Ch 14 - Autonomic Nervous System Flashcards
Divisions of the Autonomic Nervous System (ANS)
1) Parasympathetic Division - “Rest and Digest” - directs “housekeeping” activities
2) Sympathetic Division - “Fight or Flight” - quickly mobilizes the body for action
3 Differences Between the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS)
1) Effector organs - SNS = skeletal muscle; ANS = cardiac muscle, smooth muscle, glands
2) Efferent pathways and ganglia - SNS = single neuron from CNS to effector; ANS = 2-neuron chain to effector
3) Neurotransmitter effects - SNS = all release acetylcholine (ACh); ANS = release norepinephrine or ACh (can be either excitatory or inhibitory)
Neuron Chain to Reach Effector in ANS
1) Preganglionic neuron - cell body in CNS, axon synapses with second motor neuron
2) Postganglionic neuron - cell body is outside the CNS, axon extends to effector organ/
3) Ganglia - site of synapse between preganglionic neuron and postganglionic neuron
Origin of Fibers in Parasympathetic Division and Location of Ganglia
Originates in the Brain and Sacral Spinal Cord - Projects to Ganglia In or Near the Effector Organ
Preganglionic fibers are long, postganglionic fibers are short
Nerves involved in the Cranial Portion of the Parasympathetic Nervous System
III. Oculomotor nerve: innervates smooth muscle in eyes & muscle associated with lens (changes amount of light)
VII. Facial Nerve: stimulates large glands of head (salivary glands, nasal glands, lacrimal glands
IX. Glossopharyngeal nerve: activates parotid salivary gland (largest)
X. Vagus nerve: provides fibers to neck and every organ in thoracic & abd. cavities
Plexuses of Vagus Nerve
1) Cardiac plexus: supplies fibers to the heart
2) Pulmonary plexus: supplies fibers to lung
3) Esophageal plexus: fibers extend into abdominal cavity from esophageal plexus - innervates liver, gallbladder, stomach, small intestine, pancreas, proximal half of large intestine.
Basic Difference: Parasympathetic vs Sympathetic divisions of the ANS
Parasympathetic = “Rest & Digest”
Sympathetic = “Fight or Flight”
Origin of Fibers and Location of Ganglia in Sympathetic Division
Originates in the thoracolumnar region of spinal cord (T1-L2)
- short preganglionic, long postganglionic fibers - ganglia are thus close to spinal cord
- Cell bodies form lateral horns of spinal cord
Which division of the ANS is more complex - why?
Sympathetic division is more complex.
Not only innervates smooth muscle, cardiac muscle, and glands in body cavities
ALSO innervates smooth muscle & glands in superficial regions (sweat glands, arrector pili, smooth muscle in blood vessel walls)
Preganglionic fibers of Sympathetic division form:
Sympathetic trunk - allows preganglionic axons to travel to spinal nerves that are higher/lower - located on both sides of spinal cord
Pathway of sympathetic nerves to ganglion
1) Preganglionic fiber exits the spinal cord
2) Fiber passes through white ramus communicans
3) Fiber enters sympathetic trunk ganglion
What guides the preganglionic fiber to the sympathetic trunk in the Sympathetic ANS
White Ramus Communicans
Where the preganglionic fibers synapse with the postganglionic fibers in the sympathetic ANS
Sympathetic trunk ganglion
3 ways preganglionic & postganglionic fibers synapse in the Sympathetic ANS
1) Synapse at the same level - leave ventral root to sympathetic trunk ganglion at same level in spine
2) Synapse at higher/lower level - leave ventral root and pass up or down through sympathetic trunk to a different ganglion
3) Synapse at a distant collateral ganglion in abdomen or pelvis - pregang. passes through splanchnic nerve to a distant ganglion (such as the celiac)
Sympathetic pathway with synapses in trunk ganglia
1) Preganglionic neuron begins at lateral horn of dark matter in spinal cord
2) Passes out through ventral root
3) Continues through white ramus communicans to sympathetic trunk
4) Synapses with postganglionic neuron in sympathetic trunk ganglion
5) Postganglionic neuron passes out through grey ramus communicans to effectors
Sympathetic pathway to the head from synapses in trunk ganglia
1) Preganglionic fibers emerge from T1-T4
2) Synapse with postganglionic fibers at superior cervical ganglion of the sympathetic trunk
Postganglionic fibers serve skin and blood vessels of the head, stimulate dilator muscles of eyes, inhibits nasal and salivary glands, innervates muscles to upper eyelid, sends branches to heart
Sympathetic pathway to the thorax from synapses in trunk ganglia
1) Preganglionic fibers emerge from T1-T6
2) Most postganglionic axons pass through cardiac, pulmonary & esophageal plexuses to effector organ
Sympathetic pathway with synapses in collateral ganglia
1) Pregenglionic fibers from T5-L2 synapse in collateral ganglia
2) Form splanchic nerves
Greater splanchnic nerve, lesser splanchnic nerve, least splanchnic nerve
Lumbar splanchnic nerves and sacral splanchnic nerves
Function: serves abdominal viscera
Sympathetic pathway to the abdomen and pelvis with synapses in collateral ganglia
1) Fibers T5-L2 innervate abdomen Function: serve the stomach, most of the intestines, liver, spleen, and kidneys
2) Fibers T10-L2 innervate pelvis Function: serves the bladder, reproductive organs, distal half of large intestine
5 components of visceral reflex arcs
1) Receptor in viscera
2) Sensory neuron - non-encapsulated nerve endings
3) Integration center
4) Motor neurons (preganglionic and postganglionic)
5) Visceral effector
ANS Neurotransmitters
Acetylcholine (ACh) - effect depends on receptor (nicotinic or muscarinic)
Norepinephrine (NE) - effect depends on receptor it binds (Alpha or beta)
How Acetylcholine is released in ANS
Released by cholinergic fibers at:
1) All ANS preganglionic axons
2) All parasympathetic postganglionic axons at synapse with effector
Cholinergic receptors that bind ACh
1) Nicotinic receptors - found in ALL postganglionic neurons, hormone-producing cells of the adrenal medulla, sarcolemma of skeletal muscle cells (binding is always stimulatory)
2) Muscarinic receptors - all parasympathetic effectors and some sympathetic effectors (stimulatory OR inhibitory)
Ex. Binding of ACh to muscarinic receptors of heart is inhibitroy
Ex. Binding of ACh to muscarinic receptors of smooth muscle of gastrointestinal tract is stimulatory
Adrenergic receptors that bond NE
1) Alpha receptors - all sympathetic target organs
2) Beta receptors - heart, adipose tissue, kidneys, lungs, blood vessels
Binding of NE or epinephrine can be stimulatory or inhibitory
Ex. NE binding at beta receptors of heart increases activity
Ex. Epinephrine binding at beta receptors of bronchioles causes dilation
Interaction between Sympathetic and Parasympathetic Divisions of ANS
Most organs have dual innervation - send signals at the same time
Antagonistic Interactions of the Divisions - opposite effects, determined by what signal is stronger
Sympathetic and Parasympathetic Effects on blood vessels
1) Vasomotor (Sympathetic) Tone - continuous partial constriction of blood vessels, sympathetic fibers supply blood vessels & control blood vessel diameter
2) Parasympathetic Tone - present mostly in cardiac muscle tissue, smooth muscle tissue of digestive and urinary organs: slows heart rate, maintains normal activity
Sympathetic division can override parasympathetic tone
If blood pressure is low - vasomotor fibers fire more rapidly: constricts more, higher blood pressure
If blood pressure is high - vasomotor fibers fire less rapidly: muscle relaxes, blood vessels dilate
Unique Roles of the Sympathetic Division
1) Thermoregulatory response to heat - blood vessels dilate in response to heat, constrict in response to cold, sweat glands activated in response to heat
2) Renin release from kidneys - increases blood pressure
3) Metabolic changes - Increases metabolic rate of cells, raises blood glucose, mobilizes fats used fuel use
Localized vs Diffuse Effects of ANS Divisions
1) Parasympathetic division exerts highly localized, short-lived control
2) Sympathetic division exerts diffuse, long lasting control
Why are the parasympathetic division’s effects localized and short-lived
1) One preganglionic neuron synapses with one (or a few) postganglionic neurons
2) All parasympathetic fibers release ACh - quickly broken down by acetylcholinesterase
Why are the sympathetic division’s effects localized and short-lived
1) Preganglionic neurons synapse with multiple postganglionic neurons
2) NE and epinephrine prolong effects
Homeostatic Imbalances of the ANS (examples)
1) Hypertension - overactive vasoconstrictor response; heart works harder
2) Raynaud’s Disease - exaggerated vasoconstriction response due to cold or emotional stress; not enough blood
3) Autonomic dysreflexia - uncontrolled activation of autonomic neurons triggered by pain; arterial blood pressure skyrockets QUADRAPLEGIC
