Chapter 17: Lecture Midterm II Flashcards
On each side of the nose, there are 40 or so bundles of axons of
olfactory sensory neurons from the right and left olfactory (I) nerves
the olfactory nerves pass through the
cribriform foramina of the cribriform plate of the ethmoid bone
where do olfactory nerves extend to?
parts of the brain known as olfactory bulbs, which contain glomeruli
where do the second order neurons synapse with the olfactory nerves
at the glomerulus (second order neurons called; mitral cells)
Each glomerulus of the olfactory pathway recieves input from
only one type of olfactory sensory neuron
the axons of mitral cells form
the olfactory tract
where does conscious awareness of smell occur
olfactory cortex in the temporal lobe of the cerebrum
olfactory sensations are the only sensations that
reach the cerebral cortex without synapsing in the thalamus
where does out emotional responses to odours occur
some axons of the olfactory tract project to the limbic system
what type of sense is smell
chemical
the olfactory epithelium covers the…
inferior surface of the cribriform plate and extends along the superior nasal concha
extending from the dendrite of an olfactory sensory neuron are several nonmotile
olfactory cilia,
olfactory cilia are the site of
olfactory transduction
within the plasma membranes of the olfactory cilia are
olfactory receptor proteins that detect inhaled chemicals
Odorants:
chemicals that bind to and stimulate olfactory sensory neurons in the olfactory cilia
Supporting epithelial cells:
columnar epithelial cells of the mucous membrane lining the nose
- they provide physical support, nourishment and electrical insulation for the olfactory sensory neurons and help detoxify chemicals that they come in contact with
Basal epithelial cells
- stem cells located between the bases of the supporting epithelial cells
- they continue to undergo cell division to product new olfactory sensory neurons, which live for only about 2 months before being replaced
Olfactory glands (Bowman’s glands)
- within the connective tissue that supports the olfactory epithelium
- produce mucus that is carried to the surface of the epithelium by ducts
Olfactory transduction
binding of an odorant molecule to an olfactory receptor protein
Chemical reactions involving cyclic AMP (cAMP) cause
depolariztion
Neural pathway for olfaction
- action potential travels to the primary olfactory area
- impulses travel to the frontal lobe (orbitofrontal area) for odor identification
taste is a
chemical sense
taste buds contain
receptors for the sensation of taste
where are taste buds found
tongue, soft palate, pharynx, epitlottis
What kind of epithelial cells do tastebuds contain
- supporting cells
- gustatory receptor cells
- basal stem cells
Where on the tongue are taste buds located
on elevations called papillae
What are the three types of papillae on the tongue
- vallate papillae
- fungiform papillae
- foliate papillae
Vallate papillae
about 12 that contain 100-300 taste buds
Fungiform papillae:
Scattered over the tongue with about 5 taste buds each
Filiform papillae:
- cover the entire surface of the tongue
- increased friction to make it easier for the tongue to move food within the mouth
- contain tactile receptors but no taste buds
MOST ABUNDANT ON TONGUE
What are the 5 primary tastes
- sour
- sweet
- bitter
- salt
- umami (meaty)
Chemicals that stimulate gustatory epithelial cells are known as
tastants
Once a tastant is dissolved in saliva…
it can make contact with the plasma membranes of gustatory microvilli
gustatory microvilli are the sites of
Taste transduction
After there is contact with gustatory microvilli,
it results in depolarizing receptor potential which stimulates exocytosis of synaptic vesicles
After there is depolarization in the gustatory pathways…
neutrotransmitter molecyles trigger a graded potential which produces nerve impulses in the first order sensory neurons
an individual gustatory epithelial cell responds to only
one type of tastant because each cell has either ion channels or receptors for only on of the primary tastes
each taste bud contains
gustatory epithelial cells for each tupe of tastant to allow dfferent tastes to be detected in different parts of the tongue
A bitter cell cannot respond to
a sour or sweet cell and vice versa
what three cranial nerves contain axons of the first-order gustatory neurons that innervate taste buds
- facial nerve (VII)
- glossopharyngeal (IX)
- vagus (X)
The facial nerves serves taste buds on
anterior 2/3rds of the tongue
the glossopharyngeal nerves serve taste buds on
posterior 1/3rd of tongue
the vagus nerve serves taste buds in the
throat and epiglottis
from the gustatory epithelial cells in taste buds, nerve impulses propagate along cranial nerves to…
the gustatory nucleus in the medulla
from the medulla, some axons carrying taste signals project to…
the limbic system and hypothalamus, others project to the thalamus
Taste signals that go to the thalamus then go to..
gustatory cortex in the insula of the cerebrum
the gustatory cortex in the insula of the cerebrum gives rise to
conscious perception of taste and discrimination of taste sensations
Light passes through which structures of the eye
- cornea
- anterior chamber
- pupil
- posterior chamber
- lens
- vitreous humor
- retina
more than half the sensory receptors in the human body are located in the…
eyes
the eyes are responsible for visible light on the electromagnetic spectrum with wavelengths ranging from
400-700 nm
wavelength 400 would be the color —- whereas 700 is —-
violet, red
what are the accessory structures of the eye
- eyelids
- eyelashes/eyebrows
- lacrimal apparatus
- extraocular muscles
the levetator palpabrae superioris muscle controls
the upper eyelid
the tarsal plate is what
gives form and support to the eyelids
the tarsal glands secrete
fluid that prevents the eyelids from sticking to eachother
conjunctiva:
thin, protective mucus membrane that lines the eyelids and covers the sclera
eyelashes protect the eyeballs from
- foreign objects
- perspiration
- direct rays of sun
lacrimal apparatus
- group of structures that produces and drain lacrimal fluid or tears in a process called lacrimation
Lacrimal glands:
each about the size and shape of an almond, secrete lacrimal fluid which drains into 6-12 exretory lacrimal ducts that empty tears onto the surface of the conjunctiva of upper eyelid
tears pass into 2 ducts…
the superior and inferior lacrimal canaliculli which leads to the lacrimal sac
lacrimal sac
within the lacrimal fossa of the lacrimal bone
extraocular muscles extend from
the walls of the bony orbit to the sclera (white) of the eye and are surrounded by a significant quantity of periorbital fat
what are the 6 extraocular muscles
- superior rectus
- inferior rectus
- lateral rectus
- medial rectus
- superior oblique
- inferior oblique
what are the extraocular muscles supplied by
- oculomotor nerves (III)
- trochlear (IV)
- abducens (VI) nerves
What are the three layers of the eyeball:
- fibrous layer
- vascular layer
- inner layer (retina)
Fibrous layer of the eyeball:
- most superficial layer
- consists of anterior cornea and posterior sclera
Cornea:
transparent coat that covers the coloured iris; because it is curved it helps focus light onto the retina
Since the centra part of the cornea receives oxygen from outside area
contact lenses that are worn for long periods of time must be permeable to oxygen
Sclera
- the white of the eye
- dense layer of connective tissue made up of collagen fibers and fibroblasts
- gives shape to the eyeball, makes it more rigid and protects inner parts
the sclera covers the entire eyeball except for the
cornea
Vascular layer (uvula) of the eyeball:
- middle layer of the eye ball
- composed of three parts: choroid, ciliary body and iris
- numerous blood vessels provide nutrients to the posterior surface of the retina
Choroid:
- posterior portion of vascular layer; lines most of the internal surface of sclera
- contains melanocytes that produce pigment (melanin) which causes this later to appear black or dark brown in color
Melanin in the choroid absorbs
stray light rays, which prevents reflection and scattering of light within the eyeball; as a result the image cast on the retina remains sharp
In the anterior portion of the vascular layer, the choroid becomes the
ciliary body
Ciliary body:
- extends from the ora serrata; the jagged anterior margin of the retina, to a point just posterior to the junction of the sclera and cornea
- contains ciliary processes and ciliary muscle
like the choroid, the ciliary body appears
dark brown in color because it contains melanocytes
Ciliary processes:
- protrusions or folds on the internal surface of the ciliary body; contain blood capillaries that secrete aqueous humor
extending from ciliary processes are…
zonular fibers that attach to the lens
Ciliary muscle:
- circular band of smooth muscle
contraction and relaxation of the ciliary muscle changes the tightness of the zonular fibers which…
alters the shape of the lens, adapting it for near or far vision
Iris
coloured portion of the eyeball which is suspended between the cornea and the lens and is attached to ciliary processes
What helps determine eye color
melanocytes
What is a principle function of the iris
regulate the amount of light entering the eyeball through the pupil
Pupil:
hole in the center of the iris; appears black because as you look through the lens, you can see the heavily pigmented choroid and retina
What else controls the dilation and constriction of the pupil
oculomotor nerve (III)
- the pupil constricts as pupillae muscles contract
- the pupil dilates as dilator pupillae muscles of the iris contract
Inner layer of the eyeball:
- the third inner layer of the eyeball, the retina, lines the posterior three quarters of the eyeball and is the beginning of the visual pathway
the surface of the retina is the only place in the body where blood vessels
can be viewed directly ad examined for pathological changes such as those that occur with htn, DM, cataracts, and macular disease
Where do the optic nerves exit the eyeball
optic disc
bundled together with the optic nerves are the
central retinal artery and central retinal vein
The point where the optic nerve exits at the optic disc is the
blind spot
What is the exact center of the retina clled
macula lutea
In the center of the macula lutea is the
fovea centralis, area of highest visual acuity (sharpest vision)
The retina contains photoreceptors known as
rods and cones
Lens
- behind the pupil and the iris
- contains proteins called crystallins, arranged like layers of onions -makes up refractive media
the lens helps to focus
images to the retina to faciliate clear vision
The lens divides the interior of the eyeball into 2 segments
- anterior and posterior segment
The anterior segment of the eyeball
space between the cornea and the lens - consists of two chambers: anterior and posterior chamber
Anterior chamber of the anterior segment
lies between the cornea and the iris
Posterior chamber of the anterior segment
lies behind the iris and in front of the zonular fibers and lens
Both chambers of the anterior segment are filled with
aqueous humor, a transparent watery fluid that nourishes the lens and cornea
Aqueous humor continually filters out of blood capillaries in the
ciliary processes of the ciliary body and enters the posterior chamber
Flow of aqueous humor
Goes from anterior chamber - filters through the ciliary processes -enters posterior chamber - flows forward between iris and lens and throguh the pupil
the aqueous humor is replaced
every 90 minutes
The larger posterior portion of the eyeball, the posterior segment lies between
the lens and the retina
The posterior segment contains a jelly like substance;
the vitreous humor
The vitreous humor functions to
hold the retina flush against the choroid, giving the retina an even surface for the reception of clear images
- it also contains phagocytic cells that remove cell debris which keeps this part of the eye cllear for unobstructed vision
The vitreous humor occupies about
4/5ths of the eyeball
images that are focused on the retina are
inverted (upside down)
refraction is accomplished through a process called
accommodation
Convex
something that curves outward like a ball
what muscles contract during accommodation
ciliary muscles
the increase in curvature of the lens is called
accommodation
convergence
both eyes moving at the same time for example: when our eyes are focussed on a pencil that is moving closer to our eyes
the single type of photopigment in rods is
rhodopsin
light causes rod photoreceptors to
decrease their release of the inhibitory neurotransmitter glutamate
in darkness, the rod photoreceptors
increase the release of inhibitory neurotransmitter glutamate
