Chapter 10 & 11 - Muscular Tissue & System

What are the 3 types of Muscular Tissue?

- Cardiac Muscle

- Skeletal Muscle

- Smooth Muscle

Functions of the Skeletal Muscle:

- Thermoregulation

- Body movement

- Maintain Posture & Stability

- Respiration

- Storing and moving body substances within the body

Functions of the Smooth Muscle:

- Respiration

- Storing and moving body substances within the body

Functions of the Cardiac Muscle:

- Heartbeat

- Storing and moving body substances within the body

Structural Organization of Skeletal Muscles:

Muscle wrapped in Epimysium —> Muscle Fascicle wrapped in Perimysium —> Muscle Fiber wrapped in Endomysium —> Myofibril —> Myofilaments

The ______ is also known as the ______

Muscle Fiber ; myocyte (muscle cell)

The ______ is the basic contractile unit of a ________

Sarcomere ; muscle fiber

What does the Epimysium surround?

The muscle

What does the Perimysium surround?

The fascicles

What does the Endomysium surround?

The fiber (cells)

What are the 4 properties of Muscle Tissue?

- Electrical Excitability

- Contractibility

- Extensibility

- Elasticity

What is Electrical Excitability?

The muscle’s ability to respond to stimuliWh

What is Contractibility?

The muscle’s ability to shortenW

What is Extensibility?

The muscle’s ability to be stretched without tearing

What is Elasticity?

The muscle’s ability to return to it’s original length and shape

_____ fuse together to form a skeletal muscle fiber during embryonic development.

Myoblasts

________ carry out muscle repair after development.

Satellite cells

Hypertrophy:

The growth/increase in muscle mass & size

Atrophy:

The wasting and decrease in size and strength of muscle tissue

What are the 2 main types of Hypertrophy?

- Myofibrillar hypertrophy

- Sarcoplasmic hypertrophy

What are the factors that affect Muscle Growth (Hypertrophy)?

- Genetics

- Diet & Nutrition (proteins, carbohydrates, and fats)

- Resistance Training

- Anabolic Hormones (testosterone, insulin-like growth factor-1, insulin, growth hormone, and T3 thyroid hormone)

- Performance Enhancing Drugs (anabolic steroids, selective androgen receptor modulators (SARMs), insulin-like growth factor-1, human growth hormone, and myostatin inhibitors)

Understanding the Sliding Filament Model:

Step 1: Calcium Binds

- Calcium unlocks troponin —> tropomyosin shifts —> actin binding sites are exposed

Step 2: Cross-Bridge Forms

- Energized myosin head binds to the exposed actin site

Step 3: Power Stroke

- Myosin releases ADP + P —> pivots and pulls actin toward the center of the sarcomere'

Step 4: Detachment & Reset

- New ATP binds to myosin —> myosin lets go of actin —> ATP splits to re-cock myosin head for the next pull

What is a Neuromuscular Junction (NMJ)?

A specialized chemical synapse where a motor neuron meets a skeletal muscle fiber

- Precise site where the nervous system communicates with a muscle cell to trigger a voluntary muscle contraction

What is Acetylcholine (ACh)?

A specialized chemical messenger, known as a neurotransmitter, that the nervous system uses to signal muscle cells to contract

What does the binding of ACh to its receptors on the motor end plate trigger?

An electrical wave that spreads across the muscle cell and down into its deep structures, ultimately setting up the physical contraction

What is the muscle action potential initiated by?

The end-plate potential (EPP) reaching a specific electrical threshold, which triggers adjacent voltage-gated sodium channels to pop open

What is the sarcoplasmic reticulum triggered to release calcium ions by?

The muscle action potential traveling down the T-tubules and activating voltage-sensitive receptors

What happens after being released into the sarcoplasm?

The calcium ions bind directly to troponin

When is a cross-bridge formed?

When an energized myosin head binds to an exposed active site on an actin filament

What is the power stroke?

The physical pulling action of a muscle contraction

- The myosin head pivots and slides the actin filament toward the center of the sarcomere

Explaining the Sliding Filament Model step-by-step:

1. Nerve Impulse triggers Voltage-gated Ca²⁺ channels to open in Synaptic End Bulb

2. Ca²⁺ stimulates Synaptic vesicles to release neurotransmitter Acetylcholine (ACh) via exocytosis into Synaptic cleft

3. ACh binds to receptors of Motor End Plate which opens Na⁺ ion channels that are also in the ACh receptors

4. Na⁺ ions depolarize (more positively charged) muscle fiber —> initiates Muscle Action Potential

5. Muscle Action Potential then travels down T-tubules which trigger sarcoplasmic reticulum (SR)

6. Sarcoplasmic reticulum release Ca²⁺ ions into sarcoplsam

7. Ca²⁺ binds to troponin on the actin, troponin reconfigures —> moves tropomyosin, exposing myosin-binding sites

8. Myosin head hydrolyzes ATP & becomes energized and ready

9. Myosin head bind to actin, forming a cross-bridge

10. Myosin heads pivot & pull on the actin, sliding it towards the M line = power stroke

11. ADP is released from myosin head

12. Another ATP binds to ATP-binding site on myosin head —> myosin head detaches from actin

What is sarocmere?

A contractile unit

- Contractile proteins = myofilaments

What is myosin?

A thick filament —> motor protein

What is actin?

A thin filament

What is a Z disc?

A-actinin; the ends of sarcomereW

What is the M line?

Myomesin; the middle of sarcomere

What is the A band?

The entire length of myosin

- dark striations = myosin + some of actin

What is the I band?

The remaining part of actin

- light striations = actin

What is the H zone?

Myosin only; the center of the A bandW

What are the structural proteins?

Titin and Dystrophin

What is Titin?

Spans between the Z disc and M line; helps stabilize position of myosin

What is Dystrophin?

Links actin to membrane proteins of sarcolemma; helps transmit tension generated by sarcomeres to muscle tendons

What are the 3 proteins of Myofibrils?

- Contractile proteins

- Structural proteins

- Regulating proteins

(2 actin filaments for every 1 myosin filament)

Titin is the 3^rd most plentiful protein in the skeletal muscle

What changes in the Sarcomere during Muscle Contraction?

The sarcomere becomes shorter:

- Z discs get closer together

- I bands decrease in size to almost disappear

- H zone disappears

- A band stays at the same length

• - A band becomes darker since more actin is present

- M line stays the same

What is a Motor Unit?

A functional unit of muscle contraction consisting of a single motor neuron and all of the individual muscle fibers it stimulates

- Somatic Motor Neuron + all Muscle Fibers it simtulates

The Somatic Motor Neuron produces an Electrical Nerve Impulse, which converts into:

Chemical Signal at Neuromuscular Junction Triggers Muscle Fibers to contract

_____ is controlled by the _____ through 2 primary mechanisms

Muscle tension; nervous system

What are the 2 primary mechanisms of the nervous system?

- Motor unit recruitment

- Wave summation

What is the motor neuron recruitment?

The number of muscle fibers stimulated

What is the wave summation?

The frequency of the stimulation

What happens with a Twitch Contraction?

When an action potential travels down the motor neuron, it results in a contraction of all the muscle fibers in unison associated with that motor neuron

- The contraction generated by a single action potential —> muscle twitch

• - Latent period = short delay = 1-2 msec

• - Time required for Ca²⁺ to diffuse out of SR, bind to troponin, movement of tropomyosin to expose myosin-binding sites on actin, formation of cross bridges

• - Contraction period

• - When the muscle is generating tension (force)

• - Associated with cycling of cross bridges (repeating cycle of myosin heads binding to actin, pulling them to generate force and then detaching)

• - Relaxation period

• - Time for the muscle to return to its normal length

• - A short as 10 msec

• - As long as 100 msec

**Muscle twitch is the first stimulus**

What happens with a Wave Summation?

When a second stimulus excites a partially relaxed muscle, producing a stronger contraction

- Occurs when additional Ca²⁺ is released from the sarcoplasmic reticulum by subsequent stimuli while levels of Ca²⁺ in the sarcoplasm are still elevated from the first stimulus —> build up Ca²⁺ ions

What happens with an Unfused Tetanus?

Successive stimulations at the same frequency, producing a series of contractions with increasing tension

- Occurs when additional Ca²⁺ is released from the sarcoplasmic reticulum by subsequent stimuli while levels of Ca²⁺ in the sarcoplasm are still elevated from the first stimulus —> build up Ca²⁺ ions

- Successive stimulations at the same frequency excites partially relaxed muscle; produces a series of contractions with increasing tension (wavering contraction)

What happens with a Fused Tetanus?

Rapid stimulations without muscle relaxation, producing a smooth sustained contraction

- Occurs when additional Ca²⁺ is released from the sarcoplasmic reticulum by subsequent stimuli while levels of Ca²⁺ in the sarcoplasm are still elevated from the first stimulus —> build up Ca²⁺ ions

What is Hypertonia?

- Muscle ton increased (stiffness)

- High resistance to passive movements

- Hyperreflexia

- Seen in upper motor neuron lesion

- Muscles are tight and rigid

- Stiff posture and abnormal gait

What is Hypotonia?

- Muscle tone decreased (floppy)

- Low resistance to passive movements

- Hyporeflexia/absent reflexes

- Seen in lower motor neuron lesion/cerebellar lesion

- Muscles are loose/soft

- Poor posture, delayed milestones

What does Aerobic respiration provide?

The most ATP to enable sustained muscle contractions

- Aerobic respiration is the slowest but produces 30-32 ATP per glucose

- Anaerobic glycosis is fast but produces 2 ATP per glucose

- Creatine phosphate is the fastest (instant) but produces 1 ATP per CP molecule

Creatine Phosphate System:

The first source of energy used to regenerate ATP when muscle contraction begins because it us the most rapid

What are the 3 Types of Skeletal Muscle Fibers?

1. Slow Oxidative Fibers

• - Slow-twitch red muscle fibers

2. Fast Oxidative-Glycolytic Fibers

3. Fast Glycolytic Fibers

• - Fast-twitch white muscle fibers

Slow Oxidative Fibers:

Size & Color: Thin, bright red

Capillary Density (blood vessel count): Highest

Metabolism (energy conversion): Aerobic (has oxygen)

Contraction Force (amount of strength): Low

Fatigue Resistance (ability to work without getting tired): High

Fast Oxidative-Glycolytic Fibers:

Size & Color: Thick, pale red

Capillary Density (blood vessel count): Intermediate

Metabolism (energy conversion): Aerobic/Anaerobic

Contraction Force (amount of strength): Intermediate

Fatigue Resistance (ability to work without getting tired): Intermediate

Fast Glycolytic Fibers:

Size & Color: Thickest, pale pink

Capillary Density (blood vessel count): Lowest

Metabolism (energy conversion): Anaerobic (without oxygen)

Contraction Force (amount of strength): Highest

Fatigue Resistance (ability to work without getting tired): Low

____ is the proximal end’s attachment to a stationary bone

Origin

____ is the distal end’s attachment to a moveable bone

Insertion

Agonist (Prime Mover)

The contracted muscle that causes action

Antagonist

A relaxed muscle

Synergist

Assists agonist in movement and provides additional force and stability

Fixator

stabilizes the origin of agonist muscle and joints in spans and provides support and stable base for movement by holding a part of the body still, allowing other muscles to work more efficiently

Isotonic Contraction:

The length of the muscle changes and physical movement produces at the joint

- Muscle remains relatively constant as it overcomes a fixed resistance

- Example: push up rising and downward action

Isometric Contraction:

The length of the muscle remains completely unhinged, and no joint movement occurs

- Muscle generates tension, but matches the resistance exactly, so the load does not move

- Example: holding the push up position (plank)

Concentric Contraction:

The muscle shortens

- Example: the upward phase of a biceps curl

Eccentric Contraction:

The muscle lengthens

- Example: the downward phase of a biceps curl

Lever:

The bones

- Rigid structure that can move around a fixed point

Fulcrum:

The joints

- A fixed point or pivot

Effort:

The muscles

- Inputs force

- Causes movement

Load:

The object or resistance —> the force that the applied effort must overcome to produce movement

- Output force

Mechanical Advantage:

Levers can be used so that a small force (effort) can move a much bigger force (load)M

Mechanical Disadvantage:

Levers require a greater force (effort) than the load it is moving

Lever Classes:

- First-Class Lever: EFL

- Second-Class Lever: ELF

- Third-Class Lever: FEL

Example of First-Class Lever:

Skull = Lever

Atlanto-occipital joint = Fulcrum

Neck muscles = Effort

Weight of head = Load

Example of Second-Class Lever:

Foot = Lever

Ball of foot = Fulcrum

Gastrocnemius = Effort

Weight of body = Load

Example of Third-Class Lever:

Radius & ulna = Lever

The elbow joint = Fulcrum

Biceps brachii = Effort

Weight of forearm & hand + any dumbbell or additional weight = Load

Mechanical Advantages or Disadvantages of First-Class Lever:

Mechanical Disadvantage —> the effort (neck muscles) is applied very close to the fulcrum (joint) while the load (weight of head) is far away

Mechanical Advantages —> gravity pulls the head forward and down so less muscular effort —> leveraging the weight of your head for movement

Mechanical Advantages or Disadvantages of Second-Class Lever:

Mechanical Advantages —> the effort (gastrocnemius) will always be greater than the load

- Second-Class lever is the most mechanically advantageous

Mechanical Advantages or Disadvantages of Third-Class Lever:

Mechanical Disadvantages —> the effort is significantly shorter than the load, making the ratio very small —> a larger effort force is required to move a smaller load (load is too far away from the fulcrum)

Myasthenia Gravis :

A chronic autoimmune neuromuscular disease (Neuromuscular Disease)

- The immune system attacks ACh receptors —> disrupts nerve signals to muscle

- Associated with thyroid hyperplasia/tumors

- Fluctuating weakness in voluntary muscles

• - Eye movement, facial expressions, and limb movements

• - As MG progresses, difficulty with speech and chewing

Bell’s Palsy:

A condition causing sudden weakness or paralysis on one side of the face (Neuromuscular Disease)

• - Drooping face, inability to close eye, difficulty with facial expressions, tastes changes, and facial pain

- Damaged or swollen facial nerve

- Usually temporary

- Causes = viral infection

• - Varicella zoster virus —> chickenpox and shingles

Muscular Dystrophy:

A group of genetic disorders (over 30 types) —> similar to muscle atrophy but differs in cause (Myopathy)

- X-linked recessive (more common in males)

- Duchenne MD = most common

• - Genes for protein dystrophin is mutated

• - Sarcolemma tears easily during muscle contractions —> muscle fibers rupture and die

- Muscle Atrophy = disease or injury

- Main Symptoms:

• - Muscle weakness and loss, scoliosis, progresses with age —> evident in childhood to teen years

Mitochondrial Myopathy:

A group of rare genetic disorders (Myopathy)

- Mutated genes that encode mitochondrial proteins

• - Defects in mitochondrial structure or function

• - Accumulation of harmful substances within mitochondria

• - Reduces energy produce (<ATP)

- Common Symptoms:

• - Muscle weakness and fatigue, exercise intolerance, muscle pain and cramps, difficulty swallowing or speaking, eye movement problems, seizures, heart problems, and stroke-like episodes

Endocrine Myopathy:

A muscle disorder caused by imbalances in hormones (Myopathy)

- Hypothyroidism and hyperthyroidism, adrenal insufficiency, hyperparathyroidism, growth hormone deficiency, and diabetes (insulin)

- Symptoms:

• - Generalized muscle weakness, especially in legs and arms, fatigue, muscle cramps, muscle aches, pains, and difficulty with activities of daily living

Abnormal Contractions of Skeletal Muscle:

- Spasm = sudden involuntary contraction

• - Cramp = painful spasm

• - Tic = twitch

- Tremor = shaking

- Fasciculation = visible muscle twitch

- Fibrillation = heart twitch/spasm

• - Viewed on ECG

Sports Hernia:

A muscle injury or tear to lower abdomen and groin (Sports-Related Condition)

- Gilmore’s groin or athletic pubalgia

- Cause: repetitive twisting motions in sports

- Symptoms:

• - Groin pain, weakness, and difficulty with kicking and running

Impingement Syndrome:

The most common cause of shoulder pain and dysfunction in athletes (Sports-Related Condition)

- Continuous pinching of supraspinous tendon

- Causes: repetitive movement of the arm above the head

- Treatment:

• - Rest of the shoulder joint, strengthening shoulder through exercise, massage therapy, and in severe cases: surgery

Rotator Cuff Injury:

Damage to the rotator cuff muscles and tendons (shoulder joint) (Sports-Related Condition)

- Causes: repetitive motions during playing and trauma

- Symptoms:

• - Shoulder pain, weakness, and limited range of motion

Pulled Hamstrings:

A strain or tear of hamstring muscle (different grades) (Sports-Related Condition)

- Causes: sudden movements/change in direction, overuse, and improper performance of exercises

- Symptoms:

• - Sudden pain, swelling, reduced leg strength or mobility, and hematoma (bruising)

Shin Splint Syndrome:

The overuse of tibialis anterior and tendons (tibial stress syndrome) (Sports-Related Condition)

- Causes: sudden increase in activity intensity or duration, improper running or walking technique and flat feet or pronated arches

- Symptoms:

• - Pain on the inner side of the shin, pain worsens with activity and improves with rest, tenderness to the touch, and swelling or redness in severe cases

Compartment Syndrome:

External or internal pressure constricts structures within a compartment

- Damaged blood vessels —> ischemia

- Causes: crushing and penetrating injuries, contusion (damage to subcutaneous tissue without the skin being broken), muscle strain, and improperly fitted cast

- Symptoms:

• - Pain, burning, pressure, pale skin, and paralysis

- Treatment: Fasciotomy

Plantar Fasciitis:

Inflammation of plantar aponeurosis (fascia) —> “Painful Heel Syndrome“

- Causes: overstretched already tight calf muscles, flat feet or high arches, overuse & repetitive stress on feet, and excess weight gain

- Symptoms:

• - Sharp pain in heel —> especially first steps in the morning or after resting, pain worsens with activity and tenderness along bottom of foot

Muscle Cancer = Soft Tissue Sarcoma:

A painless lump or swelling that may grow over time (rare type of cancer)

- Originates in soft tissues:

• - Muscles, tendons, fat, blood vessels, and nerves

- Different Types:

• - Liposarcoma, rhabdomyosarcoma, synovial sarcoma, angiosarcoma, and leiomyosarcoma

- Risk Factors:

• - Exposure to radiation therapy, certain chemicals (vinyl chloride —> chemical used to make PVC plastic), genetic disorders, and lymphedema

- Symptoms:

• - Pain or discomfort can be present, change in size or shape of lump, numbness or tingling in that area, and swelling in lymph nodes near tumor