ANS Flashcards
(41 cards)
which parts of the brain conrol ANS ?
hypothalamus, spinal cord and brain stem.
does lower brain take part in stimulating the ANS ?
yes it does ,especially the lower cortex in which the limbic system can transmit signals to the ANS.
do any other reflexes stimulate the ANS ?
yes . ANS also is also stimulated by / operates through visceral reflexes for ex reflexes from our gut or enteric system.
what are the 2 subdivisions through which the efferent autonimic signals are transmitted to the body organs?
sympathetic and parasympathetic nervous system.
where do the sympathetic nerve fibers originate from?
they originate from T1 till L2 segments of spinal cord.
where do each of the sympathetic nerve fibers terminate?
T1 - head
T2 - neck
T3 , T4 , T5 , T6 - thorax
T7, T8, T9, T10 , T11 - abdomen
T12, L1, L2 - legs
where do the cell body of each preganglionic neuron originates from?
intermediolateral horn of the spinal cord.
identify the special nature of sympatheic nerve endings in adrenal medulla.
the preganglionic sym nerve fibers enter the adrenal medulla without synapsing at all.
( pathway : intermediolateral cells -> splanchnic nerves -> adrenal medulla-> modified neuronal cells -> release nor/epinephrine ).
where do the parasympathetic nerve fibers originate from?
they originate from caniosacral nerves :
cranial nerve 3, 7, 9, 10
sacral / pelvic nerve 2, 3, 4
where do the craniosacral nerves terminate ?
cranial nerve 3 -> pupillary sphinter + ciliary muscles of eye
cranial nerve 7 -> lacrimal, nasal, submandibular glands
cranial nerve 9 -> parotid glands
cranial nerve10 -> Vagus nerve ; passes into the entire thoracic and abdominal regions.
sacral nerve 2 and 3 -> distribute to descending colon, rectum, urinary bladder, lower portions of ureters.
which parasympathetic nerve fiber is the most important?
its the cranial nerve 10 which is the vagus nerve. about 75 % of parasympathetic nerves are supplied by vagus nerve.it distributes to the heart, lungs, esophagus, stomach, small itestine, half of the colon, liver, gallbladder, pancreas, kidneys, and upper portions of ureters.
where are the post ganglionic neurons of parasym nervous system located?
at the walls of the organs.
the preganglionic neurons synapse with which cells in the adrenal medulla ?
chromaffin cells; which then secrete epinephrine and norepinephrine.
describe the condition pheochromocytoma.
its the tumor of adrenal medulla which happens due to excessive catecholamines and increased excretion of VMA.
what are the effector organs of sympatheic and parasympathetic nervous system?
smooth , cardiac muscles and glands.
the preganglionic neurons of both; the parasympathetic or sympathetic n.s are :
cholinergic
whats the difference btw the post ganglionic neurons of the sym and parasym n.s?
- the postganglionic neurons of parasym.n.s are cholinergic.
while those of sympatheic.n.s are adrenergic ( with the exception of sweat glands and few blood vessels ). - the postganglionic neurons of parasym.n.s are shorter than those of the sym.n.s.
how is acetylcholine synthesized?
its synthesized at the cholinergic nerve endings or varicosities where it is stored in its vessicles in its concentrated form until released upon stimulation.
synthesis:
acetyl CoA + choline/acetyl choline acetyltransferase —> acetylcholine.
whats the fate of acetylcholine?
after performing its function of nerve signal transmittion to the post ganglionic neuron, acetylcholine is degraded into its constituent ions namely acetate ion and choline, by the enzyme acetylcholinesterase. the choline ion is transported back to the terminal preganglionic neuronic bulb where its used for the formation of acetylcholne again and again.
how is norepinephrine formed?
its synthesis is initiated in the terminal adrenergic nerve fibers and continued in the vesicles of the same nerve fibers :
1. tyrosine –> DOPA ( by hydroxylation)
2. DOPA –> dopamine ( by decarboxylation)
3. dopamine is tranported into the vesicles.
4 dopamine –> norepinephrine (by hydroxylation)
in case of adrenal medulla theres one more step
5. 80% norepinephrine –> epinephrine ( by methylation ).
what are the 2 main recepters that are activated by acetylcholine?
muscarinic and nicotinic.
muscurine is a poison obtained from toadstool.
both are activated by acetylcholne but each of these activate their own respective receptors.
difference between nicotinic and muscarinic receptors:
- nicotinic receptors are ligand gated whie muscarinic are activated by G proteins.
- nicotinic are classified into Nn,Nm,Ng. while muscarinic are classified into M1,M2,M3,M5.
- muscarinic receptors are present on effector cells stimulated by postganglonic cholinergic nerve fibers of either parasympathetic or sympathetic nerve fibers.
4.nicotinic receptors are present at the synapses between preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems.
what is the fate of norepinephrine?
after transmission of nerve impulse , norepinephrine removed from the synapse by either of the following 3 ways :
1. 80 to 50 % = by reuptake into the terminal nerve fibers through active transport.
2. most of the remaing: by diffusing into the blood fluids and blood stream.
3. very small amount: destruction by monoamineoxidase and catechol-O-methyl.
what are the 2 major adrenergic receptors ?
alpha : 1 and 2
beta : 1, 2, 3
