AP 1 M5 5.3: Physiology of the Muscular System Flashcards
Muscle tissue types
Muscle tissue is found in three distinct types in the body: skeletal, smooth, and cardiac.
Voluntary control
Skeletal muscle
Skeletal muscle is under voluntary control. Voluntary control means a conscious decision is made to move this type of muscle.
Skeletal muscle
Skeletal muscle tissue allows for conscious movement of the body and limbs.
involuntary control
Muscle type
Smooth muscle and cardiac muscle are under involuntary control, meaning contraction of this muscle happens without a conscious decision
Smooth muscle
Smooth muscle is found within the internal organs of the body, such as the digestive tract and blood vessels.
Cardiac muscle
Cardiac muscle is only found within the heart.
striated
Under the microscope, skeletal and cardiac muscle appear to be striated or striped in appearance, while smooth muscle is free of striations.
Skeletal muscles make up
Skeletal muscles, which make up over 40% of the body’s weight, are attached to the skeleton by tendons, made of fibrous connective tissue.
Tendons
Tendons connect muscle to bone
muscles contract
When muscles contract, they become shorter. Muscles can only pull; they cannot push. Skeletal muscles must work in antagonistic pairs because muscles are only able to pull in the direction of their fiber orientation.
ligaments
ligaments connect bone tissue to bone.
antagonistic pair
If one muscle of an antagonistic pair bends the joint and brings the limb toward the body (the flexor), the other one straightens the joint and extends the limb (the extensor), as shown in the figure below.
Flexion
Flexion - closing of a joint, “bending”
Extension
Extension - opening of a joint, “straightening”
Antagonistic pair example
Flexion and Extension
Flexor - biceps brachii
Extensor - triceps brachii
Abduction
Abduction - movement away from midline
Adduction
Adduction - movement towards midline
Antagonistic pair example:
Abduction and Adduction
Abductor: TFL (of the hip)
Adductor: adductor longus, adductor magnus
Dorsiflexion
Dorsiflexion - flexion superiorly occurring at the subtalar (ankle) joint (movement of the toes “up”)
Plantarflexion
Plantarflexion - flexion inferiorly occurring at the subtalar (ankle) joint (movement of the toes “down”)
Antagonistic pair example:
Dorsiflexor and Plantarflexion
Dorsiflexor: tibialis anterior
Plantarflexor: gastrocnemius
Radial Deviation
lateral movement of the wrist towards the radius
Ulnar Deviation
medial movement of the wrist towards the ulna
Antagonistic pair example
Radial Deviation and Ulnar Deviation
Radial Deviator: flexor carpi radialis
Ulnar Deviator: extensor carpi ulnaris
Pronation
rotation of the forearm so that the palm faces posteriorly
(or) rotation of the ankle so the sole of the foot faces laterally
Supination
rotation of the forearm so that the palm faces anteriorly
(or) rotation of the ankle so the sole of the foot faces medially
Antagonistic pair example
Pronation and Supination
Pronator: (of forearm) pronator teres
Supinator: (of forearm) biceps brachii
Elevation
Elevation – upward movement of a structure
Depression
Depression – downward movement of a structure
Antagonistic pair example:
Elevation and Depression
Elevator: levator scapulae
Depressor: trapezius (lower fibers)
Retraction
Retraction - movement of a structure to be drawn in the posterior direction (drawn backward)
Protraction
Protraction - movement of a structure to be drawn in the anterior direction (drawn forward)
Antagonistic pair example:
Retraction and Protraction
Retractor: rhomboids, trapezius
Protractor: serratus anterior
A whole skeletal muscle
A whole skeletal muscle is composed of many muscle fibers in bundles
muscle fiber
Each muscle fiber is a cell containing thousands of myofibrils, which are the contractile portions of the fibers
Myofibrils
Myofibrils are cylindrical in shape and run the length of the muscle fiber. The light microscope shows that a myofibril has light and dark bands called striations.
It is these bands that cause skeletal muscle to appear striated. Striations of myofibrils are formed by protein myofilaments within contractile units called sarcomeres
sarcomeres
It is these bands that cause skeletal muscle to appear striated. Striations of myofibrils are formed by protein myofilaments within contractile units called sarcomeres
myofilaments
A sarcomere contains two types of protein myofilaments
myosin
myofilaments
The thick filaments are made up of a protein called myosin,
actin
myofilaments
the thin filaments are made up of a protein called actin
As a muscle fiber contracts
As a muscle fiber contracts, the sarcomeres within the myofibrils shorten. When a sarcomere shortens, the actin (thin) filaments slide past the myosin (thick) filaments and approach one another. The movement of actin filaments in relation to myosin filaments causes the muscle to shorten.
Z line
Various terms help to describe the components of a sarcomere
One sarcomere is from one Z line to one Z line. Z lines connect parallel bands of thin filaments.
M line
Various terms help to describe the components of a sarcomere
The thick filaments are held together by the M line.
I band
Various terms help to describe the components of a sarcomere
The I band (light band) appears light when stained because it only contains thin filaments.
A band
Various terms help to describe the components of a sarcomere
The A band (dark band) contains thin and thick filaments; however, it stains darker because it contains the thick filaments. When a muscle contraction occurs, the Z lines move closer together towards the center of the sarcomere (M line).
acetylcholine
For a muscle to contract
Once the nerve impulse reaches the muscle fiber (called a neuromuscular junction), acetylcholine (a special chemical called a neurotransmitter) is released from the motor nerve ending (Figure 5.40). Acetylcholine binds to receptors on the muscle cell, opening sodium channels and allowing sodium to flow inside the sarcoplasm (cytoplasm of a muscle cell).
For a muscle to contract
For a muscle to contract, the nervous system must work together with the muscular system. First, a nerve impulse must be sent to the muscle.
sarcoplasm
For a muscle to contract
Acetylcholine binds to receptors on the muscle cell, opening sodium channels and allowing sodium to flow inside the sarcoplasm (cytoplasm of a muscle cell).
sarcolemma
For a muscle to contract
The presence of sodium ions causes an action potential to occur in the sarcolemma (cell membrane of a muscle fiber). The action potential causes calcium ions to be released from the sarcoplasmic reticulum
sarcoplasmic reticulum
For a muscle to contract
The sarcoplasmic reticulum is a specialized type of smoother ER found within striated muscle tissue.
movement of the many actin filaments together
For a muscle to contract
The movement of the many actin filaments together is what produces a muscle contraction. Muscle contraction ceases when the nerve impulses no longer stimulate the muscle fiber. With the cessation of a muscle action potential, calcium ions are pumped back into the sarcoplasmic reticulum by active transport. Once the calcium ions return to the sarcoplasmic reticulum, relaxation of the muscle occurs.
cross-bridges
For a muscle to contract
In the presence of calcium ions, portions of the myosin filaments called cross-bridges bend backward and attach to actin filaments. After attaching to the actin filament, the cross-bridges bend forward and the actin filament is pulled along. The cross-bridges attach and detach some fifty to 100 times as the thin filaments are pulled to the center of a sarcomere. ATP is needed on a cellular level for the myosin cross-bridges to pull the actin filaments.
