Post on 30-Dec-2015
description
Chapter 7The 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• 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. 1 2 1 2
– CNS control
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
Table 7-1, p. 234
ANS
• Autonomic nerve pathway
– Extends from CNS to an innervated organ
• Ganglion = neuronal cell bodies in the PNS
• Nuclei = neuronal cell bodies in the PNS CNS
– Two-neuron chain• Preganglionic fiber (synapses with cell body of second
neuron)
• Postganglionic fiber (innervates effector organ)
ANS
• Two subdivisions
– Sympathetic nervous system
• Thoracic and lumbar
– Parasympathetic nervous system
• Cervical and sacral
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)
Preganglionic fibers release acetylcholine (Ach)
Most postganglionic fibers release noradrenaline (norepinephrine)
Postganglionic fibers release acetylcholine
Craniosacralparasym-patheticnerves
Terminalganglion
Collateralganglion
Adrenalmedulla Blood
E,NE
NE
NE
AChACh
Terminalganglion
ACh
Sympathetic ganglion chain
= Sympathetic system
= Parasympathetic system
Thoracolumbarsympatheticnerves
Spinalcord
Brain
ACh
AChACh
Effectororgans
Cardiacmuscle
Smoothmuscle
Mostexocrineglandsandsomeendocrineglands
= Preganglionic fiber
= Postganglionic fiber
= Acetylcholine
= Norepinephrine
= Epinephrine
= Cell body
= Cell body
= Axon
Fig. 7-2, p. 235
ANS
• 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
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
Eye
Nasalmucosa
Sympathetic
Spinal nerves
Sympathetictrunk
Splanchinonerves
Liver
Gallbladder
PancreasAdrenal gland
Kidney
Smallintestine
Colon
Rectum
Urinary bladderGenitalia
Lung
Heart
Spinalnerves
Cranialnerves
Salivaryglands
ParasympatheticParotidgland
Trachea
Lacrimal gland
Stomach
SpleenSympathetic preganglionic fiber
Parasympathetic postganglionic fiber
Parasympathetic preganglionic fiber
Sympathetic postganglionic fiber
Fig. 7-3, p. 237
Effects of Autonomic Nervous System on Various Organs
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
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
Autonomic Neurotransmitters
Craniosacralparasym-patheticnerves
Terminalganglion
Collateralganglion
Adrenalmedulla Blood
E,NE
NE
NE
AChACh
Terminalganglion
ACh
Sympathetic ganglion chain
= Sympathetic system
= Parasympathetic system
Thoracolumbarsympatheticnerves
Spinalcord
Brain
ACh
AChACh
Effectororgans
Cardiacmuscle
Smoothmuscle
Mostexocrineglandsandsomeendocrineglands
= Preganglionic fiber
= Postganglionic fiber
= Acetylcholine
= Norepinephrine
= Epinephrine
= Cell body
= Cell body
= Axon
Fig. 7-2, p. 235
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– Andrenergic receptors – bind to norepinephrine and
epinephrine• Alpha (α) receptors• Beta (β) receptors
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 Receptors
– Andrenergic receptors – bind to norepinephrine and epinephrine
• G protein coupled
• Alpha (α) receptors - Ca second messenger system 1= stim cyclic amp, sympathetic tissues, vessel
constriction, contraction of smooth muscle, constrictor 2 blocks cyclic amp, decreased smooth muscle
contraction in the digestive tract, inhibitory to the effector organ
• Beta (β) receptors - cyclic amp
Found in the heart, increases contractility and rate
Found in the arterioles and airways, dilator
Spinal cord
Sympatheticpreganglionicfiber
Adrenalmedulla
BloodSympatheticpostganglionicfiber
both
= Acetylcholine
= Norepinephrine
= Epinephrine
Fig. 7-4, p. 239epinorepi
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
Regions of CNS Involved in Control of Autonomic Activities
• Can be influenced by prefrontal association complex through its involvement with emotional expression characteristic of individual’s personality
• Hypothalamus plays important role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states
• Medulla within brain stem is region directly responsible for autonomic output
• Some autonomic reflexes, such as urination, defecation, and erection, are integrated at spinal cord level
Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems
Outline
• Somatic nervous system
– Anatomy• Motor neurons
• Continuous to effector
• Voluntary
• Final common pathway
• ALS = Amyotropic lateral sclerosis, death of motor neurons
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
Comparison of Somatic and Autonomic Nervous System
Spinal cord
Sympatheticpreganglionicfiber
Adrenalmedulla
BloodSympatheticpostganglionicfiber
Target organs
= Acetylcholine
= Norepinephrine
= Epinephrine
Fig. 7-4, p. 239
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
Neuromuscular Junction
• Axon terminal of motor neuron forms neuromuscular junction with a single muscle cell
• Signals are passed between nerve terminal and muscle fiber by means of neurotransmitter ACh
• Released ACh binds to receptor sites on motor end plate of muscle cell membrane
• Binding triggers opening of specific channels in motor end plate
• Ion movements depolarize motor end plate, producing end-plate potential
• Local current flow between depolarized end plate and adjacent muscle cell membrane brings adjacent areas to threshold
• Action potential is initiated and propagated throughout muscle fiber
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
Axon of motor neuron
Myelin sheath
Axon terminal
Terminal button
Vesicle of acetylcholine
Acetylcholinereceptor site
Acetycholinesterase
Plasma membraneof muscle fiber
Voltage-gated
Na+ channel
Chemically gatedcation channel
Motor end plate
Contractile elements within muscle fiber
Voltage-gatedcalcium channel
Action potentialpropagationin motor neuron
Action potentialpropagationin muscle fiber
Fig. 7-6, p. 245
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
– Rigor mortis