Exam 2- Chapter 12 Flashcards
When a skeletal muscle contracts does it elongate or shorten?
Shorten
When a skeletal muscle contracts and then shortens, what happens?
- This places tension on tendons connecting it to a bone.
- This moves the bone at a joint.
When a skeletal muscle contracts, the bone that moves is attached at the muscle ____.
Insertion
The muscle is attached to a bone that does not move at the muscle ____.
Origin
What do flexor muscles do?
Decrease the angle between two bones at a joint
What do extensor muscles do?
Increase the angle between two bones at a joint
The main muscle responsible for movement in a given direction is the _____.
Agonist
Flexors and extensors that work together are ____.
Antagonist
Skeletal muscles are surrounded by what?
Fibrous epimysium
Connective tissue called ______ subdivides the skeletal muscle into fascicles.
Perimysium
Each fascicle of skeletal muscle is subdivided into ______ _____ surrounded by _____.
- Muscle fibers
2. Endomysium
Skeletal muscle fibers have plasma membranes called ______.
Sarcolemma
Are skeletal muscles single or multi nucleated?
multi-nucleated
Are skeletal muscles smooth or striated?
striated
Are skeletal muscle involuntary or voluntary?
voluntary
Skeletal muscles have I & A bands. Which are light bands? Dark bands?
- I bands = light
2. A bands = dark
Define neuromuscular junction (NMJ).
Site where a motor neuron stimulates a muscle fiber
Define motor end plate.
Area of the muscle fiber sarcolemma where a motor neuron stimulates it
Define a motor unit.
A single motor neuron and all the muscle fibers it innervates
Do the muscle fibers in a motor unit contract separately or at once?
All at once
Contraction strength comes from motor unit _______.
recruitment
Does finer muscle control require larger or smaller motor units?
Smaller motor units (fewer muscle fibers)
The eye muscles may have about ____ muscle fibers/motor units.
20
Larger, stronger muscles may have motor units with _____ of muscle fibers
thousands
Control and strength are _______.
trade-offs
Skeletal muscle fibers have densely packed subunits called _____ that run the length of the muscle fiber.
myofibrils
What are myofibrils composed of?
thick and thin myofilaments
What is thick myofilament called?
Myosin
What is thin myofilament called?
Actin
What are the striations on skeletal muscle produced by?
the thick and thin filaments
I bands contain ____________.
only thin filaments
A bands contain _____________.
all of the thick filament with some thin filament overlap.
Where are H bands in the center of? Do they have thin filament overlap?
- A bands
2. No
Where are z lines found?
Center of each I band
Where are m lines found? What do they help hold down?
- Center of each A band
2. Help hold down thick filaments
What does a sarcomere extend from?
area from one Z line to the next
What is titin?
protein that anchors in the thick filaments and allows elastic recoil
- What is the sliding filament theory?
- What happens to the A bands?
- What happens to the I bands?
- What happens to the thin filaments?
- When a muscle contracts, sarcomeres shorten
- A bands do not shorten
- I bands do shorten
- Thin filaments do not shorten and slide toward the H zone
Sliding is produced by several cross bridges that form between _____ and ____.
Myosin/Actin
What does the myosin head serve as in a cross bridge? What does this do? What does this allow for?
- myosin ATPase enzyme
- splitting ATP into ADP + Pi
- the head to bind to actin when the muscle is stimulated
Release of Pi upon binding does what?
cocks the myosin head, producing a power stroke that pulls the thin filament toward the center
What happens after the power stroke? What does that in-turn make happen? Then? Finally?
- ADP is released and a new ATP binds
- Makes myosin release actin
- ATP is split
- The myosin head straightens out and rebinds to actin farther back.
What is thin filament composed of?
The protein: actin
What proteins does thin filament (actin) have that prevent myosin from binding at rest?
- Troponin
2. Tropomyosin
What does troponin bind to?
tropomyosin
What does tropomyosin bind to?
actin
What specifically does tropomyosin do?
Physically blocks cross bridges
Troponin complex:
- What does Troponin I do?
- What does Troponin T do?
- What does Troponin C do?
- Troponin I inhibits binding of myosin
- Troponin T binds to tropomyosin
- Troponin C binds to calcium
When muscle cells are stimulated what is released inside the muscle fiber? What does some attach to/what does this cause? This results in what?
- Ca2+ is released inside the muscle fiber
- Some attaches to troponin C, causing a conformational change in troponin and tropomyosin
- Myosin is allowed access to form cross bridges
What is Sarcoplasmic Reticulum (SR)?
modified endoplasmic reticulum
Where is Ca2+ stored when the muscle is at rest? Specifically where is most of it stored?
Sarcoplasmic Reticulum (SR); most is stored in terminal cisternae
What are Transverse Tubules?
Narrow membranous tunnels formed from the sarcolemma
Are Transverse Tubules open or closed to the extracellular environment?
Open
Are Transverse Tubules capable or not capable of conducting action potentials?
Capable
What are transverse tubules closely situated next to?
terminal cisternae
What are 5 steps in stimulating a muscle fiber?
- Acetylcholine is released from the motor neuron.
- End plate potentials are produced.
- Action potentials are generated.
- Voltage-gated calcium channels in transverse tubules change shape and cause calcium channels in SR to open.
- Calcium is released and can bind to troponin C.
When a muscle fiber is stimulated what diffuses out of the SR? Via what?
- Ca2+
2. Calcium release channels
At the end of contraction, what happens to Ca2+?
It is actively pumped back into the SR.
What does it mean for a muscle to “twitch”?
When a muscle quickly contracts and relaxes after a single electrical shock of sufficient voltage
When increasing the voltage of a muscle twitch what happens?
Increasing the voltage increases the strength of the twitch up to a maximum
When a second shock is applied immediately after the first, a second twitch will partially piggyback the first. This is called _______.
Summation
Increasing the frequency of electrical shocks decreases the relaxation time between twitches. This is called _______ _____.
incomplete tetanus
At a certain frequency, there will be no relaxation. This is called _____ ____.
complete tetanus
Treppe: As the voltage is increased, the number of muscle fibers used __ __ _______.
in vitro increases
When will treppe reach a maximum value?
This will reach a maximum value when all muscle fibers are stimulated
If a fresh muscle is stimulated with several shocks at maximum voltage, each twitch will be _______ ______. When recorded this will produce a staircase effect called _____.
- progressively stronger
2. treppe
What does the force velocity curve state?
- For muscles to contract, they must generate force that is greater than the opposing forces
- The greater the force, the slower the contraction
Isotonic contraction
Muscle fibers shorten when the tension produced is just greater than the load
Isometric contraction
Muscles can’t shorten because the load is too great
Is isometric contraction voluntary or involuntary?
Can be voluntary
Concentric contraction
A muscle fiber shortens when force is greater than load
Eccentric contraction
A muscle may actually lengthen, despite contraction, if the load is too great
What is an example of what eccentric contraction can allow you to do?
Allows you to lower a weight gently after a full concentric contraction
Series elastic component: what must happen to non contractile parts of the muscle and tendons when muscles contract?
Noncontractile parts of the muscle and tendons must be pulled tight when muscles contract
Series elastic component: Describe in detail some features about tendons when muscles contract.****
- Tendons are elastic, resist distension, and snap back to resting length
- Tendons absorb some of the tension as muscles contract
What are 4 factors muscle strength is determined by?
- Number of fibers recruited to contract
- Frequency of stimulation
- Thickness of each muscle fiber (thicker is stronger)
- Initial length of the fiber at rest
Length tension relationship: when is tension maximal?
when sarcomeres are at normal resting length
Length tension relationship: what affect does increasing sarcomere length have on muscle tension?
decreases muscle tension/at a certain point no tension can be generated
Length tension relationship: what affect does increasing sarcomere length have on myosin and actin?
There are fewer interactions between myosin and actin
Length tension relationship: what affect does decreasing sarcomere length have on muscle tension?
also decreases muscle tension
What is another word for maximal oxygen uptake?
aerobic capacity, or VO2 max
What does the maximal oxygen uptake determine?
Determines whether a given exercise is light, moderate, or heavy for a given person
What is the maximal oxygen uptake determined by?
Determined by a person’s age, sex, size, and athletic training
Who is the maximal oxygen uptake greater for?
Greater for males and younger people
What is the maximal oxygen range?
Ranges from 12 ml O2/minute/kg body weight to 84 ml O2/minute/kg body weight
What is another name for the lactate threshold?
anaerobic threshold
What can the lactate threshold be used for?
Another way to determine exercise intensity for a given person
What exactly is the lactate threshold? Range?
- % of maximal oxygen uptake at which a rise in blood lactate levels occurs
- Occurs at about 50−70% VO2 max
What are 3 ways in which muscles can get their energy?
- From fatty acids
- From glycogen stores
- From blood glucose
What is the energy from fatty acids used for?
At rest and for mild exercise
What is the energy from glycogen stores used for?
For moderate exercise
What is the energy from blood glucose used for?
For heavy exercise
Blood glucose is used to give muscles energy for heavy exercise. What happens as exercise intensity and duration increase?
GLUT4 channels are inserted into the sarcolemma to allow more glucose into cells
Oxygen debt: When a person exercises, oxygen is withdrawn from _______________.
reserves in hemoglobin and myoglobin
Why does oxygen debt occur?
- To create cross bridges in muscle contraction and pump calcium back into SR at rest
- To metabolize lactic acid
What happens to breathing rate during oxygen debt?
Breathing rate continues to be elevated after exercise to repay this debt
ATP may be used faster than it can be created through cellular respiration. This is due to what?
Phosphocreatine
How is Phosphocreatine made?
ADP is combined with Pi from phosphocreatine
How is creatine obtained?
Creatine is produced by the liver and kidneys or obtained in the diet.
When are phosphocreatine stored replenished?
at rest
Are slow twitch fibers type 1 or 2? Fast twitch?
- Type 1
2. Type 2
Describe slow twitch fibers:
- Contraction speed?
- Contraction duration? (fatigue)
- Capillary supply?
- Mitochondria supply?
- Respiratory enzyme supply?
- Myoglobin supply?
- Slower contraction speed
- Can sustain contraction for long periods without fatigue 3. Rich capillary supply
- More mitochondria
- More respiratory enzymes
- More myoglobin
What are two other names for slow twitch (type 1) fibers? Explain why for each.
- slow oxidative fibers; because they are said to have high oxidative capacity
- red fibers; due to myoglobin content (which has a red pigment)
Where can slow twitch (type 1) fibers be found?
postural muscles
Describe fast twitch fibers:
- Contraction speed?
- Contraction duration? (fatigue)
- Capillary supply?
- Mitochondria supply?
- Respiratory enzyme supply?
- Myoglobin supply?
- Faster contraction speed
- Fatigue fast
- Fewer capillaries
- Fewer mitochondria
- Fewer respiratory enzymes
- Less myoglobin
What are two other names for fast twitch (type 2) fibers? Explain why for only one of them.
- White fibers
2. Fast glycolytic fibers; because have more glycogen stores
Where can fast twitch (type 2) fibers be found?
Found in stronger muscles
What are Intermediate (type 2A) fibers?
fast-twitch but with high oxidative capacity
What is another name for Intermediate (type 2A) fibers?
Called fast oxidative fibers
People vary greatly in the percentage of fast- or slow-twitch fibers in their muscles. What is this a result of?
genetics and training
Define muscle fatigue.
Reduced ability to generate force
What 8 things can muscle fatigue be contributed to?
- Accumulation of extracellular K+, reducing membrane potential (short duration)
- Depletion of stored glycogen
- Reduced SR calcium release
- Lactic acid accumulation and lower pH
- Increased concentration of PO4 due to phosphocreatine breakdown
- Lack of ATP
- Buildup of ADP
- Fatigue of upper motor neurons, called central fatigue
What is fatigue of upper motor neurons called?
central fatigue
What 3 things are involved with adaptation to endurance training?
- Increased ability to use fatty acids as fuel and increased intracellular triglyceride storage
- Decrease in type II and increase in type IIa muscle fibers
- Increase in number of mitochondria
What is involved with adaption to strength training?
Hypertrophy
What is hypertrophy?
Type II muscle fibers become thicker due to increased amount of actin and myosin (more sarcomeres)
Thicker fibers can split into _____ ____, which can also increase in size. What is this a result of?
- two fibers
2. hypertrophy
What 3 proteins does hypertrophy require (these proteins serve as muscle fiber scaffolding)?
- Titin
- Nebulin
- Obscurin
Where are the cell bodies of lower motor neurons?
Cell bodies in ventral horn of spinal cord
What are lower motor neurons stimulated by?
- Sensory feedback from muscles and tendons
2. Stimulation or inhibition from higher motor neurons from brain
What are two muscle sensory organs?
- Golgi tendon organs
2. Muscle spindle apparatus
What is the function of golgi tendon organs?
respond to/sense tension a muscle puts on a tendon
What is the function of the muscle spindle apparatus?
respond to/sense muscle length
Muscles that require more control have _____ spindles.
more
Stretching a muscle causes spindles to ____.
stretch
The muscle spindle apparatus contains thin muscle cells called what?
intrafusal fibers
What are the two types of intrafusal fibers?
- Nuclear bag fibers
2. Nuclear chain fibers
What are the names of the two types of sensory cells that wrap around the intrafusal fibers?
- Primary (annulospiral)
2. Secondary (flower-spray)
What are the two types of lower motor neurons?
- Alpha
2. Gamma
What to alpha motor neurons innervate?
innervate extrafusal (contracting) muscle fibers
What to gamma motor neurons innervate?
innervate intrafusal (stretch) muscle fibers
What does contraction of intrafusal (stretch) muscle fibers result in?
Contraction of these fibers does not shorten the muscle, but does increase sensitivity to stretch
The fibers lower motor neurons innervate are stimulated by upper motor neurons at the same time. What is this called?
coactivation
What is the more simpler reflex, polysynaptic or motor synaptic stretch reflex?
Monosynaptic Stretch Reflex
What does a Monosynaptic Stretch Reflex involve?
Only involves a sensory neuron synapsing on a motor neuron in the spinal cord
What does a Monosynaptic Stretch Reflex maintain?
Maintains optimal resting length of skeletal muscles
How can a Monosynaptic Stretch Reflex be stimulated?
by striking the patellar ligament in the “knee-jerk reflex” (patellar reflex)
Golgi tendon organs constantly monitor tension in ____.
tendons
How is the tension in tendons reduced (3 steps)? Is this process mono or poly(di)synaptic?
- Sensory neuron stimulates interneuron in spinal cord.
- Interneuron inhibits motor neuron.
- Tension in tendon is reduced.
— Poly/disynaptic
Give an example of reciprocal innervation.
In the knee-jerk reflex, interneurons are also stimulated in the spinal cord to inhibit antagonistic muscles on that limb.
Give an example of double reciprocal innervation.
More complex reflexes require control of muscles on the contralateral limb. This is called double reciprocal innervation.
What is a Crossed Extensor Reflex?
Type of double reciprocal innervation seen when you step on a tack
Upper Motor Neuron Control: how is the precentral gyrus involved?
sends neurons through pyramidal tracts
Upper Motor Neuron Control: how is the cerebellum involved?
Receives information from muscle spindles and Golgi tendon organs as well as other senses ———-> Inhibits regions of the basal nuclei, red nuclei, and vestibular nuclei
Upper Motor Neuron Control: how is the basal nuclei involved?
also act to inhibit motor activity through the rubrospinal tract
Are cardiac and smooth muscle voluntary or involuntary?
Involuntary
What are cardiac and smooth muscle regulated by?
ANS
What is contraction of cardiac and smooth muscle a result from?
Like skeletal muscle, contraction is due to myosin/actin cross bridges stimulated by calcium
Is cardiac muscle striated or non-striated?
striated
What is different about cardiac muscle than skeletal muscle when talking about myosin and actin fibers?
Unlike skeletal muscle fibers, these fibers are short, branched, and connected via gap junctions called intercalated discs
Where is smooth muscle found?
- blood vessel walls
- bronchioles
- digestive organs
- urinary tracts
- reproductive tracts
How does smooth muscle propel the content of the organs it is found in?
Produce peristaltic waves to propel contents of these organs
Unlike skeletal and cardiac muscle, smooth muscle has no what?
Sarcomeres
In cardiac muscle myosin and actin filaments form what?
sarcomeres
How does contraction occur in cardiac muscle?
by means of sliding thin filaments
What are long actin filaments of smooth muscle attached to?
Long actin filaments attached to dense bodies
Does smooth muscle have myosin filaments?
only some
The arrangement of the fibers in smooth muscle allows for what?
contraction even when greatly stretched
List the steps of Excitation-Contraction Coupling in Smooth Muscle.
- Begins with rise in intracellular calcium concentrations
- Calcium binds to calmodulin (no troponin in smooth muscle)—- this activates myosin light chain kinase
- Myosin light chain kinase phosphorylates myosin light chains (This allows myosin to form cross bridges with actin to initiate contraction)
What does the rise in intracellular calcium concentrations in smooth muscle come from?
- Only some comes from SR.
- Most comes across plasma membrane after voltage-gated calcium channels are opened
Is the troponin in smooth muscle?
NO
What somewhat replaces troponin in smooth muscle?
calmodulin
The stimulation in smooth muscle is ____. More stimulation allows in more calcium, which allows _____ _____.
- Graded
2. Stronger contractions
In smooth muscle contractions are ____ and ___. They may enter a “___ ___”
- Slow/ Sustained
2. Latch state
How is smooth muscle relaxation achieved?
- Calcium is pumped out using calcium ATPase active transport pumps
- Calmodulin dissociates from myosin light chain kinase
- Phosphate groups are stripped from the myosin by myosin phosphatase
Describe single unit smooth muscles.
multiple gap junctions that make neighboring cells behave as a unit
Are most smooth muscles single or multi unit?
single-unit
Do most cells in a single unit smooth muscle receive acetylcholine stimulation?
Only a few
Single unit smooth muscles display pacemaker activity moderated by __________________.
stretch or autonomic innervation
In Single unit smooth muscles, muscarinic ACh receptors respond by __________.
closing K+ channels
Describe multi-unit smooth muscles.
require individual nerve innervation (no pacemaker activity)
Do multi-unit smooth muscles have gap junctions?
Few or no gap junctions
What are examples of multi unit smooth muscles?
Arrector pili muscles in skin and ciliary muscles in eyes
How is autonomic innervation of smooth muscle achieved?
Neurotransmitter is released along the length of an autonomic neuron from varicosities.
Are smooth muscle cells stimulated in groups or one at a time when talking about autonomic innervation?
A number of smooth muscle cells are stimulated at once.
What does autonomic innervation of smooth muscle form?
synapses en passant
