Autonomic Nervous System Overview

Autonomic Nervous System

• The autonomic nervous system (ANS) regulates involuntary functions
• It operates without conscious control, though the hypothalamus and brain stem provide regulation for reflexes
• Sensors called interoceptors located in blood vessels, organs, muscles, and the nervous system monitor conditions in the internal environment
• Chemoreceptors monitor blood CO2 levels, and mechanoreceptors detect stretch in organs/blood vessels
• Autonomic motor neurons regulate visceral actions, either increasing or decreasing ongoing activities in the effector tissues
• Certain autonomic responses form the basis of polygraph testing
• Yoga and biofeedback techniques can help to manage autonomic activity
• Most autonomic motor pathways consist of two neurons in series: preganglionic and postganglionic neurons

Comparison of Somatic and Autonomic Nervous Systems

• The somatic nervous system includes sensory and motor neurons. Sensory neurons are related to touch, pain, temperature, and proprioception, sight, hearing, taste, smell and equilibrium. Voluntary. Somatic motor neurons innervate skeletal muscles, which are excitatory or inhibitory.
• The autonomic nervous system receives sensory input from organs, blood vessels, and muscles. It is involuntary, unlike the somatic nervous system.
• The autonomic nervous system is divided into two main divisions: sympathetic and parasympathetic, usually with dual innervation of organs. These two divisions often have opposite effects on the body

Anatomy of Autonomic Motor Pathways

• The autonomic nervous system has two motor neurons in series: preganglionic and postganglionic.
• The preganglionic neuron extends from the CNS to an autonomic ganglion.
• The postganglionic neuron extends from the ganglion to the effector.
• Sympathetic division ganglia are either in a vertical row alongside the vertebral column (sympathetic trunk ganglia) or anterior to the vertebral column (prevertebral ganglia).
• Parasympathetic ganglia are typically next to or within the wall of the visceral effector.

ANS Neurotransmitters and Receptors

• Cholinergic neurons release acetylcholine. Cholinergic receptors : nicotinic, muscarinic
• Adrenergic neurons release norepinephrine (noradrenaline).
• Different receptors elicit excitation or inhibition.

Receptors of the ANS

• Cholinergic receptors include nicotinic and muscarinic receptors; they are integral proteins in postsynaptic plasma membranes activated by acetylcholine. Nicotinic receptors are on postganglionic neurons of both sympathetic and parasympathetic systems. Muscarinic receptors are on effector cells of parasympathetic neurons.
• Adrenergic receptors include alpha and beta types. Alpha receptors are located in various tissues throughout the body. Beta receptors are located in tissues such as the heart and lungs.

Beta Blockers

• Beta blockers, also known as beta-adrenergic blocking agents, are medications used to lower blood pressure.
• They work by blocking the hormone epinephrine (adrenaline)
• By reducing the heart's rate and strength of contraction and widening blood vessels, they lower blood pressure and improve blood flow.

Physiology of the ANS

• Sympathetic stimulation leads to secretion of norepinephrine by the adrenal glands, increasing heart rate, constricting vessels to non-essential organs, widening vessels to skeletal muscle and the cerebral cortex, increasing breathing rate/depth, hepatic conversion of glycogen to glucose, a decrease in GI activity
• The acronym SLUDD (Salivation, Lacrimation, Urination, Digestion, Defecation) describes parasympathetic responses, which often have the opposite effect to sympathetic responses.

Integration and Control of Autonomic Functions

• Functions such as heart rate and blood pressure are regulated by autonomic reflexes
• These reflexes follow a simple pathway called the reflex arc, which includes a receptor, sensory neuron, integrating center, motor neurons, and effector organs.
• The hypothalamus plays a role in regulating the balance of sympathetic and parasympathetic tone

The Stress Response

• Various stressors activate the nervous system to generate a stress response. This involves increased heart rate, blood pressure, and breathing rates.

The Nervous System and Homeostasis

• Explains how the nervous system helps maintain homeostasis in various body systems (Integumentary, Skeletal, Muscular, Endocrine, Cardiovascular, Lymphoid)
• Provides communication and regulation of most body tissues together with hormones of the endocrine system
• Nervous system involvement in respiration, digestion, urinary, genital/reproductive systems