3. Origin of ANS
BRAIN AND SPINAL CORD
SPINAL CORD SEGMENTS
TOTAL : 31
8 CERVICAL
12 THORACIC
5 LUMBAR
5 SACRAL
1 COCCYGEAL
4. Origin of ANS
• MEDULLA OBLANGATA , located in the brainstem
above the spinal cord is a major site in brain for
regulating autonomic nerve flow to the heart and
blood vessels .
• The medulla contains cell bodies for two main
divisions of the ANS –
• SYMPATHETIC
• PARASYMPATHETIC
5. SYMPATHETIC CONTRIBUTION
The sympathetic nerves exit the medulla and travel down
the spinal cord where they synapse with relatively short
preganglionic fibers that travel to and synapse within the
sympathetic ganglia.
The preganglionic sympathetic fibers innervating the
heart arise from T1-T5 segments of the spinal cord.
They are myelinated preganglionic fibers.
Postganglionic fibers from the ganglia travel to the heart
where they synapse at the target sites.
6. The postganglionic axons are unmyelinated or thinly
myelinated, and those for the heart run in the various
cardiac branches of the sympathetic trunks.
Thus in the sympathetic component of the autonomic
nervous system the synapses between pre- and post-
ganglionic neurons are often at considerable distances
from the structure innervated.
By contrast parasympathetic postganglionic fibers are
short.
8. Parasympathetic Contribution
• The parasympathetic nerves i.e (CRANIAL NERVE X )
exit the medulla as long preganglionic efferent fibers
that form synapses with short postganglionic fibers
within the heart or vascular tissue.
• Synaptic relays close to or within the viscera supplied
are characteristic of parasympathetic innervation and
in consequence parasympathetic postganglionic
fibers are relatively short as compared with their
sympathetic counterparts, and more circumscribed in
their distribution.
10. Anatomical Differences in Sympathetic
and Parasympathetic Divisions
Length of postganglionic fibers
Sympathetic – long postganglionic fibers
Parasympathetic – short postganglionic fibers
Branching of axons
Sympathetic axons – highly branched
Influences many organs
Parasympathetic axons – few branches
Localized effect
11. Neurotransmitters of Autonomic
Nervous System
Neurotransmitter released by preganglionic axons
Acetylcholine for both branches (cholinergic)
Neurotransmitter released by postganglionic axons
Sympathetic – most release norepinephrine
(adrenergic)
Parasympathetic – release acetylcholine
12. Peculiarities of nerve supply to the
heart
Nerve supply
Features
Sympathetic innervation More at the base
than the apex
Vagal activity Greater in posterior
and inferior wall
13. Effects of ANS
Sympathetic nerve – noradrenergic fiber
Parasympathetic nerve- cholinergic fiber
Noradrenergic sympathetic nerve
to the heart increase the cardiac rate (chronotropic
effect)
the force of cardiac contraction (inotropic effect).
Cholinergic vagal cardiac fibers decrease the heart rate.