Nervous Tissue Flashcards
(45 cards)
Identify the 3 basic functions of the nervous system in maintaining homeostasis
sensory, integrates (interprets info), motor (responds to info)
Name the 3 main parts of a neuron and describe their functions.
-cell body (location of the organelles)
nuclei (of the CNS)
Ganglia (of the PNS)
-Cytoplasmic processes
-Dendrite- receptive end- may have many
-Axon- conducting end- sending messages away from cell body
Nuclei- nerve cell body location
groups of cell bodies in the central nervous system
Ganglia- nerve cell body location
Groups of cell bodies in the Peripheral nervous system
Contrast white and gray matter
Myelinated neurons are white, unmyelinated are gray.
Distinguish between the structure of a myelinated and an unmyelinated axon, and describe how a myelin sheath is formed.
-Mylen is fat that is wrapped in layers around an axon.
Made by Schwann cells in the PNS
- Made by oligodendrocytes in the CNS.
-Myelinated neurons send nerve impulses MUCH faster than unmyelinated.
Describe how a peripheral nerve is regenerated if cut, and explain why an axon of the CNS cannot regenerate as well.
- Schwann cells can regenerate axons after time by providing structural scaffolding. Slow process
- Oligodendrocytes cannot make bridge between severed axons
Explain the nature of the blood-brain barrier.
- The Astrocytes are founded between brain cell and blood vessels, they act as filters for what gets into the brain. Poisions go to astrocytes not brain. Alc can cross.
- can undergo mytosis
Define neuroglia and give an example of a neuroglial cell
- “Nerve glue”
- supporting and protecting tissue
- Schwann cells, oligodendrocytes and astrocytes
Define nerve. Where are nerves located?
-A nerve is groups of axons, found only in the PNS
Classify neurons according to structure.
- Bipolar- one dendrite one axon (nervous layer of retina)
- Multipolar- (most Common) one axon to numerous dendrites (motor)
- Unipolar- t shaped extension that branches into dendrite and axon (sensory)
Define Cation
- Cation is positively charged ion such as Na+ and K+
- responsible for message
Define anion
- Anions are negatively charged ions such as Cl-
- Responsible for message
Define membrane potentional
-Change difference inside and outside of the cell
more negative inside the cell
Explain how the Na+/K+ pump contributes to the resting membrane potential.
-The pump is not equal in charges - it pumps 3 positive sodiums out for every 2 positive potassiums in, contributing to the negativity in the cell.
What is the approximate voltage of a neuron’s resting membrane potential?
- -70mV, meaning this much more negative inside of the cell.
Describe the factors that contribute to establishing the resting membrane potential.
- Na/K pump, fixed anions that are a part of the interior of the cell
- K can diffuse relatively easily across the cell membrane and as it diffuses out due to a concentration gradient
- the negative fixed anions draw K back into the cell creating an equilibrium.
- The sodium is found primarily on the outside of the cell and wants to diffuse in, and is attracted in by the fixed anions
- but CANNOT enter the cell because the membrane is not permeable to sodium.
Describe depolarization and repolarization.
- depolarization= becomes more + in the cell due to sodium
- Repolarization= k gates (return to homeostasis) potassium diffusing out of the cell
- this is an action potential
Define local potential
- Spring loaded hinge on gate
- open sodium gate, but then the gates close and the potential is over
- i.e. it does not become a run away cycle.
Which cells have action potentials? Describe the events of an action potential.
Muscle and Nervous cells.
- depolarization( Na gates open)
- voltage regulates gates (sodium gates close)
- A stimulus causes sodium gates to open and sodium comes rushing into the cell. In fact so much sodium comes in that you reach a level called threshold in which it becomes a positive feedback cycle
- so that more and more sodium gates open until it actually becomes positive inside of the cell.
- The sodium gates are only open for a brief period of time
- potassium gates are open for a long time.
- Now that the sodium gates close, the potassium wants to leave the cell for concentration reasons and now that it is positive in the cell
- it also wants to leave since like charges are repelled by each other.
- This is the repolarization portion of the action potential.
Explain how the sodium and potassium concentrations return to the levels of an unstimulated neuron, following an action potential.
- sodium/potassium pump then follows the action potential in which sodium exits the cell and potassium enters the cell.
- 3/2 ration and active transport so that ATP is required.
Describe the events of a nerve impulse in myelinated and unmyelinated neurons.
-Series of action potentials
-Myelinated axon-leaping from action potential from node of ranvier to node of ranvier @ 225mph
(called Saltatory conduction)
-unmyelinated neuron- the current flows all the way along the axon. A series of action potentials travel along the neuron @ 2 mph.
Discuss the factors that determine the speed of impulse conduction.
- fat is an insulator against current flow, less surface area to cover thus speeds up
- The more myelin, the faster.
- increased temperature increases impulse conduction.
Define the all-or-none principle of nerve impulse transmission.
-Either an action potential reaches threshold or it doesn’t.
