•
Composed
of sensory receptors throughout the body.
–
General
senses
•
Touch,
pressure, pain, heat, cold, stretch, vibration.
–
Special
senses
•
Vision,
hearing, equilibrium, olfaction, taste.
•
Relative
to the source of the stimuli.
–
Exteroceptors
–
Interoceptors
–
Propioceptors
(sketetal muscle). Conscious.
•
General
structure
–
Modified
dendrites.
•
Free nerve
endings
•
Merkel
discs in epidermis
•
Hair
follicle receptors
•
Meissner
corpuscles: light touch
•
Ruffini
corpuscles: deep pressure and stretching.
•
Pacinian
corpuscles: pressure receptor.
•
Muscle
spindles
•
Golgi
tendon organs
•
Receptor
physiology
–
Act as
signal transducers. Direct relationship between importance and number of
clustering of the receptors; punctuate distribution.
Special Senses
- Vision
- Olfaction
- Taste
- Hearing and equilibrium
1.
Vision
·
70 percent of all sensory
receptors are in the eyes
·
Each eye has over a million
nerve fibers
·
Protection for the eye
1. Most of the eye is enclosed in a bony orbit made up of the lacrimal
(medial), ethmoid (posterior), sphenoid (lateral), frontal (superior), and
zygomatic and maxilla (inferior)
2. A cushion of fat surrounds most of the eye
Organ: Eye ball
Accessory structures
·
Lacrimal apparatus.
§ Lacrimal gland: secretes
tears; solution of salts and lyzozyme.
§ Lacrimal canals: drains
lacrimal fluid from eyes
§ Nasolacrimal canal: empties
lacrimal fluid into the nasal cavity
·
Eyelids (papebrae) – brush particles out of eye or cover eye
·
Medial and lateral canthus
·
Caruncle
·
Conjunctiva – Mucus membrane that lines inner surface of eyelids.
Stratified squamous and stratified cilindrical epithelium.
·
Eyelashes – trap particles and keep them out of the eye
·
Ciliary glands – lubricate eyeball, modified sweat glands between the eyelashes-
secrete acidic sweat to kill bacteria, lubricate eyelashes
·
Tarsal glands: lubricate eyeball
·
6 extrinsic eye muscles
Internal structure of
the eye
Composed
of 3 layers or tunics
External
•
Cornea (transparent)
and Sclera (white).
Middle
•
Anterior
–
Iris: radial smooth
muscle (III ocoulomotor)
–
Uvea: vasculariazed.
–
Cilliar body(muscles)
: control the curvature of the lens (cristaline).
–
Cilliary processes:
secrete aqueous humor.
•
Posterior
–
Choroid: dark
pigment.
Inner
•
Retina: sensory
region
Additional
internal structures
·
Humor vitreous
·
Macula lutea (yellow
spot): high cone density
·
Fovea centralis: area
of maximum (very high amount of cones) sight acuity.
·
Sclera venous sins(
Schlemm canal)
·
Ciliary zonule
Histology of the
retina
•
Sensory tunic
–
Outer pigmented
epithelial layer
–
Inner neural layer.
•
Photoreceptors: cones
or rods.
•
Bipolar neurons
•
Ganglion
•
Axons of ganglions
2.
Olfaction
·
Olfactory
receptors are in the roof of the nasal cavity
§ Neurons with long cilia
§ Chemicals must be dissolved in mucus for detection
·
Impulses
are transmitted via the olfactory nerve
·
Interpretation
of smells is made in the cortex (olfactory
area of temporal lobe)
Sensory structure:
Olfactory epithelium.
Chemoreceptor.
§ Olfactory receptor cell: bipolar neuron (I)
§ Support cells: pseudo stratified ciliated epithelium.
§ Basal cells.
3. Taste
·
Taste buds
house the receptor organs
·
Location
of taste buds
§ Most are on the tongue
§ Soft palate
§ Cheeks
The Tongue and Taste
·
The tongue is covered with projections called papillae
§ Filiform papillae – sharp
with no taste buds
§ Fungifiorm papillae –
rounded with taste buds
§ Circumvallate papillae –
large papillae with taste buds
·
Taste buds are found on the sides of papillae
Structure of Taste Buds
·
Gustatory
cells are the receptors
§ Have gustatory hairs (long microvilli)
§ Hairs are stimulated by chemicals dissolved in saliva
·
Impulses
are carried to the gustatory complex (pareital lobe) by several cranial nerves
because taste buds are found in different areas
§
Facial
nerve
§
Glossopharyngeal
nerve
§ Vagus nerve
Taste Sensations
- Sweet receptors
- Sugars
- Saccharine
- Some amino acids
- Sour receptors
- Acids
- Bitter receptors
- Alkaloids
- Salty receptors
- Metal ions
- Umami
- Glutamate,
aspartate (MSG, meats)
Sensory structure
a.
Taste bud.
Chemoreceptor. Mechanoreceptor. Thermo receptor.
i.
Basic
tastes: sweet, sour, salt, bitter.
ii.
Types
(location in figure)
1.
Fungiform
papillae (mushrooms)
2.
Circunvallate
papilla (globes)
3.
Filiform
papilla
iii.
Cell types
1.
Gustatory
(taste) cells: bipolar neurons.
2.
Support
cells
4. Hearing
and balance
Eye Reflexes
·
Internal
muscles are controlled by the autonomic nervous system
·
Bright
light causes pupils to constrict through action of radial (iris) and ciliary
muscles
·
Viewing
close objects causes accommodation
·
External
muscles control eye movement to follow objects- voluntary, controlled at the
frontal eye field
·
Viewing
close objects causes convergence (eyes moving medially)
The Ear
·
Houses two
senses
·
Hearing (interpreted
in the auditory cortex of the temporal lobe)
·
Equilibrium
(balance) (interpreted in the cerebellum)
·
Receptors
are mechanoreceptors
·
Different
organs house receptors for each sense
Organ: Ear (sensory receptor
for hearing and equilibrium).
·
The ear is
divided into three areas
§ Outer (external) ear
§ Middle ear
§ Inner ear
·
Involved
in hearing only
·
Structures
of the external ear
§ Auricle
§ External acoustic meatus
§ Tympanic membrane
§ Ceruminous glands
·
Structures
of the Middle ear
•
Tympanic
cavity
–
Osicles
»
Malleus
(hammer)
»
Incus
(anvil)
»
Staples
(stirrup). Connects with the oval window.
•
Pharingotimpanic
tube. Pressure equalization of middle ear and environment.
·
Structures
of the Inner ear
•
Bony and
membranous labyrinth
–
Cochlea:
hearing
–
Vestible:
equilibrium
–
3
perpendicular semicircular canals: equilibrium
Hearing physiology
•
Sound
waves travel from the outer ear (timpanic membrane)à middle ear (Malleus,Incus, staples, oval window)à inner ear (scala tympani)/scala vestibulià stimulates the stereocillia of the organ of cortià VIII
•
The round
window serves as a pressure relief valve.
Equilibrium physiology
•
Located in
the vestibular apparatus
–
Vestible
•
Utricle
and saccule (sacs) within vesitble.
–
Receptor:
Macculae (static equilibrium)
»
Hair cells
(stereocillia) are embedded in the otholitic membrane which contain CaCO3
(otoliths). Respond to vertical acceleration.
–
Membranous
semicircular ducts
•
Ampulla
(located at the base of each perpendicular duct). Mechism of dynamic
equilibrium (angular acceleration).
–
Receptor:
Crista ampullaris. Stereocilia covered by a gelatinous cupula. Endolymph
stimulates the recptor.
