Lecture 9 Special Sense Organ: Ear Flashcards
Special sense organs: stimuli
Stimuli exist in different energy forms
E.g
Sight: photons
Hearing: sound waves
Taste: chemoreceptors
Afferent neurons have sensory receptors at their peripheral end which respond to stimuli
Receptors convert these energy forms into electrical signals - signal transduction
Classification of sensory receptors
Mechanoreceptors
Location: special senses (ear), muscle/joints, skin/viscera and cardiovascular
E.g. cochlea and vestibular hair cells
Muscle spindles/Golgi tendon organs
Pacinican and Meissner’s corpuscle
Arterial baroreceptor (high press)
Atrial vol. Receptors (low press)
Chemoreceptors
Location: special senses, skin/viscera
E.g. olfactory/taste receptors
Nociceptors, osmoreceptors and glomus cells
Photoreceptors
location: Special sense (eye)
E.g. retinal rods and cones
Thermoreceptors
Location: skin/CNS
E.g. warm/cold (exoreceptors)
Temp. Sensing neurons in hypothalamus (interoreceptors)
The ear
External: the pinna directs sound waves into ear and down ear canal
Middle ear:
Tympanic membrane
Malleus/incus/stapes bones
Round and oval windows open to inner ear
Eustachian tube links to pharynx
Inner ear:
Semicircular canals branch off vestibular apparatus of the cochlea
Nerves connect to vestibular
Cochlea contained in ‘labyrinth’
Eustachian tube
Connects middle ear to nasopharynx
Allows equalisation of air pressure between middle ear and outside
Psuedo-stratified respiratory epithelium
Numerous goblet cells
Dilates during swallowing and yawning
Tympanus membrane
Attached to middle ear bones (ossicles)
Which pull membrane inwards and impart tension
External cuticular layer
- thin hairless epidermis and dermis
Middle, fibrous (connective tissue) layer
-type ll and type lll collagen fibrils with small amount of type l
- combination unique to requirements of the tympanum
Inner mucous layer
-continuation of respiratory epithelium of eustachian tube
- single layer of cuboidal cells
- devoid of cilia and goblet cells
- also covers ossicles
Middle ear
Ossicles conduct movement of tympanum to oval window of inner ear
Synovial joints between bones
Muscle attach to stapes and malleus to dampen vibration
- tensor tympani & stapedius
- responsible for attenuation reflex
-contraction of these muscles helps avoid damage to inner ear as result of loud sound
Inner ear
Function
Detection of sound
Detection of motion and position of head
Balancr
Sound transmission
1) transduction waves become vibrations at ear drum
2) energy transferred to ossicles
3) 2nd transduction: vibrations of oval window create fluid waves in cochlea
4) 3rd transduction: fluid waves push on membrane of cochlear duct. Hair cells (organ of Corti) bend and NT released
Kinocilia and stereocilia
Mechanoelectric - convert mechanic energy to electric energy
Respond to motion by opening ion channels in membranes.
Linked to an afferent nerve that sends info to the brain
Cochlea to brain
Organ of Corti - hairs move in response to sound (stereociliar bend)
Waves lead to electrical signals in cochlea
Primary sensory neurones send information to the brain (medulla oblongata)
Sound projected to nuclei - main pathway synapses in nuclei in midbrain and thalamus - auditory cortex
Mechanoelectric transducers - kinocilia and stereocilia
Respond to motion by opening ion channels in their membrane
Not nerve cells - no action potential
Resulting change in internal ionic composition causes neurotransmitter release
-mechanical deflection induced K+ influx
-cell depolarises
- voltage gated Ca2+ channels open in basolateral surface
- release of neurotransmitter into synaptic cleft
Synapse with a sensory nerve which depolarises in response to neurotransmitter release
Organs of Corti - hair cell rows
Inner row perceives sound and is connected to the cochlear nerve
Outer row forms an acoustic preamplifier (has no nerve connection)
Cochlea
Thicker at end that meets the middle ear . This end is linked to oval and round window then there is the saccule, vestibular duct (top) and tympanic duct (bottom), cochlear duct, organ of Corti and at far thin end the helicotrema.
The frequency of sound waves determines the displacement of the basilar membrane (that runs down centre of cochlea) The location of active hair cells creates a code that the brain translates as info about pitch of sound
Basilar membrane has variable sensitivity to sound along its length:
Stiff region near window detects high freq/pitch
flexible region near helicometra (distal end) detects low freq/pitch
Vestibular apparatus: balance
Vestibular apparatus of the inner ear responds to change of body position in space. The christae are sensory receptors for rotational acceleration. The maculae are sensory receptors for linear acceleration and head position.
Superior canal: nod for yes
Horizontal canal: shake for no
Posterior canal: head tilt left/right
Endolymph on cupula
Movement of the endolymph pushes on the gelatinous cupula and activated the receptors
When head turns right endolymph pushes the cupula to the left so endolymph moves in opposite direction to head
