Neuronal Dynamics

• かんいつ

  2017-11-16
  Human memory works with associations. If you hear the voice of an old friend on the phone, you may spontaneously recall stories that you had not thought of for years. If you are hungary and see a picture of a banana, you might vividly recall the taste and smell of a banana ... and thereby realize that you are indeed hungry.
• かんいつ

  2017-06-05
  1.1.4 Neurons are part of a big systemNeurons are embedded in a network of billions of other neurons and glial cell that make up the brain tissue. The brain is organized in different regions and areas. The cortex can be thought of as a thin but extended sheet of neurons, folded over other brain structures. Some cortical areas are mainly involved in processing sensory input, other areas are involved in working memory or motor control.The receptive field of so-called simple cells in visual cortex is not homogeneous, but has typically two of three elongated subfields. When a light dot falls into one of the positive subfields, the neuron increases its activity, i.e., it emits more spikes than in the absence of a stimulus. Whenever a light dot falls into a negative subfield, it decreases the ...
• かんいつ

  2017-06-05
  1.1.3 SynapsesThe site where the axon of a presynaptic neuron makes contact with the dendrite (or soma) of a postsynaptic cell is the synapse. The most common type of synapse in the vertebrate brain is a chemical synapse. At a chemical synapse, the axon terminal comes very close to the postsynaptic neuron, leaving only a tiny gap between pre- and postsynaptic cell membrane. This is called the synaptic cleft. When an action potential arrives at a synapse, it triggers a complex chain of bio-chemical processing steps that lead to a release of neurotransmitter from the presynaptic terminal into the synaptic cleft. As soon as transmitter molecules have reached the postsynaptic side, they will be detected by specialized receptors in the postsynaptic cell membrane and lead (either directly or vi...
• かんいつ

  2017-06-05
  The neuronal signals consist of short electrical pulses and can be observed by placing a fine electrode either on the soma or close to the soma or axon of a neuronThe pulses, so-called action potentials or spikes, have an amplitude of about 100 mV and typically a duration of 1-2 ms. The form of the pulse does not change as the action potential propagates along the axon. A chain of action potentials emitted by a single neuron is called a spike train – a sequence of stereotyped events which occur at regular or irregular intervals; Since isolated spikes of a given neuron look alike, the form of the action potential does not carry any information. Rather, it is the number and the timing of spikes which matter. The action potential is the elementary unit of signal transmission.
• かんいつ

  2017-06-05
  The junction between two neurons is called a synapse. Let us suppose that a neuron sends a signal across a synapse. It is common to refer to the sending neuron as the presynaptic cell and to the receiving neuron as the postsynaptic cell. A single neuron in vertebrate cortex often connects to more than 10^4 postsynaptic neurons. Many of its axonal branches end in the direct neighborhood of the neuron, but the axon can also stretch over several centimeters so as to reach neurons in other areas of the brain.
• かんいつ

  2017-06-05
  A typical neuron can be divided into three functionally distinct parts, called dendrites, soma, and axonRoughly speaking, the dendrites play the role of the ‘input device’ that collects signals from other neurons and transmits them to the soma. The soma is the ‘central processing unit’ that performs an important non-linear processing step: If the total input arriving at the soma exceeds a certain threshold, then an output signal is generated. The output signal is taken over by the ‘output device’, the axon, which delivers the signal to other neurons.
• かんいつ

  2017-06-05
  The elementary processing units in the central nervous system are neurons, which are connected to each other in an intricate pattern. We can distinguish several neurons with triangular or circular cell bodies and long wire-like extensions. This picture can only give a glimpse of the network of neurons in the cortex. In reality, cortical neurons and their connections are packed into a dense network with more than 10^4 cell bodies and several kilometers of ‘wires’ per cubic millimeter. Across areas of the brain the wiring pattern may look different. In all areas, however, neurons of different sizes and shapes form the basic elements.