Lab 7

Frequency

The number of occurrences of a repeating event per unit time

Amplitude

Height of the wave from baseline to crest

Waveform

Shape and form of a signal

Wavelength

Length from the crest of one peak to the crease of the next peak

Three muscle tissue types

1. Skeletal

2. Smooth

3. Cardiac

myo, mys, sarco

Muscle prefixes

Upper motor neuron lesions

Loss of muscle function as a result of strokes damaging neurons in the brain

Excitability

the electrical charge differential in muscle cell membranes that can be changed by a stimulus leading to an intracellular muscle response

Contractility

All muscle cells shorten when stimulated

Extensibility

Muscle cells can be stretched sometimes behind they’re resting length

Elasticity

After being stretched muscle cells can recoil back to the resting length

Tendons

Attach muscle to bone

Direct attachement

The periosteum or perichondrium is fused with the muscle’s epimysium

Indirect attachment

tendons or aponeurosis

More common, durable, and smaller attachment type

Indirect

Muscle components from smallest to largest

Myofilament

Myofibril

Muscle fiber

Fascicle

Muscle

Antagonistic arrangement

as one muscle contracts and shortens, an antagonist muscle relaxes and elongates

Example of two muscles working antagonistically

Biceps brachii contracts and triceps brachii relaxes, biceps brachii relaxes and triceps brachii contracts

Sarcolemma

Plasma membrane of a muscle fiber

Sarcoplasm

Cytoplasm of a muscle fiber

Myoglobin

Contained in muscle cells to store oxygen

Glycosomes

Granules of glycogen stored in muscle cells that can be broken down to supply ATP from glucose for energy

Myofibrils

Repeating units of sarcomeres that make up most of the intracellular volume of skeletal muscle cells

Sarcomeres

Smallest contractile units of skeletal muscle

Dark bands

A bands

Light bands

I bands

Middle region of A bands that is slightly light

H zone

Thick filament

Myosin

Thin filament

Actin

Dark midline of the I band

Z line

Sarcomeres run from

Z line to Z line

The thick filament myosin runs the length of the

A band

M line

Dark center line in the sarcomeres that connect thick filaments

The thin filament made of actin contains the proteins

Tropomyosin and troponin

Titin

A protein that makes up elastic filaments that run from the Z line to the thick filaments to hold them in place and provide the flexible recoil to the sarcomere as it contracts, relaxes, and stretches

Cross bridge formation

Ca2+ binds troponin and tropomyosin rolls out of the way exposing the binding site

For steps of the cross bridge cycle

1. Binding

2. Power stroke

3. Detaching

4. Cocking

Binding

A myosin head it’s its high energy configuration binds to the exposed myosin-binding spot on the actin filament

Power stroke

ADP and inorganic phosphate are released from the myosin head and it returns to its low energy state resulting in a power stroke

Detaching

ATP binds to the myosin head causing detachment

Cocking

Hydrolysis of ATP to ADP and inorganic phosphate repositions the myosin head in its high energy configuration allowing the cycle to repeat

Sarcoplasmic reticulum

Complex smooth endoplasmic reticulum that interconnects and surrounds each myofibril

Terminal cisterns

Large perpendicular cross channels formed at the A band and I band junction

Sarcoplasmic reticulum function

Stores and releases calcium to control muscle fiber contraction

T tubules

Elongated extensions of the sarcolemma located at the A bands and I band junctions that dive deeply into the cell

Triad

T tubule and two terminal cisterns

T tubules function

Carries electrical signals deep into the muscle to cause the release of calcium from the terminal cisterns

Terminal cisterns function

Release of calcium that leads to contraction

Integral proteins of the T tubules

Voltage sensors

Integral proteins of the terminal cisterns

Creates gated channels for the release of calcium

Refractory period

period of time where the cell is repolarizing and cannot be stimulated again

Muscle tension

The force exerted by a contracting muscle on an object

Load

The opposing force applied on the muscle by the mass of the object being moved

Motor unit

A motor neuron and all the individual muscle fibers it innervates

Small motor units

One neuron controlling a few muscle fibers for finer control of movement like fingers and eyes

Large motor units

One neuron controlling a large amount of muscle fibers for movement of large limb muscles

Actin, myosin, and A bands

Do not shorten during contraction

The sarcomere, H zone, and I bands

Shorten during contraction

Somatic motor neurons

Voluntary motor neurons with cell bodies located in the brain or spinal cord and axons bundled into a nerve extending to the muscle they innervate

Neuromuscular Junction/Motor end plate

Where the nerve communicates to the muscle halfway down the muscle fiber

Synaptic end bulb/Axon terminal

The mound-like end of the axon containing and abundance of synaptic vesicles filled with the neurotransmitter acetylcholine

Synaptic cleft

Space between the axon terminal and the muscle fiber

Acetylcholinesterase

Enzyme in the synaptic cleft that breaks down acetylcholine to terminate the signal to allow for fine control of muscle activation

Isotonic contractions

a body part is moved and the muscle fibers shorten or lengthen but muscle tension remains constant

Isometric contractions

Muscle tension increases but muscle fiber length remains constant, typically performed against immovable objects, help with posture and stability

Concentric

An isotonic muscle contraction where the length decreases

Eccentric

An isotonic muscle contraction where the length increases

Electromyogram (EMG)

Extracellular recording of electrical activity in a whole muscle

Compound muscle potential (CMP)

Sum of the electrical activity of many individual muscle fibers all firing at once that can be observed on an EMG

Magnitude of the CMP

Reflects the number and size of motor units that are active

Twitch

A motor unit’s reaction to a single action potential of its motor neuron

Three parts of a muscle twitch

1. Latent period

2. Period of contraction

3. Period of relaxation

Latent period

Cross bridges are beginning to form but measurable tension has not been achieved, load increases the length of the latent period

Period of contraction

once tension is measurable until tension peaks, muscle shortens as the force being generated by the contraction exceeds the resistance applied

Period of relaxation

Calcium levels drop in the cytoplasm, the number of cross bridges decreases and tension declines

Recruitment

The nervous system adjusts the number of motor axons firing to control the number of twitching muscle fibers

Henneman’s size principle

Central nervous system small motor units to be recruited first followed by larger ones as the stimulus increases

Small motor units are controlled by

Easily excitable and low threshold motor neurons

Large motor units are controlled by

Least excitable and high threshold motor neurons

Size principle explains

How the same muscle can control fine delicate movements and powerful heavy maneuvers

Stimulation intervals greater than 200ms

Intracellular calcium levels go back to baseline levels between action potentials so the contraction is separate twitches

Stimulation intervals between 200 and 75ms

Calcium levels in the muscle are still above baseline levels when the next action potential arrives so the muscle fibers aren’t completely relaxed

Summation

A muscle fiber hasn’t completely relaxed before the next action potential arrives so the next contraction is stronger than normal

Infused or incomplete tetanus

At higher stimulation frequencies, summation increases, leading to sustained graded contractions that increase in size and length

Complete or fused tetanus

At highest stimulation frequencies the muscle has no time to relax resulting in a strong tetanic contraction

Coactivation

Contraction of a muscle leads to some minor contractile activity in the antagonist muscle

Amount of ATP stored by muscle

5 seconds worth

Three ways ATP is generated in muscle

1. Creatine phosphate

2. Anaerobic glycolysis

3. Aerobic respiration

Creatine phosphate generates ATP by

Using creatine kinase to rapidly interact with ADP by transferring a phosphate to create ATP

Anaerobic glycolysis

Glycogen stores are broken down to glucose to be made into ATP, fast but doesn’t produce a lot of ATP

Aerobic respiration

Completely breaks down glucose to produce about 34 ATP, but is very slow

Causes of muscle fatigue

1. Depletion of ATP

2. Depletion of nutrients

3. Depletion of oxygen

4. Perception of muscle conditions from the brain

Factors that influence the force of muscle contraction

1. Number of motor units

2. Size of muscle fiber

3. Contraction summation

4. Stretch of the muscle

Difference between slow and fast fibers

Responsiveness of motor neurons, the speed myosin ATPase can split ATP, how fast a muscle type can pump calcium back into the sarcoplasmic reticulum

Difference between oxidative or glycolytic muscle fibers

Whether they rely on aerobic or anaerobic metabolic pathways

Main muscle fiber types

1. Slow oxidative

2. Fast oxidative glycolytic

3. Fast glycolytic