Autonomic Nervous System

• The autonomic nervous system regulates the activities of cardiac muscle, smooth muscle, and glands.

Somatic Motor System vs. Autonomic Motor System Comparison

• Somatic motor system effector organs are skeletal muscles, while autonomic motor system effector organs consist of cardiac muscle, smooth muscle, and glands.
• No ganglia are present in the somatic motor system.
• Postganglionic autonomic fibers are located in paravertebral, prevertebral (collateral), and terminal ganglia.
• The somatic motor system has one neuron from the CNS to the effector, while the autonomic motor system has two.
• The somatic motor system has a specialized motor end plate at the neuromuscular junction, while the autonomic motor system has no specialization of the postsynaptic membrane. All areas of smooth muscle cells contain receptor proteins for neurotransmitters.
• Nerve impulses on muscles are only excitatory in the somatic motor system, but either excitatory or inhibitory in the autonomic motor system.
• Heart and smooth muscle still contract in the absence of neural stimuli; innervation serves to increase or decrease activity.

Autonomic Function and Divisions

• Innervates organs with functions not normally voluntarily controlled.
• Subdivisions include parasympathetic, sympathetic, and enteric.
• Enteric nerves innervate the walls of the GI tract.

Sympathetic and Parasympathetic Nervous System

• Differences in neurotransmitters and number of neurons to the effector exist between the sympathetic and parasympathetic system.
• The parasympathetic division uses acetylcholine (ACh) as a neurotransmitter at both the ganglion and the effector.
• The sympathetic division uses ACh at the ganglion and norepinephrine (NE) or epinephrine (Epi) at the effector.
• The parasympathetic division has terminal ganglia located near the visceral effectors.
• The sympathetic division includes paravertebral ganglia, adrenal medulla, collateral ganglion.

Adrenergic Receptors

• There are two types of alpha receptors (α₁, α₂) and two types of beta receptors (β₁, β₂).
• All adrenergic receptors use G-proteins and second messenger systems.
• Beta receptors use cAMP.
• Alpha receptors use Ca²⁺ as a second messenger system.
• Certain receptors are more sensitive to norepinephrine, while others are more sensitive to epinephrine.

Sympathetic and Parasympathetic - Ganglia

• Preganglionic fibers exit at different spinal locations.
• The ganglia locations vary, impacting their proximity to the CNS.
• Sympathetic ganglia are located on either side of the spinal cord and are relatively close.
• Parasympathetic ganglia are located next to or within the organ they innervate.
• The sympathetic chain of ganglia is also called the sympathetic trunk.

Dual Innervation

• Most organs receive both sympathetic and parasympathetic input.
• Parasympathetic stimulation relaxes bladder sphincter
• Sympathetic stimulation dilates and constricts veins, and contracts bladder sphincter
• Opposite effects that act at once can fine tune the body.

Fight or Flight Response

• Divergence of impulses to ganglia of the sympathetic system and convergence of impulses within ganglia can result in mass activation, increasing activity in response to fight or flight situations.
• Release of norepinephrine from postganglionic neurons and the secretion of epinephrine from the adrenal medulla is a key component.
• Heart rate and blood pressure increase during fight or flight.
• Blood flow increases to skeletal muscles, heart, and brain.

Rest and Digest

• The parasympathetic division is antagonistic to the sympathetic division.
• Releases ACh from postganglionic neurons.
• Heart rate slows, and digestive activities increase.
• The parasympathetic division is not normally activated as a whole; mass activation doesn't typically occur.
• Parasympathetic responses are specific and local.