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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
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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
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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
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Cranial Nerve I: The Olfactory Nerve
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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
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Cranial Nerve II: The Optic Nerve
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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
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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
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Cranial Nerve V: The Trigeminal Nerve
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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
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Cranial Nerve VII: The Facial Nerve
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Cranial Nerve VIII: Vestibulocochlear Nerve
Conveys auditory and vestibular information from the inner ear to the brain
Two branches are Vestibular branch
Auditory branch
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Cranial Nerve VIII: Vestibulocochlear Nerve
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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
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Cranial Nerve IX: The Glossopharyngeal Nerve
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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
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Cranial Nerve X: The Vagus Nerve
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Cranial Nerve XI: The Accessory Nerve Carries sensory signals from neck muscles
Carries motor signals involved in swallowing, and to sternocleidomastoid and trapezius muscles
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Cranial Nerve XI: The Accessory Nerve
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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
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Cranial Nerve XII: The Hypoglossal Nerve
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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)
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Spinal Nerves: Introduction
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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
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Spinal Nerves: Roots and Branches
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Spinal Nerves: Roots and Branches
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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
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Spinal Nerves: The Cervical Plexus
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Spinal Nerves: The Cervical Plexus
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Spinal Nerves: The Brachial Plexus
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Spinal Nerves: Nerves of the Upper Limb
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Spinal Nerves: Nerves of the Upper Limb
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Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb
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Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb
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Spinal Nerves: The Lumbar Plexus and Nerves of the Lower Limb
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Spinal Nerves: Sacral and Coccygeal Plexus
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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 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)
SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)
INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)
Interneuron
2
3
1SENSORY NEURON(axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)
INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)
MOTOR NEURON(axon conducts impulses fromintegrating center to effector)
Interneuron
2
3
4
1SENSORY NEURON(axon conducts impulses from receptor to integrating center)
SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)
INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)
MOTOR NEURON(axon conducts impulses fromintegrating center to effector)
EFFECTOR(muscle or gland thatresponds to motornerve impulses)
Interneuron
2
3
4 5
Reflex Arc is a specific reflex pathway involving five components
Copyright 2010, John Wiley & Sons, Inc.
Reflex ArcsInteractions Animation
Reflex Arcs
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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 stimulatesSENSORY RECEPTOR(muscle spindle)
Antagonisticmuscles relax
1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)
SENSORYNEURONexcited
To brain
SpinalNerve
+
+
21 Stretching stimulates
SENSORY RECEPTOR(muscle spindle)
SENSORYNEURONexcited
Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron
Inhibitoryinterneuron
To brain
SpinalNerve
+
–
+
2
3
1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)
SENSORYNEURONexcited
MOTORNEURONexcited
Antagonisticmuscles relax
Motor neuron toantagonistic musclesis inhibited
Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron
Inhibitoryinterneuron
To brain
SpinalNerve
+
–
+
+
2
3
4
1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)
SENSORYNEURONexcited
MOTORNEURONexcited
EFFECTOR(same muscle)contracts andrelieves thestretching
Antagonisticmuscles relax
Motor neuron toantagonistic musclesis inhibited
Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron
Inhibitoryinterneuron
To brain
SpinalNerve
+
–
+
+
2
3
4
5
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 stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)
1
+
Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)
SENSORYNEURONexcited
+
2
1
+
Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)
SENSORYNEURONexcited
Within INTEGRATING CENTER(spinal cord), sensory neuronactivates interneurons in severalspinal cord segments
Ascendinginterneuron
Interneuron
Descendinginterneuron
Spinalnerve
+
+
+
+
+
+
2
3
1
+
Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)
SENSORYNEURONexcited
MOTORNEURONSexcited
MOTORNEURONexcited
Within INTEGRATING CENTER(spinal cord), sensory neuronactivates interneurons in severalspinal cord segments
Ascendinginterneuron
Interneuron
Descendinginterneuron
Spinalnerve
+
+
+
+
+
+
+
+
+
2
3
4
4
1
+
Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)
SENSORYNEURONexcited
MOTORNEURONSexcited
MOTORNEURONexcited
EFFECTORS(flexor muscles)contract andwithdraw leg
Within INTEGRATING CENTER(spinal cord), sensory neuronactivates interneurons in severalspinal cord segments
Ascendinginterneuron
Interneuron
Descendinginterneuron
Spinalnerve
+
+
+
+
+
+
+
+
+
2
3
4
5
4
Flexor Reflex
Copyright 2010, John Wiley & Sons, Inc.
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
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ReflexesInteractions Animation
Reflexes
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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
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Autonomic Nervous System (ANS)
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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
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Comparison of Somatic and ANS Motor Pathways
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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
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Autonomic Neurons
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ANS PathwaysInteractions Animation
ANS: Motor Pathways
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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
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Overview of the Sympathetic Division
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Sympathetic Ganglia and Postganglionic Neurons
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Overview of the Parasympathetic Division
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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)
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Pelvic Splanchnic Nerves
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Autonomic PlexusesNetworks of mixed sympathetic and parasympathetic
neurons are found in the thoracic and abdominal cavities
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Autonomic Plexuses
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Cholinergic Neurons and Receptors
Autonomic neurons are classified by the type of neurotransmitter involved
Cholinergic neurons release acetylcholine
Cholinergic receptors
Nicotinic receptors
Muscarinic receptors
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Cholinergic Neurons and Receptors
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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
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Adrenergic Neurons and Receptors
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Adrenergic and Cholinergic Receptors in the ANS
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ANS Neurotransmitters and ReceptorsInteractions Animations The ANS: Types of Neurotransmitters and Ne
urons
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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
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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
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Comparison of the Two ANS Divisions
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Physiological Effects of ANSInteractions Animation
Physiological Effects of the ANS
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Physiological Effects of the ANS on Glands
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Physiological Effects of the ANS on Smooth Muscle
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Physiological Effects on Vascular Smooth Muscle
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The Alarm ReactionInteractions Animation
The Alarm Reaction
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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.
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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.