Flashcards in Neurophysiology (Part 2) Deck (108)
Describe the optic pathway from the retina to the CNS
Axons from the retinal ganglion cells form the optic nerves and optic tracts, these synapse in the lateral geniculate body of the thalamus where they then ascend to the visual cortex in the geniculocalcarine tract
Nerve fibers from the ____ field cross at the optic chiasm and ascend contralaterally whereas nerve fibers from the ____ field remain uncrossed and ascend ipsilaterally.
What is hemianopia?
loss of vision in half of the visual field of one or both eyes
What are the 4 planes in which lesions can occur in the optic pathway?
1) optic nerve
2) optic chiasm
3) optic tract
4) geniculocalcarin tract
Lesion in the optic nerve causes loss of vision where?
Complete blindness on the side in which the optic nerve was cut
Lesion in the optic chiasm causes loss of vision where?
Loss of vision in the temporal fields in both eyes
Lesion in the optic tract causes loss of vision where?
Loss of temporal field vision in the eye opposite the lesion and nasal vision in the eye on the same side of the lesion (left tract lesion = right temporal field loss and left nasal loss)
Lesion in the geniculocealcarine tract causes loss of vision where?
Loss of temporal field vision in the eye opposite the lesion and nasal vision in the eye on the same side of the lesion (left tract lesion = right temporal field loss and left nasal loss) with macular sparing
The human ear is sensitive to tones with frequencies between __ and ____ Hz
20 - 20,000 Hz
*most sensitive only to 5000 Hz
Sound intensity greater than __ dB cab damage the auditory apparatus and those greater than __ dB can cause pain
What is the fluid in the scala vestibuli and scala tympani called? The composition of this fluid is similar to what?
extracellular fluid (high sodium)
What is the fluid in the scala media called? The composition of this fluid is similar to what?
intracellular (high potassium)
What are the 2 types of receptor cells in the organ of Corti?
inner and outer hair cells
*there are more outer hair cells
What are the 4 steps in auditory transduction?
1) sound waves are transmitted to the inner ear and cause vibration of the organ of Corti
2) this vibration causes bending of cilia on the hair cells by a shearing force as the cilia push against the tectorial membrane
3) the bending of the hair cells produces a change in K+ conductance of the hair cell membrane (depolarization can occur)
4) Depolarization opens voltage-gated Ca2+ channels which causes a release of excitatory NT which activates the afferent cochlear nerves and information is transmitted to the CNS
Describe the structure of the membranous labyrinth
It contains 3 perpendicular semicircular canals and 2 otolith organs, both in which are filled with endolymph and are surrounded by perilymph
Rotation of the head to the left stimulates the ____ semicircular canals, and rotation of the head to the right stimulates the ____ semicircular canals.
What are 2 tests that can test the integrity of the vestibular pathway?
- Barany test
> person is rotated in a special chair and nystagmus is observed
- Caloric test
> head is tilted back 60 degrees and then the ear is rinsed with warm or cold water to induce nystagmus
What does audition involve?
The transduction of sound waves into electrical energy, which can then be transmitted in the nervous system
How are sound waves produce?
With increases (compression) and decreases (decompression) in pressure
What is the usual range of frequencies in human speech?
300 to 3500 Hz
What does the external ear consist of?
the pinna and the external auditory meatus (canal)
What does the middle ear consist of?
the tympanic membrane and a chain of auditory ossicles called the malleus, incus, and stapes
What does the inner ear consist of?
a bony labyrinth that consists of 3 semicircular canals and a membranous labyrinth that consists of a series of ducts called the scala vestibuli, scala tympani, and scala media.
What is formed from the bony and membranous labyrinths of the inner ear?
the cochlea, which is a spiral-shaped structure comprised of 3 tubular canals or ducts that contains the organ of Corti
What is auditory transduction?
The transformation of sound pressure into electrical energy
Describe the process of sound makes as it travels to the inner ear
The external ear directs sound waves into the auditory canal which transmits the sound waves onto the tympanic membrane. When sound waves move the tympanic membrane, the chain of ossicles also moves, pushing the footplate of the stapes into the oval window and displacing the fluid in the inner ear.
What is considered the sensory transduction apparatus?
the organ of Corti
What structures in the inner ear are the sites of auditory transduction?
auditory hair cells
What cranial nerve serves the organ of Corti?
CN VIII the vestibulocochlear nerve