Lecture Exam 3

Question 1

Specify the functions of skeletal muscle tissue

Answer 1

-Produces movement
-Maintaining posture and body position
-Supporting soft tissues
-Guarding body entrances and exits
-Maintaining body temperature
-Storing nutrients

Question 2

Describe the organization of muscle at the tissue level (connective tissue sheaths)

Answer 2

Three layers
-Epimysium - dense layer of collagen fibers that surround the entire muscle
-Perimysium - divides the skeletal muscle into a series of compartments called fascicles
-Endomysium - delicate connective tissue that surrounds the individual skeletal muscle cells

Question 3

Identify the structural components of a sarcomere

Answer 3

Question 4

Explain the importance of how the muscle fiber organelles (myofibrils, SR, T-tubules, etc) are arranged within the cell.

Answer 4

The myofibrils are arranged in sarcomeres while the Triad are over the zone of overlap on either side of the M-line. The triad consists of the T-tubules in the middle and the terminal cisternae, which is parts of the Sarcoplasmic Reticulum (SR). This runs over and over the length of the cell

Question 5

Identify the molecular components of thick and thin filaments

Answer 5

-The thin filaments are made up of single thing filament with 4 main proteins: F-actin, nebulin, tropmysoin, and troponin.
-The thick filament contains about 300 myosin molecules, each made up of a pair of myosin subunits twisted around one another. The long tails is bound to each other. The Head has two globular protein subunits

Question 6

Describe what happens to the various regions of a sarcomere during muscle contraction

Answer 6

1)The H bands and the bands narrow
2)the zones of overlap widen
3)the Z lines move closer together
4)the width of the A band remains constant.

Question 7

Identify the components of the neuromuscular junction.

Answer 7

1) presynaptic motor nerve terminal, 2) synaptic space (synaptic cleft), and 3) the postsynaptic surface of the skeletal muscle fiber.

Question 8

Summarize the events involved in the neural control of skeletal muscle

Answer 8

1) The cystoplasm of the axon terminal contains vesicles filled with ACh (acetylcholine is a neurotransmitter). The synaptic cleft and the motor end plate have enzyme acteylocholinesterase.
2) The electrical impulse stimulates the ACh to release. An action potential is a sudden change in the membrane potential that travels along the length of the axon
3) The action potential triggers the exocytosis of ACh into the synaptic cleft.
4)ACh diffuses across the synaptic cleft and blind to ACh receptor membrane channels.This opens the membrane channel on the surface of the motor end plate. The Sodium ions rush in
5) The sudden sodium rush results in generation of an action potential in the sarcolemma. ACh is removed from the synaptic cleft. (enzyme or diffusion). This closes the ACh receptor membrane channels.

Question 9

Describe what is involved with excitation-contraction coupling

Answer 9

1)Neural control - A skeletal muscle fiber contracts when stimulated by a motor neuron at a neuromuscular junction. The stimulus arrives in the form of an action potential at the axon terminal
2) Excitation - The action potential causes the release of ACh into the synaptic cleft, which leads to excitation–the production of an action potential in the sarcolemma.
3)Release of Calcium Ions - This action potential travels along the sarcolemma and down T tubules to the triads. This triggers the release of calcium ions from the terminal cisternae of the sarcoplasmic reticulum
4)Contraction cycle begins - When the calcium ions bind to troponin, resulting in the exposure of the active sites on the thin filaments. This allows cross-bridge formation and will continue as long as ATP is available.
5) Sarcomere Shortening - As the thick and thin filaments interact the sarcomeres shorten, pulling the ends of the muscle fiber closer together.
6) Generation of Muscle Tension - During the contraction, the entire skeletal muscle shortens and produces a pull, or tension, on the tendons at either end.

Question 10

Outline the steps that are involved during the contraction cycle

Answer 10

1) Contraction Cycle Begins - Involves a series of interrelated steps. It begins with the arrival of calcium ions within the zone of overlap in a sarcomere.
2)Active-Site Exposure - calcium ions bind totropinin, weakening the bonds between actin and the troponin molecule then changes position, rolling the tropomyosin molecule away from the active sites on actin. and allowing interaction with the energized myosin heads.
3)Cross-Bridge formation - once the activesitesare exposed, the energized myosin heads bind to them, forming cross-bridges.
4)Myosin Head Pivoting - After cross-bridge formation, the energy that was stored in the resting state is released as myosin head pivots towards the M line. This action is called the power stroke; when it occurs the bound ADP and phosphate group are released.
5) Cross-Bridge Detachment - When another ATP binds to the myosin head, the link between the myosin head and the active site on the actin molecule is broken. The active site is now exposed and able to form another cross-bridge.
6)Myosin Reactivation - Myosin reactivation occurs when the free myosin head splits ATP into ADP and P. The energy released is used to recock the myosin head.

Question 11

Explain the mechanisms involved in muscle fiber relaxation.

Answer 11

1)ACh is broken down - by acetylcholinestrase (AChE), ending action potenital generation
2)Sarcoplasmic reticulum reabsorbs Calcium Ions - their concentration in the cytosol decreases
3)Active sites covered, and cross-bridge formation ends - Active sites return to being covered again.
4) Contraction ends - without cross-bridge formation, contraction ends.
5) Muscle relation occurs.

Question 12

Discuss the factors that determine the peak tension developed during a contraction of a muscle fiber.

Answer 12

A sarcomere works most efficiently within an optimal range of lengths. When the sarcomere length is within this range, the maximum # of cross-bridges can form, and the maximum amount of tension is produced. If the sarcomere length falls outside the range–stretched and lengthened, or compressed and shortened–it cannot produce as much tension when stimulated.

Question 13

Discuss the factors that affect peak tension production during the contraction of an entire skeletal muscle

Answer 13

The amount of tension produced in a muscle contraction depends on two factors: the number of muscle fibers activated, and the frequency of neural stimulation to the muscle fibers.

Question 14

Explain the significance of motor units to whole muscle contraction.

Answer 14

Motor unit is a motor neuron and all the muscle fibers that it controls. Muscle fibers of different motor units are intermingled so the forces applied to the tendon remain balanced regardless of which motor units are stimulated.

Question 15

Define muscle tone, and its relationship to normal everyday activities

Answer 15

Some motor units are always active when the entire muscle is not contracting. Not enough to produce enough tension to cause movement, but they do tense and firm the muscle. This resting tension is Muscle tone. Heightened muscle tone accelerates the recruitment process during a voluntary contraction, because some motor units are already stimulated. while little muscle tone appears limp and soft.

Question 16

Differentiate between isotonic and isometric contractions, include concentric and eccentric contractions.

Answer 16

Isotonic Concentric Contractions- the muscle tension exceeds the load and the muscle shortens.
Isotonic Eccentric Contractions - the peak tension developed is less than the load, and the muscle elongates due to the contraction of another muscle or pull gravity.
Isometric Contractions - the muscle as a whole does not change length, and the tension produced never exceeds the load.

Question 17

Describe the mechanisms by which muscle fibers obtain the energy to power contractions.

Answer 17

Normal muscle function requires (1) substantial intracellular energy reserves, (2) a normal circulatory supply, (3) a normal blood oxygen level, and (4) a blood pH within normal limits.
ATP and Creatine Phosphate Reserves. This allows for about 2 seconds and 15 seconds of work respectively
ATP Generation with glycolosis and aerobic metabolism. With glycolosis which is anaerobic metabolism allows for 130 seconds of work. And glycogen aerobic metabolism allows for 2400 seconds of work.

Question 18

Describe the factors that contribute to muscle fatigue

Answer 18

Caused by a couple things:
-Reduction on the pH in the blood due to the lactic acid build up
-Reduction of metabolites, running out of glucose and fatty acids.
-Physically damaging the myofibrils, the sarcolemmas

Question 19

Discuss the stages and mechanisms involved in muscle recovery

Answer 19

recovery period = time needed to return conditions in muscle fibers to pre-exertion levels—may take several hours, up to a week

Clear lactic acid removal and recycling
and replenish oxygen debt, need to build up the glycogen stores and creatine store

Question 20

Relate the type of muscle fibers to muscle performance

Answer 20

Fast fibers - large in diameter, white fibers, fast twitch glycofiber (eye muscles)
Slow Fibers - smaller in diameter, more vascularized, more myoglobin (oxygen store), more fatigue resistant (back muscles)
Intermediate Fibers - the other fibers can be trained to be similar to the other. Which they end up being a combination of both. Muscle fibers can not fully change from slow to fast or vice versa.

Question 21

Distinguish between aerobic and anaerobic endurance, explain their implications for muscular performance.

Answer 21

-Anaerobic endurance is the length of time muscular contraction can continue to be supported by the existing energy reserves of ATP and CP and by glycolosis. Limited by the amount of ATP and CP available, The amount of glycogen available for breakdown and the ability of the muscle to tolerate lactate and the build up of hydrogen ions generated during the period of anaerobic metabolism.
-Aerobic endurance is the length of time a muscle can continue to contract while supported by mitochondrial activities. Conditioning for aerobic endurance improves an individual’s ability to continue an activity for longer periods of time.

Question 22

Identify the structural and functional differences between skeletal muscle fibers and cardiac muscle cells.

Answer 22

Cardiac muscle is striated, branched, uninucleate, and involuntary. Do not have the terminal cisternae because it needs a continue flow of calcium since it is continuous. Intercalated discs, when two adjacent cell sarcolemma intertwined and bound together by gap junctions and desmosomes; can not do tetanus; beats on its own
Where the skeletal are too striated, however is not branched, multinucleate and voluntary. have the terminal cisternae to dump calcium ions

Question 23

Identify the structural and functional differences between skeletal muscle fibers and smooth muscle cells.

Answer 23

Smooth muscles do not have striation, so no myofibrils and sarcomeres. But does have thick and thin filaments. Randomly distributed zones of overlap distributed throughout the cell; cell plasticity and able to produce tension over wide variety of size; single nucleus; no SR so gets calcium from the extracellular matrix; each cell doesn’t need a connection to a nerve;
Skeletal muscle has sarcomere with organized thick and thin filaments; doesn’t have very much placidity; multi nucleus; SR calcium ions; each muscle cell needs a neuromuscular junction

Question 24

Discuss the role that smooth muscle tissue plays in systems throughout the body

Answer 24

Stomach in the digestive system allows for the stomach to expand with meals and still contract. Same with the urinary bladder, allows for the bladder to expand and still contract. This is called plasticity.

Question 25

Describe the anatomical and functional divisions of the nervous system

Answer 25

The anatomical division has three divisions: Central Nervous system, the peripheral nervous system and the enteric nervous system
The functional division is divided into afferent and efferent divisions.

Question 26

Identify the structure of a typical neuron and describe the functions of each component

Answer 26

Cell body - (soma) contains a large, round nucleus with prominent nucleolus
Dendrites - Sensitive processes that extend and branch out from the cell body
Axons - a long cytoplasmic process, which is capable of propagating an electrical impulse known as a action potential
Telodendria - the main axon trunk and any collaterals end in a series of fine extensions; also known as terminal branches.

Question 27

Classify neurons based on their structure

Answer 27

Anaxonic Neurons - are small and have numerous dendrites, but no obvious axons. There is an axon but it is not visible.
Bipolar neurons - have two distinct processes–one dendrite and one axon–with the cell body between the two.
Unipolar Neuron - (pseudounipolar neuron)the dendrites and axon are continuous–basically fused–and the cell body lies off to one side
Multipolar neurons - have two or more dendrites and a single axon.

Question 28

Classify neurons based on their function

Answer 28

Sensory Neurons - Afferent neurons, form the afferent division of the PNS. Unipolar neurons, whose processes, known as afferent fibers, extend between a sensory receptor and the CNS
MotorNeurons - efferent neurons; form the efferent division of the PNS. Axons of these neurons that travel away from the CNS are efferent fibers. (Efferent system are somatic nervous system and the autonomic (visceral) nervous system)
Interneurons - Are located between sensory and motor neurons.most are located within the brain and spinal cord, but some are in autonomic ganglia.

Question 29

Describe the locations and functions of neuroglia (both CNS and PNS)

Answer 29

Neuroglia - Supportive cells to Neurons
Neuroglia of CNS - Astrocytes-largest and most numerous neuroglia (maintains the BBB, creates a 3D framework for the CNS, Repairs damaged nervous tissue, guides neuron development, and controls the interstitial environment); Ependymal Cells-simple cuboidal to columnar epithelium cells that line the central canal and ventricles; Oligodendrocytes-maintain cellular organization within gray matter and provide a myelin sheath in areas of white matter; Microglia-acts as wandering janitorial service and police force by engulfing cellular debris, wastes, and pathogens.
Neuroglia of PNS - Satellite Cells-surround neuron cell bodies in ganglia and regulate the interstitial fluid around the neurons; Schwann Cells-(neurolemmocytes) either form a thick, myelin sheath or indented folds of plasma membrane around peripheral axons.

Question 30

Describe how peripheral neurons can respond to injury

Answer 30

Schwann cells can regenerate and allow the tube available for the axon stump to grow through. It is limited to just PNS

Question 31

Explain how resting potential is created and maintained

Answer 31

the extracellular fluid and intracellular fluid (cytosol) differ greatly in ionic composition.
Cells have selectively permeable membranes. They can leave by membrane channels (leak channels or active transport mechanism)
Membrane permeability varies by ion. The cells passive and active transport mechanisms do not ensure an equal distribution of charges across its plasma membrane (permeability varies by ion). Potassium diffuse out of the cell through potassium leak channel (sodium can not pass through). The sodium/potassium pump continually keeps the potassium in and the sodium out to keep the charge and the electrical potential of the sodium ready for an action potential

Question 32

Identify the various types of gated channels found in neuron plasma membranes and where they can be found

Answer 32

Chemically gated ion channel - Like a lock and key; neuromuscular junction awaiting ACh
Voltage-gated ion channel - excitable membranes of the axons of unipolar and multipolar neurons, and sarcolemma (including T-tubules) of skeletal muscle fibers and cardiac muscle cells. (for neurons the voltage-gated sodium ion channels, potassium ion channels and calcium ion channels).
Mechanically gated ion channel - changes shape when pressure is applied due to touch of a hand. Respond to touch, pressure, or vibration.

Question 33

Describe how a graded potential is generated, and describe factors which can keep it from becoming an action potential.

Answer 33

When the plasma membrane of a resting cell is exposed to a chemical that opens the chemically gated sodium ion channels:
1) Sodium ions enter the cell that are attracted to the negative charges along the inner surface of the membrane. As these additional positive charges spread out, the membrane potential shifts toward 0mV (depolarization).
2)As the plasma membrane depolarizes, sodium ions are released from its outer surface. These ions, along with other extracellular sodium ions, then move toward the open channels, replacing ions that have already entered the cell. This movement of positive charges parallel to the inner and outer surfaces of a membrane that spreads the depolarization is called a local current.

Question 34

Describe the events involved in the generation action potential

Answer 34

It is all-or-nothing action potential. From a resting membrane potential of -70 mV with the axolemma that contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed.
1)Depolarization to threshold. The stimulus that initiates the action potential is graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold. -60mV
2)Activation of Sodium Ion Channels and Rapid Depolarization. When the sodium channel activation gates open, the plasma membrane becomes much more permeable to Na+. Driven by the large electrochemical gradient sodium ions rush into the cytosol, and rapid depolarization occurs. The inner membrane surface now has more positive ions that negative ones, and the membrane potential has changed from -60mV to a positive value
3)Inactivation of Sodium Ion Channels and Activation of Potassium Ion Channels Starts Repolarization. As the membrane potential approaches +30mV, the inactivation gates of the voltage-gated sodium channels close (sodium channel inactivation) and coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward the resting level and repolarization begins.
4)Time Lag in Closing All Potassium Ion Channels Leads to Temporary Hyperpolarization. The voltage-gated sodium channels remain inactivated until the membrane has repolarized to near threshold level. At this time, they regain their normal status: closed but capable of opening. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting membrane potential (about -70mV). Until all of these potassium channels have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization.
—Back to resting membrane potential. The sodium/potassium pump is continually working to get the potassium back into the cell.

Question 35

what type of events involved propagation of an action

Answer 35

AP generated in adjacent axon segment.
local current flows to the axon segment.
axon segment depolarize to a threshold.
Voltage-gated Na+ channels open.
influx of Na+
-Continuous Propagation
-Saltatory propagation

Question 36

Describe the events involved in the Continuous propagation of an action potential

Answer 36

Continuous Propagation (unmyelinated axon)

Question 37

Describe the events involved in the Saltatory propagation of an action potential

Answer 37

Question 38

Differentiate between the absolute refractory period and the relative refractory period

Answer 38

The absolute refractory period is the first part of the action potential when
Absolute refractory period of a neuron is the period of time during which no amount of external stimulus will generate an action potential. Relative refractory period is the period of time during which only a large stimulus will generate an action potential

Question 39

Discuss the factors that affect the speed with which action potentials are propagated.

Answer 39

Axon diameter, internode distance, and myelin sheath thickness all influence the speed of action potential propagation.
-Type A fibers are the largest myelinated axons, with diameters ranging from 4-20 μm.these fibers carry action potential is at speeds of up to 120 meters per second or 268 mph.
-Type B fibers are smaller myelinated axons, with diameters of 2-4 μm. Their propagation speeds average around 18 m/sec (about 40mph).
-Type C fibers are unmyelinated and less than 2 μm in diameter. These axons propagate action potential is at the leisurely pace of 1 m/sec (only 2 mph)

Question 40

Describe the general structure of a synapse in the CNS and PNS

Answer 40

A synapse is the site where a neuron communicates with another cell. It is composed of presynaptic and postsynaptic cells whose plasma membranes are separated by a narrow synaptic cleft .
A relatively simple, round axon terminal occurs where the postsynaptic cell is another neuron. At a synapse, the narrow synaptic cleft separates the presynaptic membrane, where neurotransmitters are released, from the postsynaptic membrane. synaptic vesicles.

Question 41

Discuss the events that occur at a chemical synapse

Answer 41

-Chemical Synapses is where one neuron sends chemical signals to another cell, often a second neuron. Every synapse involves two cells: (1) the axon terminal of the presynaptic cell, which sends a message, and (2) the postsynaptic cell, which receives the message. A narrow space called the synaptic cleft.

Question 42

Discuss factors involved in synaptic delay and synaptic fatigue

Answer 42

The synaptic delay is due to the time necessary for transmitter to be released, diffuse across the cleft, and bind with receptors on the postsynaptic membrane. Chemical synaptic transmission is generally unidirectional.
Synaptic fatigue happens when the cell is under intensive stimulation and the ACh molecules can not be recycled in the time the AP is happening.

Question 43

Discuss the interactions that make possible processing of information in neural tissue (IPSP’s, EPSP’s, and presynaptic inhibition and facilitation)

Answer 43

Excitatory neurotransmitters cause depolarization and promote the generation of action potentials.
Inhibitory Neurotransmitters cause the hyperpolarization and suppress the generation of action potentials.
Excitatory postsynaptic Potential (ESPS) is graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane.
Inhibitory Postsynaptic Potential (IPSP) is a graded hyperpolarization of the post synaptic membrane.