Efferent Neurons and the Autonomic Nervous System

Vocabulary-style flashcards generated from lecture notes covering cranial nerve functions, somatic and autonomic divisions, neurotransmitters, receptor subtypes, and neuromuscular junction mechanics.

Cranial Nerve I (Olfactory)

Pure sensory cranial nerve originating from synapses with the olfactory bulb that transmits smells.

Cranial Nerve II (Optic)

Pure sensory cranial nerve originating from retina to thalamus that transmits visual stimuli.

Cranial Nerve III (Oculomotor)

Primarily motor cranial nerve originating from the dorsal midbrain to the orbit that governs pupillary dilation, lens shape, and the superior eyelid.

Cranial Nerve IV (Trochlear)

Primarily motor cranial nerve that innervates the superior oblique muscle of the eye.

Cranial Nerve VI (Abducens)

Motor cranial nerve originating from the inferior pons that controls lateral eye movements.

Cranial Nerve V (Trigeminal)

Mixed sensory and motor cranial nerve with Ophthalmic, Maxillary, and Mandibular divisions providing sensory input from the face/jaw and motor control for jaw movement.

Cranial Nerve VII (Facial)

Motor and sensory cranial nerve controlling muscles of facial expression, salivary/lacrimal glands, and taste buds on the anterior tongue.

Cranial Nerve VIII (Vestibulocochlear)

Pure sensory cranial nerve transmitting auditory information via the cochlear branch and equilibrium via the vestibular branch.

Cranial Nerve IX (Glossopharyngeal)

Sensory and motor cranial nerve governing tongue and pharynx movements for swallowing/gagging, taste on the posterior tongue, and chemoreception in the carotid artery.

Cranial Nerve X (Vagus)

Sensory and motor cranial nerve controlling swallowing and visceral movements, as well as transmitting parasympathetic sensory information from the viscera.

Cranial Nerve XI (Accessory)

Primarily motor cranial nerve emerging from rootlets of spinal cord ($C_1-C_5$) that provides motor movement to muscles including the sternocleidomastoid, trapezius, and tongue.

Cranial Nerve XII (Hypoglossal)

Primarily motor cranial nerve controlling voluntary movements of the tongue for speech and swallowing.

Somatic Nervous System

Division of the peripheral nervous system subject to voluntary control (somatomotor) originating in the ventral horn or brainstem that innervates skeletal muscle with single-neuron pathways releasing acetylcholine at nicotinic receptors.

Autonomic Nervous System (ANS)

Involuntary branch of the peripheral nervous system (visceromotor) that innervates smooth muscle, cardiac muscle, and glands using a two-neuron chain composed of preganglionic and postganglionic fibers.

Parasympathetic Division

Division of the autonomic nervous system with craniosacral origin that dominates during rest ('rest and digest') to promote housekeeping functions such as digestion, defecation, and diuresis.

Sympathetic Division

Division of the autonomic nervous system with thoracolumbar origin ($T_1-L_2$) that dominates during excitement or threatening situations ('fight or flight') to mobilize energy stores for physical activity.

Preganglionic Fiber

The first neuron in an autonomic pathway whose cell body resides in the central nervous system and whose axon synapses with a second neuron in an autonomic ganglion.

Postganglionic Fiber

The second neuron in an autonomic pathway whose cell body is located in an autonomic ganglion and whose axon extends to innervate the target effector organ.

Adrenal Medulla

A modified sympathetic ganglion that secretes $80\%$ epinephrine and $20\%$ norepinephrine directly into the bloodstream upon preganglionic stimulation.

Cholinergic Receptors

Receptors that bind and activate in response to acetylcholine, categorized into nicotinic and muscarinic subtypes.

Nicotinic Receptors

Cholinergic receptors activated by nicotine, found on postganglionic cell bodies of all autonomic ganglia and at neuromuscular junctions of skeletal muscle.

Muscarinic Receptors

Cholinergic receptors named after the Amanita muscaria mushroom, located on parasympathetic effector cell membranes such as smooth muscle, cardiac muscle, and glands.

Adrenergic Receptors

Receptors for norepinephrine and epinephrine found on sympathetic target tissues, classified into alpha ($\alpha_1, \alpha_2$) and beta ($\beta_1, \beta_2, \beta_3$) isoforms.

$\beta_1$ Adrenergic Receptor

Adrenergic receptor located predominantly in the heart, kidneys, and adipose tissue that increases heart rate, myocardial contractility, and renin release.

$\beta_2$ Adrenergic Receptor

Adrenergic receptor abundant on lungs and blood vessels serving the heart, liver, and skeletal muscle that induces vasodilation, bronchodilation, and smooth muscle relaxation.

$\alpha_1$ Adrenergic Receptor

Adrenergic receptor located on virtually all sympathetic target organs (especially blood vessels of skin and mucosae) that causes vasoconstriction, visceral sphincter closure, and pupil dilation.

Albuterol

A $\beta_2$ adrenergic agonist drug that mimics the actions of norepinephrine and epinephrine to relax bronchioles.

Beta Blockers

Antagonist drugs that block activation of beta receptors to reduce heart rate, contractility, and cardiac output by suppressing sympathetic excitation.

Neuromuscular Junction (NMJ)

Junction formed between an axon terminal of a motor neuron and a single skeletal muscle cell, where acetylcholine release initiates muscle action potentials.

Acetylcholinesterase

Enzyme that degrades free acetylcholine at the neuromuscular junction to terminate end-plate potential signaling and stop muscle contraction.

Reflex Arc

Autonomous response circuit comprising five main components: receptor, sensory neuron, integration center, motor neuron, and effector.