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BIOB34H3 Lecture Notes - Neuromuscular Junction, Endoplasmic Reticulum, Fascia

Biological Sciences
Course Code
Ted Petit

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Chapter 10 Muscle Tissue
Muscle Basics
- Three types (cells are long and thin, called fibers)
1. skeletal
a. striated
b. voluntary control
c. many nuclei per cell
d. longest fibers (extend the length of the whole muscle
2. cardiac
a. striated
b. involuntary control
c. one nucleus per cell
3. smooth
a. not striated
b. involuntary control
c. one nucleus per cell
- Functions
1. movement
a. of whole body or body parts (skeletal)
b. of substances within body (cardiac - pumps blood, smooth - substances move through
hollow organs)
2. heat production (mostly skeletal)
3. maintain posture and stabilize joints (skeletal)
- Characteristics
1. excitability - respond to stimuli like neurotransmitters (from neurons) or hormones with
electrical signals
2. contractility - ability to develop tension (muscle fiber may shorten)
3. extensibility - can stretch
4. elasticity assumes original length after stretching
Skeletal Muscle
- Associated Connective Tissue
1. superficial fascia (subcutaneous layer or hypodermis)
a. areolar & adipose
1) stores water and fat
2) decreases heat loss
3) protects underlying tissues
2. deep fascia
a. dense irregular
1) holds together functional groups of muscle
2) allows free movement of muscles
3) packs spaces between muscles, nerves and blood vessels pass through
3. less coarse CT layers
a. protect and support muscle cells, reinforce whole muscle, provide elasticity
1) epimysium - dense irregular CT, wraps whole muscle
2) perimysium - dense irregular CT, wraps bundles of fibers called fascicles
3) endomysium - similar to areolar CT, lots of reticular fibers, wraps each fiber
4. all the CT layers are continuous with one another and with the tendons that attach the muscle
to the periosteum of bone
a. tendons are dense regular CT
b. a flattened tendon is called an aponeurosis (may attach to bone, skin or another muscle)
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- Skeletal muscle cells
1. very large
a. 10 - 100 m in diameter, may be many cm long
2. plasma membrane called sarcolemma
3. cytoplasm called sarcoplasm
a. lots of glycogen (stored form of glucose) and myoglobin (a protein that binds O2)
b. contains the usual organelles plus some modified ones
4. myofibrils
a. specialized organelles that run the length of the cell (100s-1000s/cell)
b. made up of contractile units called sarcomeres
1) sarcomeres are made up of myofilaments
2) the arrangement of myofilaments causes the striations
c. myofilaments
1) thick filaments- made of the protein myosin, often called cross-bridges because they
can bind with the thin filaments
2) thin filaments- made of the proteins actin (where myosin binds), tropomyosin and
5. sarcoplasmic reticulum
a. specialized smooth ER that stores calcium and releases it when signaled by a nerve
impulse (an electrical signal from a neuron)
6. T tubules
a. the sarcolemma penetrates into deeper parts of the cell, forming hollow tubes
surrounding all the myofibrils
b. conducts electrical signals throughout the cell so all myofibrils contract at once
7. Sliding Filament Theory
a. when a nerve impulse signals the muscle cell, calcium is released from the SR
b. this allows myosin to bind to actin and pull the thin filaments toward the center of the
c. ATP required
- Blood supply
1. lots of blood needed to supply oxygen and carry away wastes from these very active cells
2. vessels penetrate CT layers, lot of capillaries in endomysium
- Nerve supply (see Chapter 14)
1. each muscle served by at least one motor nerve containing 100s of motor neurons
a. a motor unit is one motor neuron plus all the muscle fibers it innervates
b. a motor unit may have only a few muscle fibers or 1000+
c. fewer muscle fibers per motor unit where fine, delicate control needed (eyes, fingers)
d. more muscle fibers per motor unit where more power needed (limbs)
e. activating more motor units at one time means a more powerful contraction
2. neuromuscular junction
a. area where a neuron meets a muscle fiber
b. separated by a gap called synaptic cleft
c. when an electrical signal (action potential) travels to the end of a neuron, the neuron
releases a chemical message called a neurotransmitter (specifically, acetylcholine at the
neuromuscular junction, also known as ACh)
d. the ACh binds to the muscle cell, and initiates an electrical signal (action potential) there
e. this ultimately results in the muscle fiber contracting
- Muscle tone
1. small groups of motor units are periodically activated involuntarily
2. this keeps the muscle ready to contract
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