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Chapter 7 The Peripheral Nervous System: Efferent Division. Outline. Autonomic nervous system Somatic nervous System Neuromuscular Junction. Outline. Autonomic nervous system Anatomy Pre and post fibers, sympathetic ganglia chain, collateral ganglia, terminal ganglia Neurotransmitters

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slide1

Chapter 7

The Peripheral Nervous System: Efferent Division

outline
Outline
  • Autonomic nervous system
  • Somatic nervous System
  • Neuromuscular Junction
outline1
Outline
  • Autonomic nervous system
    • Anatomy
      • 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. a1a2 b1b2
    • CNS control
pns efferent division
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
slide5
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)
slide6
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
slide7

ACh

ACh

Autonomic

effectors

Terminal

ganglion

Nicotinic

receptor

Muscarinic

receptor

Cardiac

muscle

α receptor

Sympathetic

ganglion chain

NE

Adrenal

Medulla

E

NE

Blood

E

Smooth

muscle

Nicotinic

receptor

β1 receptor

E

Most

endocrine

glands

and some

endocrine

glands

NE

Collateral

ganglion

Nicotinic

receptor

E

β2 receptor

Adipose

tissue

ACh

ACh

Terminal

ganglion

Nicotinic

receptor

Muscarinic

receptor

KEY

Parasympathetic preganglionic fiber

Parasympathetic postganglionic fiber

Sympathetic preganglionic fiber

Sympathetic postganglionic fiber

Acetylcholine

ACh

NE

E

Norepinephrine

Epinephrine

Fig. 7-2, p. 241

slide8
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
slide9

Eye

Lacrimal gland

Nasal

mucosa

Parotid

gland

Sympathetic

Parasympathetic

Salivary

glands

Trachea

Lung

Cranial

nerves

Sympathetic

trunk

Heart

Spinal

nerves

Liver

Stomach

Splanchino

nerves

Spleen

Gall

bladder

Sympathetic preganglionic fiber

Adrenal

gland

Pancreas

Sympathetic postganglionic fiber

Spinal

nerves

Parasympathetic preganglionic

fiber

Kidney

Parasympathetic postganglionic

fiber

Colon

Small

intestine

Rectum

Urinary bladder

Genitalia

Fig. 7-3, p. 237

slide11
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
slide12
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
slide14

ACh

ACh

Autonomic

effectors

Terminal

ganglion

Nicotinic

receptor

Muscarinic

receptor

Cardiac

muscle

α receptor

Sympathetic

ganglion chain

NE

Adrenal

Medulla

E

NE

Blood

E

Smooth

muscle

Nicotinic

receptor

β1 receptor

E

Most

endocrine

glands

and some

endocrine

glands

NE

Collateral

ganglion

Nicotinic

receptor

E

β2 receptor

Adipose

tissue

ACh

ACh

Terminal

ganglion

Nicotinic

receptor

Muscarinic

receptor

KEY

Parasympathetic preganglionic fiber

Parasympathetic postganglionic fiber

Sympathetic preganglionic fiber

Sympathetic postganglionic fiber

Acetylcholine

ACh

NE

E

Norepinephrine

Epinephrine

Fig. 7-2, p. 241

autonomic neurotransmitter receptors
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
autonomic neurotransmitter receptors1
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
autonomic neurotransmitter receptors2
Autonomic Neurotransmitter Receptors
  • Adrenergic receptors – bind to norepinephrine and epinephrine
    • G protein coupled
    • Alpha (α) receptors - Ca second messenger system

- a1= stimulates cyclic amp, sympathetic tissues, vessel constriction, contraction of smooth muscle, constrictor

- a2 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

autonomic agonists and antagonists
Autonomic Agonists and Antagonists
  • Agonists
    • Bind to same receptor as neurotransmitter
    • Elicit an effect that mimics that of neurotransmitter
  • Antagonists
    • Bind with receptor
    • Block neurotransmitter’s response
outline2
Outline
  • 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
  • Somatic nervous system
    • Anatomy
      • Motor neurons
      • Continuous to effector
      • Voluntary
      • Final common pathway
      • ALS = Amyotropic lateral sclerosis, death of motor neurons
somatic nervous system
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
outline3
Outline
  • 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
slide24

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

Muscle fibers

Muscle

fibers

Terminal

button

Neuromuscular

junction

Fig. 7-4, p. 251

slide26

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

Action potential

propagation

in muscle fiber

Plasma membrane

of muscle fiber

Ca2+

Na+

2

8

8

6

7

Na+

7

6

3

K+

Acetylcholinesterase

9

4

5

Acetylcholine-gated

receptor-channel (for

nonspecific cation traffic)

Na+

Motor end plate

Contractile elements within muscle fiber

Fig. 7-5, p. 252

neuromuscular junction
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
neuromuscular conditions and compounds
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