Download Special senses

Special senses
general senses
Touch - mixture of general senses
Skin
temperature
pressure
pain
Muscles and Joints
proprioceptors - detect stretch, or tension (body’s position)
five special senses
Localized clusters of receptors (taste buds and olfactory epithelium)
Smell
Taste
Complex Sensory Organs (eyes and ears)
Sight
Hearing
Equilibrium
the eye and vision
70% of all sensory receptors are in the eye
anatomy of the
eye
Meibomian (tarsal) glands – modified
sebaceoous glands produce an oily secretion to
lubricate the eye
ciliary glands - modified sweat glands between
the eyelashes
Conjunctiva - membrane that lines the eyelids
and covers part of the outer surface of the
eyeball; secretes mucous to lubricate eyeball
Conjuctivitis (pinkeye, its infectious form, is
highly contagious)
anatomy of the
eye
Lacrimal gland- produces lacrimal fluid
(tears)
Tears - Dilute salt solution containing
antibodies and lysozyme; Protects,
moistens, and lubricates the eye
Lacrimal canals - drains tears from
eyes into the nasal cavity
extrinsic eye muscles
internal structures of eyeball
Eyeball - hollow sphere composed of three tunics, or coats:
Sclera - outer thick, white connective tissue; clear, central area is the cornea, which
allows light to enter eye (Cornea can be transplanted without fear of rejection.)
Choroid - blood-rich nutritive tunic that contains dark pigment to prevent light from
scattering inside the eye; anteriorly, it forms the ciliary body (smooth muscle) and the
iris (pigmented layer with pupil opening)
Retina - inner, sensory tunic; contains millions of photoreceptor cells, rods and cones
internal structures of eyeball
Lens - flexible, biconvex crystal-like structure for focusing, separates the eye
into fluid-filled chambers
Anterior segment contains aqueous humor - clear watery fluid, provides
nutrients for lens and cornea, reabsorbed into blood through canal of
Schlemm
Posterior segment contains vitreous humor - gel-like substance, helps
maintain intraocular pressure
internal anatomy of eyeball
Retina
Retina
Rods - allow us to see gray tones in dim light and provide for our peripheral
vision
Cones - allow us to see color; three varieties - one responds to blue light, one
to green, and the third to green and red wavelengths; simultaneous impulses
are seen as intermediate colors
Fovea centralis - point of sharpest vision, area lateral to the blind spot that
contains only cones
Blind spot - no photoreceptors at optic disc, where optic nerve leaves the
eyeball
Colorblindness - lack of one or more of the cone types
Lens Accommodation
Light must be focused to a point on the
retina for optimal vision
The eye is set for distance vision
(over 20 ft away)
The lens must change shape to focus for
closer objects
Images formed on the Retina
Visual Pathway
Photoreceptors of retina
Optic Nerve
Optic Nerve crosses at Optic
chiasma
Optic tracts
Thalamus
Visual cortex of occipital lobe
Eye Reflexes
Internal muscles are controlled by the autonomic nervous system
• Bright light causes pupils to constrict through action of radial and ciliary
muscles
• Viewing close objects causes accommodation (adjustment of lens shape)
External muscles control eye movement to follow objects
• Viewing close objects causes convergence (eyes moving medially)
the ear
the ear
Houses two senses:
• Hearing
• Equilibrium (balance)
Receptors are mechanoreceptors
Different organs house receptors for each sense
anatomy of ear
Divided into three areas:
Outer (external) ear
Middle ear
Inner ear
external ear
Involved in hearing only
Structures:
Pinna (auricle)
External auditory canal -narrow
chamber extending to eardrum,
contains ceruminous (wax) glands
middle ear (tympanic cavity)
Air-filled cavity within the temporal bone
Only involved in the sense of hearing
The opening from the auditory canal is covered by
the tympanic membrane
The auditory tube connecting the middle ear with
the throat
Allows for equalizing pressure during yawning
or swallowing
This tube is otherwise collapsed
bones of the middle ear
Three ossicles (bones):
Hammer (malleus)
Anvil (incus)
Stirrup (stapes)
Vibrations from the
eardrum move the malleus
and transfer sound to the
inner ear
inner ear or bony labyrinth
Includes sense organs for hearing and
balance
Filled with perilymph
A maze of bony chambers within the
temporal bone:
Cochlea
Vestibule
Semicircular canals
organs of hearing
Organ of Corti
Located within the cochlea
Receptors = hair cells on the basilar membrane
Gel-like tectorial membrane is capable of bending hair cells
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on
temporal lobe
organs of hearing
mechanism of hearing
Vibrations from sound waves move tectorial membrane
Hair cells are bent by the membrane
An action potential starts in the cochlear nerve
Continued stimulation can lead to adaptation
organs of equilibrium
Receptor cells are in two structures:
Vestibule
Semicircular canals
organs of equilibrium
Equilibrium has two functional parts:
Static equilibrium - which way is up/down
Dynamic equilibrium - movement in three planes
static equilibrium
Maculae – receptors in the vestibule
Report on the position of the head
Send information via the vestibular nerve
Anatomy of the maculae Hair cells are embedded in the
otolithic membrane
Otoliths (tiny stones) float in a gel
around the hair cells
Movements cause otoliths to bend the
hair cells.
dynamic equilibrium
Crista ampullaris – receptors in the semicircular
canals
Tuft of hair cells
Cupula (gelatinous cap) covers the hair cells
• Action of angular head movements:
• The cupula stimulates the hair cells.
• An impulse is sent via the vestibular nerve to the
cerebellum.
chemical senses - taste and smell
Both senses use chemoreceptors
Stimulated by chemicals in solution
Taste has four types of receptors
Smell can differentiate a large range of chemicals
Both senses complement each other and respond to many of the same stimuli
olfaction - sense of smell
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 cerebral cortex
sense of taste
Taste buds house the receptor organs
Location of taste buds:
•
Most are on the Tongue
•
Soft palate
•
Cheeks
•
The tongue is covered with projections called
papillae:
•
Filiform papillae – sharp with no taste buds
•
Fungiform 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 by several cranial nerves
because taste buds are found in
different areas
• Facial nerve
• Glossopharyngeal nerve
• Vagus nerve
taste sensation
Major types of taste buds:
sweet receptors (sugar,
saccharine, some amino acids)
sour receptors (acids/hydrogen ions)
bitter receptors (alkaloids)
salty receptors (metal ions in solution)
umami receptors - savory (glutamates)
All receptors can be found on all regions of the tongue. Spicy foods excite
pain receptors in the mouth.
developmental aspects of special senses
formed early in embryological development
eyes are outgrowths of brain
all special senses are functional at birth
Normal consequences of aging:
presbyopia - age-related farsightedness
presbycusis - sensorineural deafness due to atrophy of organ of Corti
dulled sense of taste and smell as receptors are replaced more slowly