Chapter 11
Efferent Division:
Autonomic and
Somatic Motor
Control
About this Chapter
• Autonomic division
• Autonomic reflexes
• Antagonistic controls
• Control of cardiac and smooth muscle, and
glands in homeostasis
• Agonists and antagonists in research and
medicine
• Somatic motor division
• CNS control of skeletal muscles through
neuromuscular junctions
Role of the Autonomic Division in Homeostasis
• Antagonistic branches
• Parasympathetic
• “Rest and digest”
• Restore body function
• Sympathetic
• “Fight or flight”
• Energetic action
Role of the Autonomic Division in Homeostasis
Figure 11-1
The Hypothalamus, Pons, and Medulla Initiate
Autonomic, Endocrine, and Behavioral Responses
• Coordination of
homeostatic
responses
• Autonomic
• Endocrine
• Behavioral
Figure 11-2
Autonomic Control Centers in the Brain
• Hypothalamus
• Water balance,
temperature, and
hunger
Temperature control
Water balance
Hypothalamus
Eating
behavior
• Pons
• Respiration
• Medulla
•
•
•
•
Respiration
Cardiac
Vomiting
Swallowing
Pons
Urinary bladder
control
Secondary
respiratory center
Blood pressure
control
Respiratory center
Medulla
Figure 11-3
Autonomic Pathways
Figure 11-4
Antagonistic Control of the Autonomic Division
• Most internal organs are under antagonistic
control
• One autonomic branch is excitatory and the
other branch is inhibitory
• Example:
• Effector organ: heart
• Parasympathetic response: slows rate
• Sympathetic response: increases rate and force of
contraction
Autonomic Sympathetic and Parasympathetic
Pathways
Hypothalamus,
Reticular formation
Ganglion
Pons
Medulla
Vagus
nerve
Spinal
cord
Sympathetic
chain
Pelvic
nerves
KEY
Parasympathetic
Sympathetic
Figure 11-5
Autonomic Sympathetic and Parasympathetic
Pathways
• Sympathetic versus
parasympathetic
pathways
• Spinal cord exit
• Neurotransmitters
• Receptors
• The major
parasympathetic tract
is the vagus nerve
Medulla
Vagus
nerve
Right lung
Liver
Proximal
two-thirds
of colon
Left lung
Spleen
Stomach
Pancreas
Entire
small
intestine
Figure 11-6
Autonomic Sympathetic and Parasympathetic
Pathways
Sympathetic pathways
use acetylcholine and
norepinephrine.
Parasympathetic pathways
use acetylcholine.
CNS
ACh
Nicotinic
receptor
Autonomic
ganglion
Norepinephrine
Adrenergic
receptor
T
Target tissue
ACh
Muscarinic
receptor
T
Figure 11-7
Sympathetic and Parasympathetic
Neurotransmitters
Table 11-1
Autonomic Targets
•
•
•
•
•
•
•
Autonomic pathways control:
Smooth muscle
Cardiac muscle
Exocrine glands (select)
Endocrine glands (select)
Lymphoid tissue
Adipose tissue
Autonomic Neuron Structure
• Neuroeffector junction
• Postganglionic axon
• Varicosities
• Axon
• Neurotransmitter synthesis
Varicosities in Autonomic Neurons
Axon of
postganglionic
autonomic
neuron
Vesicle containing
neurotransmitter
Mitochondrion
Varicosity
Figure 11-8
Varicosities
Smooth muscle cells
Figure 11-8
Norepinephrine Release at a Varicosity of a
Sympathetic Neuron
1 Action potential arrives at
the varicosity.
2 Depolarization opens
voltage-gated Ca2+ channels.
Axon varicosity
Tyrosine
Axon
1 Action
potential
8
7
Voltage-gated
Ca2+ channel
NE
Exocytosis
3
Active transport
6
NE
5 Diffuses away 4
5 Receptor activation ceases
when NE diffuses away from
the synapse.
6 NE is removed from the
synapse.
G
Adrenergic
receptor
3 Ca2+ entry triggers
exocytosis of synaptic
vesicles.
4 NE binds to adrenergic
receptor on target.
Ca2+ 2
Blood
vessel
MAO
Response
Target cell
7 NE can be taken back into
synaptic vesicles for
re-release.
8 NE is metabolized by
monoamine oxidase (MAO).
Figure 11-9, steps 1–8
Sympathetic Branch: Stimulation
•
•
•
•
•
•
Pupil dilation
Salivation
Heart beat and volume
Blood vessel and bronchiole dilation
Fat breakdown
Ejaculation
Sympathetic Branch: Inhibition
• Digestion
• Pancreas secretion
• Urination
Adrenal Medulla
• Primary neurohormone
• Epinephrine
• Multiple and distant targets
The Adrenal Medulla
Adrenal cortex is a
true endocrine gland.
Adrenal medulla is a
modified sympathetic
ganglion.
Adrenal gland
Kidney
(b)
(a)
ACh
Spinal cord
Preganglionic
sympathetic
neuron
The chromaffin
cell is a modified
postganglionic
sympathetic
neuron.
(c)
Adrenal medulla
Epinephrine is a
neurohormone that
enters the blood.
Blood vessel
To target
tissues
Figure 11-10
The Adrenal Medulla
Adrenal
gland
Kidney
(a)
Figure 11-10a
The Adrenal Medulla
Adrenal cortex is a
true endocrine gland.
Adrenal medulla is a
modified sympathetic
ganglion.
(b)
Figure 11-10b
The Adrenal Medulla
ACh
Spinal cord
(c)
Preganglionic
sympathetic
neuron
The chromaffin
cell is a modified
postganglionic
sympathetic
neuron.
Epinephrine is a
neurohormone that
Adrenal medulla
enters the blood.
Blood vessel
To target
tissues
Figure 11-10c
Parasympathetic Branch
• Acetylcholine
• Muscarinic receptors
• G protein-coupled
• Second messenger pathways
• At least five subtypes
Parasympathetic Branch: Actions
• Constricts pupils and bronchioles
• Slows heart
• Stimulates
•
•
•
•
Digestion
Insulin release
Urination
Erections
Autonomic Agonists and Antagonists
• Agonists and antagonists are important tools
in research and medicine
Table 11-3
Efferent Pathways of the Peripheral Nervous System
SOMATIC MOTOR
PATHWAY
CNS
AUTONOMIC PATHWAYS
Parasympathetic
pathway
Sympathetic
pathways
CNS
CNS
Adrenal sympathetic
pathway
CNS
ACh
Adrenal
cortex
Nicotinic
receptor
Adrenal
medulla
Ganglia
E
ACh
Ganglion
Nicotinic
receptor
 receptor
NE
ACh
Muscarinic
receptor
ACh
Nicotinic receptor
Skeletal
muscle
Autonomic effectors:
• Smooth and cardiac muscles
• Some endocrine and exocrine
glands
• Some adipose tissue
Blood vessel
 1 receptor
E
2
receptor
KEY
ACh= acetylcholine
E= epinephrine
NE= norepinephrine
Figure 11-11
Efferent Pathways of the Peripheral Nervous System
AUTONOMIC PATHWAYS
Parasympathetic
pathway
Sympathetic
pathways
CNS
CNS
Adrenal sympathetic
pathway
CNS
ACh
Adrenal
cortex
Nicotinic
receptor
Adrenal
medulla
Ganglia
E
ACh
Ganglion
Nicotinic
receptor
 receptor
NE
ACh
Muscarinic
receptor
Autonomic effectors:
• Smooth and cardiac muscles
• Some endocrine and exocrine
glands
• Some adipose tissue
Blood vessel
 1 receptor
E
2
receptor
KEY
ACh= acetylcholine
E= epinephrine
NE= norepinephrine
Figure 11-11 (2 of 5)
Efferent Pathways of the Peripheral Nervous System
Figure 11-11 (3 of 5)
Efferent Pathways of the Peripheral Nervous System
Figure 11-11 (4 of 5)
Efferent Pathways of the Peripheral Nervous System
Figure 11-11 (5 of 5)
Somatic versus Autonomic Divisions
Table 11-5
Somatic Motor Division
• Single neuron
• CNS origin
• Myelinated
• Terminus
• Branches
• Neuromuscular junction
Somatic Motor Division
Figure 11-11 (1 of 5)
Anatomy of the Neuromuscular Junction
Somatic motor neuron
The neuromuscular junction
Muscle fiber
Terminal bouton
Figure 11-12 (1 of 3)
Anatomy of the Neuromuscular Junction
Schwann cell sheath
Axon terminal
Mitochondria
Motor end plate
Figure 11-12 (2 of 3)
Anatomy of the Neuromuscular Junction
Synaptic
vesicle (ACh)
Presynaptic
membrane
Synaptic cleft
Nicotinic ACh
receptors
Postsynaptic
membrane
Figure 11-12 (3 of 3)
Events at the Neuromuscular Junction
Somatic motor
neuron
Axon terminal
Ca2+
Ca2+
ACh
Voltage-gated
Ca2+ channel
Skeletal
muscle
fiber
(a)
Action potential
Acetyl + choline
AChE
Nicotinic
receptor
Motor end
plate
Figure 11-13a
Events at the Neuromuscular Junction
Open channel
Closed channel
ACh
K+
Na+
K+
Na+
(b)
Figure 11-13b
Cigarette Smoking Among American High School
Students
Questions 11-1