Chapter 14 The Autonomic Nervous System Autonomic system System of nerves mediating involuntary actions Regulates body organ activity Maintains normal internal functions Divided into sympathetic and parasympathetic divisions Allows for varied nervous system responses in times of stress and rest
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Chapter 14 The Autonomic Nervous System Autonomic system System of nerves mediating involuntary actions Regulates body organ activity Maintains normal.
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Chapter 14The Autonomic Nervous System
Autonomic systemSystem of nerves mediating involuntary actionsRegulates body organ activityMaintains normal internal functionsDivided into sympathetic and parasympathetic divisionsAllows for varied nervous system responses in times of stress and rest
Figure 14 Section 1 1
A schematic of the somatic nervous system(SNS), which provides conscious and sub-Conscious control over skeletal muscles
BRAIN
Upper motorneurons in
primary motorcortex
Skeletalmuscle
Skeletalmuscle
Lowermotor
neurons
Spinal cord
Somaticmotornuclei ofspinal cord
Somatic motornuclei of brain
stem
Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization
• Somatic nervous system (SNS)– Includes processes perceived or controlled consciously
– Somatic sensory portion• detects stimuli from special senses, skin, and proprioceptors
• sends information to CNS
– Somatic motor portion• transmits nerve signals from CNS to control skeletal muscles
Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization
• Autonomic nervous system (ANS)– Includes processes regulated below conscious level
– Visceral sensory portion• detects stimuli from blood vessels and internal organs
– Autonomic motor portion (visceral motor)• transmits nerve signals to cardiac muscle, smooth muscle, and glands
– Functions to maintain homeostasis• constant internal environment
Divisions of the Autonomic Nervous Systems: Functional Differences
• Motor component of ANS– Subdivided into parasympathetic and sympathetic divisions
– Parasympathetic division• functions to maintain homeostasis at rest
• energy conservation and replenishing stage
• “rest-and-digest” division
– Sympathetic division• prepares the body for emergencies
• “fight-or-flight” division
• increased alertness and metabolic activity
• “three E’s”: emergency, exercise, or excitement
Figure 14.1 1
Autonomic Nervous System
Sympathetic Division Parasympathetic Division
In the sympathetic division, or thoracolumbar(thor-a-kō-LUM-bar) division, axons emerge from the thoracic and superior lumbar segments of the spinal cord and innervate ganglia relatively close to the spinal cord.
In the parasympathetic division, or cranio-sacral (krā-nē-ō-SĀ-krul) divions, axonsemerge from the brain stem and the sacralsegments of the spinal cord, and they innervateganglia very close to (or within) target organs.
The two main divisionsof the ANS: the sympatheticand parasympatheticdivisions
Cranial nerves(III, VII, IX, andX)
T1T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
S2
S3
S4
Sacral nerves(S2, S3, S4 only)
Lumbar nerves(L1, L2 only)
Thoracicnerves
Divisions of the Autonomic Nervous Systems: Anatomic Differences
• Parasympathetic– Preganglionic neuron in
brainstem or S2-S4 spinal cord
– Termed craniosacral division
– Ganglionic neuron innervating muscles or glands
– Preganglionic axons longer
– Postganglionic axons shorter
– Few preganglionic axons
– Ganglia close to or within effector
• Sympathetic– Preganglionic neuron in lateral
horns of T1-L2
– Termed thoracolumbar division
– Ganglionic neuron innervating muscles or glands
– Preganglionic axons shorter
– Postganglionic axons longer
– Many preganglionic axons
– Ganglia relatively close to spinal cord (in sympathetic trunk ganglia or prevertebral ganglia)
Autonomic ganglion(close to or within effector organ wall)
Sympathetic Division
Short, branchingpreganglionic axon
Preganglionicneuron
Autonomic ganglion(close to the vertebral column)
Ganglionic neuron
Long postganglionic axonShort
postganglionicaxon
The parasympathetic division has short axons with relatively few branches and ganglia located close to or within the wall of the organ.
The sympathetic division has long axons with many branches and ganglia located in the sympathetic trunk or prevertebral ganglia
Parasympathetic Division: Cranial Components
• Cranial components– Oculomotor(lens & iris), facial(lacrimal glands), and glossopharyngeal
nerves(parotid)• convey parasympathetic information to the head
– Vagus nerve• parasympathetic information for thoracic and most abdominal organs
• increased mucus production and decreased airway diameter
• decrease in heart rate and force
• causes increased smooth muscle motility and secretory activity
Parasympathetic Division: Cranial Components
The oculomotor nerve innervates the ciliary and constrictor muscles of the eye.The facial nerve innervates the lacrimal, submandibular, and sublingual glands.The glossopharnygeal nerve innervates the parotid salivary gland.The vagus nerve innervates the thoracic organs, most of the abdominal organs, and the gonads.
Which four cranial nerves have a parasympathetic component? What organs are innervated by each?
• Neurotransmitters– Acetylcholine (ACh) and norepinephrine (NE)
– Bind to specific receptors on postsynaptic cell
– Cause stimulation or inhibition, depending on receptor
• Acetylcholine– Synthesized and released by cholinergic neurons
• all sympathetic and parasympathetic preganglionic neurons• all parasympathetic ganglionic neurons• neurons innervating sweat glands and blood vessels of skeletal muscle
• Norepinephrine– Synthesized and released by adrenergic neurons
• most other sympathetic ganglionic neurons• form network of swellings at target organ
– termed varicosities– contain stored NE– NE released along length of axon