M6S4 Special Sense - Hearing And Equilibrium Flashcards
The receptors in the middle ear are responsible for:
-hearing and equilibrium
-one’s unconscious sense of balance and position in space
Structure of ear
-3 sections
Inner ear:
-located within the temporal bone
-houses receptors responsible for hearing and equilibrium
-vestibulocochlear (CN VIII) responsible for transmitting this information to brain
-receptors for hearing and receptors for equilibrium (balance) have unique structures in inner ear:
1. cochlea - contains receptors for hearing (looks like seashell)
2. vestibular apparatus - contains receptor for equilibrium, and made of 3 parts
Middle ear:
-located within temporal bone
-spans from tympanic membrane to oval window
-sound waves involved with hearing also transmitted through middle ear
Features:
1. Ossicles - small bones (smallest in body) located in the middle ear
2. Tympanic cavity - chamber in the temporal bone
3. Round and Oval Windows - areas at which middle ear connects to inner ear
4. Eustachian tube - connects the middle ear to the nasopharynx
MORE ABOUT OSSSICLES:
-3 smaller bones that help transit sound waves to receptors in inner ear
-muscles attached to ossicles (the tensor tympani and the stapedius) function to dampen very loud noises
1. Malleus (hammer) - most lateral ossicle that attached to and behind the tympanic membrane
2. Incus (anvil) - sits between the malleus and the stapes
3. Stapes (stirrup) - smallest bone and sits in the oval window. About 1/3 of the mass of the other ossicles
External ear:
-represents structure of ear you can touch
-sound waves from external environment travel through the external auditory canal to reach tympanic membrane, causing it to viberate
-tympanic membrane marks boundary between the external and middle ear
-ceruminous glands are microscopic glands that are present in external auditory canal and glands that secrete ear wax
*REFER TO GOODNOTES FOR IMAGES
Perforated tympanic membrane
Tympanic membrane aka eardrum is susceptible to physical damage or injury
-important structure as transmits sounds from external environment to ossicles of middle ear
-causes decreased or disrupted hearing
*refer to goodnotes
Rotational movement
Changes in the head’s position in space on an angular axis as such as side to side, up and down and tilting
Positional movement
Changes in the head’s position from one point in space to another, with respect to gravity and linear acceleration
Labyrinth
-both cochlea and vestibular apparatus are structures as two channels in the bone, called labyrinths: the membranous and bony labyrinths
-membranous labyrinth is within bony labyrinth
-both labyrinths are filled with fluids that allow us to hear (cochlea) or become aware of and mon it or the position of our (vestibular apparatus)
-membranous labyrinth = filled with endolymph
-bony labyrinth = filled with perilymph
*refer to goodnotes for image
Vestibular Apparatus
-contains the receptors for equilibrium and composed of 3 structures:
1. Semicircular canals - detect rotational movement
2. + 3. Utricle and saccule - both responsible for detecting positional movement
*refer to goodnotes
Cochlea
-contains receptors for hearing
-a cross section of cochlea reveals that structure composed of 3 ducts:
Vestibular duct
Tympanic duct
Cochlear duct
-cochlear duct contains the organ of corti, which specialized structure integral to hearing
*refer to goodnotes
Organ of Corti
-located within cochlear duct
-specialized structure integral to hearing
-made up of specialized cochlear hair cells that rest on a basilar membrane
-when membrane moved by sound waves, the hair cells fire an impulse, which sent to brain via CN VIII for interpretation
*refer to goodnotes
What is sound?
Sounds create vibrations in air that beat against ear drum that push series of tiny bones that move internal fluid inside membrane, triggering tiny hair like cells to stimulate neurons who send action potential to brain who interprets it as sound
What is the key to sound
Vibrations
What the 3 parts of ear play roles in
External and middle ear - only involved with hearing
Inner ear - involved with hearing and maintaining equilibrium
How sound works video notes
Pinnacle or auricle part of ear
made of elastic cartilage
-fun part of ear that can feel, pinch, play with
-catches sound waves and passes them along deeper into ear
Once sound caught funnel into external acoustic meatus
Sound travel down auditory canal
Sound collide with tympanic membrane which is eardrum (BOUNDARY BETWEEN EXTERNAL AND MIDDLE EAR)
When sound waves collide with eardrum, push it back and forth, making it viberate and pushing back and forth tiny bones in the middle ear
Middle ear aka tympanic cavity relay station between outer and inner ear
-will amplify sound waves so stronger when enter inner ear (need to amplify as inner ear move sound through fluid not through air)
-focuses pressure of sound waves so strong enough to move through inner ear through auditory ossicles:malleus, incus and stapes
One end of malleus connect to inner ear drum and move back and forth when sound vibrates, other end attach to incus then stapes and form chain that move vibrations to superior oval window
Here set fluid from inner ear into motion
Labyrinth deep into head 2 jobs
1. Turn those physical vibrations into electrical impulses the brain can identify as sound
2. Help maintain equilibrium
2 layers: bony labyrinth, fluid wavy system. Membranous labyrinth, continuous layer of sacs and ducts inside bony labyrinth that follow shape
Hearing function of labyrinth: cochlea
3 main chambers seperated by sensitive membrane
Main important one: basilar membrane - a still band of tissue that runs between the scale media and scale tympani (can read sound and communicate medially to nerve system)
As structure on top=organ of corti - cause sections of basalar (check spelling) membrane to back and forth
-covered in lots of fibres, longer farther down membrane go
-close to corti fibres = short and stiff (viberate for high frequency) longer and less stiff as go down (viberate for low frequency)
-fibres resonate at different frequencies
Now need to tell brain what going on
Hair cells open up sodium gated channels when triggered
Sodium leads to action potential
Action potential travel up cochlear nerve, through auditory pathway to cerebral cortex
-brain determine pitch based on location of hair cells being triggered
-louder sounds move more hairs and cause more action potential
Now brain determine what is
Maintains equilibrium video notes
-like how hear but instead of cochlea use vestibular apparatus (combination of fluid and hair cells)
-fluid controlled by movement of head
Cannals determine which way fluid goes when move head and have wide base called utricle and saccule which filled with hair like structures and sense motion of fluid
Reading fluid leads to know how much head moving brain processes it all
How do you get motion sickness
-based on sensory conflict
Ex. Spinning in chair, hair cells firing in brain but spine tell body sitting still
