Hoofdstuk 4 Flashcards
Neurons
Nerve cells, a single cell of the nervous system. Unlike most other cells in the body, neurons are not compressed together, but are separated; yet neurons communicate with each other. This communication goes through synapses, of which there are roughly 100 trillion. Neurons are constantly active, and their collective activity monitors our internal and external environments, creates all of our mental experiences and controls all of our behaviours (few millions).
Sensory neurons
Bundled together to form nerves, carry information form sensory organs (including the eyes, nose, ears, tongue and skin) into the central nervous system (few millions).
Motor neurons
Also bundled into nerves, carry messages out from the central nervous system to operate muscles and glands.
Interneurons
Exists entirely within the central nervous system and carry messages from one set of neurons to another. Interneurons collect, organize and integrate messages from one set of neurons to another. They vastly outnumber the other two types (86 billion).
Cell body
It contains the cell nucleus and other basic machinery common to all bodily cells.
Dendrites
Thin, tubelike extensions that branch extensively and function to receive input to the neuron. In motor and interneurons, the dendrites extend directly off the cell body and generally branch out of it, forming bush like structures. These structures increase the surface area of the cell and thereby allow for receipt of signals from many other neurons. In sensory neurons, dendrites branch out from one end of the axon, rather than directly from the cell body. They extend into a sensory organ and respond to sensory signals, such as sound waves in the ear or touch on the skin.
Axon
Another thin, tubelike extension of the cell body. Its function is to carry messages to other neurons or, in the case of motor neurons, to muscle cells. Most axons form many branches some distance away from the cell body and each branch ends with a small swelling called an axon terminal. Axon terminals are designed to release chemical transmitter molecules onto other neurons or, in the case of motor neurons, onto muscle cells or glandular cells. The axons of some neurons are surrounded by a casing called a myelin sheath. Myelin is a fatty substance produced by supportive brain cells called glial cells. This sheath helps to speed up the movement of neural impulses along the axon.
Action potential
Is produced by an neuron and they travel down the axon. Neurons exert their influence on other neurons and muscle cells by firing off all-or-none impulses-> they either occur or don’t occur, they don’t occur in different sizes or gradations.
Cell membrane
The membrane is a porous ‘’skin’’ that permits certain chemicals to flow in and out of the cell, while blocking others. It contains intracellular fluids and outside of it are extracellular fluids.
Resting potential
The charge across the membrane of an inactive neuron. This is the source of energy that makes an action potential possible (+/- as a battery).
Depolarization phase
Thousands of tiny channels that permit sodium ions to pass through open up in the cell membrane; as a result enough sodium moves inward to cause the electrical charges across the membrane to reverse itself and become momentarily positive inside relative to outside-> rising part of figure 4.6. The channels that permitted sodium to pass through close, but channels that permit potassium to pass through remain open.
Repolarization phase
The potassium ions are more concentrated inside the cell than outside, and because they are repelled by the temporarily positive environment inside the cell, they are pushed outward.
How do two phases of the action potential (depolarization and repolarization) result from the successive opening and closing of two kinds of channels in the cell membrane?
Because when it opens, sodium moves into the axon, making it more positive inside (depolarization) and potassium moves out of the axon, reestablishing the resting potential (repolarization).
Neurotransmitter
When an action potential reaches an axon terminal, it causes the terminal to release packets of a chemical substance (examples: dopamine, GABA and serotonin). They move across the space between the cells and alter the receiving neuron in ways that influence its production of action potentials, increasing or decreasing (that is inhibiting) the likelihood that a neuron will fire.
Synaptic cleft
Separates the axon terminal from the membrane of the cell that it influences.
Presynaptic membrane
The membrane of the axon terminal that abuts the cleft.
Postsynaptic membrane
The membrane of the cell on the other side of the cleft.
Vesicles
Within the axon, there are hundreds of, each of which contains several thousand molecules of a chemical neurotransmitter.
Excitatory synapse
The transmitter opens sodium (Na+) channels in the postsynaptic membrane. The movement of the positively charged sodium ions into the cell causes slight depolarization of the receiving neuron (the neuron becomes less negative inside), which tends to increase the rate of action potentials triggered in that neuron.
Inhibitory synapse
The transmitter opens either chloride (CL-) channels or potassium (K+) channels. The movement of negatively charged chloride ions into the cell or of positively charged potassium ions out of the cell causes a slight hyperpolarization of the receiving neuron (the neuron becomes even more negative inside than it was before). Hyperpolarization tends to decrease the rate of action potentials triggered in that neuron.
Neurogenesis
The process of creating new neurons (literally birth of neurons),and it occurs during the first 20 weeks after conception, peaking in the third and fourth months of gestation.
differentation
During this time, neurons grow in size and increase their numbers of dendrites and axon terminals, as well as the number of synapses they form.
Mirror neurons
Neurons that helps us behave in ways that mirror (mimic) what we observe or experience. They are found in various parts of the cerebral cortex. Mirror neurons are active when someone engages in behaviour, but when they observe it as well.
Transcranial magnetic stimulation (TMS)
A pulse of electricity is sent through a small copper coil, inducing a magnetic field around the coil. Repetitive pulses cause a temporary loss in those neurons’ abilities to fire normally. The effect is comparable to that of lesioning a small area of the brain, with the advantage that the effect is temporary and reversable. So it measures the inactivation of a brain area (known researcher: Sara Torriero).
Electroencephalogram (EEG)
The constant activity of the brain’s billions of neurons produces continuous electrical ‘’chatter’’ which to some degree penetrates to the skull and scalp. Placing electrodes on a person’s scalp, by which researchers detect and amplify these signals.
Patterns in EEG can be used as an index of whether a person is aroused, relaxed or asleep and can be used to identify various stages of sleep.
Neuroimages
A three-dimensional picture, that depict the relative amount of blood flowing through each part of the brain (increased blood flow reflect increased neural activity).
Positron emission tomography (PET)
This method involves injecting a radioactive substance into the blood and measuring the radioactivity that is emitted from each portion of the brain.
Functional magnetic resonance imaging (fMRI)
Involves creation of a magnetic field around a person’s head, causing haemoglobin molecules that are carrying oxygen in the blood to give off waves of a certain frequency; these waves can be detected and used too asses amount of blood in each part of the brain.
What is a difference in function between PET+ fMRI and EEG?
(1) PET and fMRI can depict activity anywhere in the brain, not just on the surface near the skull.
(2) PET and fMRI also produce more fine-grained picture of the spatial locations of activity than is possible with EEG.
Sensory perceptual hierarchy
Involved in data processing. The flow of information is primarily from bottom (sensory receptors) to top (perceptual centres of the brain).
