Autonomic nervous system and neurotransmission Flashcards
Autonomic nervous system definition
Effector system that controls viscera
Functions of the autonomic nervous system
Maintain homeostasis and respond to external stimuli
Subdivision of the ANS
Sympathetic, parasympathetic, and enteric
Major neurotransmitters in the ANS
Acetylcholine and norepinephrine
Other NT’s in the ANS
ATP, nitrous oxide, serotonin, GABA, dopamine, and glutamate
Differences between ANS synapses and CNS synapses
ANS are not as well-defined, have variable synaptic cleft distances, and are all metabotropic
Synthesis/degradation of NE
Synthesized in vesicles from Dopa, degraded in the cytosol by MAO and COMT (also some degradation enzymes in the mitochondria and in circulation)
NE release
Occurs somewhat near the target cell, but is not closely coupled
ACh synthesis and degradation
Synthesized by/broken back down to choline in the cytosol. Broken down by acetylcholinesterase
Choline is found frequently in these foods
Egg yolks, liver, and soybeans
Mechanism of nerve agents
Inhibit AChE and prevent ACh degradation, causing rapid death by overstimulation
Treatment for nerve gas agents
Drug cocktail with Diazepam to prevent seizures, atropine to block muscarinic AChRs, and pralidoxime (2PAM) to recover AChE function
Location of both ganglionic neurons
Preganglionic is within the CNS and synapses with a postganglionic neuron in an autonomic ganglion
All preganglionic neurons secrete ___
acetylcholine
Basal tone
Target organs have a resting level of activity that permits both increases and decreases from that set point.
Location of preganglionic somas
Lateral horn in the thoracic and upper lumbar segments of the spinal cord and in the C8 segment (thoracolumbar)
Type of receptors in the preganglionic-postganglionic synapse
Nicotinic (ionotropic, fast-acting)
ANS: ipsilateral or contralateral?
Mostly ipsilateral, except for the intestines and pelvis, which are bilateral
Two types of ganglia in the ANS
Paravertebral (sympathetic) and prevertebral (parasympathetic)
Path of preganglionic neurons in the sympathetic system
Go usually into the ganglion at the corresponding level, but they can travel up and down. Enter through the white communicating ramus
Superior cervical ganglion
Fused paravertebral ganglia from C1-C4 that control the head and neck
Middle cervical ganglion
Fused paravertebral ganglia from C5-C6 that control the heart, lungs, and bronchi
Stellate ganglion
Fused paravertebral ganglia from C7-C8 (T1) that also control the heart, lungs, and bronchi
Gray communicating ramus
Postganglionic neurons send out their axons to spinal nerves through these
Sympathetic postganglionic fibers secrete ___ and activate ___ ___ receptors in target organs
Norepinephrine, metabotropic adrenergic
The special case of the adrenal medulla
Preganglionic axons pass through the splanchnic nerve and directly synapse with the medulla, so it doesn’t have a post-ganglionic neuron
Chromaffin cells
Cells in the adrenal medulla that secrete epinephrine and NE directly into the blood stream as a response from the direct activation from cholinergic pre-ganglionic fiber
The adrenal medulla is responsible for the secretion of __% of epinephrine and __% of norepinephrine into the circulation
80% and 20%
Metabotropic receptors are coupled to these
G protein cascade
Exception to the sympathetic activation of postganglionic adrenergic receptors
Sweat glands - innervated by the sympathetic branch, but are activated via ACh binding to muscarinic metabotropic receptors
Location of parasympathetic preganglionic fibers
Cranial nerves in the brainstem and in the S3 and S4 sacral divisions of the spinal cord
Which cranial nuclei contain preganglionic somas?
Cranial nerves II, VII, IX, and X.
Type of receptors in parasympathetic post-ganglionic cells
Nicotinic (fast, ionotropic)
Parasympathetic ganglia are typically close to or far away from their target organs?
Close to
Parasympathetic postganglionic fibers typically activate these types of receptors with this NT
Metabotropic, ACh
Important muscarinic receptors
M1 - gastric secretion
M2/M3 - smooth muscle function
Parasympathetic smooth muscle activation generally causes ___, except . . .
dilation, except GI, where it causes contraction
Parasympathetics of the glossopharyngeal
Baroreceptor afferent fibers from the carotid sinus, which go through the nucleus solitarius and eventually control heart rate and blood pressure
Afferent fibers use this as their preferred nuerotransmitter
Glutamate
Common neuromodulators
Angiotensin II, arginine vasopressin, substance P, enkephalin, oxytocin, somatostatin, vasoactive intestinal polypeptide
Definition of referred pain
Pain in the viscera that is perceived by the CNS as somatic pain
Why does referred pain happen?
Convergence of somatic and visceral afferent fibers from the same SC level
Baroreceptor reflex
Negative feedback loop that controls arterial pressure
Location of baroreceptors
Nerve terminals in the carotid sinus and the aorta
Where afferent baroreceptor fibers end
Vasomotor and cardioregulatory centers of the medulla in the brainstem
Effect of stimulation of the vasomotor and cardioregulatory centers
- Decrease in sympathetic input to the heart
- Increase in parasympathetic input
- Decrease of sympathetic input to vascular smooth muscle
- Decreased sympathetic input to adrenal chromaffin cells
