CNS 4 Good
CNS 4 Good
CNS 4 Good
Cochlea
• Waves in cochlear fluid set the basilar membrane in vibratory motion
– Movement in basilar membrane stimulates mechanosensory (hair cells)
to transduce mechanical waves to neural signals
• Receptive hair cells are bent as basilar membrane is deflected up and down
– Mechanical deformation of specific hair cells is transduced into neural
signals that are transmitted to thalamus and then on to the auditory
cortex in temporal lobe of brain for sound perception
• Contains receptors for conversion of sound waves into nerve impulses, which
makes hearing possible
Hair cells
• Receptors for sound
• Inner hair cells and outer hair cells
• Protruding from each hair cell are stereocilia, which contact the tectorial
membrane
Vestibule apparatus
• Located in the inner ear
• Provides information necessary for sense of equilibrium and for
coordinating head movements with eye and postural movements
• Two sets of structures:
– Semicircular canals
– Otolith organs
• Detects orientation and motion relative to axis of gravity
• Vestibular apparatus is divided into two senses
– Static equilibrium (Saccule)
• Responsible for vertical linear acceleration
• Orientation of the body relative to the gravity
– Dynamic equilibrium (utricle)
• Responsible for linear acceleration in the horizontal
• Senses movement of the head in space
Semicircular canals
• Detect rotational acceleration or deceleration in any direction
• Hair cells situated on top of ampulla
• Hair cells embedded into gelatinous layer, the cupula
Role of semicircular canals
• Neural signals generated in response to mechanical deformation of hair
cells by specific movement of fluid and related structures – rotational
movement
• Acceleration or deceleration during rotation of the head in any
direction causes endolymph movement in at least one of the
semicircular canals
i. When you rotate head to the right, due to inertia, endolymph
stays in stationary position and as semicircular canals rotate,
the fluid rushes over to specialized detector and bends the
entire hair cells
• Vestibular input goes to vestibular nuclei in brain stem and to cerebellum
for use in maintaining balance and posture, controlling eye movement,
perceiving motion and orientation
Otolith organs
• Otolith organs: utricle and saccule
– Provide information about the position of the head relative to gravity
• Utricle detects changes in rate of linear movement in
acceleration and deceleration (horizontal)
• Saccule provides information important for determining head
position in relation to gravity away from a horizontal position
(veritical)
2. Explain sound waves
• Intensity (loudness)
– Depends on amplitude of air waves
– Measured in dB (decibels)
• Every 10 dB indicates a tenfold increase in loudness
– Translated through to cochlea where it produces either low
frequency or high frequency firing of autitory nerve axon
• Timbre (quality)
– Determined by overtones
• other quieter frequencies added on to the main pitch
frequency
– ability to distinguish different voices
Sound waves are detected in the ears by their movement through the pinna,
to the tympanic membrane.
- Vibration of the tympanic membrane causes movement of the middle
ear bones>malleus, incus, stapes. The movement of the stapes
causes movement of the oval window at the beginning of the cochlea, this
sound can move one of 2 ways:
Outer ear
- Consists of pinna, external auditory meatus, and tympanic membrane (ear
drum)
o Sound is gathered in pinna, sound is funneled into external auditory
meatus and reaches tympanic membrane
Tympanic membrane is stretched along the entrance to air-filled
middle ear
Tympanic membrane separates outer and middle ear
Air filled external ear is separated from air-filled middle ear by
tympanic membrane
Membrane vibrates when struck by sound
- Transmits airborne sound waves to fluid-filled inner ear
- Amplifies sound energy
– auricle (pinna) [cartilage covered with skin]
– gathers sound wave from the environment and feed it to external
auditory canal
– external auditory canal (acoustic meatus)
– passes on through the canal to eardrum
– tympanic membrane or eardrum [skin and connective tissue]
Middle ear
- Transmits airborne sound waves (via vibration in tiny bones) to fluid-filled
inner ear
- Air filled middle ear, we find 3 bones: Malleus, Incus, stapes
o These carry vibration from tympanic membrane to oval window of
cochlea (fluid filled structure)
Requires amplification in the vibration to go from air-filled to fluid-
filled structures
- Amplifies sound energy
- Vestibule
o Necessary for sense of equilibrium
o Consists of utricle and saccule
Contain hair cells (otolithic membrane)
Makes maculae
o Special detector for static equilibrium
• Bony labyrinth
– Tortuous channels worming their way through the temporal bone
– Contains the vestibule, the cochlea, and the semicircular canals
– Filled with perilymph
• Membranous labyrinth
– Series of membranous sacs within the bony labyrinth
– Filled with a potassium-rich fluid (endolymph)
6. Compare static and dynamic equilibrium and describe the structure and
function of receptor organs for equilibrium
Outer bony labyrinth
Vestibule
o Made up of Perilymph
: high Na / low K
- Contains within Inner membranous labyrinth filled with endolymph
- Saccule & utricle
o Inside saccule and utricle, special detector ‘Macula’ is present
Semicircular canal
- When your head moves around, the liquid inside the semicircular canals
sloshes around and moves the tiny hairs that line each canal.
- These hairs translate the movement of the liquid into nerve messages that are
sent to your brain. Your brain then can tell your body how to stay balanced.
- detect rotational or angular acceleration or deceleration of the head, such as
when starting or stopping spinning, somersaulting, or turning the head.
- receptive hair cells of each semicircular canal are situated on top of a ridge
located in the ampulla.
- The hairs are embedded in a gelatinous layer, the cupula, which protrudes
into the endolymph within the ampulla.
o The cupula sways in the direction of fluid movement, much like
seaweed leaning in the direction of the prevailing tide.
- Rotation of head causes endolymph movement in the canals
o Initially, fluid does not move due to inertia
o When fluid moves cupula leans in opposite direction of head roation
bending the sensory hairs embedded in it, causing depolarization