Chapter 17: Special Senses Flashcards
Sense organ
A structure composed of nervous tissue along with other tissues that enhance its response to a certain type of stimulus
Sensory receptors
Specialized structures that respond to a stimulus
2 types:
Receptors for somatic sensations: detect tactile, thermal, pain, proprioceptive sensations
Receptors for visceral sensations: detect info from internal organs (such as blood pressure changes)
Functions of eyebrows
- shade the eye from sunlight
- catch perspiration from the forehead
Functions of the eyelids
- protect eye from foreign objects and excess light
- spread lubricating secretions over the eye
- contain eyelashes which trap and sweep away foreign particles
Conjunctiva
A transparent, vascular mucous membrane which lines the inner surface of the eyelids and covers the surface of the sclera.
It secretes mucous to moisten the eyes
Extrinsic eye muscles
6 skeletal muscles (Orgin - bony orbit, insertion - sclera)
Functions:
- maintain eye shape
- hold eye in orbit
- control precise eye movements
Sty
An infected hair follicle at the base of an eyelash
How do blood shot eyes occur?
When the vessels in the conjunctiva get irritated and dilated.
Conjunctivitis
The inflammation of the conjunctiva by bacteria or virus
aka “pinkeye”
Diplopia
The eyeballs can’t be focussed on the same visual field due to paralysis, weak eye muscles, or alcohol consumption.
aka “double vision”
Strabismus
Weakness in eye muscles in which the affected eye rotates mediately or laterally.
aka “cross-eyed”
Lacrimal gland (tear gland)
Located in the superior-lateral region of each orbit.
- secretes lacrimal fluid (tears) continuously
- clears, lubricates, and moistens the eyes
What are tears made of?
- water
- salt
- mucous
- antibodies
- lysozyme
Lysozyme
Antibacterial enzyme that prevents infection
What is the pathway of tears?
- Lacrimal gland
- Lacrimal ducts
- Lacrimal fluid flows over the eye
- Lacrimal punctual
- Lacrimal canaliculus
- Lacrimal sac
- Nasolacrimal duct
- Nasal cavity
Fibrous tunic of the eye
The outermost, avascular layer
Contains:
a) Sclera - the posterior part of the fibrous tunic. It is the white of the eye, which maintains eye shape and protects the inner surface.
b) Cornea - the anterior, transparent part of the fibrous tunic. It bends (refracts) light to focus light rays
Why are almost all corneal transplants successful?
The cornea is avascular, so rejection is rare because there is no access to the immune system, therefore no blood-borne antibodies.
Vascular tunic
The highly vascularized middle layer of the eye
Contains:
Choroid - darkly pigmented layer under sclera which absorbed excess light.
Ciliary body - made of ciliary muscles (regulate shape of eye) and ciliary processes (produce aqueous humour)
Iris - made of circular (makes pupil smaller) and radial (makes pupil bigger) muscles.
Aqueous humor
A clear fluid filing the space in the front of the eyeball between the lens and the cornea
Retina
Innermost layer of the eye
Consists of 2 layers:
1. Pigmented layer - closest to choroid, and absorbs excess light to reduce scattering.
2. Neural layer - visual part of the retina (contains photoreceptors, bipolar cells, and ganglion cells)
Photoreceptor layer of retina
Contains rods, cones, and macula lutea.
Rods - dim light receptors (120mil of them) that produce images in grey.
Cones- bright light receptors (6mil of them) that provide coloured vision.
- 3 kinds (blue, green, red cones)
Macula lutea - yellow flat spot on retina.
- center of it is called the fovea centralis which contains only cones
- site of the greatest visual acuity
Bipolar cell layer of the retina
Bipolar cells relay information from photoreceptors to the ganglion cells
Ganglion cell layer of retina
Attaches the retina to the back of the eye and forms the optic disc (blind spot) which contain no photoreceptors
What is a detached retina?
When the pigmented and neural layers of the retina separate and the vitreous humor fills between them.
This deprives the neural retina of its blood supply and could result in blindness
What is age-related macular disease?
A disorder of the retina in a person 50+ of age. It is when there are abnormalities in the region of the macular lutea and will cause and inability to see straight ahead.
Lens
An avascular structure held in place by suspensory ligaments. It can change shape to focus image
Anterior cavity
Located in the front of the lens
- filled with water aqueous humor
- maintains intraocular pressure (16-20mmHg) to support the eyeball
- provides oxygen and nutrients to the lens and cornea
Posterior cavity
Located behind the lens
- filled with gel-like vitreous humor
- maintains intraocular pressure
- holds the retina in place
Light
A wave of energy that radiates from the sun and travels at high velocity.
Eyes are sensitive to the wavelengths of light in the range of 400-700nm. This is known as as the visual spectrum of light (ROYGBIV)
Visual nervous pathway
- Light
- Photoreceptor cells
- Bipolar neurons
- Ganglion neurons
- Optic chiasma
- Optic tract
- Thalamus
- Visual sensory area in the occipital lobe
Myopia
(aka “near-sighted”)
See near clearly, far is blurry
Results when an eyeball is too long or the lens is too curved. Corrected by using a concave lens (glasses)
Hyperopia
(aka “far-sighted”)
See far clearly, near is blurry
Results when an eyeball is too short or the lens is too flat. Corrected by using a convex lens (glasses)
Astigmatism
Irregular curvature of the lens/cornea that results in parts of the image being out of focus
Glaucoma
Occurs when drainage of aqueous humor is blocked
Retinal cells can die.
Physiology of vision
Involves 2 main processes:
- Retinal image formation
- Conversion of image to nerve impulse.
Retinal image formation
a) refraction of light rays which occurs as is passes through the cornea (75%), and as light enters/leaves the lens (25%)
b) accommodation of the lens to adjust focus by changing lens shape.
c) Constriction of pupil (for far vision it dilates, for close vision it constricts)
d) Convergence of the eyes - extrinsic eye muscles turn eyes medically for close vision
Conversion of image to nerve impulse
Photoreceptor cells contain photopigments, which contain opsin and retinal proteins.
Opsin proteins will allow rods and cones to absorb different wavelengths of light.
Phototransduction
A process by which light energy is converted into a graded receptor potential
A grade potential = a small deviation from resting membrane potential.
External ear
Contains 3 regions:
- Auricle - directs sound waves
- External acoustic meatus - contains hair and ceruminous glands to secrete earwax. It also directs sound waves into middle ear.
- Tympanic membrane - vibrates in response to sound waves
Middle ear
Air filled, mucus-lined cavity in the temporal bone which connects to the nasopharynx.
Contains:
Malleus, Incus, Stapes to amplify vibrations
Oval and round windows
Auditory tube to the nasopharynx
Internal ear
Contains the receptors for hearing and equilibrium.
- consists of an outer bony labyrinth that encloses an inner membranous labyrinth
Bony labyrinth
Part of the internal ear
A series of canals in hollowed out bone, therefore lined by periosteum and contains paralymph fluid.
- Lined by periostium
- contains paralymph fluid
Associated structures: vestibule, semicircular canals, cochlea
Membranous labyrinth
Part of the internal ear.
- consists of epithelial sacs
- line by endolymph
Associated structures: utricle and saccule, semicircular ducts, cochlear duct
Frequency
Differences in sound frequencies are perceived as different pitches.
High frequency = higher pitch
Measured in hertz (Hz)
Intensity
Differences in sound intensities are perceived as differences in loudness
Higher intensity = louder sounds
Measured in decibels (dB)
Pathway of sound
Auricle, external auditory canal, tympanic membrane, ossicles, oval window, scala vestibuli, vestibular membrane, cochlear duct, basilar membrane, organ of corti.
Organ of Corti
Spiral organ which contains the hearing receptors (hair cells)
Contains:
- single row of inner hair cells (send auditory info to brain)
- 3 rows of outer hair cells (enhance response of inner cells
Pathway of hearing nerve impulse
Cochlear branch of vestibular nerve VIII, medulla, midbrain, thalamus, primary auditory area of temporal lobe
Static equilibrium
Refers to control of the position of the head with respect to gravity and linear acceleration.
Receptors are found in utricle and saccule which contain patches of hair cells called the macula that are embedded in otolith membrane. (Head tilts, otoliths move -> nerve impulse)
Dynamic equilibrium
Refers to control of the position of the head during rotational movements.
Receptors found in the semicircular ducts. Contains hair cells (crista ampularis) embedded in the cupula (movement of cupula causes hair bend -> nerve impulse)
Equilibrium nervous pathway
- Nerve impulse from hair cells (macula and crista ampullaris)
- Vestibular branch
- Vestibulaocochlear nerve VIII
- Vestibular nuclei and cerebellum (balance regulators)
What are the chemical senses
Smell and taste.
Taste
Contain receptors in the taste buds (gustatory cells)
Chemicals from food dissolve in saliva and diffuse into the taste bud and contact the hairs of the cells
How often are taste cells replaced
Every 10 days
Smell
Receptors are bipolar neurons found on the roof of the nasal cavity.
Odours dissolve in mucous and olfactory hairs respond to chemical stimulus
Olfactory adaptation
When you can only smell sense for a short time, and then no longer smell the odour even though it’s still there because your ion channels close after a few minutes .
