Note: These study tests were written by a student and derived from the student's class lecture notes. They are meant to be used as a study aid, not as a substitute for personal class attendance. If you find any discrepancies, see Dr. Buono for clarification.

  BIO 336 STUDY TEST FOR EXAM #1
(ANSWERS LISTED BY NUMBER AT THE BOTTOM OF EACH PAGE)

The cell membranes of humans are composed of a 1 bilayer and 2 gates and pumps. At rest, the inside of the cell membrane is slightly 3 charged relative to the outside. The resting potential voltage is approximately 4 mv. 5 are charged particles. Potassium (K+) is a small ion that can move easily across the cell membrane; sodium (Na+) is a larger molecule and cannot move across the cell membrane unless the gates located on the membrane change shape and allow it to pass through. When the cell is at rest, the intra-cellular fluid (ICF) is highly concentrated with 6 and the extra-cellular fluid (ECF) is highly concentrated with 7 . This is because the sodium-potassium pump is constantly pumping 3 sodium ions out of the cell while at the same time pumping 2 potassium ions in.

Two driving forces are constantly at work maintaining the status quo of the resting potential: the 8 driving force, which causes K+ from the area of high concentration (inside the cell) to be attracted toward the area of low concentration (outside the cell), and the 9 driving force, in which opposite charges attract, therefore causing K+ from outside to be attracted to the inside. These two forces move K+ in and out, the net result being no change in voltage and maintenance of the status quo of -80 mv. when the cell is at rest. (Note: The electrical driving force, in which opposite charges attract and the chemical driving force, in which molecules move from areas of higher concentration to areas of lower concentration, are constant--that is, they are always at work within the body.)

ACTION POTENTIAL - The first step in an action potential is excitation of a cell. At this early phase, some 10 leaks into the cell, causing the inside of the cell to become slightly less negative. If the excitation is enough for the cell to reach 11 mv., the cell is said to have reached 12 and an action potential occurs. At this point, 13 gates open wide, and 14 rushes in, causing the cell to depolarize (become positive) rapidly. At about 15 mv., sodium gates close and potassium gates open; this allows potassium to leave the cell rapidly. Positively-charged potassium leaving the cell and positively-charged sodium blocked from entering the cell cause the cell to become negative once again. This change from a positive internal charge back to a negative internal charge is called 16 . The negative charge temporarily surpasses -80 mv.; this is known as 17 and it is a point during which the cell will not fire. It is also known as the 18 . In summary, an influx of 19 depolarizes the cell whereas an outflow of 20 repolarizes the cell.

1. phospho-lipid 2. protein channel 3. negatively 4. -80

5. Ions 6. potassium (K+) 7. sodium (Na+) 8. chemical

9. electrical 10. sodium 11. -50 12. threshold 13.Na+

14. Na+ 15.+30 16. repolarization 17. hyperpolarization

18. refractory period 19. Na+ 20. K+

The movement of an impulse (action potential) from one end of the cell to the other is called 1 , and it occurs in one direction only. This one-way movement is due to the 2 . The

3 wrapped around many axons speeds conduction of an action potential. An impulse is propagated down a myelinated axon via

4 conduction. With this type of conduction, the action potential "jumps" from one unmyelinated area to another, thus increasing the velocity of conduction. These unmyelinated areas located along the cell's axon are known as the 5 .

SYNAPTIC TRANSMISSION - Once an action potential reaches the end of a cell's axon (i.e., the terminal button), it must be transmitted to the next cell to keep the flow of information going. This is accomplished by synaptic transmission, and is mediated by the release of 6 into the space between the terminal buttons of the axons and the dendrites of other cells; this space is known as the 7 . When activated by a neurotransmitter, receptors on the dendrites' membranes cause the membrane to become permeable to different ions. Receptors that cause the membrane to become permeable to sodium (thus increasing the likelihood of an action potential occurring due to the resulting influx of sodium ions into the cell) are said to cause reactions called 8 . Receptors that cause the membrane to become permeable to potassium (thus decreasing the likelihood of an action potential occurring due to the resulting exit of more potassium ions out of the cell) are said to cause reactions called 9 . 10 is an example of an excitatory transmitter and 11 is an example of an inhibitory transmitter.

12 is an enzyme located within the receptor that breaks down ACh. The breakdown of ACh is necessary; if ACh remained at the synapse, the result would be uncontrollable muscle spasms. When ACh is present, sodium gates open; therefore, the breakdown of ACh blocks the opening of Na+ gates, the end result being decreased excitation. 13 , an ACh imitator, is the substance used in poison darts. As an ACh imitator, it fits into ACh receptors, thus blocking entry of ACh. The opposite of this effect is achieved by drugs known as 14 , which prolong the effects of ACh at the receptor sites. These drugs are used to treat persons who suffer with 15 , a muscle disease caused by damaged receptors. Treatment with these drugs serves to maximize the use of ACh at non-damaged receptor sites.

Nerves that synapse with muscles are called 16 nerves.

17 is the excitatory neurotransmitter used by most motor nerves.
 
 

1. conduction 2. refractory period 3. myelin sheath

4. saltatory 5. nodes of Ranvier 6. neurotransmitters

7. synaptic cleft or synapse 8. excitatory post synaptic potentials (E.P.S.P.'s) 9. inhibitory post synaptic potentials (I.P.S.P.'s) 10. Acetylcholine (ACh) 11. glycine

12. Acetylcholinesterase 13. Curare 14. cholinesterase inhibitors 15. myasthenia gravis 16. motor 17. ACh

The membrane of a muscle cell is called the 1 . The 2 is the part of the sarcolemma that synapses with the nerve cell. The muscle cell is made up of many units called 3 . One sarcomere stretches from one 4 line to the next. Inside the cell, surrounding the sarcomeres, is a hollow structure called the 5 which contains large amounts of 6 . Inside the sarcomere is a thick protein called 7 which has small protrusions called 8 sticking out. Another smaller (thin) protein called 9 located above and below these myosin heads contains binding sites to which the myosin heads want to bind; however, they are not able to do so because a protein called 10 blocks the binding sites. Still another protein called 11 is attached to the tropomyosin.

When muscles reach threshold, the change in voltage causes the release of 12 from the sarcoplasmic reticulum. The Ca++ then hooks onto 13 , causing it to swing tropomyosin out of the way of the binding site, thus allowing the myosin heads to bind to the actin binding sites. The myosin heads move from a 90 degree angle at rest to a 45 degree angle, thus sliding actin along the myosin. Located in the myosin is a substance known as 14 , an enzyme which causes  ATP to become ADP + P + energy. (Note: ATP stands for adenosine tri-phosphate--3 phosphate molecules hooked to each other and to an adenosine molecule. When the bond between two of the phosphate molecules is broken, energy is released, and what remains is ADP, or adenosine di-phosphate--2 phosphate molecules hooked to each other and to an adenosine molecule.). ATP causes myosin to release actin and when myosin ATPase breaks the bond of ATP, it releases enough energy to move the myosin head back to 90 degrees. So, in summary, movement of a muscle cell consists of many myosin heads binding at actin sites, moving actin at staggering intervals, releasing their bond, and repeating the process over and over again until the action potentials stop. This process is referred to as the 15 theory. As soon as action potentials in the muscle cease, 16 is pumped out of the sarcomeres and back into the sarcoplasmic reticulum. Thus, in order for a muscle to contract, we need

17 , 18 , and 19 . Energy is needed for myosin to release from actin, and for Ca++ pumps  to pump Ca++ back into the sarcoplasmic reticulum.

Each muscle fiber (cell) has one terminal button attached to it while each motor unit may innervated 10-1000 fibers. However, one motor nerve might activate many nerve fibers whereas others may activate only a few.
 
 

1. sarcolemma 2. motor end plate 3. myofibrils 4. Z

5. sarcoplasmic reticulum 6. calcium (Ca++) 7. myosin 8. myosin heads 9. actin 10. tropomyosin 11. troponin 12. CA++

13. troponin 14. myosin ATPase 15. sliding filament 16. Ca++

17. proteins 18. ATP 19. Ca++ 20. one 21. one
 
 

When a muscle fiber is innervated, all the sarcomeres (the smaller units that comprise the myofibrils) contract. This is known as the all-or-none principle. A whole muscle does not act in an all-or-none fashion; therefore, the strength of a muscle contraction can vary depending on 1 . When certain muscles are excited (contracted), their opposing muscles are inhibited (relaxed). This is known as 2 and it occurs in antagonistic pairs of muscles.

In frogs, 3 muscles are red in color, while 4 muscles are white. Slow-twitch muscles contract slowly and fatigue at a slower rate than fast-twitch muscles, which contract very quickly. Fast-twitch muscle has about 2-3x the 5 , and therefore, more 6 . Fast-twitch muscle fatigues very quickly. Humans are born with a set ratio of fast-twitch/slow-twitch muscles, with the average ratio being 50/50. Also, humans have muscles composed of both fast-twitch muscle fibers and slow-twitch muscle fibers. Fast-twitch fibers must make ATP very fast; their energy is made 7 as opposed to slow-twitch muscle fibers which make their energy 8 .

Two reasons for the differential force exerted by a muscle are variations in number or size of motor units involved (more muscle cells contracted = more force) and variations in the 9 of action potentials. When action potentials build upon ("add to") each other to cause stronger muscle contractions, this additive process is known as 10 . The term used when a muscle reaches its maximum amount of force is 11 . There are two types of muscle contractions. In a(n) 12 contraction the muscle shortens (i.e., the force of the muscle is greater than the opposing force). In a(n) 13 contraction, the muscle does not shorten (i.e., the force opposing the muscle is greater than or equal to the force of the muscle).

HUMAN NERVOUS SYSTEM - There are 14 pairs of spinal nerves. 15 or afferent nerves enter the spinal cord via the

16 root; 17 or efferent nerves exit via the 18 root. There are 19 cranial nerves which innervate facial muscles.

Compared to skeletal muscle cells, cardiac muscle cells are very 20 in size. When one cardiac cell contracts, they all contract, due to places called 21 between the cells. Because of these, many cardiac cells do not have neuromuscular junctions. (This is distinctly different from skeletal muscle, in which every muscle fiber has a terminal button.) Skeletal muscles get their Ca++ from sarcoplasmic reticulum; cardiac cells get their Ca++ from 22 , and thus have much less sarcoplasmic reticulum than skeletal muscle.
 
 

1. the number of muscle fibers contracted 2. reciprocal innervation 3. slow-twitch 4. fast-twitch 5. sarcoplasmic reticulum 6. Ca++ 7. anaerobically 8. aerobically

9. frequency 10. summation 11. tetanus 12. isotonic

13. isometric 14. 31 15. Sensory 16. dorsal 17. motor

18.ventral 19.twelve 20. small 21. gap junctions 22. the blood
 
 

Phases of an action potential of a cardiac cell - If a cardiac cell gets excited and reaches -50 mv., the cell reaches threshold and an action potential occurs. 1 gates open wide, causing further depolarization. At the peak of the action potential, 2 gates close and 3 and 4 gates open simultaneously. This results in the influx of 5 and the exiting of 6 . Because of the offsetting inflow and outflow of these ions the net voltage remains constant; this causes a long plateau in which the cell stays depolarized. Finally, the 7 gates close. Potassium gates remain open and potassium continues to exit the cell; this brings the cell back down to -80 mv.

Action potentials of cardiac cells take a 8 period of time than do action potentials of skeletal muscles. For this reason, their action potentials cannot sum as the action potentials of skeletal muscles can.

Smooth muscles are non-striated (not striped) because the 9 are not lined up as they are in skeletal muscle. They also have very slow contraction and relaxation.
 
 

1. Na+ 2. Na+ 3. K+ 4. Ca++ 5. Ca++ 6. K+ 7. Ca++ 8.longer 9. sarcomeres