General Anatomy of the Autonomic Nervous System
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Transcript of General Anatomy of the Autonomic Nervous System
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Human Anatomy 5th ed. 2005Benjamin Cummings
General Anatomy of the Autonomic Nervous System
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Human Anatomy 5th ed. 2005Benjamin Cummings
Introduction to ANS
• Regulates activity of smooth muscle, cardiac muscle and glands
• Operates without conscious control
• Named autonomic because was thought to be AUTONOMUS (working without CNS)
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Human Anatomy 5th ed. 2005Benjamin Cummings
Autonomic Nervous System
• But to operate it depends on continuous flow of sensory input from:
– Visceral organs and – Blood vessels(not consciously perceived) into
– INTEGRATING CENTERS IN THE CNS.
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Human Anatomy 5th ed. 2005Benjamin Cummings
Autonomic Nervous System
• Structurally then ANS includes:– Autonomic sensory neurons– Integrating centers in the CNS– Autonomic motor neurons to smooth
muscle, cardiac muscle and glands
Where in the CNS? Hypothalamus and brain stem
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Human Anatomy 5th ed. 2005Benjamin Cummings
Comparing the ANS and Somatic NS
• Structurally then SNS includes:
– Somatic sensory neurons
– Integrating centers in the CNS (Cortex)
– Somatic motor neuron to skeletal muscles only
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Human Anatomy 5th ed. 2005Benjamin Cummings
Comparing the ANS and Somatic NS
• Somatic- the effect of a motor neuron is always excitation
• Autonomic- the effect of a motor neuron is either excitatory or inhibitory
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Human Anatomy 5th ed. 2005Benjamin Cummings
Autonomic Nervous System
• Makes all routine adjustments in physiological systems.
• The ANS pathway from the CNS to the effector always involves 2 neurons synapsing in an autonomic ganglion
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Human Anatomy 5th ed. 2005Benjamin Cummings
ANS
– Preganglionic (neuron #1) – cell body is in the CNS, axon extends to the ganglion outside the CNS
– Postganglionic (neuron #2) – cell body is in the ganglion, axon extends to the visceral effector
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Human Anatomy 5th ed. 2005Benjamin Cummings
Nerve Fibers of the ANS
• Preganglionic (neuron #1)
– Always myelinated
– Neurotransmitter is always ACh
• Postganglionic (neuron #2)
– Always nonmyelinated
– Neurotransmitter is Ach or norepinephrine
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Subdivisions of the ANS
• Sympathetic Division
– Fight-or-flight
• Parasympathetic Division
– Rest-and-digest
• These divisions are anatomically distinct
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Human Anatomy 5th ed. 2005Benjamin Cummings
Sympathetic
• Sympathetic division (thoracolumbar) – Cell bodies for all the neurons #1 reside
in the thoracic and lumbar portions of the spinal cord.• T1 – L2
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Human Anatomy 5th ed. 2005Benjamin Cummings
Sympathetic– Stimulates
• heart beat
• tissue metabolism,
• increases alertness,
• prepares the body to deal with emergencies
• (“fight or flight” division)
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Human Anatomy 5th ed. 2005Benjamin Cummings
T1-L2
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic
•Parasympathetic division (craniosacral)
–Cell bodies reside in the brain stem (cranial nerves) or in the sacral portion of the spinal cord.
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Human Anatomy 5th ed. 2005Benjamin Cummings
Cranial & Sacral
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic
– Slows the heart rate,
– inhibits senses,
– prepares the body for rest and relaxation; (“rest and digest” division).
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Human Anatomy 5th ed. 2005Benjamin Cummings
The Sympathetic Division
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Human Anatomy 5th ed. 2005Benjamin Cummings
Sympathetic Chain Ganglia
– Synapses of neurons #1 and #2 are in a chain of ganglia that run alongside the spinal cord
– Extends on both sides of the vertebral column
– Carries preganglionic fibers and cell bodies of postganglionic neurons
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Human Anatomy 5th ed. 2005Benjamin Cummings
Ganglia
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Human Anatomy 5th ed. 2005Benjamin Cummings
Anatomy of the chain
• Rami communicantes from the spinal nerves connect to the chain
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
A closer look at spinal nerves
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Human Anatomy 5th ed. 2005Benjamin Cummings
Routes of Preganglionic Axons
• Cell bodies of neurons #1 lie in the lateral gray horns of the spinal cord
• The axons of neurons #1 leave the spinal cord via the ventral root
• These axons pass to the spinal nerve• Axons leave the spinal nerve via the white
branches (rami communicantes)• Connect with the sympathetic chain ganglia
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Human Anatomy 5th ed. 2005Benjamin Cummings
Routes of Preganglionic Axons
• There are 3 possible routes that sympathetic neurons may follow
• Possibility #1: synapses within the ganglion at that level and
– Second neuron leaves at that level via the gray ramus communicans, exits to the visceral effector
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Routes of Preganglionic Axons
• Possibility #2: neuron #1 goes up or down the chain and synapses at some other level.
– Second neuron: leaves at that other level via the gray ramus communicantes, and exits to the visceral effector.
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Routes of Preganglionic Axons
• Possibility #3: neuron #1 does not synapse in the chain (exception!!) but exits and synapses in a collateral ganglion near a major blood vessel.
– Neuron #2 travels from that ganglion to the visceral effector.
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Where are the Collateral Ganglia ?
• Location –Near a major blood vessel– Celiac ganglion
• Innervates upper abdominal viscera – Superior mesenteric
• Innervates middle abdominal viscera– Inferior mesenteric
• Innervates lower abdominal & pelvic organs
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Human Anatomy 5th ed. 2005Benjamin Cummings
The Adrenal Medulla
• Yet another type of innervation:
– Going to the adrenal medulla
– No synapse in ganglia
– No synapse in collateral ganglia
– YES synapse in the adrenal medulla
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Adrenal Medulla
• Only preganglionic neurons are in this pathway
• Neuron #1 stimulates the medulla,
• The medulla releases norepinephrine and epinephrine (adrenaline) to blood
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Human Anatomy 5th ed. 2005Benjamin Cummings
Adrenal Medulla
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Human Anatomy 5th ed. 2005Benjamin Cummings
Effects of Sympathetic Stimulation
• Widespread
– The sympathetic chain allows one preganglionic fiber to synapse with many postganglionic neurons
• Enhanced & prolonged by the adrenal medulla
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Human Anatomy 5th ed. 2005Benjamin Cummings
Convergence
• See heart
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Human Anatomy 5th ed. 2005Benjamin Cummings
Neurotransmitters of Sympathetic Division
• Preganglionic fibers release acetylcholine (Ach) Therefore they are called:– Cholinergic
• Postganglionic fibers (most) release norepinephrine (NE) (=noradrenaline)– Adrenergic
• Adrenal medulla releases norepinephrine and epinephrine (adrenalin)
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
Functions of the Sympathetic Division
• Heart: increases rate
• Lung bronchioles: dilates bronchioles
• Salivary glands: produce viscous fluid
• Stomach: decreases motility
• Pupil: dilates
• Sweat glands: produce secretions
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Human Anatomy 5th ed. 2005Benjamin Cummings
Summary of Sympathetic Division
• Cell bodies are found in the thoracic and lumbar portions of the spinal cord
• Preganglionic fibers are short, connect to the sympathetic chain, and synapse with long postganglionic fibers
• Preganglionic fibers produce ACh, postganglionic fibers produce NE or Ach
• “Fight or flight” division
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
The Parasympathetic Division
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic division
• Cell bodies are in the brain or in the gray matter of the spinal cord (sacral region)
• Neurons #1 exit the cranial region through cranial nerves 3, 7, 9, & 10 or
• Neurons #1 exit the spinal cord through the sacral spinal nerves
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic
• Neurons #1 are long and synapse with neurons #2 (short) in ganglia
• Ganglia are found on, or
– near the visceral effector
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic ganglia
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Human Anatomy 5th ed. 2005Benjamin Cummings
Neurotransmitter of Parasympathetic Division
• Preganglionic fibers: Acetylcholine
• Postganglionic fibers: Acetylcholine
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Human Anatomy 5th ed. 2005Benjamin Cummings
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Human Anatomy 5th ed. 2005Benjamin Cummings
General Functions of the Parasympathetic
• Prepares the individual for rest and repose
• “Rest & digest” division
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Human Anatomy 5th ed. 2005Benjamin Cummings
Effects on various organs:
Heart: decreases rate• Lung bronchioles: constricts bronchioles• Salivary glands: produces watery fluid
fluid• Stomach: increases motility• Pupil: constricts• Sweat glands: reduces secretions
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Human Anatomy 5th ed. 2005Benjamin Cummings
Summary of the Parasympathetic Division
• Cell bodies are found in the brain and in the sacral region of the spinal cord
• Preganglionic fibers are long and synapse with short postganglionic fibers on or near the target viscera
• Both preganglionic and postganglionic fibers produce Ach
• “Rest & digest” division
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Human Anatomy 5th ed. 2005Benjamin Cummings
Relationship Between the Sympathetic and Parasympathetic Divisions
• Most organs receive dual innervation
• It is a tug of war between the two
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Human Anatomy 5th ed. 2005Benjamin Cummings
ANS either increases excitation or inhibits the activity
– Ex. Sympathetic fibers increase heart rate, parasympathetic fibers decrease heart rate.
– Homeostasis comes from the balance of the two.
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Human Anatomy 5th ed. 2005Benjamin Cummings
ANS either increases excitation or inhibits the activity
Ex.#2 Sympathetic fibers decreases stomach motility.
Parasympathetic fibers increase stomach motitlity
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Human Anatomy 5th ed. 2005Benjamin Cummings
Parasympathetic innervation
• The cranial nerve fibers involved are motor - control smooth muscle & glands in the upper body– Cranial nerve #3 – lens & pupil – Cranial nerve #7 – lacrimal glands,
submandibular & submaxillary glands (salivary)– Cranial nerve #9 – parotid gland (salivary)– Cranial nerve #10 - viscera of thorax & abdomen
• Sacral nerves innervate the kidneys, colon, & sex organs