Special Senses

What are the five special senses?

Vision, taste, smell, hearing, and equilibrium.

What type of sensory receptors are involved in special senses?

Special sensory receptors that are distinct receptor cells localized in the head region.

What is anosmia and what can cause it?

Anosmia is the inability to smell, caused by trauma, infections, or neurologic disorders like Alzheimer's, brain tumors, or Parkinson's.

What structures are contained in the olfactory epithelium?

Support cells, basal (stem) cells, and olfactory sensory neurons (chemoreceptors) with olfactory cilia.

Describe the olfactory pathway.

Olfactory epithelia → olfactory bulbs (CN I) → olfactory tract → temporal lobe and limbic system.

What is ageusia and what can lead to it?

Ageusia is the loss of taste, caused by common cold, COVID-19, sinusitis, or dry mouth.

What is the gustatory pathway?

Gustatory receptors → CN VII & CN IX → medulla → thalamus → primary gustatory cortex on insula.

What percentage of taste is attributed to smell?

Taste is 80% smell.

What are the extrinsic eye muscles responsible for?

They are attached to the outside of the eyeball, enabling eye movement in all directions.

What does the mnemonic (LR6)(SO4)3 represent in eye muscle movement?

Lateral rectus (VI abducens), Medial rectus (III oculomotor), Superior rectus (III oculomotor), Inferior rectus (III oculomotor), Inferior oblique (III oculomotor), Superior oblique (IV trochlear).

What is the fibrous layer of the eye?

The outermost layer; dense avascular connective tissue including the sclera and cornea.

What is the function of the sclera?

It protects and shapes the eyeball and anchors extrinsic eye muscles.

What is the role of the cornea?

It is a clear window that lets light enter and bends light as it enters the eye.

What is the vascular layer of the eye also known as?

The uvea.

What is the function of the choroid region in the eye?

It supplies blood to all layers of the eyeball and absorbs light to prevent scattering.

What is the ciliary body?

A thickened ring of tissue surrounding the lens that controls the shape of the lens.

What is the iris and its function?

The colored part of the eye that regulates the amount of light entering the eye through the pupil.

How do the sphincter and dilator pupillae muscles affect pupil size?

Sphincter pupillae contract to constrict pupils in bright light; dilator pupillae contract to dilate pupils in dim light.

What is the retina and its origin?

The retina contains photoreceptor cells and originates as an outpocketing of the brain.

What are rods and their function?

Rods are photoreceptors that function in dim light and peripheral vision, but do not provide color vision or sharp images.

What is the optic disc?

The site where the optic nerve leaves the eye, lacking photoreceptors, thus referred to as the blind spot.

What are cones in the eye responsible for?

Vision receptors for bright light and high-resolution color vision.

Where are the majority of cones located in the eye?

In the macula lutea area at the posterior pole, specifically in the fovea centralis.

What is the fovea centralis?

A tiny pit in the center of the macula lutea that contains all cones, providing the best visual acuity.

What separates the eye into posterior and anterior segments?

The lens and ciliary zonule.

What is contained in the posterior segment of the eye?

Vitreous humor, which supports the posterior surface of the lens and holds the neural layer of the retina against the pigmented layer.

What is the role of aqueous humor in the anterior segment of the eye?

It supplies nutrients and oxygen to the lens and cornea and removes wastes.

What causes glaucoma?

Blockage of the scleral venous sinus, leading to increased intraocular pressure.

What is the pathway of light entering the eye?

Cornea, aqueous humor, lens, vitreous humor, neural layer of retina, and photoreceptors.

How many times is light refracted as it enters the eye?

Three times: entering the cornea, entering the lens, and leaving the lens.

What is the far point of vision?

The distance beyond which no change in lens shape is needed for focusing, typically 20 feet for an emmetropic eye.

What happens to the ciliary muscles when focusing on distant objects?

They are completely relaxed, causing the lenses to stretch flat.

What is accommodation in the context of vision?

The process of changing the lens shape to increase refraction for focusing on close objects.

What is presbyopia?

The loss of accommodation that occurs with age, typically over 50.

What is the role of the accommodation pupillary reflex?

To constrict the pupils and prevent divergent light rays from entering the eye.

What is convergence of the eyeballs?

The medial rotation of the eyeballs toward the object being viewed, controlled by the medial rectus muscles.

What is myopia?

Nearsightedness caused by an eyeball that is too long, resulting in the focal point being in front of the retina.

How is myopia corrected?

With a concave lens.

What is hyperopia?

Farsightedness caused by an eyeball that is too short, resulting in the focal point being behind the retina.

How is hyperopia corrected?

With a convex lens.

What is astigmatism?

A condition caused by unequal curvatures in different parts of the cornea or lens.

How can astigmatism be corrected?

With cylindrically ground lenses or laser procedures.

What are photoreceptors?

Modified neurons that resemble upside-down epithelial cells, consisting of rods and cones.

What are the two segments of photoreceptors?

Outer segment (light-receiving region with visual pigments) and inner segment (joins cell body and connects to outer segment via cilium).

What are the primary functions of rods in vision?

Rods are very sensitive to light, making them best suited for night vision and peripheral vision; they perceive images in gray tones only.

What are the primary functions of cones in vision?

Cones have low sensitivity and require bright light for activation; they react more quickly than rods and allow for vividly colored sight due to their multiple pigments.

What is the role of visual pigments in the retina?

Visual pigments absorb light and are located in photoreceptor cells, consisting of a protein called opsin.

How many types of opsins are present in human photoreceptors, and what are they?

Human photoreceptors contain 4 types of opsins: 1 in rod cells (rhodopsin) and 3 in cone cells (red, blue, and green opsins).

What is color blindness and how is it inherited?

Color blindness is the lack of one or more cone pigments and is inherited as an X-linked condition, making it more common in males.

What is phototransduction?

Phototransduction is the process by which photoreceptors absorb light and convert it into an electrical signal.

What types of potentials do photoreceptors and bipolar cells generate?

Photoreceptors and bipolar cells generate only graded potentials (EPSPs and IPSPs), not action potentials.

How do ganglion cells contribute to visual processing?

Ganglion cells generate action potentials that are transmitted via the optic nerve to the brain.

What is the pathway of visual information from the retina to the brain?

Axons of retinal ganglion cells form the optic nerve, with medial fibers crossing at the optic chiasma and continuing as optic tracts to the primary visual cortex.

What is the primary visual cortex responsible for?

The primary visual cortex contains a topographical map of the retina and responds to dark and bright edges and object orientation, providing inputs for form, color, and motion.

What are the three major areas of the ear?

The ear has three major areas: external ear (hearing only), middle ear (tympanic cavity, hearing only), and internal ear (hearing and equilibrium).

What structures make up the external ear?

The external ear consists of the auricle (pinna), helix, lobule, external acoustic meatus (auditory canal), and tympanic membrane (eardrum).

What is the function of the tympanic membrane?

The tympanic membrane vibrates in response to sound and transfers sound energy to the bones of the middle ear.

What is the role of the middle ear?

The middle ear is a small, air-filled cavity that transmits sound from the eardrum to the inner ear.

What are the auditory ossicles and their names?

The auditory ossicles are three small bones in the tympanic cavity: malleus (hammer), incus (anvil), and stapes (stirrup).

What is otitis media?

Otitis media is inflammation of the middle ear, commonly seen in children, and is the most frequent cause of hearing loss in children.

What connects the middle ear to the nasopharynx?

The pharyngotympanic (auditory) tube connects the middle ear to the nasopharynx.

What is the epitympanic recess?

The epitympanic recess is the superior portion of the middle ear, also known as the roof of the cavity.

What is the mastoid antrum?

The mastoid antrum is a canal for communication with mastoid air cells in the mastoid process.

What is the significance of the dense packing of cones at the fovea?

The dense packing of cones at the fovea allows for maximal resolution in vision.

How do the pathways of rods and cones differ in terms of image clarity?

Rods have converging pathways that cause fuzzy, indistinct images, while cones have nonconverging pathways that result in detailed, high-resolution vision.

What causes the eardrum to bulge outward and become inflamed in acute infectious forms?

Acute infections.

What is the internal ear also referred to as?

The labyrinth.

Where is the internal ear located?

In the temporal bone behind the eye socket.

What are the two major divisions of the internal ear?

Bony labyrinth and membranous labyrinth.

What is the bony labyrinth filled with?

Perilymph fluid, similar to cerebrospinal fluid (CSF).

What are the three regions of the bony labyrinth?

Vestibule, semicircular canals, and cochlea.

What do the semicircular canals respond to?

Angular (rotational) movements of the head.

What is the ampulla?

An enlarged area of ducts in each semicircular canal that houses the crista ampullaris, which contains equilibrium receptors.

What is the vestibule?

The central egg-shaped cavity of the bony labyrinth containing two membranous sacs.

What are the two membranous sacs in the vestibule?

Saccule and utricle.

What does the cochlea contain?

Cochlear duct, which houses the spiral organ (organ of Corti).

What is the function of the spiral organ in the cochlea?

It contains cochlear hair cells arranged in one row of inner hair cells and three rows of outer hair cells.

What is vertigo?

A spinning sensation with changes in head position.

What are some causes of vertigo?

Benign paroxysmal positional vertigo, labyrinthitis, and Meniere's disease.

What is conduction deafness?

Hearing loss due to external acoustic meatus blockage, tympanic membrane damage, or otosclerosis.

What is sensorineural deafness?

Hearing loss due to damaged cochlear hair cells, CN VIII injury, or brain injury.

What is presbycusis?

Age-related hearing loss influenced by factors such as loud noise exposure and genetics.

What is the pathway of sound waves through the ear?

Sound waves vibrate the tympanic membrane, auditory ossicles amplify pressure, and pressure waves move through the scala vestibuli.

What role do inner hair cells play in sound transduction?

They are excited by the movement of the basilar membrane, leading to the release of neurotransmitters.

How do outer hair cells protect inner hair cells?

By contracting and stretching to decrease motion of the basilar membrane.

What is the auditory pathway from cochlear bipolar cells to the auditory cortex?

Spiral ganglion, cochlear nuclei, superior olivary nucleus, lateral lemniscus, inferior colliculus, medial geniculate nucleus, primary auditory cortex.

What determines pitch and loudness in sound?

Pitch is determined by frequency, while loudness is determined by amplitude (intensity) measured in decibels (dB).