Special Senses Flashcards
Define Emmetropic
A normal eye with no change occurring in the lens with distance vision
Define Myopic and how is it corrected?
Someone who is nearsighted or short-sighted, as the image falls in front of the retina as the eyeball is too long for the lens power. Corrected with concave lens.
Define Hyperopic and how is it corrected?
Someone who’s is far-sighted, as the image falls behind the retina. A convex lens is used to converge the light rays onto the retina.
What is Presbyopia?
The old age eye. People over 50, the lens no longer accommodates.
Define Canthi and what are they also known as?
The medial and lateral angles of the eye, where the two eyelids join in the corner of the eye.
Also known as medial and lateral commissure.
Define tarsal plates and their role
They are connective tissue that support eyelids internally and help to maintain firmness of the eyelids
What do tarsal glands do?
Produce oil secretion in the eyelid so the aqueous layer doesn’t dry out and the eyelid remains lubricated
What does the levator palpebrae supeioris do?
Elevates the eyelid
Name 3 associated lubricating glands?
- Tarsal glands
- Sebaceous glands
- Ciliary glands
What moves the eyebrows medically to form a frown?
Corrugator Supercilii
What does lacrimal fluid (tears) contain?
1.Mucous
2.Antibodies
3.Lysozyme
Describe the pathway lacrimal fluid follows
- Enter the superior lateral eye via excretory ducts
- Exit medically and drain into lateral punctum
- Drain into nasolacrimal duct
What condition is caused by the inflammation of the conjunctiva?
Conjunctivitis (pinkeye)
What is the annular ring and which rectus muscle originate from it?
It is the common tendinous attachment and the lateral, medial, superior and inferior rectus originate from it.
Define strabismus
Congenital weakness of the extrinsic eye muscles
What is the interval cavity of the eyeball filled with?
Fluids called humors
What is the role of the lens?
Separates the internal cavity into an anterior and posterior segment.
What is the anterior and posterior segment filled with?
Anterior - aqueous humor
Posterior - vitreous humor
What is the fibrous layer and what are its components?
It is the outermost layer of the eye and is composed of dense avascular tissue
Composed of sclera and cornea
What is the vascular layer and what is it composed of?
It is the middle layer called the uvea and is composed of:
- Choroid
- Ciliary body
- Iris
What is the choroid and what is it’s function?
It is a dark brown pigmented membrane that forms the posterior portion of the uvea and supplies blood to the eye tunics
What is the sphincter pupillae and what is it’s role?
It is a circular muscle surrounding the eye and when it contracts, it constricts the pupil, making it small
What is the dilator pupillae and what is it’s role?
It is a muscle and when it’s fibers radiate outwards, causes pupil to dilate
Describe how the eyes have a blind spot?
- Axons of ganglion cells converge, and exiting the eyeball via the optic disc, forming the optic nerve
- The optic disc is where the optic nerve leaves the eye so it is not covered by the sclera and lacks photoreceptors, thus the light focused on the optic disc cannot be seen
What are the most important features of the retina?
Photoreceptors, rods and cones.
What is the macula lutea and where is it located?
The darker region that is lateral to the blind spot and contains mostly cones.
What is inside the center of the macula lutea?
The fovea centralis which contains only cones
What are the two muscles involved in the auditory ossicles? And how do they do it?
- Tensor tympani
- Stapedius
They contract to loud sounds and transmit the vibratory motion towards the oval window
What does the bony labyrinth consist of and what is inside it?
- Vestibule
- Cochlea
- Semicircular canals
Lined with membranous labyrinth and filled with perilymph
What is the vestibule and what does it contain?
It is the central egg shaped cavity in the bony labyrinth and it contains 2 membranous labyrinthine sacs which are suspended in perilymph, containing endolymph
Explain the two membranous sacs in the vesicle?
- Saccule - extends into cochlea
- Utricle - extends into semicircular canal
What are the 3 canals inside the semicircular canals and what is lining these ducts?
- Anterior canal
- Posterior canal
- Lateral canal
Membranous semicircular ducts line each semicircular canal communicating with the utricle anteriorly.
What do the 3 canals in the semicircular canal terminate in and what is it?
Terminates in the ampulla, and inside ampulla is crista ampullaris, which is a region where the dynamic equilibrium respond to angular or rotational movements are located
What 3 chambers is the cochlea divided into and describe their function.
- Scala Vestibuli - apart of the bony labyrinth and is filled with perilymph
- Scala media - is the cochlear duct and apart of the bony labyrinth
- Scala tympani - contains perilymph
Describe the sound pathway
- Sound vibrations enter the external ear, which amplifies the sound through the external acoustic meatus to the tympanic membrane
- Air molecules beat against the tympanic membrane, causing it to vibrate
- The vibrating tympanic membrane pushes against the auditory ossicles which transfer the vibration to the stapes, which pushes the pressure to the oval window
- The pressure in the oval window moves through fluid in the Scala vestibuli
- Sound with frequencies below the hearing range travel through the helicotrema and do not excite hair cells
- Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on the inner hair cells
How is conduction deafness caused?
When something interferes with conduction of sound waves to the fluids of the inner ear. Such as earwax blocking the external acoustic meatus.
How is sensorineural deafness caused?
Results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortex in the temporal lobe.
Results in loss of hair cells due to aging or prolonged exposure to high intensity sounds.
What does balance and equilibrium rely on?
- Vestibular apparatus
- Vision
- Stretch receptors
Describe the role of the vestibular apparatus
It contains equilibrium receptors found in the semicircular canals and in the vestibule.
It is responsible for orientation and balance in space
Name the two equilibrium receptors involved in the vestibular apparatus and their function
1.Vestibular receptors monitor static equilibrium and found in the maculae of the vestibule. These receptors monitor linear acceleration and position of the head with respect to gravity, and because gravity is constant, we term this static equilibrium.
- Semicircular canal receptors monitor dynamic equilibrium and found in the crista ampullaris in the ampullae in the semicircular canals. These receptors are stimulated by rotational and angular movements hence dynamic equilibrium.
The maculae and crista ampullaris are the equilibrium receptor organs.
What are the receptor cells for taste?
Gustatory epithelial cells
What do basal epithelial cells do?
They are stem cells producing new gustatory epithelial cells
Describe the mechanism for salty taste?
Sodium ions dissolve and causes a reaction with salt receptors, passing through sodium channels, and depolarising gustatory epithelial cells and imitating an action potential
Describe the mechanism for sour taste
Sour taste is mediated by hydrogen ions, hydrogen ions enter the cell and open the cation channels and resulting in an action potential
Describe the mechanism for bitter, sweet and umami
The bitter, sweet and umami receptors couple to a common G-protein, gustducin which activates a 2nd messenger system
Name the 3 types of cells in taste buds:
- Gustatory
- Supporting
- Basal cells
Where is taste perceived?
The gustatory cortex in the insula
Describe the physiology of smell
We first must be able to smell the substance which requires it to:
- Volatile - diffuse in the air
- Dissolve in the mucus layer coating the epithelium
- Bind to receptors in olfactory cilia
Binding initiates transduction, which activates a G protein mechanism, which uses cAMP as a 2nd messenger. cAMP opens sodium and calcium channels, causing depolarization of the receptor membrane that triggers an action potential
