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Comparison of somatic and autonomic systems
• Targets
– Somatic = skeletal muscle
– Autonomic = smooth/cardiac muscle & glands
• Efferent pathways
– Somatic = no ganglia; myelinated axon from ventral horn of cord all
the way to effector
– Autonomic = 2 neuron pathway; first is preganglionic and body
resides in brain/S.C.; 2nd is postganglionic and body resides in
autonomic ganglion. Pre’s are lightly myelinated; post’s are unmyelinated
Sympathetic and parasympathetic
system
sympathetic
SNS = short pre/long post ganglionic axon
PsNS = long pre/short post ganglionic axon
parasympathetic
Neurotransmitters
• Somatic = all motor neurons release ACH which
is always stimulatory
• Visceral = ACH & norepinephrine
– All preganglionic fibers release ACH
– All postganglionic PsNS fibers release ACH
– Most postganglionic SNS fibers release
norepinephrine (Except…….)
– Stimulation of Post ganglionic nerve fibers can be
stimulatory or inhibitory based on receptor
types
Cholinergic Receptors
• The two types of receptors that bind ACh are
nicotinic and muscarinic
• Nicotinic receptors are found on:
– Motor end plates (somatic targets)
– All ganglionic neurons of both sympathetic and
parasympathetic divisions
– Epinephrine, norepinephrine-producing cells of the
adrenal medulla
• The effect of ACh binding to nicotinic
receptors is always stimulatory
Muscarinic receptors
• M1 muscarinic receptors: located in the neural system.
• M2 muscarinic receptors: located in the heart (decreasing
rate, contractility)
• M3 muscarinic receptors: located at many places in the
body, such as:
***the lungs causing vasoconstriction & bronchoconstriction.
***They are also found in the smooth muscles of the GIT, which
help in increasing intestinal motility and dilating sphincters.
***M3 receptors are also located in many glands that help to
stimulate secretion in salivary glands and other glands of the
body.
Types of -adrenergic receptor
• They are subdivided into two types:
• 1: pupillary dilatation, coronary constriction,
sphincters constriction, constriction of blood
vessels
• 2: found in vascular smooth muscle causing
vasoconstriction, in intestine causing a
decrease intestinal secretion and in pancreatic
islets (decrease secretion of insulin).
-receptor types
• There are three known types of beta receptor, designated β1, β2
and β3.
• β1-Adrenergic receptors are located mainly in the heart (increase in
rate, contractility).
• β2-Adrenergic receptors are located mainly in the lungs (dilatation),
heart (increase in rate and contractility and dilatation of
coronaries), gastrointestinal tract, liver, uterus and vascular smooth
muscle (dilatation).
•
β3-receptors are located in fat cells (lipolysis).
FIGHT OR FLIGHT RESPONSE
• increase in heart rate, blood pressure and
cardiac output
• Diversion of blood flow from the skin and
splanchnic vessels to those supplying skeletal
muscle
• Increased pupil size, bronchiolar dilation,
contraction of sphincters and metabolic
changes such as the mobilization of fat and
glycogen