module 3:

vision pathway

1. Optic Nerve 2. Optic Chiasma 3. Optic tracts 4a. Thalamus --> Primary Visual Cortex 4b. Midbrain --> Superior Colliculi

semicurcular canals

3 of them, filled with fluid. each contains equilibrium receoptors, which cause action potentials in response to different types of motion (head movements or rotation). the action potentials are sent through the vestibular portion of CN VIII. the canals contribute in this way to the body's vestibular sense (balance and upright orientation)

bolus

A soft mass of chewed food. the tongue pushes the bolus back to the pharynx to begin the process of swallowing.

olfactory tracts

a bundle of axons connecting the cells of the olfactory bulb to several target regions in the brain.

the other sense, touch

a somatic sense that does not have a specialized sense organ. instead, touch uses general receptors composed of modified dendrites of sensory neurons. touch includes pressure, vibration, pain, heat, and the combined information is carried in general somatic afferents and general visceral afferents

cochlea

a spiral, bony chamber containing the membranous endolymph-filled cochlear duct. it houses the organ of corti and terminates in the cochlear nerve

olfactory receptors

activated by airborne chemical substances dissolved in fluid on the surface of nasal mucous membranes

note about facial nerve CN VII

also located in the inner ear region. The facial nerve innervates a muscle called the stapedius, which is attached to the stapes. The stapedius controls the amount of tension on the bone, allowing for increased or decreased vibration to help control the intensity of sounds.

middle ear (tympanic cavity)

an air-filled chamber containing the three smallest bones in the body, which are known as the ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup).

cornea

anterior portion of the outer layer of the eye. it's the transparent part of the eye where light enters

iris

anterior to the ciliary body and contains the circular body ady and contains the circular colored portion of the eye. the iris controls the amount of light let into the pupil. it uses its muscle fiber to contract or dilate based on the amount of light in the environment

ciliary body

anterior, changes shape of the lens, allowing it to focus

gustatory cells

are the chemoreceptor cells inside the taste buds. each gustatory cell terminates in a gustatory hair, which projects into the saliva to detect dissolved chemicals

tectorial membrane

as the fluid within the cochlear duct receives vibrations, the tectorial membrane moves and bends the attached stereocilia. the mechanical movement of the stereocilia initiates an action potential in neurons that is transmitted through the cochlear nerve portion of CN VIII

why is the auditory pathway a unique sensory pathway?

because the ascending pathways cross in addition to sending signals to the same side of the brain. The result is that sounds from each ear are equally interpreted on the left and right sides of the brain.

taste pathway

begins as food chemicals contact the gustatory hairs, which generate an action potential in dendrites that are wrapped around the gustatory cells. the nerve impulse is carried by afferent fibers through two cranial nerve pathways, the facial nerves, and the glossopharyngeal nerves, which transmit the impulse to the thalamus and ultimately to the parietal lob to be interpreted as taste.

olfactory nerves (CN I)

bipolar receptor cells found in the olfactory epithelium on the roof of the nasal cavity. the olfactory nerves travel through the ethmoid bone in a location called the cribiform plate. the dendrites extend from the cell body to the surface of the epithelium where it terminates in olfactory bulbs

cranial nerve damage

can cause vision problem.s several diff cranial nerves supply the muscles to move the eye. for example, the abducens nerve is responsible for the lateral movement (left and right) of the eyes. damage to the abducens nerve would cause diplopia, or double vision.

middle layer of eye

choroid, the ciliary muscle, and the iris

inner ear

composed of the bony and membranous labyrinths filled with fluid. the bony labyrinth system is divided into three sections: the vestibule, semicircular canals, and cochlea

vestibule

connects to three semicircular canals, which house receptors to provide the body's vestibular (equilibrium and balance) system

external ear

consists of the auricle and external acoustic canal (meatus)

taste buds

contain chemical receptors that are stimulated by the chemical composition of food. Taste buds are found primarily on the tongue as well as on the surface of the mouth and wall of the pharynx. Taste buds are formed from gustatory cells and supporting cells.

retina

contains two types of photoreceptors, cells that are sensitive to light. rods and cones are the photoreceptros

deafness

damage to the auditory pathway results in deafness. it can be partial if hearing is impaired but not completely lost.

choroid

darkly colord posterior, prevents light from dispersing throughout the eye. it's highly vascular and supplies blood to the other layers of the eye.

smell

defined as a combination of a limited number of primary odors that are detectable by the brain. animals, such as dogs, have a much wider range of detectable smells, and therefore, have a larger amount of brain space dedicated to smell interpretation

savory taste

due to certain amino acids and is found in many foods like fish, ripe tomatoes, aged cheeses and soy sauce

left visual field, right visual field

each eye has both

damage inside brain and vision

ex, damage from CVA or brain tumor, can cause vision impairments. for example, if the right optic nerve is damaged, the right eye will be unable to see

eye muscles

eye movements are controlled by the 6 extrinsic eye muscles.

nerves in taste

facial nerve carries info from the anterior two thirds of the tongue, while the glossopharyngeal nerve carries info from the posterior one third of the tongue

aqueous humor

fills the spaces between the cornea and the lens

supporting cells

form the bulk of the taste bud and separate the taste receptors cells from one another

where does each eye receive info from

from the left and right sides of the body

test for abducens nerve damage

have a person look left and rigth while keeping head still. if the lateral rectus does not receive nervous signals form the abducens nerve, the eye is unable to rate laterally when looking to the same side. the affected eye deviates medially when looking forward bc of the imbalance in muscle tone between medial and lateral recti.

inner sensory layer of eye

includes retina

where will sensory information from the eye be interpreted in the brain

info gathered from left side (bilateral left visual fields) will be eventually interpreted in the right side of hte brain and is reversed for the right visual fields. Information from the left visual field of each eye is gathered onto the ride side of each retina. The information from each retina is carried through the optic nerves to the optic tract. Only the medial fibers of the optic nerves cross at the optic chiasm. The left side of the brain receives information from the medial side of the left eye and the lateral side of the right eye (bilateral right visual fields). The situation is reversed for the right side of the brain, with the right side of the brain receiving information from the bilateral left visual fields.

vitreous body

interior of the eye, posterior to the lens. it is a chamber filled with vitreous fluid, which helps to hold the retina firmly to the choroid.

how does light pass into eye

it passinto eye moving progressively through cornea, aqueous humor, lens and vitreous humor to the posterior surface of the eye on the retina

cataracts

lenses that slowly become hardened and cloudy over time. they make vision look blurry because the light is unable to enter the lense clearly to be refracted onto the retina

frenulum

located on the inferior surface of the tongue along the midline

lens

located posterior to the iris and pupil.

eye muscles innervated by third cranial nerve, oculomotor

medial rectus, superior rectus, inferior oblique

inferior rectus

moves the eye medially and depresses it

superior rectus

moves the eye medially and elevates it

optic radiations

nerve pathway from LGN to primary visual cortex of the occipital lobe. in the occipital lobe, the incoming sensory information is interpreted as a vision

optic tracts

nerve pathways traveling from the optic chiasm to the thalamus, hypothalamus, and midbrain. they terminate in the thalamus in a region called the lateral geniculate nucleus (LGN)

temperature and spice

nociceptors and thermoreceptors both contribute to taste

nerve deafness

occurs from damage to the nerve pathway. damage can occur to the receptor cells or to the cochlear nerve that transmits the nerve impulses to the brain. nerve deafness can be partial or complete in one or both ears depending on the amount of damage to the nerve pathway.

conduction deafness

occurs from damage to the outer or middle ear structures. for example, a build up of cerumen can partially block sound waves entering the external acoustic meatus. another cause of conduction deafness is if the ossicle bones fuse, decreasing the amount of vibrations transmitted to the inner ear. conduction deafness is not complete bc the sound waves can be conducted through the cranial bones to move the organ of corti.

nasal visual field

of each eye is closest to the nose

apex

of the tongue. located anteriorly

root

of tongue is attached to the floor of the posterior surface of the mouth

peripheral vision field

on the lateral side of each eye.

eye layers

outer fibrous layer includes the sclera and cornea

binocular visual field

overlapping info in the nasal visual fiedls allow for 3D vision

nociceptors

pain receptors, found in mouth as well

olfactory bulbs

paired masses of gray matter. in the olfactory bulbs, olfactory nerve axons synapse with other cell bodies of the olfactory pathway. the axons then travel together from the bulbs to form the olfactory tracts, which carry info to the temporal lobes. here the signals are interpreted in the primary olfaction area as smell

optic chiasm

point at which optic nerve fibers cross in the brain, located at the base of the hypothalamus, where the

sclera

posterior portion of the outer fibrous layer of the eye, also known as the white of the eye

sour taste

produced by acids like acetic acid (in vinegar)

sweet taste

produced by many compounds, including sugars and some amino acids.

bitter taste

produced by many drugs like aspirin

salty taste

produced by many metal salts, especially NaCl.

papillae

raised bumps on the tongue. 3 types that help to grip food: circumvallate, fungiform, and filiform. circumvallate and fungiform both contain taste buds

malleus

receives the vibrations from the eardrum and transfers them along through the incus, then finally the stapes, which conveys them to the inner ear

inferior oblique

responsible for eye elevation, lateral movement, and external rotation

tongue

responsible for gripping food and repositioning it between the teeth, forming it into a compact mass called a bolus

gustatory system

responsible for the special sense of taste. taste is one of the chemical senses bc its receptors are activated by chemical substances dissolved in saliva. taste receptors are inside taste buds mostly on the tongue but are also throughout the mouth and throat

cones

retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensations.

ear

sensory organ for hearing three areas: external, middle and inner ears

process of hearing

series of events. 1. sound waves are funneled into the external auditory canal causing the eardrum to vibrate. the vibrations transmit to the ossicles, which push against fluid inside the cochlear duct. the movement of the fluid causes movement of the stereocilia in the organ of corti. the movement of the stereocilia then stimulates the neurons to send impulses through the cochlear nerve to the primary auditory cortex of the temporal lobe.

basal cells

serve as stem cells, which divide and differentiate into new supporting cells that then form new gustatory cells.

cerumen

serves to trap foreign materials

odor isolations

seven primary odors: floral (roses), ethereal (dry cleaning fluid), camphorates (mothballs), musky (perfumes), peppermint (mint gum), pungent (vinegar), and putrid (rotten eggs)

auricle

shaped to funnel sound waves into the external acoustic canal so that sounds can be detected. the auricle is the part of the ear that can be seen externally. it's composed of elastic cartilage covered with skin making up the rim (helix) and the lobule that lacks cartiliage

lateral rectus

sixth eye muscle. innervated by abducens nerve, turns the eye laterally

olfaction

special sense and one of the chemical senses - smell

fifth eye muscle

superior oblique, controlled by the fourth cranal nerve, the trochlear nerve. the superior oblique is responsible for eye depression, lateral movement, and internal rotation

five primary tastes

sweet, salty, sour, bitter, and savory (also called umami)

thermoreceptors

temperature receptors, also found in mouth

anosmia

the loss of smell. Anosmia from a TBI can be temporary or permanent depending on the severity of the injury and what part of the pathway was damaged. Anosmia can also happen gradually, such as in the case of a growing brain tumor that blocks the olfactory pathway.

ageusia

the loss of the sensation of taste. Stimulation of olfactory receptors has a great effect on the sensation of taste in addition to taste bud stimulation. When the olfactory receptors are obstructed by nasal congestion or other factors, the sensation of taste is dulled or completely lost. Other factors, such as TBI or a brain tumor inside the brain, can also cause ageusia if the taste pathway is damaged.

rods

the more numerous cells of the retina are rods, which are stimulated in dim light. rods are more sensitive to light but do not generate sharp or color images.

organ of corti

the sense organ for the auditory system. the organ of corti contains the tectorial membrane and tiny hairs called stereocilia

external acoustic meatus

the tunnel between the auricle and typmanic membrane. the external acoustic meatus is composed of elastic cartilage near the auricle and becomes a cylinder through the temporal bone. the canal is lined with skin containing hairs and glands that secrete cerumen (earwax)

medial rectus

turns the eye medially

special senses

vision, smell, taste, hearing and equilibrium (balance) are the senses that have specialized organs containing specialized recepotr cells, which carry their impulses by way of specialized somatic and visceral afferents.

tympanic membrane (eardrum)

where the inner end of the canal terminates, a thin membrane of connective tissue whose vibration transmits sound energy to the middle ear