1. Properties of Muscle Tissue
Excitability: respond to stimuli
Conductivity: propagate signals over membrane
Contractility: shorten and generate force
Extensibility: stretch without damage
Elasticity: return to their original length after being shortened or stretched

2. Functions of Muscular Tissue
Body Movements
Walking and running
Stabilize Body Positions
Posture
Support Soft Tissue
Move Substances Within the Body
Blood (cardiac m.)
Digestive tract (smooth m.; sphincters and oropharynx skeletal m.)
Generate heat
Shivering: contraction of muscle produces heat (ATP)

3. Organization of Muscle
Epimysium
The outermost layer
Separates muscle fibers into bundles called fascicles
Perimysium
Surrounds numerous bundles of fascicles
Endomysium
Separates individual muscle fibers (cells) from one another
Epi-, Peri-, Endomysium converge into tendon
CT that attaches a muscle to periosteum of bone
Aponeurosis = Broad, flattened tendon

4. Functional Organization
Muscle
Fascicle
Myofiber
Myofibril
Sarcomere
Myofilaments
Speak to the myofilaments and structure of the sarcomere here.
When skeletal muscles are viewed under a microscope, they have distinct bands called striations
They are formed by the arrangement of myofibrils within the muscle cell
Each myofibril contains groups of long myofilaments
Each myofilament is composed of myosin and actin filaments

5. 5

6. Sarcomere From Z to Z is a functional unit: the sarcomere
This is looking at one myofibril in the myofiber. It is misleading in that there are several myofibrils in each myofiber and the Z line is actually a disc. The M line indicates areas of protein filaments that join the thick myosin filaments together. The titan filaments are large, elastic proteins that run through the myosin filaments,beginning at the M lines and ending at the Z discs. Their function is to stabilize myosin during contraction and help return the myofiber to its resting length after contraction.
Realize that there are numerous sarcomeres in a myofibril, and many myofibrils in one myofiber.

7. Motor Neuron Motor neuron
How do we get the sarcomere to contract? Motor neurons.
Neuromuscular
junction
Skeletal
muscle cells
Motor unit

8. Neuromuscular Junction (Motor End Plate)
Each myofiber receives a single axon terminal
Neuromuscular junction (a.k.a. motor end plate)
Specialized region of sarcolemma
Neurotransmitter: Acetylcholine
Each somatic neuron can branch. These branches innervate the myofibers at specialized areas called motor end plates. When acetylcholine is released at this site, the muscle fiber (the post-synaptic cell) undergoes membrane depolarization and a change in permeability (muscle cells, like neurons, are "excitable cells"). The result is a change in electrical charge on the plasma membrane that spreads to cover the entire surface. This in turn results in the release of calcium ions from the myofiber's sarcoplasmic reticulum, triggering the "ratcheting" of actin and myosin filaments past each other, and the overall shortening of that specific myofiber. This is called "excitation-contraction coupling". Note carefully that as with neurons, depolarization and the subsequent contraction it induces is an all or nothing response; when depolarization takes place, all the myofibrils inside that myofiber contract simultaneously and maximally.

9. SR and T Tubules: Excitation Contraction Coupling
Sarcoplasmic reticulum (SR)
Terminal cisternae
Ca2+ is normally sequestered in the SR; released by stimulation from the motor end plate transferred from
T Tubules
Indentations of sarcolemma to transfer depolarization from motor end plate
Triads

10. Nerve and Blood Supply Nerves Blood Supply
Neurons stimulate skeletal muscle to contract
Neuromuscular junction
The axon of a somatic motor neuron typically branches many times
Each branch extends to a different skeletal muscle fiber
Blood Supply
Each muscle fiber is in close contact with one or more capillaries

11. Organization of Muscle Fibers
Power, range of movement, and speed of contraction all vary with the arrangement of fascicles in a muscle
Four different arrangements
Parallel
Convergent
Pennate
Circular
Parallel: fascicles are parallel to the long axis of the muscle (most of the muscles in the body are of this type). Muscle acts like individual muscle fiber: As muscle contracts, body increases in diameter. Decrease in length is dramatic, but power is not as strong as some following.
Convergent muscles: come together at a single attachment. Direction of pull can be changed, but if the entire muscle is contracted the power is not as great since some fibers will be in opposition to eachother.
Pennate: fascicles are oblique to tendon: powerful, but decrease in ability to shorten length. Unipennate (extensor digitorum) vs. bipennate (powerful: rectus femoris) vs. multipennate (really powerful: deltoid).
Circular: sphincters, fibers arranged concentrically around orifice.

12. Actions of Muscles Review movement of joints Prime mover (agonist)
Contraction of the muscle is the main reason for producing a movement
Synergist
Assists prime mover
Antagonist
Act in opposition to the prime mover
Fixator
Immobilize origin of prime mover

13. Muscle Nomenclature
Directions: Rectus (straight), Transversus (across), Oblique (at an angle)
Number of heads: Biceps (2 origins), Triceps (3 origins), Quadriceps (4 origins)
Shapes: trapezoid, deltoid, rhomboid, orbicular
Length: Longus or longissimus (long), teres (long and round), brevis (short)
Size: magnus (big), major (bigger), maximus (biggest), minor (smaller), minimus (smallest)
Externus (superficialis) vs. Internus (profundus)
Extrinsic (outside) vs. Intrinsic (inside)
Origins and insertions (first name is origin, second insertion)
Primary function: flexor, extensor, retractor
Don’t spend a lot of time here…they should already be familiar. Just remind them…
Trapezoid: (trapezius); deltoid (triangle), orbicular (circle)