The Nervous System The nervous system contains billions of cells called neurons. The nervous system contains billions of cells called neurons. Neurons communicate with one another through the central and peripheral nervous system. Neurons communicate with one another through the central and peripheral nervous system.

Neuron and Its Parts Neuron: Individual nerve cell; cell of the nervous system Neuron: Individual nerve cell; cell of the nervous system Dendrites: Short part of a neuron that receives messages from other neurons Dendrites: Short part of a neuron that receives messages from other neurons Soma: Cell body; body of the neuron Soma: Cell body; body of the neuron Axon: Fiber that carries information away from the cell body toward other neurons, muscles, and glands Axon: Fiber that carries information away from the cell body toward other neurons, muscles, and glands Axon Terminals (Terminal Buttons): Branches that link the dendrites and somas of other neurons Axon Terminals (Terminal Buttons): Branches that link the dendrites and somas of other neurons The Myelin Sheath: Fatty protein substance that covers some axons, increasing the speed of transmission The Myelin Sheath: Fatty protein substance that covers some axons, increasing the speed of transmission

Neuron and Its Parts (cont) The Myelin Sheath: Fatty protein substance that covers some axons, increasing the speed of transmission The Myelin Sheath: Fatty protein substance that covers some axons, increasing the speed of transmission Glia cell-Cell found in the nervous system that forms the myelin sheath Glia cell-Cell found in the nervous system that forms the myelin sheath Nodes of Ranvier-Gaps in the myelin sheath Nodes of Ranvier-Gaps in the myelin sheath Multiple Sclerosis-Disease caused by degeneration of myelin in the central nervous system. Multiple Sclerosis-Disease caused by degeneration of myelin in the central nervous system.

Figure 2.1 FIGURE 2.1 A neuron, or nerve cell. In the right foreground you can see a nerve cell fiber in cross section. The upper left photo gives a more realistic picture of the shape of neurons. Nerve impulses usually travel from the dendrites and soma to the branching ends of the axon. The nerve cell shown here is a motor neuron. The axons of motor neuron stretch from the brain and spinal cord to muscles or glands of the body.

Synapses  Messages from one neuron to another pass over a microscopic gap called a synapse Synapse: Microscopic gap between two neurons over which messages pass Synapse: Microscopic gap between two neurons over which messages pass synapse connections in the brain synapse connections in the brain

Figure 2.5 FIGURE 2.5 A highly magnified view of a synapse. Neurotransmitters are stored in tiny sacs called synaptic vesicles (VES-ihkels). When a nerve impulse reaches the end of an axon, the vesicles move to the surface and release neurotransmitters. These molecules cross the synaptic gap to affect the next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch. Some transmitter molecules excite the next neuron, and some inhibit its activity.

Neurotransmitters Chemicals that alter activity in neurons; brain chemicals that carry messages across the synaptic gap. Examples include: Chemicals that alter activity in neurons; brain chemicals that carry messages across the synaptic gap. Examples include: Excitatory: Acetylcholine (activates muscles) Dopamine (muscle control) and Serotonin (mood and appetite control) Excitatory: Acetylcholine (activates muscles) Dopamine (muscle control) and Serotonin (mood and appetite control) Inhibitory: GABA Inhibitory: GABA Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmittersReceptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters

Neural Regulators Neural Peptides: Regulate activity of other neurons Neural Peptides: Regulate activity of other neurons Endorphins: Released by pituitary gland; also help to relieve pain Endorphins: Released by pituitary gland; also help to relieve pain Agonists: Drugs that enhance the operation of a neurotransmitter (i.e. caffeine) Agonists: Drugs that enhance the operation of a neurotransmitter (i.e. caffeine) Antagonists: Drugs that block the operation of a neurotransmitter Antagonists: Drugs that block the operation of a neurotransmitter Neuromodulators: Chemicals that may have a widespread or general effect on the release of neurotransmitters (i.e. morphine) Neuromodulators: Chemicals that may have a widespread or general effect on the release of neurotransmitters (i.e. morphine)

Nerves and Neurons Nerves: Large bundles of axons and dendrites (Not neurons) Nerves: Large bundles of axons and dendrites (Not neurons) Neurogenesis: Production of new brain cells Neurogenesis: Production of new brain cells

Neural Networks Central Nervous System (CNS): Brain and spinal cord Central Nervous System (CNS): Brain and spinal cord Peripheral Nervous System (PNS): All parts of the nervous system outside of the brain and spinal cord Peripheral Nervous System (PNS): All parts of the nervous system outside of the brain and spinal cord Somatic System: Links spinal cord with body and sense organs; controls voluntary behavior Somatic System: Links spinal cord with body and sense organs; controls voluntary behavior Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressure Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressure

Figure 2.6 FIGURE 2.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

Two Divisions of the Autonomic System Sympathetic: Arouses body; emergency system Sympathetic: Arouses body; emergency system Parasympathetic: Quiets body; most active after an emotional event Parasympathetic: Quiets body; most active after an emotional event

Figure 2.8 FIGURE 2.8 Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays its messages through clusters of nerve cells outside the spinal cord.

Figure 2.7 FIGURE 2.7 Subparts of the nervous system.