Copyright 2010, John Wiley & Sons, Inc. Chapter 14 The Peripheral Nervous System

Copyright 2010, John Wiley & Sons, Inc. Chapter 14: The Peripheral Nervous System The peripheral nervous system consists of nerves and ganglia outside of the CNS. There are two functional subdivisions of the PNS  Somatic nervous system - consists of sensory (or afferent) nerves and motor (or efferent) nerves. These nerves carry signals from somatic receptors and to skeletal muscles. The somatic nervous system controls voluntary / conscious activities.  Autonomic nervous system - includes autonomic sensory nerves and autonomic motor nerves. The autonomic integrating centers in the CNS are usually included with this system. The autonomic nervous system controls involuntary / unconscious regulation of cardiac muscle, smooth muscle, and glands.

Copyright 2010, John Wiley & Sons, Inc. Nerves Nerves contain nerve fibers, connective tissues, and blood vessels Nerves contain several notable connective tissue layers:  Endoneurium  Fascicles  Perineurium  Epineurium

Copyright 2010, John Wiley & Sons, Inc. Nerves

Copyright 2010, John Wiley & Sons, Inc. Nerves

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerves Twelve pairs of nerves originate from the brain and pass through cranial foramina  Cranial nerves are referred to by names and by Roman numerals  Three cranial nerves are purely sensory and have cell bodies in ganglia outside the brain  Nine cranial nerves are mixed, and carry a variety of sensory, and autonomic and somatic motor signals

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerves

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve I: The Olfactory Nerve Conveys information about odors to the brain Consists only of axons passing through small foramina in ethmoid bone Axons synapse in the olfactory bulb, optic tract fibers carry the information onto the cerebrum

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve I: The Olfactory Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve II: The Optic Nerve Conveys visual information to the brain Visual pathway includes the optic nerves, optic chiasm, and optic tracts Visual signals from each eye split in the optic chiasm, so each visual cortex receives signals from both eyes

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve II: The Optic Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerves Controlling Eye Movements Oculomotor (III) nerve controls 4 eye muscles plus autonomic input to the ciliary muscle and lens Trochlear (IV) nerve controls the superior oblique muscle Abducens (VI) nerve controls the lateral rectus muscle

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerves Controlling Eye Movements

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve V: The Trigeminal Nerve The trigeminal nerve carries sensory signals from the mouth and much of the face, and motor signals to muscles of mastication The three branches are Ophthalmic nerve Maxillary nerve Mandibular nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve V: The Trigeminal Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve VII: The Facial Nerve Carries sensory signals from the tongue, and from the facial muscles Carries motor signals for facial and neck muscles Carries autonomic signals to lacrimal and salivary glands

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve VII: The Facial Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve VIII: Vestibulocochlear Nerve Conveys auditory and vestibular information from the inner ear to the brain Two branches are  Vestibular branch  Auditory branch

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve VIII: Vestibulocochlear Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve IX: The Glossopharyngeal Nerve Sensory fibers carry signals for taste, from pharyngeal muscles, and for blood pressure and blood chemistry Motor fibers carry signals to pharyngeal muscles involved in swallowing

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve IX: The Glossopharyngeal Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve X: The Vagus Nerve Sensory fibers carry information from a wide variety of cranial and visceral sources Motor fibers carry parasympathetic signals to most thoracic and abdominal organs

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve X: The Vagus Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve XI: The Accessory Nerve Carries sensory signals from neck muscles Carries motor signals involved in swallowing, and to sternocleidomastoid and trapezius muscles

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve XI: The Accessory Nerve

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve XII: The Hypoglossal Nerve Carries sensory signals from the muscles of the tongue Carries motor signals to tongue muscles for speech and swallowing

Copyright 2010, John Wiley & Sons, Inc. Cranial Nerve XII: The Hypoglossal Nerve

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Introduction Thirty-one pairs of spinal nerves connect the spinal cord to sensory receptors, muscles, and glands Spinal nerves are named by where they emerge from the spinal cord  Cervical nerves (8 pairs)  Thoracic nerves (12 pairs)  Lumbar nerves (5 pairs)  Sacral nerves (5 pairs)  Coccygeal nerves (1 pair)

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Introduction

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Roots and Branches Spinal nerves connect to the spinal cord through posterior roots and anterior roots. The posterior root ganglion contains cells bodies of sensory neurons. Spinal nerves split into several branches  Posterior ramus  Anterior ramus  Meningeal branch  Rami communicantes

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Roots and Branches

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Roots and Branches

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Nerve Plexuses Axons from spinal nerves in several regions form networks with axons from other spinal nerves (plexus = braid, or network) Several major plexuses are  Cervical plexus  Brachial plexus  Lumbar plexus  Sacral plexus Nerves exit plexuses to peripheral regions of the body

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Nerve Plexuses

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Cervical Plexus

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Cervical Plexus

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Brachial Plexus

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Nerves of the Upper Limb

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Nerves of the Upper Limb

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Sacral and Coccygeal Plexus

Copyright 2010, John Wiley & Sons, Inc. Spinal Nerves: Sacral and Coccygeal Plexus

Copyright 2010, John Wiley & Sons, Inc. Reflexes Reflexes are rapid, involuntary responses to stimuli. Reflexes are predictable: a specific stimulus always gives the same response  Cranial reflexes are integrated in the brainstem  Spinal reflexes are integrated in the spinal cord  Somatic reflexes have responses involving skeletal muscles  Autonomic reflexes involve internal processes, and are usually not consciously perceived  Many reflexes are tested clinically because they provide us with functional information about the heath of the nervous system

Copyright 2010, John Wiley & Sons, Inc. 1 SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) 2 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) Interneuron SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) MOTOR NEURON (axon conducts impulses from integrating center to effector) Interneuron SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) MOTOR NEURON (axon conducts impulses from integrating center to effector) EFFECTOR (muscle or gland that responds to motor nerve impulses) Interneuron Reflex Arc is a specific reflex pathway involving five components

Copyright 2010, John Wiley & Sons, Inc. Reflex Arcs Interactions Animation Reflex Arcs You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Reflexes: The Stretch Reflex Stretch reflexes cause contraction of a skeletal muscle in response to stretching of the muscle  The sensory receptor is the muscle spindle, which responds to changes in length of the muscle  Stretch reflexes, which occur for all skeletal muscles, are monosynaptic  Stretch reflexes are ipsolateral, which means they remain on one side of the body and spinal cord

Copyright 2010, John Wiley & Sons, Inc. 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) Antagonistic muscles relax 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited To brain Spinal Nerve Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited MOTOR NEURON excited Antagonistic muscles relax Motor neuron to antagonistic muscles is inhibited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited MOTOR NEURON excited EFFECTOR (same muscle) contracts and relieves the stretching Antagonistic muscles relax Motor neuron to antagonistic muscles is inhibited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – Stretch Reflex

Copyright 2010, John Wiley & Sons, Inc. Reflexes: The Stretch Reflex Stretch reflexes also cause inhibition of antagonistic muscles - this is an example of reciprocal innervation Axon collaterals of the sensory neuron relay information about muscle stretch to the brain, where it is used to coordinate activity of skeletal muscles The patellar reflex is a commonly tested reflex, yielding information about possible damage to the nervous system

Copyright 2010, John Wiley & Sons, Inc. Reflexes: The Withdrawal (Flexor) Reflex Most reflexes are polysynaptic - involving at least three neurons and two synapses The withdrawal reflex involves moving the body away from a harmful stimulus Multiple muscles must be activated for the withdrawal reflex, this involves intersegmental reflexes arc up and down the spinal cord

1 Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) 1 + Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending interneuron Spinal nerve Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited MOTOR NEURONS excited MOTOR NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending interneuron Spinal nerve Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited MOTOR NEURONS excited MOTOR NEURON excited EFFECTORS (flexor muscles) contract and withdraw leg Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending interneuron Spinal nerve Flexor Reflex Copyright 2010, John Wiley & Sons, Inc.

Reflexes: The Withdrawal (Flexor) Reflex The sensory neurons in the withdrawal reflex send signals to several other targets: There is reciprocal innervation of flexors in the injured limb there is contralateral innervation of the extensors in the opposite limb - this limb exerts more force Sensory information is sent to the brain, and eventually reaches our conscious perception

Copyright 2010, John Wiley & Sons, Inc. Reflexes Interactions Animation Reflexes You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Autonomic Nervous System (ANS) The autonomic nervous system regulates much of what goes on inside our bodies - via the heart, smooth muscle, and glands Autonomic sensory neurons provide information about the status of our internal environment Several specific areas in the CNS (hypothalamus, brainstem, lumbar spinal cord) integrate autonomic information The autonomic nervous system has two main motor divisions  Sympathetic division regulates short term responses  Parasympathetic division regulates long term processes

Copyright 2010, John Wiley & Sons, Inc. Autonomic Nervous System (ANS)

Copyright 2010, John Wiley & Sons, Inc. Comparison of Somatic and ANS Motor Pathways Somatic pathways have a single neuron Autonomic pathways have two neurons and a ganglion Sympathetic and parasympathetic pathways differ in terms of the length of the neurons and the location of the ganglia The two divisions also differ in terms of the final neurotransmitter released The adrenal medulla is a modified sympathetic ganglion that releases epinephrine as a hormone

Copyright 2010, John Wiley & Sons, Inc. Comparison of Somatic and ANS Motor Pathways

Copyright 2010, John Wiley & Sons, Inc. Autonomic Neurons Somatic motor neurons are all alike Autonomic motor neurons come in two types  Preganglionic neurons have cell bodies in the CNS and are myelinated  Postganlionic neurons have cell bodies in an autonomic ganglion and are unmyelinated

Copyright 2010, John Wiley & Sons, Inc. Autonomic Neurons

Copyright 2010, John Wiley & Sons, Inc. ANS Pathways Interactions Animation ANS: Motor Pathways You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Autonomic Ganglia Autonomic ganglia differ between the two divisions Sympathetic ganglia - are found in two general locations  Sympathetic trunk ganglia - lie along the spinal cord, generally innervating thoracic organs  Prevertebral ganglia - anterior to the spinal cord, generally innervating abdominal organs Parasympathetic ganglia - are referred to as terminal ganglia because they are located close to or within their target organs

Copyright 2010, John Wiley & Sons, Inc. Overview of the Sympathetic Division

Copyright 2010, John Wiley & Sons, Inc. Sympathetic Ganglia and Postganglionic Neurons

Copyright 2010, John Wiley & Sons, Inc. Overview of the Parasympathetic Division

Copyright 2010, John Wiley & Sons, Inc. Pelvic Splanchnic Nerves ■Parasympathetic axons exit the sacral region of the spinal cord and form the splanchnic nerves ■These nerves innervate organs in the pelvic region (colon, ureters, bladder, and reproductive organs)

Copyright 2010, John Wiley & Sons, Inc. Pelvic Splanchnic Nerves

Copyright 2010, John Wiley & Sons, Inc. Autonomic Plexuses Networks of mixed sympathetic and parasympathetic neurons are found in the thoracic and abdominal cavities

Copyright 2010, John Wiley & Sons, Inc. Autonomic Plexuses

Copyright 2010, John Wiley & Sons, Inc. Cholinergic Neurons and Receptors Autonomic neurons are classified by the type of neurotransmitter involved  Cholinergic neurons release acetylcholine  Cholinergic receptors Nicotinic receptors Muscarinic receptors

Copyright 2010, John Wiley & Sons, Inc. Cholinergic Neurons and Receptors

Copyright 2010, John Wiley & Sons, Inc. Adrenergic Neurons and Receptors Autonomic neurons are classified by the type of neurotransmitter involved  Adrenergic neurons release norepinephrine  Adrenergic receptors Alpha-adrenergic receptors Beta-adrenergic receptors  Many sub-types of adrenergic receptors exist, and drugs specific to the different types exist

Copyright 2010, John Wiley & Sons, Inc. Adrenergic Neurons and Receptors

Copyright 2010, John Wiley & Sons, Inc. Adrenergic and Cholinergic Receptors in the ANS

Copyright 2010, John Wiley & Sons, Inc. ANS Neurotransmitters and Receptors Interactions Animations The ANS: Types of Neurotransmitters and Neurons The ANS: Types of Neurotransmitters and Neurons You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects of the Sympathetic Division In general the two divisions of the ANS have opposing effects The fight-or-flight response is a way to recall the general pattern of effects that mobilize energy and prepare for activity  Dilation of the pupils  Increases in heart rate and blood pressure  Dilation of airways  Decrease in blood flow to non-essential organs, and increase in flow to organs useful during activity and in emergencies  Release of stored energy by liver and adipose tissue Sympathetic tone is a useful term, because it reminds us that the level of activity of the sympathetic system is continuous and not all-or-none

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects of the Parasympathetic Division The effects of the parasympathetic division are summarized by the phrase rest-and-digest  SLUDD = salivation, lacrimation, urination, digestion, defecation  “Three decreases” include decreased heart rate, diameter of airways, and diameter of pupils The parasympathetic division will be active during safe, restful times - allowing the body to “catch up on” many important physiological activities If an emergency arises the parasympathetic system will rapidly slow down, and the sympathetic division will rapidly increase in activity

Copyright 2010, John Wiley & Sons, Inc. Comparison of the Two ANS Divisions

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects of ANS Interactions Animation Physiological Effects of the ANS You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects of the ANS on Glands

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects of the ANS on Smooth Muscle

Copyright 2010, John Wiley & Sons, Inc. Physiological Effects on Vascular Smooth Muscle

Copyright 2010, John Wiley & Sons, Inc. The Alarm Reaction Interactions Animation The Alarm Reaction You must be connected to the internet to run this animation.

Copyright 2010, John Wiley & Sons, Inc. Autonomic Reflexes The autonomic nervous system plays a central role in homeostasis. There are many autonomic reflexes that maintain stable conditions in the body. Autonomic reflexes have five components 1) Sensory receptor2) Sensory pathway 3) Integrating center4) Motor pathway 5) Effectors The hypothalamus is the major integrating center for ANS reflexes. The hypothalamus collects information from autonomic sensory neurons, and from the brainstem and spinal cord. Signals also arrive in the hypothalamus from the limbic system and higher cortical centers.

Copyright 2010, John Wiley & Sons, Inc. End of Chapter 14 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.