Muscular System

6 Functions of Skeletal Muscles

Moves bones

Posture

Support soft tissue

Sphincter protection

Heat

Store nutrients

Nutrients

Glycogen and proteins

4 Components

Muscle tissue

Connective tissue

Nerves

Blood vessels

Muscles Organs

They contain multiple tissue types (muscle, connective, nervous, vascular)

Nerves

Control voluntary muscle contraction

Control System

CNS

Extensive Blood Supply

Delivers oxygen

Deliver nutrients

Remove waste products

Oxygen

Needed for ATP production

3 Connective Tissue Layers

Endomysium

Perimysium

Epimysium

Smallest → Largest

Endomysium → Perimysium → Epimysium

Endomysium

Surrounds individual muscle fibers

Inside Endomysium

Capillaries

Nerve fibers

Myosatellite cells

Myosatellite Cells

Stem cells that repair muscle damage

Endomysium Importance

Supports and nourishes each muscle fiber

Perimysium

Surrounds fascicles

Inside Perimysium

Blood vessels and nerves supplying fascicle

Fascicle

Perimysium

Bundle of muscle fibers

Epimysium

Surrounds entire muscle

Epimysium Connects to

Deep fascia

Epimysium Function

Separates muscle from surrounding tissue

Muscle Ends

Endomysium, perimysium, and epimysium merge together

Attachment to Bone

Occurs when connective tissue merges

Tendon

Rope-like bundle

Aponeurosis

Flat sheet

Muscle Fiber Structure

Muscle fiber → Fascicle → Whole muscle

Muscle Fiber

Endomysium

Whole Muscle

Epimysium

Connective Tissue Importance

Provides structure

Carries blood vessels/nerves

Forms attachments to bone

Transverse Tubules

Transmit action potential through cell

Allow entire muscle fiber to contract simultaneously

Have same properties as sarcolemma

Sarcoplasmic Reticulum

Membranous structure surrounding each myofibril

Helps transmit action potential to myofibril

Similar in structure to smooth ER

Forms chambers (terminal cisternae) attached to T tubules

CIsternae

Concentrate Ca²⁺ via ion pumps

Release Ca²⁺ into sarcomeres to begin muscle contraction

Triad

Triad

Formed by 1 T tubule and 2 terminal cisternae

Myofibrils

Lengthwise subdivisions within muscle fiber

Made up of protein filaments

Myofilaments

Responsible for muscle contraction

Thin Filaments

Made of actin

Thick Filaments

Made of myosin

Sarcomeres

Contractile units of muscle

Structural units of myofibrils

M Line

Center of A band

At midline of sarcomere

H Zone

Area around M line

Has thick filaments but no thin filaments

Zone of Overlap

Densest, darkest area on a light micrograph

Where thick and thin filaments overlap

I Band

Z lines

Titin

A Band

M line

H Zone

Zone of overlap

Z Lines

Centers of I bands

At 2 ends of sarcomere

Titin

Strands of protein

Stabilize filaments

Sarcomere Function

T Tubules encircle sarcomere near zones of overlap

Ca²⁺ released by SR causes thin and thick filaments to interact

4 Thin Filament Proteins

F actin

Nebulin

Tropomyosin

Troponin

F actin

2 twisted rows of globular G actin

Active sites on G actin strands bind to myosin

Nebulin

Holds F actin strands together

Tropomyosin

Double strand

Prevents actin-myosin ineraction

Troponin

Globular protein with 3 subunits

Binds tropomyosin to G actin

Controlled by Ca²⁺

Action Potential Travels

Across sarcolemma

Action Potential Enters

Through T tubules until it reaches triad

Action Potential in Triad

Binds to troponin → change shape

Change in shape

Moves to tropomyosin

Moves to Tropomyosin

Myosin binds to actin