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57 Cards in this Set

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Autonomic Nervous System
The ability of our internal environment depends on the ANS which is a system of motor neurons that innervates smooth and cardiac muscle and glands.
What does the ANS do?
The ANS shunts blood to needy areas, speeds or slows heart rate, adjusts blood pressure and body temperature, and increases or decreased stomach secretions.
Other names for ANS
The ANS is also called the involuntary nervous system which reflects its subconcious control, or the general visceral motor system, which indicates the location of most of its effectors.
The ANS uses a two-neuron chain to its effectors. Explain in detail how.
The cell body of the first neuron, the pregnangloionic neuron, resides in the brain or spinal cord. Its axon, the pregnaglionic axon, synapses with the second motor neuron, the ganglionic neuron, in an autonomic ganglion outside the CNS. The axon of the ganglionic, called the postganglionic axon, extends to the effector organ.
Preganglionic Neuron
Autonomic motor neuron that has its cell body in the CNS and projects its axon to a peripheral ganglion
A collection of nerve bodies outside the CNS
Ganglionic Neuron
Autonomic Motor Neuron that has its cell body in a peripheral ganglion and projects its (posteganglionic) axon to an effector
Pregnaglionic/ Postganglionic Axon (fiber)
Preganglionic Axons are lightly myelinated, thin fibers, and postganglionic axons are even thinner and are unmyelinated. Most pre and post ganglionic fibers are incorporated into spinal or canial nerves.; Postganglion def. - Axon of a ganglionic neuron, an autonomic motor neuron that has its cell body in a peripheral ganglion; the axon projects to an effector
Autonomic Ganglion
Collection of sympathetic or parasympathetic ganglionic neuronal cell bodies
Sympathetic Division
The division of the ANS that prepares the body for activity or to cope with some stressor (danger, excitement, etc.); the fight, fright, and flight subdivision.
Parasympathetic Division
The division of the ANS that oversees digestion, elimination, and glandular function; the resting and digesting subdivision
Norepinephrine (NE)
While all Somatic Motor neurons release ACh to make muscles contract, Neurotransmitters releaed into visceral effector organs by postganglionic autonomic fibers include NE secreted by most sympathetic fibers, and ACh released by parasympathetic fibers. Depending on the type of receptors present on the target organ, the organ's response may be either excitation or inhibition.
Dual Innervation
The ANS uses the parasympathetic and sympathetic divisions to serve the same visceral organs, but cause opposite effects. The sympathetic mobilizes the body during activity and the parasympathetic promotes maintenance functions and conserves body energy.
Easy way to remember Parasympathetic and Symathetic Divisions
Parasympathetic is the D division: Digestion, defecation, and diuresis (urination).
Sympathetic is the E division: Exercise, excitement, emergency, embarrassment.
Sympathtic and Parasympathetic Divisions differ in:
1. Their origion sites
P- brain and sacral spinal cord
S- thoracolumbar region of the spinal cord
2. The relative lengths of their fibers
P-long preganglionic and short postganglionic fibers
S- has the opp. condition
3. The location of their ganglia
P-located in the visceral effector organs
S- lie close to the spinal cord
Craniosacral Division
Parasympathetic Division is also called this b/c its preganglionic fibers spring from opp. ends of the CNS- the brain stem and sacral region of spinal cord.
Terminal Ganglia
In the Parasympathetic Division, the preganglionic axons extend from CNS almost to structures to be innervated, There the axon synapse with ganglioniv neurons located in terminal ganglia that lie very close to or within the target organs. Very short postganglionic axons issue from the terminal ganglia and synapse with effector cells in their immediate area.
Preganglionic fibers run in what nerves?
They run in oculomotor, facial, glossopharyngeal, and vagus cranial nerves. Their cell bodies lies in associated motor cranial-nerve nuclei in the bain stem.
Oculomotor Nerves (III)
Ciliary Ganglia:
• innervate smooth muscle in eyes to constrict pupils & bulge lenses (for close vision)
Facial Nerves (VII)
Pterygopalatine Ganglia:
travel to nasal mucosa, palate & pharynx; stimulate secretion from nasal and lacrimal glands
Submandibular Ganglia: stimulate submandibular & sublingual salivary glands
Glossopharyngeal Nerves (IX)
Otic Ganglia: stimulate parotid salivary glands
* Preganglionic fibers from cranial nerves III, VII & IX join branches of the trigeminal
nerve as postganglionic fibers to their targets
Vagus Nerves (X)
most (~90%) of preganglionic parasympathetic
fibers; branches to:
• cardiac plexuses: to slow heart rate
• pulmonary plexuses: to slow breathing rate
• esophageal plexuses: branches to the liver, gallbladder, stomach, small intestine,
kidneys, pancreas, & and half of large intestine to stimulate digestion
Sacral Outflow
arises from sacral spinal nerves S2-S4; branch to form pelvic splanchnic
nerves & synapse in distal half of large intestine, the urinary bladder, ureters &
reproductive organs
Pelvic Splanchnic Nerves and Inferior Hypogastric (Pelvic) Plexus
In sacral outflow, axons of the neurons (located in S2-S4) run in the ventral roots of the spinal nerves to the ventral rami and then branch off to from the pelvic splanchnic nerves, which pass through the inferior hypogastric (pelvic) plexus in the pelvic floor. Some preganglionic fibers synapse with ganglia in this plexus, but most synapse in intramural ganglia in the walls of the following organs: distal half of the large intestine, urinary bladder, ureters, and reproductive system.
Thoracolumbar division
The sympathetic division is also referred to as the thoracolumbar division b/c all preganglionic fibers of the sympathetic division arise from cell bodies of preganglionic neurons in spinal cord segments T1 through L2.
Lateral Horns (so-called Visceral Motor Zones)
produced from the presence of numerous preganglionic sympathetic neurons in the gray matter of the spinal cord.; posterolateral to the ventral horns that house somatic motor neurons.
After leaving the cord via the ventral root, preganglionic sympathetic fibers pass through ......
A white ramus communicans to enter an adjoining sympathetic trunk ganglion forming part of the sympathetic trunk. Looking like strands of glistening white beads, the sympathetic trunks flank each side of the vertebral column, The sympathetic trunk ganglia are also called chain ganglia or paravertebral ganglia.
Once a preganglioniv axon reaches a trunk ganglion, one of three things can happen to the axon...
1. The axon can synapse with a ganglionic neuron in the same trunk ganglion
2. The axon can ascend or descend the sympathetic trunk to synapse in another trunk ganglion.
3. The axon can pass through the trunk ganglion and emerge from the sympathetic trunk without synapsing.
Collateral or prevertebral ganglia
located anterior to the vertebral column; Unlike sympathetic trunk ganglia, the collateral ganglia are neither paired nor segmentally arranged and occur only in the abdomen and pelvis.
Pathways to the Head
Sympathetic preganglionic fibers serving the head emerge from spinal cord segments T1-T4 and ascend the sympathetic tunk to synapse with ganglionic Neurons in the superior cervical ganglion
Pathways to the Thorax
Sympathetic preganglionic fibers innervationg the thoracic organs originate at T1-T6. From there the preganglonic fibers run to synapse in the cervical trunk ganglia. Postganglionic fibers emerging from the middle and inferior cervical ganglia enter cervical nerves C4-C8. Some of these fibers innervate the heart via the cardiac plexus, and som innervate the thyroid gland, but most serve the skin.
Pathways with Synapses in Collateral Ganglia
Most of the preganglionic fibers from T5 down synapse in collateral ganglia, and so most of these fibers enter and leave the sympathetic trunks without synapsing. They form several nerves called splanchnic nerves, including the thoracic splanchnic nerves (greater, lesser and least) and the lumbar and sacral splanchnic nerves.
Splanchnic Nerves
These nerves contribute to a number of interweaving nerve plexuses known as the abdomina aortic plexus which clings to the surface of the abdominal aorta. This complex plexus contains several ganglia that serve the abdominopelvic viscera. From superior to inferior th most important of these ganglia are the celiac, superior mesenteric and inferior mesenteric named for the arteries they closely associate with.
Pathways to the Abdomen
Sympathetic innervation of the abdomen is via preganglionic fibers from T5 to L2 whgich travel in the thoracic splanvchnic nerves to snapse mainly at the celiac and superior mesenteric ganglia. Postganglionic fibers issuing from these ganglia serve the stomach intestines, liver spleen and kidneys.
Pathways to the Pelvis
Preganglionic fibers innervating the pelvis originate from T10 to L2 and then descend in the sympathetic trunk to the lumbar and sacral trunk ganglia. Some fibers sunapse there and the postganglionic fibers run in lumar and sacral splanchnic nerves to plexuses on the lower aorta and in the pelvis. Others pass directly to these autonomic plexuses to the pelvis organs and also the distal half of the large intestines. For the most part, sympathetic fibers inhibit the acitivity of the muscles and glands in these visceral organs.
Pathways with Synapses in the Adrenal Medulla
Some fibers traveling in the thoracic splanchnic nerves pass through the celiac ganglion without synapsing and terminate by synapsing with the hormone producing medullary cells of the adrenal gland. When stimulated by preganglionic fibers, the medullary cells secrete NE and epinephrine into the blood, producing the excitatory effects we have all felt as a surge of adrenaline.
Visceral Reflexes
Visceral reflex arcs have the same 5 elements as somatic reglex arcs. The visceral afferent (sensory) fibers are found both in spinal nerves and in automatic nerves
5 elements of Visceral Reflexes
1. Sensory receptor in viscera
2. Visceral sensory neuron
3. Integration center may be preganglionic neuron, may be a dorsal horn interneuron, may be within walls of gastrointestinal tract
4. Efferent pathway (two-neuron) chain: Pregnanglionic Neuron, Ganglionic Neuron
5. Visceral Effector
Visceral Sensory Neurons
Send info concerning chemical changes, stretch, and irritation of the viscera, are the first to link in autonomic reflexes
Visceral Reflex Arcs
have the same components as somatic reflex arcs- receptors, sensory neuron, integration center, motor neuron, effector- except that a visceral reflex arc has two neurons in its motor component.
Referred Pain
The fact that visceral pain afferents travel along the same pathways as somatic pain fibers helps explain the phenomenon of referred pain. Pain stimuli arising in the viscera are perceived as somatic in origin. Ex. heart attack pain in arm.
Cholinergic Fibers
ACh releasing fibers.
Major neurotransmitters released by ANS neurons
Acetylcholine (ACh) and Norepinephrine (NE)
Adrenergic Fibers
NE releasing fibers. Most sympathetic postganglionic axons release NE.
2 receptors that bind ACh
Nicotinic receptors and Muscarinic receptors
Nicotinic Receptors
respond to nicotine; found on sarcolemma of skeletal muscles at neuromuscular junctions; all are ganglionic neurons both sympathetic and parasympathetic and the hormone producing cells of the adrenal medulla; the effect is always stimulatory
Muscarinic Receptors
activated by a mushroom poison (muscarine); stimulated by postganglionic cholinergic fibers. All parasympathetic target organs and a few sympathetic targets such as eccrine sweat glands and some blood vessels of skeletal muscles. The effect can be either inhibitory or stimulatory.
Adrenergic Receptors
2 classes: alpha (stimulatory) and beta (inhibitory) which are further divided into subclasses. NE or epinephrine can have either excitatory or inhibitory effects on target organs depending on which subclass of receptor predominates in that organ.
Locations: Heart predominatly, but also kidneys and adipose tissue
Effect of binding: increases heart reate and strength; stimulates renin release by kidneys
Location: Lungs and most other sympathetic target organs; abundant on blood vessels serving the heart, liver and skeletal muscle
Effect: mostly inhibitory, dilates blood vessels and bronchioles. relaxes smooth muscle walls of digestive and urinary visceral organs; relaxes uterus
Location: Adipose tissue
Effect: Stimulates lipolysis by fat cells
Sympathetic or Vasomotor Tone
the vascular system is innervated by sympathetic fibers that keep the blood vessels in a continual state of partial contriction.
Parasympathetic Tone
Slows the heart and dictates the normal activity levels of the digestive and urinary tracts
Cooperative Effects
Parasympathetic stimulation causes vasodilation of blood vessels in the external genetalia and is responsible for erection
Unique Roles of the Sympathetic Division
1. Thermoregulatory Responses to Heat
2. Release of Renin from the Kidneys
3. Metabolic Effects
-increase the metabolic rate of body cells
- raises blood glucose levels
- mobilizes fats for use as fuels
ANS Control by Higher Centers:
-Brain stem & spinal cord: reticular formation of brain stem, regulation of pupil size, respiration, heart, blood pressure, swallowing, etc.
-Spinal Cord- Urination, defecation, erection, ejaculation reflexes
- Hypothalamus: Overall integration center of ANS, the boss. (regulates heart activity, blood pressure, body temperature, water balance & endocrine system activity)
- Cerebral Cortex: although most autonomic functioning is involuntary, in some cases
voluntary control appears possible
(high blood pressure) may result from increased
vasoconstriction by sympathetic fibers (could be stress-induced)