Lecture 3: Autonomic Nervous System Flashcards
Define the autonomous nervous system
ANS controls the viscera
It has control over nonconcious bodily functions.
It conducts impulses from the CNS to cardiac muscle, smooth muscles and glands
Afferent vs efferent
Afferent is the ascending pathway: travels from peripheral sensory receptors up to the brain
Efferent is the descending pathway of the brain sending signals to motor neurons
Example: If you touch a hot stove, the afferent pathway is the sensory receptors sending a signal to your brain that it’s hot. The efferent pathway is your brain then sending a signal to your arm/hand to move away from the stove
Describe the three subdivisions of the autonomous nervous system
Sympathetic NS: Mobilizes body systems during fight or flight
Parasympathetic: rest, conserves energy, promotes “housekeeping functions” at rest
Enteric: GI function, the “gut brain”
Areas of the CNS involved in control of ANS
Pons: respiratory control, urination (micturitum)
Reticular Formation: Medulla oblongata, vasomotor and vasodialator, respiratory control, water intake
Hypothalamus: the master of the master gland.. temp regulation, food, fighting, fleeing, fucking
Other regions: cerebral cortex, amygdala (emotions, fear), stria terminalis (stress, anxiety)
Two functions of the ANS
- Maintain homeostatis/steady state internal enviornment: efferent fibers innervate and modulate organ activity, sensory fibers (afferents) located in the target organs report status back to brain… can invoke experiences like pain, hunger, fear, etc
- Respond to external stimuli: the “fight or flight” response after an external threat is caused by a generalized activation of the sympathetic outflow telling many systems to wake up (cardiovascular, respiratory, metabolism)
Describe what a “two neuron system” is
The preganglionic neuron (the first one aka one on the right) originates in the CNS (specifically in the spinal cord) and synapses with the postganglionic neuron in a place called an autonomic ganglion.
The postganglionic neuron then synapses with the target organ.
ALL PREGANGLIONIC NEURONS SECRETE ACh
What is the NT that ALL preganglionic neurons secrete?
ACh (acetylcholine)
What are the divisions of the ANS?
Sympathetic (thoracolumbar)(fight or flight)
Parasympathetic (craniosacral) (“rest and repose”)
ENS (enteric NS, “gut brain”)
What are the common NT’s for both the afferent and efferent nerves in the ANS?
Efferent/Motor “two neuron system”
- Sympathetic: AcH——-> Norepi and Epi
- Parasympathetic ACh —-> Ach
Afferent/Sensory:
- Glutamate and GABA
Note: Epi functions as a hormone in the ANS
Explain adrenergic neurotransmission (where are these adrenergic neurons located and what do they do)
- Adrenergic neurons are exclusively found in sympathetic NS, specifically in postganglionic fibers
- NE is synthesized from dopamine. Then an AP can trigger calcium channels to open, letting calcium flood the cell. This causes fusion of the vesicles carrying NE to the membrane. Then they are released into synaptic cleft via exocytosis. NE can then bind to beta or alpha receptors. Then, NE is taken back into cytosol and degraded by MAO or COMT
Explain cholinergic neurotransmisson
Cholinergic neurons, whether in the sympathetic or parasympathetic release ACh. ACh is synthesized in the cytosol from choline and transported into the vesicles. After an AP triggers calcium to enter the cell, the vesicles fuse to the membrane and leave via exocytosis. ACh is inactivated by acetyl cholinesterase (AChE). Choline is then reuptaken into the presynaptic terminal for reusage.
How do nerve agents like sarin gas work? How do we treat them?
Nerve agens like sarin gas inhibit AChE and prevent ACh degradation, causing death in minutes via overstimulation. Current treatment is a drug cocktail of diazepam (sedative to prevent seizures). atropine to block muscarinic AChRs, and pralidoxame (2PAM) to recover AChE function.
Explain the differences in neurotransmission between preganglionic and postganglionc nerves. (describe the synapse, the cleft distance, the post synaptic receptor type, the NT effect, and the post synaptic potential).
Neuron-Neuron (CNS)/ first neuron in system:
- well defined synapse
- 20-40 nm cleft distance
- ionotropic, fast receptor type, nicotinic
- Direct NT effect
- EPSP/IPSP postsynaptic potential
Neuron-Viscera/ 2nd neuron in system:
- “en passant”/ varicosities in synapse
- variable cleft distance (20-40 nm in viscera vs 1-2 mm in blood vessels)
- Metabotropic, slow post synaptic receptors, muscarinic AChR
- variable NT effect
- Junction potential is postsynaptic potential
What are adrenergic receptors?
Name the four types.
Which one is inhibitory?
Which one is most important for heart? Vascular?
Adrenergic receptors are receptors that bind adrenaline (NE). The four kinds are alpha 1, alpha 2, beta 1, and beta 2. Beta 1 and Beta 2 both stimulate adenylate cyclase. While alpha 1 INHIBITS adenlyate cyclase. Beta 1 is most important for heart. Alpha one is most important for vascular (alpha one also increases intracellular calcium and IP3)
What are cholinergic receptors? Explain the two different types.
Cholinergic receptors bind ACh. There are two types, nicotinic and muscarinic.
The nicotinic receptors are on ALL postganglionic neurons, on skeletal muscle, and adrenal medulla.
The muscarinic receptors are on all effector organs of the parasympathetic organs, and on sweat glands in sympathetic ns.
Overview of ANS: explain overview of symp vs parasymp, what a basal tone is and what dual innervation means
ANS includes sympathetic and parasympathetic. The two branches are complementary and coordinated. Sympathetic is arousing/fight or flight, whereas parasympathetic is calming/rest and digest.
Target organs have a basal tone or resting level of activity that permits both increases and decreases from that set point. They receive both sympathetic and parasympathetic innervation (dual innervation) which typically produce opposite effects.
ALL preganglionic neurons secrete____ which acts on postganglionic ______ receptors.
All preganglionic neurons secrete ACh, which acts on postganglionic nicotonic receptors (ionotropic, fast)
Describe all of the following for the sympathetic ns:
Region of spinal cord, function, location of preganglionic somans, location of postganglionic somas, length of preganglionic fiber, length of postganglionic fiber, preganglionic fiber NT
postganglionic receptor, postganglionic fiber NT, receptor at the target organ
Sympathetic NS:
- Thoracolumbar Division
- Function is homeostatis and fight or flight
- Preganglionic somas are in Thoracic T1-T12 (C8) and upper lumbar L1-L3
- Postganglionic somas: paravertebral ganglia (two sets lateral to SC) and prevertebral ganglioa (in abdominal cavity)
- SHORT preganglionic fibers (somas are in SC)
- LONG postganglionic fibers
- ACh is released by preganglionic
- Nicotonic receptors are the postganglionic receptor
- Postganglionic fibers secrete NE, E (80% of E comes from adrenal medulla) EXCEPTION IS THAT in the sweat glands, the postganglionic fibers secrete Ach
- Receptor at the target organ: adrenergic receptor
Explain the following about the parasympathetic nervous system:
Region of spinal cord, function, location of preganglionic somans, location of postganglionic somas, length of preganglionic fiber, length of postganglionic fiber, preganglionic fiber NT
postganglionic receptor, postganglionic fiber NT, receptor at the target organ
Parasympathetic NS:
- Craniosacral Division
- Function: homeostatus, complements sympathetic response
- Preganglionic somas are located in brainstem and sacral spinal cord
- Postganglionic somas ganglia licated near or in the walls of target organs
- Preganglionic Fibers are LONG
- Short postganglionic fiber length (somas are by the target organs)
- Preganglionic fibers release Ach
- Nicotonic postganglionic receptors
- Postganglionic fibers release ACh
- Receptor at the target organ is muscarinic
Fill in the blank for sympathetic NS:
All preganglionic fibers secrete ___ which acts on post ganglionic ____ receptors>
In the SNS, Post ganglionig neuron somas are found in either _______ or _______ ganglia.
Sympathetic postganglionic fibers secrete_____ and activate ________ receptors in target organs.
Sympathetic NS:
All preganglionic fibers secrete ACh, which acts on post ganglionic nicotonic receptors.
In the SNS, post ganglionic neuron somas are found either paravertebral (majority) or prevertebral ganglia.
Sympathetic postganglionic fibers secrete NE and activate metabotropic adrenergic receptors at target organs (alpha and beta).
How is the adrenal medulla a special exception in terms of sympathetic nervous system structure?
The adrenal medulla is a special case, because preganglionic neurons pass through the splacnhnic nerve and directly synpase with the medulla. Therefore, there is no postganglionic neuron. Chromaffin cells in the adrenal medulla secrete NE and E directly into the bloodstream as a response from direct activation of cholinergic pre-ganglionic fibers; the adrenal medulla is responsible for 80% of E and 20% of NE in circulation.
How are sweat glands an exception to the normal sympathetic nervous system structure?
The sweat glands are innervated by the sympathetic branch but they are activated post-ganglionically via ACh binding to muscarinic metabotropic receptors.
Fill in the blank for parasympathetic nervous system:
The parasympathetic preganglionic fibers are located in the _________ nerves in the brainsteam and in the ___ and ___ divisions of the _____.
Four cranial nuclei contain preganglionic somas:_____, ____, _____, _____.
Preganglionic fibers secrete____, receptors on post ganglionic cells are ____.
Ganglia are typically close to _____.
Postganglionic fibers typically secrete ____, and activate ______ receptors in smooth muscle, cardiac and glands.
Parasympathetic smooth muscle activation generally causes_____, with the exception of ____ where it causes_____.
PSNS preganglionic fibers are located in the cranial nerves in the brainsteam and in the S3 and S4 sacral divisions of the craniosacral division.
Preganglionic somas are in the cranial nerves III, XII, IX, X.
Preganglionic fibers secrete ACh, receptors on post ganglionic cells are nicotonic.
Ganglia are typically close to target organs.
Postganglionic fibers typically secrete ACh, and activate muscarinic receptors in smooth muscle, cardiac muscle and glands.
Parasympathetic smooth muscle activation generally causes dilation, with the exception of the GI where it causes contraction.
Explain why referred pain is a thing
Referred pain is pain originated in viscera but percecived by the CNS as originating elsewhere. It results from convergence of somatic and visceral afferent fibers from the same SC level of the spinal cord.
