Chapter 10: Muscular System (Gross Anatomy)/Chapter 9: Muscular System (Histology and Physiology)

Tendons

attach muscle to bone

Aponeurosis

A broad, flat tendon

Origin/head of a muscle

muscle end attached to the more stationary spot

Insertion of a muscle

muscle end attached to the bone that moves when the muscle contracts

Belly of a muscle

the largest portion, between the origin and insertion

Agonist

muscle that causes an action

Antagonist

muscle that acts in opposition to agonist

When you are doing the flexion motion of a biceps curl, what muscle is the agonist? What muscle is the antagonist?

Biceps are the agonist, triceps are the antagonist

Synergists

muscles that work together

Examples of synergists muscles

biceps brachii & brachialis = elbow flexion

Quadrangular muscle shape

Rhomboidal muscle shape

Fusiform muscle shape

Trapezium muscle shape

Triangular muscle shape

Digastric muscle shape

Bicipital muscle shape

Muscles are named according to: (7 things) LSSOONF

1. Location: pectoralis, gluteus, brachial.
2. Size: maximus, minimus, longus, brevis.
3. Shape: deltoid, quadratus, teres.
4. Orientation: rectus.
5. Origin and insertion: sternocleidomastoid, brachioradialis.
6. Number of heads: biceps, triceps.
7. Function: abductor, adductor, masseter (chewer).

Muscular system functions (7 things)

1. Body movement.
2. Maintenance of posture.
3. Respiration.
4. Production of body heat.
5. Communication.
6. Constriction of organs and vessels.
7. Heartbeat.

Contractility

muscle shortens with force

Excitability

respond to a stimulus

Extensibility

muscle can be stretched beyond its normal resting length and still contract

Elasticity

recoil to original resting length after stretched

Comparison of skeletal, smooth, and cardiac muscle

Each skeletal muscle =

a complete organ

Muscle cells are associated with

connective tissue, blood vessels, & nerves

Skeletal muscle fibers develop from

myoblasts

Number of skeletal muscle fibers are

"constant" from birth.

Which of these is not a major functional characteristic of muscle?
A. Contractility
B. Elasticity
C. Excitability
D. Secretability

D. Secretability

Which of these is true of skeletal muscle?
A. Spindle-shaped cells.
B. Under involuntary control.
C. Forms the walls of hollow organs.
D. Many peripherally located nuclei per muscle cell.

D. Many peripherally located nuclei per muscle cell.

What is a group of muscle fibers called?

a fasciculus

4 layers of connective tissues coverings of skeletal muscle (SEPE)

Starts with the muscle fiber, then goes:
1. Sarcolemma
2. Endomysium
3. Perimysium
4. Epimysium

Sarcolemma

surrounds the muscle cell (example: plasma membrane of muscle fiber)

Endomysium

Also around muscle cell

Perimysium

Denser C.T. surrounding fasciculus

Epimysium

C.T. that surrounds the muscle (many fasciculi make up muscle)

Fascia

connective tissue sheet in muscles that is continuous with tendons and periosteum

Functions of fascia (4 things)

1. Forms layer under the skin.
2. Holds muscles together - separates them into functional groups.
3. Allows free movements of muscles
4. Carries nerves (motor neurons, sensory neurons), blood vessels, and lymphatics

Motor neurons

stimulate muscle fibers to contract

Structure of motor neurons

Neuron cell bodies are in brain/spinal cord, then branched axons attach to skeletal muscle fibers

Each muscle fiber is

innervated

Muscle fiber anatomy

Nuclei is inside sarcolemma, and the muscle cell is packed with myofibrils within the sarcoplasm

Sarcoplasm

muscle cell cytoplasm

Myofibrils

groups of myofilaments

2 types of myofibrils in a muscle fiber

1. Actin myofilaments
2. Myosin myofilaments

Actin myofilaments

THIN threadlike, protein threads (letter R in picture)

Myosin myofilaments

THICK threadlike, protein threads

Sarcomeres (Z disk to Z disk)

basic structural & functional repeating unit of skeletal muscle (because it is the smallest portion of skeletal muscle capable of contracting) that is the attachment site for actin myofilaments

Z disk

F actin

a fibrous protein made of a long chain of G actin molecules strung together and twisted into a helix

Tropomyosin

a long protein that covers active binding sites on actin to prevent myosin from binding

Troponin

a globular protein complex that has 3 subunits that bind to the actin, tropomyosin, and Ca++

What does the tropomyosin/troponin complex do?

regulates active sites on G actin and myosin

How do myosin heads work? (2 steps)

1. Binds to active sites on actin - forms cross-bridges
2. Breaks down ATP (with ATPase Enzyme) releasing energy used to bend hinge region

Muscle fiber striated appearance is cause by (4 things) IAM and H

1. I bands - ends of myosin
2. A bands - length of myosin
3. M line - filaments holding myosin in place
4. H zone - only myosin, no overlapping actin

Which myofilament is the thick one?
A. Actin
B. Myosin
C. Troponin
D. Tropomyosin

B. Myosin

Does actin or myosin change length when the muscle contracts?

No

Relaxation: sarcomeres lengthen by _________ muscles.

antagonistic

Sarcomere shortening

During contraction, Z disks are brought closer together as the actin myofilaments at each end of the sarcomere slide past the myosin toward each other. The H zones (yellow) and the I bands (blue) narrow. In a fully contracted muscle, the ends of the actin myofilaments overlap at the center of the sarcomere and the H zone disappears.

Physiology of skeletal muscle fibers includes: (3 things)

1. ion channels
2. action potentials
3. neuromuscular junction (NMJ)

Action Potential Phases

1. Membrane at resting potential (R.P.) then voltage hits absolute threshold because of a stimulus
2. Depolarization
3. Repolarization
4. Hyperpolarization
5. Back to R.P.

During the depolarization phase of an action potential, the permeability of the plasma membrane to
A. Na+ decreases
B. K+ increases
C. Ca++ decreases
D. Na+ increases

D. Na+ increases

Which direction does Na+ travel during depolarization?
A. Into the cell.
B. Out of the cell.
C. It doesn't go much of anywhere.
D. It goes to Hulsey Wellness Center.

A. Into the cell.

Synapse of a NMJ

axon terminal resting in a depression of the sarcolemma

Another name for postsynaptic membrane

motor end-plate

What does acetylcholine do?

stimulates/inhibits action potentials in the postsynaptic membrane

Acetylcholinesterase

Degrading enzyme in synaptic cleft that prevents accumulation of acetylcholine

Acetylcholinesterase is an important molecule in the neuromuscular junction because it
A. Stimulates receptors on the presynaptic terminal.
B. Stimulates receptors on the postsynaptic membrane
C. Breaks down acetylcholine.
D. Causes the release of Ca++ from the sarcoplasmic reticulum.

C. Breaks down acetylcholine.

Excitation-contraction coupling

The Mechanism where an action potential causes contraction of a muscle fiber

Excitation-contraction coupling involves (5 things)

1. Sarcolemma
2. Transverse (T) tubules: depression in the sarcolemma
3. Terminal cisternae of the Sarcoplasmic reticulum (smooth ER)
4. Ca2+
5. Troponin

Relaxation process (3 things)

1. Ca2+ moves back into sarcoplasmic reticulum by active transport, which requires energy. (Diffusion of Ca2+ out of Sarcoplasmic Reticulum is rapid, but active transport of Ca2+ back into the Sarcoplasmic Reticulum is slow in comparison.)
2. Ca2+ moves away from troponin-tropomyosin complex.
3. Tropomyosin complex re-establishes its position and blocks binding sites on actin again.

What is the neuromuscular junction?

the axon terminal and the area of the sarcolemma they innervate

Given these events for muscle contraction:
1. Sarcoplasmic reticulum releases Ca++
2 Sarcoplasmic reticulum takes up Ca++
3. Ca++ ions diffuse into the cytoplasm where the myofibrils are located.
Choose the correct order.

1, 3, 2

What happens if something destroys (or blocks) the acetylcholine receptor site in the neuromuscular junction?

myasthenia gravis

Myasthenia gravis

an autoimmune disease where muscles have flaccid paralysis (are weak) because of the destruction of the ACh receptors by antibodies

Muscle twitch phases

1. latent/lag
2. contraction
3. relaxation

Motor unit

a single motor neuron and all muscle fibers innervated by it.

Summation

increasing the force of contraction of the muscle fibers within the muscle

Recruitment

increasing the number of muscle fibers contracting

Multiple motor unit summation

increased force of contraction
because more motor units are
Stimulated

the amount of tension is determined by

the amount of motor units responding

Muscle tetany

sustained muscle contraction

As the frequency of action potentials increase, the frequency of contraction increases until

tetanus is achieved

Incomplete tetanus

muscle fibers partially relax between contractions

Complete tetanus

no relaxation between contractions, with very rapid AP's

Isotonic muscle contraction

tension is constant, and has change in length (ex: upper limb movement, fingers typing)

Isometric muscle contraction

tension increases, and no change in length (ex: postural muscles of body)

Most muscle contractions are not strictly isotonic or isometric.

True, for example walking

Concentric muscle contraction

(Isotonic) Tension is great enough to overcome opposing resistance and muscle shortens (ex: loaded backpack off the floor - as muscle shortens tension increases

Eccentric muscle contraction

(Isotonic) Tension is maintained but opposing resistance lengthens the muscle (ex: lower a heavy weight)

Muscle tone

constant tension by muscles over a long time that keeps back and lower limbs straight, head upright, abdomen flat

Choose the correct statement.
A. Isometric: change in length and tension.
B. Isometric: no change in length but the tension increases.
C. Isotonic: no change in length but the tension increases.
D. Isotonic: change in length and tension.

B. Isometric: no change in length but the tension increases.

Fatigue

decreased capacity to work and reduced efficiency of performance

3 types of fatigue

1. Psychological
2. Muscular
3. Synaptic

Psychological fatigue

Perceives can't/but can! (Involves CNS, most common, and depends on emotional state of individual.)

Muscular fatigue

results from ATP depletion. (ex: marathon runners, swimmers,
2nd most common

Synaptic fatigue

occurs in NMJ due to lack of acetylcholine (occurs in cases of extreme exertion, rarely occurs)

Rigor Mortis

muscles become rigid several hours after death

Why does Rigor Mortis happen?

Low levels of ATP and the breakdown of the SR Membrane cause Ca2+ to leak into sarcoplasm, which causes the myosin heads to attach to actin cross bridges. Then because of a low ATP concentration (shortly after death ATP production stops) myosin can't let go.

When does Rigor Mortis end?

when tissues deteriorate