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Definition
| Star-shaped cells found between neurons and blood vessels. Their processes cover nearly all the capillaries in the brain, make contact with the surfaces of neurons. Are 50% of all cells in the brain |
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Definition
-are important in the uptake of glucose from the capillaries supplying nervous tissue. Their plasma membranes transport glucose into the interior where it produces two ATP (glycolysis)
-Involved in the uptake of neurotransmitters released by neurons (glutamate)
-Act to modify the concentration of calcium in neurons
-Responsible for homeostasis of ions such as potassium in the surrounding medium
-Can turn into cancer (astrocytomas and gliomas) |
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Definition
-Resemble astrocytes, but processes are fewer and shorter.
-Give support to neurons by arranging themselves in rows along nerve fibers.
-Produce a phospholipid myelin sheath around axons of neurons in the central nervous system |
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Definition
| They phagocytize bacteria and cellular debris, and can migrate into an area of damaged nervous tissue. |
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| -Cuboidal or columnar in shape and may have cilia. --Form a continuous epithelial lining for ventricles of the brain (spaces that contain the cerebrospinal fluid) and the central canal of the spinal cord. |
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Definition
| Develop from astrocytes. They are often low-grade tumors. Survival can be over several years and the tumors can be easily removed. |
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Definition
| They are high-grade tumors and survival is usually less than two years. Spread easily into surrounding brain tissue. |
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Definition
| Develop from oligondendrocytes and may be operable in their early stages |
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Definition
| Convey sensory information to the central nervous system |
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Definition
Convey information from one neuron to another neuron.
In some parts of the central nervous system, interneurons inhibit or stop neurons from firing. Such interneurons are said to be inhibitory. |
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Definition
| Convey motor commands, usually to skeletal muscles. |
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Definition
| Neurons contain neurofibils and Nissl bodies or granules. The latter are modified rough endoplasmic reticulum and function in protein synthesis. |
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Definition
| Short and highly branched. Function is to conduct nerve impulses toward the cell body. |
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Definition
| A long tubular process arising from the axon hillock on the cell body. The axon conducts nerve impulses away from the cell body to another neuron or muscle or gland cells. |
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Term
Collaterals
Axon terminals
Synaptic end bulbs
Presynaptic terminals |
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Definition
| Axons give off branches called collaterals, and their axon terminals have many specialized, bulb-like endings that are called synaptic end bulbs or presynaptic terminals. The presynaptic terminals are in close contact with the plasma membranes of other cells |
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Definition
| The specialized structure formed at the point of close contact between the presynaptic terminal and the plasma membrane of the receiving cell |
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Definition
| A slow process which is responsible for carrying soluble proteins synthesized in the cell body down to the axon terminals |
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Definition
a faster, ATP requiring process. This process is involved in the transport of organelles (such as synaptic vesicles, mitochondria) through the axon.
The transport occurs on the surfaces of micro- or nuerotubules, fine threads composed of special proteins that course inside the axon along its entire length |
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Term
| Retrograde axonal transport |
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Definition
the opposite of anterograde axonal transport, and can move particles toward the neural cell body.
Ex: Herpes, polio, rabies viruses. |
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Term
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Definition
| Many axons, especially those outside the central nervous system, are covered by a multilayered, white, phospholipid, segmented covering called a myelin sheath. |
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Definition
forms the myelin sheath. (they are the main target of the bacterium that causes leprosy) The myelin sheath is also destroyed in diseases such as multiple sclerosis.
Schwamm cells produce neurotrophic factors, that promote axonal regeneration, whereas oligodendrocytes seem to have proteins that inhibit axonal regeneration. |
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Term
| Regeneration of Nerve Axons |
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Definition
-Damaged part of of axon dies, myelin sheath breaks down
-The Schwann cells remain alive and able to replicate
-Cut axon send out axonal sprouts
-The Schwann cells then start to multiply and form rows along the course previously taken by the axon. |
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Definition
| Proteins that include nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CTNF) and neurotrophin-3 |
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Term
| Neurotrophic Factors: Growth, differentiation and survival |
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Definition
| Neurotrophic factors are important during early development of the nervous system, when they are responsible for the growth and development of neurons, for survival of neurons, and for maintaining them in functional condition |
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Term
| Neurotrophic Factors: Maintenance of neurons in the mature nervous system |
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Definition
| In the adult nervous system, neurotrophic factors are involved in the survival of neurons, and for maintaining them in functional condition. In the absence of neurotrophic factors, neurons will die. |
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Term
| Neurotrophic factors: experimental situations |
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Definition
| Neurotrophic factors can make damaged neurons regrow their axons in experimental situations, and therefore they present opportunities for reversing the damage caused to neurons by trauma and by degenerative diseases such as Alzheimer’s disease, Huntington, Parkinson |
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Term
| Axonal or growth cone guidance |
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Definition
| Comes under the control of various molecules. Some are found on the surfaces of cells and act at short range. |
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Term
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Definition
| In a resting neuron the inner surface of the plasma membrane is negatively charged and paired with its external surface. The cell membrane is then said to be electrically polarized. |
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Term
| resting potential or membrane potential |
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Definition
| The difference in electrical potential (voltage) between the two sides of the membrane. Typically, the resting potential is 60-100 millivolts |
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Term
| The Ionic Permeability of the Membrane of a resting neuron |
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Definition
| The cell membrane is very permeable to K+ and Cl-. It is not very permeable to Na+ and is impermeable to the large, negatively charged proteins and other organic molecules in the cell interior. |
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Term
| ATP-driven pump in resting membrane |
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Definition
Pumps 3 sodium ions out of the cell, and 2 potassium ions into the cell. The result is a highly distribution of ions across the cell membrane, with a high concentration of sodium ions outside the cell and a high concentration of potassium ions cell.
The membrane potential depends on maintaining this distribution of ions on either side of the membrane. Therefore, it is essential that there is a supply of ATP to power the sodium/potassium exchange pump. |
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Term
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Definition
| For the resting potential, we will only consider potassium ions. This is because the resting membrane is very permeable to potassium but not sodium ions. The high potassium permeability is caused by the presence in the membrane of large numbers of potassium leak channels. |
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Term
| Negatively charged proteins |
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Definition
| The resting membrane is impermeable to the negatively charged proteins and other large organic molecules inside the cell. They are too big to diffuse through the plasma membrane, and there are no pores in the membrane to allows them to pass through it |
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Term
| Potassium Ions in resting membrane |
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Definition
| Given a high concentration of potassium ions within the cell, given that the cell membrane is permeable to potassium ions and impermeable to negatively cha proteins within the cell. At first, positively charged potassium ions start diffusing out of the cell through their leak channels. They diffuse outwards because their concentration is much higher inside the cell than outside. |
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Term
| Creation of potential gradient |
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Definition
| The negatively charged proteins inside the cell cannot diffuse out. The result is that the inside of the cell becomes more and more negatively charged as positively charged potassium ions leak out. This negative charge creates a potential gradient that tends to draw positively charged potassium ions back into the cell. |
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Term
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Definition
| When the electrical forces drawing potassium ions into cell balance the diffusion forces driving potassium ions out of the cell, there is a potential (voltage) across the membrane called the resting potential. This potential can be calculated to about -97 millivolts |
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Term
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Definition
| The resting membrane is slightly permeable to sodium ions, and so sodium is continually and slowly leading into the nerve fiber. (If this were allowed to continue, the concentration of potassium and sodium ions inside and outside the membrane would equalize and the resting membrane potential would become zero.) |
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Term
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Definition
| Pumps out any sodium ions that leak into the cell and exchange pump, which pumps out any sodium ions that lead into the cell and exchanges them for potassium. This pump therefore maintains the low concentration of sodium ions inside the cell, and keeps the concentration of potassium ions high. |
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Term
| How nerve cells get excited |
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Definition
- some nerve cells specialized as sensory receptors, and are excited when are exposed to light, heat, pressure, touch, sound, etc
- Other nerve cells respond to signals coming from neurons that connect with them by special junctions called synapes. These signals are often chemical agents called neurotransmitters. |
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Term
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Definition
| After excitement, often a signal will act to make the inside of the cell membrane less negative with respect to the outside, in which case it is said to depolarize the membrane. Depolarization events can occur in graded steps. |
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Term
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Definition
| When a depolarization event changes the membrane potential to a value called the threshold, an action potential is generated. At threshold (about -55mV), the membrane, which has previously been impermeable to sodium ions, starts to become highly permeable to them. |
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Term
| Voltage-gated sodium channels |
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Definition
| After depolarization, the permeability of the membrane to sodium ions becomes much, much greater than the permeability of the membrane to potassium ions. The sudden increase in permeability to sodium is due to the opening in the cell membrane of voltage-gated sodium chanels. |
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Term
| Result of increase in Sodium |
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Definition
When the membrane permeability to sodium increases far above potassium because of these newly-opened sodium channels, sodium now dominates the equation for the membrane potential. Consequently, the membrane potential swings away from the potassium resting potential of -97mV and moves toward the sodium potential of +81mV.
The sudden depolarization of the membrane caused by an initial threshold depolarization event is the first phase of the action potential |
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Term
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Definition
The action potential is an all-or-none response, the initial small depolarization of the membrane is either sufficient to reach threshold and trigger an action potential, or it isn’t
Like swing doors, the voltage-gated sodium channels remain open for only a short time, then they start to swing closed. Sodium permeability then drops below potassium permeability, so returning the membrane potential back to its resting condition, which is often close to the potassium Nernst potential. |
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Term
| Voltage-gated potassium channels |
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Definition
The return of the membrane potential back to its resting value is accelerated because the potassium permeability actually rises above its resting calue for a short period of time. The transient rise of potassium permeability is due to the presence of slowly-openinging voltage-gated potassium channels in the the membrane.
Since the potassium leak channels are alway open, the membrane actually becomes more permeable to potassium than it was during the resting phase
This causes a transient hyper-polarization or over-swing at the terminal phase of the action potential. Finally, the voltage-gated potassium channels close, and the membrane returns to the resting potential. |
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Term
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Definition
| During action potential, the nerve will not respond to further stimuli, and is said to be in its refractory period. |
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