1. The Peripheral Nervous System: Efferent Division
Chapter 7
The Peripheral Nervous System: Efferent Division

2. Outline Autonomic nervous system Somatic nervous System
Neuromuscular Junction

3. Outline Autonomic nervous system Anatomy Neurotransmitters
Pre and post fibers, sympathetic ganglia chain, collateral ganglia, terminal ganglia
Neurotransmitters
Pre = Acetylcholine (ach)
Post = adrenaline (epinepherine) noradrenaline (norepinepherine)
Sympathetic and parasympathetic branches
Dual innervation
Sympathetic dominance “fight or flight”
Parasympathetic dominance “rest and digest”
Receptor types
Cholinergic, muscarinic, nicotinic
Adrenergic. a1 a2 b1 b2
CNS control

4. PNS: Efferent Division
Communication link by which CNS controls activities of muscles and glands
Two divisions of PNS
Autonomic nervous system (ANS)
Involuntary branch of PNS
Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue
Somatic nervous system
Subject to voluntary control
Innervates skeletal muscle

5. ANS Autonomic nerve pathway Extends from CNS to an innervated organ
Ganglion = neuronal cell bodies in the PNS
Nuclei = neuronal cell bodies in the CNS
Two-neuron chain
Preganglionic fiber (synapses with cell body of second neuron)
Postganglionic fiber (innervates effector organ)

6. Sympathetic Nervous System Parasympathetic Nervous System
Fibers originate in thoracic and lumbar regions of spinal cord
Fibers originate from cranial and sacral areas of CNS
Most preganglionic fibers are short
Preganglionic fibers are longer
Long postganglionic fibers
Very short postganglionic fibers
Preganglionic fibers release acetylcholine (Ach)
Most postganglionic fibers release noradrenaline (norepinephrine)
Postganglionic fibers release acetylcholine
Most visceral organs innervated by both sympathetic and parasympathetic fibers
In general produce opposite effects in a particular organ
Dual innervation of organs by both branches of ANS allows precise control over organ’s activity

7. Figure 7.2: Autonomic nervous system.
ACh
ACh
Autonomic
effectors
Terminal
ganglion
Nicotinic
receptor
Muscarinic
receptor
Cardiac
muscle
α receptor
Sympathetic
ganglion chain NE
Adrenal
Medulla E NE
Blood E
Nicotinic
receptor
Smooth
muscle
β1 receptor E
Most
endocrine
glands
and some NE
Collateral
ganglion
Nicotinic
receptor E
β2 receptor
Figure 7.2: Autonomic nervous system.
The sympathetic nervous system, which originates in the thoracolumbar regions of the spinal cord, has short cholinergic (acetylcholine-releasing) preganglionic fibers and long adrenergic (norepinephrine-releasing) postganglionic fibers. The parasympathetic nervous system, which originates in the brain and sacral region of the spinal cord, has long cholinergic preganglionic fibers and short cholinergic postganglionic fibers. In most instances, sympathetic and parasympathetic postganglionic fibers both innervate the same effector organs. The adrenal medulla is a modified sympathetic ganglion, which releases epinephrine and norepinephrine into the blood. Nicotinic cholinergic receptors are located in the autonomic ganglia and adrenal medulla and respond to ACh released by all autonomic preganglionic fibers. Muscarinic cholinergic receptors are located at the autonomic effectors and respond to ACh released by parasympathetic postganglionic fibers. α1, α2, β1, β2 adrenergic receptors are variably located at the autonomic effectors and differentially respond to norepinephrine released by sympathetic postganglionic fibers and to epinephrine released by the adrenal medulla.
Adipose
tissue
ACh
ACh
KEY
Terminal
ganglion
Nicotinic
receptor
Muscarinic
receptor
Parasympathetic preganglionic fiber
Parasympathetic postganglionic fiber
Sympathetic preganglionic fiber
Sympathetic postganglionic fiber
ACh NE E
Acetylcholine
Norepinephrine
Epinephrine
Fig. 7-2, p. 241

8. ANS
Sympathetic system dominates in emergency or stressful (“fight-or-flight”) situations
Promotes responses that prepare body for strenuous physical activity
Parasympathetic system dominates in quiet, relaxed (“rest-and-digest”) situations
Promotes body-maintenance activities such as digestion

9. Fig. 7-3, p. 237 Eye Lacrimal gland Nasal mucosa Parotid gland
Sympathetic
Parasympathetic
Salivary
glands
Trachea
Lung
Cranial
nerves
Spinal
nerves
Sympathetic
trunk
Heart
Liver
Stomach
Splanchino
nerves
Gall
bladder
Spleen
Sympathetic preganglionic fiber
Adrenal
gland
Pancreas
Sympathetic postganglionic fiber
Spinal
nerves
Parasympathetic preganglionic
fiber
Kidney
Parasympathetic postganglionic
fiber
Small
intestine
Colon
Rectum
Urinary bladder
Genitalia
Fig. 7-3, p. 237

10. Table 7-02a p244

11. ANS
Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system
Most arterioles and veins receive only sympathetic nerve fibers (arteries and capillaries are not innervated)
Most sweat glands are innervated only by sympathetic nerves
Salivary glands are innervated by both ANS divisions but activity is not antagonistic – both stimulate salivary secretion

12. ANS Adrenal medulla is a modified part of sympathetic nervous system
Modified sympathetic ganglion that does not give rise to postganglionic fibers
Stimulation of preganglionic fiber prompts secretion of hormones into blood
About 20% of hormone release is norepinephrine
About 80% of hormone released is epinephrine (adrenaline)
Broadcast vs. localized

13. Table 7-1 p242

14. Figure 7.2: Autonomic nervous system.
ACh
ACh
Autonomic
effectors
Terminal
ganglion
Nicotinic
receptor
Muscarinic
receptor
Cardiac
muscle
α receptor
Sympathetic
ganglion chain NE
Adrenal
Medulla E NE
Blood E
Nicotinic
receptor
Smooth
muscle
β1 receptor E
Most
endocrine
glands
and some NE
Collateral
ganglion
Nicotinic
receptor E
β2 receptor
Figure 7.2: Autonomic nervous system.
The sympathetic nervous system, which originates in the thoracolumbar regions of the spinal cord, has short cholinergic (acetylcholine-releasing) preganglionic fibers and long adrenergic (norepinephrine-releasing) postganglionic fibers. The parasympathetic nervous system, which originates in the brain and sacral region of the spinal cord, has long cholinergic preganglionic fibers and short cholinergic postganglionic fibers. In most instances, sympathetic and parasympathetic postganglionic fibers both innervate the same effector organs. The adrenal medulla is a modified sympathetic ganglion, which releases epinephrine and norepinephrine into the blood. Nicotinic cholinergic receptors are located in the autonomic ganglia and adrenal medulla and respond to ACh released by all autonomic preganglionic fibers. Muscarinic cholinergic receptors are located at the autonomic effectors and respond to ACh released by parasympathetic postganglionic fibers. α1, α2, β1, β2 adrenergic receptors are variably located at the autonomic effectors and differentially respond to norepinephrine released by sympathetic postganglionic fibers and to epinephrine released by the adrenal medulla.
Adipose
tissue
ACh
ACh
KEY
Terminal
ganglion
Nicotinic
receptor
Muscarinic
receptor
Parasympathetic preganglionic fiber
Parasympathetic postganglionic fiber
Sympathetic preganglionic fiber
Sympathetic postganglionic fiber
ACh NE E
Acetylcholine
Norepinephrine
Epinephrine
Fig. 7-2, p. 241

15. Autonomic Neurotransmitter Receptors
Tissues innervated by autonomic nervous system have one or more of several different receptor types for postganglionic chemical messengers
Alter tissue/cell response instead of chemical message
Alter the distribution (localized – varicosity, broadcast – adrenal medulla)
Cholinergic receptors – bind to ACh
Nicotinic receptors – found on postganglionic cell bodies of all autonomic ganglia
nicotine
Muscarinic receptors – found on effector cell membranes
Mushroom poison
Adrenergic receptors – bind to norepinephrine and epinephrine
Alpha (α) receptors
Beta (β) receptors

16. Autonomic Neurotransmitter Receptors
Cholinergic receptors – bind to ACh
Nicotinic receptors – found on postganglionic cell bodies of all autonomic ganglia
Nicotine
Respond to Ach, opens Na and K channels, triggers AP
Muscarinic receptors – found on effector cell membranes
Mushroom poison
Smooth muscle, cardiac muscle, glands
5 subtypes
G protein linked

17. Autonomic Neurotransmitter Receptors
Adrenergic receptors – bind to norepinephrine and epinephrine
G protein coupled
Alpha (α) receptors - Ca second messenger system
- a 1= stimulates cyclic amp, sympathetic tissues, vessel constriction, contraction of smooth muscle, constrictor
- a 2 blocks cyclic amp, decreases smooth muscle contraction in the digestive tract, inhibitory to the effector organ
Beta (β) receptors - cyclic amp
- b1 Found in the heart, increases contractility and rate
- b2 Found in the arterioles and airways, dilator

18. Table 7-3 p246

19. Autonomic Agonists and Antagonists
Bind to same receptor as neurotransmitter
Elicit an effect that mimics that of neurotransmitter
Antagonists
Bind with receptor
Block neurotransmitter’s response

20. Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems

21. Outline Somatic nervous system Anatomy Motor neurons
Continuous to effector
Voluntary
Final common pathway
ALS = Amyotropic lateral sclerosis, death of motor neurons
Neuromuscular junction
Anatomy
Muscle fiber, terminal button
“motor end plate”
Ach release
Presynaptic vesicular
Postsynaptic intracellular
Ach activation of end plate potentials
Activation of nicotinic receptors
Inflow of sodium and potassium
Ap propagated along the muscle fiber
Ach breakdown
AChe

22. Somatic Nervous System
Consists of axons of motor neurons of motor neurons that originate in spinal cord or brain stem and end on skeletal muscle
Motor neuron releases neurotransmitter, Ach, which stimulates muscle contraction
Motor neurons are final common pathway by which various regions of CNS exert control over skeletal muscle activity
These areas of CNS include spinal cord, motor regions of cortex, basal nuclei, cerebellum, and brain stem

23. Outline Neuromuscular junction Anatomy Ach release
Muscle fiber, terminal button
“motor end plate”
Ach release
Presynaptic vesicular
Postsynaptic intracellular
Ach activation of end plate potentials
Activation of nicotinic receptors
Inflow of sodium and potassium
Ap propagated along the muscle fiber
Ach breakdown
AChe

24. Muscle fibers innervated by red motor neuron
Axons of two efferent
motor neuron
Muscle fibers innervated by red motor neuron
Muscle fibers innervated by red motor neuron
Spinal cord (section)
Axon terminals
Axon
terminals
Terminal buttons
Neuro-
muscular
junction
Muscle
Figure 7.4: Motor neuron innervating skeletal muscle cells.
The cell body of a motor neuron originates in the ventral horn of the spinal cord. The axon (somatic efferent fiber) exits through the ventral root and travels through a spinal nerve to the skeletal muscle it innervates. When the axon reaches a skeletal muscle, it divides into many axon terminals, each of which forms a neuromuscular junction with a single muscle cell (muscle fiber). The axon terminal within a neuromuscular junction further divides into fine branches, each of which ends in an enlarged terminal button. Note that the muscle fibers innervated by a single axon terminal are dispersed throughout the muscle, but for simplicity they are grouped together in this figure.
Muscle fibers
Muscle
fibers
Terminal
button
Neuromuscular
junction
Fig. 7-4, p. 251

26. Axon terminal of
motor neuron
Action potential
propagation
in motor neuron
Myelin sheath 1
Terminal button
Voltage-gated
Na+ channel
Vesicle of
acetylcholine
Voltage-gated
Ca2+ channel
Plasma membrane
of muscle fiber
Action potential
propagation
in muscle fiber
Ca2+
Na+ 8 2 8 6 7 7
Na+ 3 6
Figure 7.5: Events at a neuromuscular junction.
1. An action potential in a motor neuron is propagated to the axon terminal (terminal button).
2. This local action potential triggers the opening of voltage-gated Ca2+ channels and the subsequent entry of Ca2+ into the terminal button.
3. Ca2+ triggers the release of acetylcholine (ACh) by exocytosis from a portion of the vesicles.
4. ACh diffuses across the space separating the nerve and muscle cells and binds with receptor-channels specific for it on the motor end plate of the muscle cell membrane.
5. This binding brings about the opening of these nonspecific cation channels, leading to a relatively large movement of Na+ into the muscle cell compared to a smaller movement of K+ outward.
6. The result is an end-plate potential. Local current flow occurs between the depolarized end plate and the adjacent membrane.
7. This local current flow opens voltage-gated Na+ channels in the adjacent membrane.
8. The resultant Na+ entry reduces the potential to threshold, initiating an action potential, which is propagated throughout the muscle fiber.
9. ACh is subsequently destroyed by acetylcholinesterase, an enzyme located on the motor end-plate membrane, terminating the muscle cell’s response. K+
Acetylcholinesterase 4 9 5
Acetylcholine-gated
receptor-channel (for
nonspecific cation traffic)
Na+
Motor end plate
Contractile elements within muscle fiber
Fig. 7-5, p. 252

27. Comparison of Somatic and Autonomic Nervous System

28. Neuromuscular Junction
Acetylcholinesterase
Inactivates ACh
Ends end-plate potential and the action potential and resultant contraction
Neuromuscular junction is vulnerable to chemical agents and diseases
Black widow spider venom causes explosive release of ACh
Botulism toxin blocks release of ACh
Curare blocks action of ACh at receptor sites
Organophosphates prevent inactivation of ACh
Myasthenia gravis inactivates ACh receptor sites

29. Neuromuscular conditions and compounds
ALS
Lou Gehrig’s Disease
death of motor neurons
Black widow venom
Explosive release of Ach
Paralysis of the diaphram
Botulinum toxin
Inhibits Ach release
Curare
Ach receptor blocker (chloinergic)
Organophosphates
Ache inhibition
Mysanthia Gravis
Autoimmune, body attacks Ach receptors