Chapter 7

The Peripheral Nervous

System: Efferent Division

V edit. Pg. 237-255

VI edit. Pg. 233-251

VII edit. Pg. 237-255

Nervous System

Central Peripheral

Nervous Nervous

System (CNS) System (PNS)

Brain, Spinal Cord Cranial/Spinal

Nerves

© Brooks/Cole - Thomson Learning

Organization of the Nervous System

Peripheral Nervous System

Somatic Autonomic

Nervous Nervous

System System

Consist of cranial Consist of

and spinal nerves nerve fibers

innervating innervating

skeletal muscles visceral organs

Differences between autonomic and

somatic nervous systems

Somatic

Nervous System

Autonomic

Nervous System

Carry motor information out of

the NS

Regulate autonomous body

functions

Efferent motor fibers originate

in brain stem or spinal cord

Efferent fibers originate in

brain stem or spinal cord

There is only one efferent

neuron innervating the

effector organ (skeletal

muscles)

There are two efferent

neurons innervating the

effector organ (visceral

organs)

Motor nerve fibers release

acetylcholine which acts on

nicotinic ACh receptors

Efferent fibers release two

types of neurotransmitters

(see difference between

sympathetic and

parasympathetic systems)

© Brooks/Cole - Thomson Learning

Efferent Output in the Autonomic

Nervous System: Two-Neuron Chain

(Brain stem or Spinal cord) (Visceral organ)

Functional Division Between

Autonomic Nervous System

Sympathetic Parasympathetic

System System

Mediate fight or Mediate rest or

flight responses digest responses

Autonomic Nervous System:

Sympathetic and Parasympathetic

Branches

Sympathetic efferent

fibers originate in the

thoracic/lumbar segments

of the spinal cord (blue)

Parasympathetic fibers

originate in brain stem and

sacral portion of spinal cord

(red)

Origin of Sympathetic Preganglionic

Fibers in Spinal Cord

Sympathetic autonomic

ganglia run along the spinal

cord (sympathetic ganglion

chain or trunk)

Parasympathetic ganglia

is located near the

effector organ

Preganglionic neurons and

parasympathetic

postganglionic fibers release

acetylcholine (ACh)

Sympathetic

postganglionic fibers

release noradrenaline

(norepinephrine, NE)

Acetylcholine (ACh) acts on two type of

receptors: muscarinic or nicotinic

1) Nicotinic AChR

(nAChR): found on

postganglionic

neurons. Ligand-

gated receptors

2) Muscarinic AChR

(mAChR): found on

the effector organs

innervated by

parasympathetic

fibers. G-protein

coupled receptors

nAChR

nAChR

mAChR

mAChR

Noradrenaline acts on two types of

receptors: Adrenergic Receptors

Adrenergic receptors (AR):

G protein coupled receptors

1) Alpha AR: a1, a2

(NA binding > A binding)

2) Beta AR: b1, b2

b1, NA binding=A binding

b2, NA binding < A binding

Arteries AirwaysHearthttp://www.medmovie.com/2003demos/alphav12.swf

The Adrenal Medulla(a modified component of the sympathetic

nervous system)

1) The adrenal medulla

is the inner

component of the

adrenal gland

2) Preganglionic fibers

release ACh that

binds to nAChR to

release NA (20%)

and A (80%) into the

circulation

nAChRACh

The adrenal medulla is a modified sympathetic ganglion

found in the adrenal gland that releases adrenaline and

noradrenaline into the general circulation

Functional Division Between

Autonomic Nervous System

Sympathetic Parasympathetic

System System

Mediate fight or Mediate rest or

flight responses digest responses

Sympathetic

System

Parasympathetic

System

Flight or fight response Rest or digest response

Autonomic fibers

originate from thoracic

and lumbar spinal

segments

Autonomic fibers

originate from brain stem

and sacral spinal

segments

Autonomic ganglion is

located near the spinal

cord, far from effector

organ

Autonomic ganglion is

located far from the

spinal cord, near the

effector organ

Postganglionic fibers

release noradrenaline

Postganglionic fibers

release acetylcholine

Eye

Nasal mucosa

Sympathetic

Spinal

nerves

Sympathetic

trunk

Splanchino

nerves

Liver

Gall

bladder

PancreasAdrenal

gland

Kidney

Small

intestine

Colon

Rectum

Urinary bladderGenitalia

Lung

Heart

Spinal

nerves

Cranial

nerves

Salivary

glands

Parasympathetic

Parotid gland

Trachea

Lacrimal gland

Stomach

SpleenSympathetic preganglionic fiber

Parasympathetic postganglionic

fiber

Parasympathetic preganglionic

fiber

Sympathetic postganglionic fiber

Tonic activity

Dual innervation of

visceral organs by

the sympathetic

and

parasympathetic

systems (except

blood vessels,

sweat glands,

salivary glands)

Autonomic Control of Pupilary Reflex

http://www.drugs.com/mtm/atropine_ophthalmic.html

Autonomic Control of Lens:

Accommodation

To focus on a distant object To focus on a close object

Fight or Flight Response

Stress

Danger

Increase heart beats (b1)

Increase blood pressure (Vasoconstriction, a1)

Increase air flow into airways (b2)

Release of glycogen into blood stream

Dilation of skeletal blood vessels (a2)

Dilation of pupils

Increase sweating (ACh)

Down regulation of digestion and urinary activity

How does the heart and blood vessels

respond to activation of

the sympathetic nervous system?

Heart

Blood vessels

Increase contraction of

muscles in wall of heart:

increase pumping force

Increase dilation of

skeletal blood vessels:

bring more blood to

muscles

Sympathetic NS

b1

a2

http://www.ac-creteil.fr/biotechnologies/doc_heartregulation.htm

http://www.cvphysiology.com/Blood%20Pressure/BP010.htm

Vasoconstriction: reduce

blood supply to skin

a1

Peripheral Nervous System

Somatic Autonomic

Nervous Nervous

System System

Consist of cranial Consist of

and spinal nerves nerve fibers

innervating innervating

skeletal muscles visceral organs

The Somatic Nervous SystemSomatic motoneurons innervate skeletal muscles

Skeletal muscles consist of individual muscle fibers (cells)

Cross section of a muscle

Motor Unit: consist of all muscle fibers

innervated by one motor neuron

© Brooks/Cole - Thomson Learning

Neuromuscular Junction

Generation of End Plate Potential

Action potential arrives at nerve terminal

Ca entry into nerve terminal

Release of acetylcholine into synaptic cleft

Binding of Ach to Ach receptors at the motor end plate

Generation of action potential in muscle fiber

http://www.blackwellpublishing.com/matthews/myosin.htmlhttp://www.blackwellpublishing.com/matthews/nmj.html

© Brooks/Cole - Thomson Learning

Termination of neuromuscular activityThe enzyme acetylcholinesterase breakdowns

acetylcholine

Electrical Activity at the Neuromuscular

JunctionElectromyogram: A test used to record the electrical activity of

muscles. When muscles are active, they produce an electrical

current that is usually proportional to the level of muscle activity.

An electromyogram (EMG) is also called a myogram.

The electromyogram can be use to detect changes in

the motor unit

Normal

Fibrillations

Muscle fiber diseaseMotor neuron disease

Fasciculation

Drugs Affecting Neuromuscular

TransmissionCurare: Bind to

nAChR

Black widow

spider venom:

Stimulate ACh

release

Botulinum toxin:

Block release of

ACh