Special Senses Flashcards
What are the special senses?
Smell, taste, vision, hearing and equilibrium
What is olfaction?
The sense of smell
What does it mean that olfaction is a chemical sense?
the sensation arises from the interaction between
olfactory receptors and molecules
Where are olfactory receptors located?
in the olfactory epithelium within the nose
Where is the olfactory epithelium located?
in the superior part of the nasal cavity
What do olfactory glands do?
produce mucous to moisten the olfactory
epithelium and promote dissolving of the chemical odorants
What nerve is involved with the olfactory glands’ production of mucous?
the facial (VII) nerve allows glands to produce more or less mucous as needed (causes a runny nose)
What occurs in the olfactory pathway?
-Chemical molecules (odorants), trigger nerve impulses along olfactory receptor neurons as they converge to form the olfactory (I) nerves
-The impulse is carried along different paths of the olfactory tract
-One path carries the impulse to the primary olfactory area (temporal lobe of the cerebral cortex) where conscious awareness of smells occurs
-The other path carries the impulse to the limbic system which triggers emotional responses to odors
-The impulse travels from the primary olfactory area to the frontal lobe for odor identification
What is gustation?
The sense of taste
What kind of sense is gustation?
Chemical
What are the 5 primary tastes?
Salty - triggered by sodium ions
Sweet - triggered by sugars and artificial sweeteners
Sour - triggered by hydrogen ions (acids)
Bitter - triggered by a wide variety of substances (defense mechanism)
Umami (savory) - triggered by amino acids
Where are tastebuds located?
The majority of our taste buds are located on the tongue, but some can also be found on the soft palate, pharynx and epiglottis
What do taste buds contain?
gustatory receptors, supporting cells, and gustatory hairs that are grouped together in elevations on the tongue called papillae
What do the papillae do?
increase the surface area of the taste bud and produce the rough texture of the surface of the tongue
What are gustatory hairs (aka gustatory microvilli)?
project from each receptor cell to the external
surface of the taste bud - they are the site of contact between the receptor and the tastant molecules
What are tastants?
-The chemicals that stimulate the gustatory receptors, must be dissolved by saliva in order to trigger the receptors
-The stimulus triggers specific gustation receptors and initiates an impulse that travels along 3 different cranial nerves to the medulla oblongata
What nerves are involved in gustation?
-Facial (VII) nerve, Glossopharyngeal (IX) nerve, and vagus (X) nerve
What is involved in the emotional trigger of gustation?
The limbic system and the hypothalamus
How fast can we detect sounds?
The ear can detect sounds 1000 times faster than photoreceptors in our eye respond to light
What sense other than hearing is involved with the ear?
The ear also contains receptors for equilibrium
What is equilibrium?
the sense that helps maintain balance and awareness of our orientation in space
Anatomically, the ear is divided into which three sections?
External (outer) ear, middle ear, and internal (inner) ear
What is the external ear composed of?
Composed of the pinna, external auditory canal and eardrum
What is the pinna (aka auricle, aka earlobe)?
Flap of elastic cartilage covered by skin
What is the external auditory canal?
passageway to the eardrum
What is the tympanic membrane?
partition between the external and middle ear
What can be found at the opening of the external auditory canal?
specialized sweat glands called ceruminous glands
What is cerumen (aka earwax)?
prevents foreign objects from entering
What is the middle ear?
A small air-filled cavity designed to alter the tension of the tympanic membrane to help protect the inner ear from loud noises
What 3 bones are considered the auditory ossicles?
Malleus, incus, and stapes (aka hammer, anvil, and stirrup)
What does the auditory tube (eustachian tube) connect?
the middle ear and nasopharynx
What are the two main structural divisions of the inner ear?
an outer bony labyrinth that contains an inner
membranous labyrinth
What are the cavities in the bony labyrinth called?
Semicircular canals, vestibule, and cochlea
What is between the bony and membranous labyrinth?
a protective fluid similar in chemical composition to CSF
What is the structure of the membranous labryinth?
The membranous labyrinth follows the same general structure as the bony labyrinth and contains the receptors for hearing and equilibrium
What are the steps involved in the physiology of hearing?
- The pinna directs sound waves into the external auditory canal
- Sound waves strike the tympanic membrane causing it to vibrate (slowly to low-pitched sounds, fast to high-pitch)
- Vibrations travel from the tympanic membrane, through the auditory ossicles (malleus, incus, stapes)
- The stapes carries the vibrations through membranous fluid and ultimately to the auditory receptors which triggers a nerve impulse
What occurs in the auditory pathway?
-Auditory receptors send an impulse to the medulla oblongata through a branch of the vestibulocochlear (VIII) nerve
-Fractional impulse delays between the left and right ear allow us to determine the location of the sound origin
-Impulse then travels through the thalamus to the primary auditory area of the cerebral cortex (temporal lobe) - conscious awareness of sound
-The impulse then travels to the auditory association area for complex sound integration
What are receptors for equilibrium stimulated by?
linear and angular acceleration and deceleration
What is the collection of receptor organs involved in equilibrium referred to as?
the vestibular apparatus
What are the sensory receptors for equilibrium called?
hair cells
What are the projections on one end of the hair cells called?
hair bundles
When the hair bundles bend due to positional changes, it generates an impulse along which nerve?
The vestibulocochlear (VIII) nerve to the medulla and the pons
What aids in gathering information for equilibrium?
the eyes and internal proprioceptors
Where are impulses sent (via effector neurons) once the information has been integrated?
-Eyes/head - help maintain focus on the visual field
-Head/neck - control head and neck movements to maintain equilibrium and muscle tone
-Cerebral cortex - provides conscious awareness of the head and limbs
Where are more than half the sensory receptors in the body located?
The eyes
What is the lacrimal apparatus?
A group of structures that produce and drains lacrimal fluid, tears, in a process called lacrimation
What does lacrimal fluid do?
protects, cleans, moistens and lubricates the eyeball
How is fluid spread along the eyeball?
by blinking the eyelids
What is the fibrous tunic?
the superficial layer of the eyeball
What is the eyeball recessed and protected by?
the orbit (concave indent of the orbital bone)
What does the fibrous tunic consist of?
The cornea and sclera
What is the cornea?
-transparent coat that covers the coloured iris
-curved surface helps to focus light onto the retina
What is the sclera?
-“whites of the eye”
-dense connective tissue that encircles and protects the eyeball
-site of attachment for extrinsic eye muscles
-coated by a thin mucous membrane called the conjunctiva
What is the vascular tunic?
the middle layer of the eyeball
What does the vascular tunic consist of?
The choroid, ciliary body, iris and the pupil
What is the choroid?
Vasculature provides nutrients to the retina
What is the ciliary body?
Alters the shape of the lens and secretes aqueous humour
What is the iris?
-coloured portion of the eyeball
-regulates the diameter of the pupil
What is the pupil?
-the whole in the centre of the iris
-enervated by the oculomotor (III) nerve to dilate in response to low light and constrict in response to bright light
What is the retina (Inner Tunic)?
-the hole in the centre of the iris
-enervated by the oculomotor (III) nerve to dilate in response to low light and constrict in response to bright light
What is the function of the retina?
Receives light and generates nerve impulses to the brain via the optic (II) nerve
What are the two types of photoreceptors in the retina?
rods and cones
What do rods do?
allow us to see in dim light (black and white only)
What are cones?
stimulated by brighter light (coloured vision)
What are red, blue, and green cones?
stimulated in various combinations to produce our main coloured vision
What is the lens?
-behind the pupil and the iris
-composed of layers of crystalin proteins that refract light onto the retina (focus)
-the lens divides the interior of the eyeball into two cavities that are responsible for maintaining intraocular pressure
What are the two cavities of the lens?
The anterior cavity and vitreous chamber
What is the anterior cavity?
space anterior to the lens, filled with aqueous humour
What is aqueous humour?
transparent watery fluid that nourishes the lens and
cornea
What is the vitreous chamber?
between the lens and the retina - contains the vitreous body
What is the vitreous body?
transparent jellylike substance that holds the retina
in place
What are the three processes involved in image formation?
-Refracting (bending) of light by the lens and cornea
-Accommodation (changing the curvature of the lens)
-Constricting or dilating the pupil
What is refraction?
when light rays travelling through a transparent substance (air) pass into a second transparent substance with a different density (water), they bend at the junction of the two substances
What occurs in the refraction of light rays?
-When light enters the eye the majority of refraction occurs in the cornea.
-The lens then completes the final “sharp” focus to produce an image on the retina
-Images focused on the retina are inverted and reversed left to right
-The brain learns in early life to “fix” the image we see
What occurs in accommodation?
-The lens is convex on both the anterior and posterior surfaces, which causes the incoming light rays to refract closer together
-The lens can increase its curvature to view an object that is close
-This process is called accommodation and occurs via muscles controlled by the oculomotor (III) nerve
-Near point of vision - refers to the minimum distance that an object can be clearly focused with maximum accommodation (~10cm)
What occurs in the constriction of the pupil?
-The muscle fibres of the iris contract and relax to constrict or dilate the pupil -autonomic reflex
-This occurs simultaneously with accommodation to prevents light rays from entering the eye through the periphery of the lens
-If light rays do enter through the periphery of the lens it would create blurred vision
What is myopia (nearsightedness)?
when the eyeball is too long (relative to the cornea and lens)
What is hyperopia (farsightedness)?
when the eyeball is too short
What is astigmatism?
irregular curvature in the cornea or lens
What is an emmetropic eye?
A normal eye
What is binocular vision?
-Humans use both eyes to focus on one set of objects at a time (some animals see entirely different sets of objects with their left and right eyes at the same time - based on distance between eyes)
-Binocular vision allows us to have accurate depth perception and 3D vision
What is convergence?
medial movement of eyeballs to track an object and allow for continued binocular vision
What occurs in the visual pathway?
-Visual stimulation of photoreceptors on the retina trigger an impulse that travels along the optic (II) nerve and provides output from the retina to the brain
-The impulse travels through the thalamus to the primary visual area in the occipital lobe of the cerebral cortex
-The impulse is then relayed to the visual association area for more complex processing
-The visual association area also stores visual memories for recognition of known object
