Muscle Anatomy and Functions

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Questions and Answers

What initiates the contraction of skeletal muscle fibers?

Presence of potassium ions

Decrease in temperature

Stimulus from a motor neuron (correct)

Release of myoglobin

What is the process that leads to rigor mortis?

Loss of muscle tone

Accumulation of calcium in the sarcoplasm (correct)

Increased ATP production

Enhanced ion pump function

What distinguishes isotonic contraction from isometric contraction?

Isotonic contraction occurs only during relaxation

Isometric contraction involves sliding filaments

Isotonic contraction requires no energy

Isotonic contraction changes muscle length while isometric does not (correct)

What is muscle tone?

Normal tension and firmness of a muscle at rest Signup and view all the answers

What occurs during complete tetanus?

Sustained contraction with no relaxation Signup and view all the answers

How does treppe differ from wave summation?

Treppe involves relaxation between stimuli Signup and view all the answers

What is required for muscle relaxation and return to resting length?

Active transport of calcium ions Signup and view all the answers

What characterizes incomplete tetanus?

Muscle fibers relax between contractions Signup and view all the answers

What initiates the muscle contraction process after an action potential reaches the T tubule?

Sarcoplasmic reticulum releases calcium ions Signup and view all the answers

What role do calcium ions play in muscle contraction?

They expose active sites on thin filaments Signup and view all the answers

What process occurs repeatedly during the contraction cycle?

Cross-bridge binding and detachment Signup and view all the answers

What occurs when acetylcholine (ACh) is broken down?

Action potential generation ends Signup and view all the answers

How does the reabsorption of calcium ions affect the muscle fibers?

Decreases calcium concentration in the cytosol Signup and view all the answers

What happens to cross-bridge formation when calcium ions decrease?

Cross-bridge formation ends Signup and view all the answers

What is the final event in the muscle contraction process?

Contraction ends and relaxation occurs Signup and view all the answers

What returns to its normal position after muscle contraction ceases?

Tropomyosin Signup and view all the answers

What is the primary function of skeletal muscles?

Maintain body position Signup and view all the answers

Which connective tissue layer surrounds the entire muscle?

Epimysium Signup and view all the answers

What is the role of the sarcoplasmic reticulum in muscle contraction?

To store and release calcium ions Signup and view all the answers

What structure is formed by the combination of two terminal cisternae and one T tubule?

Triad Signup and view all the answers

What is NOT a component of a sarcomere?

Transverse tubule Signup and view all the answers

How does acetylcholine (ACh) affect muscle contraction?

Binds to receptors and allows sodium influx Signup and view all the answers

What happens to the H zone during muscle contraction according to the sliding filament theory?

It narrows Signup and view all the answers

Which type of muscle tissue is NOT voluntary?

Both B and C Signup and view all the answers

What is the role of myofilaments in muscle fibers?

Responsible for muscle contraction Signup and view all the answers

Which layer of connective tissue surrounds individual muscle fibers?

Endomysium Signup and view all the answers

What does the sliding filament theory describe?

The interaction of thin and thick filaments during contraction Signup and view all the answers

Which protein is NOT part of thin filaments?

Myosin Signup and view all the answers

What initiates the muscle action potential?

Acetylcholine binding to receptors Signup and view all the answers

What is the predominant role of satellite cells in skeletal muscle?

Repair and regeneration of damaged fibers Signup and view all the answers

Which condition is characterized by continuous muscle contractions due to a toxin from a specific bacteria?

Tetanus Signup and view all the answers

What is the primary energy source generated during anaerobic respiration in muscle fibers?

ATP Signup and view all the answers

During peak muscle exertion, which process do muscles primarily rely on for ATP production?

Glycolysis Signup and view all the answers

What occurs to pyruvic acid during conditions of low oxygen availability in muscles?

It is converted to lactic acid. Signup and view all the answers

What is a significant result of muscle fatigue during prolonged exertion?

Accumulation of lactic acid Signup and view all the answers

What is measured by an electromyogram (EMG)?

Electrical activity of muscle fibers Signup and view all the answers

How much ATP is generated from 1 glucose molecule during anaerobic glycolysis?

2 ATP Signup and view all the answers

What happens to the muscle fibers during the recovery period after exertion?

Mitochondria resume activity. Signup and view all the answers

What is the main consequence of muscle contractions in terms of heat production?

Increased body temperature Signup and view all the answers

During moderate activity, which substrates are primarily utilized for energy?

Glucose and glycogen Signup and view all the answers

What is the relationship between creatine phosphate and ATP in muscle fibers?

Creatine phosphate helps restore ATP levels. Signup and view all the answers

What causes the inability of skeletal muscle to perform required activities?

Lactic acid accumulation Signup and view all the answers

Which of the following is true regarding the Krebs cycle?

It relies on oxygen. Signup and view all the answers

What is the primary effect of growth hormone on skeletal muscles?

Stimulating protein synthesis Signup and view all the answers

Which hormone is responsible for elevating energy consumption in skeletal muscles?

Thyroid hormones Signup and view all the answers

What defines the term 'power' in muscle performance?

Maximum amount of tension produced Signup and view all the answers

How can muscle hypertrophy be achieved?

By engaging in heavy training Signup and view all the answers

What happens to muscles that remain inactive for an extended period?

They may become flaccid Signup and view all the answers

What is a characteristic of cardiac muscle tissue?

Intercalated discs Signup and view all the answers

What is the primary function of intercalated discs in cardiomyocytes?

To maintain structural integrity Signup and view all the answers

Smooth muscle is typically found in which of the following systems?

Digestive and urinary systems Signup and view all the answers

What distinguishes smooth muscle cells from skeletal muscle cells?

Fusiform shape Signup and view all the answers

Which physiological characteristic is NOT present in cardiac tissue?

Tetany Signup and view all the answers

Which component is NOT found in smooth muscle cells?

Sarcomeres Signup and view all the answers

How do electrical signals travel between cardiomyocytes?

Through gap junctions in intercalated discs Signup and view all the answers

What is the primary function of smooth muscle in blood vessels?

Regulating blood flow and pressure Signup and view all the answers

Which type of muscle is characterized by being involuntary and non-striated?

Smooth muscle Signup and view all the answers

Which muscle is NOT part of the rotator cuff?

Teres major muscle Signup and view all the answers

What is the primary function of the gluteus maximus muscle?

Extension and lateral rotation at the hip Signup and view all the answers

Which of the following muscles contributes to the adduction of the thigh?

Pectineus Signup and view all the answers

Which muscles are classified as hip flexors?

Psoas major and iliacus Signup and view all the answers

What is a characteristic of the pelvic girdle?

Is tightly bound to the axial skeleton Signup and view all the answers

Which muscles are primarily responsible for controlling the position of the eye?

Extrinsic eye muscles Signup and view all the answers

Which of the following muscles constricts the mouth opening?

Orbicularis oris Signup and view all the answers

Which nerve supplies the muscles of facial expression?

Facial Nerve Signup and view all the answers

What is the primary function of the masseter muscle?

Lifts the mandible Signup and view all the answers

Which muscles in the eye are supplied by the Oculomotor Nerve, besides the lateral rectus?

Medial rectus and superior rectus Signup and view all the answers

What is the main function of the triceps brachii muscle?

Extension of the elbow Signup and view all the answers

Which of the following muscles is NOT part of the rotator cuff?

Teres major Signup and view all the answers

What is the role of pronator teres and supinator in the forearm?

Rotating the radius Signup and view all the answers

Which muscle primarily flexes and adducts the wrist?

Flexor carpi ulnaris Signup and view all the answers

What condition results from the thickening of the flexor retinaculum?

Carpal tunnel syndrome Signup and view all the answers

Which of the following statements about extrinsic muscles of the hand is true?

Their tendons cross the wrist. Signup and view all the answers

What is the primary role of tendon sheaths in the wrist?

To protect tendons from friction Signup and view all the answers

Which of the following muscles are considered intrinsic muscles of the hand?

Dorsal interossei Signup and view all the answers

Which type of muscle is characterized by fibers that run parallel to the long axis of the muscle?

Parallel muscles Signup and view all the answers

Which of the following describes the arrangement of fascicles in a unipennate muscle?

Fibers arranged on one side of the tendon Signup and view all the answers

What term describes a muscle that opposes the action of the agonist?

Antagonist Signup and view all the answers

Which skeletal muscle type is primarily responsible for opening and closing body openings?

Circular muscles Signup and view all the answers

What is typically the origin of a muscle in relation to its insertion?

The origin is usually proximal to the insertion Signup and view all the answers

Which of the following is NOT a characteristic used in the naming of skeletal muscles?

Historical significance Signup and view all the answers

In a bipennate muscle, the fascicles are arranged in what manner?

Fibers on both sides of the tendon Signup and view all the answers

What is the function of a synergist muscle?

To assist the agonist in performing a movement Signup and view all the answers

Which muscle group primarily consists of the hamstrings responsible for knee flexion?

Flexors of the knee Signup and view all the answers

What is the role of the quadriceps tendon?

Enclose the patella and connect quadriceps to the tibial tuberosity Signup and view all the answers

Which extensor muscle is primarily responsible for plantar flexion of the ankle?

Gastrocnemius Signup and view all the answers

What is the primary action of the popliteus muscle?

Unlocks the knee by rotating the tibia Signup and view all the answers

Which muscle is NOT part of the quadriceps femoris group?

Biceps femoris Signup and view all the answers

What common type of hernia occurs in the abdominal wall?

Umbilical hernia Signup and view all the answers

Which muscle opposes the extensors and is responsible for dorsiflexion?

Tibialis anterior Signup and view all the answers

Which two muscles are commonly considered flexors of the toes?

Flexor digitorum longus and Flexor hallucis longus Signup and view all the answers

As skeletal muscle fibers age, which of the following changes is NOT typically observed?

Increased elasticity Signup and view all the answers

What are the four muscles that comprise the quadriceps femoris?

Vastus medialis, vastus lateralis, rectus femoris, vastus intermedius Signup and view all the answers

Which of the following structures directly holds tendons of the toes as they cross the ankle?

Extensor retinacula Signup and view all the answers

How do skeletal muscles rely on energy during prolonged exertion?

Primarily through anaerobic glycolysis Signup and view all the answers

What is the main role of the iliopsoas muscle group?

Flexion of the hip Signup and view all the answers

What does the term 'agonist' refer to in the context of muscle actions?

The muscle that performs the desired action Signup and view all the answers

What is the primary function of the diaphragm?

Main muscle of respiration Signup and view all the answers

Which muscle is considered the main flexor of the elbow?

Biceps brachii Signup and view all the answers

The fibers of the external oblique muscle run in which direction?

Downward and medially Signup and view all the answers

What role do the rotator cuff muscles primarily serve?

Stabilization of the shoulder joint Signup and view all the answers

What is the primary action of the trapezius muscle?

Stabilizing the scapula Signup and view all the answers

Which muscle primarily assists with lateral rotation at the shoulder?

Infraspinatus Signup and view all the answers

Which group of muscles compresses the underlying structures and rotates the vertebral column?

Oblique muscles Signup and view all the answers

Which statement correctly describes the structure of the rectus abdominis muscle?

Divided transversely by tendinous inscriptions Signup and view all the answers

Which muscle assists the deltoid for the first 15 degrees of abduction?

Supraspinatus Signup and view all the answers

Which muscle is responsible for flexing the vertebral column and opposing the erector spinae muscle?

Rectus abdominis Signup and view all the answers

What is the main action of the serratus anterior muscle?

Protracting and stabilizing the scapula Signup and view all the answers

How do flexor muscles typically position themselves in the arm and forearm?

Anteriorly and medially Signup and view all the answers

Which pelvic floor muscle has a role in controlling the movement of urine through the urethra?

External urethral sphincter Signup and view all the answers

Study Notes

Support & Movement

The muscular system is responsible for skeletal movement, maintaining body position, supporting soft tissues, guarding body openings, and maintaining body temperature.

Muscle Tissue

Skeletal muscle tissue
Cardiac muscle tissue
Smooth muscle tissue

Skeletal Muscles

Attached to the skeletal system
Allow body movement
The muscular system only includes skeletal muscles.

Functions of Skeletal Muscles

Produce skeletal movement
Maintain body position
Support soft tissues
Guard body openings
Maintain body temperature

Structure of Skeletal Muscle

Muscle cells (fibers)
Connective tissues
Blood vessels
Lymphatics
Nerves

Levels of Organization of Muscle Tissue

Level 1: skeletal muscle
Level 2: muscle fascicles
Level 3: muscle fiber
Level 4: myofibril
Level 5: sarcomere

Connective Tissue Covering of Skeletal Muscles

3 layers: epimysium, perimysium, endomysium

Epimysium

Surrounds the entire muscle
Connected to deep fascia
Separates muscle from surrounding tissue

Perimysium

Surrounds muscle fascicles
Contains blood vessels and nerve supply to fascicles

Endomysium

Surrounds individual muscle fibers
Contains capillaries and nerve fibers
Contains satellite (stem) cells for repair

Muscle Attachments

Endomysium, perimysium, and epimysium meet together at muscle ends to form connective tissue attachments to bone matrix: tendons (bundles), or aponeuroses (sheets).

Innervations & Blood Supply

Skeletal muscles are voluntary muscles, controlled by somatic nerves.
Muscles have extensive vascular systems to supply large amounts of oxygen and nutrients, and carry away wastes.

Skeletal Muscle Cells (Fibers)

Very long
Multinucleated (hundreds of nuclei)
Develop through fusion of myoblasts (mesodermal cells).

Structure of Skeletal Muscle Fibers

Sacrolemma (= cell membrane)
Sarcoplasm (= cytoplasm)
Sarcosome (= mitochondrion)
Sarcoplasmic reticulum (= SER)
Transverse (T) tubule
Myofibrils

Sarcolemma

Cell membrane of muscle cell
Surrounds the sarcoplasm
Change in transmembrane potential begins muscle contraction.

Transverse (T) Tubules

Deep invaginations of the sarcolemma
Run transversely
Allow electrical potentials to quickly spread throughout the muscle fibers.

Sarcoplasmic Reticulum (SR)

Smooth endoplasmic reticulum (SER)
Surrounds each myofibril
Forms cisternae; chambers that store Ca2+
Releases Ca2+ into sarcomeres to begin muscle contraction.

Triad

Formed by 2 terminal cisternae + 1 T tubule
Required for excitation-contraction coupling.

Myofibrils

Lengthwise threads within muscle fibers
Divided into a number of sarcomeres
Made up of bundles of proteins (myofilaments).

Myofilaments

Part of the cytoskeleton
Responsible for muscle contraction
Composed of proteins; two types
- Thin filaments
- Thick filaments

Thin Filaments

4 proteins: actin, nebulin, tropomyosin, troponin.

Thick Filaments

2 proteins: myosin, titin

Sarcomere

Contractile unit of the muscle
Structural unit of myofibrils
Consists of thin and thick myofilaments
Contains alternating dark and light bands (striations).

Lines & Zones

A bands: myosin filaments (with actin on both ends)
M line: center of the A band
I bands: actin filaments only
Z line: center of the I bands
H zone (band): area around the M line; myosin filaments only
Zone of overlap: thick and thin filaments overlap
Each sarcomere is composed of one A band in the middle, and ½ of an I band on each side.

Neuromuscular Junction (NMJ)

Specialized intercellular connection between: a synaptic terminal of a neuron & motor end plate of a skeletal muscle fiber.

Nerve Action Potential

Electrical signal travels along the nerve axon ending at the synaptic terminal,
Synaptic terminal releases neurotransmitter acetylcholine (ACh) into the synaptic cleft (gap between synaptic terminal and motor end plate).

Acetylcholine (ACh)

Neurotransmitter required for muscle contraction
Stored in synaptic vesicles
Travels across synaptic cleft
Binds to membrane receptors on sarcolemma
Causes Na+ to rush into sarcoplasm
Initiates muscle action potential
Quickly breaks down by acetylcholinesterase (AChE).

Muscle Action Potential

Electrical signal generated by sodium influx
Travels along the T tubules
Leads to excitation-contraction coupling

Excitation-Contraction Coupling

Action potential reaches a triad, triggering Ca2+ release from cisternae
Requires myosin heads to be loaded by ATP

Muscle Contraction

Caused by interactions of thick and thin filaments of sarcomeres
Triggered by Ca2+ ions
Follows the sliding filament theory

Sliding Filament Theory

During muscle contraction, thin filaments slide between thick filaments toward the M line.
Z lines move closer, H zone gets narrower, A band does not change, and zone of overlap gets thicker

A Review of Muscle Contraction (Steps 1-10)

Steps 1-6: ACh release, Action Potential travels along T tubules, SR release of Ca2+, Active site exposure, Cross-bridge formation, and Contraction cycle begins.
Steps 7-10: ACh is broken down, SR reabsorbs Ca2+, Active sites covered, Contraction ends, Muscle returns to resting length

Muscle Fatigue

Inability of a skeletal muscle to perform required activities
Results
- Depletion of metabolic reserves
- Muscle exhaustion from lactic acid accumulation
- Damage to sarcolemma and sarcoplasmic reticulum

Muscle Metabolism

At rest & mild exertion: oxygen is available, ATP generation starts in cytoplasm (glycolysis), and is completed in mitochondria (Krebs cycle - aerobic).
At peak exertion: muscles lack oxygen to support mitochondria, muscles rely on glycolysis for ATP, pyruvic acid builds up and is converted to lactic acid, and Sustained condition causes muscle fatigue.

Recovery Period

Time required by muscles after exertion to return to normal.
Oxygen becomes available
Mitochondria resume activity

Muscles & Heat Production

Muscle contraction produces heat
Up to 70% of muscle energy can be spent as heat, and helps maintain body temperature.
Shivering in cold weather helps enhance body heat generation.

Hormones & Muscle Metabolism

Growth hormone and testosterone stimulate synthesis of contractile proteins and enlargement of skeletal muscles.
Thyroid hormones elevate rate of energy consumption in resting and active skeletal muscles.
Epinephrine increases duration and force of contraction

Muscle Performance

Power: maximal amount of tension produced.
Endurance: amount of time an activity can be sustained.
Power and endurance depend physical condition and types of muscle fibers.

Types of Skeletal Muscle Fibers

Properties of fast fibers
Properties of slow fibers
Properties of intermediate fibers

Muscle Hypertrophy & Atrophy

Hypertrophy: increases in diameter and number of myofibrils of muscle fibers; due to heavy training.
Atrophy: due to lack of muscle activity; reduces muscle size, tone, and power

Use it or lose it!

Muscle tone indicates base activity in motor units of skeletal muscles.
Muscles become flaccid when inactive for days or weeks.
With prolonged inactivity, fibrous tissue may replace muscle fibers
What you don't use, you lose.

Cardiac Muscle

ONLY in the heart
Contains cardiac muscle fibers (cardiomyocytes = cardiocytes)

Characteristics of Cardiomyocytes

Short – branched
Involuntary
Mononucleated
Striated
Short and wide T tubules
SR has no terminal cisternae
No triads
Aerobic (high in myoglobin, mitochondria)
Have intercalated discs

Intercalated Discs

Specialized contact points between cardiomyocytes; join cell membranes (gap junctions, desmosomes) and branching sites.
Functions
- Maintain structure
- Enhance molecular and electrical connections
- Conduct action potentials

Coordination of Cardiomyocytes

Intercalated discs connect cardiomyocytes mechanically, chemically, and electrically, causing the heart to work like a single fused mass of cells.

Physiological Characteristics of Cardiac Tissue

Automaticity; SA node
Contractibility
Conductivity
Excitability; no tetany

Smooth Muscles

Fusiform shaped
Involuntary
Mononucleated
Nonstriated
Controlled by pacesetter cells
No tendons, or aponeuroses
No T tubules
No sarcomeres: scattered myofilaments, thin filaments attached to dense bodies
Dense bodies; transmit contractions between cells

Comparing Skeletal, Cardiac, & Smooth Muscle Tissues

Properties of skeletal, cardiac, and smooth muscles

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Description

Explore the intricacies of the muscular system, including muscle tissue types, skeletal muscle functions, and structural organization. This quiz will test your knowledge on how skeletal muscles support movement, maintain posture, and regulate body temperature.