Physiology of autonomic nervous system

Comparison of Somatic and Autonomic Nervous System Somatic Skeletal muscle Conscious and unconscious movement Skeletal muscle contracts One synapse Acetylcholine Autonomic Smooth and cardiac muscle and glands Unconscious regulation Target tissues stimulated or inhibited Two synapses Acetycholine by preganglionic neurons and ACh or norepinephrine by postganglionic neurons

Autonomic nervous system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons Pre-ganglionic Ganglion Post-ganglionic

Comparison of ANS & PNS Figure 15.2 n Compare the one motor neuron of the somatic motor division with the two neuron chain of the autonomic nervous system

Somatic and Autonomic Nervous System

Divisions of ANS There are two division of the ANS Parasympathetic Sympathetic Metasympathetic Generally the two divisions have chains of two motor neurons that innervate same visceral organs but cause essentially opposite effects If one division stimulates certain smooth muscle to contract or a gland to secrete, the other division inhibits that action Through this process of duel innervation the two systems counterbalance each other

Divisions of ANS Both the sympathetic and parasympathetic divisions issue from the brain and spinal cord Two neuron pathways are shown for both divisions Solid lines indicate pre-ganglionic axons while broken lines indicate post- ganglionic axons

Where they come from Parasympathetic: craniosacral Sympathetic: thoracolumbar

N αβ Sympathetic ACh NE Nicotine Tyramine, Ephedrine amphetamine + +

Divisions of the Autonomic Nervous System Sympathetic – “fight, flight, or fright” Activated during exercise, excitement, and emergencies Parasympathetic – “rest and digest” Concerned with conserving energy

Functions of the Autonomic Nervous System Sympathetic activities Sympathetic activities “E situations” “E situations” Exercise Exercise Emergency Emergency Excitement Excitement Embarrassment Embarrassment

Functions of the Autonomic Nervous System Parasympathetic activities Parasympathetic activities Stimulated by: Stimulated by: Quiet periods Quiet periods Paradoxical fear Paradoxical fear Produces “rest-and-digest” response Produces “rest-and-digest” response Supports body functions that conserve and restore body energy Supports body functions that conserve and restore body energy Reduce body functions that support physical activity Reduce body functions that support physical activity SLUDD

Function of the Sympathetic Nerve Sympathetic nervous system prototypically “fight” or “flight”. Associated with increased  energy expenditure,  cardiopulmonary adjustments for intense activity,  blood flow adjustments for maximum energy expenditure.

SNS - Fight & Flight Reaction You’re walking alone at night and all the sudden you hear an unfamiliar noise near by… In a matter of seconds,  your heart rate increases dramatically,  blood vessels in your skeletal muscles dilate,  blood vessels in the visceral muscles constrict,  digestion is ceased,  your liver ramps up glucose release,  your pupils dilate,  salivary production decreases,  sweat increases.

Sympathetic Preganglionic cell bodies in lateral horns of spinal cord T1-L2

Sympathetic Trunk Ganglia Located on both sides of the vertebral column Linked by short nerves into sympathetic trunks Joined to ventral rami by white and gray rami communicantes Fusion of ganglia  fewer ganglia than spinal nerves

Sympathetic Pathways to Periphery Figure 15.9

Sympathetic Pathways to the Head Figure 15.10

Sympathetic Pathways to Thoracic Organs Figure 15.11

Parasympathetic Nervous System If that noise turns out to be the result of wind, then the body is returned to “pre-noise” state. This is the job of the parasympathetic nervous system.

Autonomic Nervous System Parasympathicus Wind down, relaxation, digestion Dominated by Acetylcholine Sympathicus Fight & Flight Reaction Dominated by Noradrenaline (Adrenaline) Fear, exercise, rage

Different Lengths of their Fibers Sympathetic is the opposite with short preganglionic and long postganglionic fibers Parasympathetic division has long preganglionic and short postganglionic fibers

Anatomical Differences in Sympathetic and Parasympathetic Divisions Figure 15.4a

Divisions of ANS Therefore, all sympathetic ganglia lie near the spinal cord and vertebral column, and all parasympathetic ganglia lie far from the CNS, in or near the organs innervated

Parasympathetic

Parasympathetic Division The parasympathetic division is most effective in non-stressful situations This division is chiefly concerned with keeping body energy use as low as possible, even as it directs body processes such as digestion and elimination Resting and digesting division

N M ACh Parasympathetic Nicotine + Black widow Spider venom +

Parasympathetic Nervous System: Sacral Outflow Emerges from S 2 -S 4 Innervates organs of the pelvis and lower abdomen Preganglionic cell bodies Located in visceral motor region of spinal gray matter Form splanchnic nerves

Sacral Outflow The sacral outflow arises from neurons located in the lateral horn of the spinal cord at S2 - S4 The axons of these neurons run in the ventral roots of the spinal nerves to the ventral rami

Sacral Outflow From the ventral rami the neurons branch to form the pelvic splanchnic nerves Most neurons synapse in the intramural ganglia located in the walls of the distal large intestine, urinary bladder and reproductive organs

Neurotransmitters and Neuroreceptors Acetylcholine and Norepinephrine All preganglionic neurons are cholinergic Parasympathetic post ganglionic neurons are cholinergic Sympathetic post ganglionic neurons are adrenergic except Sympathetics innervating sweat glands, blood vessels in skeletal muscle, and piloerection muscles are cholinergic

Cholinergic Receptors The two types of receptors that bind ACh are nicotinic and muscarinic These are named after drugs that bind to them and mimic ACh effects

Acetylcholine Nicotinic receptors Nm (muscular-type or N 2 ): skeletal muscle Nn (neuron-type, or N 1 ): autonomic ganglia, CNS Muscarinic receptors Postganglionic parasympathetic and a few sympathetic sites, CNS (also autonomic gang.) Receptor subtypes: M 1-5

Thank you!