Monday, week 2 A&P Flashcards
Compare the three muscle types for location
Sk: attatched to bones or (some facial) to skin
C: Walls of heart
Sm: Unitary muscle in walls of hollow visceral organs (other than heart); multi unit m. in intrinsic eye m’s, airways, large arteries
Compare the three muscle types for cell shape and appearance
Sk: single, very long cylindrical multinucleate cells with obvious striations
C: branching chains of cells; uni or binucleate; striations
Sm: Single fusiform, uninucleate, no striations
Compare the three muscle types for connective tissue components
Sk: epimysium, perimycium, and endomycium
C: Endomysium attached to fibrous skeleton of heart
Sm: endomysium
Do all three muscle types have myofibrils composed of sarcomeres?
Skeletal muscles does; cardiac muscle’s myofibrils are of irregular thickness. Smooth muscle doesn’t, but actin and myosin filaments are present throughout; dense bodies anchor actin filaments
Do all three muscle types have T tubules and site of invagination?
Sk: yes; two in each sarcomere at A-1 junctions
C: yes; one in each sarcomere at Z disc; larger diameter than those of skeletal muscle
Sm: no; only coeval
Do all 3 muscle types have an elaborate SR?
Sk: yes
C: less than skeletal m; scant terminal cisterns
Sm: equivalent to cardiac muscle; some SR contacts the sarcolemma
Do all 3 muscle types have gap junctions?
Sk: no
C: yes, at intercalated discs
Sm: yes, in unitary muscle
Do the cells of all 3 muscle types have individual neuromuscular junctions?
Sk: yes
C: no
Sm: Not in unitary muscle, yes in multi unit muscle
What is the regulation of contraction for each of the 3 muscle types?
Sk: Voluntary via axon terminals of the somatic nervous system
C: involuntary; intrinsic system regulation; also autonomic nervous system controls; hormones, stretch
Sm: involuntary; autonomic nerves, hormones, local chemicals; stretch
What is the source of Ca2+ for calcium pulse for each muscle type?
Sk: SR
C: SR and from ECF
Sm: SR and from ECF
What is the site of calcium regulation for each of the three muscle types?
Sk: troponin on actin containing thin filaments
C: troponin on actin containing thin filaments
Sm: calmodulin in the cytosol
Do all three muscle types have pacemaker cells?
cardiac does and unitary smooth muscle does
What is the effect of nervous system stimulation on each of the three muscle types?
Sk: excitation only
C; Excitation or inhibition
Sm: Excitation or inhibition
What is the speed of contraction for each of the three muscle types?
Sk: slow to fast
C: slow
Sm: Very slow
Do each of the three muscle types exhibit rhythmic contraction?
Sk: no
C: yes
Sm: yes in unitary muscle
What is the response to stretch in each of the three muscle types?
Sk: Contraction strength increases to a point
C: Contractile strength increases with degree of stretch
Sm: stress-relaxation response
What kind of respiration is used for each of the 3 muscle types?
Sk: aerobic and anaerobic
C: aerobic
Sm: Mainly aerobic
How does skeletal muscle provide nutrient stores for the body?
Glycogen stored in muscle; proteins in muscle can be broken down into amino acids
What are the three components of skeletal muscle in gross terms?
Skeletal muscle fibers (cells), nerves, blood vessels
What is an epimysium?
This is the dense layer of collagen fibers surrounding the muscle
What is the perimysium?
a fibrous layer of collagen and elastic fibers that divides the skeletal muscle into a series of compartments. it also contains the blood vessels and nerves
What is the endomysium?
This is the thin layer of auroral tissue that surrounds each muscle fiber. It contains capillaries, myosatellite cells, and neural axons.
What is a myofibril? Define and describe it.
These are bundles of protein filaments (actin, myosin, or titan) found in each muscle fiber. They are cylindrical and run the length of the fiber. They are banded in appearance.
What are myosatellite cells?
Stem cells that reside in the endomysium to repair damaged muscle tissue
Describe skeletal muscle development
Myoblasts fuse to form multinucleate cells (some remain as myosatellites), which further develop by enlarging, differentiating, and producing proteins for contraction.
What is the sarcolemma? sarcoplasm?
The specialized plasma membrane of the skeletal muscle fibers.
The cytoplasm of the fibers.
What takes up most of the space in a skeletal muscle fiber?
hundreds to thousands of myofibrils.
What do myofibrils mostly consist of?
bundles of myofilaments (thick and thin filaments)
What protein makes up thin filaments?
actin
What protein makes up thick filaments?
myosin
What are sarcomeres?
Repeating contractile units made of myofilaments
Draw a sarcomere complete with the following components: H band M line A band Z line I band
Compare to page 310 in the book
What is each band/line? H band M line A band I band Z line
H bande: thick filaments only; this shortens during contraction
M line: This connects the central portion of each thick filament; it is pulled toward the Z line during contraction
A band: this is the dense region of sarcomere that contains thick filaments
I band: this contains only thin filaments
Z line: this marks the boundary between adjacent sarcomeres; it is pulled toward the M line during contraction
Describe T tubules
These are narrow tubes that are continuous with the sarcolemma
Describe the sarcoplasmic reticulum (SR)
similar to smooth ER, it forms a network around each individual myofibril. It surrounds T tubules on either side to form terminal cisternae.
What is a triad on a myofibril?
a T tubule plus two terminal cisternae on either side
What is calsequestrin?
A protein that reversibly binds some calcium ions to store them in the SR (Some are free in the SR solution)
When muscles are resting, where is the intercellular calcium?
In the terminal cisternae of the SR. It can be released for contraction through voltage gated channels
Describe thin filaments in general and the two different kinds. Also, what other two proteins are associated with its structure within a resting sarcomere?
Actinin connects thin filaments to the z-line
F (fibrous) actin is a twisted strand composed of two rows of several hundred G (globular) actin.
Nebulin is a protein that holds F actin together
What does Tropomyosin do?
It masks the G-actin active sites (which are binding sites for myosin heads)
What is the structure of troponin and what are its three functions?
It is composed of three globular subunits:
One interlocks with tropomyosin, one binds one G-actin, and the third subunit has a receptor for binding two calcium ions.
Describe a thick filament in a sarcomere
It is composed of many myosin molecules; the tails are bound together to expose a spiral of hinged heads.
Describe the sliding filament theory
Thin filaments slide past thick filaments. In this process:
- the H bands and I bands get smaller (HI!!)
- The zones of overlap get bigger
- The Z lines move closer together (ZZZZ)
- the width of the A band remains constant (consistent straight A’s)
What happens to myofibrils during contraction?
They get shorter
Describe the events that produce an action potential
- resting voltage is -70mV. A charge reversal begins with a small increase in sodium ion membrane permeability up to a set threshold (-55mV).
- Now, voltage gated Na+ channels open and all those positively charged ions rush into the cell. The membrane potential becomes positive and considered depolarized (+30mV).
- Now the voltage gated sodium channels close and voltage gated potassium ions move out of the cell to repolarize.
- Repolarization continues until the resting potential is reached, when the voltage gated potassium channels begin closing.
- As the voltage gated potassium channels close, the membrane potential stabilizes at resting levels. After the refractory period, the former concentrations of the sodium and potassium ions across the plasma membrane are restored.
What can’t happen during a refractory period?
The membrane cannot respond to another stimulus. A second depolarization cannot occur.
How many NMJ’s does each muscle fiber have?
Only one
Most neurotransmitters are what kind of molecule?
amino acid or short peptide
What events at the synaptic cleft lead to excitation of the muscle fiber?
When an action potential reaches the axon terminal, voltage gated calcium channels on the neural membrane open, allowing calcium ions in. These bind to a protein on the vesicles of acetylcholine, which are then signaled to fuse with the plasma membrane (exocytosis). ACh diffuses across the synaptic cleft and binds to ACh receptors on the surface of the motor end plate (muscle fiber). The binding of ACh opens sodium channels and sodium travels down its concentration gradient into the sarcoplasm. This generates an action potential in the sarcolemma. ACh diffuses away or gets broken down by AChE in the synaptic cleft, inactivating the ACh receptors. The action potential passes along the sarcolemma down the T tubules and between the terminal cisternae, opening voltage gated calcium channels on its surface. Calcium ions flood into the sarcomeres at the zones of overlap where they cause contraction.
What does calcium do in the sarcomere?
It binds to troponin, exposing the myosin binding sites on actin. Cross bridges can now form.
What kind of enzyme is a myosin head?
an ATPase
Describe crossbridge cycling
- Calcium ions arrive within the zone of overlap
- Ca binds to troponin, exposing the myosin binding sites on the actin filaments
- the cross bridge forms when energized (cocked) myosin heads bind to the active sites
- the myosin heads pivot toward the M line (power stroke). when this happens, the bound ADP and P are released
- Another ATP binds to the myosin head, which causes the myosin to release from the actin binding site.
- The myosin head gets rechecked using the energy it gleans from splitting ATP into ADP and P.
Steps of excitation/contraction coupling?
- neural control
- excitation
- calcium ion release
- contraction cycle begins
- sarcomeres shorten
- muscle tension released
How do we control muscle tension?
Cannot activate only a few sarcomeres. Muscle fiber is either on or off. Tension is affected by fiber’s resting length at the time of stimulation.
When are sarcomeres able to produce the most tension? the least?
Most: There is an optimal range of resting lengths. within this range, the maximum number of cross bridges can form
least When thick filaments are pressed against the z lines. or there is no zone of overlap.
What is a muscle twitch?
A single stimulus/contraction/relaxation sequence
What are the phases of a twitch?
- resting
- latent period (when AP occurs, SR releases Ca)
- Contraction phase (when tension reaches a maximum)
- Relaxation phase (ca levels fall, tropomyosin masks active sites, tension falls to resting levels)
The peak tension developed by a skeletal muscle depends on what?
The frequency of stimulation and the number of muscle fibers stimulated
Describe Treppe muscle tension
Stimulus applied immediately after relaxation phase has ended; the tension rises in steps (not common in skeletal muscles)
Describe wave summation muscle tension
If a second stimulus arrive before the relaxation, the subsequent contraction is more powerful, increase in tension
Describe incomplete tetanus
A muscle producing almost peak tension during rapid cycles of contraction and relaxation
Describe complete tetanus
A higher stimulation frequency eliminates the relaxation phase. Action potentials arrive so rapidly that the SR can’t reclaim the Ca ions.
What causes tetanus in humans?
tetanolysin toxin released by Clostridium bacteria. The toxin blocks the release of inhibitory neurotransmitters; muscles therefore constantly stimulated. There is a constant release of ACh.
What is a motor unit?
Most motor neurons control hundreds of muscle fibers. The muscle fibers controlled by a single motor neuron are a motor unit.
What influences the size of the motor unit?
The amount of control necessary for that movement. muscles in the eye have small MU’s; legs have big ones.
Number of fibers stimulated correlates to what?
Amount of tension produced
What is asynchronous motor unit summation?
During a sustained contraction, motor units are activated on a rotating basis, allowing some to rest and recover while others contract. Relay approach.
what is muscle tone?
A number of motor units are active even when the entire muscle isn’t contracting. More tone=more energy consumed
Describe Isotonic contractions
tension rises and muscle length changes
Can be concentric: muscle contracts and overcomes the load
can be eccentric: the load is greater than the peak tension, so the muscle elongates
Describe isometric contractions
muscle as a whole doesn’t change length
Describe two types of muscle fatigue
Nervous fatigue (refractory period) Metabolic fatigue: either a shortage of substrates (calcium ions or ATP) or an accumulation of metabolites which interfere with the release of calcium or its ability to stimulate muscle contraction
Name the 4 sources of energy stored in a typical muscle fiber
free ATP, creatine phosphate, glycogen from anaerobic metabolism (glycolysis), or glycogen from aerobic metabolism
How is the metabolite lactate removed from the muscles?
diffuses into blood stream and then the liver absorbs and converts it into pyruvate
What are fast, slow and intermediate fibers?
Most skeletal muscle are fast fibers. These have powerful contractions but fatigue quickly. Slow fibers are smaller and are specialized for endurance. Intermediate fibers more closely resemble fast fibers, but have a more extensive capillary network and are more resistant to fatigue.
What physiological change in muscle occurs in hypertropy
More mitochondria, more glycolytic enzymes, higher glycogen reserves, more myofibrils. Equals bigger
What are 3 pathogens that interfere with muscular function?
Polio: attacks motor neurons in the spinal cord and brain
Tetanus: suppresses the inhibition of motor neuron activity
Botulism affects neuromuscular communication
What happens to the muscle without adequate ATP?
Ca remains in cytosol and cross bridges can’t detach, causing muscle fibers to lock in contracted state
What causes rigor mortis
SR deteriorates, releasing calcium for sustained contraction. ATP reserves exhausted, locking muscles into contracted state.
What are parallel muscles?
Fasicles run parallel to long axis of muscle, thus, contraction only shortens muscle about 30%
What is convergent muscle?
fan shaped. Stimulation of different portions of the muscle can change the direction of the pull.
What is a pennate muscle?
Fascicles form a common angle with the tendon so that fibers pull at an angle. produces more tension than parallel muscles but not as far.
Describe the three classes of levers
1st class: fulcrum between the force and the load (seesaw)
2nd class: load between the AF and the fulcrum (Wheelbarrow) we don’t go as far, but can carry a heavy load.
3rd class: AF is between the fulcrum and the L. Most common in the body. We can go far fast, but the load has to be relatively small.
