IHS Chapter 9

Ability of muscle to shorten forcefully

Contractility

The capacity of muscle to respond to an electrical stimulus.

Excitability

A muscle can be stretched beyond its normal resting length and still be able to contract.

Extensibility

Ability of muscle to spring back to its original resting length after it has been stretched.

Elasticity

Major functions of all 3 types of muscle:

1. Movement of the body

2. Maintenance of posture

3. Respiration

Supports the muscle during contraction

Connective Tissue

Forms a connective tissue sheath that surrounds each skeletal muscle.

Epimysium

The layer of connective tissue between adjacent muscles and between muscles and skin.

Muscular fascia

A loose connective tissue serving as passageways for blood vessels and nerves that supply each fascicle.

Perimysium

A delicate layer of connective tissue that separates the individual muscles and between fibers within each fascicle.

Endomysium

The specialized nerve cells responsible for stimulating skeletal muscle contraction

Motor neurons

Develop from the fusion of several hundred embryonic cells and contain its own nucleus

Myoblasts

True or False:

The number of skeletal muscle fibers is not relatively constant after birth

False

• It remains constant

The plasma membrane of muscle fibers

Sarcolemma

Carry electrical impulses into the center of the muscle fibers

Transverse tubules / T tubules

Highly specialized smooth endoplasmic reticulum in skeletal muscle fibers that stores high levels of Ca2+

Sarcoplasmic reticulum

Enlarged portions of the sarcoplasmic reticulum.

Terminal cisternae

Two terminal cisternae and their associated T tubule form a critical structure for muscle contraction.

Triad

These organelles constitute the cytoplasm in muscle fibers.

Sarcoplasm

Long threadlike structures extending the entire length of the muscle.

Myofibrils

Provides the mechanical aspect of muscle contraction.

Myofilaments

2 types of myofilaments

Actin and Myosin

Smallest portion of a muscle that can contract and is the basic unit of the muscle fiber.

Sacromeres

Filamentous networks of proteins called?

Z disks

Contains only actin myofilaments and thus appear lighter staining.

I band

Darker staining band in the center of each sacromere is called?

A band

Contains only myosin myofilaments.

H zone

Consists of delicate filaments that hold myosin myofilaments in place.

M line

Gives muscle the ability to stretch and recoil.

Titin

Globular subunits that form a long chain of about 200 subunits

G actin

200 G actins forms into strand called?

Fibrous (F) actin

A long fibrous proteins that lies in the groove along the fibrous actin strand.

Tropomyosin

Actin myofilament slide past to the myosin myofilament until the _ ____ is lost

H zone

A single motor neuron and all the skeletal muscle fibers it inner ates constitute a motor unit

Neuromuscular Junction

Carries electrical signals

Action potentials

Each axon terminal is called the?

Presynaptic terminal

The space between the presynaptic terminal and the muscle fiber is the?

Synaptic cleft

The plasma membrane in the area of the junction is called?

Motor end plate

Each presynaptic terminal contains numerous mitochondria and many small spherical sacs called?

Synaptic vesicles

A molecule that allows a neuron to communicate with its target.

Neurotransmitter

True or False:

Muscle fibers, like other cells of the body, are not electrically excitable.

False

• It is electrically excitable

True or False:

Action potentials travel from brain or heart along the axons to muscle fibers and cause them to contract.

False

• It travels from brain or spinal cord.

The cell is more like a sprinter in starting blocks; it is ready to respond at a moments notice.

Resting membrane potential

True or False:

Action potential occurs when the excitable cell is stimulated.

True

When the inside of the plasma membrane becomes more positive.

Depolarization

The return of the membrane potential to its resting value.

Repolarization

Action potentials occur in one area of the plasma membrane and then travel, or ______, along the plasma membrane.

Propagate

A stronger stimulus causes more action potentials to be sent.

Action potential frequency

Rapid sequence of events will cause the sarcomeres to shorten and the muscle will contract.

Cross-bridge movement

When Ca2+ binds to troponin it moves the tropomyosin exposing the active sites.

Exposure of active sites

Myosin head moves using the stored energy (ADP) which causes the actin myofilament to slide past the myosin myofilament

Power stroke

ATP molecule binds to myosin head causing it to detach from the active site

Cross-bridge release

ATP is split into ADP and P

Hydrolysis of ATP

Myosin head return to its resting position

Recovery stroke

Occurs when acetylcholine is no longer released at the neuromuscular junction.

Muscle relaxation.

The response of a muscle fiber to a single action potential along its motor neuron.

Muscle twitch

The beginning of contraction.

Lag phase

Commences once Ca2+ is released from the sarcoplasmic reticulum and cross-bridge cycling occurs

Contraction phase

Concentration of Ca2+ in the sarcoplasm decreases slowly due to active transport into the sarcoplasmic reticulum.

Relaxation phase

Type of contraction increases the tension in the muscle, but the length of the muscle stays the same.

Isometric contractions

Type of contraction increases the tension in the muscle and the length of the muscle decreases.

Isotonic contractions

True or false:

The amount of force generated in a single muscle fiber depends on the number of cross bridges formed.

True

The muscle fiber will contract with greater force with each successive stimulus.

Treppe

An increase in stimulus frequency increases the overall force of contraction.

Summation

A sustained contraction that occurs when the frequency stimulation is so rapid that no relaxation occurs.

Tetanus

The nervous system regulates muscle force by increasing the number of contracting motor units.

Recruitment

Responsible for keeping the back and lower limbs straight, the head upright, and the abdomen flat.

Muscle tone

Transfers one phosphate from one ADP to a second ADP, resulting in one ATP and one AMP.

Adenylate kinase

Does not require O2 and invloves breakdown of glucose to produce ATP and lactate.

Anaerobic respiration