17.4 The Peripheral Nervous System
17.4 The Peripheral Nervous System The peripheral nervous system is composed of nerves and ganglia. Nerves are bundles of axons. Ganglia are collections of cell bodies. The peripheral nervous system is subdivided into the somatic system and the autonomic system.
spinal nerve dorsal root ventral root dorsal root ganglion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. spinal nerve dorsal root ventral root dorsal root ganglion b.
Somatic System Somatic System The somatic system serves the skin, skeletal muscles, and tendons. Some actions in the somatic system are due to reflexes, which are automatic responses to a stimulus. Most actions in the somatic system are voluntary
Somatic System The Reflex Arc programmed, built-in circuits that allow for protection and survival. require no conscious thought Nerve impulses travel from the sensory neuron to the spinal cord and back to the motor neuron.
cell body of sensory neuron Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pin dorsal root ganglion dorsal horn central canal white matter sensory receptor (in skin) gray matter Dorsal dorsal horn cell body of sensory neuron axon of sensory neuron cell body of interneuron axon of motor neuron effector (muscle) ventral root cell body of motor neuron ventral horn ventral horn Ventral
Autonomic System function automatically and usually in an involuntary manner regulates the activity of cardiac and smooth muscle and glands. composed of the sympathetic and parasympathetic divisions. innervate all internal organs utilize two motor neurons that synapse at a ganglion.
Autonomic System Sympathetic Division Parasympathetic Division important during emergency situations “fight or flight” response: adrenalin released, increasing heart rate, increased breathing rate, etc. Parasympathetic Division sometimes called the housekeeper division because it promotes all the internal responses we associate with “rest and digest.”
Table 17.1