copyright 2010, john wiley & sons, inc. chapter 14 the peripheral nervous system

Copyright 2010, John Wiley & Sons, Inc.

Chapter 14

The Peripheral Nervous System


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.


Nerves Nerves contain nerve fibers, connective tissues, and blood

vessels Nerves contain several notable connective tissue layers:

Endoneurium Fascicles Perineurium Epineurium


Nerves


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


Cranial Nerves


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


Cranial Nerve I: The Olfactory Nerve


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


Cranial Nerve II: The Optic Nerve


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


Cranial Nerves Controlling Eye Movements


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


Cranial Nerve V: The Trigeminal Nerve


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


Cranial Nerve VII: The Facial Nerve


Cranial Nerve VIII: Vestibulocochlear Nerve

Conveys auditory and vestibular information from the inner ear to the brain

Two branches are Vestibular branch

Auditory branch


Cranial Nerve VIII: Vestibulocochlear Nerve


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


Cranial Nerve IX: The Glossopharyngeal Nerve


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


Cranial Nerve X: The Vagus Nerve


Cranial Nerve XI: The Accessory Nerve Carries sensory signals from neck muscles

Carries motor signals involved in swallowing, and to sternocleidomastoid and trapezius muscles


Cranial Nerve XI: The Accessory Nerve


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


Cranial Nerve XII: The Hypoglossal Nerve


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)


Spinal Nerves: Introduction


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


Spinal Nerves: Roots and Branches


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


Spinal Nerves: Nerve Plexuses


Spinal Nerves: The Cervical Plexus


Spinal Nerves: The Brachial Plexus


Spinal Nerves: Nerves of the Upper Limb


Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb


Spinal Nerves: Sacral and Coccygeal Plexus


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


1 SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

1SENSORY NEURON(axon conducts impulses from receptor to integrating center)

SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

2 1SENSORY NEURON(axon conducts impulses from receptor to integrating center)


INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)

Interneuron

2

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MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

Interneuron

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MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

EFFECTOR(muscle or gland thatresponds to motornerve impulses)

Interneuron

2

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4 5

Reflex Arc is a specific reflex pathway involving five components


Reflex ArcsInteractions Animation

Reflex Arcs

You must be connected to the internet to run this animation.

http://www.wiley.com/college/jenkins/0470227583/animations/index_14_04_01.html


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


1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)

Antagonisticmuscles relax


SENSORYNEURONexcited

To brain

SpinalNerve

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21 Stretching stimulates

SENSORY RECEPTOR(muscle spindle)


Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron

Inhibitoryinterneuron

To brain

SpinalNerve

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MOTORNEURONexcited


Motor neuron toantagonistic musclesis inhibited



To brain

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MOTORNEURONexcited

EFFECTOR(same muscle)contracts andrelieves thestretching


Motor neuron toantagonistic musclesis inhibited



To brain

SpinalNerve

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Stretch Reflex


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


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 stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)

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Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)


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Within INTEGRATING CENTER(spinal cord), sensory neuronactivates interneurons in severalspinal cord segments

Ascendinginterneuron

Interneuron

Descendinginterneuron

Spinalnerve

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MOTORNEURONSexcited

MOTORNEURONexcited



Interneuron


Spinalnerve

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MOTORNEURONSexcited

MOTORNEURONexcited

EFFECTORS(flexor muscles)contract andwithdraw leg



Interneuron


Spinalnerve

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Flexor Reflex



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


ReflexesInteractions Animation

Reflexes



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


Autonomic Nervous System (ANS)


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


Comparison of Somatic and ANS Motor Pathways


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


Autonomic Neurons


ANS PathwaysInteractions Animation

ANS: Motor Pathways



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


Overview of the Sympathetic Division


Sympathetic Ganglia and Postganglionic Neurons


Overview of the Parasympathetic Division


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)


Pelvic Splanchnic Nerves


Autonomic PlexusesNetworks of mixed sympathetic and parasympathetic

neurons are found in the thoracic and abdominal cavities


Autonomic Plexuses


Cholinergic Neurons and Receptors

Autonomic neurons are classified by the type of neurotransmitter involved

Cholinergic neurons release acetylcholine

Cholinergic receptors

Nicotinic receptors

Muscarinic receptors


Cholinergic Neurons and Receptors


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


Adrenergic Neurons and Receptors


Adrenergic and Cholinergic Receptors in the ANS


ANS Neurotransmitters and ReceptorsInteractions Animations The ANS: Types of Neurotransmitters and Ne

urons



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


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


Comparison of the Two ANS Divisions


Physiological Effects of ANSInteractions Animation

Physiological Effects of the ANS



Physiological Effects of the ANS on Glands


Physiological Effects of the ANS on Smooth Muscle


Physiological Effects on Vascular Smooth Muscle


The Alarm ReactionInteractions Animation

The Alarm Reaction



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 receptor 2) Sensory pathway3) Integrating center 4) Motor pathway5) 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.


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.

copyright 2010, john wiley & sons, inc. chapter 14 the peripheral nervous system

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