Special Senses PPT/PDF

 

Special Senses 

        
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

  1. Vision

  2. Olfaction

  3. Taste

  4. 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.

 

Special Senses PDF


Special Senses PPT



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