PART 2 Flashcards
What is the echo delay?
this provides information about the distance of target
what is doppler shift?
this occurs when bats send out a signal and sound waves are compressed such that the frequency of the returning echo is different from the pulse
FM/FM area
neurons are tuned for echo delays. We see that across the structure, neurons are tuned to increasing echo-delay
CF-CF area
neurons only respond when the CF of pulse and CF component of echo are present. It maps the target velocity and it increases across the structure
acoustic fovea
this is the range in which the bat has optimal sensitivity, this area is overrepresented in the cortex
doppler shift compensation
when the bat sends a pulse, due to the Doppler shift the returning echo frequency may be above or below the acoustic fovea.
Therefore, this mechanism the bat reduces the frequency of the outgoing pulse so the returning echo frequency falls within the acoustic fovea
hypothesis for echo delay
the neurons in the FM/FM act as coincidence detectors such that it must receive signal from the individual neurons of inferior colliculus.
[in IC] the FM1 neuron only responds to the pulse while FM2 neuron only responds to echo
A delay line may be present in order for both signals to convert in the FM/FM area
Describe the pathway of auditory system (mammals)
cochlea –> cochlear nuclei –> superior olive –> inferior colliculus –> medial geniculate nucleus (thalamus) –> A1
auditory pathway in owls
auditory nerve –> Nucleus Magnocellularis (NM) –> Nucleus Laminaris (NL) –> External nucleus
Gustatory pathway (mice)
Gustation sensory –> Geniculate ganglion –> Nucleus of solitary Tract –> parabrachial nucleus –> thalamus –> gustatory cortex
Geniculate Ganglion
experiment showed single-tuned cells and double-tuned cells (which shows that there may be some convergence of info)
Nucleus of Solitary Tract (NST)
in Medulla
Use GCamp and 2-photon microscopy
- found bitter and sweet cells
- sst (somatostatin) and calbindin
- cells are intermingled with no topographical organization but this does not affect the label line coding
Gustatory cortex part of the Insula
- there are hot spots enriched with bitter or sweet (there are hotspots of taste modalities)
Top-down control from gustatory cortex
- gustatory cortex bitter cells activates the amygdala neurons which inhibits sweet cells in the NST
- GC bitter cells enhances activity of bitter cells in NST
acronym for the six layers of cortex
AHIPF
(axon, horizontal, input, projection, feedback)
AHIPF - Explain A
layer 1 only has axons, no cell bodies
AHIPF - Explain H
layer 2/3: axons project horizontally across cortical columns to provide integration of information
AHIPF - Explain I
layer 4: the main input layer for somatosensory information, this is the first layer that receives information from the thalamus
AHIPF - Explain P
layer 5: layer that projects to other cortical layers and other parts of the brain
AHIPF - explain F
layer 6: layer that sends feedback information to the thalamus, important for gating the information that comes into the layers
RA1
mechanoreceptor that is rapid adapting and has a small RF
- important for later motion
SA1
mechanoreceptor that is slow adapting and has a smaller RF than RA1
- provides faithful representation of dots
RA2
rapid adaptive, but has larger RF
- vibration
SA2
slow adaptive
- skin stretch
Name the aspects of somatosensory
intensity: rate of AP firing
timing: sudden change in AP firing
location: where the stimulus occurs and how many receptors are present
modality: depends on the types of receptors
the homunculus
this explains the representation of body parts in the cortex
the body parts that are innervated by more mechanoreceptors are overrepresented in the cortex
cortical columns
an electrode was inserted vertically and Mountcastle discovered that the neurons responded to the stimulus
–> this led to the idea that there are cortical columns
- these columns represent the somatosensory map
why is it important to have different receptive field cells?
they convey different information about the stimulus
- some may encode for the movement of stimulus while others for the shape
motor unit
a motor neuron and the fibers it innervates
motor neuron pool
located in the spinal cord, includes all motor neurons that innervate one muscle
where are alpha motor neurons found
they are found in the ventral horn
transmission at NMJ
Spike reaches presynaptic side of alpha neuron –> this depolarization opens ca2+ vchannels –> vesicles release Ach into the synaptic cleft –> Acytocholine binds to nicotinic AChR –> muscle fiber depolarizes
spike in muscle fiber
muscle fiber depolarization opens Na+ vchannels –> AP in muscle fiber is generated –> Ca2+ release from the ER
contraction via ca2+
ca2+ binds to troponin –> actin + myosin contraction
small motor unit size
innervates few slow fibers, produces low force but firing does not fatigue
Large motor unit
innervates many fast fibers that generates large forces but fatigue quickly
Brain control of muscle force
- the size principle of recruitment of motor units
- firing rate of alpha neurons
size principle of recruitment of motor units
with increasing strength of input onto motor neurons, smaller motor neuron units are recruited and fire action potentials before larger motor neurons are recruited.
a small amount of synaptic current will be sufficient to cause the membrane potential of a small motor neuron to reach firing threshold, while for large motor units, more current is necessary to reach threshold
firing rate of alpha neurons
changing the firing rate of alpha neurons within one motor unit will change force
- if the rate of firing of the motor neuron increases, such that a second action potential occurs before the muscle has relaxed back to baseline, then the second action potential produces a greater amount of force than the first –> eventually there can be summation
feedback control
spinal circuits receive feedback from sensory system to correct movements
stretch reflex
alpha only
stretch sensed by muscle spindle –> 1a afferent (stretch receptor whose body is in DRG) synapses directly on alpha motor neurons –> alpha neurons fire –> causes reflex contraction of the muscle
muscle spindle
stretch receptors that sense change in muscle length
stretch reflex
inhibitory neuron
stretch receptor afferent is activated and it synapses directly to alpha neurons and interneurons (inhibitory) in spinal cord –> the firing rate of inhibitory interneuron increases –> this synapses with alpha neuron(2) of antagonist
muscle –> firing rate of alpha neuron(2) decreases –> muscle relaxes
basal ganglia
nuclei important for the initiation of motor movement
- it includes the substantia nigra compacta which has dopaminergic neurons
Dopamine
a neurotransmitter that acts as a neuromodulator
- MAO: enzyme that oxidizes it in presynaptic
-DAT: re-uptake transporter
- VMAT: vesicle transporter
D1 receptor
involved in the direct pathway
Gs –> adenylyl cyclase is activates –> ATP to cAMP –> cAMP binds to PKA –> enzyme that can phosphorylate channels and open them
D2
involved in the indirect pathway
Gi–> adenylyl cyclase is inhibited–> less ATP to cAMP –> less cAMP binds to PKA
Dopamine synthesis
it has two precursors:
1. tyrosine –> DOPA –> dopamine
2. Epinephrine –> norepinephrine –> Dopamine
Regulation of neurotransmission
dopamine concentration must be regulated:
- DAT:transmitter reuptake
- glial cells also have reuptake systems
- it can also diffuse
Direct pathway [basal ganglia]
Substantia nigra compacta and motor cortex send gluta info –> D1 in striatum receives it –> more GABA is released from striatum to GPi and substantia nigra pars reniculata –> less GABA is released to the thalamus
indirect pathway
substantia nigra compacta nd cortex send glutamate –> D2 in striatum receives it –> GABA is sent to GPe –> GPe sends less GABA to STN –> STN receives less inhibition thus it sends more Glu to GPi and substantia nigra reticulata –> GABA to thalamus
name the three deep nuclei
dentate
interposed
fastigial
name the 3 pathways for motor control
cerebrocerebellum
spinocerebellum
vestibulocerebellum
1st direct pathway
inferior olive –> climbing fiber (+) –> PC
(complex spikes)
2nd direct pathway
spinal cord and brainstem –> mossy fibers (+) –> Granule cells –> parallel fibers (+) –> PCs
(simple spikes)
innermost layer of cerebella cortex
Granulate layers
- Golgi (-)
Granule (+)
middle layer
Purkinje cell (-)
outer layer
molecular layer
- Basket (-)
- stellate (-)
indirect pathway 1
later inhibition
Granule cells –> parallel fiber (+) –> stellate and basket (-) –> PCs
indirect pathway 2
negative feedback
- Granule cells –> parallel fibers (+) –> golgi cells (-) –> Granule cells
functions of cerebellum
motor learning
eye- hand coordination
Vestibulo-ocular reflex (VOR)
vestibulo-ocular reflex
this is the coordinated response to keep eyes fixed on the target when head is rotated
- in order to maintain the image maintained, there is a linear relationship and the cerebellum is important for this reflex
VOR adaptation
the cerebellum is involved in this process
- when the image moves when you move your head, such that as your head moves, there is no linear relationship –> it triggers an error signal in the climbing fibers such that the next time when same condition occurs, eye movement will match head movement due to parallel fibers sending adjustment signals
* lession in the cerebellum = no adaptation
VOR adaptation pathway
eye movement –> inferior olive –> climbing fibers –> PC
vestibular system –> mossy fiber Pc
eye-hand coordination
placing a prism on person’s eyes increases the likelihood of that person throwing the dart off-center, however, after 30 tried, the person learns to correctly throw the darts
but people with damages in the cerbellum show no adaptation
two ways the brain controls muscle force
- the principle of recruitment of motor units (the brain sends synaptic input to the motor neuron pool, and as it sends stronger input it starts to recruit from the small motor units to the larger motor units which generate large forces)
- by changing the firing rate of alpha neurons, the brain can affect what motor force is generated. for example, high firing rate results on the summation of APs resulting in generating a larger force
lateral projections on Projection neurons (PNs)
this lateral lateral connections to cells in the glomeruli are important because they adjust the dynamic range, tunning PNs to be able to distinguish among different neurons
convergence in fly
this occurs because there are around 1400 Olfactory senstory neurons that project to glomeruli, here they synapse to 150 PN
the PNs pool information from the ORN thus reducing noisy input by signal avereging
divergence in fly system
from 150 PNs to 2500 MBNs
- responds only when combinations of PNs are activated
-
sparse code in MC neurons
the odor is represented by different combination of same set of underlying neurons
PNs synpase into KCs and these cells can encode different odors based on the combination that they receive
Piriform cortex
cortical area that receives input from mitral cells with no discernable patterns, cells that respond to the same odor are distributed broadly
- but each neuron can respond to more tha one odor (note: not all neurons are activated at the same time)
coding in piriform cortex
- sparse: few neurons are involved in coding for one neuron
- combinatorial: each neuron can respond to more than one odor, thus odor is represendted by grouped of neurons
amygdala
it has orderly spatial patterns
- a more ordered distribution that follows the patterns in the olfactory bulb
- important for innate behavior
labeled line in olfaction
1 receptor type olfactory neuron –> goes to 1 glomerulus
(but this only describes the receptor-neuron projection, do not get it confused because a neuron can respond to multiple odorants)
combinatorial (olfaction)
odor is represented by overlap population of neurons –> group of active glomeruli encode for one odor
expression of T2Rs
bitter receptors can be co-expressed in the same cell because animal does not need to identify the bitter compound, it just needs to detect it.
expression of T1Rs
they are not expressed on the same cell
labeled line: bitter cells express bitter receptor and sweet cells express T1Rs
bitter vs sweet cells
each taste receptor cell expresses one receptor type –> labeled line for modality
BUT for bitter, one cells can express many different T2Rs
taste perception
the type of cell is required for perception, not the type of receptor expressed
Example: bitter receptor expressed in sweet cells, when given a bitter tastant, preference increased
taste pathway in the mouse brain
sensory nerves –> geniculate ganglion –> NST (medulla) –> Pbn (Pons) –> thalamus (VPM) –> Gustatory cortex
tonotopic map of auditory nerve fibers
this map is created by presenting sound at different frequencies and identifying the minimal frequency for a auditory nerve to fire
- this shows that different auditory nerve fibers are tuned for specific frequencies, although they can still respond to broader freq, their optimal activity is at specific frequencies
pattern recognition in A1
this area has higher function of identification, it can detect frequency transitions (pitch) or fM sweeps
patter recognition in belt area
more identification across spectro-temporal RF, it can identify different phonemes, or natural sounds and show preference to where sound may be coming from
receptive field
this is the region of space where stimulus can alter the firing rate of a neuron
fours aspects of sensory coding
how spiking of neurons encode for the physical stimuli
- intensity
- timing
- location
- modality
intensity
encoded the by the firing rate
the size of APs do not change, only the rate at which they fire
modality
different type of receptors encode for different types of touch –> labeled line
although many cells can overlap, they habe their own labeled line that gets sent to the brain
