Heart Nerve Anatomy Cardiac Innervation

Heart Nerve Anatomy Cardiac Innervation

1. CARDIAC INNERVATION SUBMITTED TO : DR. I.N MITRA SUBMITTED BY : MEGHA DHADWAL ROLL NO : 34

2. AUTONOMIC NERVOUS SYSTEM SYMPATHETIC PARASYMPATHETIC

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.

7. Sympathetic pathway

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.

9. Parasympathetic pathway

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.

14. SUMMARY

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