Block 3 PSIO 201 Lecture

Functions of skeletal muscle

Locomotion, Facial expression, Posture and body position, Control of body openings/passages, Regulations of temp, Metabolism and endocrine functions

What is an origin

Where muscle starts on bone(stationary)

What is an insertion

Place where muscle ends on bone (insertion moves towards origin)

1st class Lever and example

fulcrum is between load and effort

ex. scissors

in body = skull & first cervical vertebrae

provide mechanical advantage(greater than 1) distance effort is applies is further away from fulcrum compared to load

2nd class Lever and example

being able to stand on tip-toes, wheel barrow

mechanical advantage bc load is closer to fulcrum compared to where effort is applied

3rd class Lever and example

most common in body, effort applied between fulcrum and load

ex. hinge joints

does not allow force to be multiped to move greater load bc load is further away from fulcrum than effort

not greater than 1 so force needs to be greater than load

benefits: small changes in length of muscle result in big movement (faster and increased ROM)

General benefits or tradeoffs with each lever type for body movement

Role of agonist

muscle that does movement

Role of synergist

multiple different muscles that help

Role of antagonist 

muscle that does opposite movement of agonist

Role of fixator

special synergist that stabilizes joint

What is the agonist, antagonist, synergist, and fixator of abduction of arm

Agonist: deltoid

Antagonist: latissimus dorsi

Synergist: supraspinatus

Fixator: trapezius

Describe the fundamentals of muscle cell development, including the role of myoblasts, satellite cells

Before birth myoblasts increase in number then fuse to from immature muscle fibers. Subset don’t fuse and remain outside fibers= satellite cells=stem cells (can undergo mitosis after birth to aid in muscle regeneration)

difference between hyperplasia and hypertrophy.

Hyperplasia = increase in cell number

Hypertrophy = increase cell size after birth

Describe the organization of muscle and the connective tissues surrounding each structure

overall: bundles within bundles each covered by CT

Skeletal muscle ECM to epimysium, perimysium, endomysium 

Describe the functional role of connective tissue within and around skeletal muscle

CT gives spring-like properties

1-10% of skeletal muscle volume

transmits force that is generated by muscle fibers so it meets tendon

Describe the function of each protein of contractile muscle cell. Structural: a actin, Nebulin, Titin, Dystrophin, Myomesin

a-actinin- forms Z-line. Binds to actin and titan to keep them connected to Z-line

Nebulin- spans length of actin. Anchors thin filaments to Z disc

Titan- Largest protein in body. Stabilizes thick filament. Also acts like spring

Dystrophin - links thin filaments to sarcolemma. Also anchors EC proteins in CT(collagen). Overall: transmits tension from sarcomere to sarcolemma via CT around muscle fiber ten ultimately the tendon. 

Myomesin - function to bind titin and thick filaments to connect at M line

Give a general description of the sliding filament mechanism and describe the expected changes in sarcomere bands/zones during contraction

I band length decreases

A band length constant

H zone length decreases

Zone of overlap increase

1) Myosin binding sites on actin become exposed when Ca2+ binds to tropoinin

2)Myosin heads bind to actin forming crossbridges

3) Myosin heads pivot toward the center of the sarcomere(power stroke)

4) ATP binds to myosin head leading to detachment of myosin head from actin (crossbridge break)

5) ATP is hydrolyzed and the energy released is used to re-energize the myosin head back to its start position (cocked) so a new crossbridge can form

6) The contraction cycle repeats until myosin binding sites on actin are no longer available(no more calcium)

Myotendinous junction

interface between skeletal muscle and tendon. Collagen weaves = increase SA of contact between tendon and muscle

Network of fascia

groups of muscles coved in fascia to make compartments

web/network of CT (situ that holds everything in place)

Collagen and elastin

like “liquid crystal” rapidly shift between fluid and solid

receptors(mechano- and pain) allowing perception in 3-dimensional space and 10x more pain receptors than muscle

Three Units of Subcellular organization

1) conduction of electrical signals(sarcolemma)

• sarcolemma: encloses cytoplasm of fiber

• transverse tubules: bio electrical signals to center

2) Control of muscle contraction (sarcoplasmic reticulum)

• SR (close to t-tubules): stores calcium

• Triad: T-tubule and terminal cisterns (on both sides of tubule)

3) Contraction(myofibrils-create tension)

Regulatory proteins Troponin and Tropomyosin

Troponin - on thing filaments (attached to tropomyosin). Hold tropomyosin in place when relaxed. During contraction, Ca2+ bind to it causing a confirmational change to shift tropomyosin away from myosin binding sites

Tropomyosin - on thin filaments, covers myosin binding sites on actin when muscle is relaxed.

Characteristics of anaerobic and aerobic oxidative metabolism

Anaerobic(in cytoplasm)= without O2 - creatine phosphate and glycolysis

Aerobic (mitochondrial)= with O2 - products of glycolysis and fatty acids

ATP sources

1. cell “pool” of ATP - 2 sec

2. Anaerobic (creatine phosphate) - 10-15sec

3. Anaerobic (blood glucose, glycogen => glucose) - few min

4. Aerobic - fat, glycogen => glucose, protein - 40 to several hours

Creatine Phosphate

Creatine= amino -acid like molecule made in liver, kidney, and pancreas. Then goes to skeletal muscle fibers though blood

it stores a high energy phosphate (creatine phosphokinase/creatine kinase) supports contraction of 10-15sec

Anaerobic

glucose cleaved from glycogen it can be used to quickly produce ATP through glycolysis in cytoplasm, results in pyruvate. When oxygen limited, pyruvate is made into lactate. Glucose enters cell through glucose transporters which can be stimulated by insulin or exercise

Aerobic metabolism

Slow compared to creatine phosphate and glycolysis but makes the most ATP. Pyruvate enter mitochondria and undergo citric acid cycle to electron transport chain.

Define fatigue and describe what is believed to be the most common physiological causes

progressive increase in effort required to maintain desired force (sustained by repetitive contractions). Causes psychological(save from injury), Nervous system (depletion of neurotransmitters), Muscle

Describe the Cori cycle and its importance in metabolism.

Lactate(made from anaerobic) that is produced by muscle enters blood and taken to liver to be converted to glucose (gluconeogenesis)

Describe the basis of oxygen debt (i.e. excess post-exercise oxygen consumption

The rate of oxygen you consume during that exercise is only enough to account for part of that energy expenditure (the other non-oxygen dependent systems like creatine phosphate and glycolysis account for the rest).

Breath heavy to:

Need to restore glucose and glycogen( Cori cycle and muscle enzymes)

Resynthesize creatine phosphate

Replace o2 removed from myoglobin(heme - protein with iron group)

Repair

Causes for Muscle Fatigue

Depletion of ATP and CP

Glycogen depletion - no more stored

Metabolic acid production - high acid production from ATP hydrolysis, inhibits gylcolysis and impair muscle contraction)

Elevated phosphate levels - interfere with protein function

Ion imbalances - inability to maintain NA= and K = concentrations (doesn’t have enough ATP to sustain pump)

Lactate

Does not cause muscle fatigue or soreness. it reduces acid load on skeletal muscle cell and travels to other cells for energy substate (converted to pyruvate). There is no “lactic acidosis”. We now know this, but the idea that lactic acid is responsible for acidosis continues to be propagated.. The acid load from exercise actually comes from H+ production that occurs from ATP hydrolysis.

List and describe the three phases of a muscle twitch.

1) Latent period(<2ms)

• AP travels over sarcolemma, calcium just starts releasing from SR

2) Contraction

• Calcium binds troponin allowing myosin heads to attach to actin making crossbridge

3) Relaxation

• Calcium depletes myosin has less places to bind

Compare and contrast the characteristics of a muscle twitch and tetanic contraction. Describe the development of tetanus in terms of temporal summation.

Twitch = time for fiber to contract and relax

To increase force we increase the amount of twitches, temporal summation is the act of increasing time the fiber is contracting, so to not let it relax.

Tetanus = state where muscle is in sustained contraction

Define a motor unit and discuss it in the context of spatial summation

Motor unit = motor neuron + all the fibers it innervates

Spatial summation = increase of motor units to generate more tension

first small motor units are activated and then larger as more force is required

 Compare and contrast between isometric, concentric, and eccentric contractions.

Isometric - no shortening

Concentric - muscle shortens

Eccentric - muscle lengthens

 Describe the strategies used to increase force in the muscle including increasing motor unit recruitment, frequency of activation, and the length of the sarcomere at the beginning of a contraction.

1) increase motor unit recruitment - spatial summation

2) increase frequency - temporal summation

3) gross-anatomical  - fiber orientation, pennate (run at angle to have higher cross-sectional area)

4) Micro-anatomical - optimal muscle fiber length. in length-tension relationship, different sarcomeres have different amount of actin and myosin, over crowded(not stretched enough) leads to lower force (thin filaments running into each other), and over stretch you are decreasing the amount of overlap which also leads to decrease in force. 

Compare and contrast the force-generating capabilities and metabolic characteristics of fast fibers (FG), slow fibers (SO), and intermediate fibers (FOG) [see the reference table for fiber type comparison]

do chart

 Describe “hybrid” muscle fiber types and how they differ from “pure” muscle fiber types. Also, be able to describe how they change with activity/exercise.

brownish color, mix of two fiber types, have more hybrid when you are inactive and you can make them into pure fiber types, like doing more endurance training will give you more type 1 fibers. Hybrid can be Type I/Type IIA or Type IIa/Type IIx

Describe what myoglobin is, its function, where it is located, and characteristics it imparts to certain muscle fiber types (i.e. color)

Protein with heme (iron group)

Binds and releases oxygen

responsible for muscles red color (more slow twitch fibers (aerobic) = more red)

Describe the effects of exercise training on skeletal muscle. In particular, describe hypertrophy and atrophy in the context of skeletal muscle physiology.

Hypertrophy = increase in muscle diameter, mitochondrial and glycolytic enzyme activity

Atrophy= decrease in muscle stimulation

Mechanism = Stimulation (physical) with Microtears, activates satellite cells, which then fuse with muscle fiber

Mitochondrial density

slow twitch muscles that rely on aerobic activity have a lot of mitochondria (lines are very clear like in soleus)

Strength vs endurance training

Strength = more hypertrophy less capillary density and mitochondria

Endurance = less hypertrophy and more capillary density and mitochondria

Compare and contrast the structure and function of cardiac muscle and skeletal muscle

Function: Involuntary contraction, pumps blood, synchronized contraction (gap junctions), longer length of time for a single twitch(longer AP)

Structure: NO motor units, 1-2 nuclei, intercalated discs, not a lot of Calcium in SR so it has to come from blood

Describe the differences between cardiac muscle and skeletal muscle related to motor units, speed of contraction, and the involvement of the nervous system in contraction

Cardiac = no motor units, nervous system can adjust the rate of contraction and strength, contracts slower to have effective pumping of blood(100 ms) 

Compare and contrast the function of smooth muscle with skeletal muscle

Function: control diameter of tissue tubes, autonomic NS does involuntary control , slowest contraction(seconds long)

Describe the basic structure and function of smooth muscle.

Structure: small single nucleas, lacks clear organization, no T-tubules or SR, can be autorhythmic and synchronized (gap junctions), still has myosin and active that have loose overlapping organization for crossbridge.