Lecture 15- Autonomic Nervous System Flashcards
What are the 3 divisions of the autonomic nervous system?
parasympathetic
sympathetic
enteric
What are the two parts of the peripheral nervous system?
Autonomic
Somatic
What are three differences between the autonomic and somatic nervous system?
Autonomic
- 2 neurons b/t CNS and effector organ
- innervates smooth, cardiac muscle and glands
- either excitatory or inhibitory
Somatic
- single neuron between CNS and skeletal muscle
- innervates skeletal muscle
- leads only to muscle contraction
What levels do the preganglionic sympathetic fibers exit the spinal cord?
T1-L3- thoracolumbar
Where are the cell bodies of the preganglionic sympathetic neurons found?
Intermediolateral column of the thoracic and upper lumbar spinal cord
Where are the cell bodies of the preganglionic parasympathetic neurons found?
brainstem and s2-4
Where do the preganglionic sympathetic neurons project to?
the sympathetic chain and prevertebral ganglia before projecting to their targets
Where are the cell bodies of the postganglionic parasympathetic neurons found?
in the walls of the target organs or in ganglia very close
Which cranial nerves carry parasympathetic fibers?
3, 7, 9, 10
III, VII, IX, X
Occulomotor, Facial, Glossopharyngeal
Where do the preganglionic fibers of the oculomotor nerve (CN III) project?
ciiary ganglion
Where do the preganglionic fibers of the facial nerver (CN VII) project?
PPG/submaxillary (submandibular) ganglion
Where do the preganglionic fibers of the glossopharyngeal (CN IX) project?
otic ganglia
Where do the preganglionic fibers from the vagus (CN X) project?
innervate viscera in thoracic and abdominal cavities
Where do preganglionic fibers from S2-4 project?
pelvic viscera such as the colon bladder and genitalia
Which 3 organs have only sympathetic innervation compared to most organs that receive dual innervation from both sympathetic and parasympathetic systems?
- sweat glands
- adrenal medulla
- peripheral blood vessels
What are the two most important neurotransmitters in the autonomic nervous system?
Acetylcholine
Norepinephrine
What neurotransmitters is released by neurons in the somatic nervous system to innervate skeletal muscle? What receptor do they bind to on the skeletal muscle?
Acetylcholine
Binds to N1 receptors
Where are N1 receptors found? What neurotransmitter binds to them?
found on skeletal muscle
acetylcholine binds to them
What does curare block?
N1 receptors on skeletal muscle-prevents acetylcholine binding thus inhibiting muscle contraction
What substance blocks N1 receptors on skeletal muscle?
curare
What neurotransmitter is released between preganglionic and postganglionic neurons in both the sympathetic and parasympathetic nervous systems?
N2 receptors- bind to acetylcholine
Where are N2 receptors found? What substance blocks them?
Found on postganglionic parasympathetic and sympathetic neurons…blocked by hexamethonium
What substance blocks N2 receptors?
hexamethonium
What does hexamethonium block?
N2 receptors found on the postganglionic parasympathetic and sympathetic cells…blocks communication between pre and post ganglionic cells
What type of receptors are found in the adrenal medulla?
N2 receptors that bind to acetylcholine
What does the adrenal medulla secrete?
epinephrine (80%)
norepinephrine (20%)
Where are muscarinc receptors found?
blood vessels smooth muscle cardiac muscle glands sweat glands
What neurotransmitter stimulates muscarinic receptors?
acetycholine
Which type of fibers used Ach to stimulate the muscarinic receptors on blood vessels and sweat glands?
sympathetic
Which type of fibers use Ach to stimulate muscarinic receptors on smooth muscle, cardiac muscle and glands?
parasympathetic
Which type of fibers use norepinephrine to stimulate smooth muscle, cardiac muscle and glands?
sympathetic
What does atopine block?
muscarinic receptors on smooth muscle, cardiac muscle and glands that receive parasympatheic input via Ach
What blocks the muscarinic receptors on smooth muscle, cardiac muscle and glands?
atropine
The adrenal medulla receives direct input from the preganglionic nerve fibers of the ____________ nervous system via ACh binding to _____ receptors.
sympathetic
N2
Which type of ACh receptors are associated with the autonomic NS? somatic NS?
autonomic (Para and Synm)- N2, M
somatic- N1
Would blocking N1 receptors with curare affect skeletal muscle activity? Would it affect smooth muscle activity?
It would affect skeletal muscle activity but not smooth muscle because they use N2 and M receptors
What are the 4 types of NE receptors?
alpha 1 and 2, beta 1 and 2
What is the role of the alpha 1 NE receptor?
activation leads to contraction of smooth muscles and glands, stimulated by release of NE from postganglionic sympathetic fibers
What is the role of the alpha 2 NE receptor?
autoreceptor that inhibits NE release
What is the role of the adrenergic beta 1 receptor?
activation by release of NE from the postganglionic sympathetic cell causes increased heart rate and force of contraction
What is the role of the adrenergic beta 2 receptor?
activation by release of NE from the postganglionic sympathetic cell causes relaxes GI tract smooth muscle
What ANS division uses varicosties to release NT from postganglionic neurons?
sympathetic
What enzyme converts dopamine to NE?
dopamine beta-hydroxylase (DBH)
How is DBH (dopamine beta-hydroxylase used as a measure of sympathetic activity?
It is often released in vesicles from postganglionic neurons along with NE and can be used to show how much NE is being release (i.e. how much sympathetic activity)
Which receptors on the preganglionic memebrane acts to inhibit further release of NE from preganglionic sympathetic neurons?
alpha-2 receptors
What four factors regulate release of NE from varicosities on the postganglionic sympathetic neuron?
- The flux of Calcium (determined by the rate of firing)
- Amount of NE available (DBH enzyme need for synthesis)
- Receptors of other NTs
- Autoreceptors- alpha 2 receptors
What enzyme breaks down NE?
Monoamine oxidase in mitochondria (MAO)
What are the three mechanisms of termination of NE action?
- re-uptake and MAO predown inside pre-synaptic cell
- diffusion
- Extra neuronal uptake and breakdown my MAO enzymes
Which enzyme synthesizes NE? Which enzyme breaks it down?
synthesize- Dopamine Beta Hydroxalase (DBH)
breakdown- Monoamine oxidase (MAO)
Can somatic neurons be inhibitory?
no- they are only excitatory
