Chapter 12 & 13 Muscle Flashcards
What are the three types of muscle fibers?
Skeletal
Cardiac
Smooth
What are the physiological characteristics of skeletal muscle?
Striated appearance
Innervated primarily by somatic motor neurons
Voluntary control
What are Muscle cells filled with?
Muscle cells are filled with myofibrils
SK M is a collection of muscle cells, or muscle fibers
What is a myofibril?
Myofibrils consist of repeated elements (proteins) called sarcomeres which are repeating contractile structures
What are the proteins that make up the myofibril?
Describe
Actin - primary component of thin filaments
Myosin - Primary component of thick filaments
The sarcomeric arrangement shows what? Meaning what can we see?
Sarcomeric arrangement gives a distinctive banding pattern
What is the darkest part of the sarcomere’s bands and encompasses the entire length of a thick filament.
A Band
what filaments are found within the A band? Inner, outer, and middle?
Outer edges of the A band, the thick and thin filaments overlap.
Center is only the thick filaments
What band is associated with mo overlap between actin and myosin, and where is this?
H band that is located within the A band
The central region of the A band
Only occupied by thick filaments only
Which band corresponds to thin filaments?
Describe them?
I-band
The lightest color bands of the sarcomere.
What runs through the I band and how many?
Z-disk runs through the middle of every I band, therefor each half of an I band belongs to a different sarcomere.
What is the anchor for the thin filaments?
Z- line
One sarcomere has how many z disks? What are they for?
One sarcomere is composed of two Z disks and the filaments found between them
What is the anchor for thick filaments?
M-line
What divides the A band in half?
The M line
What innervates muscle cells?
Somatic motor neurons
The synapse (space between) the motor neuron and the muscle cells is referred to as what?
The neuromuscular junction
What is the term for the postsynaptic membrane?
The motor endplate, which is the muscles cell’s plasma membrane
How are muscle fibers innervated?
Several muscle fibers within a given muscle may be inner aged but a single motor neuron
What is a motor unit?
Describe small and large motor units
Consists of the motor neuron and all of the muscle fibers that it innervates
Small motor units contains a few muscle cells (10-50 cells)
Large motor units contain many cells (100+)
What happens as the muscle contracts? What proteins does this involve and how?
When a muscle contrast the sarcomere shortens
The shortening involves filaments sliding next to each other
Describe the thin filaments
They are polymers of actin proteins, arranged as a twisted strand
Describe the think filaments?
Arranged as dimmers of myosin
The myosin head interacts with the thin filaments
Myosin head hydrolyzes ATP
Myosin head can bend which is referred to a the power stroke.
Which areas of the Sarcomere shorten and which areas remain the same during contraction?
The H zone and the I band both shorten while the A band remains constant.
When contraction takes place the actin and myosin do not change length but instead slide past each other.
What is the sliding filament theory of contraction?
Overlapping actin and myosin filaments of fixed length slide past one another in an energy-requiring process, which results in muscle contraction.
During contraction what is formed between the two filaments and what is this phenomenon called?
Contraction involves Cross-bridge formation between the the two filaments
The phenomenon is call the power stroke.
Describe the steps of the contraction process?
Cross bridge binding
Power stroke
Unbinding this is ATP association which cause the cross bridge dissociation
Recock the head
How is contraction regulated?
Contraction is regulated via regulatory proteins
Tropomyosin
Troponin
Associated with the thin filament
Prior to contraction, tropomyosin blocks the binding sites on the thin filament
How does the muscle relax?
What has to happen?
Stop NT release by the alpha-motor neuron. ACh
Cease endplate depolarization. –> No muscle AP
V-gated Ca2+ channels close
Ca2+ ATPase pumps CA2+ back into the SR.
Decreased free calcium will cause the bound calcium to unbind from troponin, which causes tropomyosin to recover the binding site. The heads will then release and the elastic elements will pull the filaments back to their relaxed state.
If a single muscle cell contracts, what is the result?
The result is a twitch that is relatively small in magnitude, and has a short duration
This is considered to not be a useful contraction.
What happens if a muscle cell were to be repeatedly stimulated at a high frequency?
The twitches will summate and the overall force of contraction increases
What are the two forms of summation?
Incomplete summation and complete summation
What is incomplete tetanus?
The muscle fibers is being stimulated at a rate that is not at maximum value which allows the muscle fiber to slightly relax between stimuli.
What is complete tetanus?
This is fused tetanus this is where the stimulation rate is fast enough that the fiber is unable to relax
How does summation occur?
Arises from the accumulation of intracellular calcium.
What type of muscle contraction happens with the muscle contracts and shortens and creates enough force to move a load
Isotonic Contraction
What is isometric contraction?
The muscle contracts but does not shorten. The force created cannot move the load.
How do you increase the force of contraction?
We can increase the force of contraction by recruiting more and larger motor units
What happens of the fibers of a muscle contract at a very long sarcomere length?
The think and thin filaments barley overlap and can only form very few crossbridges. Can’t generate that much force.
Force development not only depends on the number of the muscle cells that are activated, what else contributes to contraction strength?
The initial length of the muscle fiber
the contractile force generated is directly proportional to the crossbridge number between think and thin filaments.
What happens if the sarcomere is shorter than optimum length at the beginning of the contraction?
The thick and thin filaments have too much overlap. The Think filaments can only move the thin filaments a short distance before it causes the opposite ends of the sarcomere to start to overlap preventing cross bridge formation.
If the sarcomere is so short what happens?
The think filaments run into the z-disks and tension decreases rapidly
What monitors the muscle length?
The muscle spindle monitors the muscle length by responding to changes in muscle length typically stretch
What are the muscle spindles made up of?
Made up of intrafusal fibers that run parallel to the contractile extrafusal fibers
What is the sensory neurons that intrafusal fibers are wrapped around?
The 1 alpha afferent
What does the stretch information from a contracting muscle induce?
Induces the Myotatic reflex
What happens to the intrafusal fibers when the alpha motor neuron tells the extrafusal fibers to contract?
When the alpha motor neurons fire the muscle shortens releasing tension on the muscle spindle capsule. To keep the spindle from becoming floppy the gamma motor neuron that innervates the contractile ends of the muscle spindle also fire shortening the intrafusal fibers.
When a weight is added to someone’s hand that is already flexed what takes place?
The muscle spindle stretches and the arm extends, which cause the muscle spindle 1 a afferents to fire more frequently.
This signal is sent to the spinal cord then increased efferent output through the alpha motor neurons cause the muscle to contract
Once the muscle contracts after the increased efferent alpha motor neuron signals what takes place in the 1 a afferent sensory neurons and the intrafusal fibers?
The firing rate of afferent sensory neurons decreases
The gamma motor neuron fires at the same time to keep tension on the intrafusal fibers.
During contraction what takes place with the alpha motor neuron and the gamma motor neuron?
Both the alpha and the gamma motor fibers are coactivated. Therefore both muscle and the intrafusal fibers both contract
What is the purpose of the Golgi Tendon Organ?
Links the muscle and the tendon to provide information about the muscle length and tension during isometric phase of contraction not stretch.
How does the golgi tendon organ release tension of the muscle?
Tension on the tendon activated the afferent sensory neuron that then stimulates the interneuron.
The interneuron inhibits the alpha motor neuron causing the tension on the tendon to be reduced.
During mild exercise what is the fuel for muscle metabolism?
Plasma free fatty acids are the primary fuel source
When you do moderate exercise what is the fuel source?
Carbohydrates (muscle glucose) and FFA are utilized via Glycolysis
During high intensity exercise what fuel is primarily used for muscle metabolism?
Carbohydrates provide 2/3 of the energy which is metabolized by anaerobic metabolism
When exercise intensity increases what is happening to oxygen and ATP.
Oxygen utilization and ATP synthesis can decrease
Due to the use of oxygen quickly the greater proportion of ATP synthesis relies on anaerobic metabolism, which yields lactate.
What is Lactate Threshold?
It’s s the exercise level at which the blood lactate rises significantly
This is also called anaerobic threshold
Where is ATP coming from in intense exercise once anaerobic metabolism begins.
Glycolysis is generating ATP in small amounts and lactate is being produced at high rates bringing it to the lactate threshold
How does lactate reach its threshold?
Can occur as the lactate removal is exceeded by lactate production
What is another way ATP can be generated during exercise
ATP can also be quickly made through substrate-level phosphorylation
Phsophocreatine provides the high energy phosphate to form ATP during exercise but its not enough to maintain long term exercise
What are the two ways muscle fibers can be classified by?
The contraction speed
The duration of the contraction before the fiber fatigues
Where does the difference in speed of contraction come from?
Arises from how easily the myosin head can split the ATP, which cause the head of the myosin to detach from actin and cock back.
What does the duration of the contraction depend on?
Calcium supply, meaning the influx and removal
Oxygen delivery/ blood supply
Mitochondria density, the amount of mitochondria present
Number of muscle contractile units
What are the three primary classification for muscle fiber types
Slow- twitch, slow fatigue: Slow oxidative or Type 1
Fast twitch, medium fatigue: Fast Oxidative or Type IIa
Fast-twitch, fast-fatigue: Fast Glycolytic or Type IIb
Describe Slow oxidative or Type I muscle fiber by its contraction, the type of metabolism and blood supply?
And fibrils?
Contract relatively slowly
Depends on aerobic metabolism mainly
Have many mitochondria
Plenty of blood supply by the number of capillaries that are present and has lots of myoglobin
Generally fewer myofibrils
What is another name for this fiber? What type of athlete would have more of this fiber?
This is the endurance fiber and probably find this in a long distance runner.
Describe fast oxidative or type IIa muscle fiber by its contraction speed, its metabolism, blood supply, and myofibrils?
Where are these seen?
Contracts quickly
Primarily aerobic, but utilizes some anaerobic metabolism
Rich blood supply, and lots of Mitochondria.
Pinkish in color
Has many contractile myofibrils. The muscle cells are larger than slow oxidative muscle and these are NOT very common.
Describe fast Glycolytic or Type IIb by its contraction speed, metabolism, blood supply, what it uses for fuel, and what its best for?
Contracts very quickly, but fatigues faster. It uses anaerobic metabolism because it uses up O2 very fast due to the very fast strong contraction.
Low blood supply, therefore very low O2 for metabolism. It generates lactate, which contributes to fatigue.
Uses glycogen reserves for fuel
Best for short term, high intensity contractions. Like high jumper or weight lifter.
What types of fibers are found in muscle groups?
Many muscles contain a mix of the fibers, which allows a given muscle to accomplish a variety of functions
What does aerobic exercise due to muscle?
Changes the muscle by:
Increased vasculature
Increased mitochondria
More myoglobin
Very pronounced in slow oxidative, but can also change fast glycolytic into fast oxidative.
Know slide 35!!!
Where do you find myotatic reflexes or pain withdrawal? What are the pathways that are involved?
There are several levels of control exist
Usually in the lower motor or spinal that are related to reflexes.
The spinal cord receives afferent input via primary afferent fibers, which arise within the ventral root of the spinal cord
When a painful stimulus is sensed what happens to the signal during the painful withdrawal reflex?
The nociceptor is activated
The primary sensory neuron enters the spinal cord and diverges
One pathway activates the ascending pathways for sensation of pain and the postural adjustment takes place shifting the center of gravity
Then the extensors are inhibited while the flexor of the affected foot contract, then the opposite occurs for the other leg.
Where does upper motor control occur?
What does it control? How does it send info to control it?
Output from neurons within the cerebral cortex. Controls lower motor neurons.
Control occurs by two primary tracts:
Pyramidal Tract
Extra Pyramidal Tract
Where do the Pyramidal tract arise from?
What are the two areas it crosses over?
Pyramidal tract neurons arise from the motor cortex, and they control skeletal muscle on the opposite side
Lateral corticospinal (85% of the fibers)-cross in the medulla, and allows fin control of distal muscles (fingers and toes)
Anterior corticospinal- cross at the spinal column. Allows coarse control proximal musculature.
Where do the Extra Pyramidal tract arise from?
Arise from the brainstem
What is a key feature of these tracts and what do they control?
The nerve tracts are multisnaptic and control:
Axial muscles involved with balance and posture
Muscles involved with course limb movements
Head, neck and upper limb movements in response to startling stimuli (bright lights, loud noises, and sudden movements
What tract of the Extra Pyramidal tract can be involved with fine motor control of the distal upper limbs?
Rubrospinal tract
What does the Cerebellum control?
Motor control
It adjusts output by the upper motor neurons
What sensory input does the cerebellum receive?
Visual
Vestibular
Proprioceptive
Auditory
Where does the output of the cerebellum go?
Goes to the premotor and association cortex and tot the brainstem.
What does the circuitry of the cerebellum do?
Behaves like and error detector/corrector
It corrects movements so that the actual motor movements match the intended planned movements.
What does the output controls do of the cerebellum?
Output controls balance and coordination
What other regions of cerebrum refers to a collection of nuclei that are deep called the basal ganglia?
Caudate/Putamen
Globes Pallidus
Substantia Nigra of the midbrain
Subthalamic Nucleus in the ventral thalamus
What does these area do in conjunction with the basal ganglia?
These brain regions receive process sensory information from the cerebral cortex and thalamus
Then the basal nuclei project to the upper motor neurons of the cerebral cortex and the brainstem.
The major output of the basal ganglia do?
They are inhibitory.
Thought that the basal ganglia suppresses inappropriate movements, and reinforces motor instructions for the appropriate movements
