Lecture 6: Autonomic Nervous System

how many neurons are in the autonomic nervous system vs somatic nervous system?

autonomic: 2 neurons
somatic: 1 neuron

where are the cell bodies located in the autonomic nervous system vs somatic nervous system?

autonomic: cell body in brain (brainstem) or spinal cord and autonomic ganglion 
somatic: spinal cord

what are the effector organs in the autonomic motor system?

cardiac muscle, smooth muscle, glands

what is the effect of nerve impulse on muscle in autonomic motor system?

either excitatory or inhibitory

what are the type of nerve fibers in autonomic motor system?

slow-conducting; preganglionic fibers lightly myelinated but thin 
postganglionic fibers unmyelinated and very thin

autonomic neurons

innervate organs NOT under voluntary control and carries out automatic and unconscious visceral response

parasympathetic (division of autonomic nervous system)

"feed and breed" or "rest and digest" 
-craniosacral

sympathetic (division of autonomic nervous system)

"fight or flight"
-thoracolumbar

what 4 cranial nerves that carry parasympathetic preganglionic neurons ? (*IMPORTANT TO REMEMBER*)

1. cranial nerve III (oculomotor) : pupil size & eye movement 
2. cranial nerve VII (facial) : expression & sense of taste 
3. cranial nerve IX (glossopharyngeal) : taste & swallowing
4. cranial nerve X (vagus) : heart rate & digestion

sympathetic responses

-HR & contractile strength increases
-blood vessels constrict (shunt blood to where it's needed)
-blood pressure increases 
-bronchial tubes dilate (allow for more air) 
-pupils dilate 
-adrenal medulla secretes epinephrine & norepinephrine 
-excess sweating (diaphoresis)

parasympathetic responses

-HR decreases 
-blood pressure decreases
-digestive tract stimulates motility & secretion

autonomic tone (balancing each other)

-sympathetics and parasympathetics continuously fire at a LOW level 
-each system dominates in SPECIFIC situations 
->resting HR : parasympathetics 
->vasomotor (blood vessel) tone : sympathetics

visceral reflex pathway

-activation of receptor 
-transmission of sensory info to CNS
-processing of sensory info by CNS
-transmission of motor response to effector organ(s) 
-visceral response!

where do preganglionic neurons originate?

originate in the midbrain or hindbrain or from thoracic, lumbar, or sacral spinal cord

where do postganglionic neurons originate?

in ganglion

where are autonomic ganglia located?

head, neck, and abdomen as well as CHAINS along either side of spinal cord

where are sympathetic neurons located and what are the naming of fibers?

-location : close to and parallel to SPINAL CORD, we want short/close because we want it acting fast! (paravertebral ganglia) 
-fibers : 
preganglionic -> cholinergic (NT: acetylcholine) 
postganglionic -> adrenergic (NT: norepinephrine)

where are parasympathetic neurons located and what are the naming of fibers?

-location : near or in EFFECTOR ORGAN, we want long preganglionic because want time to rest!
-fibers : 
preganglionic -> cholinergic (NT: acetylcholine)
postganglionic -> cholinergic (NT: acetylcholine)

sympathetic division

-preganglionic neurons come from thoracolumbar region in spinal cord 
-preganglionic neurons synapse in sympathetic ganglia that run parallel to spinal cord (paravertebral ganglia) 
-these ganglia are connected forming: sympathetic ganglia chain

parasympathetic division

-preganglionic neurons come from craniosacral region of spinal cord 
-synapse on ganglia located near or in effector organs called terminal ganglia
-preganglionic neurons DONT travel with somatic neurons (as symp postganglionic neurons do)

terminal ganglia

supply very short postganglionic neurons to the effectors

how does the vagus nerve work in the parasympathetic division?

preganglionic fibers exit medulla and branch into several plexi & nerves, and travel to ganglia within effector organs (heart, lungs, esophagus, stomach, pancreas, liver, small intestine, upper portion large intestine)

what is the role of sacral nerves?

preganglionic nerves from sacral region of spinal cord provide innervation to lower part of large intestine, rectum, urinary & reproductive organs 

terminal ganglia are located within these organs!!

when "fight or flight" is stimulated, what does the symapthetic division release and secrete?

norepinephrine from POSTganglionic neurons & secretion of epinephrine from adrenal medulla

when "rest and digest is stimulated, what does the parasymapthetic division release?

acetylcholine from POSTganglionic neurons

cholinergic synaptic transmission

acetylcholine is a NT used by ALL preganglionic neurons (symp & parasymp) 
-it is also a NT released from MOST parasympathetic POSTganglionic neurons 
-some sympathetic POSTganglionic neurons (those that innervate sweat glands & skeletal muscle blood vessels) release acetylcholine 
-> these synapses are called CHOLINERGIC

adrenergic synaptic transmission

norepinephrine is the NT releaseed by MOST sympathetic POSTganglionic neurons 
-> these synapses are called ADRENERGIC

what NT does the somatic motor neurons release?

ONLY acetylcholine which is ALWAYS excitatory

what NT do autonomic neurons release ?

mainly acetylcholine and norepinephrine BUT may be excitatory or inhibitory

what are the 2 types of NT in the ANS ?

1. Acetylcholine (ACh)
2. norepinephrine

what are the 2 types of fibers in the ANS ?

1. cholinergic 
2. adrenergic

what are the 2 types of receptors for cholinergic in the ANS ?

1. muscarinic 
2. nicotinic 

**to remember: 
"Chole (for cholinergic) is muscular & likes nicotine"

what are the 2 types of receptors for adrenergic in the ANS ?

1. alpha 1 
2. beta 1 & beta 2

response to adrenergic stimulation

 can stimulate OR inhibit (dependent on receptors) 

stimulation: heart, dilatory muscles of iris, smooth muscles of many blood vessels (causes vessel constriction)

response to adrenergic inhibition

 can stimulate OR inhibit (dependent on receptors) 

inhibition: bronchioles in lungs, other blood vessels; inhibits contraction & causes dilation of these structures

alpha & beta adrenergic receptors

-alpha receptors (A1 & A2): more sensitive to norepinephrine 

-beta receptors (B1 & B2): more sensitive to blood epinephrine

when alpha 2 receptors are stimulated, what is the result ?

when stimulated -> result in INHIBITION of norepinephrine release in the synapse (some drugs to lower BP act on these alpha 2 receptors)

what is the response to cholinergic stimulation ?

-ACh released from PREganglionic neurons of both symp & parasymp division is stimulatory 

-ACh released from POSTganglionic neurons of parasymp division is usually stimulatory BUT some are inhibitory, depending on receptors 

* in general: symp & parasymp effects are OPPOSITE!! *

nicotinic ACh receptor

postsynaptic membrane of: 
-ALL autonomic ganglia 
-ALL neuromuscular junctions 
-SOME CNS pathways

muscarinic ACh receptor

produces PARASYMPATHETIC nerve effects in: 
-heart
-smooth muscles
-glands
-G-protein-coupled receptors (receptors influence ion channels by means of G-proteins)

what pathology is relevant to the disruption of cholinergic signaling (nicotinic and muscarinic receptors) ?

-alzheimers disease
-myasthenia gravis

organs with dual innervation

most visceral organs are innervated by both sympathetic & parasympathetic neurons 
-most of the time these systems are antagonists (going back and forth): heart & GI motility

organs without dual innervation

these organs are innervated by sympathetic division only: 
-adrenal medulla 
-arrector pilli muscles (in skin) 
-sweat glands in skin 
-most blood vessels 

-regulated by increase & decrease in symp nerve activity 
-important for body temp regulation through blood vessels & sweat glands

cooperative effects

occur when BOTH divisions produce DIFFERENT effects that work together to promote a single action 

-ex: erection & ejaculation-> parasymp division causes vasodilation & erection; symp division causes ejaculation

complementary effects

occur when BOTH divisions produce SIMILAR effects on the SAME target 

-ex: salivary gland secretion -> parasymp division stimulates secretion of watery saliva and symp division constricts blood vessels so secretion is thicker