anatomy exam 2
A neurotransmitter derived from choline; responsible for sending the excitatory signal in the neuromuscular junction.
ACh acetylcholine
The enzyme responsible for stopping the ACh signal. Functions by metabolizing ACh into choline, which is recycled, and acetate.
AChE
Skeletal muscle has several specialized structures that are modified from the generic cell model. Describe these specializations and how they impact the functioning of the skeletal muscle cell.
Structural proteins make up sarcomere sarcoplasmic reticulum (SR)-specialized endoplasmic reticulum for the muscle, store calcium sarcolemma-cell membrane t-tubules carry the exitability stimulus signal into the muscle fiber triad- bring exitability signal to level of sarcomere, all of the above combined
The ion responsible for depolarizing the muscle membrane by traveling through the ACh receptor, down its electrochemical gradient.
sodium
At rest, active sites on the actin are blocked by:
tropomyosin molecules
Describe the events that couple excitation to contraction.
(1) initiation and propagation of an action potential along the plasma membrane, (2) spread of the potential throughout the transverse tubule system (T-tubule system), (3) dihydropyridine receptors (DHPR)-mediated detection of changes in membrane potential, (4) allosteric interaction between DHPR and sarcoplasmic reticulum (SR) ryanodine receptors (RyR), (5) release of Ca2+ from the SR and transient increase of Ca2+ concentration in the myoplasm, (6) activation of the myoplasmic Ca2+ buffering system and the contractile apparatus, followed by (7) Ca2+ disappearance from the myoplasm mediated mainly by its reuptake by the SR through the SR Ca2+ adenosine triphosphatase (SERCA), and under several conditions movement to the mitochondria and extrusion by the Na+/Ca2+ exchanger (NCX)
Excitation
1 signal arrived from nerve (Calcium channel opens) 2 calcium stimulates ACh release 3 ACh diffuses across synapse 4 ACh binds to ACh receptors 5 Na rushes into cell and creates Ap
Contraction
10 myosin binds to actin 11 power stroke 12 ATP binds and to detach head 13. ATP hydrolysis ( recocks myosin head(
Relaxation
14 ACh release stops 15 ACh dissociates from receptor 16 SR actively pumps excess Ca back in 17 Ca dissociates from troponin 18 tropomyosin moves back to block myosin from binding
Given these events: 1.The sarcoplasmic reticulum releases Ca2+ 2.The sarcoplasmic reticulum takes up Ca2+ 3.Calcium ions diffuse into the sarcoplasm 4.An action potential moves down the T-tubule 5.The sarcomere shortens 6.The muscle relaxes Choose the arrangement that lists the events in the order they occur following a single stimulation of a skeletal muscle fiber.
413526
EC coupling
6 Ap wave spreads in all direction (continues down t-tubules 7 Ap signals opening of Ca channels in SR 8 Ca binds to troponin 9 troponin moves tropomyosin out of way
Describe a motor unit. Differentiate between small and large motor units and the reasons behind having different sizes.
A motor unit is made up of a motor neuron and all of the skeletal muscle fibers, also known as sarcomere innervated by the neuron's axon terminals. Small motor units permit very fine motor control of the muscle. A large motor unit is an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle. Large motor units are concerned with simple, or "gross," movements, such as powerfully extending the knee joint. There is a wide range of motor units within many skeletal muscles, which gives the nervous system a wide range of control over the muscle. The small motor units in the muscle will have smaller, lower-threshold motor neurons that are more excitable, firing first to their skeletal muscle fibers, which also tend to be the smallest. Activation of these smaller motor units, results in a relatively small degree of contractile strength (tension) generated in the muscle. As more strength is needed, larger motor units, with bigger, higher-threshold motor neurons are enlisted to activate larger muscle fibers
Differentiate between resting membrane potential, graded potential and action potential.
An action potential is a binary all-or-nothing event, while a graded potential is an analog signal. Graded potential may lose the strength as they are transmitted through the neuron but, action potentials do not lose their strength during the transmission. Resting potential and action potential are two types of membrane potentials that occur on the axon membrane of nerve cells. Resting potential is relatively static while action potential is a rapid rise and fall when considering a particular location on the membrane
Explain how an action potential is generated
An action potential is generated in the following steps: depolarization, repolarization, hyperpolarization and a refactory period.
Explain the importance of leak channels, Na+/K+ pump, chemically and electrically gated channels to both resting and action potentials.
Because they are charged, ions can't pass directly through the hydrophobic ("water-fearing") lipid regions of the membrane. Instead, they have to use specialized channel proteins that provide a hydrophilic ("water-loving") tunnel across the membrane. Some channels, known as leak channels, are open in resting neurons. Of special interest is the carrier protein referred to as the sodium/potassium pump that uses energy to move sodium ions (Na+) out of a cell and potassium ions (K+) into a cell, thus regulating ion concentration on both sides of the cell membrane.
Explain the roles of Ca2+ and ATP during skeletal muscle contraction.
Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. (2) ATP then binds to myosin. (3) ATP is then hydrolyzed. (4) A cross-bridge forms and myosin binds to a new position on actin. (5) Pi is released and myosin changes conformation, resulting in the power stroke that causes the filaments to slide past each other. (6) ADP is then released.
List and describe the factors that influence muscle tension.
Composition of motor units-overall size of muscle, # of muscle fibers Frequency of stimulation Recruitment - size principal, small motor units recruited first, allows increase in force position of sarcomeres during contraction
Compared to slow oxidative muscle fibers, how are fast glycolytic muslce fibers different?
Fast glycolytic fibers fatigue more easily
Describe the relationship between the degree of overlap of the myofilaments and the amount of tension that can be created.
If a sarcomere is stretched too far, there will be insufficient overlap of the myofilaments and the less force will be produced. If the muscle is over-contracted, the potential for further contraction is reduced, which in turn reduces the amount of force produced.
Describe the reasons muscles experience muscle fatigue and oxygen debt.
Muscle use can quickly overwhelm the ability of the body to deliver oxygen. Muscle fibers must switch to anaerobic metabolism and produce lactic acid, at which point the muscle begins to fatigue.
During the depolarization phase of an action potential in skeletal muscle cells, the permeability of the plasma membrane to
Na+ Increases
Determine which energy source would be utilized under which conditions during skeletal muscle contraction.
Phosphocreatine provides phosphates to ADP molecules, producing high-energy ATP molecules. It is present in low levels in the muscle. Glycolysis converts glucose to pyruvate, water and NADH, producing two molecules of ATP. Excess pyruvate is converted to lactic acid which causes muscle fatigue. Cellular respiration produces further molecules of ATP from pyruvate in the mitochondria. It is also required to resynthesize glycogen from lactic acid and restore stores of phosphocreatine and ATP in the muscle Explain the difference between slow oxidative, fast oxidative and fast glycolytic muscle fibers. Be sure to explain under which circumstances they would be used and the different specializations they may have as a result.
Inside cell _____ is high
Potassium
_____ makes the cell more negative than it was at rest
Potassium
The functional unit of a skeletal muscle fiber is the
Sarcomere
Describe the events of skeletal muscle contraction.
Skeletal Muscle Contraction. (a) The active site on actin is exposed as calcium binds to troponin. (b) The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge. (c) During the power stroke, the phosphate generated in the previous contraction cycle is released. This results in the myosin head pivoting toward the center of the sarcomere, after which the attached ADP and phosphate group are released. (d) A new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach. (e) The myosin head hydrolyzes ATP to ADP and phosphate, which returns the myosin to the cocked position.
Compare and contrast the 3 different types of muscles with regards to their voluntary/involuntary nature as well as their general differences.
Skeletal Muscle- it has striations, lots of nuclei, voluntary Cardiac Muscle-it has striations, involuntary smooth muscle- no striations, involuntary
Outside cell ____ is high
Sodium
______ makes the cell more positive than it was at rest
Sodium
Explain the establishment and impact of the electrochemical gradient and how it is impacted by changes in permeability of the cell membrane to different ions.
The active transport of ions across the cell membrane causes an electrical gradient to build up across this membrane. The number of positively charged ions outside the cell is usually greater than the number of positively charged ions in the cytosol. This results in a relatively negative charge on the inside of the membrane, and a positive charge on the outside. This difference in charges causes a voltage to exist across the membrane.
Understand the events that occur during a muscle twitch from initial stimulation through relaxation.
The contraction generated by a single action potential is called a muscle twitch. A single muscle twitch has three components. The latent period, or lag phase, the contraction phase, and the relaxation phase. The latent period is a short delay (1-2 msec) from the time when the action potential reaches the muscle until tension can be observed in the muscle. This is the time required for calcium to diffuse out of the SR, bind to troponin, the movement of tropomyosin off of the active sites, formation of cross bridges, and taking up any slack that may be in the muscle. The contraction phase is when the muscle is generating tension and is associated with cycling of the cross bridges, and the relaxation phase is the time for the muscle to return to its normal length. The length of the twitch varies between different muscle types and could be as short as 10 ms (milliseconds) or as long as 100 ms (more on this later).
Describe which ions are most important for maintaining and generating membrane potentials in general.
The resting membrane potential is a result of different concentrations inside and outside the cell. The difference in the number of positively charged potassium ions (K+) inside and outside the cell dominates the resting membrane potential
Draw and provide a description of how the resting membrane potential is established and maintained.
The resting membrane potential is a result of different concentrations inside and outside the cell. The difference in the number of positively charged potassium ions (K+) inside and outside the cell dominates the resting membrane potential.When the membrane is at rest, K+ ions accumulate inside the cell due to a net movement with the concentration gradient. The negative resting membrane potential is created and maintained by increasing the concentration of cations outside the cell (in the extracellular fluid) relative to inside the cell (in the cytoplasm). The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement. In neurons, potassium ions are maintained at high concentrations within the cell while sodium ions are maintained at high concentrations outside of the cell. The cell possesses potassium and sodium leakage channels that allow the two cations to diffuse down their concentration gradient.
Explain the difference between wave summation (incomplete tetanus) and complete tetanus.
Treppe is when the muscle comes to rest before contracting again, but each contraction is stronger than the last. Wave summation is rapid stimulation that does not have a full rest in between. Unfused tetanus does not have a consistent contraction while fused has a sustained contraction.
Identify, explain, and draw the events that occur during an action potential (resting membrane potential, threshold, depolarization, depolarization & hyperpolarization).
When there no arrival of an impulse/action potential, the neuron is at it's resting potential . They have a high amount of potassium ions in the axon and a high amount of sodium ions outside ( potential difference ). However, the amount of sodium ions outside are much greater than the potassium ions inside - thus results in an electrochemical gradient. This is maintained by sodium-potassium pumps. Depolarization: when an electric current stimulates the axon, voltage-gated channels open in the membrane to allow sodium ions to pass through. It diffuses down the electrochemical gradient. This causes the potential different to become less negative inside the axon (as there is an inflow of sodium ions!). Resulting in depolarization. (the second part in the diagram!) Repolarization: due to depolarization, the axon becomes positive (because of the inflow of postassium ions). Thus, voltage-gated channels for sodium close and potassium ion channels open, so that potassium diffuses out. This is to restore the initial potential difference. Hyperpolarization: during repolarization, potassium ions tend to diffuse out toooo much. Causing, hyperpolarization briefly. Finally, the refractory period: at this stage, the axon is not responsive. It is recovering from the action potential to restore its resting potential. (aka back to the resting potential where the axon has a high amount of potassium and outside, there's a high amount of sodium!)
Thin contractile protein involved in cross-bridge formation, comes in filamentous or globular forms.
actin
Identify and describe the different proteins that make up a sarcomere.
actin-Thin contractile protein involved in cross-bridge formation, comes in filamentous or globular forms. myosin-Thick filamentous contractile protein involved in cross-bridge formation, has a club-like appearance with a "head."
Jerry Jogger's 3-mile run every morning takes about 30 minutes. Which of these sources provides the most energy for this run?
aerobic respiration
The sarcoplasmic reticulum stores
calcium ions
Explain the functional significance of the neuromuscular junction (NMJ).
chemical synapse between a motor neuron and a muscle fiber. allows motor neuron to transmit a signal to the muscle fiber which then causes muscle contraction.
An electrical change which brings the relative charge of the inside of the cell more positive; necessary for transmission of electrical impulses within a cell, or from one cell to another. f
depolarization
A L-type calcium channel in the muscle cell membrane, activated upon depolarization, couple depolarization signal to release of calcium. l
dihydropryidine receptor
Describe 4 characteristics of all muscle tissue.
excitability- can be stimualted contractility-cells can shorten extensibility-can lengthen elasticity-can stretch
During muscle contraction, the think and thin filaments are physically shortented.
false
A weight lifter attempts to lift a weight from the floor, but the weight is so heavy that he is unable to move it. The type of muscle contraction the weight lifter is doing is mostly
isometric
There are two different types of contraction isotonic and isometric. Differentiate between these two and give examples of when you might be using each type.
isotonic-generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions. example: walking isometric- generate force without changing the length of the muscle. example:biceps curl
Rigor mortis (the stiffening of muscles in the hours after their death) is cause by
lack of ATP
Identify the different levels of anatomical organization of skeletal muscle. Be sure to include the connective tissue that compartmentalizes everything.
microscopic level-sarcomere (functional unit) and myofibrils (single muscle cell, that is striated, also called muscle fiber) cell level- myoblasts and myofibril tissue level- neuromuscular junctions and fascicles Organ level- major skeletal muscles of the body PIC ON DOCS
Large and complex terminal formation by which an axon of a motor neuron establishes synaptic contact with a skeletal muscle fiber, transmitting neural impulses to a muscle.
motor end plate
Thick filamentous contractile protein involved in cross-bridge formation, has a club-like appearance with a "head."
myosin
Which of the following proteins is not a component of the thin filaments?
myosin
Responsible for opening a ligand-gated Na+ /K+ channel in the muscle membrane when the proper ligand binds to it.
nicotininc acetycholine receptor
Describe the 4 main functions of skeletal muscle.
produce movement maintain posture and body position (core muscles) stabilize joints (major stabilizing forces on joints) generate heat (hydrolysis or breakdown of ATP)
Located on the sarcoplasmic reticulum and once opened, allows Ca2+ flow from the sarcoplasmic reticulum into the sarcoplasm.
ryanodine receptor
The plasma membrane of a muscle fiber.
sarcolemma
The functional unit of the muscle fiber that includes the A-band, I-band, H-zone and the M-line.
sarcomere
Modified endoplasmic reticulum, stores and releases calcium. k
sarcoplasmic reticulum
Which of these is not a major property of muscle?
secretability
Describe the steps by which a skeletal muscle is excited.
step 1: action potential spread along the sarcolemma to the t-tubles step 2: calcium is released into the sarcoplasmic reticulum step 3: calcium binds to actin and the blocking action of the tropomyosin is removed step 4: myosin heads attach to begin contraction step 5: calcium is removed and the binding site on actin become blocked again by tropomyosin step 6: muscle relaxes
Store neurotransmitters, and following a Ca2+ driven signal, dump neurotransmitters into the synapse.
synapse vesicles
The structure at the end of the axon that contains neurotransmitters and vesicles.
synaptic terminal
These invaginations allow depolarization of the muscle membrane to quickly penetrate from the sarcolemma to the myofibril
t-tubule
As a sarcomere is stretched beyond its optimal length, muscle tension starts to decline from its maximum value. This is because
the degree of overlap between the thick and thin filaments decreses
Myofibrils are composed of regular repeating units. Be able to identify the different regions, and the impact contraction has on their appearance within skeletal muscle.
the regular repeating units are sarcomeres. thick and thin filamnets add in picture of annotated sarcomere PIC ON DOCS
All of the following are TRUE of the neuromuscular junction, EXCEPT
there re multiple neuromuscular junctions associated with each muscle cell
Muscles used for delicate, finely controlled movements have smaller motor units than muscles used for high power activities.
true
