Nervous Tissue

Question 1

1. Identify the 3 basic functions of the nervous system in maintaining homeostasis.

Answer 1

1. Sensory integration motor

Question 2

2. Classify the organs of the nervous system into central and peripheral divisions. Include in your classification the terms afferent efferent somatic visceral and autonomic nervous system (parasympathetic/sympathetic).

Answer 2

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.

Question 3

3. Name the 3 main parts of a neuron and describe their functions.

Answer 3

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.

Question 4

4. Define nuclei and ganglia as they relate to nerve cell body location.

Answer 4

4. Nuclei are a clump of cell bodies of neurons in the CNS and ganglia are clumps of cell bodies in the PNS

Question 5

5. Contrast white and gray matter.

Answer 5

5. Myelinated neurons are white unmyelinated are gray.

Question 6

6. Distinguish between the structure of a myelinated and an unmyelinated axon and describe how a myelin sheath is formed.

Answer 6

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.

Question 7

7. Describe how a peripheral nerve is regenerated if cut and explain why an axon of the CNS cannot regenerate as well.

Answer 7

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.

Question 8

8. Explain the nature of the blood-brain barrier.

Answer 8

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.

Question 9

9. Define neuroglia and give an example of a neuroglial cell.

Answer 9

9. About half of nervous tissue is supportive cells called neuroglia. This includes the Schwann cells oligodendrocytes and astrocytes.

Question 10

10. Define nerve. Where are nerves located?

Answer 10

10. Nerves found only in the PNS are groups of axons.

Question 11

11. Classify neurons according to structure.

Answer 11

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.

Question 12

12. Define cation and anion.

Answer 12

12. Cation is positively charged ion such as Na+ and K+; anions are negatively charged ions such as Cl-.

Question 13

13. Describe a membrane potential.

Answer 13

13. A charge difference in the outside vs. the inside of a cell.

Question 14

14. Explain how the Na+/K+ pump contributes to the resting membrane potential.

Answer 14

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.

Question 15

15. What is the approximate voltage of a neuron’s resting membrane potential?

Answer 15

15. -70mV meaning this much more negative inside of the cell.

Question 16

16. Describe the factors that contribute to establishing the resting membrane potential.

Answer 16

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.

Question 17

17. Describe depolarization and repolarization.

Answer 17

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.

Question 18

18. Define local potential.

Answer 18

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.

Question 19

19. Which cells have action potentials? Describe the events of an action potential.

Answer 19

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.

Question 20

20. Explain how the sodium and potassium concentrations return to the levels of an unstimulated neuron following an action potential.

Answer 20

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.

Question 21

21. Describe the events of a nerve impulse in myelinated and unmyelinated neurons.

Answer 21

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.

Question 22

22. Discuss the factors that determine the speed of impulse conduction.

Answer 22

22. Primarily it is the presence of myelin. Fast with myelin. The more myelin the faster. Also increased temperature increases impulse conduction.

Question 23

23. Define the all-or-none principle of nerve impulse transmission.

Answer 23

23. Either an action potential reaches threshold or it doesn’t.

Question 24

24. Explain why normal nerve impulses tend to be unidirectional.

Answer 24

24. Only because they always START at one end of the neuron & therefore can only go in one direction.

Question 25

25. Define synapse presynaptic neuron postsynaptic neuron synaptic cleft synaptic vesicle and neurotransmitter.

Answer 25

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.

Question 26

26. Describe the action of neurotransmitters. Give an example of a neurotransmitter.

Answer 26

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.

Question 27

27. Contrast excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP).

Answer 27

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.

Question 28

28. Name the enzyme that breaks down acetylcholine.

Answer 28

28. Acetylcholinesterase

Question 29

29. Define catecholamine.

Answer 29

29. Neurotransmitters that are structurally similar include dopamine epinephrine and norepinephrine and are the catecholamines.

Question 30

30. Define neuromodulator and give an example.

Answer 30

30. This is a chemical that influences the neurotransmitter or the response to it. For example endorphins block the pain neurotransmitters.

Question 31

31. Contrast convergence and divergence as it relates to neural integration.

Answer 31

31. One presynaptic neuron synapsing with several postsynaptic neurons is divergence; many presynaptic neurons synapsing with one postsynaptic neuron is convergence.

Question 32

32. Describe temporal and spatial summation.

Answer 32

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.

Question 33

33. Define receptor and describe how a stimulus leads to a nerve impulse and how we can distinguish a weak from a strong stimulus.

Answer 33

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.

Question 34

34. Describe adaptation. Which sensation does not adapt?

Answer 34

34. Pain does not adapt. With an unchanging stimulus receptors stop responding.

Question 35

35. Define effector and end-plate potential.

Answer 35

35. The stopping point for the neuron - such as a muscle or a gland. The depolarization in the effector is the end-plate potential.