Bio 257 Day 22 Today’s topics:  Special Senses  Eye Anatomy & Physiology  Ear Anatomy & Physiology

Senses 5 Special Senses: –t–taste, smell, vision, hearing, equilibrium

Special Senses Smell or Olfaction (Nose): –C–Chemoreceptors (olfactory receptor cells) nasal mucosa epithelium underneath cribriform plate for any chemical (gas) to be detected (smelled) it must be partially water soluble = dissolve in nasal mucus

– Chemoreceptors (olfactory receptor cells) chemical substance dissolves in nasal mucus and bind to cilia of olfactory cells stimulating them olfactory nerve is stimulated nerve impulse is sent to olfactory cortex (within temporal and frontal lobes)

Special Senses – Smell: not much is known about how we detect good odors from bad smell is tied in with taste  much of what is considered taste is actually due to olfaction

Special Senses – Taste (Gustation): chemoreceptors = gustatory (taste) cells on tongue that contain taste hairs Taste hairs containing receptors extend into a small opening called a taste pore taste buds = barrel-shaped containing taste cells & supportive cells (specialized epithelium)

Special Senses – Taste (Gustation): 5 primary taste modalities 1. Sweet = tip of tongue 2. Sour = sides of tongue (margins) 3. Salty = widely distributed on tongue 4. Bitter = back of tongue 5. Umami

sweet soursaltybitter

Special Senses – Taste (Gustation): chemical substances must first be somewhat water soluble & dissolve in saliva Dissolved chemicals bind to specific taste buds stimulating them Facial nerve = front 2/3 of tongue (sweet, salty, sour)

Special Senses – T– Taste (Gustation): Glossopharyngeal nerve = back 1/3 of tongue (bitter) parietal lobe = gustatory center

Specific Senses Vision Photoreceptors (rods & cones) housed in eye Eye structure: –Accessory structures & eye

Specific Senses Vision Accessory structures –Eyelids (likened to windshield wipers) –Eyelashes –Lacrimal apparatus (gland and nasolacrimal duct and associated structures) –Conjunctiva = mucous membrane –6 extrinsic eye muscles

Specific Senses Vision Eye structures –Cavities –Wall of eye = arranged eye layers (tunics)

Specific Senses Vision Eye Cavities (interior) – Posterior cavity = large cavity w/ jelly- like vitreous humor (fluid) – Anterior Cavity Anterior chamber/Posterior chamber = smaller cavities w/ watery aqueous humor (fluid)

Specific Senses Vision Wall of eye –3 eye layers (tunics) Fibrous tunic Vascular tunic Neural tunic

Specific Senses Vision Fibrous tunic = outermost layer of eye  dense connective tissue –Includes sclera & cornea

Specific Senses Vision Fibrous tunic – sclera = “white” of eye support, protect, provide site of eye muscle attachment – cornea = transparent “window” of eye powerfully focuses light entering eye (bends light) primary focusing structure

Specific Senses Vision Vascular tunic = middle eye layer  blood vessels & intrinsic eye muscles –Includes: iris, choroid coat, & ciliary body

Vision Vascular tunic structures –Iris (smooth muscles) = colored portion of eye (melanin) regulates amount of light entering eye by constricting or dilating pupil – Pupil = circular hole in middle of iris (similar to camera shutter)

Vision Vascular tunic structures –ciliary body = ciliary muscle + suspensory ligaments = controls shape of lens Lens = transparent elastic –changes shape for near & far vision = accommodation – 2 nd most powerful focusing structure (bends light)

Specific Senses Vision Vascular tunic structures –choroid coat = irridescent, dark tissue layer (melanin)  keeps interior of eye dark by absorbing excess light –highly vascular  delivers O 2 and nutrients to neural tunic

Specific Senses Vision Nervous Tunic = innermost eye layer – nerve tissue = photoreceptors & neurons – retina = several layers of neurons & photoreceptors

Specific Senses Vision NervousTunic – retina photoreceptors 2 types: 1.Cones = for daylight & color vision  gives sharp, clear vision, but requires more light  3 types of cones (red, blue, green)- various colors seen due to stimulation of different combinations of these cones.

Specific Senses Vision NervousTunic – retina photoreceptors 2 types: 2. Rods = for night vision = very light sensitive  requires less light (fxn in dim light) rhodopsin = light sensitive pigment

Specific Senses Vision Neural Tunic – retina = arrangement of photoreceptors Macula lutea (yellow spot) = area on retina –highest concentration of cones Fovea centralis = center of macula –site center of color & sharpest vision

Specific Senses Vision Neural Tunic – retina = arrangement of photoreceptors optic disc = circular area medial to fovea and anterior to optic nerve –blind spot (no rods or cones)

Specific Senses Vision Visual Pathway: – Light rays entering the eye from an object must be bent and fall on fovea centralis

Specific Senses Vision Visual Pathway: – light  cornea (bends light)  anterior cavity (aqueous humor)  pupil (iris)  lens (bends light)  posterior cavity (vitreous humor)  retina (fovea centralis)

Visual System

Specific Senses Vision Neural Pathway: retina (fovea) optic nerves optic chiasma thalamus occipital lobe AP

Special Senses Ear functions: –Hearing –Equilibrium

Specific Senses Hearing Mechanoreceptors housed in ear (cochlear duct) Mechanoreceptors = hair cells in the organ of Corti

Specific Senses Hearing Anatomy of ear –3 regions External ear Middle ear Inner ear

Specific Senses Hearing External ear includes: auricle or pinna – fleshy/cartilaginous portion  collects sounds external auditory meatus = ear canal  funnels sound waves to middle ear

Specific Senses Hearing External ear includes: tympanic membrane = eardrum  thin sheet separates external ear from middle ear  vibrates, passing sound waves

Specific Senses Hearing Middle ear includes tympanic cavity = space filled with air  houses middle ear bones (ossicles)  3 ossicles (vibrate in order w/ passing sound waves) –Malleus (hammer) –Incus (anvil) –Stapes (stir-up)

Specific Senses Hearing Middle ear includes: eustachian or auditory tube = tube leaving tympanic cavity & connecting to pharynx  equalizes pressure on either side of eardrum

Specific Senses Hearing Inner ear- (vestibulocochlear apparatus) interconnecting tunnels and chambers consist of membranous labyrinth surrounded by bony labyrinth & filled with fluid

Specific Senses Hearing Inner ear (vestibulocochlear apparatus) bony labyrinth = perilymph (fluid) membranous labyrinth = endolymph (fluid)

Specific Senses Hearing Inner ear (vestibulocochlear apparatus) oval window = is displaced by stapes vibrations & moves inner ear fluid round window = is displaced as fluids move, removes excess sound waves

Specific Senses Hearing Bony Labyrinth consists of 3 areas – Vestibule – 3 Semicircular canals – Cochlea, coiled (snail- shaped)

Specific Senses Hearing Vestibule = has membranous sacs called saccule & utricle, which house mechanoreceptors for equilibrium (balance)

Specific Senses Hearing 3 Semicircular canals = house mechanoreceptors for equilibrium (balance) Cochlea, coiled (snail-shaped) = contains membranous labyrinth called cochlear duct

Specific Senses Hearing Cochlea = houses cochlear duct, which contains mechanoreceptors for hearing

Specific Senses Hearing Cochlea (cochlear duct) contains hearing receptors (Organ of Corti) and are stimulated as fluid (endolymph) & membranes move –Movement of stapes at the oval window transmits vibrations that pass through various fluids and structures –Vibrations enter the endolymph of the cochlear duct and different frequencies of vibrations stimulate different sets of receptor cells

Specific Senses Hearing Hearing Pathway auricle  external auditory meatus  tympanic membrane  malleus  incus  stapes  oval window  cochlear duct

Auditory System

Specific Senses Hearing Neural Pathway cochlear duct (organ of Corti) vestibulocochlear nerve thalamus (cochlear branch) temporal lobe Nerve impulse impulse Nerve impulse

Specific Senses Equilibrium Static equilibrium = head movements while body is stationary and under influence of gravity (ie evaluate position of head relative to gravity) –Utricle & saccule (2 chambers of the vestibule) Contain maculae  specialized patches of epithelium w/ hair cells

Hair cells

Specific Senses Equilibrium Dynamic equilibrium = evaluate changes in the direction and rate of head movements (ie head & body rotational movements) – 3 Semicircular Canals Positioned at nearly rt angles to each other Contains crista ampullaris which has hair cells embedded in a gelatinous mass  cupula

Vestibular System

Semicircular Canals

Hair Cell hair cells are involved with processing sound by the auditory system and processing information on balance and equilibrium by the vestibular system. one tiny cell performs these amazing functions in two widely different systems. the cilia at the top of the hair cells is important. –hair cells at rest, release a small resting level of neurotransmitter from their base onto the sensory nerve, which fires action potentials. –smaller stereocilia when bent toward the larger kinocilium (during an acceleration, for example) cause the hair cell to releases more neurotransmitter  resulting in more action potentials in the sensory nerve. –stereocilia bending away from the kinocilium (during a deceleration, for example), cause the hair cell to releases less neurotransmitter  resulting in fewer action potentials.