Phys III

Describe a muscle contraction

The process where muscle fibers generate tension or change length to create movement, stability, and posture

In general terms, how does a neuron induce a muscle contraction? Does a muscle always shorten during contraction?

-By releasing a chemical signal at the neuromuscular junction that causes calcium release inside the muscle cell, prompting internal fibers to pull against each other.

-No, a muscle does not always shorten during a contraction.

Describe the three cellular components of a neuromuscular junction.

-Presynaptic Axon Terminal

-Postsynaptic Motor End Plate

-Perisynaptic Schwann Cells

What are the steps that lead to the influx of Calcium? (4)

-Arrival of an Action Potential

-Membrane Depolarization

-Volted gated calcium channels open

-Calcium Inlfux.

How does calcium affect thin filaments?

The direct switch that unlocks the thin filaments.

What are troponin and tropomyosin? How does this result in sliding of filaments?

-Regulatory proteins attached to thin filament serve as gatekeepers of muscle contractions.

-Occurs because removing these gatekeeper proteins allows myosin to perform a mechanical rowing motion called the cross-bridge cycle

Describe the structure and function of the microscopic anatomy of skeletal muscle tissue at the tissue, cellular, and subcellular level.

Skeletal muscle is highly organized, structured like a cable made of smaller ropes, which are in turn made of tiny threads. This design allows microscopic cellular movements to translate into powerful macroscopic physical forces.

Describe the microstructure of a myofibril.

-Long, cylindrical organelle that is just a continuous chain of thousands of sarcomeres linked end-to-end runs parallel along the entire length of a muscle cell. Makes muscles contract.

Describe the regions of a sarcomere: A band, H zone, M line, and I band.

-A band: The large, dark central region of the sarcomere.

-H zone: A lighter, less dense subdivision located in the exact center of the A-band.

-M line: A thin, dark line running directly down the absolute center of the H-zone (and the center of the entire sarcomere)

-I band: The large, light-colored region that straddles the Z-line boundaries between two adjacent sarcomeres

Describe how a sarcomere changes during a contraction

-Shortens because thin actin filaments slide past thick myosin filaments toward the center, while the actual lengths of the filaments remain unchanged

Understand the steps in the sliding filament theory.(4)

1.Binding Site Exposure-A nerve impulse triggers the release of calcium ions (Ca²⁺) inside the muscle cell. Calcium binds to a protein called troponin, causing a structural shift that moves another protein, tropomyosin, away from the active sites on the actin filament. This exposes the spots where myosin needs to attach.

2.Cross-Bridge Formation-The energized myosin head binds directly to the newly exposed active sites on the actin filament, forming a physical link called a cross-bridge.

3.The Power Stroke-The myosin head releases the phosphate and ADP molecules. This release of stored energy causes the myosin head to pivot sharply. This physical pulling action slides the actin filament inward toward the center of the sarcomere, effectively shortening the muscle.

4.Detachment & Re-cocking-A fresh molecule of ATP binds to the myosin head, which forces it to detach. The ATP is then hydrolyzed back into ADP and phosphate, releasing energy that "re-cocks" the myosin head back into its high-energy position.

Where is ATP used during cross-bridge interactions that result in contractions?

-To detach the myosin head, breaking the cross bridge

-And to reset the myosin head into a high-energy cocked position via hydrolysis

Define a motor unit.

A single somatic motor neuron and all the individual skeletal muscle fibers it stimulates

How do motor units of varying sizes differ? What kind of body actions are driven by small and large motor units?

-Vary in size based on the number of muscle fibers a single motor neuron controls.

-Small: Fine & Precise Actions-Visual Tracking, Manual Dexterity, Vocal Adjustments

-Large: Gross & Powerful Actions- Locomotion/Power, Heavy lifting, Postural Support

What is a latent period? Why does it take time?

-The brief, microscopic delay that occurs between the exact moment a muscle receives an electrical stimulus and the actual beginning of physical tension or contraction.

-Takes time because a muscle cannot physically slide its filaments until a sequence of chemical and electrical steps occurs first

Describe the mechanics of single-fiber contractions

-Through the sliding filament theory. This process allows a single muscle cell (muscle fiber) to generate tension and shorten

What are the three types of contractions?

-Concentric Contraction (Shortening)-Upward swing bicep lift.

-Eccentric Contraction (Lengthening)-Lower swing of bicep curl. Muscle remains actively engaged to control the movement

-Isometric Contraction (Static)-The muscle generates force without changing its length or moving the joint, holding a plank.

What is a twitch?

A single, rapid contraction and relaxation cycle of a muscle fiber in response to a single electrical stimulus (action potential)

Explain how muscle can contract but lengthen as a result of contraction.

-Occurs when the external force (the load) is greater than the internal force generated by the muscle's cross-bridges

-Like lowering a weight.

What are fast-twitch fibers? Slow-twitch fibers?

-(slow)Engineered for sustained, long-duration endurance activities. They generate force slowly but are highly resistant to fatigue.

-(fast)Engineered for rapid, explosive, and high-intensity movements. They generate massive force instantly but fatigue very quickly.

How does stimulus frequency affect a muscle twitch?

Increasing stimulus frequency raises the total force generated by a muscle by causing overlapping contractions

Describe the tension curves of a muscle during a normal twitch, unfused tetanus, and fused tetanus

Normal Twitch-An isolated, smooth wave that rises to a peak and returns completely back to the zero baseline

Unfused tetanus-Repeated stimuli delivered at a moderate frequency, where the muscle starts to relax but gets stimulated again

Fused tetanus-High-frequency, continuous stimuli leaving zero time for the muscle to relax

Describe the relationship between the force-length tension curve.

A muscle's capacity to generate active force depends entirely on the initial structural length of its sarcomeres before contraction begins

Describe the energy sources of ATP production for muscles.

Creatine Phosphate (Phosphagen) System-When muscle contraction starts, it rapidly donates a phosphate group to ADP

Anaerobic Glycolysis (Glycolytic System)-Breaks down stored muscle glycogen into glucose and converts it to pyruvic acid and lactic acid.

Aerobic Respiration (Oxidative System)-Completely breaks down glucose, pyruvic acid, and fatty acids inside the mitochondria using oxygen

Describe how creatine phosphate generates ATP

Acting as an immediate, high-energy chemical reservoir that directly donates a phosphate group to depleted ADP

Describe how glycolysis generates ATP.

Breaking down a single molecule of glucose into two molecules of pyruvate through a sequence of 10 enzymatic reactions. 2 ATP into 4

Describe how oxidative phosphorylation generates ATP.

Transferring electrons from nutrient-derived molecules through an electron transport chain to create a proton gradient, which then powers the enzyme ATP synthase via chemiosmosis.

Describe the three primary types of skeletal muscle fibers

1. Slow Oxidative Fibers (Type I / "Slow-Twitch")-Posture maintenance, standing

2.Fast Oxidative-Glycolytic Fibers (Type II-a / "Intermediate")-Walking and middle-distance running

3.Fast Glycolytic Fibers (Type II-b / Type II-x / "Fast-Twitch")-Short explosive movement’s like sprinting

Which of these fiber types resist fatigue? Which produce high-force rapid contractions?

Type 1 / Slow Oxidative (SO) fibers are the most fatigue-resistant fiber

(*) Type 2A / Fast Oxidative-Glycolytic (FOG) fibers possess intermediate fatigue resistance. Also produce rapid, high-force contractions.

Type 2X / 2B / Fast Glycolytic (FG) fibers produce the highest-force, most rapid contractions.

Which muscle type would sustain activities like full day walks? Which sustain Olympic sprinters? A couch potato?

1. Full-Day Walks: Type 1 / Slow Oxidative (SO) Fibers

2. Olympic Sprinters: Type 2X (2B) / Fast Glycolytic (FG) Fibers

3. Deconditioned / Inactive Muscle: Type I for short move.

Describe how lever type effect muscle output.

Depending on how these three components are arranged (F.E.L), a muscle will either gain a mechanical advantage (allowing it to lift heavy loads with less effort) or a mechanical disadvantage (requiring more effort but gaining speed and a greater range of motion).

What are the fulcrum, effort, and load in a lever system?

Fulcrum (F): The fixed pivot point around which the movement occurs. In the human body, the joints act as the fulcrums

Effort (E): The internal force applied to the lever to cause movement. In the body, this is the tension generated by a contracting skeletal muscle at its specific insertion point on the bone

Load (L): The external resistance or weight that must be overcome or moved. This includes the physical weight of the limb itself, surrounding tissues, or any external object you are trying to lift (such as a dumbbell)

What are the different lever types?

Levers are categorized into three distinct types based on which of the three components sits in the exact middle of the system.

Class 1: Fulcrum in the middle (E-F-L) Scissor

Class 2: Load in the middle (F-L-E) Wheelbarrow

Class 3: Effort in the middle (L-E-F) Shovel

How much effort needs to be put into a type III lever that hold 20kg knowing the distances between fulcrum, load, and effort. Know this equation.

We use the Law of the Lever equation. Effort x Effort Arm=Load x Load Arm

• Effort: The muscle force required measured in Newtons or kilograms.

• Effort Arm: Exact distance from the Fulcrum to the Effort insertion point.

• Load: The mass or weight being held.

• Load Arm: The full distance from the Fulcrum to the Load.

Describe general functions of smooth muscles

Smooth muscle is an involuntary, non-striated tissue specialized for maintaining hollow organ regulation, internal transport throughout the body and involuntary, slow, and sustained contraction.

Where are smooth muscles located.

-Primarily within the walls of hollow visceral organs, tubes, and passageways throughout the body, as well as in a few specialized microscopic structures

Explain what triggers smooth muscles to contract and how this occurs.

Smooth muscle contract in response to membrane depolarization and uses calcium as a biochemical switch to activate the myosin head directly. It completely lacks troponin.

Where is the calcium source that smooth muscles use for contraction?

-The extracellular fluid and the sarcoplasmic reticulum.

Describe inputs stimulate contraction of smooth muscles

Because smooth muscle membranes house a diverse array of specialized receptor proteins and ion channels, they can translate neural, hormonal, mechanical, and chemical inputs

What are the five major inputs that influence smooth muscle contraction activity?

Neural Stimulation

Hormonal Signals

Mechanical Stretch

Local Chemical Factors

Spontaneous Pacemaker Activity

What are pacemaker potentials? How do these influence smooth muscles?

-Are spontaneous, rhythmic fluctuations in a cell's membrane potential THAT automatically drive the cell toward its threshold to trigger an action potential that occur without any external nervous or chemical stimulation.

-Pacemaker potentials dictate exactly when, where, and how smoothly muscle tissues contract

How are smooth muscles arranged?

-Structurally arranged into dense, sheet-like networks or functional bundles.

Describe general functions of cardiac muscles

To act as an involuntary, highly resilient muscular pump that propels blood continuously throughout the cardiovascular system.

Where are cardiac muscles located? How are their thick and thin filaments organized?

Myocardium

Featuring a highly ordered, repeating structural arrangement:

What are the functions of the intercalated discs

Transmitting electrical signals instantly so the heart beats as a single unit, and anchoring cells together so the heavy force of pumping blood doesn't rip the tissue apart

Where is the Ca source that cardiac muscles uses for contraction?

extracellular fluid (outside the cell) and the intracellular sarcoplasmic reticulum (SR)

Describe how cardiac muscles are stimulated to contract.

-Set by a built-in electrical clock called the Sinoatrial (SA) Node and through autorhythmicity (self-generated electrical impulses)

- excitation-contraction coupling (converting a spontaneous electrical wave to the squeeze)

How are calcium ions distributed through the cardiac muscle cells rapidly?

Through cardiac muscle cells (cardiomyocytes) via transverse tubules (T-tubules) and a process called calcium-induced calcium release (CICR)

What sets the rhythm of the cardiac muscles? What tells the muscles to contract?

-Set by a built-in electrical clock called the Sinoatrial (SA) Node and through autorhythmicity (self-generated electrical impulses)

- excitation-contraction coupling (converting a spontaneous electrical wave to the squeeze)

What are the steps that lead to cardiac muscle contraction?

1. Generation and Spread of the Action Potential

2. The Electrical Highway (T-Tubule Depolarization)

3. Calcium-Induced Calcium Release (CICR)

4. Filament Sliding (The Cross-Bridge Cycle)

How do action potential and muscle tension differ between skeletal muscles vs cardiac muscles? Why?

1. The Electrical Signal (Action Potential)

• Skeletal Muscle (A Quick Zap)

• Cardiac Muscle (A Long Flow)

• The long signal gives the heart time to perform a deep, steady squeeze to wring out blood, rather than a frantic twitch

2.The Muscle Squeeze (Tension)

• Skeletal Muscle (Can Lock Up)

• Cardiac Muscle (Cannot Cramp)

• If your heart suffered a cramp or locked up in tetanus , it could not relax to refill with blood, which would cause instant death. Skeletal muscles are designed for voluntary, graded movements.

Define the following: sarcomere, z-lines, thick and thin filaments

-Sarcomere: The fundamental, repeating functional unit of contraction within a myofibril.

-Z-lines: Structural protein bands that form the boundaries of each sarcomere. They act as anchors, securing the thin filaments in place and connecting adjacent myofibrils to one another

-Thick filaments-The larger protein strands located in the middle of the sarcomere grab onto thin filaments.

-Thin filaments-The narrower protein strands attached to the Z-lines and extending toward the center.

How does the lack of ATP result in rigor mortis?

-Calcium leaks out into the muscle fiber, binding to troponin and permanently exposing the binding sites on the actin filaments.

-Any remaining energized myosin heads instantly reach up and bind to the actin filaments to perform a power stroke.

-With zero ATP left, the myosin heads can never detach.

What is a single-unit vs multiunit smooth muscles?

-The most common arrangement contracts together as a coordinated single sheet.

-Smooth muscle consisting of independent cells that contract separately to allow for fine, precise control.