord is C.C.C.C.

Motor neuronMotor neuron

4)Carries message 4)Carries message from control center from control center to effector organ to effector organ dictating responsedictating response

Effector organEffector organ

5)Receives 5)Receives message and message and conducts actual conducts actual responseresponse

Afferent vs. Efferent Afferent vs. Efferent pathwaypathway

Afferent pathwayAfferent pathway Includes receptor Includes receptor

and sensory and sensory neuron (aka neuron (aka afferent neuron)afferent neuron)

Efferent pathwayEfferent pathway Includes motor Includes motor

neuron (efferent neuron (efferent neuron) and neuron) and effector organeffector organ

Positive Feedback loopPositive Feedback loop Process by which Process by which

stimulus causes a stimulus causes a response which will response which will increase the stimulationincrease the stimulation

Ie. Oxytocin in Ie. Oxytocin in childbirth childbirth

Rate constantly Rate constantly increases until action is increases until action is completecomplete

Least commonLeast common

Graph of Positive FeedbackGraph of Positive Feedback

X-axis is timeX-axis is time

Y-axis is hormone Y-axis is hormone secretedsecreted

Negative Feedback loopsNegative Feedback loops

Receptors detect Receptors detect change and initiate change and initiate response that will response that will counter that changecounter that change

Tries to maintain a Tries to maintain a medianmedian

Ie. Blood glucose, Ie. Blood glucose, temp, blood Otemp, blood O22/CO/CO22 levelslevels

(draw graph from (draw graph from board into your notes)board into your notes)

Example: Breathing PatternExample: Breathing Pattern Body is designed to detect blood pH.Body is designed to detect blood pH. Too high = too much COToo high = too much CO22

Receptor = chemoreceptors in arteriesReceptor = chemoreceptors in arteries Afferent neuron = vagus nerveAfferent neuron = vagus nerve C.C. = brain stemC.C. = brain stem Efferent neuron = phrenic nerveEfferent neuron = phrenic nerve Effector organ = intercostals and diaphragmEffector organ = intercostals and diaphragm

High pH will trigger quicker breathing, lower High pH will trigger quicker breathing, lower pH will slow it down (negative feedback)pH will slow it down (negative feedback)