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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
Nervous
System (CNS)
Brain, Spinal Cord
Peripheral
Nervous
System (PNS)
Cranial/Spinal
Nerves
Organization of the Nervous System
© Brooks/Cole - Thomson Learning
Peripheral Nervous System
Somatic
Nervous
System
Consist of cranial
and spinal nerves
innervating
skeletal muscles
Autonomic
Nervous
System
Consist of
nerve fibers
innervating
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)
Efferent Output in the Autonomic
Nervous System: Two-Neuron Chain
(Brain stem or Spinal cord)
(Visceral organ)
© Brooks/Cole - Thomson Learning
Functional Division Between
Autonomic Nervous System
Sympathetic
System
Parasympathetic
System
Mediate fight or
flight responses
Mediate rest or
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
mAChR
nAChR
nAChR
mAChR
1) Nicotinic AChR
(nAChR): found on
postganglionic
neurons. Ligandgated receptors
2) Muscarinic AChR
(mAChR): found on
the effector organs
innervated by
parasympathetic
fibers. G-protein
coupled receptors
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
Heart
Airways
http://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
ACh
nAChR
2) Preganglionic fibers
release ACh that
binds to nAChR to
release NA (20%)
and A (80%) into the
circulation
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
System
Parasympathetic
System
Mediate fight or
flight responses
Mediate rest or
digest responses
Sympathetic
System
Parasympathetic
System
Flight or fight response
Rest or digest response
Autonomic fibers
originate from thoracic
and lumbar spinal
segments
Autonomic ganglion is
located near the spinal
cord, far from effector
organ
Postganglionic fibers
release noradrenaline
Autonomic fibers
originate from brain stem
and sacral spinal
segments
Autonomic ganglion is
located far from the
spinal cord, near the
effector organ
Postganglionic fibers
release acetylcholine
Eye
Lacrimal gland
Parotid gland
Nasal mucosa
Sympathetic
Salivary
glands
Spinal
nerves
Sympathetic
trunk
Liver
Splanchino
nerves
Adrenal
gland
Tonic activity
Dual innervation of
Parasympathetic
visceral organs by
Trachea
the sympathetic
Lung
Cranialand
nerves
parasympathetic
systems (except
Heart
blood vessels,
Stomach
sweat glands,
salivary glands)
Gall
bladder
Pancreas
Spleen
Sympathetic preganglionic fiber
Sympathetic postganglionic fiber
Spinal
nerves
Kidney
Small
intestine
Colon
Rectum
Urinary bladder
Genitalia
Parasympathetic preganglionic
fiber
Parasympathetic postganglionic
fiber
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?
Sympathetic NS
b1
Heart
Blood vessels
a2
a1
http://www.ac-creteil.fr/biotechnologies/doc_heartregulation.htm
http://www.cvphysiology.com/Blood%20Pressure/BP010.htm
Increase contraction of
muscles in wall of heart:
increase pumping force
Increase dilation of
skeletal blood vessels:
bring more blood to
muscles
Vasoconstriction: reduce
blood supply to skin
Peripheral Nervous System
Somatic
Nervous
System
Consist of cranial
and spinal nerves
innervating
skeletal muscles
Autonomic
Nervous
System
Consist of
nerve fibers
innervating
visceral organs
The Somatic Nervous System
Somatic 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
Neuromuscular Junction
© Brooks/Cole - Thomson Learning
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.html
http://www.blackwellpublishing.com/matthews/nmj.html
Termination of neuromuscular activity
The enzyme acetylcholinesterase breakdowns
acetylcholine
© Brooks/Cole - Thomson Learning
Electrical Activity at the Neuromuscular
Junction
Electromyogram: 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
Motor neuron disease
Fibrillations
Muscle fiber disease
Fasciculation
Drugs Affecting Neuromuscular
Transmission
Curare: Bind to
nAChR
Black widow
spider venom:
Stimulate ACh
release
Botulinum toxin:
Block release of
ACh