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Nervous System

Nervous System. FUNCTION: Senses, processes, interprets, and determines the response to stimuli from the environment Central Nervous System (CNS) - made of the brain and spinal chord Peripheral Nervous System (PNS) - all nerve cells outside of the CNS .

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Nervous System

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  1. Nervous System FUNCTION: Senses, processes, interprets, and determines the response to stimuli from the environment • Central Nervous System (CNS) - made of the brain and spinal chord • Peripheral Nervous System (PNS) - all nerve cells outside of the CNS

  2. Divisions of the Nervous System (see pages 388-89 for more detail on each) Sensory division - receives Information (senses) Motor division - relays information to organs/glands voluntary involuntary “Fight or flight” “rest & digest”

  3. Cells of the Nervous System • Neurons - cells that conduct nerve impulses (action potentials) to communicate with organs and glands • Neuroglia (glial cells) - support, protect and nourish neurons (do not send nerve impulses

  4. Structure of a Neuron • Axon - transmits nerve impulses to communicate with other cells and organs • Dendrites - receive signals from other neurons • Myelin sheath - fatty coating on axon that speeds up action potential • Nodes of Ranvier - gaps in the myelin sheath where the axon is exposed • Cell body - part of neuron from which dendrites arise (also contains nucleus of cell) • Axon terminals - end of axon/part that releases neurotransmitters to communicate with other neurons

  5. Functional Regions of the Neuron • Receptive zone • Receives • input from other • neurons • Conducting zone • generates action potential • (nerve impulse) • Secretory zone • Releases • neurotransmitters

  6. Functional Classification of Neurons Sensory (afferent) neurons • Receive information from the environment (senses) Motor (efferent) neurons • Send signals to muscles/glands/organs to carry out response Interneurons • Relay signals between sensory and motor neurons

  7. Nerves vs. Neurons Nerves are bundles of neurons

  8. Synapse - area where two or more neurons communicate with each other

  9. Action Potentials • A brief reversal in charge across a membrane • Happens in the axon membrane at Nodes of Ranvier (Saltatory conduction) • Voltage gated ion channels for Na+ and K+ open and close in response to changes in membrane potential (charge) Action potential is initiated by the axon hillock

  10. Stages of an Action Potential • More Na+ outside cell/more K+ inside • Na+ enters the axon (charge becomes more positive - depolarization) • K+ leaves axon (charge becomes more negative) • Too much K+ has left (hyperpolarization - more negative than resting) • Na/K pump restores original conditions View action potential stages in action

  11. Neurotransmitters • Chemical messengers that cross the synapse allowing one neuron to communicate with another • Can be excitatory (cause post-synaptic neuron to depolarize (become more positive)) • Can be inhibitory (cause post synaptic membrane to hyperpolarize (become more negative))

  12. Neurotransmitters (cont.) • Stored in vesicles in axon terminals • Ca2+ rushes into the terminal in response to arriving action potentials • Ca2+ causes vesicles to release neurotransmitters into synaptic cleft (example) • Neurotransmitters bind to their receptors on the post-synaptic membrane • Neurotransmitters are broken down by enzymes in the synaptic cleft or are taken back up by the pre-synaptic neuron via transporter proteins

  13. Neurotransmitters (cont) Examples: • GABA (inhibitory) • Glutamate (excitatory) • Dopamine, serotonin, norepinephrine (excitatory or inhibitory depending on the nature of the synapse) • Over 50 identified

  14. IPSP vs. EPSP • Inhibitory post-synaptic potentials (IPSP) decrease the likelihood of the post-synaptic neuron sending an action potential (hyperpolarizes post-synaptic neuron: lets Cl- in or lets K+ out) • Excitatory post-synaptic potentials (EPSP) increase the likelihood of the post-synaptic neuron sending an action potential (depolarizes post-synaptic neuron: lets Na+ in)

  15. Summation • Additive effect of the inputs of all pre-synaptic neurons • If there are more excitatory than inhibitory signals, then depolarization may occur and an action potential may be sent by the post-synaptic neuron

  16. Long-term Potentiation (LTP) • LTP is the long-lasting strengthening of synapses between two neurons • Post-synaptic neurons become more sensitive to neurotransmitters coming from the pre-synaptic neuron(s) by: 1) making more receptors 2) increased sensitivity of existing receptors • Involved in learning and memory formation

  17. BEFORE: Glutamate (excitatory neurotransmitter) stimulates NMDA receptors (in green) at a high frequency AFTER: Because of the frequency of stimulation, there is an increase in the number and sensitivity of receptors on the post-synaptic neuron (increasing the strength of the synapse) What causes this to happen?

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