The Peripheral Nervous System Chapter 13

Functional Organization of the PNS Central nervous system (CNS) Peripheral nervous system (PNS) Motor (efferent) division Sensory (afferent) division Sympathetic division Parasympathetic Somatic sensory General: Touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs Special: Hearing, equilibrium, vision Visceral sensory General: Stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger Special: Taste, smell Somatic nervous system Motor innervation of all skeletal muscles Autonomic nervous system (ANS) Motor innervation of smooth muscle, cardiac muscle, and glands Figure 14.1

Figure 7.25 Slide 7.73 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Cranial Nerves Attach to the brain and pass through foramina of the skull Numbered from I–XII Cranial nerves I and II attach to the forebrain All others attach to the brain stem Primarily serve head and neck structures The vagus nerve (X) is the only cranial nerve that extends into the abdomen

Hypoglossal nerve (XII) The Cranial Nerves Frontal lobe Temporal lobe Infundibulum Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Filaments of olfactory nerve (I) Olfactory bulb Olfactory tract Optic chiasma Optic nerve (II) Optic tract Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Cerebellum Medulla oblongata Figure 14.4a

Spinal Nerves Posterior View Cervical nerves C1 – C8 Thoracic T1 – T12 Lumbar L1 – L5 Sacral S1 – S5 Coccygeal nerve Co1 Cervical plexus Intercostal enlargement Cauda equina Brachial plexus Lumbar plexus Sacral plexus Figure 14.5

Spinal Nerves 31 pairs—contain thousands of nerve fibers Connect to the spinal cord Named for point of issue from the spinal cord 8 pairs of cervical nerves (C1–C8) 12 pairs of thoracic nerves (T1–T12) 5 pairs of lumbar nerves (L1–L5) 5 pairs of sacral nerves (S1–S5) 1 pair of coccygeal nerves (Co1)

Spinal Nerves Sensory axon and cell body Dorsal root ganglion Dorsal Axon of motor neuron Ventral ramus root Neuromuscular junction Sensory receptors in skin (e.g., free nerve endings of sensory neuron) Dorsal root ganglion Dorsal Sensory axon and cell body Nerves Figure 14.6

Sensory Receptors: Classification by Stimulus Type Mechanoreceptors—respond to touch, pressure, vibration, and stretch Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (e.g., retina) Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

Spinal Nerves and Nerve Plexuses Characteristics: Somatic sensation (conscious) and somatic motor control (voluntary control) of skeletal muscles. Mixed nerves Sensory Motor Dorsal and ventral rami (nerve branches)  plexuses (network of nerves)

Comparison of Somatic and Autonomic Nervous Systems Figure 7.24 Slide 7.69 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Cord Anatomy Exterior white mater – conduction tracts Figure 7.19 Slide 7.53a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Cord Anatomy Internal gray matter - mostly cell bodies Dorsal (posterior) horns Anterior (ventral) horns Figure 7.19 Slide 7.53b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Peripheral Nervous System Nerves and ganglia outside the central nervous system Nerve = bundle of neuron fibers Neuron fibers are bundled by connective tissue Slide 7.55 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of a Nerve Endoneurium surrounds each fiber Groups of fibers are bound into fascicles by perineurium Fascicles are bound together by epineurium Figure 7.20 Slide 7.56 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Classification of Nerves Mixed nerves – both sensory and motor fibers Afferent (sensory) nerves – carry impulses toward the CNS Efferent (motor) nerves – carry impulses away from the CNS Slide 7.57 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Nerves There is a pair of spinal nerves at the level of each vertebrae. Slide 7.63 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Nervous System The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions Sympathetic division Parasympathetic division Slide 7.67 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Functioning Sympathetic – “fight-or-flight” Response to unusual stimulus Takes over to increase activities Remember as the “E” division = exercise, excitement, emergency, and embarrassment Slide 7.74a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Autonomic Functioning Parasympathetic – housekeeping activites Conserves energy Maintains daily necessary body functions Remember as the “D” division - digestion, defecation, and diuresis Slide 7.74b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Development Aspects of the Nervous System The nervous system is formed during the first month of embryonic development Any maternal infection can have extremely harmful effects The hypothalamus is one of the last areas of the brain to develop Slide 7.75a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Development Aspects of the Nervous System No more neurons are formed after birth, but growth and maturation continues for several years (new evidence!) The brain reaches maximum weight as a young adult However, we can always grow dendrites! Slide 7.75b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings