Autonomic Nervous System - Structure and Function

Structure of the ANS - Sympathetic

Accelerate the body (fight or flight response) Involves the use of energy and runs things at a heavy energy concentration Exceptions -Most blood vessels -Most sweat glands -Salivary glands

Sympathetic Varicosties

Contain neurotransmitters, whether it be ACh or noradrenaline Found in mitrochondria for the production of ATP Found in smooth muscle for the innervation of smooth muscle

Structure of the ANS - Parasympathetic

Decelerate the body (rest and digest) Involves the conservation of energy, putting energy away for later use

Structure of the ANS

Generally, if we are looking at the neuromuscular junction, the motor neurons are sitting in the spinal cord and they send out an axon and it goes straight to the muscle. Different to this is the ANS in that there is an interruption. The interruption is caused by an autonomic ganglion, which stops the preganglionic fibers from reaching the organ that they are going to innervate. So we have a preganglionic fiber and a post ganglionic fiber Now in both parasympathetic and sympathetic nervous systems the preganglionic fiber terminals are at a ganglia, and the ganglion releases ACh, and teh ACh acts on nicotinic receptors (specialised nicotonic receptors that are found in autonomic ganglia) and that stimulation leads to an activation of AP of the post ganglionic fiber which then terminates with a set of varicosties

PNS (all neurons are outside the CNS)

Goes to Afferent (sensory) and Efferent (motor)

Efferent (Efferent - Exit - Motor)

Goes to Somatic (skeletomotor) and Visceral (autonomic) controls all organs

Sympathetic Dominance

Increased cardiac output Generalised vasocontriction - especially the skin and GI tract Vasodilation of blood vessels supplying skeletal muscles - including brain and heart Increased blood pressure Airway dilation - heart beating faster, need more O2 (muscles need more O2) Pupil dilation (far vision) Glycogenolysis (production of glycogen) Increased sweating Inhibition of urinary and digestive activities

Parasympathetic Dominance

Increased urinary activity Increased digestive activity (e.g. insulin secretion, increased motility of digestive tract) Stimulation of mucus production in airways

Sympathetic

Lie within the thoracic lumbar

Parasympathetic

Motor neurons lie within the brain stem and come out as cranial nerves. Also some motor neurons are found in sacral part of spinal cord to innervate pelvic region

Endocrine cells - adrenal medulla

Sympathetic activation - Adrenaline and Noradrenaline Parasympathetic activation - None

Blood Vessels

Sympathetic activation - Constriction Parasympathetic activation - Dilation (penis and clitoris only)

Endocrine cells - endocrine pancreas

Sympathetic activation - Decreased insulin Parasympathetic activation - Increased insulin and glucagon

Digestive Tract

Sympathetic activation - Decreased motility, contraction of sphincters Parasympathetic activation - Increased motility, relaxation of sphincters, increased digestive secretion

Exocrine cells - exocrine pancreas

Sympathetic activation - Decreased secretion Parasympathetic activation - Increased secretion

Lungs

Sympathetic activation - Dilation of airways Parasympathetic activation - Constriction of airways

Eye

Sympathetic activation - Dilation of pupil Parasympathetic activation - Constriction of pupil

Genitals

Sympathetic activation - Ejaculation and orgasmic contraction Parasympathetic activation - Erection (penis and clitoris)

Liver

Sympathetic activation - Glycogenolysis Parasympathetic activation - None

Brain activity

Sympathetic activation - Increased alertness Parasympathetic activation - None

Exocrine cells - sweat glands

Sympathetic activation - Increased secretion (most sweat glands) Parasympathetic activation - Increased secretion (some sweat glands)

Heart

Sympathetic activation - Increases HR, increases force of contraction Parasympathetic activation - Decreases HR, decreased force of contraction (atrium)

Adipose cells

Sympathetic activation - Lipolysis Parasympathetic activation - None

Gallbladder

Sympathetic activation - Relaxation Parasympathetic activation - Contraction (emptying)

Urinary bladder

Sympathetic activation - Relaxation Parasympathetic activation - Contraction (emptying)

Exocrine cells - salivary glands

Sympathetic activation - Small volume of thick saliva Parasympathetic activation - Large volume of watery saliva

Function of the ANS

The ANS regulates visceral activities normally outside the realm of consciousness and voluntary control - such as circulation, digestion, sweating and pupillary size

The adrenal medulla is a modified sympathetic ganglion that, on stimulation by the preganglionic fiber, secretes hormones into the blood

This organ sits above the kidneys and plays a very important role in stress and fight or flight response. The adrenal gland, the middle portion (the adrenal medulla) when activated by preganglionic fibres coming from sympathetic nervous system, they release ACh onto the adrenal medulla, which then releases into the blood mainly Adrenalin. Adrenalin lasts for 20 minutes or more. Not only noradrenaline released by peripheral nerves which only lasts a minute or 2, but we have adrenaline which is released into the blood stream that lasts 20 mins and that causes the main emphasis of teh flight or fight response