Special Senses: Vision, Taste, Smell, Hearing, and Equilibrium

Fibrous tunic

Composed of sclera and cornea.

Vascular tunic (Uvea)

Composed of choroid, ciliary body, and iris.

Sensory tunic (Retina)

Composed of photoreceptors; optic nerve (CN II) is made up of the axons of the retinal ganglion cells.

Lens

Used to focus light on the retina by changing shape.

Anterior segment

Anterior to the lens and filled with aqueous humor.

Posterior segment

Posterior to the lens and filled with vitreous humor.

Superior rectus muscle

Action: Elevation of eyeball; Innervation: Oculomotor nerve (CN III).

Inferior rectus muscle

Action: Depression of eyeball; Innervation: Oculomotor nerve (CN III).

Medial rectus muscle

Action: Adduction of eyeball; Innervation: Oculomotor nerve (CN III).

Lateral rectus muscle

Action: Abduction of eyeball; Innervation: Abducens nerve (CN VI).

Superior oblique muscle

Action: Depression and abduction of eyeball; Innervation: Trochlear nerve (CN IV).

Inferior oblique muscle

Action: Elevation and abduction of eyeball; Innervation: Oculomotor nerve (CN III).

Oculomotor Nerve (CN III)

Parasympathetic nerve involved in eye function.

Visual Pathway

Order: 1. Photoreceptors 2. Ganglion cells 3. Optic chiasm 4. Optic tract 5. Thalamus 6. Primary visual cortex.

Photoreceptors

Convert light into an electrical signal.

Optic nerve (CN II)

Retinal ganglion cell axons leave the eye as the optic nerve.

Optic chiasm

Partial crossover of fibers from the nasal aspect of each retina.

Optic tract

Carries information from the contralateral visual field.

Thalamus

Most fibers in the optic tracts synapse with neurons here.

Primary visual cortex

Final destination for visual information processing.

Fibers from the thalamus

Project to the primary visual cortex in the occipital lobes.

Right primary cortex

Integrates information from the left visual field.

Left primary cortex

Integrates information from the right visual field.

Visual information from the left eye

Travels in the Left Optic nerve.

Visual information from the left visual field

Travels in the Left Optic tract.

Peripheral vision crossing over

Occurs in the Optic Chiasm.

Five special senses

Include vision, hearing, taste, smell, and equilibrium.

Special sense of taste

Includes receptor type, location of sensory receptor organ, and how special and general sensation to the tongue is supplied.

Extrinsic muscles of the tongue

Include three muscles, their action, and innervation.

Special sense of smell

Includes receptor type, location of sensory receptor organ, and how impulses travel from the olfactory epithelium to the brain.

Special sense of hearing and equilibrium

Includes receptor type, parts of the ear, sensory receptor organs, and how impulses travel to the brain.

Primary cortical areas for smell, sight, and hearing

Located in specific lobes of the brain, supplied by anterior, middle, or posterior cerebral arteries.

Mechanoreceptors

Respond to mechanical force that deforms.

Thermoreceptors

Respond to change in temperature.

Chemoreceptors

Respond to chemicals.

Nociceptors

Respond to potentially damaging stimuli.

General Senses

Associated with touch, lack special sense organs.

Special sensory innervation to the anterior 2/3rds of the tongue

Comes from CN VII.

Sensory innervation to the posterior 1/3 of the tongue

Includes special sensory for taste and general sensory from Glossopharyngeal n. (CN IX) and Facial n. (CN VII).

General sensory innervation to the tongue

Supplied by the mandibular division of trigeminal n.

Styloglossus

Extrinsic muscle of the tongue.

Genioglossus

Extrinsic muscle of the tongue.

Hyoglossus

Extrinsic muscle of the tongue.

Primary Olfactory Cortex

Located mostly at the medial aspect of the temporal lobe; conscious awareness of odors.

Subcortical Route

Pathway to the Hypothalamus, Amygdala, and Other Regions of Limbic System to elicit emotional and memory-evoked responses to odors.

External Auditory Canal

Structure of the external ear.

Auditory Ossicles

Includes Malleus, Incus, and Stapes.

Malleus

Also known as the 'Hammer'.

Incus

Also known as the 'Anvil'.

Stapes

Also known as the 'Stirrup'.

Pharyngotympanic Tube

Structure of the middle ear.

Ossicles Amplification

Ossicles amplify sound waves received at the tympanic membrane 20X.

Semicircular Canals

Structure of the internal ear.

Cochlea

Structure of the internal ear.

Oval Window

Structure of the internal ear.

Round Window

Structure of the internal ear.

Tympanic Membrane

Sound waves enter ear and cause it to vibrate.

Cochlear Branch of CN VIII

Initiates a nerve signal when hair cells in the spiral organ are distorted.

Mechanoreceptor

Receptor type used for equilibrium.