L-41 Autonomic Nervous System I: Anatomy And Cell Physiology

Front 1

Functions of autonomic nervous system

Back 1

Maintains internal body system in state of homeostasis

Controls response to external environment

Involuntary

Front 2

Divisions of ANS

Back 2

Sympathetic (thoracolumbar)

Parasympathetic (craniosacral)

Enteric (independent, controls secretion and motility in gut)

Front 3

Basic organization of autonomic fibers/ganglion

Back 3

Two step signaling process.

CNS neuron has preganglionic neuron which projects to ganglion. Ganglion has postganglionic neuron which projects to target organ.

Target organs are smooth/cardiac muscles and secretory glands.

Front 4

Location of sympathetic and parasympathetic ganglia

Back 4

Sympathetic ganglia are right outside or very close to spinal cord. Postganglionic fibers are long.

Parasympathetic ganglion are located near or within target organs. Postganglionic fibers are short.

All autonomic ganglia are located outside the blood brain barrier although preganglionic neuron is within blood brain barrier.

Front 5

Possible destinations of presynaptic sympathetic fibers

Back 5

1. Synapse on sympathetic chain ganglion

2. Go up or down some ganglia before synapsing on sympathetic chain ganglion - generally to sweat glands, piloerector muscles, as well as vasculature for blood pressure.

3. Pass through chain and synapse in celiac, superior mesenteric, and inferior mesenteric ganglion.

Front 6

Somatic and sympathetic simple spinal cord circuits

Back 6

Sensory cell bodies synapse in dorsal horn. Interneuron goes to upper motor neuron cell body in ventral horn which projects out.

Autonomic sensory neurons are in dorsal root ganglion also. Make single synapse on lateral horn cells. Postganglionic cells project through ventral root.

Peel off through white ramus to enter sympathetic chain ganglion. Postganglionic neuron either synapses in dorsal root and passes through gray ramus to target, travel up and down to different ganglions, or go to collateral (celiac, sup mes, inf mes) ganglion.

Front 7

Basic layout of parasympathetic division

Back 7

Preganglionic parasympathetic neurons are located in accessory nuclei in brainstem/cervical and sacral regions.

Long preganglionic fibers synapse in discrete ganglion or in target tissue. Postganglionic fibers are shorter.

Front 8

Basic layout of enteric division

Back 8

From inside to out:

Mucosal layer - produces secretions and is responsible for absorption.

Submucosal (Meissner's plexus)

Circular muscle

Myenteric plexus

Longitudinal muscle

Plexi have parasympathetic and sympathetic activity.

Front 9

Function of Enteric Nervous System

Back 9

Sensory neurons detect presence of food. System performs peristalsis independent of consciousness and CNS.

Front 10

Autonomic control of enteric nervous system

Back 10

Although functions autonomously, can be modified/turned off by vagal input or sympathetic from prevertebral ganglion.

Front 11

Generalization of function of PS vs S

Back 11

Fight/flight (sympathetic) - Induced by rapid change in environment - pupil dilation, increased flow to skeletal muscle and brain. inhibit defecation, urination, digestion.

Rest/digest (parasympathetic) - Defecation, urination, digestion.

Front 12

Second property of PS vs S function

Back 12

Generalized response - sympathetic system. All functions is carried out simultaneously and by same system.

Discrete/localized response - parasympathetic system. Functions are not elicited in generalized way.

Front 13

Does activity of sympathetic or parasympathetic ever completely turn off?

Back 13

No - there is tonic activity in these systems.

Rest/digest response increases tonic activity of parasympathetic neurons and decreases tonic activity of sympathetic neurons.

Fight/flight response decreases tonic activity of parasympathetic neurons and increases tonic activity of sympathetic neurons.

Front 14

Parasympathetic and sympathetic preganglionic neurotransmitter

Back 14

Presympathetic neurotransmitter is ACh for both parasympathetic and sympathetic system.

Front 15

Parasympathetic and sympathetic postganglionic neurotransmitter

Back 15

Parasympathetic postganglionic neurotransmitter is ACh.

Sympathetic postganglionic neurotransmitter is usually NE, except for cholinergic synapses for sweat glands and peripheral microvasculature.

Front 16

What does target response of autonomic nerve fiber depend on?

Back 16

Depends on the receptor

Front 17

Adrenal chromaffin cell

Back 17

Sympathetic neuron-like cell which is innervated by preganglionic cholinergic neurons.

When stimulated, releases Epi and NE directly into blood which reaches target organ via bloodstream.

Reinforces generalized sympathetic discharge. Also has different kinetics - takes time to clear from body. Slower, longer-lasting sympathetic response.

Embryologic origin is similar to peripheral neurons.

Front 18

Receptors on autonomic ganglion

Back 18

Nicotinic AChR - depolarize postganglionic neuron

Muscarinic AChR

Neuropeptides are co-released at ganglion and have slow modulatory roles.

Front 19

Autonomic receptors on target organ

Back 19

Parasympathetic - mAChR

Sympathetic - NE acts on alpha and beta adrinergic receptors, ACh activates mAChR.

Front 20

Convergence of inputs at Autonomic Ganglia

Back 20

Multiple preganglionic fibers innervate single neuron (S - 50:1, PS 2:1)

Because multiple subthreshold signals needed to activate postganglionic fiber

Front 21

Divergence of inputs at autonomic ganglion

Back 21

Single preganglionic fibers innervate multiple postganglionic neurons (S 1:200, PS 1:3)

Amplification mechanism - small signal can affect multiple postganglionic neurons. Makes sympathetic response generalized.

Front 22

Electrophysiology of autonomic ganglion - experimental set up

Back 22

Put electrode into postganglionic neuron and record membrane potential and action potentials.

Stimulate white ramus and look at response.

Stimulate at time 0. Delay for propogation ofaction potential down preganglionic neuron, release and action of neurotransmitter. Causes potential change in postganglionic cell that causes AP if exceeds threshold.

Front 23

Autonomic ganglion electrophysiological event following action potential

Back 23

Following AP, a second depolarizatoin (fast EPSP) that occurs which takes 40 ms to return to baseline. Occurs due to ACh released from preganglionic axon.

If place Na channel blocker, action potential is abolished but fast EPSP still results.

Front 24

Autonomic ganglion - final electrophysiological event

Back 24

If then add curare or hexamethonium to block nicotinic receptors, fast EPSP is abolished but slow hyperpolarization (slow IPSP) is still visible. This is potential induced by ACh acting at muscarinic receptors.

Front 25

Summary of elements of electrpohysiological activity at autonomic ganglion

Back 25

1. Fast EPSP - induced by ACh binding to nicotinic receptors. Induces action potential if reaches threshold.

2. Slow IPSP - induced by ACh binding to metabotropic receptors. Hyperpolarizes cell for a couple of seconds afterwards.

3. Peptidergic EPSP - Moderately large, slow (1 minute) depolarization due to binding of peptide.

Front 26

What kind of post synaptic potentials do muscarinic receptors induce?

Back 26

Can be slow EPSP or slow IPSP, depending on which metabotropic receptor there is.

Front 27

Effect of slow potential on electrophysiology of postganglionic neuron

Back 27

Slow EPSPs make postganglionic neuron hyperexcitable - more action potentials generated from same stimulus.

Opposite is true for slow IPSPs.

Front 28

Ionic basis of F-EPSP, S-IPSP, S-EPSP, and P-EPSP (potential, concductance changes, channel, and blocker)

Back 28

F-EPSP - Nicotinic ACh, increase in K and Na conductance. Blocked by curare and hexamethonium (C6)

S-IPSP - Muscarinic ACh, increase in K conductance. Blocked by atropine.

S-EPSP - Muscarinic ACh, decrease in K conductance. Blocked by atropine.

P-EPSP - Peptidergic (LHRH) receptor, decrease in K conductance.