Autonomic Nervous System (ANS) and Neurotransmitters

Autonomic Nervous System (ANS)

• Regulates autonomic functions that occur without conscious control
• Consists of three parts: sympathetic, parasympathetic, and enteric nervous systems

Sympathetic vs Parasympathetic Nervous System

• Sympathetic Nervous System (SNS): "Fight or flight" response, supports survival during times of stress
• Parasympathetic Nervous System (PNS): "Rest and Digest" response, opposite effects of SNS

Neurotransmitters

• Acetylcholine (ACh): found in parasympathetic neuroeffector junctions, autonomic ganglia, somatic neuromuscular junctions, and sympathetic innervation of the adrenal gland
• Norepinephrine (NE): found in sympathetic postganglionic neuroeffector junctions

Cholinergic Receptors

• Muscarinic (M) receptors: found in organs that receive parasympathetic innervations, subtypes include M1, M2, M3, M4, M5
• Nicotinic (N) receptors: found in vertebrate skeletal muscle (Nm) and autonomic ganglia and adrenal glands (Nn)

Adrenergic Receptors

• Alpha (α) receptors: subtypes include α1 (α1A, α1B, α1D) and α2 (α2A, α2B, and α2C)
• Beta (β) receptors: subtypes include β1, β2, β3

ANS Anatomy

• Sympathetic Nervous System (SNS): arises from the thoracic and lumbar spinal cord
• Parasympathetic Nervous System (PNS): includes portions of cranial nerves III, VII, IX, and X, and sacral spinal cord, craniosacral distribution
• Vagus nerve (X) is the most important

Ganglia

• Efferent path consists of a two-neuron chain with a synapse interposed between the CNS and effector cells
• Function is to transfer and modify signals from the presynaptic neuron to the postsynaptic neuron
• Sympathetic Nervous System (SNS): short preganglionic fiber and long postganglionic fiber, widespread activation of organs during sympathetic stimulation
• Parasympathetic Nervous System (PNS): long preganglionic fibers and short postganglionic fibers, with ganglia often located in the innervated organs, allowing for more controlled regulation

Enteric Nervous System (ENS)

• Consists of a network of nerves located in the gut wall that regulates gastrointestinal motility and secretion
• Innervated by the sympathetic and parasympathetic nervous systems
• Integrates autonomic input with localized reflexes to synchronize propulsive contractions of gut muscle (peristalsis) and regulate glandular secretion

Understand the Autonomic Nervous System, its parts, and functions, including the sympathetic and parasympathetic nervous systems, as well as neurotransmitters like Acetylcholine.