final Flashcards
Acoustic radiation
Axons leaving the mgn project to auditory cortex via the internal capsule in an array called acoustic radiation
Damage to auditory areas and hearing
A normal degree of hearing can be retained after unilateral lesions in the auditory cortex (this is not the same for hearing). But because of tonotopic organization in A1, its possible to make a restricted cortical lesion that destroys neurons with characteristic frequencies within a limited range
Mcgurk effect
Our hearing is largely based on vision
Strips of neurons running across a1 contain neurons that have fairly similar characteristic frequencies
Isofrequency bands
Auditory receptive fields vs visual receptive fields
We cannot place auditory receptive fields into simple/complex categories like visual fields
Cortical neurons have different temporal response patterns, some have a transient response to a brief sound while others have a sustained response
stimuli that evokes the strongest response in higher auditory
tend to be more complex than those that best excite neurons.
Some neurons are intensity tunes and give a peak response to a particular sound intensity
Isofrequency bands
Strips of neurons running across a1 contain neurons that have fairly similar characteristic frequencies
Example of tonotopy
Moving from base to the apex of the cochula, a progressive decrease in frequency that produces a maximal deformation of the basilar membrane
Tonotopy
When the baslair membrane resonates with a particular frequency in a particular spot
Tonotopic organization also occurs within the primary auditory cortex.
How different frequencies are represented by brain stem neurons
At low frequencies, phase locking is used
At intermediate frequencies, both phase locking and tonotopy are used
At high frequencies, tonotopy must be used to indicate sound frequency
Phase locking
Constant firing of cell at the same phase of a sound wave(at low frequencies some neurons fire action potentials every time the sound is at a particular phase. This makes it easy to determine the frequency of sound since it is the same as the firing frequency of the neurons action potential
How is frequency represented in Specific Movement of basliar membrane
Hair cells near apixal basilar membrane have characteristics of low frequencies
Hair cells near basal basilar membrane have high characteristic frequencies
There is a map of basilar membrane within cochlear nuclei
Auditory nerve fibers fire faster to same sound frequencies when the intensity is increased. What does this do to the basilar membrane
Produces movements of basilar membrane over greater distance and leads to activation of more hair cells. Increase in activated hair cels cause a broadening of the frequency range to which the fiber responds.
Loudness we perceive is correlated with..
Number of active neurons in the auditory nerve and their firing rate
Characteristic frequency
A neuron has characteristic frequency when it is most responsive to one frequency. Its less responsive to neighboring frequencies
Nature of input from the neurons in the spinal ganglion of the cochlea
Most spiral ganglion cells receive input from a single inner hair cell at a particular location on the baslar membrane.
Each Cochlear nucleus receives input from
Just one ear on the ipsilateral side (all other auditory nuclei in brain stem receive input from both ears)
Ways for extensive feedback for auditory pathways
Auditory cortex sends axons to MGN and inferior colliculus
Brainstem sends axons that contact outer hair cells
Projections from brainstem to other auditory pathways
Inferior colliculus sends axons to superior colliculus
Cerebellum
Outer hair cells
Axons in superior olive then intervate to..
Inferior colliculus in midbrain
Where does integration of auditory and visual information occur
Superior colliculus (inferior colliculus sends axons here)
Cells in ventral cochlear nucleus send axons to..
Superior olive (on both sides of brain stem)
Medullas sound processing structures
Dorsal cochlear nucleus
Ventral cochlear nucleus ipsilateral to the cochlea where the axon is originated)
Protein essential for outer hair cells motor and cochlear amplifer functioning
Prestin
Decending input from brain to cochlea
Regulates auditory sensitivity
Effect of outer hair cells on the response of inner hair cells can be modified by..
Neurons outside the cochlea
Theres also fibers projecting from the brain stem to the cochlea
They can synapse onto outer hair cell and release Ach (this can change shape of outer hair cell and therefor affect response of inner hair cell
stages of amplification by outer hair cells
starts with motor proteins in membranes of outer hair cells
bending of stereocilia acauses K to enter hair cell and depolarizes it
this triggers motor proteins to activate and change length of hair cell
this increases the flexing of basilar membrane
Conchular amplifier
Outer hair amplify movement of baslar membrane during low intensity sound stimuli
- They involve motor proteins (only found in membrane of outer hair)
- Outer hair cells respond to sound by both receptor potential and change in length
- When outer hair amplify response of baslar membrane, inner hair cells bend more and produces a greater response in the auditory nerve
What does the spiral ganglion mostly communicate with
Inner hair cells (less than 5% receive output from outer hair even though they are more abundant)
are inner hair cells or outer hair cells more abundant
outer hair. 3/1.
Displacement of cilia in one direction..
Increases tension on tip link and increases amount of K movement
-Entry of k causes cell to depolarize (different from normal neurons because of high k concentration in endolynph)
this entry of k causes volted gated calcium channels to open
-incoming calcium lead to release of NT from synaptic vesicle then diffuses to postsynaptic neurite from spinal ganglion
Ion channel and tip of stereocilium
Ion channel opens and closes when stereocilium is bent
They only have two channels at the tip and the entire hair cell may only have 100
What happens with extremely loud sound..
Receptor potential of hair cell is saturated and tips of stereocilia move about 20nm to the side. This can cause damage
Lateral motion of the reticular membrane bends stereocilia on outer hair one way or the other…
One direction depolarizes while the other hyperolerizes
When baslar membrane moves up…
Lamina moves up and toward the modiolus (opposite happens when it it moves down)
how to restore hearing when auditory nerve is still intact
cochlear implant artificial cochlea)
whats the most common case of deafness
hair cell damage
what happens when basilar membrane moves in response to a motion at the stapes
entire foundation supporting the hair cells move because the basilar membrane, rods of corti, reticular lamina and hair cells are rigidly connected
spiral ganglion
bipolar neurites extending to the bases and sides of the hair cells where they receive synaptic input
-axons from these cells enter the auditory vestibular nerve which projects to the cochlear nuclei in the medulla
what kinds of cells are hair cells
specialized epithelial cells
outer hair cells location
farther out than rods of corti
critical event for transduction of cells into neural signals
bending of celia
organ of corti and its function/structures
place in ear where neurons are first involved. Converts mechanical energy into change of membrane depolarization
has hair cells with stereocilia extending from top
response of basilar membrane to sound
high frequency sound produce waves traveling wave which dissipates near the arrow and stiff base of the basilar membrane
low frequency-wave propagates all the way to the apex of basilar membrane before disssapating
Tonotopy
Systematic organization of sound frequency within an auditory structure
(like retinotopy in visual system)
Hebbian synapses
Neurons that fire together wire together
Apoptosis
Expression of cell death genes cause neurons to die. This process is apropos
Neurotrophins
A family of Tropic proteins. Nerve growth factors was one of these.
Neurons compete with one another for limited quantities of trophies factors produced by target neurons
Tropic factors
Life sustaining substances that are provided in limited quantities by target cells
Auditory pathway
Auditory receptors (cochlea/ganglion)
Superior olive (brain stem)
Inferior colliculus?
MGM
auditory cortex
Visual pathway
Photoreceptors
Retinal neurons
Lgn
Visual cortex
Outer hair cells
Receive signals from the brain and serve as mini biomechanics amplifier
Attention
Loud noises damage cells
Inner hair cells
Carry nerve signal of sound along the auditory to the brain
What are the ossicles
Mallius
Incus
Stapes
What happens during protective attenuation reflux
The tensor tympani muscle and stafpedius muscle lock down the middle ear within 50-100ms
Ganglion cells combine to form the receptive field of…
A single LGN cell
The receptive fields of many LGN cells combine to form the receptive field of..
A single V1 cell
What are the five vertebrae regions
Cervical nerves
Thoracic nerves
Lumbar nerves
Sacral nerves
What are the three cuts
Midsaggital
Horizontal
Coronal
Basal telencephalon function
Helps with initiating voluntary movement. Cortex communicates with neurons in basil ganglia, a collection of cells in basal telencephalon
Amygdela is located here which is involved in fear and emotion
Thalamus function
Send axons to the cortex via internal capsule .
It’s considered gateway to cerebral cortex because of sensory pathways serving vision and audition and somatic sensation relays in thalamus
Hypothalmus function
Controls autonomic nervous system and regulates body function in response to organ
Fight or flight response
Hormones
Pon function
Connection cerebral cortex to cerebellum
Medulla function
Relay information from spinal chord to thalamus such as taste and feeling.
Telencephalon
Deals with high level processing
Diencephalon/thalamus
Supports mammalian brain, parenting and four basic f’s
Midbrain
Helps keep us safe. Deals with visual orientation and motor reflexes
Hindbrain
Controls physiological needs and homeostasis
Tract
CNS axons
Nerve
PNS axons
Locus
Well defined group of cells
Ganglion
Collection of neurons in PNS
Substantia
Less distinct borders of group of neuron
Nucleus
Well defined group of neurons
Corner function
Acts as first lens and has focusing power by refracting light.
Where is central part of vision located
Back of brain
Where is perennial areas of visual field located
More Anteriorly
Top part of visual field is located ____
Bottom is located ____
Top-lower part
Bottom-upper part
Where is central part of vision located
Back of brain
Where is perennial areas of visual field located
More Anteriorly
Top part of visual field is located ____
Bottom is located ____
Top-lower part
Bottom-upper part
Number of rods
100 million
Number of cones
5-6 million
Number of ganglion cells
It has about 50 rods and cones. In fovea ganglion cells gave 12-20 of them for high definition
What is center surround receptive fields
Two concentric areas with antagonistic responses to light on and light off
What is reFLECtion
Light rays bouncing off a surface
Only retinal neurons that fire action potentials
Ganglion cells
What is a receptive field
Area of retina that when stimulated with light, changes a cells membrane potential
What is dark current
Photoreceptors are depolarizer in the dark because of a steady influx of sodium ions
What is focal distance
Refractive surface to point where parallel rays converge
I why do we say that ganglion cells are mainly responsive to differences in illumination that occur within receptive field
Center surround ganglion cells respond best when a light or dark edge falls at boundary between the center and surround regions of receptive field
Which layer of retinal neurons has axons leave retina
Ganglion cells
Spatial sensitivity of green cone pigment
530 nm
What is meant by phototransduction
Process that occurs hen photoreceptors convert light energy in neuronal membrane potential
Why is retina said to be duplex
It works under both scotopic and photopic lighting conditions
Distinguish between m cells and p cells
M cells respond with transient burst of action potentials and p cells respond with a sustained discharge
What is visual acuity
Ability of the eye to distinguish two nearby points
Choroid plexus
Produce CSF and form blood CSF barrier
Nucleus
A clearly distinguishable mass of neurons usually deep in the brain
Substantia is like this but with less defined borders
What does Weber’s law state
The brighter the light, the more change in brightness is required for us to notice a difference
What does Weber’s law state
The brighter the light, the more change in brightness is required for us to notice a difference
Henninger synapses
Synapses that can be modified
Hebbian modifications
Synaptic rearrangement
Retinal activity and synapses
Whenever a wave of retinal activity drives a postsynaptic LGN neuron to fire an action potential, the synapse between them are stabilized
Cells of V1
They detect direction of certain properties (lines, orientation, edges)
They are automatic and fast
Simple cells
Have excitatory and inhibitory areas
They respond most to lines or bars of orientated light
Complex cells
No fixed excitatory or inhibitory areas
They respond most to a moving line or bar
Hyper complex cells
Primary stimuli is a moving bar of light like the complex cells except the bar has an end
Located in V1 and v2
Hyper complex cells
Primary stimuli is a moving bar of light like the complex cells except the bar has an end
Located in V1 and v2
What does the peripheral nervous system (PNS) consist of?
Nerves and ganglion outside of the brain and spinal cord. Its not protected by bone or the blood brain barrier like the CNS so its more exposed to toxins and mechanical injuries
What is a way to avoid spine bediphia
Folic acid
What are the divisions of the PNS?
Somatic nervous system-associated with body under voluntary control. (cell bodies of somatic motor neurons are in CNS but axons in PNS) (somatic sensory neurons lie outside of spinal cord in clusters called dorsal root ganglia. There is a dorsal root ganglia for each spinal nerve)
Autonomic nervous system-involuntary control over smooth muscle and glands. Also called visceral PNS. It rings info about visceral functions to CNS such as oxygen content in blood.
Somatic nervous system
associated with body under voluntary control. (cell bodies of somatic motor neurons are in CNS but axons in PNS) (somatic sensory neurons lie outside of spinal cord in clusters called dorsal root ganglia. There is a dorsal root ganglia for each spinal nerve)
Autonomic nervous system
involuntary control over smooth muscle and glands. Also called visceral PNS. It rings info about visceral functions to CNS such as oxygen content in blood.
What are the divisions of the autonomic nervous system?
Sympathetic nervous system-fight or flight (stimulatory)
Parasympathetic nervous system-rest and digest (inhibitory)
What happens if dura is ruptured?
Blood can collect in between dura and arachnoid which is called a subdural hematoma. This buildup of fluid can disrupt brain function by compressing parts of CNS. This can be fixed by drilling a hole in the skull
What is the binocular visual field?
The central portion of both left and right hemifields put together
Ocular dominance columns
Bands of cells extending through the thickness of the striate cortex. They contain neurons with input dominated by one eye and the columns alternate between left and right eye
Orientation selectivity
Neurons that prefer a particular orientation. Thee neurons can be in columns called orientation columns. Their greatest response is given to a bar with a particular orientation
Organization of the lgn
Its arranged in six distinct layers of cells. Different types of retinal info are being kept separate at this synaptic relay
How do neurons of retinal ganglion cells and lgn cells respond to stimulation pf their receptive field centers?
Increase in the frequency of action potentials.
How to record a ganglion cells receptive field
Record the neurons axon in the optic nerve
Small spot of light projected onto retina
Receptive field consist of locations that increase or decrease cells firing rate
Move light to map region of the visual field that causes spiking in the ganglion cell
(light anywhere outside of its field will have no firing rate)
What is the membrane potential of rods photoreceptos in the dark
-30mV
steps of transduction of light by rods
light bleaches rhodopsin
g protein is stimulated
effector enzyme is activated
PDE (the effector enzyme) reduces cGMP level
Na+ channels close and cell membrane hyperpolarizes
Role of calcium in light adaptation
Ca2+ enters a cone through he same cGMP channels as Na. it inhibits the synthesis of cGMP
what happens when dark in ganglion cells hits middle receptive field vs when its in the areas that surround the center of receptive field?
Center-cell depolarizes
Surround-hyperpolarize
If darkness fills the surrpund, the center response is canceled
