Lecture 3: Autonomic Nervous System

Question 1

Define the autonomous nervous system

Answer 1

ANS controls the viscera

It has control over nonconcious bodily functions.

It conducts impulses from the CNS to cardiac muscle, smooth muscles and glands

Question 2

Afferent vs efferent

Answer 2

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

Question 3

Describe the three subdivisions of the autonomous nervous system

Answer 3

Sympathetic NS: Mobilizes body systems during fight or flight

Parasympathetic: rest, conserves energy, promotes “housekeeping functions” at rest

Enteric: GI function, the “gut brain”

Question 4

Areas of the CNS involved in control of ANS

Answer 4

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)

Question 5

Two functions of the ANS

Answer 5

1. 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
2. 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)

Question 6

Describe what a “two neuron system” is

Answer 6

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

Question 7

What is the NT that ALL preganglionic neurons secrete?

Answer 7

ACh (acetylcholine)

Question 8

What are the divisions of the ANS?

Answer 8

Sympathetic (thoracolumbar)(fight or flight)

Parasympathetic (craniosacral) (“rest and repose”)

ENS (enteric NS, “gut brain”)

Question 9

What are the common NT’s for both the afferent and efferent nerves in the ANS?

Answer 9

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

Question 10

Explain adrenergic neurotransmission (where are these adrenergic neurons located and what do they do)

Answer 10

• 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

Question 11

Explain cholinergic neurotransmisson

Answer 11

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.

Question 12

How do nerve agents like sarin gas work? How do we treat them?

Answer 12

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.

Question 13

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).

Answer 13

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

Question 14

What are adrenergic receptors?

Name the four types.

Which one is inhibitory?

Which one is most important for heart? Vascular?

Answer 14

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)

Question 15

What are cholinergic receptors? Explain the two different types.

Answer 15

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.

Question 16

Overview of ANS: explain overview of symp vs parasymp, what a basal tone is and what dual innervation means

Answer 16

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.

Question 17

ALL preganglionic neurons secrete____ which acts on postganglionic ______ receptors.

Answer 17

All preganglionic neurons secrete ACh, which acts on postganglionic nicotonic receptors (ionotropic, fast)

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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.

Answer 20

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).

Question 21

How is the adrenal medulla a special exception in terms of sympathetic nervous system structure?

Answer 21

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.

Question 22

How are sweat glands an exception to the normal sympathetic nervous system structure?

Answer 22

The sweat glands are innervated by the sympathetic branch but they are activated post-ganglionically via ACh binding to muscarinic metabotropic receptors.

Question 23

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_____.

Answer 23

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.

Question 24

Explain why referred pain is a thing

Answer 24

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.

Question 25

The baroreceptor reflex is a _______ feedback loop that controls _______.

Explain where baroreceptors are, what they connect to in order to reach the brain.

Answer 25

Baroreceptor reflex is a negative feedback loop that controls arterial pressure.

Baroreceptors are mechanoreceptors located in the carotid sinus and aorta. The afferent fibers for the carotid sinus travels through nerve IX (glossopharangyl) and the aorta travel through the nerve X (vagus nerve). They both end at the vasomotor and cardioregulatory centers of the medulla in the brainstem.

Question 26

Explain how the baroreceptor reflex works to control and increase in BP.

Answer 26

The baroreceptors are mechanoreceptors, so they get activated when theres a change in pressure. When BP increases, there is an increase in stretcher, which causes an increase in baroreceptor AP firing to the brain, the brain will do the following:

• decrease sympathetic input to the heart, resulting in decrease HR and decrease contraction strength (via withdrawl of beta adrenergic receptor simulation)
• increase parasympathetic input to the heart, resulting in decreased HR (via muscarinic receptors)
• decrease of sympathetic input to vascular smooth muscle, resulting in relaxation
• decreased sympathetic input to adrenal chromaffin cells, resulting in decreased E and NE levels in blood stream

Question 27

Aortic arch transmits via _____ nerve to medulla. Responds to BP ______.

Carotid sinus transmits via _____ nerve to solitary nucleus of medulla. Responds to _____.

Answer 27

Aortic arch transmits via vagus nerve (X) to medulla. Responds to only increases in BP.

Carotid sinus transmits via glossopharyngeal nerve (IX) to solitary nucleus of medulla. Responds to both increases and decreases in BP.

Question 28

What happens during a carotid massage?

Answer 28

Carotid massage increases pressure on carotid artery, which causes an increased stretch, which increases afferent baroreceptor firing and ultimately decreases your HR.

Question 29

Explain the actions of the baroreceptor reflex in response to low BP. What life threatening event is this reflex important for?

Answer 29

Decrease in BP causes a decrease in stretch, which will decrease the firing of APs from the baroreceptors to the brain.

This is what the brain then does:

Increase efferent sympathetic firing

Decrease efferent parasympathetic firing.

These two things cause the following: increase in constriction, increase in HR, increase in contractility, increase in BP.

This is important for severe hemmorage events.

Question 30

Explain the divisions of the ENS.

Describe the two intrinsic innervations

Answer 30

ENS is primary nervous system controling gut functionf of motility, secretions and blood flow. It has autonomous functions (intrinsic innervation) and is controlled by SNS and PSNS (extrenisic innervation).

Intrinsic Innervation: Myenteric vs Submucosal

Myenteric Plexus (Aurbach’s plexus): essential in peristalsis, in contact with parasympathetic neurons, located between inner and outer layers

Submucosal (Meissner’s Plexus): regulated local secretion, blood flow, absorption, in contact with parasympathetic neurons, located btw mucosa and inner layer

Question 31

Explain the peristaltic reflex. What controls it? What happens to contract vs relax?

Answer 31

Peristaltic refle is inherent property of the gut controlled by intrinsic ENS, specifically myenteric plexus (auerbach) w/out the need for external input.

• To propel food bolus forward:
  
  • release of ACh and substance P causes circular muscle to contract
  • inhibitory neurons release NO and ATP to relax long muscle
  • These two things cause a ring to develop behind the food bolus and propel it forward

In the propulsive segment: circular is contracted and longitudinal is relaxed

In receiving segment: circular is relaxed and longitudinal is contracted

Question 32

Draw the neuronal pathways in sympathetic and parasympathetic NS. Include the shape of preganglionic, the NT those release, the receptors they bind to, and then the postganglionic neurons, the NTs they release, the receptors they bind to. Also draw sweat gland and adrenal medulla.

Answer 32

Check the image on your phone.