Autonomic Nervous System Flashcards
Autonomic Nervous System
Control system that acts largely unconsciously; regulates bodily functions such as heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal; regulates reflex responses that people typically take for granted when they’re working properly; involuntary and maintains homeostasis; important to know how developing drug may effect physiological processes
Parts of autonomic nervous system
- Sympathetic nervous system
- Parasympathetic nervous system
- Smooth and cardiac muscle, exocrine glands, some endocrine glands - Enteric nervous system
- Digestive organs only
Autonomic Efferent Pathway
Two neurons in both sympathetic and parasympathetic system
- 1st neuron located in brain or spinal cord
- 2nd neuron is located in ganglia
- “Preganglionic neurons” synapse onto “postganglionic neurons” that innervate target organs
- Release neurotransmitter from “varicosity”
Somatic Efferent Pathway
One neuron system
- Alpha motor neurons project directly from the spinal cord to skeletal muscle
- 1 nerve per muscle fiber
- Release neurotransmitter into traditional “neuromuscular junction”
Autonomic Nerve
Preganglionic fiber from CNS releases preganglionic neurotransmitter at autonomic ganglion; postganglionic fiber branches off of autonomic ganglion and releases postganglionic neurotransmitter from varicosity on effector organ
- Do not always from chain ganglia and to target organ (synapse in same area, travel up and synapse, travel down and synapse, and some make their own ganglion)
Sympathetic Preganglions
Cell body located in the lateral horn of the thoracic and upper lumbar spinal cord; short and synapse in ganglia (clusters of neurons) located just outside of the spinal cord; innervate tissues throughout the body
- T1 to L2
What tissues do sympathetic system innervate?
Eye, lacrimal and salivary glands, lungs, heart, liver, pancreas, stomach, kidney, adrenal glands, small and large intestines, rectum, bladder, and genitalia
Sympathetic Postganglionics
Cell body located in sympathetic chain; long and innervates effector organ; EXCEPTION in adrenal instead preganglionics continue through the ganglia (splanchnic nerves) and innervate adrenal medulla
Parasympathetic Preganglionics
More restricted; located in brain stem and extend via cranial nerves (III, VII, IX, and X); long and extend to series of ganglia very close to visceral target (sometimes synapse on organ); located in sacral spinal cord and extend via pelvic nerve (craniosacral)
What tissues do parasympathetic system innervate?
- Cranial nerve III = eyes
- Cranial nerve VII = lacrimal glands
- Cranial nerve IX = salivary glands
- Cranial nerve X = lungs, heart, stomach, spleen, pancreas, and large and small intestine
-Sacrum innervates large intestine, rectum, bladder, and genitalia
Parasympathetic Postganglionics
Short and reside in ganglia very close to visceral target; activity to the heart, lungs, and abdominal visceral organs travels through the Vagus nerve which synapses; Vagus nerve synapses on very short post ganglionic neurons on heart
Dorsal Motor Nucleus of the Vagus
Neurons within the dorsal motor nucleus of the Vagus (DMV) are parasympathetic motor neurons as they project to the periphery and regulate the tone to most of the subdiaphragmatic organs and thus, regulate feeding, digestion, energy, and glucose homeostasis
Sympathetic Ganglia
- Sympathetic Paravertebral Ganglia
- Sympathetic Prevertebral Ganglia
Sympathetic Paravertebral Ganglia
Run on either side of the vertebral bodies
- Cervical ganglia
- Thoracic ganglia and rostral lumbar ganglia
- Caudal lumbar ganglia and sacral ganglia
Sympathetic Prevertebral Ganglia
- Celiac ganglion
- Aorticorenal ganglion –> in front of aorta and close to kidneys
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
Parasympathetic Ganglia
- Ciliary (cranial nerve III)
- Submandibular (cranial nerve VII)
- Pterygopalatine (cranial nerve VII) - roof of mouth
- Otic (cranial nerve IX)
- In or near the wall of an organ innervated by vagus (cranial nerve X) or sacral nerves (S2, S3, S4)
Dual Innervation
Many organs are innervated by both sympathetic and parasympathetic divisions; “opposite” actions where one branch activates a physiological response and the other inhibits; more precise and faster control
Parasympathetic
- Digestion
- Relaxation
- Metabolism
- “Rest and digest”
Sympathetic
- Stress
- Physical Activity
- Emergencies
- “Fight or flight”
Dual innervation of heart
Parasympathetic system slows heart rate via long preganglionic neurons located in brainstem extend via the Vagus nerve to short postganglionic neurons on heart; sympathetic system increases heart rate and cardiac contractility via short preganglionic neurons located in spinal cord that project to long postganglionic neurons in the sympathetic chain and project to the heart
Pupil Constriction
Increased parasympathetic activity (cholinergic) to circular muscles constrict the iris while sympathetic activity (adrenergic) to radial longitudinal muscles decreases
Pupil Dilation
Decreased parasympathetic activity (cholinergic) to circular muscles dilate iris while sympathetic activity (adrenergic) to radial longitudinal muscles increases
Preganglionic Neurotransmitters
- Primary neurotransmitter for both is acetylcholine (Ach) which classifies all of them as cholinergic neurons
Postganglionic Neurotransmitter Parasympathetic
Always Ach = cholinergic
Sympathetic postganglionic neuron neurotransmitter for enteric neurons, smooth muscle cells, or cardiac cells
Epinephrine and/or norepinephrine = adrenergic
Sympathetic postganglionic neuron neurotransmitter for secretory cells
Ach = cholinergic; muscarinic receptors
Sympathetic postganglionic neuron neurotransmitter for chromaffin cells in adrenal medulla
Ach and then release of epinephrine and norepinephrine from target organ
Nicotinic Cholinergic Receptors (nAchR)
Main receptor types found on both sympathetic and parasympathetic postganglionic neurons; acts as a Na+ and K+ conducting channel; gated not only by Ach but also nicotine
Types of nAchR
- Expressed by neurons (nAchR)
- Expressed by muscle (mAchR)
- Both are ligand-bound ionic channels
Muscarinic Cholinergic Receptors (mAchR)
Main receptor types found on parasympathetic target cells (exception of sweat glands); G-coupled protein activated by presynaptic Ach –> has natural antagonist extracted from “nightshade” plants that inhibit muscarinic receptors
Types of mAchR
M1-M5
M1 Receptor
Autonomic ganglia and CNS
M2 Receptor
SA node, AV node, atria, and ventricles
M3 Receptor
Smooth muscle
M4 Receptor
CNS
M5 Receptor
CNS
Adrenergic Receptors
Main sympathetic receptors on effector organ; all G-coupled and expressed as alpha and beta; expression of receptor subtype determines function and influence of sympathetic activity at end of organ
Alpha Adrenergic Receptors
Alpha 1 and alpha 2
Beta Adrenergic Receptors
Beta 1, Beta 2, and Beta 3
Excitatory Adrenergic Receptors
Alpha 1, Beta 1, Beta 2, and Beta 3
Inhibitory Adrenergic Receptors
Alpha 2
Alpha 1
Smooth muscle, heart, and liver
- Effects contraction of vascular and genitourinary smooth muscle, relaxation of intestinal smooth muscle, excitability of heart, and glycogenolysis/gluconeogenesis of liver
Alpha 2
Pancreatic beta cells, platelets, nerves, vascular smooth muscle
- Low insulin secretion of pancreatic beta cells
- Aggregation of platelets
- Lower norepinephrine release from nerves
- Contraction of smooth vascular smooth muscle
Beta 1
Heart and renal juxtaglomerular cells
- Increased chronotropy and inotropy as well as AV node conduction velocity in heart
- Increased renin secretion of renal juxtaglomerular cells
Beta 2
Smooth muscle, liver, skeletal muscle, and lungs
- Relaxation of smooth muscle
- Glycogenolysis/gluconeogenesis of liver
- Glycogenolysis and K+ uptake for skeletal muscle
Beta 3
Lipolysis of adipose tissue
Autonomic control of heart
Heart maintains own intrinsic heart rate at 100 bpm; relative tone of sympathetic and parasympathetic activation dictate HR; parasympathetic tone dominates at rest (70 bpm); regulated by CV control center in brainstem; endocrine epinephrine impacts HR
Myocardium
Interlacing bundles of cardiac fibers arranged spirally around circumference of heart; arrangement causes reduced diameter of ventricular chamber and the apex being pulled upward in rotating manner when ventricular muscle contracts = wringing effect
Sympathetic effect in heart
Cardiovascular control center in medulla oblongata –> sympathetic neurons (NE) –> B1 receptors of autorhythmic cells –> increased Na+ and Ca2+ influx –> increased rate of depolarization –> increased heart rate
Parasympathetic effect in heart
Cardiovascular control center in medulla oblongata –> parasympathetic neurons (Ach) –> muscarinic receptors of autorhythmic cells –> increased K+ influx and decreased Ca2+ influx –> hyperpolarizes cell and decreases rate of depolarization –> decreased heart rate
Parasympathetic Stimulation of Heart
- Releases Ach and binds to mAchR to elicit inhibition (via 2nd messenger) that acts on SA node
- Decrease HR by increasing K+ permeability and hyperpolarizing SA node
- Decreases rate of spontaneous depolarization and prolongs time required to drift to threshold
- Effect on AV node decreases the node’s excitability = increased AV nodal delay
- Shortens contractions of atrial cells by decreasing plateau phase of AP
Sympathetic Stimulation of Heart
- Increased release of NE and is coupled to excitatory 2nd messenger system
- Speeds up depolarization so threshold is reached more readily
- Increased Na+ and Ca2+ permeability = quicker drift to threshold
- Reduced AV nodal dela
- Increased contractile strength = increased force of contraction and more blood being pumped out
- Occurs with prolonged opening of L-type Ca2+ channels = increased excitation contraction coupling
Cardiac Output
CO = SV x HR
- Volume of blood pumped by each ventricle/min
- Can increase from average 5 L/min to 20-25 L/min during exercise
- Parasympathetic nervous system, sympathetic nervous system, and intrinsic control of heart
EDV
End diastolic volume (120-150mL)
ESV
End systolic volume (40-50mL)
SV
Stroke volume; EDV-ESV (80mL)
- Intrinsic control factor from extent of venous return
- Extrinsic control factor from extent of sympathetic stimulation
- Determined by extent of venous return and sympathetic activity
HR
Determined primarily by by autonomic control of SA node (pacemaker around 70 bpm); innervated by both sympathetic and parasympathetic divisions that can modulate rate and force of contraction
Cardiac Output Parasympathetic
Vagus nerve ends supplies atrium, more specifically AV and SA node
Cardiac Output Sympathetic
Innervates the atria AV and SA nodes and more primarily the ventricles
%EF
Ejection fraction = portion of blood that’s pumped out and used as indicator of contractility
- SV/EDV
- Normal resting 50-75%
- Exercise around 90%
- Failing < 30%
Sympathetic activation leads to increased HR and venous return
Constriction of veins occurs and squeezes more blood to heart which increases EDV
Intrinsic Control
Increased EDV –> increased SV (increased blood return = increased blood pumped); heart doesn’t pump all of blood out of the heart
- Frank-Starling Law of the Heart
Frank-Starlin Law of the Heart
- Intrinsic control depends on the length-tension relationship of the cardiac muscle
- Increase in cardiac muscle length increases tension created for contraction
Extrinsic Control
Sympathetic activation increased contractility
- Cardiac sympathetic nerves and epinephrine
- Both increase cardiac contractility (more ejection)
- Occurs because of Ca2+ influx (myocardial fibers cross bridge more)
What causes cardiac muscle to vary in length before contraction?
- Degree of diastolic filling (increased diastolic filling –> increased length –> increased force of contraction)
- Heart normally pumps out during systole the amount of blood returned during diastole (increased venous return –> increased SV)
- Extent of filling is the preload (work imposed on heart prior to contraction)
- Advantageous because it keeps both sides of heart working equally and an increased venous return = increased EDV and increased SV
Sympathetic and Starling Curve
Shifts curve to left; depending on stimulation curve can be shifted up to a maximal increase in contractile strength
- Same diastolic volume will have greater SV
- Greater force of contraction and greater blood ejection
High BP and Heart
Increases workload; when ventricle contracts to open semilunar valve must be enough pressure to exceed pressure in aorta (arterial pressure is afterload); if valve is stenotic the heart must create more pressure to overcome the afterload and can result in hypertrophy (disease or age); contractility of heart decreases in heart failure which is inability of cardiac output to keep pace with body’s demands
Heart Failure
-Ventricle cannot pump enough blood efficiently enough the veins become congested
- Common reasons are damage to heart from MI or impaired circulation or prolonged pumping against chronically increased afterload (stenosis)
- Weak cardiac muscles contract less efficiently and heart operates on lower length-tension curve point
Starling Curve and Heart Failure
Shifts curve downward and to right
Compensation of Heart Failure
- Increased sympathetic flow –> temporary as heart will become less sensitive to NE
- Renal where kidneys attempt to increase blood flow by retaining salt and water –> increased volume which increases EDV and force
- Heart pumping same amount of blood but at higher length-tension relationship
Cardiac Deterioration
Decreased ability to compensate and produce normal SV, all blood returned cannot be pumped
- Cardiac muscles operating on length-tension relationship of descending curve because they are stretched too far
