The Ear: An Organ of Hearing and Equilibrium PDF

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’ N.D. The Ear: An Organ of Hearing and Equilibrium Hearing and equilibrium are contained in the temporal bone of the cranium. What is sound? - Sound is produced when matter (solid, liquid, gas, etc.) is vibrated. - Vibrating...

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’ N.D. The Ear: An Organ of Hearing and Equilibrium Hearing and equilibrium are contained in the temporal bone of the cranium. What is sound? - Sound is produced when matter (solid, liquid, gas, etc.) is vibrated. - Vibrating matter produces a fluctuation in air pressure in the atmosphere. - High pitch sounds = a high air frequency (air fluctuates frequently). - Low pitch sounds = a low air frequency (air fluctuates slowly). - Frequency is measured in Hertz. - Humans can hear between 20 and 20,000 Hertz. Canines can hear well above 20,000 Hertz. - Loud sounds = an increase in wave amplitude - Soft sounds = a decrease in wave amplitude 3 Parts to the Ear: 1. Outer ear - Pinnae or Auricle, catches sound 2. Middle ear – AKA Tempanic Cavity, air filled cavity, sound is sensed here by the 3 ossicles 3. Inner Ear – contains the sensory organs to translate fluctuations of air 3 actions must occur to hear sound: 1. Sound waves must be directed to the ear ----Pinnae or Auricle does this 2. Air pressure fluctuations must be sensed 3. Translate the fluctuations of air into electrical signals your brain can comprehend Directing sound waves to the ear: The Pinna (AKA Auricle) - The pinnae are made of elastic cartilage. - It is pointed slightly forward to catch the sound. - One will hear sound coming from the front better than if it is coming from the rear because of the shape of the pinna. Humans do not have movable pinna (like canines) so that’s why we put our hands behind our ears (create a larger surface area to catch the sound). - Sound waves then travel from the pinnae to the external auditory meatus (AKA ear canal). External Auditory Meatus (AKA ear canal). - The external auditory meatus contains sebaceous glands (oil glands) and cerumenous glands (makes cerumen or earwax, which is actually a mixture of sebum and sweat). - Ear wax functions include: keeps ear drum pliable, waterproofs the canal, possesses a bacterial effect. - The external auditory meatus ends at the tympanic membrane (ear drum) - The eardrum is located between the external auditory meatus and the middle ear. Ear Drum (tympanic membrane) - The ear drum structure:  o Outer (Superficial layer) – thin piece of skin that is semitransparent o Middle – tightly stretched fiber layer (this vibrates like a drum with sound waves) o Inner (Deepest layer) – mucous membrane - Air pressure regulation: Air travels toward the eardrum from 2 directions: 1. From the atmosphere into the ear canal then toward the eardrum 2. From the mouth towards the eardrum This pressure must remain equal so the eardrum moves freely back and forth to regulate any fluctuations. The tensor tympani muscle is attached to the eardrum and pulls the drum inward to allow the membrane to remain taut. This tautness is important so that if any sound hits it a vibration will occur. - With loud sounds – eardrum moves a greater distance - With soft or low sounds – eardrum moves a lesser distance - With high pitch sounds – the eardrum moves at a faster rate - With low pitch sounds – the eardrum moves at a slower rate - How to protect your ears from long-term low pitched? A reflex of two muscles (tensor tympani muscle and the stapedius muscle) contract at the same time pulling the eardrum in opposite directions resulting in a very rigid eardrum that dampens the sound. Additionally, the reflex action of these muscles allow one to hear noises around oneself without drowning out the sound of their own voice while speaking. Unfortunately, this reflex is not fast enough to protect the ear from gunshots and explosions. Middle Ear (AKA Tempanic Cavity) (Deep to the Ear Drum) – Contains ossicles and the Eustachian tube - Contains the 3 ossicles (smallest bones of the body): they are named for their shapes. 1. Malleus (AKA hammer) – connected to the eardrum; moves back and forth when the eardrum moves 2. Incus (AKA Anvil) – connected to the malleus and stapes 3. Stapes (AKA Stirrup) – the faceplate of the stapes acts as a piston and pushes on the cochlear fluid creating waves - The function of the ossicles is to amplify the pressure changes the eardrum has sensed. Due to the extreme sensitivity of the eardrum, a small fluctuation is air pressure causes movement of the eardrum. However, in order for the inner ear (specifically the cochlea), which must conduct the sound through a fluid to sense these changes it must amplify the pressure. It is easier to move through air (middle ear) than to move through a fluid (inner ear). - The middle ear is also connected to the Eustachian tube. Inner Ear: - The temporal bone contains the organ of hearing: Organ of Corti “(located in the cochlea) and equilibrium (vestibular apparatus). - These 2 organs are located in the bony labyrinth, which contains perilymph (continuous with CSF) and endolymph (similar to intracellular fluid). - Cochlea: o Shaped like a snail with 3 chambers. The Organ of Corti is in the middle chamber.  o Organ of Corti contains thousands of hairs that respond to vibrations. When the hairs move they stimulate an action potential and send it to the cochlear nerve and then to the brain for interpretation. - Equilibrium (vestibular apparatus): o Located next to the cochlea. o Sensory parts of the Vestibular apparatus: they sense acceleration and deceleration – not continuous motion. 1. saccule 2. utricle 3. 3 semicircular canals Clinical Diseases of Hearing – Cochlear Dysfunction: 1. Nerve deafness – damage to the cochlea, characterized by damage or death to the hairs. 2. Tinnitus – “ringing of the ears”, characterized by damage of the cells. Clinical Diseases of Equilibrium—Vestibular Dysfunction: 1. Vertigo – used synonymously as dizziness BUT does not mean the same thing. Vertigo is a spinning sensation unrelated to body position. 2. Dizziness – spinning sensation in an upright position