Download The Peripheral Nervous System: Efferent Division

Chapter 7
The Peripheral Nervous System:
Efferent Division
Objectives
PNS: Efferent Division
• System by which CNS communicates and
controls muscles and glands
• Autonomic and somatic systems
Overview of Nervous System
octc.kctcs.edu
Autonomic Nervous System
• System of motor neurons that innervates
smooth and cardiac muscle and glands
• Involuntary nervous system
• General visceral motor system
Characteristics
• Effectors
– Cardiac and smooth muscle
– Glands
• Efferent Pathway
– Involves two neurons
• Ganglia
– Preganglionic neuron > preganglionic axon > ganglionic neuron >
postganglionic axon > effector
• Neurotransmitter
– Norepinephrine, acetylcholine
– Excitatory, inhibitory
– All preganglionic neurons release acetylcholine
Divisions of ANS
• Sympathetic
– Fight or flight
– Norepinephrine
– Cholinergic fibers
• Parasympathetic
– Rest and digest
– Acetylcholine
– Adrenergic fibers
• Dual innervation
– Counterbalance
– Tonic activity
• Ongoing activity of both divisions
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Parasympathetic Division
• Anatomically simpler
• Craniosacral origin
– Cranial nerves III, VII, IX, X
•
•
•
•
Oculomotor
Facial
Glossopharyngeal
vagus
– Splanchnic nerves S2 - S4
anatomy.med.umich.edu
Sympathetic Division
• Anatomically more complex
– Innervates more organs
• Thoracolumbar origins
– T1 – L2
• Sympathetic chain (A)
– Paravertebral ganglia
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Paravertebral Ganglia
• Synapse within
same chain ganglion
• Ascend or descend
then synapse in
chain ganglion
• Pass through chain
ganglion without
synapsing
– Collateral ganglia
anatomy.med.umich.edu
Receptor Types
• Initiate tissue specific response
• Cholinergic receptors
– Acetylcholine receptors
• Nicotinic
– Opens nonspecific ion channels in postganglionic cell
– Action potential results
– Excitatory
• Muscarinic
– Activate secondary messengers via G proteins
– Cardiac and smooth muscles, exocrine and few endocrine glands
– Excitatory of inhibitory
Receptor Types
• Adrenergic receptors
– Norepinephrine and epinephrine receptors
• Alpha1
– Most sympathetic tissues
– Activates IP3/Ca2+ secondary messenger pathway
– Excitatory
• Alpha2
– Digestive organs
– Inhibitory (inhibits cAMP)
• Beta1
– Heart
– Activates cAMP
– Excitatory
• Beta2
– Smooth muscle of small vessels
– Activates cAMP
– inhibitory
Somatic Nervous System
• Motor neurons supply skeletal muscle
• Single neuron with cell bodies in ventral horn
of spinal cord
• Release acetylcholine
– Only excitatory
Neuromuscular Junction
• Junction of motor axon with a muscle cell
– Only one junction per muscle cell
• Motor end plate
– Specialized area on muscle cell for synapse
– High concentration of cholinergic receptors
– Open nonspecific ion channels
• Na+ rushes in producing an end-plate potential
• Action potential on muscle cell
– EPP opens ion channels in adjacent membrane
– Threshold is reached and an action potential propagates
away from the motor end plate
Acetylcholinesterase
• Enzyme that inactivate Ach
– Ensures that muscles only contract when needed
• Please look at chemicals and disease
associated with the neuromuscular junction