11. Muscular System + Flashcards
1
Q
Skeletal muscle consists of numerous muscle cell called muscle fiber. Distinguishing characteristics:
A
- Sarcolemma (plasma membrane). Highly invaginated by transverse tubules (T tubules) that permeate the cell.
- Sarcoplasm (cytoplasm). Contain calcium-storing sarcoplasmic reticulum, specizlied endoplasmic reticulum of a muscle cell.
- Skeletal muscle cells are multinucleate. The nuclei lie along the periphery of the cell, forming swelling visible through the sarcolemma.
- Entire volume of muscle cell is filled with numerous, long myofibrils. Myofibrils consist of two types of filaments —> 1. Thin filaments: two strands of globular protein actin arranged in a double helix, along length of helix are troponin and tropomyosin molecules that cover special binding sites on actin; 2. Thick filaments: groups of filamentous protein myosin, array of myosin filaments possesses protruding heads at numerous positions at both ends.
2
Q
Sarcomere
A
- each repeating unit within a myofibril
- from z-line to z-line
- actin attached to z-line. myosin located between actin, unattached to z-lines.
3
Q
Sliding Filament Model of Muscle Contraction
A
- ATP binds myosin head –> ADP + Pi. Remain attached to myosin head.
- Ca+2 binds troponin —> tropomyosin exposes myosin head attachment on actin filament
- When attachment sites on actin are exposed –> myosin heads bind to actin to form cross bridges.
- Attachment of myosin to actin —> release of ADP and Pi —> change in shape of myosin head —-> sliding movement pulling actin to center of sarcomere —> z-lines pulled together contracting the muscle fiber.
- When a new ATP molecule attaches to myosin head, cross bridge between myosin head and actin breaks returning myosin head to its unattached position.
*** without addition of a new ATP, cross bridges remain attached to actin —> reason corpses are stiff (new ATP unavailable)
4
Q
Neurons form specialized synapses with muscles called…
A
Neuromuscular junctions
5
Q
Muscle contraction is STIMULATED through the following steps:
A
- When action potential of a neuron reaches neuromuscular junction —> neuron secretes neurotransmitter acetylcholine, which diffuses across synaptic cleft
- Receptors on sarcolemma initiate a depolarization event and action potential –> action potential travels along sarcolemma throughout the transverse system of tubules.
- —-> sarcoplasmic reticulum releases Ca+2
- —> myosin cross bridges form. {Ca+ from sarcoplasmic reticulum binds troponin (on actin), causing tropomyosin to expose myosin binding sites -> if ATP is available, muscle contraction begins.}
6
Q
Human and other vertebrates have three kinds of muscles:
A
- Skeletal muscle. Attached to bones. Causes movement of body.
- Smooth muscle. Lines walls of blood vessel and digestive tract. No striated appearance due to its arrangement of actin and mysoin. Sarcolemma doesn’t form system of T-tubules –> contraction is controlled and slow.
- Cardiac muscle. Rhythmic contractions of heart. Striated. Differ from skeletal muscle in that it is highly branched w/ cells connected by gap junctions. In addition, cardiac muscle generates its own action potential which spreads rapidly by electrical synapses across gap junction.
7
Q
Organization of Vertebrate Skeleton:
A
- Axial skeleton: basic framework (skull, vertebral column, rib cage)
- Appendicular skeleton: bones of appendages, pectoral and pelvic girdles.
- Bone organization:
a. sutures - immovable joints (holds bones of skull)
b. Moveable joints - bones that move relative to each other. 1. Ligament (bone to bone) 2. Tendon (muscle to bone) - Origin: point of attachment of muscle to stationary bone.
- Insertion: point of attachment of muscle to bone that moves
- Extension: straightening of joint
- Flexion: bending of joint
8
Q
Joint Types
A
- Fibrous - connect bones w/o allowing movement (ex. skull, pelvis, spinous process and vertebrae)
- Cartilaginous: bones attached by cartilage. allow little movement. ex. spine and ribs
- Synovial - allow for much more movement. Most common type. Filled w/ synovial fluid as a lubricant. ex. carpals, wrist, elbow, humerus and ulna, shoulder and hip joints, knee joint.
9
Q
Myofibrils are filament divided into…
A
Sarcomeres
10
Q
Individual contractile units
A
Sarcomere
11
Q
Wraps several myofibrils together to form a muscle cell/muscle fiber?
A
Sarcolemma (plasma membrane)
12
Q
Present in large amount in myofibrils?
A
Mitochondria
13
Q
Sarcomere Features:
A
- composed of thin (actin) and thick (myosin) filaments
- z-line: boundary of a single sarcomere. anchor actin
- M-line: center of sarcomere
- I band: region of actin only
- H zone: region containing myosin only
- A band: overlapping of actin and myosin
** H and I reduce during contraction, while A does not
14
Q
All or nothing!
A
- Strength of contraction of single muscle fiber cannot be increased, but strength of overall contraction can be increased by recruiting more muscle fibers.
15
Q
Type of Muscle Response
A
- Simple Twitch - response of single muscle fiber to a brief stimulus; latent, contraction, relax
a. latent period - time btw stimulation and onset of contraction. Action potential spreads on sarcolemma and Ca+ ions released
a. Contraction
c. Relaxation (absolute refractory period) - unresponsive to stimulus - Summation and Tetanus -
a. Summation: contractions combine and become stronger and more prolonged (repeated AP)
b. Tetanus: continues sustained contraction; muscle can’t relax. - Tonus - state of partial contraction; muscle never completely relaxed.
