Module 5

Types of Muscle Tissue

Skeletal, Cardiac, and Smooth.

Differentiations of Muscle tissue.

Excitability, Contractility, Extensibility, and Elasticity.

• Microscopic organization of Actin and Myosin (Striations).

  • Regular

  • Irregular

Regular Muscle Tissue

Has striations.

Ex. Cardiac and Skeletal

Irregular Muscle Tissue

Non-striated.

Ex. Smooth

Excitability

Responds to stimuli

• Also called responsiveness or irritability.

Ex. Polarized to Depolarized.

Contractility

Shortens when stimulated.

Extensibility

Stretches.

Elasticity

Recoils to a resting length.

Skeletal Muscle Tissue.

Attached to bones to produce movement.

• One cell of skeletal muscle = One muscle fiber.

  • Cell shape is long and cylindrical.

• Multinucleated.

• Voluntary control.

  • Diaphragm switches between voluntary and involuntary.

• Produce heat when they contract.

  • Body temp rises, helps maintain body temp homeostasis.

• Become fatigued after contraction.

  • Recovery time needed.

• Formed during early development.

Cardiac Muscle Tissue.

Pump blood.

• Cells only in the heart.

  • Cell shape is cylindrical, branched.

• One nucleus per cell.

• Cells connected by intercalated discs.

  • Syncytium.

• Involuntary.

  • Pacemakers.

• Does not fatigue.

  • Must continuously pump blood throughout the body.

Intercalated discs

Allow muscle fibers to be connected to each other.

Syncytium

When the entire heart contracts as one unit.

Smooth Muscle Tissue

Move substances, alters internal volume.

• Cell shape is spindle.

  • One nucleus

• No striations.

• Involuntary contractions.

  • Multiple sources cause contractions → Neurotransmitters, Local chemicals, Mechanical stretching, and Hormones.

• In hollow or tube-like structures.

• Does not fatigue.

Action potential

An electrical wave sen along the entire length of the membrane.

Functions of Skeletal Muscle Tissue

Produce movement

• Holds joints in place.

  • Prevent excess movement and skeletal damage

• Sphincters.

• Protect internal organs.

  • Barrier

  • Supports weight of internal organs (pelvic floor muscles).

• Maintain body temp homeostasis.

  • Generate heat with contractions.

  • Heat is produced when ATP is broken down.

  • Noticeable during exercise

  • Shivering

• Nutrients stores.

  • If the body does not have enough calories, proteins in skeletal muscle can be broken down and used for energy.

Spinhcters

Openings of internal tracts

• Allow voluntary control over surrounding, urinations, and defection.

Shivering

Mechanism in cold to generate heat by muscle contractions.

Structures of Skeletal Muscle Tissue

Epimysium, Perimysium, Endomysium, Sarcolemma, Sarcoplasm.

Epimysium

Wrapped around each skeletal muscle.

• Dense, Irregular connective tissue.

• Dense, Irregular connective tissue.

• Connected to the deep fascia.

• Allows for muscle to be contracted and maintain structure.

• Separates muscle from other tissues.

Perimysium

Surrounds groups of muscle fibers grouped together in bundles.

• Also known as Fascicles.

Contain:

• Collagen fibers.

• Elastic fibers.

• Blood vessels.

• Nerves.

Endomysium

Surround each muscle fiber

Contain:

• Capillary networks.

• Extracellular fluid.

• Myosatellite cells.

• Nerve fibers.

Sarcolemma

Muscle cell membrane, encloses the muscle cells.

Sarcoplasm

Muscle cell cytoplasm.

Skeletal Muscle Attachments

At the end of the muscle is a fusion of the three layers + collagen.

• Form a tendon or Aponeurosis

• Other end fuses with periosteum of the bone

  • This helps produce movement.

Aponeurosis

A broad sheet.

Blood and Nerve Supply of Skeletal Muscle

Have extensive blood and nerve supply.

• Blood vessels and nerves follow same pathways.

• Capillary networks supply the Endomysium which then supply each muscle cell.

  • Contributions are direct signals from the nervous system.

  • Each made fiber is innervated by an axon of motor neuron.

Organs

Consists of various integrated tissue.

Tendon

Forms in a bundle.

Myoblasts

Early embryonic cells.

• Fuse with hundreds of other myoblasts.

  • Form multinucleated cells with hundred of nuclei.

• Each has their own nucleus.

Myosatellite cells

Can divide to replace damaged muscle fibers.

• When some myoblasts remain during development and do not fuse.

Transerve Tubules (t-tubules)

Branching network of the sarcolemma.

• Extend from the surface deep into the sarcolemma.

• Ensure the Action Potential reaches all parts of the cell.

  • Cause a muscle contraction.

Myofibril

Division of a muscle fiber.

• Smaller, organized cylindrical portion of a muscle fiber.

• Surrounded by bunches of (t-tubules).

Myofilaments

Division of a myofibril.

• Thick and thin protein filaments.

Thick Myofilaments

Mostly myosin.

Thin Myofilaments

Mostly actin.

Sarcoplasmic Reticulum (SR)

Specialized smooth endoplasmic reticulum.

• Surrounds each Myofibril.

• Stores, releases, retrieves calcium ions.

Terminal Cisternae

Enlarged, Specialized chambers of the SR.

• Attach to the t-tubules.

• Calcium ions actively transported to the terminal cisternae.

Triad

Arrangement of t-tubule with terminal cisternae on each side.

• Surrounds cylindrical myofibril.

Mitochondria and Glycogen Granules

Many scattered throughout and around myofibrils in the sarcoplasm.

• Glycogen = Storage form of glucose.

  • Breaks down to provide ATP and energy for muscular contraction.

  • Large amounts of ATP needed!

Calcium Ions

Responsible for initiating cellular processes.

• All cells in the body pump calcium out of the cell into the extracellular fluid.

  • Intracellular concentration of Ca2+ is kept low.

• Is removed from sarcoplasm.

• Pumped inside the terminal cisternae of the sarcoplasmic reticulum.

• Calsequestrin.

Calsequestrin

Special calcium-binding protein inside the sarcoplasmic reticulum.

• Binds to Ca2+ and releases it when needed.

• Allows the SR in muscle cells to hold 6000x concentrations of calcium higher than the sarcoplasm.