Chapter 15- Special Senses Flashcards
What does the olfactory system do?
Allows for the detection of odorants in the air and transduces them into signals perceived as odors
Where is olfaction initiated?
At olfactory epithelium
What are the cells of the olfactory epithelium that are involved in olfaction?
Olfactory neurons- modified bipolar neurons, which respond to certain chemicals in the air
Basal cells- stem cells that continually replace olfactory neurons and have a loimited lifespan of 30-60 days
Supporting cells- columnar cells that surround olfactory neurons
What is the anatomical structure of the olfactory epithelium?
Olfactory nerve- combined axons of olfactory neurons
Olfactory bulb- location of synapses with next neurons in the pathway
Olfactory tract- composed of axons that exit olfactory bulb and travel to other regions of the CNS for interpretation
What is the physiology of olfaction? How is a chemical odorant transduced into a neural signal?
- Odorants are dissolved in the mucus surrounding olfactory neurons’s cilia
- Odorant binding proteins transport odorants to receptors on the olfactory cilis
- Binding of an odorant to its receptor activated a G protein
- The activated G protein triggers enzyme adenylate cyclase to convery ATP to cyclic AMP (cAMP)
- cAMP opens ion channels that allow sodium and calcium to enter the cell causing depolarization and an action potential is generated if threshold is reached
What is the olfactory pathway to the CNS?
- The axons of olfactory neurons carry olfactory stimuli to the olfactory bulb in the CNS. The axon terminals synapse on mitral cells in the olfactory bulb
- An olfactory stimulus travels from the olfactory bulb to the primary olfactory complex in the temporal lobe
What is the only sensory pathway that does not synapse in the thalamus?
Olfaction
What are the cells involved in gustation (taste buds)?
Gustatory taste cells- specialized epithelial cells with microvilli that contain receptors that detect different tastes
Basal cells- are stem cells that differentiate into new gustatory cells, which have a lifespan of 10-14 days
Supporting cells- surround the gustatory cells and have no role in sensation
What are the special receptor cells that detect taste?
Taste buds
Does gustation involve chemoreceptors? Olfaction?
Yes and yes
Vallate (circumvallate) papillae?
Largest and dome shaped; each contains hundreds of taste buds
Fungiform papillae?
Are mushroom shaped and contain only a few taste buds
Foliate papillae?
Ridges on the sides of the tongue and contain taste buds only in childhood
Filiform papillae?
Long, thin cylinders scattered across the tongue. Do not contain taste buds but have sensory nerve endings that detect the texture and temperature of food
Where do sensory neurons of gustation carry taste stimuli?
To CNS via CN VII, CN IX, and CN X
What are the taste sensations?
Sweet Sour Salty Bitter Umami
When is taste stimuli detected?
When they bind to receptors on the microvilli of gustatory cells (taste buds)
What process occurs to activate taste receptors?
- Changes in ion movements depolarize the gustatory plasma membrane. Ion movement depends on particular space. The decreased K ions moving out of the cell produces depolarization
- Depolarization of the membrane opens voltage gated Ca ion channels, and calcium enters the cell
- The Ca ions trigger the release of neurotransmitters, which produce an action potential in the axon of the sensory neuron
Do gustatory cells trigger an action potential?
No, gustatory cells usually do not generate an action potential because they are small enough that the local potential can quickly spread across their membrane
How do taste stimuli travel to the CNS?
- Axons of the facial, glossopharyngeal, and vagus nerves carry taste stimuli from the tongue into the CNS.
- Axons of these three nerves terminate in the solitary nucleus in the medulla oblongata by synapsing on central sensory neurons
- Axons from the solitary nucleus synapse on neurons in the thalamus, which then send the taste signals to the primary gustatory cortex in the parietal lobe
What are the three layers of the eyeball?
Fibrous
Vascular
Neural (retina)
What structures are within the fibrous layer?
- Sclera: The white part of the eye, covers 5/6ths of its surface; opaque
- Cornea: Sclera is continuous with cornea; translucent
Function of sclera?
Has numerous irregularly shaped collagen fibers, which allow it to resist deformation from external and internal forces and maintain its shape
Function of cornea?
Because the cornea is translucent, it plays an important role in admitting light into the eye and focusing it
What are the structures of the vascular layer?
- Choroid
- Ciliary body- Continuous anteriorly with choroid
- Iris
Function/description of choroid?
- Most extensive component of vascular layer
- Contains many tiny blood vessels called capillaries as well as a pigment to reduce the scattering of light
Function/description of ciliary body?
- Contains a ring of smooth muscle that surrounds the lens
- Suspensory ligaments connect ciliary body to the lens
- Contraction and relaxation of smooth muscle changes the shape of the lens to focus light on the retina
Functions/ description of iris?
- Colored portion of eye
- Contains pigment melanin
- Surrounds circular pupil, which is an opening that light passes through
What are the two muscles of the iris?
- Pupillary sphincter- muscle contracts following parasympathetic stimulation and constricts the pupil to reduce amount of light entering the eye
- Pupillary dilator- muscle contracts following sympathetic stimulation. Enlarges pupil to permit the entrance of light thorugh eye
What are the structures of the neural layer?
- The retina
- Photoreceptor cells (rods and cones)
- Fovea centralis
- Macula lutea
- Optic disc
- Ora serrata
Where are the photorecpetor cells that detect the presence of light and produce a neural signal located?
The retina
What is the fovea centralis?
An area in the retina that contains a high density of photoreceptors (cones) relative to the rest of the eye. It allows for extremely detailed vision enabling us to focus on a particular object
What is the macula lutea?
Yellowish central region of fovea; contains a large number of photoreceptors (cones)
What is the optic disc?
The location where the optic nerve exits from the retina. It does not contain photoreceptors, so it is called the blind spot
Where is aqueous humor located?
Within the anterior cavity (includes both the anterior and posterior chamber)
Where is the vitreous humor located?
Within the posterior cavity
What is vitreous humor?
A gelatinous material that is within the posterior cavity. It presses the retina against the choroid and helps maintain the shape of the eyeball.
What is aqueous humor?
A watery substance within the anterior and posterior chambers.
What happens if aqueous humor does not drain properly?
Glaucoma
What does emmetropic mean?
When the eye is relaxed and focusing on a distant object (normal eye)
What is accommodation?
When the lens increases total refraction by changing its shape from flattened to round. When the lens is rounded, its curved surface refracts light to a greater extent and can focus it on the retina
What does converge mean?
A convex lens has a surface that bulges outward and causes rays of light to converge, or come together as they pass through
What does diverge mean?
A concave lens has a surface that “caves” in and causes they rays to diverge, or spread out, so they do not focus
What occurs during accommodation when an object is nearby?
The ciliary muscle contracts causing the ciliary body to move closer to the lens. This decreases tension on the suspensory ligaments, which reduces their pull on the lens. Therefore, the lens can round up, which increases refraction— This is why eyes get tired when looking at something close up
What occurs during accomodation when an object is far away?
The ciliary body relaxes, which moves the ciliary body away from the lens. This movement increases tension in the suspensory ligaments, which flattens the lens and reduces refraction
What is needed to focus on nearby objects?
- Accommodation
- Pupillary constriction
- Convergence
Farsightedness
Hyperopia. The lens cannot round up enough and light focuses behind the retina when viewing nearby objects. Convex lens will fix this
Nearsightedness
Myopia. The lens cannot flatten enough and light rays focus in front of the retina when viewing distant objects. Concave lens can fix this
Astigmatism
Occurs when the curvature of the lens or the cornea is irregular and the rays of light are not evenly refracted
What are the two types of photoreceptors?
Rods and cones
What do rods and cones synapse on?
Bipolar cells
With what do bipolar cells communicate with ?
Retina ganglion cells
Characteristics of cones
- Contain pigment that allows us to perceive color
- Function best in bright light
- Highly concentrated in fovea centralis
Characteristics of rods
- Very sensitive and capable of responding in less intense light
- Rods are in the periphery of the retina
Describe the structure of photoreceptors
They consist of cell bodies connected to portions called inner and outer segments. The outer segments house stacks of flattened discs that absorb light and are formed from segments of the plasma membrane. The inner segments generate new discs for the outer layers
What is the pigment present in the discs of rods?
Rhodopsin, which has two components, the protein opsin and pigment retinal
What is the pigment present in cones?
Iodopsin, which is composed of protein photopsin and pigment retinal
What is special about photopsin?
It has a slightly different structure than rhodopsin, which allows it to absorb different wavelenghts of light. Therefore, photopsin determines color! Three forms of photopsin that respond to wavelength we perceive as either blue, green, or red.
What from is retinal in in the dark?
In a bent conformation know as cis- retinal
When does the transduction of light into a neural signal begin?
When a photon strikes a disc in the outer segment of a rod or cone
What are photoreceptors in the dark?
The photoreceptors are depolarized and continually releasing neurotransmitters onto adjacent neurons
What are photoreceptors in the light?
The presence of light hyperpolarizes the photoreceptor and reduces the release of neurotransmitter
What is included in the outer ear?
- Auricle
- External auditory canal
- Ceruminous glands that secrete cerumen or ear wax
- Tympanic membrane
Function of cerumen?
Lubricates and waterproofs the external auditory canal and tympanic membrane; traps debris before reaches tympanic membrane
What is included in the middle ear?
- Pharyngotympanic tube
- Auditory ossicles: Malleus, Incus, Stapes
- Tensor tympani
- Stapedius Muscle
- Oval window
Function of pharyngotympanic tube?
Equalizes pressure on both sides of the tympanic membrane
What is the boundary between the air filled middle ear and fluid filled inner ear?
The oval window
Function of auditory ossicles?
Play an important role in amplifying and converting sound waves in the air into fluid movement
What is included in the inner ear?
- Cochlea
- Vestibule
- Semicircular canals
Perilymph
A fluid that has a higher concentration of sodium ions than potassium ions and so resembles extracellular fluid. Located between walls of bony labyrinth and membranous labyrinths
Endolymph
A fluid that has a higher concentration of potassium ions than sodium ions and so resembles intracellular fluid. Located within the membranous labyrinth
Bony Labyrinth and membranous labyrinth
Inner ear called bony labyrinth with a membrane that lines the inner walls of bony labyrinth
Vestibule
- Contains oval window
- Houses the utricle and saccule, which are membranous labyrinth with endolymph
Utricle and Saccule
Contain receptor cells that convey stimuli about head tilting and linear movement (static equilibrium)
What is the utricle continuous with?
Membranous labyrinth called semicircular ducts, which are enclosed by bony labyrinth called semicircular canals
What is at the base of each semicircular duct?
Ampulla
What separates the middle and inner ear?
The round window
What is the cochlear duct or scala media filled with?
Endolymph
What are the scala tympani and scala vestibuli filled with?
Perilymph
What is the boundary between cochlear duct and scala vestibuli?
Vestibular membrane- serves as a diffusion barrier between endolymph and perilymph to maintain concentrations of fluids
What separates cochlear duct and scala tympani?
Basilar membrane
Basilar membrane structure
Narrow and stiff at base of cochlea, but as it nears the tip, it widens and becomes more flexible, which plays a role in detecting variations of sound
What does the basilar membrane support?
The spiral organ (Organ of Corti), which contains receptor cells for hearing
Function of spiral organ?
Where energy from sound waves is transduced to neural impulses
What is pitch or frequency?
Determined by how many times the object vibrates back and forth during a certain period
What is amplitude or loudness?
Determined by the difference between areas of high and low pressure
Where do high frequency vibrations occur?
Close to the base of the cochlea, where the basilar membrane is narrow and stiff
Where do low frequency vibrations occur?
They travel further into the cochlea and make the basilar membrane vibrate where it is wider and more flexible
What happens to very low frequencies that we cannot hear?
The waves travel all the way to the tip of the cochlea, where the scala vestibuli connects with the scala tympani at an opening called the helicotrema and travel back to round window
What is pitch determined by?
Which area of the basilar membrane vibrates
What is loudness determined by?
How much the basilar membrane vibrates
What are the receptor cells in the spiral organ called?
Hair cells
- Single row of inner hair cells
- Three rows of outer hair cells
What are stereocilia?
Present on each hair cell, which project from the cell into the endolymph of the cochlear duct arranged from tallest to shortest and bend because of the tectorial membrane
How do the hair cells and tectorial membrane interact?
When the basilar membrane vibrates up and down in response to sound waves, the hair cells move with it toward and away from the tectorial membrane
What does bending of the stereocilia cause?
It opens potassium channels that depolarize the hair cell. The depolarized cell then releases neurotransmitters triggering action potentials in the axon of cochlear nerve
What is sensory hearing loss?
Occurs when action potentials cannot be generated int the cochlea, usually due to dysfunction of hair cells
- exposure to loud noises, certain medications
What is conduction hearing loss?
Due to a problem in the outer or middle ear that prevents sound wave from reaching inner ear.
- ear wax
What is neural hearing loss?
Occurs when the signals fail to travel through the cochlear branch of the vestibulocochlear nerve or CNS pathway
- tumor
What is static equilibrium?
Refers to maintaining balance when the head and body are not moving but the head is tilted
What is dynamic equilibrium?
Refers to maintaining balance when the hear or body is undergoing rotational or angular motions
What is static equilibrium monitored by?
The utricle and saccule– specifically the macula, which contains receptor cells for head position and movement called kinocilium
What are the stereocilia and kinocilium of the utricle and saccule embedded in?
A gelatinous mass referred to as the otolithic membrane, which contains otoliths that are crystals of calcium carbonate that increase its density
Where is dynamic equilibrium detected?
By hair cells located in the anterior, posterior, and lateral semicircular ducts of the membranous labyrinth—the ampulla— and specifically the hair cells are within the crista ampullaris
What drains aqueous humor?
Scleral venous sinus
