anatomy final - lecture #22 - special senses II: hearing & equilibrium

what three parts is the ear divided into?

outer, middle, and inner ear

what is the auricle?

• the visible part of the ear, made of cartilage, that sticks out from the side of the head

• main job is to gather sound waves and direct them into the ear canal

what is the auditory canal?

• tube that carries sound waves towards the tympanic membrane that naturally amplifies sounds in the 2000-5000 Hz range

• contains glands that produce cerumen, which cleans, lubricates, and protects the ear

what is the tympanic membrane?

the eardrum; vibrates when sound waves reach it, then vibrations are transmitted to the ossicles in the middle ear, initiating sound transduction

what does the middle ear consist of?

ossicles and the oval window

what are the ossicles?

• three tiny bones (the smallest in the human body) that form a chain across the middle ear cavity

• malleus, incus, and stapes

what is the oval window?

a membrane covered opening that leads to the inner ear

why is the amplification of sound important?

the inner ear is filled with fluid, which is harder for sound to travel through than air

what are the two muscles in the middle ear?

tensor tympani (attached to malleus) and stapedius (attached to stapes)

what is the acoustic reflex?

it is a natural defense mechanism against loud sounds that is caused by the muscles to reduce the amplitude of sound vibrations reaching the cochlea

what is the auditory tube?

a narrow passage connecting the middle ear to the back of the throat that equalizes air pressure

how does the auditory tube work?

it is usually closed, but when you swallow or yawn, the tube opens briefly, allowing air to flow in or out of the middle ear

what are the two main parts of the inner ear? what can they further be divided into?

the bony labyrinth and the membranous labyrinth; the semicircular canals, vestibule, and cochlea

what are the semicircular ducts?

• membraneous tubes located inside the bony semicircular canals that are filled with endolymph

• responsible for detecting rotational movements of the head, contributing to our sense of balance

what is the cochlear duct?

located within the cochlea, it contains the organ of corti

what is the cochlea?

spiral shaped structure that contains the organ of corti that transforms sound vibrations into electrical signals that are sent to the brain

what is a vestibule?

a central chamber within the bony labyrinth that houses the utricle and saccule, two important structures of the membranous labyrinth

what are semicircular canals?

three bony tubes within the bony labyrinth that provide housing for the membranous ducts

what does the membranous labyrinth consist of?

the cochlear duct, semicircular ducts, utricle, and saccule, and is filled with endolymph

what does the bony labyrinth consist of?

the delicate inner ear structures, filled with perilymph

what is a saccule?

small, sac like structure that detects vertical movement and acceleration of the head

what is a utricle?

a sac like structure that detects horizontal movement and acceleration of the head, also contributes to balance and spatial awareness

what are the three chambers in the cochlea?

scala vestibuli, scala media, and scala tympani

what fills the scala vestibuli?

perilymph

what is the tectorial membrane?

• gelatinous structure that lies above the organ or corti

• plays a vital role in stimulating the hair cells during sound perception

what is the basilar membrane?

the floor of the scala media that supports the organ of corti

what is the vestibular (reissner’s) membrane?

membrane that separates the scala media from the scala vestibuli, acting as a barrier between endolymph and perilymph

what is the scala tympani filled with?

perilymph

what is the scala media filled with?

• endolymph

• high in potassium, low in sodium

what is the organ of corti?

the primary sensory organ for hearing that consists of a specialized epithelium made up of hair cells and supporting cells

what are the supporting cells of the organ of corti?

• non-sensory cells that maintain the structural integrity and proper function of the sensory hair cells

• also regulate the ionic environment surrounding hair cells

what are the outer hair cells of the organ of corti?

• tiny, hair like cells that help us hear more clearly

• ~20,000 cells arranged in 3 rows

• amplify for dampen vibrations in the ear

what are the inner hair cells of the organ of corti?

• responsible for converting mechanical vibrations into electrical signals that are sent to the brain

• ~3,500 and arranged in a single row

what are stereocilia in the organ of corti?

tiny hair like projections that are positioned near the tectorial membrane to bend against it, triggering the generation of electrical signals

what are the nerve fibers in the organ of corti?

located at the base of each hair cell, they carry electrical signals generated by hair cells to the brain via the cochlear nerve

what is the process of mechanical vibrations into electrical signals?

resonance and basilar movement → opening of ion channels → depolarization of hair cells (K+ influx) → NT release (Ca ions through voltage gated channels release NTs) → adjacent sensory neuron stimulation

what happens when stereocilia bend toward vs away the tallest cilium?

depolarization and hyperpolarization

what is the auditory projection pathway?

cochlea → cochlear nerve/vestibulocochlear nerve → medulla (cochlear nuclei) → pons (superior olivary complex) → midbrain (inferior colliculus) → thalamus (medial geniculate nucleus) → and auditory cortex (temporal lobe)

what is the vestibular system?

a complex sensory apparatus that is responsible for maintaining balance and spatial orientation that functions through the mechanical stimulation of hair cells

what are the two primary components of the vestibular system?

semicircular canals and otolith organs

what is crista ampullaris?

holds sensory hair cells at the base of each semicircular canal and detects angular acceleration

what are maculae?

sensory epithelia in otolith organs that detects static equilibrium and linear acceleration (horizontal in utricle, vertical in saccule)

what is the otolithic membrane?

a gelatinous structure topped with tiny crystals called otoconia

what is otoconia made out of?

calcium carbonate

what is static equilibrium?

the body’s ability to stay balanced and steady when it’s not moving, which allows us to sense the position and angle of our head

what is dynamic equilibrium?

the body’s ability to sense and react to movement, especially during spinning or turning

what is a cupula?

the large, dome shaped, translucent structure above hair cells that moves in response to fluid displacement within the semicircular canals