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The Nervous System Functions of the Nervous System Figure 7.1 Functions of the Nervous System Sensory input — gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed Functions of the Nervous System Motor output A response to integrated stimuli The response activates muscles or glands Crash Course: Part 1 https://www.youtube.com/watch?v=qPix_X-9t7E Organization of the Nervous System Figure 7.2 Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerves outside the brain and spinal cord Spinal nerves Cranial nerves Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary Neuron Classification Figure 7.6 Neurons = nerve cells Cells specialized to transmit messages Figure 7.4 Nervous Tissue: Neurons Figure 7.5 Nervous Tissue: Neurons Cell body Main functional unit of the neuron Contains: Nucleus Large nucleolus Processes outside the cell body Dendrites—conduct impulses toward the cell body Axons—conduct impulses away from the cell body Dendrite - conduct impulses toward the cell body Nissle substance (bodies) – rough ER Neurofibrils – filaments that help maintain cell shape Axon hillock – the beginning of the axon Axon - conduct impulses away from the cell body Schwann cells – cells that surround the axon Nodes of Ranvier -- gaps in myelin sheath along the axon Myelin sheath -- white, fatty material covering axons (insulates) Axon terminals – ends of the axon Nervous Tissue: Neurons Axons end in axonal terminals Most cells average about 10,000 axon terminals Axon terminals contain vesicles with neurotransmitters (chemicals that excite or inhibit neurons or effector cells) Axon terminals are separated from the next neuron by a gap Synaptic cleft—gap between adjacent neurons Synapse—junction between nerves Neuron Cell Body Location Most neuron cell bodies are found in the central nervous system WHITE MATTER – condensed areas of myelinated fibers GRAY MATTER — areas of unmyelinated fibers Ganglia —collections of cell bodies outside the central nervous system Structural Classification of Neurons Multipolar neurons—many extensions from the cell body Where found? BRAIN Figure 7.8a Structural Classification of Neurons Bipolar neurons—one axon and one dendrite Where found? SENSE ORGANS Figure 7.8b Structural Classification of Neurons Unipolar neurons—have a short single process leaving the cell body Where found? SKIN Figure 7.8c Crash Course: Part 2 https://www.youtube.com/watch?v=OZG8M_ldA1M Nerve Impulse The principle way neurons communicate is by generating and propagating ACTION POTENTIALS (AP). Only cells with excitable membranes (like muscle cells and neurons) can generate APs. An AP is a brief reversal of membrane potential. In neurons, an AP is called a NERVE IMPULSE and only axons can generate one. An AP involves the movement of Na+ and K+ ions moving in and out of the neuron, resulting in changes in POLARITY. All or None Response If the action potential (nerve impulse) starts, it is propagated over the entire axon There are NO partial impulses. The impulse happens completely or not at all. Impulses travel faster when fibers have a myelin sheath. Action Potential First, remember how DIFFUSION works… http://www.youtube.com/watch?v=OXCKjhE1xco Bozeman Nerve Impulses Resting neuron The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell Depolarization A stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron Nerve Impulses Repolarization Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane The sodium-potassium pump, using ATP, restores the original configuration Action Potential video http://www.youtube.com/watch?feature=player_detail page&v=yQ-wQsEK21E Nerve Impulses Figure 7.9a–b Nerve Impulses Figure 7.9c–d Nerve Impulses Figure 7.9e–f Action Potential explained https://www.youtube.com/watch?v=SdUUP2pMmQ4 Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Transmission of a Signal at Synapses Synaptic cleft Receiving neuron Synapse Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Synaptic cleft Ion channels Neurotransmitter binds to receptor on receiving neuron’s membrane Receiving neuron Neurotransmitter Receptor Neurotransmitter broken down and released Na+ Na+ Ion channel opens Ion channel closes Figure 7.10 Axon of transmitting neuron Axon terminal Action Action potential potential arrives arrives Vesicles Synaptic cleft Receiving neuron Synapse Figure 7.10, step 1 Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Synaptic cleft Receiving neuron Synapse 2. Vesicle fuses with plasma membrane Transmitting neuron Vesicle fuses with plasma membrane Synaptic cleft Ion channels Receiving neuron Figure 7.10, step 2 Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Synaptic cleft Receiving neuron Synapse Transmitting neuron 3. Neurotransmitter is released into synaptic cleft Vesicle fuses with plasma membrane Synaptic cleft Ion channels Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Receiving neuron Figure 7.10, step 3 Axon of transmitting neuron Axon terminal Action potential arrives Vesicles Synaptic cleft Axon of Receiving transmitting neuron neuron Axon terminal Action potential Synapse arrives Vesicles Transmitting neuron Neurotransmitter binds to receptor on receiving neuron’s membrane Synaptic cleft Vesicle fuses with plasma membrane Transmitting neuron Neurotransmitter is released into synaptic cleft Receiving neuron Synapse 4. Neurotransmitter binds to receptor on receiving neuron’s membrane Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Synaptic cleft Ion channels Synaptic cleft Ion channels Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter molecules Neurotransmitter Receiving neuron molecules Receiving neuron Figure 7.10, step 4 Receiving neuron Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft Synapse Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter molecules Synaptic cleft Ion channels Receiving neuron Neurotransmitter Receptor Na+ Figure 7.10, step 5 Ion channel opens Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter is released into synaptic cleft Transmission of a Signal at Synapses Neurotransmitter molecules Synaptic cleft Ion channels Receiving neuron Neurotransmitter broken down and released Neurotransmitter Receptor Na+ Na+ Figure 7.10, step 6 Ion channel opens Ion channel closes Transmitting neuron Vesicle fuses with plasma membrane Neurotransmitter binds to receptor on receiving neuron’s membrane Neurotransmitter is released into synaptic cleft Neurotransmitter molecules Synaptic cleft Ion channels Receiving neuron Neurotransmitter broken down and released Neurotransmitter Receptor Na+ Na+ Figure 7.10, step 7 Ion channel opens Ion channel closes