Special sense - ear Flashcards
Anatomy of the ear
3 parts
External ear: pinna, ear canal, tympanic membrane
Middle ear: 3 ossicles, oval and round window, eustachian tube
Internal ear: cochlear, semi-circular canals
Middle ear 3 ossicles
Maleus, Incus and Stapes
Hearing and balance
-The outer and middle ear are involved with hearing
-The inner ear functions in both hearing and equilibrium
-Receptors for hearing and balance
Respond to separate stimuli
Are activated independently
-Afferent fibres from:
Hearing receptors in cochlear vestibular division
Transmit information from the inner ear in from of action potentials via vestibulocochlear nerve to the brain
The inner ear
2 things
Bony Labryinth:
Tortuous channels worming their way through the temporal bone, filled with perilymph
Contains the vestibule, the cochlea and the semicircular canals
Membranous labyrinth:
Series of membranous sacs within the bony labyrinth, filed with potassium-rich fluid
How we perceive sound
-The outer ear and external auditory canal act passively to capture the acoustic energy
-Sound waves strike the tympanic membrane causing it to vibrate
-Formation of a perilymph (fluid) wave within the cochlea
-Wave travels the length of the cochlea = displacement of the basilar membrane
-Stereocilia are bent due to a shearing force causing change in resting membrane potential of hair cell
3 structures in the inner ear amplify the sounds
Sound transduction by hair cells
- Oscillations of cochlea membranes cause hair cell sterocilia to bend
- Sterocilia are different lengths
- Bend either towards or away from tallest stereocilium (transmit the sounds to the brain by creating the action potential)
- Signals from hair cells transmitted to brain via cochlear nerve
- In ends of stereocilia of hair cells are mechanically-gated K+ channels
- Bending of stereocilia towards tallest stereocilium (kinocilium) opnes mechanically0gates K+ channels in ahir cells
- Allows K+ to enter cell depolarisation Ca2+ enters cell release of neurotransmitter = action potential
Auditory pathway to the brain
- Vestibulocochlear nerve
- Spiral ganglion transmit to the brainstem via cranial nerve VIII
- Synapses on the 2 cochlear nuclei
- Main pathway involves axons from the ventral cochlear nucleus to the inferior colliculus
- Travels to and synapse at the medial geniculate body of the thalamus = MGN
- Finish at the auditory cortex
- Vestibular nerve (balance) joins the cochlear nerve (hearing) entering the internal acoustic meatus from this point on they are collectively called vestibulocochlear nerve
Deafness = hearing aids
3 basic parts
Microphone
Amplifier
Speaker
Vestibular apparatus –> balance
Comprised of
Comprides: 3 semicircular canals, 1 utricle, 1 saccule
- Semicircular canals contain endolymph
- At base of each semicircular canal is ampulla (jug)
- Within each ampulla is cupula (cap)
- Utricle and saccule = linear acceleration
- Cupula and ampulla = rotational acceleration
Structure of ampulla
- Ampulla sits as base of each semicircular canal
- Each ampulla has ridge (crista) that extends with cupula = cap into the lumen of fluid filled inside the ampulla
- Cupula bridges width of ampulla
- Forms mobile barrier through which endolymph (fluid) cannot circulate
- Mechanoreceptor hair cells extend out of crista into gelatinous cupula
- If head it tilted endolymph pushes against hair bundles in cupula
- Mechanoreceptor hair cells transmit information to vestibulocochlear nerve
Transduction of rotation
- The movement of stereocilia towards or away from Kino cilium causes K+ channels to open or close
- Causes depolarisation or hyperpolarisation of hair cells, increasing or decreasing Ca2+ concentration within cells
- End result is increase or decrease in number of action potentials
- Information is interpreted in the brain
Anatomy of utricle and saccule
- Utricle and saccule detect linear acceleration in same way that semicircular canals that detect rotational acceleration
- Receptor cells are hair cells with stereocilia that extend into gelatinous layer containing small calcium carbonate crystals
Chemical sense - smell and taste
Chemoreceptors
-Respond to chemicals in aqueous solution
-Membrane of sensory neurons becomes depolarised action potentials
-Respond to different classes of chemicals
-Complement each other
-Smell and taste are related
in severe rhinitis loss of specific taste of food
Smell
- Chemoreceptor animals have much better olfactory ability to humans
- This superior ability is reflected in:
Greater surface are of nasal cavity lining
The size of the olfactory region of the brain
Olfactory nerves
- Sensory nerves of smell
- Run from nasal mucosa to olfactory bulbs
- Pass though cribriform plate of ethmoid bone
- Fibres synapse in olfactory bulb
- Pathway terminates in primary olfactory cortex
- Purely sensory (olfactory) function
