THE NERVOUS SYSTEM CH 48 AND 49 Designed to sense an animal’s external environment, initiate a response, and return the animal to HOMEOSTASIS Involves a series of cell-cell interactions

I. Nervous systems consist of circuits of neurons and supporting cells Single celled organisms can respond to environment Most multicelled animals need neurons Simplest nervous system is in cnidarians, radially symmetrical animals with nerve net All bilaterally symmetrical animals have centralized nervous system

What is the trend here? Importance?

II. The vertebrate nervous system A. Organization of the nervous system Central nervous system (CNS) – Brain and spine – Where integration takes place Peripheral nervous system (PNS) – Neurons that send info to CNS and receive info from CNS – Sensory neurons: send info to CNS – Motor neurons: receive info from CNS

B. Neurons Sensory (afferent) neurons – carry nerve impulses from the sensory receptors to the CNS – sensory receptors are located in: – skin, eyes, ears, mouth, nose Motor (efferent) neurons – Carry the nerve impulse from the CNS to effectors – Effectors are muscles and glands interneurons – Located in the CNS – link sensory and motor neurons

Sense receptors send info to sense neurons which send info to interneurons which send info to motor neurons which send info to muscles or glands

1. Neuron structure and function Cell body: contains organelles Dendrites: short extensions off cell body that receive signals Axon: Long extension off of the cell body that relays the stimulus synaptic terminal: sends info from one cell to another thru neurotransmitters synapse: space between two cells

presynaptic cell sends info to postsynaptic cell

C. How information is sent thru the nervous system all cells have a difference in charge on either side of plasma membrane called a membrane potential Rest membrane potential: Membrane potential of unstimulated neuron Change in resting membrane potential results in transmission of nerve impulse

What do you notice about the resting membrane potential?

1. Forming the resting membrane potential Uses energy in active transport [ K + ] is highest in cell, [Na + ] is highest out Na+/K+ pumps use NRG of ATP to maintain these K + and Na + gradients across the plasma membrane (active transport: low to high concentration using NRG) These concentration gradients represent chemical potential energy

2. Generating the action potential Stimulus from the environment causes the membrane of the nerve cell to depolarize: – Na+ diffuses into the nerve cell – K+ diffuses out As soon as this happens, the Na+/K+ pump restores the membrane potential

3. Propagating the action potential The action potential travels down the nerve cell from dendrites to axon in a wave of depolarization and restoration of the membrane potential

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D. How the nerve impulse moves from one cell to another The space between two nerve cells is called a synapse Two nerves communicate with each other by synaptic signaling How: – When the action potential reaches the end of the axon, it stimulates the release of neurotransmitters into the synapse – The neurotransmitters bind to receptors on the postsynaptic cell to transmit the nerve impulse

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E. What are neurotransmitters? Small molecules stored in vesicles in the presynaptic neuron Most are made in RER and golgi

Types: – Dopamine: the “reward” neurotransmitter, cocaine and meth increase dopamine release – Serotonin: the “feel good” neurotransmitter. MDMA either increases or prevents degradation of serotonin. Low serotonin is associated with depression – Acetylcholine: involved in muscle contraction. Broken down by acetylcholinesterase to control muscle contraction M&list=PLFCE4D99C4124A27A&index=50 M&list=PLFCE4D99C4124A27A&index=50