Download SPECIAL SENSES

SPECIAL SENSES
Olfaction - sense of smell
- chemical sense
- least understood
- olfactory nerve fibers go to the cortex memory association areas
Histology of the Olfactory Apparatus
- receptors (millions)
- on surface of the superior and middle nasal concha
- cover and area of 5 square cm
- three types of cells involve
1. Olfactory Receptors
- bipolar neurons
- dendrite is olfactory hair with:
- sites of action potentials through chemical transduction
- can reproduce through mitosis
2. Support Cells (sustentacular)
- columnar epithelium
3. Basal Cells
- stem cells
- produce new olfactory receptors
- Bowman's Glands
- produce mucous
- dissolves gases with odor causing molecules
- moistens olfactory epithelium
- washes away old odors so stimulation does not continue
Physiology of Olfaction
- may be several to hundreds of primary scents
- different smells may be related to different combinations of sensors being stimulated
simultaneously
- molecules to be scented must dissolve in fluids around olfactory hairs and be lipid
soluble in order to be detected
- this is how it works
- a molecule dissolves in the watery mucous solution around the hair cells and
comes in contact with a receptor G-protein on the plasma membrane
- action potential initiated in olfactory nerve
Adaptation
- initial sensation to any odor quickly fades
- decreased 50% in the first second
- complete insensitivity in l minute
GUSTATORY SENSATION (Taste)
- enhances olfaction
- any substance that will stimulate taste receptors will stimulated olfactory receptors
thousands times more
- Histology of Gustatory Receptors
- receptors located in taste buds
- 10,000
- most on tongue
- also on soft palate, larynx, and pharynx
- 3 kinds of cells in taste buds (like olfaction)
1. Support cells (sustentacular)
- form a capsule around about 50 taste receptor cells.
2. Gustatory (Taste Receptor Cells)
- have microvilli (Gustatory Hairs)
- where taste occurs
3. Basal Cells
- produce support cells which in turn become receptor cells
- taste buds located in papillae
Physiology of Gustation
- chemical must dissolve in saliva
- contacts gustatory hairs
- 4 primary tastes
- salty, sour, bitter, sweet
- position of tongue different for different tastes
Adaptation
- takes one to five minutes
- neurons in pathway most responsible for adaptation
VISUAL SENSATIONS
Accessory Structure of the Eye
Eyelids (Palpebrae)
- act as a light and physical barrier
- spread lacrimal fluid over the eye
Eyelashes
- protection from dust etc.
- have sebaceous glands
- infection called sty
- have their own mites
Lacrimal Glands
- secrete lacrimal fluid that lubricates, and moistens the eye
EYEBALL ANATOMY
1. Fibrous Tunic
- makes up the sclera and the cornea
- composed of dense connective tissue
- has a canal around the border of the cornea called the Canal of Schlemm
that drains aqueous humor
2. Vascular Tunic (uvea)
- 3 portions
1. Choroid
- supplies nutrients to the retina
- darkly colored
2. Ciliary Process
- secretes aqueous humor
- contains ciliary muscle that changes shape of the lens
3. Iris
- colored
- two muscular layers
- hole in center called pupil
- innervated by:
- parasympathetic N.S.
- contracts circular iris muscle which decreases pupil size
- sympathetic N.S.
- contracts radial muscle which increases pupil size
Note: the figure above illustrates the dilation and constriction of the pupil. In dim
light, the radially arranged smooth muscle fibers are stimulated to contract by
sympathetic stimulation, dilating the pupil. In bright light, the circularly arranged smooth
muscle fibers are stimulated to contract by parasympathetic stimulation, constricting the
pupil.
3. Nervous Tunic (retina)
- optic disc
- blind spot where optic nerve enters the eye
- two major portions to the retina
- Pigmented Layer
- nonoptical retina
- black color prevents light from bouncing around inside the eye
- Optical portion
- responsible for vision
- multi-layered (10 layers including the pigmented layer)
- 6 million cones - 120 million rods
- rods - black and white vision in dim light
- cones - color vision - need bright light
- most concentrated in the fovea
Central Fovea
- found inside depression called macula lutea
- on the visual axis (means when light enters the eye it lands directly on the fovea)
- no rods (cones for color vision)
- Area of acute vision because neurons are bent out of the way allowing light to
reach the cones in the bottom layer
Note on the photo above the dark circle (macula lutea) with the light center (central
fovea). The nerve fibers in the center of the macula are bend to the side to allow the
light to directly impact the cones in the fovea
Lens
- function is to focus image on central fovea and make adjustments for distance
(accommodation) - see illustration below.
Control of Light entering the eye
- pupil constriction (parasympathetic) - sphincter muscle - less light
- pupil dilation (sympathetic) - radial muscles - more light
Convergence
- single binocular vision
- as an object moves closer the eyes move closer together to maintain depth of field
Physiology of Vision
- photoreceptors (rods and cones) transduce light stimulus into a receptor potential
which is relayed to the bipolar neurons where an action potential is started.
- then to the visual cortex in the occipital lobe
Color Vision
- the Trichromatic theory of color vision
- there are three types of cones - blue, green, and red
- color perception is dependent on the relative degree to which each cone
is stimulated by a wavelength of light that hits it.
HEARING ( Auditory Sense)
- ear is divided into three regions - external, middle and inner ear
The External Ear
- the Auricle or Pinna collects sound waves and directs them into the
External Auditory Canal
- the sound waves cause the Tympanic Membrane (eardrum) to vibrate
The Middle Ear
- is the air filled cavity that communicates with the Nasal Pharynx via the
Eustachian Tube (Auditory Tube)
- equalizes air pressure across the tympanic membrane
- Auditory Ossicles connect the tympanic membrane to the oval window of the inner
ear - these consist of three bones
1. Malleous - attaches to the tympanic membrane - shaped like a hammer
2. Incus - attaches to the stapes - shaped like an anvil
3. Stapes - fits on oval window of the inner ear
- the Round Window
- has a membrane called the Secondary Tympanic Membrane
- it absorbs vibrations in the inner ear
-The Inner Ear
- has two divisions
1. an outer Osseous Labyrinth
2. an inner Membranous Labyrinth
The Bony (Osseous) Labyrinth
- has three areas
1. The Semicircular Canals of which there are three
- each canal has a area at its end called an ampulla ( a swelling)
- each ampulla contains an organ of equilibrium called a
Crista Ampullaris
- the membranous portion inside is called the semicircular ducts
2. The Vestibule
- contains the Utricle and the Saccule
- organs of static equilibrium
3. The Cochlea
- contains the Organ of Corti (hearing)
- consists of canals spiraling around a modiolus
Organ of Corti
- sits on basilar membrane
- organ of hearing
- has 16,000 hair cells that synapse with the cochlear nerve
Physiology of Hearing - events involved in hearing
1. auricle collects the sound waves and reflects them down the external auditory canal
toward the tympanic membrane.
2. tympanic membrane vibrates.
3. the vibration is transmitted to the oval window by the malleus, incus, and stapes.
4. the oval window vibrates causing the hair cells of the Organ of Corti to vibrate.
5. the vibration causes the round window to bulge outward and absorb the sound.
6. action potential develops in the cochlear branch of the vestibulocochlear nerve
Physiology of Equilibrium
- two types Static and Dynamic
- Utricle and Saccule
- static equilibrium
- have macula perpendicular to each other
- each has two types of hair cells
- hair (receptor) cells
- supporting cells
- each macula has otoliths which pull the macula down due to gravity when the
head is bent
- bends hair cells producing a receptor potential
- action potential develops in the vestibular branch of the vestibulocochlear
nerve
- Semicircular ducts
- dynamic equilibrium
- each duct has a crista (see figures on preceding pages)
- each crista has hair cells and support cells
- when endolymph is set in motion it bends the crista which bend hair cells
- a receptor potential develops
- action potential develops in the vestibular branch of the vestibulocochlear nerve