14

Typically 'presynaptic' and 'postsynaptic' are used to indicate two neurons that are connected, as you indicate correctly in your second example. Information flow in the nervous system basically goes one way. If one neuron fires (presynaptic cell) it can chemically activate another cell on which it synapses (the postsynaptic cell), as shown in the following ...


13

I basically agree with @Nick Stauner, but I want to add another important aspect, namely the gradient of photoreceptor densities in the human retina: In the fovea there is a sharp peak in cone density compared to more eccentric regions, as described in Curcio et al. (1990) and see the following graph obtained from Web Vision: The cones have a different ...


11

Basically, the retina contains two different kinds of receptors: rods and cones. Cones are concentrated in the fovea and activate ganglion cells more discretely than rods. Rods are more interconnected by horizontal cells (if I'm not mistaken...), so multiple rods can often activate the same ganglion cell, whereas each cone is more likely to have its own ...


10

There are two very different questions here. The first question is simple (although it could be interpreted a few different ways). The second question is very tricky and I am actually not certain we know the answer. 1. What do PSPs look like if the resting membrane potential is 0 mV? If a cell is being held at 0 mV, its voltage-gated conductances are ...


10

Apparently your question is on backward masking, which means that the masker follows the stimulus (probe) in time. Backward masking generally occurs at higher levels, typically the cortex. In case of visual stimuli this can be the primary visual cortex, or V1 (Mace et al. 2005). Ongoing processing of the probe is then thought to be interfered with by the ...


10

As far as I know, it is not possible for a neuron to change which type of neurotransmitter it releases. However, it is the case that the neurotransmitter GABA changes from excitatory to inhibitory over the course of development. This is occurs because GABA activates Cl- (chloride) channels. The chloride concentration gradient across the cell membrane ...


8

You are right that active adult neurogenesis is generally considered to be restricted to the dentate gyrus of the hippocampus, and the subventricular zone of the lateral ventricles. The latter generates neurons that subsequently migrate through the rostral migratory stream to the olfactory bulb to become interneurons (Ming & Song, 2011). Although the ...


8

This will be a long post. FYI. To my knowledge, there is no evidence for back propagation in the brain. If you're interested specifically in that topic, Geoffrey Hinton (Dept. of CS @ UofT) has written about it. I'll try to focus on the biology. Some basic neurophysiology first. Neurons have a slightly negative electrical resting potential (prototypically ~...


8

I assume you're referring to the experiment by Strack, Martin, and Stepper (1988) in which people rated a cartoon as funnier when they had to hold their face in a smile shape by gripping a pencil in their teeth. This has been applied to negative affect by Larsen, Kasimatis, and Frey (1992) who had participants furrow their brows during an activity. Golf ...


7

There are quite a few stations between cochlea and the brain and I will focus on the auditory nerve. That said, your theories (a) and (b) are both correct, and therefore (d) applies as well. (a) Neurons in the auditory nerve increase their firing rate when sound level is increased (Heil et al, 2011). This can be regarded as the primary mechanism for ...


7

Potential is relative, so having a negative resting potential simply means that the inside of the cell is negative with respect to the outside. Since an EPSP is going to be an overall positive change, yes, the negative resting potential does keep the cell at far below the threshold, but recall that over a short time duration, these EPSPs sum up to ...


7

I will try to answer all of your main and sub questions structurally below: How do neurotransmitters manage to depolarize the inside of the cell? Do they force the cell to give up pumping out Na ions? No, the Na,K-ATPase (the sodium potassium pump) keeps active, also during the action potential (AP). Do the neurotransmitters themselves contain positively ...


7

Short answer Hair cells in the cochlea can code sound intensity via the amount of neurotransmitter they release. Higher sound levels result in more neurotransmitter release and in turn to higher firing rates in the spiral ganglion cells of the auditory nerve. Background Sound waves are picked up by the mechanoreceptors in the inner ear: the hair cells. ...


7

EEG research all started with Hans Berger, who in 1929 reported that brain activity could be recorded by measuring electrical activity on the scalp. Although the notion of ‘brain waves’ that were found by Berger was controversial, over the years many researchers replicated the results, which led to the acceptance of EEG as a real phenomenon. Neurons Before ...


7

Cortical columns are groups of neurons in the brain that are oriented perpendicularly to the cortical surface. Cells within a column respond to the same stimulus property (Fig. 1). For example, primary visual cortex columns extract small bars with a specific orientation. A single cortical column consists of six distinct layers of neurons. The upper three ...


7

As far as I know, auditory clicks are the shortest possible auditory stimuli. The shortest auditory click I was able to find in the literature, and which was used in a psychophysical context (i.e., audible to a human) was 10 microseconds (Leshowitz, 1971). The longest sound we can hear is pretty much defined as a human's maximum age I guess. While the ...


6

From my undergraduate biology degree, I am only familiar with the second use of the terms which you describe. That is, the terms pre-synaptic and post-synaptic describe a spatial relationship to the synapse, which has directionality, as you know. If the terms are used to describe whole cells, as AliceD covers, and as people often do when describing a neural ...


6

Multipolar neurons have multiple inputs (dendritic connections), and one output (the axon).There are also bipolar cells in the retina, these have one dendrite (input) and one axon (output) (Nelson & Connaughton, 2012). Regarding dendrites: A striking example are the Purkinje cells in the cortex. These cells have elaborate dendritic trees making 100,000 ...


6

Short answer The retinal image corresponds more to a bitmap, than a vector-based image Background The retina contains a layer of about 100 million photoreceptors that are topographically organized. In other words, each photoreceptor codes one specific pixel in the field of view. In turn, the nerve fibers running from the eye to the brain are also ...


6

More dendritic input makes a neuron more suitable as an integrator. The more dendrites a neuron has, however, the less faithful it will transmit a single incoming signal, as other incoming input may interfere with transmission. Hence, a neuron with a single dendrite will be better suited to faithfully relay incoming signals. Among the most faithful ...


6

Objects are visually perceived when they reflect light. A black object does not reflect any light. In other words, no photons are reflected to be detected by the photoreceptors in the retina. A black shape on a colored background appears black because its brightness approaches zero relative to its surroundings. Black, as any other perceived hue, is a ...


6

In terms of the shortest stimuli, the auditory system can process acoustic impulses, but defining the duration of an impulse is problematic. As the duration of the impulse gets shorter, the bandwidth gets broader. A 25 us impulse has frequencies between 0 and 20 kHz, as you decrease the duration of the impulse you add higher frequency components such that a ...


5

There are other meanings of "potential" than the regular meaning "having or showing the capacity to become or develop into something in the future" (source: Google Translate). In case of "resting potential" it refers to the voltage difference across the cellular membrane. Every cell maintains a voltage difference across the membrane (see a related question ...


5

Interesting question! The paper you read should have inserted an appropriate citation. Moreover, "little input" is a subjective statement and doesn't make much sense in the context, as it can mean that there are few efferent axons (which may still have large effects on retinal functioning), or that the efferent input is relatively unimportant when compared ...


5

Short answer Muscles are controlled by motor neurons in the spinal cord. The number of motor neurons that fire, as well as their individual firing rates govern the control of muscle force. Background Muscles consist of contractile elements: the muscle fibers. These muscle fibers are under direct control of the motor neurons in the spinal cord (Purves et al.,...


5

Short answer A cap of magnets, or state-of-the-art TMS protocols, will not make you smarter. Background First off, TMS uses bursts of magnetic stimulation in the order of milliseconds (Rothkegel et al., 2010). Pulses of magnetic stimulation are used, because permanent magnetic fields will not induce current flow. Hence, wearing a cap of permanent magnets ...


5

Gap junctions can couple cells directly electrically. Cell types electrically coupled via gap junctions include neurons, the pancreatic islets of Langerhans (Andreu et al, 1997) and cardiac cells (Fig. 1.). In contrast to chemical synapses, information transfer via electrical "synapses" (gap junctions) is nearly instantaneous. In chemical information flow, ...


5

Caveat: I know very little about the structure of digital images. Assuming you mean the biological retina and not the prosthetic one, the Wikipedia page on color opponent process is quite good; basically, the four receptor types respond maximally to different wavelengths, and the ranges overlap slightly, so the visual cortex does the differences between the ...


5

Short answer Neurons can increase or decrease the amplitude of their response. A neuron's response strength can be regulated by adjustment of the cell-surface expression of excitatory receptors. Background First off, this question is very broad. To narrow it down I will focus on learning processes in the hippocampus involving long-term potentiation (LTP). ...


5

Short answer Intracortical projections can be routed directly to other cortical areas (cortico-cortical projections), or via the thalamus (cortico-thalamo-cortical projections). Background Intracortical projections do not have to cross the thalamus or other subcortical structures. Take for example the visual system - it features many cortical projections ...


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