Skeletal Muscle Tissue- Ch 9 Part 1

17. Sarcolemma

Beneath each skeletal muscle fiber is the sarcolemma or plasma membrane

14. Neuromuscular junction

Each axon ending gives off several short, curling branches that collectively form an elliptical neuromuscular junction, or end plate, with a single muscle fiber. * Each muscle fiber has only one neuromuscular junction, located approximately midway along its length

5. Axon terminal

The axon ending of motor neuron *The process begins when the nerve impulse reaches the axon terminal and opens voltage-gated calcium channels in the axonal membrane

7. Epimysium

The epimysium is an overcoat of dense irregular connective tissue that surrounds the whole muscle. * Sometimes it blends with the deep fascia that lies between neighboring muscles or the superficial fascia deep to the skin

16. Perimysium

The perimysium is a layer of fibrous connective tissue that surrounds each fascicles.

18. Sacromere

The region of a myofibril between two successive Z discs * It contains an A band flanked by half an I band at each end *a sarcomere is the smallest contractile unit of a muscle fiber

21. Sliding filament model of contraction

The sliding filament model of contraction states that during contraction states that during contraction the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree *When the nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch onto myosin- binding sites on acting in the thin filaments, and the sliding begins

2. Actin

The thin filaments are composed chiefly of the protein actin. *Actin has kidney-shaped polypeptide subunits, called globular actin *In the thin filaments, G actin subunits are polymerized into long actin filaments called filamentous

4. Axon

These motor neurons reside in the brain or spinal cord, but their long threadlike extensions called axons travel, bundled within nerves, to the muscle cells they serve. *The axon of each motor neuron divides profusely as it enters the muscle *each axon ending gives off several short, curling branches that collectively form an elliptical end plate.

13. Myosin

Thick filaments are composed primarily of the protein myosin. * Each myosin molecule consists of two heavy and four light polypeptide chains and has a rod like tail attached by a flexible hinge to two globular heads. *The globular heads, each associated with two light chains, are the "business end" of myosin

1. Acetylcholine

A neurotransmitter found in small membranous sacs, synaptic vesicles , within the mound-like axon terminal * The trough-like part of the muscle fiber's sarcolemma that helps form the neuromuscular unction is highly folded * These junctional folds provide a large surface area for the millions of ACh receptors located there.

25. Striations

A repeating series of dark and light bands * the dark A bands and light I bands are nearly perfectly aligned, giving the cell its striated appearance *They are evident along the length of each myofibril

10. Myofibril

A single muscle fiber contains hundreds to thousands of rod-like myofibrils that run parallel to its length. * The myofibrils, each 1-2 um in diameter, are so densely packed in the fiber that mitochondria and other organelles appear to be squeezed between them. *Myofibrils contain the contractile elements of skeletal muscle cells called sarcomeres.

22. Synaptic cleft

A space filled with a gel-like extracellular substance rich in glycoproteins and collagen fibers *Axon terminals remain separated by the synaptic cleft

6. Endomysium

A wispy sheath of connective tissue that surrounds each individual muscle fiber. * It consists of fine areolar connective tissue

26. Tropomyosin

Tropomyosin is a rod-shaped protein *They spiral about the actin core and help stiffen and stabalize it. *Successive tropomyosin molecules are arranged end to end along the actin filaments, and in a relaxed muscle fiber, they block myosin-binding sites on actin so the myosin heads on the thick filaments cannot bind to the thin filaments

24. Origin

When a muscle contacts, the movable bone, the muscle's insertion, moves toward the immovable or less movable bone, the muscles's origin * In the muscles of the limbs, the origin typically lies proximal to the insertion

23. Insertion

When a muscle contacts, the movable bone, the muscle's insertion, moves toward the immovable or less movable bone, the muscles's origin *Muscle attachments, whether origin or insertion, may be direct or indirect

8. Fascicle

Within each skeletal muscle, the muscle fibers are grouped into fascicles that resemble bundles of sticks. * Surrounding each fascicle is a layer of fibrous connective tissue called perimysium.

9. Motor unit

a motor unit consists of one motor neuron and all the muscle fibers it innervates. * When a motor neuron fires all the muscle fibers it innervates contracts *the number of muscle fibers per motor unit may be as high as several hundred or as few as four

12. Myoglobin

a red pigment that stores oxygen. * Myoglobin is similar to hemoglobin, the pigment that transports oxygen in blood

3. Action potential

Action potential is an electrical current *the action potential is automatically propagated along the sarcolomma *Intracellular calcium ion levels must rise briefly, providing the final trigger for contraction

20. Sarcoplasmic reticulum

An elaborate smooth endoplasmic reticulum. * Its interconnecting tubules surround each myofibril the way the sleeve of a loosely crocheted sweater surrounds your arm *Most SR tubules run longitudinally along the myofibril, communicating with each other at the H zone

28. T tubule (Transverse tubule)

At each A band- I band junction, the sarcolemma of the muscle cell protrudes deep into the cell interior, forming an elongated tube called the T tubule *The T tubules tremendously increase the muscle fiber's surface area *Each T tubule runs between the paired terminal cisterns of the SR, forming triads, successive groupings of the three membranous structures

19. Sarcoplasm

the cytoplasm of a muscle cell * Similar to cytoplasm in other cells, but it contains unusually large amounts of glycosomes *

11. Myofilaments (filaments)

the muscle equivalents of the actin- or myosin-containing microfilaments. *examining the banding pattern of a myofibril at the molecular level, shows that it arises from orderly arrangement of even smaller structures within the sarcomeres

27. Troponin

the other major protein in thin filaments, is a globular three-polypeptide complex *One of its polypeptides (TnI) is an inhibitory subunit that binds to actin. *Both tropopin and tropomyosin help control the myosin-actin interactions involved in contraction

15. Neurotransmitter

when the impulse reaches the axon terminals, it causes neurotransmitters- signaling chemicals usually stored in vesicles- to be released into the extracellular space. * The neurotransmitters either excite or inhibit neurons with which the axon is in close contact *Because each neuron both receives signals from and sens signals to scores of other neurons, it carries on vonversations with many different neurons at the same time.