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Flashcards in Ch. 19 ANS Deck (24)


autonomic sensory neurons: located in visceral organs and in blood vessels that convey information to CNS
integrating centers: in the CNS
autonomic motor neurons: propagate from CNS to various effector tissues to regulate that activity of smooth muscle, cardiac muscle, and many glands
Enteric Division: specialized network of nerves and ganglia forming an independent nerve network within the wall of GI tract


Anatomy of Autonomic Motor Pathway

- first of two motor neurone in any autonomic motor pathway is called preganglionic neuron
- cell body is in the brain or spinal cord, and its axon exits the CNS as is a small-diameter, myelinated fibres that usually extends to an autonomic ganglion
- postganglionic neuron lies entirely outside the CNS, its cell body and dendrites are located in an autonomic ganglion, where it forms one or more synapses with preganglionic neutrons
- axon of a postganglionic neutron is a small-diameter, unmyelinated Type C finer that terminates in a visceral effector


Sympathetic: Preganglionic Neurons

- cell bodies go preganglionic neutrons are located in lateral horns of gray matter in 12 thoracic segments and first two lumbar segments of spinal cord
- thoracolumbar division origin
3 general groups of autonomic ganglia: sympathetic ganglia are sites of synapses between sympathetic preganglionic and postganglionic neutrons
- sympathetic trunk ganglia: lie in a vertical row on either side of vertebral column
- prevertebral ganglia: lies anterior to vertebral column and close to large abdominal arteries
- postganglionic axons: from prevertebral ganglia innervate organs below the diaphragm


Autonomic Ganglia

4 major prevertebral ganglia
- celica ganglion: is on either side of celiac artery just inferior to the diaphragm
- superior mesenteric ganglion: near beginning of superior mesenteric artery in upper abdomen
- inferior mesenteric ganglion: near beginning of inferior mesenteric artery in middle of the abdomen
- aorticorenal ganglion: near the renal artery as it branches from arota


Sympathetic Postganglionic Neurons

- sympathectic preganglionic neutrons pass to sympathetic trunk ganglia, connect with postganglionic neutrons in one of the ways...
1. axon may synapse with postganglionic neutrons in first ganglion it reaches
2. axon may ascend or descend to higher or lower ganglion before synapsing with postganglionic neurons
3. axon may continue, without synapsing, through the sympathetic trunk ganglion to end at a prevertebral ganglion and synapse with postganglionic neutrons there


Parasympathetic: Parasympathetic Ganglion

- cell bodies of preganglionic neutrons of parasympathetic division are located in nuclei of four cranial nerves in the brain stem (3, 7, 9, 10) and in lateral gray horns of 2-4 sacral segments of spinal cord
- cranialsacral division
- sympathetic preganglionic axons are relatively short, while para axons are long
- preganglion axons of para synapse with post ganglion neutrons in terminal ganglia
- most ganglia are located close to or within wall of visceral organ; longer than most axons of sympathetic pre ganglion neurons


Terminal Ganglia

- in the head have specific names:
- ciliary ganglion
- pterygopalatine ganglion
- submandibular ganglion
- otic ganglion


Parasympathetic Postganglionic Neurons

- pass to terminal ganglia near or within visceral effector
- in ganglion the presynaptic neuron synapses with only four or five postsynaptic neutrons, all supply single visceral effector
- parasympathetic responses can be localized to a single effector
- parasympathetic postganlionic axons are short


Postganglionic Neurons

- postganglionic autonomic fibers do not end in a single terminal swelling like a synaptic knob or end plate
- terminal branches of autonomic fibres contain numerous swellings, called varicosities, that simultaneously release neurotransmitter over a large area of inverted organ rather than on single cells
- extensive release of neurotransmitter and greater number of postganglionic neurons means that entire organs, rather than discrete cells, are typically influenced by autonomic activity


Structure of Sympathetic Division

- cell bodies of sympathetic preganglionic neutrons are part of lateral horns of all thoracic segments and of first two lumbar segments (thoracolumbar division) of spinal cord
- preganglionic axons leave spinal cord along with somatic motor neutrons at same segmental level
- exiting through the intervertebral foramina, myelinated preganglionic sympathetic axons pass into the anterior root of a spinal nerve and enter a short pathway called a white rams before passing to the nearest sympathetic trunk ganglion on same side


Superior Cervical Ganglion

superior cervical ganglion: serve head, heart, sweat glands, smooth muscle of eye, blood vessels of face, lacrimal glands, nasal mucosa, salivary glands
- gray rami communicates from superior cervical ganglion also pass to the upper two or four cervical spinal nerves
- middle cervical and inferior cervical ganglion: postganglionic neutrons leaving middle cervical ganglion and inferior cervical ganglion innervate the heart
- thoracic portion: region receives most of the sympathetic preganglionnic axons and its postganglionic neurons innervate the heart, lungs, bronchi, and other thoracic viscera; in skin, neutrons innervate sweat glands, blood vessels, and arrestor pili muscles of hair follicles


Lumbar region of Sympathetic Trunk

- unmyelinated postganglionic axons from lumbar and sacral sympathetic trunk ganglia enter a short pathway called gray rams and then merge with a spinal nerve or join the hypogastric plexus via direct visceral branches
- gray rami communicantes: structures containing postganglionic axons that connect ganglia of various portions of sympathetic trunk ganglion to spinal nerves
- preganglionic axons extend from white rams commuicans into sympathetic trunk ganglion, they give off several axon collaterals
- splanchnic nerves: extend to and terminate in outlying prevertebral ganglia


Structure of Parasympathetic Division

- cranio-sacral origin
- axons emerge as part of a cranial nerve or as part of anterior root of a spinal nerve
- cranial parasympathetic outflow consists of preganglionic axons that extend from brain stem in four cranial nerves
- sacral parasympathetic outflow consists of preganglionic axons in anterior roots of second through fourth sacral nerves
- preganglionic axons of both cranial and sacral outflows end in terminal ganglia, where they synapse with postganglionic neurons


ANS neurotransmitters and Receptors: Cholinergic Neurons and receptors

- release acetylcholine
- cholinergic neurons include:
1. all sympathetic and para pre ganglion neutrons
2. sympathetic postganglionic neutrons that innervate most sweat glands
3. all para postganglionic neurons
- ACh is stored in synaptic vesicles and released by exocytosis
- 2 types of cholinergic receptors, both bind ACh, are nicotinic and muscarinic receptors


Nicotinic and Muscarinic Receptors

Nicotinic: present in plasma membranes of dendrites and cell bodies of both sympathetic and parasympathetic preganglionic neutrons and in motor end plate at neuromuscular junction
Muscarinic: present in plasma membranes of all effectors innervated by sympathetic and parasympathetic post ganglion axons
- most sweat glands which receive innervation from cholinergic sympathetic postganglionic neutrons, possess muscarinic receptors


Adrenergic Neurons and Receptors

- adrenergic neurons release NE
- most sympaethic postganglionic neutrons are adrenergic; NE is synthesized and stored in synaptic vesicles and released by exocytosis
- adrenergic receptors bind both NE and E
- main types are: alpha and beta receptors which are found on visceral effectors innervated by most sympathetic postganglionic axons


Autonomic Neurotransmitters

- postganglionic sympathetic neutrons are adrenergic
- postganglionic para neurons release ACh
- sympathetic preganglionic neutrons release ACh


Functions of ANS

sympathetic- adrenergic effects
1. gears body for action
2. fight or flight
parasympathetic- cholinergic effects
1. converses body's energy
2. rest and digest


Functions of Sympathetic

- pupils dilate
- heart rate, force of contraction and blood pressure increase
- airways dilate, faster movement of air into and out of lungs
- blood vessels supply organs that are involved in exercise or fighting off danger dilate
- liver cells perform glycogenolysis and adipose tissue cells perform lipolysis
- release glucose by liver increases blood glucose level
- processes not needed for stressful situation inhibited


Effects of Sympathetic Stimulation

- longer lasting and more widespread
1. sympathetic postganglionic axons diverge more extensively; many tissues are activated simultaneously
2. AchE quickly inactivated ACh, but NE lingers in synaptic cleft
3. E and NE secreted as hormones into blood from adrenal medulla intensifies and prolong responses caused by NE released as a neurotransmitter from sympathetic postganglionic axons
- in time blood-borne NE and E are inactivated by enzymatic destruction in liver


Function of Parasympathetic Responses

- rest and digest
- support body functions that conserve and restore body energy during times of rest and recovery
- quiet intervals between periods of exercise, impulses to digestive glands and smooth muscle of GI tract predominate over sympathetic impulses


Autonomic Plexuses

- in thorax, abdomen, and pelvis, axons of both sym. and para pregnalgionic neutrons form tangles networks called autonomic plexuses, many lie in major arteries
- may contain sympathetic ganglia and axons of autonomic sensory neutrons
- autonomic reflexes are responses that occur when nerve impulses pass over an autonomic reflex arc
- reflex play a key role in regulating controlled conditions in body such as: bp by adjusting heart rate, force ventricular contraction and blood vessel diameter
- digestion by adjusting motility and muscle tone of GI tract
- defecation and urination by regulating opening and closing of sphincters


Types of Plexuses

1. Cardiac Plexus: increased sympathetic activity increases heart rate and bp; increased para. activity decrease heart rate
2. Pulmonary Plexus: para. pathway causes bronchoconstriction and increased secretion from mucous glands of bronchial tree; sym. innervation causes bronchodilation
3. Esophageal Plexus: para. axons control swallowing reflex
4. Abdominal Arotic Plexus: consists of celiac plexus, superior mesenteris plexus, and inferior mesenteric plexus
5. Hypogastric Plexus: supplies pelvic viscera


Components of Autonomic Reflexes

Receptor: sensory in nature
Sensory: conducts merve impulses from receptors to CNS
Integrating center: consists of interneurons in CNS that relay signals from sensory neutrons to motor neurone
Motor neurons: connect CNS to an effector; preganglionic neuron conducts motor impulses from CNA to autonomic ganglion, and postganglionic neuron conducts motor impulses from autonomic ganglion to an effector
Effector: smooth muscle, cardiac muscle, and glands, and the reflex is called autonomic reflex