Ch 15 pt 3) Special Senses

Question 1

Two Major Divisons of Internal Ear

Answer 1

• Known as labyrinths because of complicated shape
• Bony Labyrinth) System of channels and cavities that worm through the bone
  
  • made of Vestibule, Semicircular canals, and cochlea
  • Filled with Perilymph fluid.
• Membranous Labrynth) series of membranous sacs and ducts in the bony labryinth
  
  • filled with potassium-rich endlymph

Question 2

Vestibule

Answer 2

• Central Cavity of the bony labyrith
• Contains two membranous sacs
  
  • Saccule) Continuous with cochlear duct
  • Utricle) Continuous with semicircular canals
  • Sacs contain equilibrium receptor regions (maculae) that respond to gravity/change in head position.

Question 3

Semicircular Canals

Answer 3

• Three Canals oriented in three planes of space
  
  • Anterior, Posterior and Lateral
  • Anterior and Posterior are at right angles to eachther, lateral canal is horizontal
• Membranous semicular ducts line each canal and communicate with the utricle
• Ampulla) enlarged area of each duct that houses an equilibrium receptor called the crista ampullaris (Crest of ampulla)
  
  • Crista ampullaris responds to angular movments of the head.
  • Two ampulla per semicircular canal

Question 4

The Cochlea

Answer 4

• Small, spiral, conical bony chamber
  
  • extends from vestibule
  • coils about 2.5 times around bony pilar
• Cochlear duct) houses spiral organ and ends at cochlear apex
• Three chambers of the Cochlea
  
  • Scala Vestibuli) located on oval window, contains perilymph
  • Scala Media (cochlear duct) contains endolymph
  • Scala Tympani) terminates at round window; contains perilymph
    
    • Continous with vestibuli at helicotrema
• Vestibular membrane) “roof” of the coclear duct that seperated scala media from scala vestubuli.
• Stria Vascularis) External wall of cochlear duct composed of musocsa that secreted endolumph
• “floor” of coclear duct
  
  • Bony spiral Lamina) Bony shell
  • Basilar membrane) supports spiral organ
• Spiral Organ) contains coclear hairs
  
  • one row of inner hairs
  • three rows of outer hair cells
  • Hair cells are located between tectorial and basilar membranes
  • Cochlear branch of vestibulocochlear nerve (VII) runs from spiral organ to brain

Question 5

Sound Detection (Properties of Sound)

Answer 5

• Hearing is the reception of a sound wave that stimulates mechanosensative coclear hairs
  
  • send impules to the brain for interpretation
• Sound) a pressure disturbance produced by a vibrating objects. moves molecules of air in waves. Sound declines with time and distance.
• Frequence) mumber of waves in a given time
  
  • Wavelength) distance between two wavecreasts (shorter wavelength= higher frequency)
  • Pitch) perception of frequenies (higher frequency=higher pitch)
  • Quality) Characteristics of counds (provided richness and complexity of sounds)
  • Humans can hear ar frequencys of 20-20,000 Hertz (waves per second) but hear best at 1500-4000 Hz
• Amplitude) Height of creasts
  
  • Precived as loundness (more amplitide= Louder)
  • Measured in decibals
  • We can hear up to 120dB before hearing damage occurs

Question 6

Transmission of Sound waves to internal ear

Answer 6

• Tympanic Membrane) soundwaves enter external acoutic meatus and vibrate tympanic membrane
  
  • more intense sound = more vibrations
• Asditory Ossicles) Transfer vibration of eardrum to oval window
  
  • the vibration is amplified about 20x during this process
• Scala Vestibuli) stapes rocks back and forth on oval window causing mition in the perilymoh. Waves end at round window which cause it to buldge outward
• Two paths after
  
  • Helicotema path) waves with frequencies below the thershold of hearing travel through helicotrema and scala tympani to round window. Do not activate the spiral organ
  • Basilar Membrane Path) sounds are in hearing frequency and pass through the cochlear duct and vibrate the basilar membrane at a specific location according to frequency.

Question 7

Resonance of the Basilar Membrane

Answer 7

• Resonance) movment of diffrent areas of the basilar membrane in response to a particular frequency.
• Basilar membrane changes
  
  • Fibers near oval window are short and stiff; resonate with higher frequncies
  • Fibers near cochleat apex are longer and floppier; resonate with lower-frequency waves.

Question 8

Excitation of Inner Hair Cells

Answer 8

• Movment of the basilar membrane stimulates hairs of inner hair cels
• Cochlear hair cells have mircovilli that contain sterocilia (hairs) that only bend at the base
• Longest hair cells are connected to shortest hair cells via tip-links
  
  • when a tip link is pulled on it opens every ion channel it is attached too.
• When Sterocilla bend toward the TALLEST one
  
  • K+ and Ca2+ flow into the cell causing the release of nuerotranmiter
  • This creates an AP which sends signal from sound down cochlear nerve
• When Sterocilla bend toward the SHORTEST one
  
  • Ion channels close leading to repolarization of hair cells.

Question 9

Role of Outer Hair Cells

Answer 9

• Nerve endings of outer hair cells are effrent nurons which convay info from the brain to ear
• Outer hair cells can contract and stretch which changes the stiffness of the outer basilar membrane.
  
  • Increases bility to “fine tune” hearing by amplifying motion of basilar membrane
  • Protects inner hair cells by decreasing motion of the basilar membrane.

Question 10

Auiditory Pathway and Processing

Answer 10

• Nueral impulses from cochlear bipolar cells travel on vestibulocochlear nerve to auditory cortex
  
  • Some fibers cross over and some do not; both auditory cortexes recive info from both ears.
• Auditory Processing
  
  • Perception of pitch) impuleses from diffrent positions along basilar membrane are interoreted as specific pitches
  • Loudness) frequency of waves/AP’s is interpreted as loundess
  • Localization of Sound) Depends on intensity of sound from both ears
    
    • if timing is increased on one side brain interoreted sound as if coming from that side.

Question 11

Mantenance of Equalibrium

Answer 11

• Equilibrium is response to various movments of our head that rely on input from inner ear, eyes, and streatch receptors.
• Vestibular Apparatus) Equilibrium receptors in semicircular canals and vestibule.
  
  • Vestibular Receptors moniter Static equilibrum
  • Semicular Canal receptors moniter dynamic equalibrium

Question 12

the Macula

Answer 12

• Maculae) Sensory recptor organs that moniter static eqilibrim
  
  • one located in each saccule wall and one in each utrile wall
  • Moniter position of head in space
  • Help in control of posture
  • Respond to linear acceleration but not rotational forces.
• Anatomy of a Maculae)
  
  • Flat epithelium patch containin hair and supporting cells.
    
    • hair cells have special “true steroculium” called kinocilium.
  • Sterocillia are embedded in otolith membrane, a jelly like structure studded with otoliths.
    
    • Increase membranes weight/ inertia.
  • Utricle Meculea are horizontal with vertical hairs
    
    • respond to forward/ backward movent of the head
  • Saccule Maculea are vertical with horizontal haird
    
    • respond to up/down movments (Ex elevator)
  • Hair fibers synapse with vestubular nerve.

Question 13

Activation of Receptors of a Macula

Answer 13

• Macula hair cells continuosly release nuerotranmsitter.
  
  • acceleration/deceleration causes change in the ammount of nuerotansnmiter released.
  • Leads in a change of frequency of AP’s sent to brain.
• The density of the otolith membrane causes it to lag behind the movment if hair cells when the head changes position
  
  • This causes the hairs to bend and ion chanels open
• Bending of hairs IN direction of Kinocilia
  
  • depolarizes hair cells
  • More nuerotranmitters relased = more AP’s to brain.
• Bending of hairs AWAY from kinocilia
  
  • Hyperpolarizes recptors
  • Less nuerotranmiter released = less AP’s to brain
• Changing of AP’s to brain informs the body of changing head position.

Question 14

The Cristae Ampullares

Answer 14

• Crista Ampullaris (crista) are the reptors for rotational acceleration.
• Anatomy of a Crista
  
  • Hair and supporting cells extend into gel like mass called Ampullary Cupula
  • Dendrites of vestibular nerve fibers encircle base of hair cells.

Question 15

Activating Receptors of Crista Ampullaris

Answer 15

• Respond to roational movments
  
  • Endolymph of semicurcular ducts move oppisite to the body rotation casuing hair to bend.
• Bending haird in cistae causes depolariztion
  
  • Send more impules to the brain
• hairs bent in the opposite direction hyperpolarize
  
  • send fewer impiles to the brain,
• Because axeses of hair cells in semicircular ducts are opposite; depolarization in one means hyperpolarization is occuring in the other.

Question 16

Vestibular Nystagmus

Answer 16

• Semicircular canal impules are linked to reflex movment of the eyes
• Nystagmus) strange eye movments during and after roatation
  
  • often accompanied by vertigo.
  • As you rotate, eyed slowly drift in other direction in an attempt to fixate on an object. When object cannot be located eyes rapidly jump to a new fixation point.
  • When roation ends eyes jerk to normal position.

Question 17

Equilibrium Pathway in the Brain

Answer 17

• Equlibrium info goes to reflex centers in brain stem
  
  • allows fast reflexive movements so we don’t fall down
• Three imputs for equilibribium sensation
  
  • Vestibular receptors (in ear)
  • Visual receptors (in eye)
  • Somatic Receptors (in limbs)
• Integration centers for equilibrium
  
  • Cerebellum and Vestibular Nuclei
• Effectors
  
  • Oculomotor control (nerves III, IV, VI)
  • Spinal motor control) nerve XI and vestibulospinal tracts.

Question 18

Motion Sickness

Answer 18

• Sensory Imputs are mismatched
  
  • Visual imput differs from equilibrum impit

Question 19

Defness

Answer 19

• Conduction Deafness) Blocked sound concution to fluids of inner ears
  
  • can inclued impacted earwax, ruptured eardru, or middle ear infmmation
• Sensorineural deffness) damage to nueral structres from the cochlear hair cells to the auidory lobe.
• Choclear implants can convert sound energy into eletrical signals that are effective to replace damage.
  
  • Inserted into temporal bone

Question 20

Tinnitus

Answer 20

• Ringing, buzzing, or clicking sound in ears in absence
of auditory stimuli
• Due to cochlear nerve degeneration, inflammation of
middle or internal ears, side effects of aspirin

Question 21

Meiniere’s Syndrome

Answer 21

• Labyrinth disorder that affects cochlea and semicircular canals
  
  • Causes vertigo, nausea, and vomiting
• Treatment: anti–motion sickness drugs in mild cases
  
  • A last resort is removal of the entire malfunctioning labyrinth

Question 22

Develepomental Aspects of Special Senses

Answer 22

• Taste and Smell) functional at birth, deteriorates as we get older
• Vision) not fully functioning at birth
  
  • Color vision develops at age 3, eye is full grown at 8-9
  • at age 40 eye begins to deteriorate
• Hearing and Balance) Ear develops in week 3 embryo
  
  • By month 4 infants can turn heads to voices
  • Few ear problems until 60s when detoriation of spiral organs becomes noticable.