Mod 8 - Cranial Nerves, Support Systems, and Special Anatomy of the Head

Vocabulary flashcards covering functional fiber types, cranial nerves and their lesions, extra-ocular muscles, head and neck anatomy (scalp, arteries, veins, larynx, pharynx, glands, lymphatics, cervical regions), special senses (eye, ear), and clinical conditions like palsies, trigeminal neuralgia, Bell's palsy, glaucoma, and cataracts.

Motor efferent (somatic) fibers

Nerve fibers that transmit signals to skeletal muscle controlled voluntarily, such as eye, tongue, mastication, and facial expression muscles.

Visceral efferent fibers

Nerve fibers that transmit signals to smooth muscle and glands, controlling functions like pupil constriction, tear/saliva glands, and thoracoabdominal organs.

Sensory (somatic) fibers

Nerve fibers that carry touch, pain, and temperature sensations from the skin and mucosa, including the face, cornea, oral, and nasal cavities.

Sensory (visceral) fibers

Nerve fibers providing internal organ feedback, such as from the carotid sinus/body and thoracoabdominal viscera.

Sensory (special sense) fibers

Nerve fibers dedicated to special senses like taste (CN VII, IX, X), hearing/balance (CN VIII), smell (CN I), and vision (CN II).

Oculomotor Nerve (CN III)

Cranial nerve responsible for innervating superior, medial, inferior rectus, inferior oblique, and levator palpebrae muscles (GSE), and for pupil constriction and lens accommodation (GVE).

Lesion of Oculomotor Nerve (CN III)

Results in ptosis, eye 'down and out' deviation, dilated pupil, diplopia, and loss of accommodation.

Trochlear Nerve (CN IV)

Cranial nerve that innervates the superior oblique muscle, which depresses and intorts the eye in adduction.

Lesion of Trochlear Nerve (CN IV)

Causes vertical diplopia, often worse when looking down stairs or reading, and a compensatory head tilt away from the lesioned side.

Trigeminal Nerve (CN V)

Cranial nerve with three divisions (ophthalmic, maxillary, mandibular) responsible for general sensation of the face, scalp, cornea, nasal/oral cavities, teeth, and motor innervation for mastication muscles.

Trigeminal Nerve (V1 Ophthalmic division)

Sensory division of CN V that exits via the superior orbital fissure, providing sensation to the scalp/forehead, cornea, upper eyelid, and dorsum of nose.

Trigeminal Nerve (V2 Maxillary division)

Sensory division of CN V that exits via foramen rotundum, providing sensation to the cheeks, lower eyelid, lateral nose, upper lip, maxillary teeth, and palate.

Trigeminal Nerve (V3 Mandibular division)

Mixed sensory and motor division of CN V that exits via foramen ovale, supplying sensation to the lower face, mandibular teeth, anterior 2/3 tongue (general), and motor to muscles of mastication.

Lesion of Trigeminal Nerve (CN V)

Leads to loss of facial sensation/corneal reflex (afferent), weak bite, and jaw deviation toward the side of the weak pterygoids.

Abducens Nerve (CN VI)

Cranial nerve that innervates the lateral rectus muscle, responsible for abducting the eye.

Lesion of Abducens Nerve (CN VI)

Causes medial strabismus, inability to abduct the eye, and horizontal diplopia.

Facial Nerve (CN VII)

Cranial nerve with SVE fibers for facial expression muscles, GVE for lacrimal/salivary glands, SVA for taste anterior 2/3 tongue, and small GSA for the ear.

Lesion of Facial Nerve (CN VII)

Results in Bell's palsy (ipsilateral facial paralysis), hyperacusis, decreased tear/saliva production, and loss of taste on the anterior 2/3 of the tongue.

Glossopharyngeal Nerve (CN IX)

Cranial nerve with SVE to stylopharyngeus, GVE to parotid gland, GSA to ear/posterior 1/3 tongue (general), SVA for taste posterior 1/3 tongue, and GVA for carotid sinus/body and oropharynx.

Lesion of Glossopharyngeal Nerve (CN IX)

Leads to loss of gag reflex afferent limb, decreased parotid saliva, loss of posterior 1/3 tongue taste, and dysphagia.

Vagus Nerve (CN X)

Cranial nerve involved in SVE to palate/pharynx/larynx (swallow/voice), GVE for thoracoabdominal parasympathetic functions, GSA to larynx/lower pharynx/ear, SVA (taste epiglottis), and GVA for thoracoabdominal viscera.

Lesion of Vagus Nerve (CN X)

Causes hoarseness, dysphagia, uvula deviation away from the lesion, and loss of the gag reflex efferent limb.

Accessory Nerve (CN XI)

Cranial nerve (spinal accessory) with SVE/branchial motor fibers innervating the sternocleidomastoid (SCM) and trapezius muscles.

Lesion of Accessory Nerve (CN XI)

Results in weak head turning to the opposite side (SCM), shoulder droop (trapezius), and weak arm abduction above 90 degrees.

Hypoglossal Nerve (CN XII)

Cranial nerve with GSE fibers innervating intrinsic and extrinsic tongue muscles (except palatoglossus).

Lesion of Hypoglossal Nerve (CN XII)

Causes the tongue to deviate toward the lesion upon protrusion, along with dysarthria, atrophy, and fasciculations.

Levator Palpebrae Superioris (LPS)

An extra-ocular muscle innervated by CN III, responsible for elevating the upper eyelid.

Superior Rectus

Extra-ocular muscle innervated by CN III, primarily responsible for eye elevation, with secondary adduction and intorsion.

Inferior Rectus

Extra-ocular muscle innervated by CN III, primarily responsible for eye depression, with secondary adduction and extorsion.

Medial Rectus

Extra-ocular muscle innervated by CN III, primarily responsible for strong adduction of the eye.

Lateral Rectus

Extra-ocular muscle innervated by CN VI, primarily responsible for strong abduction of the eye.

Inferior Oblique

Extra-ocular muscle innervated by CN III, primarily responsible for eye extorsion, with secondary elevation and abduction.

Superior Oblique

Extra-ocular muscle innervated by CN IV, primarily responsible for eye intorsion, with secondary depression and abduction.

Olfactory Nerve (CN I)

Cranial nerve originating above the brainstem, responsible for the sense of smell.

Optic Nerve (CN II)

Cranial nerve originating above the brainstem, responsible for vision, carrying information from the retina to the brain.

Trigeminal Neuralgia (Tic douloureux)

A condition characterized by brief, electric-shock like facial pain in a V distribution (often V2/V3), triggered by light touch, chewing, or wind, commonly caused by neurovascular compression.

Bell's Palsy

An acute idiopathic lower motor neuron (LMN) CN VII palsy, causing complete ipsilateral facial weakness, hyperacusis, decreased tearing/saliva, and loss of taste on the anterior 2/3 of the tongue.

UMN vs LMN Facial Palsy

Upper motor neuron (UMN) facial palsy (e.g., stroke) spares the forehead, while lower motor neuron (LMN) facial palsy (e.g., Bell's palsy) involves the forehead.

Scalp Layers

Consists of 5 layers: Skin, Connective tissue (dense), Aponeurosis, Loose connective tissue, and Pericranium.

Scalp Connective Tissue

A dense, tough layer containing blood vessels and nerves; bleeding here is hard to stop because vessels are held open.

Scalp Loose Connective Tissue

Allows the scalp to move over the skull; infections can spread easily through this layer to the brain via emissary veins.

Facial Artery

A branch of the external carotid artery that winds around the lower jaw and supplies blood to most of the face, including cheeks, lips, and nose.

Middle Meningeal Artery

Enters through the foramen spinosum and supplies the meninges (coverings of the brain); a major source of epidural hematomas.

Facial Vein

The main drainage vein of the face, communicating with the cavernous sinus (inside the skull), posing a risk for infection spread to the brain.

Larynx (Voice Box)

An organ in the neck that contains the vocal cords and is responsible for producing sound; composed of cartilages like thyroid, epiglottis, and cricoid.

Epiglottis

A flap of cartilage that covers the airway during swallowing, preventing food from entering the trachea.

Pharynx (Throat)

A shared pathway for food and air, divided into the nasopharynx, oropharynx, and laryngopharynx.

Thyroid Gland

Located in the neck below the Adam's apple, it controls metabolism through the production of thyroid hormones (T3, T4).

Parotid Gland

The largest salivary gland, located in front of the ear, producing watery saliva rich in enzymes like amylase.

Submandibular Gland

Located beneath the jaw, it produces saliva to aid digestion.

Sublingual Gland

Located under the tongue, it secretes mucus-rich saliva.

Carotid Triangle

A small triangular space in the anterior neck bordered by muscles, containing the carotid artery, carotid sinus, carotid body, and deep cervical lymph nodes.

Carotid Artery

The main artery bringing blood to the head and brain, splitting into internal (to brain/eyes, no neck branches) and external (to face, scalp, thyroid, tongue, jaw) branches.

Carotid Sinus

A bulge at the base of the internal carotid artery containing baroreceptors (pressure sensors) that help regulate blood pressure.

Carotid Body

A small structure at the carotid bifurcation containing chemoreceptors that detect oxygen, carbon dioxide, and pH levels in the blood, influencing breathing rate.

Internal Jugular Vein

The main vein draining blood from the brain, face, and neck, joining the subclavian vein to form the brachiocephalic vein.

External Jugular Vein

A superficial vein visible on the side of the neck, draining the scalp and face into the subclavian vein; its prominence can indicate high central venous pressure.

Spinal Accessory Nerve (CN XI)

Controls the sternocleidomastoid and trapezius muscles, enabling head turning and shoulder shrugging.

Phrenic Nerve

Formed by C3-C5 nerve roots, it controls breathing by innervating the diaphragm.

Swallowing Mechanism

Involves the tongue pushing food back into the pharynx, epiglottis closing the airway to prevent aspiration, and food passing into the esophagus; controlled by CN IX, X, and XII.

Cornea

The clear, front window of the eye that bends (refracts) light.

Sclera

The white, tough outer part of the eye that provides protection.

Iris

The colored part of the eye.

Pupil

The central opening of the eye that controls light entry.

Sphincter Pupillae

Muscles that constrict the pupil, under parasympathetic control (CN III).

Dilator Pupillae

Muscles that widen the pupil, under sympathetic control.

Retina

The inner layer of the eye containing photoreceptors (rods for night, cones for color/day vision).

Optic Disc (Blind Spot)

The area where the optic nerve exits the eye, lacking photoreceptors.

Macula

An area of sharp central vision on the retina.

Fovea

The tiny center of the macula, having the highest visual acuity.

Lens

Focuses light onto the retina, with its shape changed by the ciliary muscle for accommodation.

Ciliary Muscle

Contracts to change the lens shape for accommodation, allowing focus on close or far objects.

External Acoustic Meatus (Ear Canal)

Carries sound waves to the eardrum (tympanic membrane).

Tympanic Membrane (Eardrum)

Vibrates in response to sound waves.

Auditory Ossicles

The three middle ear bones (malleus, incus, stapes) that amplify and transfer sound vibrations to the inner ear.

Cochlea

The spiral organ of the inner ear responsible for hearing.

Semicircular Canals

Parts of the vestibular labyrinth that sense rotational head movements.

Utricle and Saccule

Parts of the vestibular labyrinth that sense linear movement and head position relative to gravity.

Vestibulocochlear Nerve (CN VIII)

Cranial nerve with cochlear branch for hearing and vestibular branch for balance.

Glaucoma

A condition characterized by increased pressure in the eye due to blocked aqueous humor drainage, damaging the optic nerve and leading to gradual vision loss (peripheral first).

Cataracts

Clouding of the lens of the eye, causing blurry vision, glare, and poor night vision, often treated with surgical lens replacement.