A. NERVOUS TISSUE
1. Sensory, integration, motor
2. CNS is brain & spinal cord. PNS is everything traveling toward or away from the CNS. In PNS, impulses traveling toward the CNS are afferent or sensory. Impulses traveling away from the CNS are efferent or motor. If the impulses are going to your skeletal muscle, they would be somatic efferent. If the impulses are going to smooth muscle, cardiac muscle or glands they are visceral efferent = ANS.
3. Dendrite – receiving end or receptor end, may have many dendrites; Cell body – location of the organelles such as nucleus, mitochondria…; Axon – conducting end sending messages away from the cell body.
4. Nuclei are a clump of cell bodies of neurons in the CNS and ganglia are clumps of cell bodies in the PNS
5. Myelinated neurons are white, unmyelinated are gray.
6. Myelin is a fatty substance wrapped in layers around an axon. The myelin is made by Schwann cells in the PNS and oligodendrocytes in the CNS. Myelinated neurons send nerve impulses MUCH faster than unmyelinated.
7. Schwann cells, only in PNS, can make a regeneration tube which is a scaffolding for the cut ends of the axon to follow during regeneration.
8. The astrocytes are between the blood and the brain cells. Thus a poison would not go directly to the brain from the blood, but rather to the astrocyte.
9. About half of nervous tissue is supportive cells called neuroglia. This includes the Schwann cells, oligodendrocytes and astrocytes.
10. Nerves, found only in the PNS are groups of axons.
11. Bipolar neuron has one axon and one dendrite, multipolar – the most common (e.g. motor neurons) have numerous dendrites and one axon; Unipolar have one extension that branches into the dendrite and the axon and are found in sensory neurons.
12. Cation is positively charged ion such as Na+ and K+; anions are negatively charged ions such as Cl-.
13. A charge difference in the outside vs. the inside of a cell.
14. 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.
15. -70mV, meaning this much more negative inside of the cell.
16. Na/K pump, as described above; the fact that there are fixed anions that are a part of the interior of the cell, the fact that 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.
17. Depolarization is when the sodium is allowed to enter the cell causing the inside of the cell to become less negative or more positive. Repolarization is the return to a resting membrane potential due to the potassium diffusing out of the cell. Both of these stages comprise an action potential.
18. Localized depolarization where sodiums can enter the cell due to an open sodium gate, but then the gates close and the potential is over , i.e. it does not become a run away cycle.
19. Depolarization to threshold. 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, and the 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.
20. 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.
21. In unmyelinated neurons, the current flows all the way along the axon. A series of action potentials travel along the neuron at about 2 mph. In myelinated neurons, the myelin insulates against electrical current so that the action potentials can only occur at the nodes of Ranvier and therefore the current jumps from node to node called saltatory conduction which is very fast, up to 250 + mph.
22. Primarily, it is the presence of myelin. Fast with myelin. The more myelin, the faster. Also, increased temperature increases impulse conduction.
23. Either an action potential reaches threshold or it doesn’t.
24. Only because they always START at one end of the neuron & therefore can only go in one direction.
25. Synapse is the junction between adjacent neurons involving the neuron entering the synapse called the presynaptic neuron and the one exiting is the postsynaptic neuron. The physical space between the 2 is the cleft. The vesicle is the bubble filled with neurotransmitter in the presynaptic neuron. The neurotransmitter is the chemical released that bridges the synapse.
26. Neurotransmitters are released at the synapse and diffuse across the synapse. There are receptors for the neurotransmitter at the postsynaptic neuron. The combination of the neurotransmitter in the receptor leads to depolarization in the postsynaptic neuron because their sodium gates at this location are chemical (neurotransmitter) regulated rather than the voltage regulated gates on the rest of the neuron. Acetylcholine, norepinephrine and dopamine are some examples.
27. If the neurotransmitter causes depolarization in the postsynaptic neuron it is an EPSP, if it causes hyperpolarization (more negative) in the postsynaptic neuron it is an IPSP. These are graded changes – i.e. not all or none.
29. Neurotransmitters that are structurally similar include dopamine, epinephrine and norepinephrine and are the catecholamines.
30. This is a chemical that influences the neurotransmitter or the response to it. For example, endorphins block the pain neurotransmitters.
31. One presynaptic neuron synapsing with several postsynaptic neurons is divergence; many presynaptic neurons synapsing with one postsynaptic neuron is convergence.
32. Temporal summation is summation in time. If at a synapse you have one EPSP and another one rapidly follows & then another one… you will likely have enough depolarization to reach threshold. Spatial summation is summation in space. This would occur in a situation such as convergence where each presynaptic neuron releases a little bit of neurotransmitter going to the post synaptic neuron and all of the pre’s together will add their neurotransmitter together & it will likely be enough to reach threshold in the postsynaptic neuron and send the message along its way.
33. The dendrite is the receiving end of the neuron. Its job is to take the stimulus and turn it into depolarization which is what the neuron understands. The more dendrites stimulated, the stronger the stimulus. Also, a strong stimulus will send a high frequency of impulses to the brain.
34. Pain does not adapt. With an unchanging stimulus, receptors stop responding.
35. The stopping point for the neuron – such as a muscle or a gland. The depolarization in the effector is the end-plate potential.