Senses: Hearing and Equilibrium

Ch. 17-3

Hearing

• Anatomy of the ear– External ear• Collects sound waves and

channels them inward– Middle ear• Conveys sound vibrations to the

oval window– Inner ear• Houses the receptors for hearing

and equilibrium

Ear Anatomy

Outer Ear

• Auricle (pinna) – flap of elastic cartilage shaped like a trumpet

• External auditory canal – curved tube that lies in the temporal bone and leads from the auricle to the eardrum

• Eardrum (tympanic membrane) – thin, semitransparent partition between the external auditory canal and the middle ear

• Ceruminous glands – produce wax to protect ear from dust and foreign objects

Outer Ear

Middle Ear

• Small, air-filled cavity• Contains 3 smallest bones in the body– Auditory ossicles

• Malleus, incus, and stapes

• contains auditory tube (eustachian tube) – connects middle ear to the throat and nasal cavities– Helps maintain air pressure– Can lead to ear pain during sore throats

Middle Ear

Inner Ear

• Labyrinth – communicating chambers and tubes

• Contains– Semicircular canals – sense of equilibrium– Cochlea – sense of hearing– Organ of Corti – contains hearing receptors, hair

cells detect vibrations• Turn pressure waves into electrical signals to the brain

Inner Ear

Hearing

• Pinna directs sound waves into auditory canal• Sound waves strike ear drum and it vibrates• Auditory ossicles amplify vibrations to cochlea• Organs of Corti contain receptor cells (hair

cells) that deform the vibrations• Impulses sent to nerves• Temporal lobe interprets sensory impulses

Hearing

Equilibrium

• Balance – 2 types– Static – maintenance of body relative to gravity– Dynamic – maintenance of body in response to

sudden movements like rotation, acceleration, and deceleration

• Organs that control this are called the vestibular apparatus – all lined with hairs– Saccule and utricle– Semicircular ducts (canals)

Equilibrium

• The hair cells send signals to the brain that tell it the position of the head

• As the hair cells move, the brain can interpret and fix balance