Transcript Introduction to the ANS - obsidian

•
The Autonomic nervous system (ANS) is largely
autonomous (independent) in that its activities
are not under direct conscious control. It is
concerned primarily with visceral functions—
that are necessary for life, such as cardiac
output, blood flow to various organs, digestion,
etc
•
The Somatic division is largely concerned with
consciously controlled functions such as
movement, respiration, and posture.
Three major differences in the ANS and SNS:
Effectors
Efferent pathways
Target organ responses
Heavily myelinated axons of the somatic motor neurons
extend from the CNS to the effector (lacking a ganglia)
Pathways in the ANS are a two-neuron chain
The preganglionic neuron has a lightly myelinated
axon. The ganglionic unmyelinated neuron extends
to an effector organ via the postganglionic axon
All somatic motor neurons release Acetylcholine
at their synapses, Ach always has an excitatory effect
In the ANS:
Preganglionic fibers release ACh
Postganglionic fibers release norepinephrine (if
sympathetic) or ACh ( if parasympathetic) and the effect is
either stimulatory or inhibitory.
ANS effect on the target organ is dependent upon the
neurotransmitter released and the receptor type of the
effector
Division into two major portions:

Sympathetic (thoracolumbar) division

Parasympathetic (craniosacral) division
Rest and Digest
Keeps body energy use low, directs “housekeeping”
activities
Involves the D activities – digestion, defecation, and
diuresis
Decreases blood pressure, heart rate, respiratory rate
Increases GI function
Contricts Pupil
The sympathetic division is the “fight-or-flight”
system – response to threat
Involves E activities – exercise, excitement,
emergency, and embarrassment
Promotes adjustments during exercise – blood flow
to GI organs are reduced, flow to muscles are
increased
Increases heart rate, BP, RR
Dilates Pupil

Acetyl choline

Epinephrine(Adrenaline)

Norepinephrine (Noradrenaline)


Dopamine
Several co transmitters
Based on the neurotransmitter they are:
Cholinergic fibers….
› Acetylcholine is the neurotransmitter
Adrenergic/noradrenergic fibers
› Epinephrine (Adrenaline) or
Norepinephrine (noradrenaline) is the
neurotransmitter
Pre-ganglionic fibers: Are all Cholingeric
Post ganglionic:

For Parasympathetic NS – Cholinergic
› M1-3
› Nm and Nn

For Sympathetic NS – Adrenergic
› α1 , α2
› Β1,β2
M1
Secretory
glands
salivation, stomach acid, sweating, lacrimation
M2
Heart
Decreases heart rate  bradycardia
M3
Smooth
Contraction of smooth muscles (some) 
muscle
diarrhea, bronchospasm, urination
(GI/GU/Resp)
M3
Pupil and
ciliary
muscle
Contracts  Miosis
Increased flow of aqueous humor
Nm
Skeletal
muscle end
plate
Contraction of skeletal muscle
Nn
Autonomic
ganglia,
Adrenal
Medulla
Secretion of Epinephrine
Controls ANS
A1 •Blood vessels
•Pupil (Iris)
•Smooth
muscle (GI/GU)
Vasoconstriction
Mydriasis
sphincter contraction Decreased motility of
GI/GU tract
A2 Presynaptic
neurons
Reduces release of norepinephrine (as a
negative feedback mechanism) 
bradycardia,hypotension
B1 Heart
Contraction  Increased heart rate
B2 Smooth
muscles
(Respiratory,
Uterus, GI, GU)
Relaxation Bronchodilation, urinary retention,
constipation, uterus relaxation
Cholinergic and
adrenergic
transmission
Five key features of neurotransmission
 Synthesis
 Storage
 Release
 Activation of receptors
 Termination of action/ reuptake
Pre-ganglionic ANS is Acetyl Choline
 Roles of the
Parasympathetic/Sympathetic Nervous
System
 Different receptors in body organs and
their effects if stimunlated

Know Rate limiting step for Ach synthesis
 Rate limiting step for catecholamine
synthesis
 What terminates cholinergic
neurotransmission?
 What termintes adrenergic
neurotransmission?
