Chapter 15: Autonomic Nervous System Flashcards
(95 cards)
1
Q
Autonomic Function
A
- Processes regulated below conscious level
- Responds to visceral sensory inputs
- Signals from CNS to heart, smooth muscle, glands
- Maintains homeostasis
2
Q
Hypothalamus
A
ANS control center
Sympathetic and parasympathetic responses
Influenced by frontal cortex and limbic system
3
Q
Brainstem
A
Controls visceral reflexes
- Blood pressure regulation
- Direction of blood flow
- Cardiac activity
4
Q
Spinal cord
A
Controls two important visceral reflexes
- Urination and defecation
5
Q
Posterior root ganglion
A
Cell bodies of unipolar sensory neurons
6
Q
Parasympathetic Division of Autonomic Nervous System
A
- “Sex and digest”
Regeneration of tissue, absorption of nutrients, energy diverted to digestive, reproductive, urinary, and immune systems
7
Q
Sympathetic Divisions of Autonomic Nervous System
A
- “Fight or flight”
Emergency response, exercise, excitement
8
Q
Parasympathetic “Craniosacral” Division
A
- Originates at cranial nerves III, VII, IX, X and sacral nerves 2, 3, 4
- Long preganglionic neurons
- Synapse with short postganglionic fibers
- Ganglions found close to organs
9
Q
Terminal ganglia
A
- Parasympathetic
- Close to effector organ
10
Q
Intramural ganglia
A
- Parasympathetic
- Embedded in the wall of the organ
11
Q
Sympathetic “Thoracolumbar” Division
A
-Originates in lateral horn of spinal segment t1 to L2
-Short preganglionic neurons
-Synapses with long postganglionic neurons
-Ganglia found close to spinal column
12
Q
Sympathetic chain ganglia
A
On either side of the spinal column
Essentially operate as a relay station for the Sympathetic Nervous System
-Myelinated presynaptic neurons originate in lateral horns of spinal cord
Three options for synapsing:
1. Synapse in ganglion with postsynaptic neuron
2. Axon passes through ganglion and continues as part of splanchnic nerve
3. Axon ascends/descends in chain to synapse at higher or lower levels and continues as part of that spinal nerve
13
Q
White Rami
A
Myelinated preganglionic sympathetic axons from nerve to ganglion
-“Exit ramp” from nerve; “entrance ramp” to ganglion
14
Q
Gray Rami
A
Unmyelinated postganglionic sympathetic axons from ganglion to spinal nerve
15
Q
Sympathetic Spinal Nerve Pathway
A
- Preganglionic myelinated axons synapse in ganglion with unmyelinated postganglionic neuron
Postganglionic axons returns to spinal nerve - Targets integumentary structures
16
Q
Postganglionic Sympathetic Nerve Pathway
A
- Myelinated preganglionic axons synapse with unmyelinated postganglionic neurons in ganglion or ascend/descend chain to synapse with postganglionic neuron
- Targets head, neck, thoracic viscera
Cardiac nerve innervates heart
17
Q
Splanchnic Nerve Pathway
A
- Postganglionic axon passes through ganglion without synapsing
- Continues as part of splanchnic nerve
Greater splanchnic nerve
Lesser splanchnic nerve
Least (lowest) splanchnic nerve - Targets abdominal and
pelvic viscera
18
Q
Adrenal Medulla Pathway
A
- Preganglionic axon passes through ganglion to lesser splanchnic nerve
- Targets adrenal glands
Stimulates release of adrenaline from adrenal glands
Maintains fight or flight response
19
Q
Acetylcholine
A
Neurotransmitter of parasympathetic division
Cholinergic neurons
- All ANS preganglionic neurons
- All parasympathetic postganglionic neurons
Target cells have cholinergic receptors
20
Q
Norepinephrine
A
“Catecholamine”
- Neurotransmitters of sympathetic division
Adrenergic neurons
- Most sympathetic postganglionic neurons are adrenergic
Target cells have adrenergic receptors
21
Q
Nicotinic receptors
A
Bind acetylcholine
Found on postganglionic neurons and adrenal medulla cells
Always excitatory
Directly opens ion channel
- Sodium moves into cell
- Cell depolarizes
- Faster
22
Q
Muscarinic receptors
A
Bind acetylcholine
Found in all target organs of parasympathetic division
Excitatory or inhibitory
Muscarinic receptors use second messengers
- Rather than directly opening channel, a signaling cascade sends message
- Slower
23
Q
Alpha (α) receptors
A
Bind norepinephrine
Stimulated by NE
24
Q
Beta (b) receptors
A
-bind norepinephrine
-stimulated or inhibited by NE
-b1 = stimulated
-b2 = inhibited
-b3 = either
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Autonomic Tone
- Balance between sympathetic and parasympathetic systems
- Dual innervation
Most effectors innervated by both ANS divisions simultaneously
Regulation of activity
Heart rate
Blood pressure
Tone of smooth muscle of digestive tract
Bronchodilation/ constriction
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Autonomic Reflexes
“Visceral reflexes”
Shortest pathway between stimulus and response
Includes: Receptor, Sensory neuron, CNS integration center, Motor neuron, Effector
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Cardiovascular reflex
Blood pressure
- Autonomic Reflex
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Gastrointestinal reflex
Defecation
- Autonomic Reflex
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Micturition reflex
Urination
- Autonomic Reflex
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what does the ANS do in basic terms?
responsible for maintaining your internal homeostasis.
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what are the 2 main divisions of the autonomic nervous system?
Sympathetic and parasympathetic
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autonomic neurons innervate what structures?
smooth muscle, cardiac muscle, and glands
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SNS starts where
in the middle of the spinal cord
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SNS preganglionic neurons are:
short, myelinated, cholinergic
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SNS post ganglionic neurons are:
long, unmyelinated, adrenergic, and release norepinephrine or epinephrine onto target tissues.
- tissues that receive sympathetic innervation have adrenergic receptors.
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Cell bodies of sympathetic pre-ganglionic neurons are located where?
in the thoracic and lumbar segments of the spinal cord
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PNS starts where
ends of spinal cord, up at brain stem or at the bottom of the spinal cord.
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PNS preganglionic neuron are:
long, myelinated, cholinergic -> release acetylcholine
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PNS postganglionic neurons are:
short, unmyelinated, nicotinic acetylcholine receptors. they are also cholinergic, and they release acetylcholine onto target tissues
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target tissues have what type of receptors
muscarinic acetylcholine receptors
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SNS know as:
fight or flight
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PNS known as:
sex and digest or rest and digest
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PNS functions
SLUD (salivation, lacrimation, urination, and defection) but also decreasing heart rate and blood pressure, and increases motility and secretion in the digestive system, the excretion of waste products, and sexual arousal.
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craniosacral
parasympathetic preganglionic fibers originate from the cranial and sacral segments of the spinal cord, aka the ends.
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parasympathetic pathway: oculomotor
where does it originate?
where does it project?
what does it innervate?
- originating in Cranial Nerve III
- project to the ciliary ganglia
- innervate the ciliary muscles and lens of the eye
46
parasympathetic pathway: facial
where does it originate?
where does it project?
what does it innervate?
- originating in Cranial Nerve VII
- project to the pterygopalantine and submandibular ganglia
- innervate the lacrimal and mucosal glands of the nasal cavity and salivary glands
47
parasympathetic pathway: glossopharyngeal
where does it originate?
where does it project?
what does it innervate?
- originating in Cranial Nerve IX
- project to the otic ganglia
- innervate the parotid salivary gland
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parasympathetic pathway: Vagus
where does it originate?
where does it project?
what does it innervate?
- responsible for the vast majority of the body’s parasympathetic output (80% to 95%).
- originating in Cranial Nerve X
- pre-ganglionic fibers travel to the thorax where they project to many places
- project to the cardiac plexus
- innervate the heart
- project to the pulmonary plexus
- innervate the lungs
- project to the esophageal plexus
- innervate nearby tissues
- project to the stomach wall or the celiac plexus or mesenteric plexus
- innervate digestive organs like the gallbladder, liver, pancreas, small intestine, and colon
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parasympathetic pathway: Pelvic Nerves
where does it originate?
where does it project?
what does it innervate?
- originating in S2 to S4 enter the pelvic nerves
- project to the hypogastric plexus
- innervate the transverse colon, rectum, urinary bladder, and reproductive organs.
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What happens to your body during fight or flight response
SNS increases in heart and respiration rate, increased blood flow to skeletal and cardiac muscle, and sweating.
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sympathetic chain ganglia
axons of sympathetic neurons travel with spinal nerves for a short distance and then enter ganglia on either side of the vertebral column.
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Spinal nerves containing sympathetic fibers
sympathetic fibers synapse in the sympathetic chain ganglia. The post-ganglionic neurons then exit the spinal nerve to innervate cutaneous sweat glands, cutaneous and skeletal blood vessel smooth muscle, and arrector pili smooth muscle.
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Sympathetic nerves
- extend to the head and neck, branching to innervate cutaneous sweat glands and smooth muscle.
May Join branches of
- the trigeminal nerve to supply the face, salivary glands, iris, and the ciliary muscle of the eye
- the cardiac plexus to supply the heart
- the pulmonary plexus to supply the lungs and thorax
- the celiac plexus to supply the diaphragm, stomach, spleen, liver, gallbladder, adrenal glands, kidneys, testes, and ovaries
- the superior mesenteric plexus to supply the pancreas, small intestine, ascending colon, and transverse colon
- the inferior mesenteric plexus to supply the transverse colon to the rectum
- the hypogastric plexus to supply the urinary bladder, reproductive organs, and descending colon to the rectum
54
The splanchnic nerve
- formed from fibers that do not synapse in the sympathetic chain
- extends to the visceral ganglia, celiac ganglia, and inferior mesenteric ganglia
- most important structure innervated by the splanchnic cerver is the adrenal medulla
55
adrenal medulla
- most important structure innervated by the splanchnic nerve
- made of modified post-ganglionic sympathetic cells that are round, lack axons and dendrites, and are known as chromaffin cells.
- Chromaffin cells are responsible of epinephrine (80%) and norepinephrine (20%).
56
Chromaffin cells
- Found in the adrenal medulla, which is innervated by the splanchnic nerve
- modified post-ganglionic sympathetic cells that are round, lack axons and dendrites.
- responsible of epinephrine (80%) and norepinephrine (20%).
57
Efferent sympathetic outflow pathways
- originates in the lateral horn
- exits via ventral horn
- spinal nerve
- white ramus communicans
- goes into sympathetic chain ganglia/sympathetic trunk/paravertebral ganglia
-normal
- synapses at sympathetic ganglia
- gray ramus
- spinal cord
- target organ
-ascend or descend
- ascends or descends the chain root ganglia
- synapses at sympathetic ganglia
- gray ramus
- spinal cord
- target organ
-post ganglionic splanchnic nerve
- synapses at sympathetic ganglia
- leaves by it's own nerve
-pre ganglionic splanchnic nerve
- leaves sympathetic ganglia without synapsing
- leaves by it's own nerve
- synapses in a peripheral ganglion near the target organ
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antagonistic control
ANS regulate the tissue through this system when both divisions are innervating the same tissue
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Ionotropic
- neurotransmitter makes it let in ions
- cause graded potentials -> rapid effect on potential of near by membrane that is brief and local
- usually excitatory if receptor allows Na^+ or Ca ^2+ to flow in bringing in their positive charge, because of depolarization
- usually inhibitory if receptor allows Cl^- in or K^+ out
60
Metabotropic
- when neurotransmitter binds to receptor they activate second messengers inside the neuron
- second messengers can effect the behavior of ion channels, or change activity of proteins inside neuron, or even gene expression
- occurs more slowly, but effects may be larger or more wide spread, because their can be amplification through second messenger systems
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3 major neurotransmitters in the ANS
acetylcholine, epinephrine, and norepinephrine
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cholinergic receptor
A receptor that is activated by acetylcholine
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nicotinic acetylcholine receptor
A cholinergic receptor (a receptor that is activated by acetylcholine) that is ionotropic (ion let in)
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Nicotinic receptors
- found in a variety of tissues, including the ANS, neuromuscular junction, and the brain.
- Nicotinic ACh receptors are cation specific, and their activation produces an inward Na+ current
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muscarinic acetylcholine receptor
- cholinergic receptor that is metabotropic (e.g., one that activates signaling enzymes)
- located on target tissue
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adrenergic receptor
- A receptor that is activated by epinephrine or norepinephrine
- All adrenergic receptors are metabotropic and are located on target tissues.
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cholinergic neurons
Neurons that release ACh
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adrenergic neurons
Neurons that release norepinephrine and epinephrine
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Agonist
A chemical that can bind to the same receptor as a particular neurotransmitter and have the same effect.
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antagonist
can bind to the same receptor protein as the neurotransmitter either at the same place or nearby, but blocks the effect of the neurotransmitter.
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muscarinic receptors have how many subclasses
5 subclasses of muscarinic receptors, M1–M5
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tissues that receive sympathetic innervation have what receptors
adrenergic receptors
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adrenergic receptor subtypes
α1, α2, β1, β2, and β3
- all adrenergic receptors can bind Epi and NE (but not with the same affinity)
- the adrenergic subtypes are based upon the degree of binding and the response produced.
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α1 receptor
- generally produces a stimulatory response
- directly stimulated by NE released from post-ganglionic sympathetic nerves
- actions mainly involve smooth muscle contraction.
- causes vasoconstriction in many blood vessels including those of the skin, gastrointestinal system, renal artery, brain, ureter, vas deferens, arrector pili muscle of hair, uterus (when pregnant), urethral sphincter, and bronchioles.
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α2 receptor
- response varies a great deal between target cells.
- receptors do not associate with post-ganglionic sympathetic synapses and are activated by Epi released from the adrenal medulla. The adrenergic receptors act to excite or inhibit cellular processes by working through a second messenger system
- actions mainly involve the following: inhibition of insulin release from the pancreas, stimulating the release of glucagon from the pancreas, and contraction of sphincters of the gastrointestinal tract.
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β1 receptor
- receptors generally produces a stimulatory response
- receptors are directly stimulated by NE released from post-ganglionic sympathetic nerves
- Actions involve stimulation of salivary gland amylase secretion, increased kidney juxtaglomerular secretion of renin, lipolysis in adipose tissue, relaxation of the bladder detrusor muscle, tachycardia (increased heart rate), increased force of heart muscle contraction, and increased automaticity of the AV (atrioventricular) node.
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β2 receptor
- receptors do not associate with post-ganglionic sympathetic synapses and are activated by Epi released from the adrenal medulla. The adrenergic receptors act to excite or inhibit cellular processes by working through a second messenger system
- response of the receptors varies a great deal between target cells.
- Actions involve smooth muscle relaxation in the uterus, decreased GI smooth muscle motility, relaxation of the bladder detrusor muscle, bronchodilation, increased pancreatic release of insulin, dilation of hepatic and skeletal muscle arteries, and increased liver glycogenolysis
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β3 receptor
- Actions involve increased adipocyte lipolysis, increased thermogenesis, and relaxation of the bladder detrusor muscle.
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sympathetic innervation of the heart
- preganglia release ACh
- ACh goes to synapse with nicotinic receptor on postganglionic neuron
- postganglionic neuron sends norepinephrine or epinephrine out to synapse with beta 1 adrenergic receptor
- SA and VA node are located at that synapse and cause an increase in cardiac output
- Increases: HR, Contracticity, Automaticity, and Conduction velocity
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parasympathetic innervation of the heart
- preganglia release ACh
- ACh goes to synapse with intramural ganglia
- ACh binds with nicotinic receptor causing of post ganglionic neuron
- post ganglionic neuron releases ACh to synapse with SA and VA node. ACh binds to a muscarinic receptor
- causes a antagonistic response which decreases cardiac output
- Decreased: HR, Contracticity, Automaticity, and Conduction velocity
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During a somatic reflex, information travels the following route
- Proprioceptive receptors in the skin, muscle, or tendon send information to dorsal root neuronal cell bodies.
- Afferent dorsal root sensory cells send information via the posterior gray matter of the spinal cord or the brainstem, where they synapse onto interneurons.
- Cells within the motor cortex project to interneurons in the cord that synapse on a α- motor neuron in the dorsal horn.
- Interneurons send information through the thalamus to the motor cortex in the cerebral cortex.
- The α-motor neuron then synapses with skeletal muscle.
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Baroreceptor
- A specialized mechanoreceptor stretch receptor in the walls of the aorta and carotid sinuses.
- It senses the stretch of those organs when blood volume or pressure changes
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Chemoreceptor
Responds to chemical stimuli. Chemoreceptors are found throughout the body.
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Carotid body
A cluster of chemoreceptors near the bifurcation of the carotid artery that monitor arterial blood pH, CO2, and partial pressure of O2
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Osmoreceptors
Sensory receptors found in the hypothalamus that detect changes in osmotic pressure and the tonicity of CSF.
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Orthostatic hypotension
- occurs when a patient’s blood pressure suddenly drops when going from a lying position to a sudden standing position.
-Definition: a fall in systolic blood pressure of at least 20 mm Hg or diastolic blood pressure of at least 10 mm Hg when a person assumes a standing position.
- occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain an adequate blood pressure when changing position to standing.
- blood pools in the blood vessels of the legs for a longer period and less is returned to the heart, thereby leading to a reduced cardiac output.
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ANS Reflex
- The visceral sensory receptor responds to sensory information by sending a signal to dorsal root neurons.
- Dorsal root neurons directly send sensory information to the CNS without synapsing onto an interneuron.
- Efferent information is sent to the hypothalamus or cranial nerve nuclei in the brainstem or into the lower cord to pre-ganglionic neurons.
- Pre-ganglionic neurons project out to ganglia and synapse onto post-ganglionic cells, which in turn then project out to and synapse onto target cells.
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Autonomic reflex integrating centers
- location: scattered throughout the brainstem, hypothalamus, and spinal cord
- critically important for the maintenance of homeostasis.
- The most important is the hypothalamus, which can influence or control almost all autonomic reflexes. The hypothalamus has connections with many regions of the CNS, is part of the limbic system, and acts as the integrating center that processes CNS inputs that affect ANS responses.
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Some of the many organs and tissues that are innervated by both divisions of the ANS include
- the digestive tract, urinary bladder, and reproductive tract.
- Salivary glands are innervated by both sympathetic and parasympathetic systems, and both stimulate salivary secretion, but different types of secretions. Sympathetic stimulation causes the secretion of viscous saliva, whereas parasympathetic stimulation causes the secretion of watery saliva.
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Some examples of organs and tissues that are innervated by only one branch of the ANS include
- sweat glands, cutaneous arterioles and veins, and adrenal medulla, which are innervated exclusively by the sympathetic system.
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Examples of organs or tissues that are regulated by both branches of the ANS but are dominated by the parasympathetic branch
heart, lungs, stomach, salivary gland
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Examples of organs or tissues that are regulated by both branches of the ANS but are dominated by the sympathetic branch
kidney, reproductive tissues, ureter, uterus, pancreas, liver, and skin.
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Range of effects from sympathetic division
- more systematic effect because the response is enhanced by the release of Epi and NE from the adrenal medulla. These neurohormones circulate in the blood and affect a wide range of target cells.
- time course of Epi and NE effects is measured in minutes
- systematic effect is enhanced because a single sympathetic pre-ganglionic cell will synapse on many post-ganglionic cells (up to 20)
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Range of effects from parasympathetic division
- less systematic effect
- release ACh
- the time course of ACh effects is much shorter (milliseconds)
- a single parasympathetic cell will synapse on one or just a few post-ganglionic cells.
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Raynaud’s Syndrome
hyper-activation of the sympathetic nervous system causing extreme vasoconstriction of some peripheral blood vessels leading to hypoxia and associated pain
