chapter 11 efferent division: autonomic and somatic motor control
TRANSCRIPT
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
Figure 11-3
Autonomic Control Centers in the Brain
• Hypothalamus• Water balance,
temperature, and hunger
• Pons• Respiration
• Medulla• Respiration• Cardiac• Vomiting• Swallowing
Eating behavior
Secondaryrespiratory center
Respiratory center
Hypothalamus
Medulla
Pons
Urinary bladdercontrol
Water balance
Temperature control
Blood pressurecontrol
Figure 11-4
Autonomic Pathways
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
Figure 11-5
Ganglion
Pons
Medulla
Spinalcord
Vagusnerve
Sympatheticchain
Pelvicnerves
Hypothalamus,Reticular formation
KEY
Parasympathetic
Sympathetic
Autonomic Sympathetic and Parasympathetic Pathways
• Sympathetic versus parasympathetic pathways• Spinal cord exit• Neurotransmitters• Receptors
• The major parasympathetic tract is the vagus nerve
Figure 11-6
Right lung
Liver
Proximaltwo-thirds
of colonEntire smallintestine
Pancreas
SpleenStomach
Left lung
Medulla
Vagusnerve
Figure 11-7
Autonomic Sympathetic and Parasympathetic Pathways
CNS
Autonomicganglion
Norepinephrine
ACh
Adrenergicreceptor
Sympathetic pathwaysuse acetylcholine andnorepinephrine.
Parasympathetic pathwaysuse acetylcholine.
Nicotinicreceptor
Muscarinic receptor
ACh
Target tissueT T
Table 11-1
Sympathetic and Parasympathetic Neurotransmitters
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
Figure 11-8
Figure 11-8
Varicosities in Autonomic Neurons
Mitochondrion
Varicosities Smooth muscle cells
Vesicle containingneurotransmitter
Axon ofpostganglionic
autonomicneuron
Varicosity
Figure 11-9, steps 1–8
Norepinephrine Release at a Varicosity of a Sympathetic Neuron
NE
Axon varicosity
Adrenergicreceptor
Tyrosine
Exocytosis
Ca2+
Voltage-gatedCa2+ channel
Action potential
Axon
Active transport
Response
MAO
Bloodvessel
Diffuses away
Action potential arrives at the varicosity.
Depolarization opens voltage-gated Ca2+ channels.
Ca2+ entry triggers exocytosis of synaptic vesicles.
NE binds to adrenergicreceptor on target.
NE is metabolized by monoamine oxidase (MAO).
Receptor activation ceases when NE diffuses away from the synapse.
NE can be taken back intosynaptic vesicles for re-release.
NE is removed from the synapse.
NE
Target cell
G
1
2
3
4
5
6
7
8
1
2
3
45
6
78
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
Figure 11-10
The Adrenal Medulla
ACh
Adrenal medulla is a modified sympathetic ganglion.
Adrenal medulla
Adrenal cortex is a true endocrine gland.
Adrenal gland
(b)
Kidney
(a) The chromaffincell is a modifiedpostganglionicsympatheticneuron.Preganglionic
sympatheticneuron
Spinal cord
(c)
Blood vessel
Epinephrine is aneurohormone thatenters the blood.
To target tissues
Figure 11-10a
The Adrenal Medulla
Adrenalgland
Kidney
(a)
Figure 11-10b
The Adrenal Medulla
Adrenal medulla is a modified sympathetic ganglion.
Adrenal cortex is a true endocrine gland.
(b)
Figure 11-10c
The Adrenal Medulla
ACh
Adrenal medulla
The chromaffincell is a modifiedpostganglionicsympatheticneuron.Preganglionic
sympatheticneuron
Spinal cord
(c)
Blood vessel
Epinephrine is aneurohormone thatenters the blood.
To target tissues
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
Table 11-3
Autonomic Agonists and Antagonists
• Agonists and antagonists are important tools in research and medicine
Figure 11-11
Efferent Pathways of the Peripheral Nervous System
Ganglion
Ganglia
ACh
Nicotinicreceptor
Nicotinicreceptor
Autonomic effectors:• Smooth and cardiac muscles• Some endocrine and exocrine
glands• Some adipose tissue
CNSCNS
AUTONOMIC PATHWAYS
Skeletalmuscle
KEYACh= acetylcholineE= epinephrineNE= norepinephrine
ACh
ACh
1 receptor
2
receptor
receptor
Muscarinicreceptor
CNSCNS
Adrenal medulla
Adrenal cortex
Blood vessel
E
E
NE
Nicotinic receptor
SOMATIC MOTORPATHWAY Parasympathetic
pathwaySympathetic
pathwaysAdrenal sympathetic
pathway
ACh
Figure 11-11 (2 of 5)
Efferent Pathways of the Peripheral Nervous System
Ganglion
Ganglia
Nicotinicreceptor
Nicotinicreceptor
Autonomic effectors:• Smooth and cardiac muscles• Some endocrine and exocrine
glands• Some adipose tissue
CNS
AUTONOMIC PATHWAYS
KEYACh= acetylcholineE= epinephrineNE= norepinephrine
ACh
ACh
1 receptor
2
receptor
receptor
Muscarinicreceptor
CNSCNS
Adrenal medulla
Adrenal cortex
Blood vessel
E
E
NE
Parasympatheticpathway
Sympatheticpathways
Adrenal sympatheticpathway
ACh
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)
Efferent Pathways of the Peripheral Nervous System
Table 11-5
Somatic versus Autonomic Divisions
Somatic Motor Division
• Single neuron • CNS origin• Myelinated
• Terminus • Branches• Neuromuscular junction
Figure 11-11 (1 of 5)
Somatic Motor Division
Figure 11-12 (1 of 3)
Anatomy of the Neuromuscular Junction
Somatic motor neuron
Muscle fiber
The neuromuscular junction
Terminal bouton
Figure 11-12 (2 of 3)
Anatomy of the Neuromuscular Junction
Motor end plate
Mitochondria
Schwann cell sheath
Axon terminal
Figure 11-12 (3 of 3)
Anatomy of the Neuromuscular Junction
Synaptic vesicle (ACh)
Presynapticmembrane
Synaptic cleft
Postsynapticmembrane
Nicotinic AChreceptors
Figure 11-13a
Events at the Neuromuscular Junction
Skeletal muscle
fiber
AChE
Voltage-gatedCa2+ channel
Action potential
ACh
Ca2+Ca2+
Acetyl + choline
Nicotinicreceptor(a)
Motor endplate
Somatic motor neuron
Axon terminal
Figure 11-13b
Events at the Neuromuscular Junction
K+
Na+
Na+
K+
ACh
Closed channel
(b)
Open channel
Questions 11-1
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