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Introduction to the Autonomic Nervous System

• The autonomic nervous system (ANS) is a part of the peripheral nervous system.
• It controls involuntary processes in the body.
• This includes blood pressure, gastrointestinal motility, secretion, urinary bladder emptying, sweating, body temperature, and other body activities.

Organization of the Nervous System

• The nervous system is divided into two main parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• The CNS includes the brain and spinal cord.
• The Peripheral Nervous System (PNS) includes the somatic nervous system and autonomic nervous system.

Somatic Nervous System

• Part of the PNS.
• Controls voluntary activities, like skeletal muscle movements.

Autonomic Nervous System

• Regulates involuntary activities.
• Further divided into sympathetic and parasympathetic divisions.

Sympathetic Nervous System

• Also known as the "fight-or-flight" system.
• Activated during stressful or emergency situations.
• Originates from the thoracic and lumbar regions (T1-L3).
• Fibers synapse in sympathetic chains (sympathetic ganglia) located alongside the spinal cord.
• Preganglionic fibers are short.
• Postganglionic fibres are long.

Parasympathetic Nervous System

• Also known as the "rest-and-digest" system.
• Active during relaxation and rest.
• Originates in the cranial nerves (III, VII, IX, X) and sacral regions (S2-S4).
• Preganglionic fibers are long.
• Postganglionic fibres are short.

Autonomic Ganglia

• Collections of neurons outside the CNS.
• Function as synapses between preganglionic and postganglionic neurons.
• Relay station for the autonomic nervous system.

Types of Autonomic Ganglia

• Lateral (paravertebral/sympathetic chain) ganglia: Located alongside the spinal column.
• Collateral (prevertebral) ganglia: Located near large arteries.
• Terminal ganglia: Located close to or within the target organ.
• Adrenal medulla: A specialized sympathetic ganglion.

Chemical Transmission at Autonomic Junctions

• Transmission happens through neurotransmitters at synapses.
• Primary neurotransmitters: Acetylcholine (for parasympathetic) and Norepinephrine (for sympathetic), except for some postganglionic sympathetic fibers.
• Neurotransmitters exert their effects by binding to specific receptors on the target tissue.

Chemical Transmission in Autonomic NS

• Parasympathetic NS: Postganglionic transmission is primarily through acetylcholine and thus is called the cholinergic system.
• Sympathetic NS: Postganglionic transmission is primarily through norepinephrine, and thus is called the adrenergic system.

Autonomic Receptors

• Proteins on the surface of target cells.
• Receive neurotransmitter signals.
• Classified into cholinergic (muscarinic and nicotinic) and adrenergic (alpha and beta) types.

Functions of the sympathetic Nervous System

• Main function: prepaing the body for an emergency.
• Characterized by generalized response.

Types of Divisions of the Sympathetic NS

• Cervical division (head and Neck)
• Cardio-pulmonary division (Thoracic viscera, heart and lungs)
• Splanchnic division (abdomen and pelvis)

Functions of the parasympathetic NS

• Primarily responsible for slowing down bodily processes when at rest.

Dual Innervation

• Most visceral organs receive input from both sympathetic and parasympathetic systems
• These systems typically have opposing effects.

Structures Supplied Primarily by the Sympathetic System

• Skin (sweat glands, hair follicles, blood vessels)
• Blood vessels (of skeletal muscles and heart)
• Adrenal medulla
• Spleen
• Portions of the uterus

Structures Supplied Primarily by the Parasympathetic System

• Constrictor pupillae muscle
• Gastric glands
• Esophageal muscles

Neurotransmitters

• Sympathetic & Parasympathetic preganglionic fibers: Release acetylcholine.
• Parasympathetic postganglionic fibers: Release acetylcholine.
• Sympathetic postganglionic fibers (most): Release norepinephrine.
• Some postganglionic sympathetic fibers: release acetylcholine.

Fight or Flight Reactions

• The sympathetic nervous system is responsible for triggering these reactions.
• The reactions may include accelerating the heart rate and increasing blood pressure to increase oxygen levels to the working muscles.

Summary Table