Study Guide on Muscle Tissue Types and Contraction

Skeletal Muscle

Long, cylindrical fibers with multinucleated, periphery nuclei and clear striations.

Cardiac Muscle

Short, branched fibers with 1-2 nuclei located centrally and less distinct striations.

Smooth Muscle

Spindle-shaped (fusiform) fibers with a single nucleus located centrally and no striations.

Epimysium

Connective tissue surrounding the entire muscle organ.

Perimysium

Connective tissue surrounding a bundle of muscle fibers (fascicle).

Endomysium

Connective tissue surrounding an individual muscle fiber (cell).

Myofibril

Long organelle within the muscle fiber, made of sarcomeres.

Sarcomere

Basic contractile unit of the muscle; composed of thick (myosin) and thin (actin) filaments.

Myofilaments

Actin (thin) and myosin (thick) filaments.

Striations

Visible banding pattern due to the arrangement of thick (myosin) and thin (actin) filaments in repeating units called sarcomeres.

A bands

Dark bands in striations that consist of thick filaments (myosin) and some overlapping thin filaments.

I bands

Light bands in striations that consist of only thin filaments.

Thick Filament

Composed of myosin molecules, with heads that bind actin and ATP, and tails that form the shaft.

Thin Filament

Composed of actin, tropomyosin, and troponin, with actin providing binding sites for myosin.

Action Potential (AP)

Electrical signal that travels down the motor neuron to initiate muscle contraction.

Acetylcholine (ACh)

Neurotransmitter released into the synaptic cleft at the neuromuscular junction to trigger an action potential in the muscle fiber.

T-tubules

Extensions of the sarcolemma that conduct action potentials into the muscle fiber.

Sarcoplasmic Reticulum (SR)

Organelle that stores calcium ions and releases them during muscle contraction.

Calcium (Ca²⁺)

Ion that binds to troponin, causing tropomyosin to move and expose binding sites on actin.

Cross-bridge cycle

Process where myosin heads attach to actin, perform a power stroke, and detach, requiring ATP.

Rigor Mortis

Condition where muscles cannot relax due to lack of ATP, leading to sustained contraction.

Role of ATP in Contraction

ATP energizes myosin heads, detaches myosin from actin, and powers calcium pumps in the SR.

Creatine Phosphate

Immediate ATP resupply (short-term) with a yield of 1 ATP per CP.

Anaerobic Glycolysis

Short-term energy production without oxygen, yielding 2 ATP per glucose.

Aerobic Respiration

Long-term, efficient energy production with oxygen, yielding approximately 36 ATP per glucose.

H Zone

Shortens during muscle contraction.

I Band

Shortens during muscle contraction.

A Band

Stays the same during muscle contraction.

Z lines

Move closer together during muscle contraction.

Overall Sarcomere

Shortens during muscle contraction.

Slow Oxidative (Type I)

Muscle fiber type with slow speed of contraction, high resistance to fatigue, many mitochondria, rich blood supply, high myoglobin amount, small fiber diameter, red color, aerobic metabolism, and function in posture and endurance.

Fast Oxidative (Type IIa)

Muscle fiber type with fast speed of contraction, intermediate resistance to fatigue, many mitochondria, moderate blood supply, moderate myoglobin amount, intermediate fiber diameter, pink color, aerobic and anaerobic metabolism, and function in sprinting and walking.

Fast Glycolytic (Type IIb)

Muscle fiber type with fast speed of contraction, low resistance to fatigue, few mitochondria, low blood supply, low myoglobin amount, large fiber diameter, white color, anaerobic metabolism, and function in short bursts and powerlifting.

Skeletal Muscle

Striated, multinucleated muscle attached to bones.

Cardiac Muscle

Striated, branched muscle with 1-2 nuclei found in the heart wall.

Smooth Muscle (Single Unit)

Non-striated muscle with 1 nucleus, located in the walls of hollow organs.

Smooth Muscle (Multi Unit)

Non-striated muscle with 1 nucleus, found in the iris and arrector pili muscles.

Energy Production in Skeletal Muscle

Mainly aerobic.

Energy Production in Cardiac Muscle

Aerobic.

Energy Production in Smooth Muscle (Single Unit)

Aerobic.

Energy Production in Smooth Muscle (Multi Unit)

Aerobic.

Innervation of Skeletal Muscle

Somatic nervous system.

Innervation of Cardiac Muscle

Autonomic nervous system.

Innervation of Smooth Muscle (Single Unit)

Autonomic nervous system.

Innervation of Smooth Muscle (Multi Unit)

Autonomic nervous system.

Initiation of Contraction in Skeletal Muscle

Neuron (voluntary).

Initiation of Contraction in Cardiac Muscle

Pacemaker cells + nervous system.

Initiation of Contraction in Smooth Muscle (Single Unit)

Pacemaker cells + nervous system.

Initiation of Contraction in Smooth Muscle (Multi Unit)

Nervous stimulation.

Role of Calcium in Skeletal Muscle

Troponin binding.

Role of Calcium in Cardiac Muscle

Troponin binding.

Role of Calcium in Smooth Muscle (Single Unit)

Calmodulin binding.

Role of Calcium in Smooth Muscle (Multi Unit)

Calmodulin binding.

Presence of T-tubules in Skeletal Muscle

Yes.

Presence of T-tubules in Cardiac Muscle

Yes (larger).

Presence of T-tubules in Smooth Muscle (Single Unit)

No.

Presence of T-tubules in Smooth Muscle (Multi Unit)

No.

SR Development in Skeletal Muscle

Well-developed.

SR Development in Cardiac Muscle

Moderate.

SR Development in Smooth Muscle (Single Unit)

Poor.

SR Development in Smooth Muscle (Multi Unit)

Poor.

Source of Calcium in Skeletal Muscle

Sarcoplasmic reticulum.

Source of Calcium in Cardiac Muscle

Sarcoplasmic reticulum + extracellular.

Source of Calcium in Smooth Muscle (Single Unit)

Extracellular > sarcoplasmic reticulum.

Source of Calcium in Smooth Muscle (Multi Unit)

Extracellular > sarcoplasmic reticulum.

Calcium Mechanism in Skeletal Muscle

Troponin-tropomyosin system.

Calcium Mechanism in Cardiac Muscle

Troponin-tropomyosin system.

Calcium Mechanism in Smooth Muscle (Single Unit)

Calmodulin activates myosin light-chain kinase (MLCK).

Calcium Mechanism in Smooth Muscle (Multi Unit)

Same as single-unit.

Means of Grading Tension in Skeletal Muscle

Frequency of stimulation, number of motor units recruited.

Means of Grading Tension in Cardiac Muscle

Amount of Ca²⁺ influx, length-tension relationship.

Means of Grading Tension in Smooth Muscle (Single Unit)

Variable Ca²⁺ entry, gap junctions allow coordination.

Means of Grading Tension in Smooth Muscle (Multi Unit)

Recruitment of individual cells.