Nervous system Part 3 Flashcards
Outer layer of eye
Consists of the sclera and cornea
posterior potion is know as sclera -the “white of the eye”
anterior potion is the cornea and it is the transparent part of the eye where light enters
aqueous humor fills the space between the cornea and lens
Middle layer of the eye
Choriod, ciliary muscle, and iris
choroid
darkly colored posterior choroid prevents light from dispersing throughout the eye
choroid is highly vascular and supplies blood to the other layers of the eye
ciliary muscle
ciliary body changes the shape of the lens allowing it to focus
iris
anterior to the ciliary body and contains the circular colored portion of the eye
it controls the amount of light that is let in to the pupil - a hole in the center of the iris
the iris uses its muscle fibers to contract or dilate based on the amount of light in the environment.
retina
The inner sensory layers include the retina which has two types of photoreceptors that are sensitive to light.
Rods and cones
rods
stimulated by dim light.
Rods are more sensitive to light but do not generate sharp or color images
cones
operate in bright light, helping to generate bright, sharp images
lens
located posterior to the iris and the pupil
vitreous body
the interior of the eye posterior to the lens is called the vitreous body and is filled with vitreous fluid - this helps hold the retina firmly to the choroid.
Vision pathway from environment to the brain
cornea
aqueous humor
lens
vitreous humor
posterior surface of retina
photoreceptors detect light
optic nerve
optic chasm
optic tracts
LNG of the thalmus
optic radiations
occipital lobe
interrupted as vision
optic nerve, optic chiasm, optic tracts, LGN, optic radiations,
photoreceptors in the retina send a signal through the optic nerve on to the optic chiasm located in the hypothalamus.
the medial fibers of the optic nerve then cross to the other side when they reach the optic chiasm where the optic tracts are formed.
optic tracts terminate in the thalamus in the lateral geniculate nucleus (LNG)
The info continues from the thalamus through the optic radiations to the primary visual area of the occipital lobe
Last it is interpreted as vision in the occipital lobe
nasal visual field
the visual field closest to the nose
each eye receives information from the left and right eye
peripheral vision field
field of vision on the lateral side of each eye
binocular vision field
overlapping information in the nasal fields allows for 3-D vision called binocular visual field
Each eye has a left and right visual field
Sensory info from the left side of the body (bilateral left visual fields) will eventually be interpreted by the right side of the brain and is reversed for the right visual fields
what fibers cross at the optic chiasm?
only the medial fibers
the information from each retina is carried through the optic nerves to the optic tract
the left side of the brain receives info 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 for the bilateral left visual fields
six muscles of the eye
medial rectus, inferior rectus, superior rectus, inferior oblique, superior oblique, lateral rectus
medial rectus
turns the eye medially. CN III
inferior rectus
moves the eye medially and depresses it. CN III
superior rectus
moves the eye medially and elevates it. CN III
inferior oblique
is responsible for eye elevation, lateral movement and external rotation. CN III
superior oblique
controlled by the 4th cranial nerve - trochlear nerve
responsible for eye depression, lateral movement, and internal rotation
lateral rectus
controlled by the 6th cranial nerve, abducens, and turns the eye laterally
cataracts
lens that slowly become hardened and cloudy over time - makes vision appear more blurry because light is unable to enter the lens clearly to be refracted onto the retina.
CVA or brain damage and vision
damage from a stroke or brain tumor can also cause vision impairments. For example is the right optic nerve is damaged, the right eye will be unable to see.
cranial nerve damage
many cranial nerves supply the muscles to move the eye.
Damage to the abducens nerve causes diplopia, or double vision.
how to test for diplopia
one way to test for abducen nerve damage is to have a person look left and hold their head still
if the lateral rectus does not receive nervous signals from the abducen nerve, the eye us unable to rotate laterally when looking at the same side
the effected eye deviates medially when looking forward because of the imbalance in muscle tone between the medial and lateral recti.
divisions of the ear
external, middle, and inner ears
external ear
consists of the auricle and the external canal (meatus)
auricle- is shaped to funnel sound waves into the acoustic canal so that sounds can be detected. part of the ear that can be seen externally
what is the auricle made of?
part of the ear that can be seen externally -composed of elastic cartilage covered with thin skin making up the rim (helix) and the lobule (that lacks cartilage)
external acoustic meatus
the tunnel between the auricle and tympanic membrane
composed of elastic cartilage near the auricle and becomes a cylinder through the temporal bone
canal is lined with skin containing hairs and glands that secrete cerumen (earwax) which traps foreign particles
inner end of canal terminates at tympanic membrane
tympanic membrane
eardrum
a thin membrane of connective tissue whose vibration transmits sound into the middle ear
middle ear
or tympanic cavity
air filled chamber containing the three smallest bones in the body- the stapes (stirrup), incus (anvil), and malleous (hammer)
the malleous receives vibrations from the eardrum and transfers them along through the incus and then finally the stapes, which conveys them to the inner ear
inner ear
composed of the bony and membraneous labyrinths filled with fluid
bony labyrinths divided into three sections. the vestibule, semicircular canals, cochlea
vestibule
connects to three semicircular canals, which house receptors to provide the body’s vestibular (equilibrium and balance) systems
semicircular canals
also filled with fluid. each semicircular canal contains equilibrium receptors, which cause action potentials in response to different types of motion (head movements or rotation).
action potentials sent through the vestibular portion of CN VIII (vestibular cochlear nerve)
vestibular sense
the semicircular canals contribute to the body’s vestibular sense (balance and upright orientation
CN VII and the ear
CN VII is also located in the inner ear region
the facial innervates a muscle called 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 sound
cochlea
a spiral, bony chamber containing the membraneous endolymph-filled cochlear duct.
the cochlea houses the organ corti and terminated in the cochlear nerve
The organ of corti
the sense organ in the auditory system
contains the tectorial membrane and tiny hairs called sterocillia
as fluid within the cochlear ducts receive vibrations, the tectorial membrane moves and bends the stereocillia
this mechanical movement of stereocilla initiates an action potential in neurons that is transmitted through the cochlear nerve portion of CN VIII
What happens with the mechanical movement of stereocilla?
the mechanical movement of stereocillia initiates an action potential in the neurons that is trnamistted through the cochlear nerve portion of CN VIII
What is the process of hearing (events)?
First sounds waves are funneled into the external auditory canal causing the eardrum to vibrate
The vibrations transmit to the ossicles which push against the fluid inside the cochlear ear duct
The movement of the fluid causes movement of the stereocillia in the organ of Corti
The movement of the sterocillia then stimulates the neurons to send impulses through the cochlear nerve to the primary audiroty cortex of the temporal lobe
How is the auditory pathway unique?
the auditory pathway is a unique sensory pathway because the ascending pathways cross in addition to sending signals to the same side of the brain.
the result is the sounds from each ear are equally interpreted on the left and right sides of the brain.
deafness
damage to the auditory pathways results in hearing loss called deafness
deafness can be partial (if hearing is impaired but not completely lost or total
conduction deafness
occurs from damage to the outer or middle ear structures.
for example, build up of cerumen (earwax) 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
**This type of deafness is NOT complete because sound waves can be conducted through the cranial bones to move to the organ of Corti.
Nerve deafness
occurs when there is damage to the nerve pathway
damage can occur to the receptor cells to the cochlear nerve that transmits the nerve impulses to the brain
Nerve deafness can be complete or partial in one or both ears depending on the amount of damage to the nerve pathway
olfaction
special sense of smell -chemical
olfactory receptors are activated by airborne chemical substances dissolved in fluid on the surface of the nasal mucus membrane
olfactory nerves
CN 1 are 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 CRIBRIFORM PLATE
dendrites extend from the cell body to the surface of epithelium where it terminates in the olfactory bulbs.
olfactory bulbs
paired masses of gray matter
this is where dendrites extend from the cell body to the surface of epithelium where it terminates in the olfactory bulbs
In the olfactory bulbs, olfactory nerve axons synapse with other cell bodies of the olfactory pathway
The axons then travel together from the olfactory bulbs to form the olfactory tracts.
olfactory tracts
carry information to the temporal lobes where they get interpreted in the primary olfaction area as smell
gustatory system
is responsible for special sense of taste.
Taste is a chemical sense because its receptors are activated by chemical substances dissolved in saliva
These receptors are mainly in tastebuds on the tongue, but also throughout the mouth and throat
Taste buds
contain chemical receptors that are stimulated by the chemical composition of food
primarily found on the tongue, as well as the surface of the mouth and wall of the pharynx.
tastebuds are formed by gustatory cells and supporting cells
gustatory cells
are the chemoreceptor cells inside the tastebuds
each gustatory cell terminates in a gustatory hair, which projects into saliva to detect dissolved chemicals
supporting cells
form the bulk of the tastebud and separate the taste receptor cells from one another
basal cells
these are stem cells that divide and differentiate into new supporting cells that then form new gustatory cells
nocireceptors
detect pain
thermoreceptors
detect hot and cold and can contribute to the taste experience of food.
Spice and temperature
both of these impact how we perceive taste by the brain
Taste pathway
Starts when food chemicals come into contact with gustatory hairs
This generates an action potential in dendrites that are wrapped around gustatory cells
the nerve impulse is carried by afferent fibers through cranial nerves (the facial and glossopharyngeal nerve)
these transmit the impulse to the thalamus and then the parietal lobe to be interpreted as taste.
Facial nerve and glossopharyngeal
facial nerve carries info from the anterior 2/3 of tongue and the glossopharyngeal nerve carries info from the posterior 1/3 part of the tongue
5 primary tastes
sweet- produced by many compounds including sugar and some amino acids
salty-many metal salts like NaCl
sour-acids like acetic acid/vinegar
bitter -produced by many drugs like aspirin
savory (umami)-due to certain amino acids and found in foods like fish, ripe tomatoes, aged cheeses, and soy sauce
Anosomia
loss of smell
common to have after a traumatic brain injury - can be temporary or permanent depending on the severity of the injury or what part of the pathway was damaged
Can happen gradually such as in the case of a growing brain tumor that blocks the olfactory pathway
Ageusia
loss of sensation of taste
stimulation to olfactory receptors has a great affect on sense of taste in addition to taste bud stimulation
when olfactory receptors are obstructed by nasal congestion or other factors - the sensation of taste is dulled or completely lost
TBI can also cause ageusia if a taste pathway is damaged.
What is smell
smell is defined as a combination of a limited number of primary odors that are detectable by the brain
