Kinesiology - Muscles

purpose of musculoskeletal system

supports body, keeps it upright, allows movement, and protects vital organs

Skeletal system stores…

calcium, phosphorus, and components of blood

Musculoskeletal system is made up of

• body’s bones, skeletal muscles, and connective tissue that binds them together 

• tendons

• ligaments

• cartilage

tendons

skeletal muscle fibre that connects bones directly through tough tissue fibres

ligaments

tightly bounds bones to other bones

cartilage

at end of bones that prevent bones from grinding against one another

smooth muscle

• surrounds internal organs (blood vessels, hair follicles…) 

• contracts more slowly than skeletal muscle

• remain contracted longer

• involuntary

cardiac muscle

• found in heart

• responsible for creating action that pumps blood

• involuntary

Skeletal muscle

• attach to bones

• 30-40% of human weight

• voluntary 

• referred to as striated or striped

how many individual muscles make up musculoskeletal system

600

muscles rarely….

work alone, they always function as groups

how skeletal muscles are names

typically after their action, location, shape, direction of fibres, number of divisions / heads, or points of attachement

How they’re named - direction of fibres

rectus, transversus ex: rectus abdominus, transverse abdominus

How they’re named - location of muscles

anterior / posterior ex: tibialis anterior, tibialis posterior

How they’re named - number of divisions / heads

number of heads (2-3) ex: biceps brachii, triceps brachii

Shape of muscle

ex: Deltoid (triangle), trapezius (representing trapezoid)

Types of muscle contraction

• concentric contraction (shortening) 

• eccentric contraction (lengthening) 

• isometric contraction (static) 

Muscles…

pull, they never push

agonist muscle

muscle primarily responsible for movement of a body part

orgin

The point where the muscle attaches to the more stationary of the bones of the axial skeleton

Insertion

the other end, the point where the muscle attaches to the bone that is moved the most

example of orgiin / insertion

Contract biceps —> pull forearm towards shoulder (origin), insertion of one of bones of forearm

Synergistic muscles

muscles that contract together and are coordinated in accomplishing a particular movement (ex: elbow flexion: brachialis and biceps brachii contract tg) 

Antagonistic muscles

Muscles that perform opposite functions and are generally located on the opposite side of limb / body (ex: elbow flexion: triceps brachii contracts to extend elbow) 

fixator

stabilize more proximal joints during weight bearing function of distal joints (ex: deltoids in dumbbell chest press stabilize shoulder)

Neutralizer (synergists)

resists undesired movements (ex: deltoids in dumbbell chest press prevent in and out movement) 

How do skeletal muscles attach to bones?

Indirectly via tendons or directly when the outer membrane of the muscle attaches to the outer membrane of the bone

Most common form of attachment of muscles

indirect

Sarcolemma

Plasma membrane that lies beneath the endomysium, sheath of connective tissue surrounding muscle fibre

Sarcoplasm

Muscle cell’s cytoplasm, contained by sarcolemma

Sarcomeres

Units of skeletal muscle containing cellular proteins myosin and actin

Sarcoplasmic reticulum

Network of channels in each muscle fibre that transport electrochemical substances involved in muscle activation

Motor unit

the motor neuron, its axon, and muscle fibres it stimulates

Nerves transmit impulses in…

waves that ensure smooth movements

muscle twitch

A single nervous impulse and the resulting contraction

one neuron may…

be responsible for stimulating a number of muscle fibres

All or none principle

When a motor unit is stimulates to contract, it will do so to its fullest potential. All fibres contract or none contact

Process of muscle contraction referred to as

excitation - contraction coupling

where does excitation-contraction coupling begin?

electrical signal originates at spinal cord and moves along nerve axon to the neuromuscular junction

Second part of excitation-contraction coupling

signal is then transmitted down muscle fibre through tubular membranes

What is released into the sarcoplasm? 

calcium ions

Last step of excitation contraction coupling

The interaction of calcium with the proteins troponin and tropomyosin removes obstacles to actin-myosin interaction