Cranial Nerves Quiz

Cranial Nerves

• 12 pairs of nerves that leave the skull
• Innervate the face, neck, thoracic, abdominal structures, and sensory organs
• Each nerve numbered with roman numerals

Mnemonic Devices

• Classical: On old Olympus's towering top a Finn and German viewed some hops
• Modern: On, On, On, They Traveled And Found Voldemort Guarding Very Ancient Horcruxes

Nerves & Functions

• I. Olfactory: Sense of smell
  • Small nerves located in the nasal cavity roof
  • Pass through the cribriform plate of the ethmoid bone
• II. Optic: Vision
  • Axons from the ganglionic cells of the retina form the optic nerve
• III. Oculomotor, IV. Trochlear, VI. Abducens: Control skeletal muscles that move the eyeball
  • Oculomotor: Also supplies autonomic impulses that constrict the pupil and change the shape of the lens
• V. Trigeminal: Sensation for the skin of the face and teeth, and cavities of the head
  • Innervates the muscles of mastication: masseter, temporalis, medial pterygoid, lateral pterygoid
• VII. Facial: Controls muscles of facial expression, taste sensation from the anterior 2/3 of the tongue, and autonomic control of the lacrimal, submandibular, and sublingual glands
• VIII. Vestibulocochlear: Hearing and balance
• IX. Glossopharyngeal: Taste and touch from the posterior 1/3 of the tongue, autonomics to the parotid gland
• X. Vagus: Somatic motor and sensory to the pharynx and larynx
  • Autonomics to the heart and airway
  • Autonomics control of smooth muscle and gland secretion in the digestive system
• XI. Spinal Accessory: Motor to the sternocleidomastoid and trapezius muscles
• XII. Hypoglossal: Muscles of the tongue including the styloglossus, genioglossus, hypoglossus, and intrinsic tongue mm.

Autonomic Nervous System (ANS)

• Visceral motor system that acts on cardiac muscle, smooth muscle, and glands
• Unconscious control - not voluntary, it's 'automatic'
• Important for the fight or flight response

ANS Components

• Central Nervous System: Limbic system, hypothalamus, brainstem, and spinal cord
• Peripheral Nervous System: Peripheral nerves, cranial nerves, spinal nerves

ANS: Two Neuron Chain

• Ganglion: Collection of nerve cell bodies
• Sympathetic and parasympathetic
• Each impulse is carried on two types of neurons
  • Preganglionic: Cell bodies in the CNS, axon begins in the CNS, exits, and synapses with postganglionic neuron
  • Postganglionic: Exclusively in the peripheral nervous system, axon goes to target tissue, e.g., the heart, blood vessels, GI tract

Somatic vs. Autonomic Motor Systems

• Somatic: conscious and voluntary, single neuron to effector, thick/heavily myelinated, rapid impulse conduction, innervates skeletal muscle, stimulatory
• Autonomic: not under conscious control, involuntary, two neuron chain, preganglionic=myelinated, postganglionic=unmyelinated, slow impulse conduction, innervates smooth muscle, cardiac muscle, and glands, can be stimulatory or inhibitory

Sympathetic Nervous System

• Differs from parasympathetic in pre/postganglionic neuron location, type of neurotransmitter used, and effects on the body
• Preganglionic location: Grey matter of the thoracic and lumbar spinal cord - 'thoracolumbar' system (T1-T12 and L1-L2)
• Sympathetic chain: Located just outside the spinal cord - preganglionic neurons synapse within the chain
  • Some neurons pass through the chain and synapse in abdominal/pelvic ganglia, e.g., nerves to digestive organs

Sympathetic - Neurotransmitters & Effects

• Neurotransmitters: preganglionic=Acetylcholine, postganglionic=epinephrine and norepinephrine
• Effects: "Fight or Flight" response, e.g., increased heart rate, cessation of peristalsis, sweating, blood shunted to skeletal muscle, short term response that requires increased energy
• Adrenal Medulla: Suprarenal glands sit on top of the kidneys, cells inside act as postganglionic neurons and secrete norepinephrine and epinephrine that travel via the bloodstream as hormones leading to an "adrenaline surge"

Sympathetic Pathway Summary:

• From the brain (e.g., limbic system)
• Descend to specific level of spinal cord
• Exit the spinal cord
• Enter sympathetic chain
  • Synapse in chain
  • Pass through chain and synapse in abdominal/pelvic ganglion
  • Synapse with postganglionic neurons in adrenal medulla

Parasympathetic Nervous System

• "CranioSacral system"
• Preganglionic neuron locations: Nuclei of cranial nerves III, VII, IX, and X in the brainstem, and nuclei in the sacral region of the spinal cord
• Postganglionic neuron locations: Close to the organ innervated, e.g., eye, glands, and visceral organs of the neck, thoracic, and abdominal cavity

Parasympathetic - Neurotransmitters & Effects

• Neurotransmitters: Preganglionic=Acetylcholine, Postganglionic=Acetylcholine
• Effects: "Resting/Digesting", active when the body is at rest, blood shunted toward the internal organs, long term response,conserves energy, regulates heart beat, breathing rate, etc.

Sympathetic vs. Parasympathetic Effects on Organ Systems

• Heart Rate: Sympathetic=Increased, Parasympathetic=Decreased
• Smooth Muscle of Bronchioles: Sympathetic=Dilate, Parasympathetic=Constrict
• Urinary Bladder: Sympathetic=Fill, Parasympathetic=Expel
• Digestive Movement: Sympathetic=Decreased, Parasympathetic=Increased
• Sweat Glands: Sympathetic=Increased, Parasympathetic=Neutral
• Arrector Pili Muscles: Sympathetic=Contracted, Parasympathetic=Neutral
• Eye: Sympathetic=Dilate, Parasympathetic=Constrict