G.Response - Stimulus/Response Respond to Stimuli Respond...

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Stimulus/Response Heyer 1 Respond to Stimuli A key characteristic of Life Respond to Stimuli stimulus sensor Integration & Cognition effector response Respond to Stimuli: Nervous System stimulus sensor effector Sensory Nerves Motor Nerves Central Nervous System = specific muscle or gland response Respond to Stimuli: Endocrine System stimulus sensor Endocrine Gland effector response effector response effector response Nervous System via bloodstream effector = various target tissues throughout the body response Cellular Communication — Chemical Messengers & Receptors 1. Synapse: the messenger (neurotransmitter) diffuses across a small gap between a neuron and its target cell (effector). 2. Paracrine: the messenger (paracrine factor, growth factor, cytokine) diffuses to nearby target cells. 3. Endocrine: the messenger (hormone) diffuses into the bloodstream to travel to target cells all over the body. 4. Exocrine: the messenger (pheromone) diffuses outside of the organism’s body to travel to another organism. One cell releases a molecule (messenger) that initiates a change in another cell by binding to a protein receptor on that target cell. Neurons conduct impulses and transmit electrochemical messages to other cells
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Stimulus/Response Heyer 2 Parts of a Neuron • Cell body: location of the cell’s nucleus and most other major organelles. • Dendrites: highly branched extensions of the cell body membrane to increase surface area for receiving excitatory and inhibitory stimuli. May be several hundred per cell. Parts of a Neuron • Axon: long extension that can initiate and conduct nerve impulses. – Only one per cell — but may be branched. – Impulse is initiated at the hillock adjacent to the cell body; then conducted outward to the axon terminus. – The axon may be wrapped by glial cells in a segmented myelin coat that increases the conduction rate of the axon. Electrochemical Signaling • Electrical potential • Excitability • Conduction • Transmission Membranes of neurons are electrically charged Chemical gradients of ions produces electrical gradients Electrical gradient produces a membrane potential Membranes are electrically charged Voltage (= electrical potential ): – The difference in charge between two points – Potential energy created by attractive forces between opposite charges separated by distance. Membrane potential: – difference in charge between inside of cell membrane and outside. – Always measured as the charge inside the cell relative to outside. – Units: millivolts (mV). Significant ions Fig. 6.23
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Stimulus/Response Heyer 3 Resting Membrane Potential Depends upon 2 factors: Ratio of the concentrations of each ion on the 2 sides of the plasma membrane.
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