Week 10 Autonomic Nervous System -...
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1 1 Collin County Community College BIOL 2401: Week 10 Autonomic Nervous System 2 Organization Central NS Peripheral NS Sensory Division Motor Division Visceral Division Somatic Division Autonomic Division Sympathetic Parasympathetic Enteric
Transcript of Week 10 Autonomic Nervous System -...
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Collin County Community College
BIOL 2401:
Week 10
Autonomic NervousSystem
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Organization
Central NS Peripheral NS
Sensory Division Motor Division
Visceral DivisionSomatic Division
Autonomic Division
Sympathetic
ParasympatheticEnteric
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The Autonomic Nervous System
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Differences between Somatic & Autonomic
Somatic NS
• stimulates skeletal muscles• referred to as the voluntary system• heavy, myelinated type A fibers (fast transmission)
Autonomic NS
• stimulates glands, smooth muscle, heart muscle• referred to as the involuntary system• light to un - myelinated fibers (slower transmission)
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The somatic nervous system is composed of motor neurons thatcontrol the contraction of the skeletal muscles.
The ganglion is an anatomically visible area where the pre- andpost-ganglionic neurons of the ANS form their synaptic junctions.
The autonomic nervous system is composed of sets of 2 neuronsthat control the activities of involuntary processes.
Important Anatomical Differences
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The Autonomic Nervous System
• always a two neuron chain that innervates cardiac,smooth muscle and glands
• cell body of the first neuron (the pre-ganglionic axon)resides in the brain or spinal column.
• synapses with a second neuron (ganglionic neuronwith postganglionic axon) in an autonomic ganglionoutside the CNS
• postganglionic axon extends to the effector organ (cellbody of postganglionic neuron is in the ganglion)
• pre-ganglionic neurons are lightly myelinated;postganglionic ones are thin and unmyelinated
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Anatomical Differences Within ANS
• Sympathetic fibers originate fromthoraco-lumbar region of SC
• Sympathetic pathways have shortpre-ganglionic fibers, longpostganglionic fibers.
• They have long pre-ganglionic fibers,short postganglionic fibers
• PS nerves originate from Brain andSacral area of the spinal column
PS - NS
S - NS
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Voluntarycommand:
Move!
Skeletal muscle contraction
Involuntarycommand:
Rest & digest.
Involuntarycommand:
Emergency!
M o t o r n e u r o n
Heart, smoothmuscle, glands,many “involuntary”targets”
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The Sympathetic Nervous System
• All cell bodies of the preganglionic fibers arise inthe SC segments T1-L2
• The nuclei of the preganglionic fibers are located inthe lateral gray horn
• Pre ganglionic fibers leave the SC and enter theventral roots of the spinal cord segment
• They form ganglions with postsynaptic neurons inthree major areas, which will innervate therespective target organs
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Sympathetic Ganglions
Sympathetic Chain Ganglia
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Sympathetic Ganglions
Sympathetic Chain Ganglia
• Although the presynaptic neurons originate from SCsegments T1-L2, this chain of ganglia runs up and down thespinal cord (remember that the preganglionic neuron isshort ! )
• There are 3 cervical, 12 thoracic , 5 lumbar, 5 sacral and 1coccygeal ganglion.
• These nerves provide autonomic motor commands forstructures in body wall, thoracic cavity, head, neck or limbs
• The nerves that serve heart and lungs are known as thesympathetic nerves
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Sympathetic Ganglions
Sympathetic Chain Ganglia• In general, the preganglionic fibers are
myelinated while the postganglionic fibersare un-myelinated.
• Because of the chain, every spinal nerve hasa gray ramus that carries sympatheticpostganglionic fibers for distributionthrough the body
• If ventral roots of thoracic spinal nerve isdamaged, motor function and sympateticfunction will be lost on that side
• If ventral root of cervical spinal nerve isdamaged, motor function is lost but notsympathetic function.
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Sympathetic Ganglions
Collateral ganglia
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Sympathetic Ganglions
Collateral ganglia
• These ganglia are formed by presynaptic neurons thatpass through the synaptic chain without forming asynapse there
• These presynaptic sympathetic fibers are called thespalnchic nerves
• They form a synapse with postsynaptic neurons inareas anterior to the vertebral column , known as thecollateral ganglia
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Sympathetic Ganglions
Collateral ganglia
The celiac ganglia (D)• postganglionic neurons serve the
stomach, liver, spleen
The superior mesenteric ganglia (E)• postganglionic neurons innervates small
intestine and upper part of large intestine
The inferior mesenteric ganglia (F)• postganglionic neurons serve the rest of
large intestine, kidneys, urinary bladderand sex organs
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Sympathetic Ganglions
Adrenal Medullae
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Sympathetic Ganglions
Adrenal Medullae
Preganglionic sympathetic fibers enter the centerarea of the adrenal gland, called the adrenalmedulla
In contrast to the other systems discussed, thepostganglionic neurons are very short, modifiedneuro-endocrine cells that reside within theadrenal medulla area
On stimulation, these cells release thecatecholamines epinephrine (80 %) andnorepinephrine into the bloodstream.
They then function similarly as hormones. Theyonly will have an effect on those target organsthat have receptors for these molecules.
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Sympathetic System
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Sympathetic Ganglions
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The Sympathetic Nervous System
In crises, the entire sympathetic division responds
This is called the Sympathetic activation• Controlled by centers in the Hypothalamus• Affects include
• increased alertness, energy and euphoria,• increased cardiovascular and respiratory activities• elevation in muscle tone,• mobilization of energy resources
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The Para Sympathetic Nervous System
• The ParaSympatethic system arises frompreganglionic neurons in the brainstem and sacralsegments of spinal cord
• The preganlionic neurons are long while theGanglionic neurons are short and reside in peripheralganglia located within or near target organs
• In contrast to SNS, all ganglionic neurons are locatedin the same ganglion and influence thus the sameorgan; the effect is thus more localized and specific.
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The Para Sympathetic Nervous System
• Preganglionic fibers leave the brain as cranial nerves III, VII,IX, X
• Those from III, VII and IX synapse in the head ganglia areknown as ciliary, pterygopalatine, submandibular and oticganglia.
• The vagus nerve provides innervation in the neck, thorax andabdominal cavity
• Sacral neurons form the pelvic nerves• These latter innervate kidneys, urinary bladder, terminal
portion of large intestine, sex organs
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The Para Sympathetic Nervous System
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The Para Sympathetic Nervous System
Effects produced by the PSNSdivision– Secretion of salivary glands,
intestinal glands– Food processing by
increasing activity of smoothmuscle
– Constriction of respiratorypathways
– Reduction in heart rate andcontraction
– Sexual arousal– Energy absorption
