Anatomy and Physiology / Unit 6: The Nervous System and Senses
6.1 Organization of the Nervous System and Neuron Structure
Notes
The central nervous system (CNS) is the brain and spinal cord. The peripheral nervous system (PNS) is the nerves outside. The PNS has a sensory (afferent) division carrying information to the CNS and a motor (efferent) division carrying commands out.
- Motor division: somatic (voluntary, skeletal muscle) and autonomic (involuntary: smooth muscle, cardiac muscle, glands). The autonomic system has sympathetic ("fight or flight") and parasympathetic ("rest and digest") parts.
- A neuron has a cell body (soma), dendrites (receive signals), and one axon (sends signals away). Many axons are wrapped in a fatty myelin sheath that speeds conduction; gaps between wraps are nodes of Ranvier.
- Glial cells support neurons. In the CNS, oligodendrocytes make myelin; in the PNS, Schwann cells do. Astrocytes help form the blood-brain barrier.
- Multiple sclerosis is an autoimmune destruction of CNS myelin.
Practice
Which part of a neuron receives incoming signals?
Dendrites receive signals and carry them toward the cell body.
A runner's heart rate rises and her pupils dilate during a race start. Which division is most active?
The sympathetic division prepares the body for action.
Which cell forms myelin around axons in the peripheral nervous system?
Schwann cells wrap PNS axons, while oligodendrocytes do so in the CNS.
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