Autonomic Nervous System Function

• The autonomic nervous system controls the adrenal gland, smooth muscle in the walls of the aorta, cardiac muscle in the right atrium, and parotid salivary gland, but not skeletal muscle in the rectus abdominis.
• Autonomic nervous system fibers are involved in changing the diameter of the pupil, adjusting heart rate and force, altering salivary mucus secretion, regulating gastrointestinal motility, and maintaining tonicity of the muscles of the neck.

Visceral Reflex Order

• The visceral reflex order is: sensory receptor → afferent nerve fiber → interneuron → efferent nerve fiber → gland.

Autonomic vs Somatic Effects on Target Cells

• Autonomic fibers on target cells have excitatory or inhibitory effects.
• Somatic fibers on target cells always have excitatory effects.

Response to High Blood Pressure

• In response to high blood pressure, baroreceptors (stretch receptors) in the walls of arteries carrying blood to the head trigger a reflex.
• This reflex causes the heart to decrease its beats per minute.

Motor Pathway of the Autonomic Nervous System

• The motor pathway of the autonomic nervous system usually involves two neurons.

Preganglionic Axons

• Preganglionic axons run from the gray matter to the autonomic ganglia.

Preganglionic Axons Characteristics

• Preganglionic axons of the autonomic efferent pathway are myelinated.
• They secrete acetylcholine.

Somatic vs Visceral Reflex Speed

• Somatic reflexes act faster than visceral reflexes, except because the effector organs in the somatic reflex are closer to the spinal cord.
• Reasons somatic reflexes are faster: the effector pathway in the somatic reflex arc is myelinated, the effector pathway in the visceral reflex arc involves more neurons and chemical synapses, some neurons in the effector pathway in the visceral reflex arc are unmyelinated.

Parasympathetic Tone

• Parasympathetic tone holds the resting heart rate below its intrinsic rate.

Sympathetic Axons

• Sympathetic axons are not associated with stimulation of digestion.
• They are associated with anger, exercise, stress, and arousal.

Background Rate of Activity

• The background rate of sympathetic and parasympathetic activity is called autonomic tone.

Autonomic Nervous System

• Regarding the autonomic nervous system, denervation causes hypersensitivity.
• It doesn't control skeletal muscle contraction, lack ganglia along its nerves, uses acetylcholine exclusively, or usually controls conscious actions.

"Fight-or-flight" Reaction

• Reduced urinary output is associated with the "fight-or-flight" reaction.

Parasympathetic Nervous System Axons

• Most axons of the parasympathetic nervous system travel in the vagus nerve.

Sympathetic Axons Origin

• Sympathetic axons arise only from the thoracic and lumbar regions of the spinal cord.

Sympathetic Chain of Ganglia

• The sympathetic chain of ganglia is found at the thoracic, lumbar, and sacral levels of the spinal cord.

Sympathetic Division of the ANS

• A feature not of the sympathetic division of the ANS is short preganglionic axons
• Sympathetic division does arise from the thoracolumbar region of the spinal cord, has long postganglionic axons, has ganglia adjacent to the spinal column, and has extensive neural divergence.

Parasympathetic Division of the ANS

• A characteristic not of the parasympathetic division of the ANS is its effects are local.
• Parasympathetic Division does have terminal ganglia that are very close to or within their target organs, arises from the craniosacral regions of the CNS, and has short preganglionic axons/postganglionic axons.

Neurotransmitter Release

• The sympathetic preganglionic axon releases neurotransmitter molecules in a paravertebral ganglion.

Structures Not Associated with the Autonomic Nervous System

• All preganglionic neuron, postganglionic neuron, splanchnic nerve, and oculomotor nerve are associated with the autonomic nervous system.

Sympathetic Nervous System Synapse

• Most preganglionic axons in the sympathetic nervous system synapse with 10-20 postganglionic neurons.

Solar Plexus

• The solar plexus refers to the celiac and mesenteric ganglia.

Parasympathetic Division Origin

• The parasympathetic division arises from the brain and sacral regions of the spinal cord.

Vision Accommodation

• Damage to the oculomotor nerve (CN III) may affect near vision accommodation.

White and Gray Rami

• White rami carry myelinated preganglionic neurons.
• Gray rami carry unmyelinated postganglionic neurons.

Sympathetic Ganglia

• Splanchnic nerve(s) pass throughout sympathetic ganglia without synapsing.

Adrenal Medulla Secretions

• The adrenal medulla secretes mostly epinephrine (adrenaline).

Enteric Plexus

• A characteristic not of the enteric plexus is that its reflex arcs are associated with the spinal cord.
• Enteric Plexus does have signaling pathways that do not begin in the spinal cord, innervates smooth muscle and glands, and signaling pathways that do not begin in brainstem.

Preganglionic Neurotransmitters

• The neurotransmitter(s) released by preganglionic neurons is(are) acetylcholine (ACh).

Sympathetic Axon Terminals

• Sympathetic axon terminals do not release acetylcholine.

Adrenal Medulla Synapse

• A neuron that synapses in the adrenal medulla is a preganglionic neuron.
• It releases the neurotransmitter acetylcholine.

Adrenergic Receptors

• If a cell has α1 adrenergic receptors, it is sensitive to norepinephrine (NE).

Propranolol

• Propranolol, a beta-blocker, is typically used to decrease heart rate.

Bronchodilation

• Acetylcholine is more effective in producing bronchodilation.

Muscarinic Receptors

• Muscarinic receptors bind acetylcholine.

Nicotinic Receptor Binding

• The binding of acetylcholine to a nicotinic receptor of a muscle fiber will excite it.

Pupil Dilation

• Atropine blocks muscarinic receptors.

Sympathetic Effects

• Sympathetic effects tend to last longer than parasympathetic effects.
• One reason is that norepinephrine can diffuse into the bloodstream without being broken down.

Norepinephrine Breakdown

• The enzyme that breaks down norepinephrine (NE) is called monoamine oxidase (MAO).

Monoamine Oxidase (MAO) Inhibitors

• Drugs that are monoamine oxidase (MAO) inhibitors would most likely decrease the amount of NE destroyed and may be used as an antidepressant.

Caffeine Effects

• A possible explanation for the effect of caffeine is that it blocks the receptor for a neuromodulator in the brain called adenosine.
• Adenosine inhibits ACh release by cholinergic neurons.

Autonomic Nervous System Antagonistic

• Antagonistic effects of the two divisions of the autonomic nervous system are exemplified in the control of gastrointestinal motility.

Cooperative Autonomic Effects

• Orgasm is an example of the cooperative effect between the two autonomic nervous system divisions.

Adrenergic Fibers

• Postganglionic neurons of the sympathetic division mainly contain adrenergic fibers.

ANS Dual Control

• Adrenal medulla activity is not under dual control of the ANS.

Autonomic Control

• The medulla oblongata is an especially important center of autonomic control.

Autonomic Function Input

• Somatic branch of the peripheral nervous system is not a source of input to autonomic function.
• Autonomic function does receive input from the spinal cord, cerebral cortex, hypothalamus, and medulla oblongata

Emotions and the ANS

• Anxiety increases sexual function is not an example of how emotions influence the ANS.

Autonomic Reflex

• Vasoconstriction is not controlled by the spinal cord.