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Anatomy & Physiology I
Lecture 13
Chapter 13: The Reflex Arc
Chapter 14: The Autonomic Nervous
System
Motor Integration (Review)
• Skeletal Muscle
– Takes place at neuromuscular junction
– Neurotransmitter acetylcholine (ACh) released
when nerve impulse reaches axon terminal
• Smooth and Cardiac Muscle
– Branches form synapses via varicosities
– Acetylcholine and norepinephrine act indirectly
via second messengers
Figure 9.8 When a nerve impulse reaches a neuromuscular junction, acetylcholine (ACh) is released.
Myelinated axon
of motor neuron
Action
potential (AP)
Axon terminal of
neuromuscular
junction
Sarcolemma of
the muscle fiber
Synaptic vesicle
containing ACh
Axon terminal
of motor neuron
Synaptic
cleft
Fusing synaptic
vesicles
ACh
Junctional
folds of
sarcolemma
Sarcoplasm of
muscle fiber
Postsynaptic
membrane
ion channel opens;
ions pass.
ACh
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Acetylcholinesterase
Degraded ACh
Ion channel closes;
ions cannot pass.
Slide 1
Figure 9.26 Innervation of smooth muscle.
Varicosities
Autonomic
nerve fibers
innervate
most smooth
muscle fibers.
Synaptic
vesicles
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Smooth
muscle
cell
Mitochondrion Varicosities release
their neurotransmitters
into a wide synaptic
cleft (a diffuse junction).
Levels of Motor Control
• Cerebellum and basal nuclei are ultimate
planners and coordinators of complex motor
activities
• Complex motor behavior depends on complex
patterns of control
– Segmental level
– Projection level
– Precommand level
Segmental Level
• Lowest level of motor hierarchy
– Reflexes and automatic movements
• Central pattern generators (CPGs)
– circuits that activate networks of ventral horn
neurons to stimulate specific groups of muscles
– Controls locomotion and specific, repeated motor
activity
Projection Level
• Direct control of the Spinal Cord
• Consists of
– Upper motor neurons initiate direct pathways to
produce voluntary skeletal muscle movements
– Brain stem motor areas oversee indirect pathways to
control reflex and CPG-controlled motor actions
• Projection motor pathways send information to
lower motor neurons, and keep higher command
levels informed of what is happening
Precommand Level
• Neurons in cerebellum and basal nuclei
– Regulate motor activity
– Precisely start or stop movements
– Coordinate movements with posture
– Block unwanted movements
– Monitor muscle tone
– Perform unconscious planning and discharge in
advance of willed movements
Figure 13.14a Hierarchy of motor control.
Precommand Level (highest)
• Cerebellum and basal nuclei
• Programs and instructions
(modified by feedback)
Projection Level (middle)
• Motor cortex (pyramidal pathways)
and brain stem nuclei (vestibular,
red, reticular formation, etc.)
• Conveys instructions to spinal cord
motor neurons and sends a copy of
that information to higher levels
Segmental Level (lowest)
• Spinal cord
• Contains central pattern generators
(CPGs)
Sensory
input
Reflex activity
Motor
output
Levels of motor control and their interactions
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Precommand Level
• Cerebellum
– Acts on motor pathways through projection areas
of brain stem
– Acts on motor cortex via thalamus to fine-tune
motor activity
• Basal nuclei
– Inhibit various motor centers under resting
conditions
Figure 13.14b Hierarchy of motor control.
Precommand level
• Cerebellum
• Basal nuclei
Projection level
• Primary motor cortex
• Brain stem nuclei
Segmental level
• Spinal cord
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Structures involved
Reflexes
• Inborn (intrinsic) reflex - rapid, involuntary,
predictable motor response to stimulus
– maintain posture, control visceral activities
– Can be modified by learning and conscious effort
• Learned (acquired) reflexes result from
practice or repetition,
– driving skills
The Reflex Arc
• The highly specific neural pathway that
creates reflexes.
• Receptors detect internal or external stimuli
that elicit a rapid, stereotyped response
– effectors are muscles or glands
Components of a reflex arc
1. Receptor—site of stimulus action
2. Sensory neuron—transmits afferent impulses to
CNS
3. Integration center—either monosynaptic or
polysynaptic region within CNS
4. Motor neuron—conducts efferent impulses from
integration center to effector organ
5. Effector—muscle fiber or gland cell that responds
to efferent impulses by contracting or secreting
Figure 13.15 The five basic components of all reflex arcs.
Stimulus
Skin
1 Receptor
Interneuron
2 Sensory neuron
3 Integration center
4 Motor neuron
5 Effector
Spinal cord
(in cross scetion)
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Reflexes
• Two Functional classifications
• Somatic reflexes
– Activate skeletal muscle
• Autonomic (visceral) reflexes
– Activate visceral effectors (smooth or cardiac
muscle or glands)
Spinal Reflexes
• Somatic reflexes mediated by the spinal cord
– No direct involvement of higher brain centers
• brain does have overall control
– Integration center in spinal cord
– Effectors are skeletal muscle
Stretch and Tendon Reflexes
• For smooth coordination of skeletal muscle
nervous system must receive proprioceptor
input regarding
– Length of muscle
– Amount of tension in muscle
Muscle Fibers
• Specialized, non-contractile muscle fibers used
for motor reflexes
– Informs the brain on the status of the muscle
• Intrafusal muscle fibers
– noncontractile fibers receptive to the CNS/PNS
– contraction on their ends
• Extrafusal muscle fibers
– Effector muscle fibers that contract in response to
simulit
Nerves and Nerve endings
• Two types of afferent endings:
• Anulospiral endings (primary sensory endings)
– Stimulated by rate and degree of stretch
• Flower spray endings (secondary sensory
endings)
– Respond to stretch
Nerves and Nerve endings
• Contractile end regions innervated by:
• Gamma () efferent fibers
– Innervate intrafusal muscle fibers
– Maintain spindle sensitivity
• Alpha () efferent fibers
– Innervate extrafusal muscle fibers
– Stimulate muscle contraction
Figure 13.16 Anatomy of the muscle spindle and tendon organ.
Flower spray endings
(secondary sensory
endings)
Anulospiral
endings
(primary
sensory
endings)
Muscle
spindle
Capsule
(connective
tissue)
Tendon organ
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Efferent (motor)
fiber to muscle spindle
 Efferent
(motor) fiber
to extrafusal
muscle fibers
Extrafusal
muscle
fiber
Intrafusal
muscle
fibers
Sensory
fiber
Tendon
Muscle Spindle Excitement
• Excited in two ways:
• External stretch of muscle and muscle spindle
• Internal stretch of muscle spindle
– Activating motor neurons stimulates ends to
contract, thereby stretching spindle
• Stretch causes increased rate of impulses to
spinal cord
– Coactivation
• – coactivation maintains tension and
sensitivity of spindle during muscle
contraction
• Stimulating intrafusal fibers maintains the
spindle’s tension and sensitivey during muscle
contraction
– brain continues to be notified of changes in the
muscle length
Figure 13.17a Operation of the muscle spindle. (1 of 2)
How muscle stretch is detected
Muscle
spindle
Intrafusal
muscle fiber
Sensory
fiber
Extrafusal
muscle fiber
Time
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Unstretched muscle.
Action potentials (APs)
are generated at a
constant rate in the
associated sensory fiber.
Figure 13.17a Operation of the muscle spindle. (2 of 2)
How muscle stretch is detected
Time
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Stretched muscle.
Stretching activates the
muscle spindle, increasing
the rate of APs.
Figure 13.17b Operation of the muscle spindle. (1 of 2)
The purpose of  - coactivation
Time
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If only  motor neurons
were activated. Only the
extrafusal muscle fibers
contract. The muscle
spindle becomes slack
and no APs are fired. It is
unable to signal further
length changes.
Figure 13.17b Operation of the muscle spindle. (2 of 2)
The purpose of   coactivation
Time
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But normally  -
coactivation occurs. Both
extrafusal and intrafusal
muscle fibers contract.
Tension is maintained in
the muscle spindle and it
can still signal changes in
length.
The Stretch Reflex
• The brain sets a muscle’s length
– Stretch reflex makes sure muscle stays this length
• Maintains muscle tone in large postural
muscles, and adjusts it reflexively
– Causes muscle contraction in response to
increased muscle length (stretch)
Stretch Reflex
• How stretch reflex works
– Stretch activates muscle spindle
– Sensory neurons synapse directly with  motor
neurons in spinal cord
–  motor neurons cause stretched muscle to
contract
– Reciprocal inhibition also occurs – fibers synapse
with interneurons that inhibit  motor neurons of
antagonistic muscles
Figure 13.18 Stretch Reflex (1 of 2)
Slide 2
The events by which muscle stretch is
damped
1 When stretch activates muscle spindles,
the associated sensory neurons (blue)
transmit afferent impulses at higher
frequency to the spinal cord.
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
+
+
–
Spinal cord
Muscle spindle
Antagonist muscle
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Figure 13.18 Stretch Reflex (1 of 2)
Slide 3
The events by which muscle stretch is
damped
Sensory
neuron
Initial stimulus
(muscle stretch)
2 The sensory neurons synapse directly with
alpha motor neurons (red), which excite
extrafusal fibers of the stretched muscle.
Sensory fibers also synapse with interneurons
(green) that inhibit motor neurons (purple)
controlling antagonistic muscles.
Cell body of
sensory neuron
+
+
–
Spinal cord
Muscle spindle
Antagonist muscle
© 2013 Pearson Education, Inc.
Figure 13.18 Stretch Reflex (1 of 2)
Slide 4
The events by which muscle stretch is
damped
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
+
+
–
Spinal cord
Muscle spindle
Antagonist muscle
3a Efferent impulses of alpha motor
neurons cause the stretched muscle
to contract, whichresists or reverses
the stretch.
© 2013 Pearson Education, Inc.
Figure 13.18 Stretch Reflex (2 of 2)
Slide 7
The patellar (knee-jerk) reflex—an example of a stretch reflex
+
Quadriceps
(extensors)
1
+
Patella
Muscle
spindle
Hamstrings
(flexors)
+ Excitatory synapse
– Inhibitory synapse
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Patellar ligament
–
Spinal cord
(L2–L4)
1 Tapping the patellar ligament
stretches the quadriceps and
excites its muscle spindles.
Figure 13.18 Stretch Reflex (2 of 2)
Slide 8
The patellar (knee-jerk) reflex—an example of a stretch reflex
2
+
Quadriceps
(extensors)
1
+
Patella
Muscle
spindle
Hamstrings
(flexors)
+ Excitatory synapse
– Inhibitory synapse
© 2013 Pearson Education, Inc.
Patellar ligament
–
Spinal cord
(L2–L4)
2 Afferent impulses (blue) travel to
the spinal cord, where synapses
occur with motor neurons and
interneurons.
Figure 13.18 Stretch Reflex (2 of 2)
Slide 9
The patellar (knee-jerk) reflex—an example of a stretch reflex
2
Quadriceps
(extensors)
1
+
3a
+
Patella
Muscle
spindle
Hamstrings
(flexors)
–
Spinal cord
(L2–L4)
Patellar ligament
3a The motor neurons (red) send
activating impulses to the
quadriceps causing it to contract,
extending the knee.
+ Excitatory synapse
– Inhibitory synapse
© 2013 Pearson Education, Inc.
Figure 13.18 Stretch Reflex (2 of 2)
Slide 10
The patellar (knee-jerk) reflex—an example of a stretch reflex
2
Quadriceps
(extensors)
1
3a
+
3b
Patella
Muscle
spindle
Hamstrings
(flexors)
+ Excitatory synapse
– Inhibitory synapse
© 2013 Pearson Education, Inc.
+
3b
–
Spinal cord
(L2–L4)
Patellar ligament
3b The interneurons (green) make
inhibitory synapses with ventral
horn neurons (purple) that prevent
the antagonist muscles (hamstrings)
from resisting the contraction of the
quadriceps.
The Tendon Reflex
• Opposite effect of stretch reflex
– Muscles relax and lengthen in response to tension
• Helps prevent damage due to excessive
stretch
• Important for smooth onset and termination
of muscle contraction
The Tendon Reflex
• Produces muscle relaxation (lengthening) in
response to tension
• Contraction or passive stretch activates tendon
reflex
– Afferent impulses transmitted to spinal cord
– Contracting muscle relaxes; antagonist contracts
(reciprocal activation)
– Information transmitted simultaneously to cerebellum
and used to adjust muscle tension
Figure 13.19 The tendon reflex.
Slide 2
1 Quadriceps strongly contracts.
Tendon organs are activated.
Interneurons
Quadriceps
(extensors)
Hamstrings
(flexors)
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–
+
+
Spinal cord
Tendon organ
+ Excitatory synapse
– Inhibitory synapse
+
Figure 13.19 The tendon reflex.
Slide 3
2 Afferent fibers synapse with
interneurons in the spinal cord.
Interneurons
Quadriceps
(extensors)
Hamstrings
(flexors)
© 2013 Pearson Education, Inc.
–
+
+
Spinal cord
Tendon organ
+ Excitatory synapse
– Inhibitory synapse
+
Figure 13.19 The tendon reflex.
Slide 4
Interneurons
+
Quadriceps
(extensors)
–
Hamstrings
(flexors)
© 2013 Pearson Education, Inc.
+
Spinal cord
Tendon organ
+ Excitatory synapse
– Inhibitory synapse
+
3a Efferent
impulses to muscle
with stretched
tendon are damped.
Muscle relaxes,
reducing tension.
Figure 13.19 The tendon reflex.
Slide 5
Interneurons
Quadriceps
(extensors)
+
–
+
+
Spinal cord
Tendon organ
Hamstrings
(flexors)
3b Efferent impulses
to antagonist muscle
cause it to contract.
+ Excitatory synapse
– Inhibitory synapse
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The Flexor Reflexes
• Flexor (withdrawal) reflex
– Initiated by painful stimulus
– Causes automatic withdrawal of threatened body
part
– Protective; important
• Brain can override
– finger stick for blood test
Crossed-Extensor Reflex
• Crossed extensor reflex
– Occurs with flexor reflexes in weight-bearing limbs
to maintain balance
– step barefoot on broken glass
• Stimulated side withdrawn (flexed)
• Contralateral side extended
Figure 13.20 The crossed-extensor reflex.
+ Excitatory synapse
– Inhibitory synapse
Interneurons
+
+
–
+
Afferent
fiber
+
–
Efferent
fibers
Efferent
fibers
Extensor
inhibited
Flexor
stimulated
Site of stimulus:
A noxious stimulus
causes a flexor
reflex on the same
side, withdrawing
that limb.
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Arm movements
Flexor
inhibited
Extensor
stimulated
Site of reciprocal
activation: At the
same time, the
extensor muscles
on the opposite
side are activated.
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 14.1 Place of the ANS in the structural organization of the nervous system.
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
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Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
The Autonomic Nervous System
• ANS consists of motor neurons that
– Innervate smooth and cardiac muscle, and glands
– Make adjustments to ensure optimal support for
body activities
– Operate via subconscious control
• Also called involuntary nervous system or
general visceral motor system
Somatic Versus Autonomic Nervous
Systems
• Both have motor fibers
• Differ in
– Effectors
– Efferent pathways and ganglia
– Target organ responses to neurotransmitters
Effectors
• Somatic nervous system
– Skeletal muscles
• ANS
– Cardiac muscle
– Smooth muscle
– Glands
ANS Neuron Chain
ANS pathway uses two-neuron chain
• Preganglionic neuron (in CNS) has a thin,
lightly myelinated axon.
• Postganglionic neuron (outside CNS) has
nonmyelinated axon that extends to effector
organ
Neurotransmitters
• Preganglionic fibers release Ach
• Postganglionic fibers release norepinephrine
or ACh at effectors
– Effect is either stimulatory or inhibitory,
depending on type of receptors
Figure 14.2 Comparison of motor neurons in the somatic and autonomic nervous systems.
Cell bodies in central
nervous system
Neurotransmitter
at effector
Peripheral nervous system
Effector
organs
Effect
SOMATIC
NERVOUS
SYSTEM
Single neuron from CNS to effector organs
+
ACh
Stimulatory
Heavily myelinated axon
Skeletal muscle
Two-neuron chain from CNS to effector organs
NE
SYMPATHETIC
Lightly myelinated
preganglionic axons
Nonmyelinated
postganglionic axon
Ganglion
ACh
Acetylcholine (ACh)
Norepinephrine (NE)
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Ganglion
Stimulatory
or inhibitory,
depending
on neurotransmitter
and receptors
on effector
organs
Blood vessel
ACh
ACh
Lightly myelinated
preganglionic axon
+–
Epinephrine and
norepinephrine
Adrenal medulla
PARASYMPATHETIC
AUTONOMIC NERVOUS SYSTEM
ACh
Nonmyelinated
postganglionic
axon
Smooth muscle
(e.g., in gut), glands,
cardiac muscle
ANS vs PNS Motor Neurons
• Conduction is slower in ANS than PNS neurons
• Autonomic glanglia are motor ganglia
• Somatic motor neurons lack ganglia
– dorsal root ganglia are for sensory neurons
The ANS/PNS Connection
• Most spinal and many cranial nerves contain
both somatic and autonomic fibers
• Adaptations usually involve both skeletal
muscles and visceral organs
ANS Divisions
• Sympathetic division
• Parasympathetic division
• Dual innervation
– All visceral organs served by both divisions, but
cause opposite effects
– Dynamic antagonism between two divisions
maintains homeostasis
Parasympathetic Division: “Rest and
Digest”
• Promotes maintenance activities and conserves
body energy
– Directs digestion, diuresis, defecation
• Think about relaxing and reading after a meal:
– Blood pressure, heart rate, and respiratory rates are
low
– Gastrointestinal tract activity high
– Pupils constricted; lenses accommodated for close
vision
Sympathetic Division: “fight or flight”
• Mobilizes body during activity
• Exercise, excitement, emergency,
embarrassment
– Increased heart rate; dry mouth; cold, sweaty skin
– dilated pupils and bronchioles
– cause liver to release glucose into blood
Figure 14.3 The subdivisions of the ANS.
Parasympathetic
Eye
Brain stem
Salivary
glands
Heart
Sympathetic
Eye
Skin*
Cranial
Sympathetic
ganglia
Salivary
glands
Cervical
Lungs
Lungs
T1
Heart
Stomach
Thoracic
Stomach
Pancreas
Pancreas
Liver
and gallbladder
L1
Liver and
gallbladder
Adrenal
gland
Lumbar
Bladder
Genitals
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Inc.
Bladder
Sacral
Genitals
Parasympathetic (Craniosacral)
Division
• Long preganglionic fibers from brain stem and
sacrum
– Extend from CNS almost to target organs
– Synapse with postganglionic neurons in terminal
ganglia close to/within target organs
• Short postganglionic fibers synapse with
effectors
Figure 14.4 Parasympathetic division of the ANS.
Eye
Ciliary
ganglion
CN III
Lacrimal
gland
CN VII
Pterygopalatine
ganglion
CN IX
CN X
Submandibular
ganglion
Otic ganglion
Nasal
mucosa
Submandibular
and sublingual
glands
Parotid gland
Heart
Cardiac and
pulmonary
plexuses
Lung
Celiac
plexus
Liver and
gallbladder
Stomach
Pancreas
S2
Large
intestine
S4
Small
intestine
Pelvic
splanchnic
nerves
Inferior
hypogastric
plexus
Rectum
Urinary
bladder
and ureters
Genitalia (penis, clitoris, and vagina)
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CN
S
Preganglionic
Postganglionic
Cranial nerve
Sacral nerve
Parasympathetic (Craniosacral)
Division
• Cranial Part
– Consists of CN III, CN VII, and CN IX for smooth
muscles of the eyes, nasal, lacrimal and parotid
glands
– Vagus Nerve (CN X) acdount for 90% of
preganglionic fibers in body
• Heart, Lungs, Liver, Stomach, Pancreas, Small Intestines
and Early Large Intestines
Parasympathetic (Craniosacral)
Division
• Sacral Part
– Neurons cord segments S2-S4
– Genitals (Penis, Vagina, Clitoris)
– Urinary bladder
– Sigmoid Colon (Large Intestines) and Rectum
Sympathetic (Thoracolumbar) Division
• Preganglionic neurons are in spinal cord
segments T1 – L2
• Preganglionic fibers pass through white rami
communicantes and enter sympathetic trunk
ganglia
– Also called paravertebral since it runs alongside
the vertebra
Sympathetic Trunks and Pathways
• Paravertebral ganglia vary in size, position,
and number
• There are 23 paravertebral ganglia in the
sympathetic trunk (chain)
–
–
–
–
–
3 cervical
11 thoracic
4 lumbar
4 sacral
1 coccygeal
Figure 14.5a Sympathetic trunks and pathways.
Spinal cord
Dorsal root
Ventral root
Rib
Sympathetic
trunk ganglion
Sympathetic
trunk
Ventral ramus
of spinal nerve
Gray ramus
communicans
White ramus
communicans
Thoracic
splanchnic nerves
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Location of the sympathetic trunk
Figure 14.6 Sympathetic division of the ANS.
Eye
Lacrimal gland
Nasal mucosa
Pons
Sympathetic trunk
(chain) ganglia
Superior
cervical
ganglion
Salivary glands
Middle
cervical
ganglion
Inferior
cervical
ganglion
T1
Blood vessels;
skin (arrector pili
muscles and
sweat glands)
Heart
Cardiac and
pulmonary
plexuses
Greater splanchnic nerve
Lesser splanchnic nerve
Celiac ganglion
L2
Lung
Liver and
gallbladder
Stomach
White rami
communicantes
Sacral
splanchnic
nerves
Superior
mesenteric
ganglion
Inferior
mesenteric
ganglion
Spleen
Adrenal medulla
Kidney
Lumbar
splanchnic nerves
Small
intestine
Large
intestine
Rectum
Preganglionic
Postganglionic
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Genitalia (uterus, vagina, and
penis) and urinary bladder
Serving the Head
• Fibers emerge from T1 – T4 and synapse in the
superior cervical ganglion
• These fibers
– Innervate skin and blood vessels of the head
– Stimulate dilator muscles of the iris
– Inhibit nasal and salivary glands
– Innervate smooth muscle of upper eyelid
– Branch to the heart (cardiac and pulmonary
plexus)
Collateral Ganglia
• Most fibers from T5 – L2 synapse in collateral
ganglia
• They form thoracic, lumbar, and sacral
splanchnic nerves
• Their ganglia include the celiac and the
superior and inferior mesenteric
Ganglions
• Celiac Ganglion
– serves the liver, gallbladder, stomach and spleen adrenal
gland
• Superior mesenteric Ganglion
– serves the small and large intestines
• Inferior mesenteric Ganglion
– serves the sigmoid colon and rectum
• Sacral splanchnic nerve directly serves genitals, and
bladder
Visceral Reflexes
• Visceral reflex arcs have same components as
somatic reflex arcs
– visceral reflex arc has two neurons in motor
pathway
Figure 14.7 Visceral reflexes.
Stimulus
1 Receptor in viscera
2 Visceral sensory
Dorsal root ganglion
Spinal cord
neuron
3 Integration center
• May be preganglionic
neuron (as shown)
• May be a dorsal horn
interneuron
• May be within walls
of gastrointestinal
tract
4 Motor neuron
(two-neuron chain)
• Preganglionic neuron
• Postganglionic neuron
5 Visceral effector
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Inc.
Autonomic ganglion
Neurotransmitters of ANS
• Cholinergic fibers release neurotransmitter
ACh
– All ANS preganglionic axons
– All parasympathetic postganglionic axons at
effector synapse
• Adrenergic fibers release neurotransmitter NE
– Most sympathetic postganglionic axons
Cholinergic Receptors
• Two types of receptors bind ACh
– Nicotinic
– Muscarinic
• Named after drugs that bind to them and
mimic ACh effects
– Nicotine
– Muscarine (mushroom poison)
Nicotinic Receptors
• Found on
– Sarcolemma of skeletal muscle cells
(Chapter 9) at NMJ
– All postganglionic neurons (sympathetic and
parasympathetic)
– Hormone-producing cells of adrenal medulla
• Effect of ACh at nicotinic receptors is always
stimulatory
– Opens ion channels, depolarizing postsynaptic cell
Muscarinic Receptors
• Found on
– All effector cells stimulated by postganglionic
cholinergic fibers
• Effect of ACh at muscarinic receptors
– Can be either inhibitory or excitatory
– Depends on receptor type of target organ
Adrenergic Receptors
• Two major classes
– Alpha ( ) (subtypes 1, 2)
– Beta ( ) (subtypes 1, 2 , 3)
• Effects of NE depend on which subclass of
receptor predominates on target organ
– effects vary and can be adjusted depending on
receptors present
Control of ANS Function
• Hypothalamus—main integrative center of
ANS activity
• Subconscious cerebral input via limbic system
structures on hypothalamic centers
• Other controls come from cerebral cortex,
reticular formation, and spinal cord
Hypothalamic Controls
• Control may be direct or indirect (through
reticular system)
• Centers of hypothalamus control
– Heart activity and blood pressure
– Body temperature, water balance, and endocrine
activity
– Emotional stages (rage, pleasure) and biological drives
(hunger, thirst, sex)
– Reactions to fear and "fight-or-flight" system
Figure 14.8 Levels of ANS control.
Communication at
subconscious level
Cerebral cortex
(frontal lobe)
Limbic system
(emotional input)
Hypothalamus
The “boss”: Overall
integration of ANS
Brain stem
(reticular formation, etc.)
Regulates pupil size, heart,
blood pressure, airflow,
salivation, etc.
Spinal cord
Reflexes for urination,
defecation, erection,
and ejaculation
© 2013 Pearson Education, Inc.
The End of the Nervous System
• Lab Today
– Continue working on lab exercises:
– Lab Exercise 21
• Activity 1 – 3 only (Activity 3 Wednesdays' lecture)
– Lab Exercise 22
• Introduction to the reflex arc (Wednesday)
• Optional Activities 1 - 4

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