Biomedical Science - Auditory pathway

sound info from inner ears needs to be interpreted in what different ways?

-intensity

-location

-frequency

-duration

vision is processed by

visual cortex/ occipital lobe

smell is processed by

olfactory cortex/ temporal lobe

taste is processed by

gustatory cortex/ insula

sound is processed by

auditory cortex/ temporal lobe

balance is processed by

cerebellum

outer ear

-Auricle/ pinna collects and directs sound waves

-ear canal known as external acoustic meatus transmits sound waves deep into skull to tympanic membrane (eardrum)

middle ear

-Irregular chamber; air filled known as tympanic cavity

-connected to pharynx by the air filled Eustachian tube

-3 bones (auditory ossicles): Malleus, Incus, Stapes, carry sound vibrations from the tympanic membrane to inner ear

inner ear

-Bony chamber that is fluid filled

-The middle ear joins the inner ear at the place called the oval window

-The oval window receives vibrations from the stapes bone (last one of the ossicles)

-Vibrations from the oval window travel through the fluid which fills the cochlea, the vestibule and the semi-circular canals

-The moving fluid activates tiny hairs on the end of nerve cells, which fires and action potential (nerve impulse)

-The cochlea detects sound

-The vestibule and semi-circular canals detect changes in head position for maintaining balance

-Nerve impulses from the cochlea (hearing) and vestibule/semi-circular canals (balance) travel along the vestibulocochlear nerve (CN VIII) to brain stem

cochlear nuclei in medulla

-The vestibulocochlear nerves convey auditory info to cochlear nuclei in the medulla near the junction with the pons

-information from each ear reaches the cochlear nuclei of the same side

superior olivary nuclei

-info from each cochlear nucleus is distributed to the superior olivary nuclei in the pons on both sides

-each SON compares intensity and delay in sound from each ear

-differences in the 2 nuclei enables sound location accurate to 1^0 of arc

inferior colliculi nuclei

-Auditory info passes from SON to inferior colliculi (most is contralateral)

-The inferior colliculi have important connections to the superior colliculi: nuclei controlling eye movement, spinal cord controlling muscles of the neck, spinal cord controlling postural muscles

-These connections enable following of moving sound sources with the eyes, head and, if necessary, alteration of bodily posture

Thalamus

-auditory info passes through thalamus

-acts as a relay station

-sends incoming info to whole cortex as well as to specific auditory complex to alert brain to incoming info

auditory pathways

-convey sound info from cochlea to auditory cortex

-cross and recross repeatedly

-several nuclei in the auditory pathways where synapses occur

-each synaptic relay nucleus plays a different part in auditory function

-mostly contralateral pathways

temporal lobes

-Auditory info reaches primary auditory cortex in transverse temporal gyri on superior surface of temporal lobe

primary auditory cortex

arranged tonotopically with neurons responding to low frequencies situated anteromedially and those responding to high frequencies situated posterolaterally

secondary auditory complex

important role in sound localisation and analysis of complex sounds: in particular for human language. It also has a role in auditory memory