Autonomics I Flashcards
major subdivisions of the motor portion of the peripheral nervous system
autonomic and somatic nervous systems
signaling to effector organs via the ANS
two-step process. preganglionic neuron sends neurotransmitter to ganglionic transmitter, which passes it on to a postganglionic neuron. the postgang sends a neuroeffector transmitter to the effector organ
sympathetic division of ANS
pregang fibers leave CNS through thoracic and lumbar spinal nerves. most terminate in ganglia located in the paravertebral chains (some exceptions: adrenal medulla)
pregang fibers tend to be short, and post gang fibers tend to be long
parasymp division of ANS
pregang fibers leave CNS through cranial nerves and sacral nerves. terminate on ganglion cells distributed diffusely or in networks in the walls of innervated organs. some exceptions: submandibular gland. pregang fibers long, postgang fibers short
what do pregang fibers release?
Acetylcholine (ACh). acts at nicotinic receptors on postsynptic membrane of postganglionic neuron
what do postgang parasymp fibers release?
neurotransmitter is ACh, but the receptor is a muscarinic receptor of type M1-M5
what do postgang symp fibers release?
neurotransmitter is norepinephrine. receptor is a metabotropic adrenergic receptor of subtype A or B.
enteric nervous system
large and highly organized collection of neurons located in the walls of the GI tract. consists of neuronal networks that receive modulary input from pregang parasym, postgang symp, and sensory input from wall of the gut. controls motility and secretion
role of acetylcholine
primary transmitter at the ANS ganglia, at the somatic neuromuscular junction, and at parasymp postgang nerve endings. a primary excitatory transmitter to smooth muscle and secretory cells in the ENS. probably also the major neuron-to-neuron transmitter in the ENS
role of norepinephrine
the primary transmitter at most symp postgang nerve endings
cholinergic transmission
ACh is synthed from acetyl-CoA and choline and is transported into vesicles for storage. ACh release is triggered by an action potential. Released ACh interacts with receptors and signal is terminated by Acetylcholinesterase-mediated cleavage to choline and acetate which are recycled rather than excreted.
adrenergic transmission
Norepi is synth in a multistep process. Norepi is released in same way as ACh, and it interacts with the receptors. termination is diffusion and reuptake, rather than metabolism.
nicotinic receptors
two types, Nn (neuronal) and Nm (muscle). both are pentameric, ACh-gated, non-selective cation channels. in the ANS, ACh binds Nn receptor, opens the non-selective ion channel and causes depolarization at the postsynaptic terminal causing rapid neurotransmission
muscarinic receptors
5 types (M1-M5) which are located on target cells. They are all G-coupled receptors. different receptors couple to and activate different G proteins. M2 and M4 couple to Gi and inhibit adenylate cyclase and/or activate K+ channels. M1, M3, and M5 receptors couple to Gq and activate phospholipase C
adrenergic receptors
G coupled, can activate phospholipase C or stimulate/inhibit adenylate cyclase, depending on which subtype is activated. alpha receptors are in vascular smooth muscle, presynaptic nerve terminals, and platelets and in the brain. Beta receptors are located on most types of smooth muscle, cardiac muscle, some presynaptic nerve terminals and in the brain, and all activate adenylate cyclase
