The Peripheral Nervous System PART 1 The Peripheral Nervous System

The Peripheral Nervous System Nervous structures outside the brain and spinal cord Nerves allow the CNS to receive information and take action Functional components of the PNS Sensory inputs and motor outputs Categorized as somatic or visceral Sensory inputs also classified as general or special Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Peripheral Nervous System Autonomic nervous system (ANS) General visceral motor part of the PNS ANS has two divisions Parasympathetic Sympathetic Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Functional Organization of the PNS Figure 14.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Basic Structural Components of the PNS Sensory receptors – pick up stimuli from inside or outside the body Motor endings – axon terminals of motor neurons Innervate effectors (muscle fibers and glands) Nerves and ganglia Nerves – bundles of peripheral axons Ganglia – clusters of peripheral neuronal cell bodies Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve Figure 14.2 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Peripheral Sensory Receptors Structures that pick up sensory stimuli Initiate signals in sensory axons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Peripheral Sensory Receptors Two main categories of sensory receptors Free nerve endings of sensory neurons Monitor general sensory information Complete receptor cells – specialized epithelial cells or small neurons Monitor most types of special sensory information Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Peripheral Sensory Receptors Wednesday Sensory receptors also classified according to Location Type of stimulus detected Structure Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Location Exteroceptors – sensitive to stimuli arising from outside the body Located at or near body surfaces Include receptors for touch, pressure, pain, and temperature Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Location Interoceptors – (visceroceptors) receive stimuli from internal viscera Monitor a variety of stimuli Proprioceptors – monitor degree of stretch Located in musculoskeletal organs Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Stimulus Detected Mechanoreceptors – respond to mechanical forces Thermoreceptors – respond to temperature changes Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Stimulus Detected Chemoreceptors Respond to chemicals in solution Photoreceptors – respond to light Located in the eye Nociceptors Respond to harmful stimuli that result in pain Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Structure General sensory receptors Widely distributed Nerve endings of sensory neurons monitor Touch Pressure Vibration Stretch Pain Temperature Proprioception Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Classification by Structure General sensory receptors are Divided into two groups Free nerve endings Encapsulated nerve endings Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Abundant in epithelia and underlying connective tissue Free Nerve Endings Abundant in epithelia and underlying connective tissue Respond to pain and temperature Monitor affective senses Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Two specialized types of free nerve endings Merkel discs – lie in the epidermis Slowly adapting receptors for light touch Hair follicle receptors – wrap around hair follicles Rapidly adapting receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Unencapsulated Nerve Endings Table 14.1 (1 of 4) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Encapsulated Nerve Endings Consist of one or more end fibers of sensory neurons Enclosed in connective tissue Mechanoreceptors Include four main types Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Encapsulated Nerve Endings Meissner’s corpuscles Spiraling nerve ending surrounded by Schwann cells Occur in the dermal papillae Rapidly adapting receptors for discriminative touch Occur in sensitive, hairless areas of the skin Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Meissner’s Corpuscles Table 14.1 (2 of 4) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Encapsulated Nerve Endings Pacinian corpuscles Single nerve ending surrounded by layers of flattened Schwann cells Occur in the hypodermis Sensitive to deep pressure – rapidly adapting receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Encapsulated Nerve Endings Ruffini’s corpuscles Located in the dermis and respond to pressure Monitor continuous pressure on the skin – adapt slowly Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Pacinian Corpuscles and Ruffini’s Corpuscles Table 14.1 (3 of 4) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Encapsulated Nerve Endings Proprioceptors Monitor stretch in locomotory organs Three types of proprioceptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Three Types of Proprioceptors Muscle spindles – measure the changing length of a muscle Imbedded in the perimysium between muscle fascicles Golgi tendon organs – located near the muscle-tendon junction Monitor tension within tendons Joint kinesthetic receptors Sensory nerve endings within the joint capsules Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Proprioceptors Table 14.1 (4 of 4) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Structure of Proprioceptors Figure 14.4 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Peripheral Nervous System PART 2 The Peripheral Nervous System

Attach to the brain and pass through foramina of the skull 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) extends into the abdomen Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The 12 Pairs of Cranial Nerves Figure 14.5 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory nerves of smell Olfactory Nerves Sensory nerves of smell Table 14.3 (1 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Sensory nerve of vision Optic Nerve Sensory nerve of vision Table 14.3 (2 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervates four of the extrinsic eye muscles Oculomotor Nerve Innervates four of the extrinsic eye muscles Table 14.3 (3 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervates the superior oblique muscle (an extrinsic eye muscle) Trochlear Nerve Innervates the superior oblique muscle (an extrinsic eye muscle) Table 14.3 (4 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Provides sensory innervation to the face Trigeminal Nerve Provides sensory innervation to the face Motor innervation to chewing muscles Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Trigeminal Nerve Table 14.3 (5 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Peripheral Nervous System PART 3 The Peripheral Nervous System

Abducts the eyeball – innervates lateral rectus muscle Abducens Nerve Abducts the eyeball – innervates lateral rectus muscle Table 14.3 (6 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervates muscles of facial expression Facial Nerve Innervates muscles of facial expression Table 14.3 (7 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Vestibulocochlear Nerve Sensory nerve of hearing and balance Table 14.3 (8 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Glossopharyngeal Nerve Innervates structures of the tongue and pharynx Table 14.3 (9 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

A mixed sensory and motor nerve Vagus Nerve A mixed sensory and motor nerve “Wanders” into thorax and abdomen Parasympathetic innervation of organs Table 14.3 (10 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

An accessory part of the vagus nerve Accessory Nerve An accessory part of the vagus nerve Innervates trapezius muscle Table 14.3 (11 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Runs inferior to the tongue Hypoglossal Nerve Runs inferior to the tongue Innervates the tongue muscles Table 14.3 (12 of 12) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Peripheral Nervous System PART 4 The Peripheral Nervous System

31 pairs – contain thousands of nerve fibers 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) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Spinal Nerves Posterior View Figure 14.6 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Connect to the spinal cord by the dorsal root and ventral root Spinal Nerves Connect to the spinal cord by the dorsal root and ventral root Dorsal root – contains sensory fibers Cell bodies – located in the dorsal root ganglion Ventral root – contains motor fibers arising from anterior gray column Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Branch into dorsal ramus and ventral ramus Spinal Nerves Branch into dorsal ramus and ventral ramus Dorsal and ventral rami contain sensory and motor fibers Rami communicantes connect to the base of the ventral ramus Lead to the sympathetic chain ganglia (Chapter 15) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Spinal Nerves Figure 14.7a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Back Dorsal rami Innervate back muscles Follow a neat, segmented pattern Innervate a horizontal strip of muscle and skin In line with emergence point from the vertebral column Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Back Figure 14.7b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Anterior Thoracic and Abdominal Wall Thoracic region Ventral rami arranged in simple, segmented pattern Intercostal nerves – supply intercostal muscles, skin, and abdominal wall Each gives off lateral and anterior cutaneous branches Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Introduction to Nerve Plexuses Nerve plexus – a network of nerves Ventral rami (except T2 – T12) Branch and join with one another Form nerve plexuses In cervical, brachial, lumbar, and sacral regions Primarily serve the limbs Fibers from ventral rami crisscross Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Formed by ventral rami of first four cervical nerves (cn 1 – 4) The Cervical Plexus Buried deep in the neck Under the sternocleidomastoid muscle Formed by ventral rami of first four cervical nerves (cn 1 – 4) Most are cutaneous nerves Some innervate muscles of the anterior neck Phrenic nerve – the most important nerve of the cervical plexus Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Brachial Plexus and Innervation of the Upper Limb Brachial plexus lies in the neck and axilla Formed by ventral rami of C5 – C8 Cords give rise to main nerves of the upper limb Figure 14.9d Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Nerves from the Lateral and Medial Cords Musculocutaneous – main branch of the lateral cord Innervates the biceps brachii and brachialis Median – originates from both lateral and medial cords Innervates anterior forearm muscles and lateral palm Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Nerves from the Lateral and Medial Cords Ulnar – branches from the medial cord Innervates intrinsic hand muscles and skin of the medial hand Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Nerves from the Posterior Cord Radial – continuation of the posterior cord Largest branch of the brachial plexus Innervates muscles of the posterior upper limb Axillary Innervates the deltoid and teres minor Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Brachial Plexus Figure 14.9a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Axillary and Radial Nerves Figure 14.11 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Peripheral Nervous System PART 5 The Peripheral Nervous System

The Lumbar Plexus and Innervation of the Lower Limb Arises from L1– L4 Smaller branches innervate the posterior abdominal wall and psoas muscle Main branches innervate the anterior thigh Femoral nerve – innervates anterior thigh muscles Obturator nerve – innervates adductor muscles Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Lumbar Plexus Figure 14.12a, b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Arises from spinal nerves L4–S4 Caudal to the lumbar plexus The Sacral Plexus Arises from spinal nerves L4–S4 Caudal to the lumbar plexus Often considered with the lumbar plexus Lumbosacral plexus Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Lower Limb Sciatic nerve – the largest nerve of the sacral plexus Actually two nerves in one sheath Tibial nerve – innervates most of the posterior lower limb Common fibular (peroneal) nerve – innervates muscles of the anterolateral leg Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Lower Limb Superior and inferior gluteal nerves Innervate the gluteal muscles Pudendal nerve Innervates muscles of the perineum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Sacral Plexus Figure 14.13 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Innervation of the Skin: Dermatomes Dermatome – an area of skin Innervated by cutaneous branches of a single spinal nerve Upper limb Skin is supplied by nerves of the brachial plexus Lower limb Lumbar nerves – anterior surface Sacral nerves – posterior surface Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Map of Dermatomes – Anterior View Figure 14.14a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Map of Dermatomes – Posterior View Figure 14.14b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Shingles (herpes zoster) Disorders of the PNS Shingles (herpes zoster) Viral infection Stems from childhood chicken pox Often brought on by stress Mostly experienced by those over 50 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Disorders of the PNS Migraine headache Myasthenia gravis Relates to sensory innervation of cerebral arteries Arteries dilate and compresses and irritate sensory nerve endings Myasthenia gravis Progressive weakening of the skeletal muscles An autoimmune disorder Antibodies destroy acetylcholine receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The PNS Throughout Life Spinal nerves form late in week 4 Each of the 31 pairs of spinal nerves Sends motor fibers to an individual myotome Sends sensory fibers to the overlying band of skin During week 5 nerves reach the organs they innervate Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The PNS Throughout Life Embryonic muscles migrate to new locations Some skin dermatomes become displaced Muscles and skin always retain their original nerve supply Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings