Autonomic Nervous System Lecture Powerpoint Flashcards
Here we go
2 components of autonomic NS, what is the primary neurotransmitter associated with it, and what are the receptors associated with it?
- Sympathetic/thoracolumbar (norepi, adrenergic)
- Parasympathetic/craniosacral (acetycholine, cholinergic)
General functions of ANS (2)
- motor innervation to glands, cardiac, and smooth muscle (visceral motor system)
- unconscious homeostasis (BP, body temp, etc)
2 Examples of cooperative effects of SANS and PANS
- Erection occurs by parasympathetic division, ejaculation occurs via sympathetic division
- parasympathetic NS increases salivary serous cell secretion, sympathetic increases salivary mucous cell secretion (thicker, stringy mucus)
Example of opposing effects of SANS and PANS
Sympathetic NS activity increases heart rate, while parasympathetic NS activity slows heart rate
Somatic vs autonomic pathways of efferent innervation
ANS has 2 neurons opposed to one that span distance form CNS to effectors with presynaptic neuron cell body in CNS followed by a myelinated preganglionic fiber (same as somatic) that then transfers to a postsynaptic neuron cell body which carries the rest of the signal thru an unmyelinated postganglionic fiber to the target organ
In sympathetic division, pregangionic fibers tend to be very ___ and postganglionic tend to be very ___. In parasympathetic division, preganglionic are very ___ and post are very ___
short, long, long, short
Adrenal medulla function (include what percentage of released catecholamines are epi vs norepi)
Very large modified sympathetic ganglion that receives pregangionic innervation and is stimulated to release epi (80%) and norepi (20%) into the body, causes prolonged activity of the substances, helps the body deal with stress, takes longer to metabolize from body leading to prolonged “keyed up” feeling
Results of increased SANS stimulation (7)
- increased heart rate and force
- dilation of blood vessels in cardiac and skeletal muscle
- constriction of blood vessels in intestinal tract/kidneys/nonessential areas
- dilation of airways
- glycogen breakdown/fat cell breakdown
- body temp rises
- dilation of pupil (mydriasis)
Cranial nerves are classified as ____ _____ nerves, which is the most important one?
- Autonomic parasympathetic
- Vagus nerve (X), responsible for majority of parasympathetic stimulation to different viceral systems of the body
Results of increased PANS stimulation (5)
- heart rate slows
- GI tract increases digestion and contraction
- bladder and bowel emptying
- eye focusing on near vision (miosis)
- bronchial smooth muscle contraction
Parasympathetic fibers tends to elicit very ____ responses
localized
Dual innervation
Refers to tendency of most viscera of the body to receive nerve fibers from both parasympathetic and sympathetic divisions that often have antagonistic effects or occasionally cooperative effects desppite not normally innervating the organ equally
Dual innervation of the iris (don’t forget the names of the muscles that perform the actions!)
The radial muscle is controlled by the sympathetic NS, stimulation sees contraction causing pupilary dilation (mydriasis) while parasympathetic stimulates the circular muscles, stimulation causes constriction of pupil (myosis)
Control without dual innervation
Certain areas of the body that only receive predominantly one type of innervation
Examples of control without dual innervation (4)
- adrenal medulla
- erector pili muscles
- sweat glands
- vasomotor tone (only has sympathetic as baseline, with increased firing of stretch receptors causing constriction and decreased causing dilation)
CNS controllers of autonomic function (4)
- limbic system (emotions)
- hypothalamus (primitive functions like hunger and sex)
- reticular formation and brainstem nuclei
- spinal cord reflex inhibition/activation (such as defacation and micturition)
2 major neurotransmitters of ANS, what releases them, and where are they found
- acetylcholine: released by cholinergic neurons to all pre ganglionic neurons and postganglionic parasympathetic neurons)
- norepi: released by adrenergic neurons from postganglionic sympathetic neurons
On rare occasion such as in the stimulation of sweat glands we see….
….release of acetycholine from postganglionic sympathetic nerve fibers (very uncommon in other parts of body mostly only release norepi)
Effect of a neurotransmitter on any postsynaptic cell is determined by the characteristics of…
….the receptor, NOT the neurotransmitter
3 types of cholinergic receptors
Nicotinic type I and type II and muscarinic
4 types of adrenergic receptors
alpha 1 and alpha 2 and B1 and B2 receptors
a1 vs a2 vs B receptor functional 2ndary messenger systems
- a1 receptors utilize Ca2+ as a secondary messenger
- a2 receptors suppress cyclic AMP as a 2ndary messenger
- B receptors activate cyclic AMP as a 2ndary messenger
a1 adrenergic receptors
Bound by catecholamines (epi or norepi), found on virtually all sympathetic target organs, sees vasoconstriction of vascular smooth muscle, ejaculation, contraction of bladder neck and prostate, and pupillary dilation
a2 adrenergic receptors
Bound by catecholamines (epi or norepi), located in synaptic cleft between target organ and post synaptic neuron where upon being bound it inhibits its further release of catecholamines
B1 adrenergic receptors
Bound by catecholamines (epi or norepi), located at the heart causes increased heart rate, force of contraction, and increased velocity of conduction to AV node, as well as stimulates renin release at the JG cells of the kidney
(think about B blockers Tav)
B2 adrenergic receptors
Bound only by epi, seen in the lungs to cause bronchial dilation, uterine muscle relaxation (premature labor prevention with drugs), coronary and skeletal muscle blood vessels vasodilation, stimulate glycogenolysis
Dopamine receptors
Bind dopamine released from adrenergic neurons in the kidney that then dilates renal blood vessels to increase blood flow to kidney
catechol-o-methyl-transferase (COMT) and monoamine oxidase (MAO)
- COMT functions to breakdown circulating NE and Epi in tissues thruout the body
- MAO functions to desrtroy NE released from adrenergic nerve fibers reabsorbed into the presynaptic nerve ending
Nicotinic type I receptors
Bound by acetycholine, found in the autonomic ganglia in both divisions of the ANS between pre and post ganglionic fibers as well as in the adrenal medulla
Nicotinic type II receptors
Bound by acetycholine, found in the somatic nervous system on motor end plates of skeletal muscle acting excitatory
Muscarinic receptors
Bound by acetylcholine, found on all target tissues of parasympathetic NS, either excitatory or inhibitory when ACh binds depending on subclass of muscarinic receptors
Acetylcholinesterase
Enzyme responsible for Ach degradation in the synaptic cleft causing parasympathetic stimulation to have a short duration of effect
Sympathetic responses tend to be widespread for these 2 reasons
- neuronal divergance to many organs from preganglionic to postganglionic fibers having a ratio of 1:17
- release of epi and norepi from adrenal gland into blood stream
Sympathetic and parasympathetic divisions influnce the ____ NS thru autonomic reflexes, even though this system can function independently thru local reflexes
Enteric
