PSIO LAB 3.1 Review

Muscular System

• facilitates movement in the human body

• contractile tissues - skeletal, cardiac, and smooth muscle

• skeletal muscle and system work together to generate motion by contracting and pulling bones

• each muscle fiber contracts in a uniform manner

• efficiency depends on how their fibers are arranged and how they attach to bones

• body functions - balance, position, and actions

Skeletal Muscle Tissue

• 3 defining characteristics

1. cylindrical-shaped muscle fibers

2. 3-5 nuclei per muscle fiber

3. striations - organization of actin (Thin F) and myosin (Thick F)

• Locations - combined with connective tissues and neutral tissue in skeletal muscles

• Functions - moves + stabilizes position of skeleton, guards entrances and exits of digestive, respiratory, and urinary tract

• generates heat and protects internal organs

Sarcomere

• Most basic unit of contraction in skeletal muscle

• Z Disc - forms the boundary of each sarcomere and anchors the thin filaments

• I Band - contains only thin filaments (actin)

• A Band - spans the length of the thick filament including areas where thick and thin filaments overlap

• H Zone - contains only thick filament (Myosin)

• Zone of overlap - the region where thick and thin filaments interact to produce contractions

• M Line - a central structure that helps stabilize the thick filaments

• in a contracted sarcomere the zone of overlap increases

Origins and Insertions

• two points where a muscle attaches to bones or other muscle attaches to bones or other structures to facilitate movement

• origin - the fixed or less moveable attachment

• insertion - more moveable attachment

• During muscle contraction - insertion (proximal) typically pulled toward the origin (distal) w/in limbs especially

• more than one original or insertion is possible

• example - the biceps brachii has two origins, both of which are on the scapula and a single insertion on the radius (pulls forearm towards the shoulder

Functional Classifications of Muscles

• muscles mainly work together to execute complex movements efficiently

• functional groups - agonists, synergists, and antagonists - depending on their role in a given movement

• examples - biceps brachia (agonist), triceps brachia (antagonist), brachioradialis (synergist)

Agonist

• “prime mover” the muscle primarily responsible for producing a specific movement at a joint.

• example - brachialis acts as the agonist because it is the main muscle driving that motion.

Synergist

• Assists the agonist in performing its action, by contributing additional pull or stabilizing the origin of muscles

• useful at beginning the movements when the agonist is in a stretched person and less able to generate maximum force

• the biceps brachii muscle works synergistically with the brachilis to flex the forearm

• fixators - stabilizing joints to prevent unwanted movement and enabling the agonist to function more efficiently.

Antagonist

• opposes the action of an agonist, if agonist produces flexion, the antagonist produces extension

• example - brachialis flexes the forearm, the triceps brachii serves as the antagonist by extending the forearm to counteract the flexion.

Flexion - Body Movements

• movement in the anterior-posterior place that decreases the angle between two bones, bringing them closer together

• examples - fist by bending the fingers toward the palm, bending the forearm at the elbow, raising the arm forward at the shoulder, and bending the head forward to look at your feet.

Lateral Flexion - Body Movements

• occurs when the trunk of the body moves in a frontal plane laterally away from the body

• examples - between the vertebrae in the cervical and lumbar regions of the vertebral column

Extension - Body Movements

• opposite of flexion, a straightening movement that increases the angle between two bones

• examples - straightening the arm and forearm so the limb points forward, or straightening the fingers after making a fist.

Hyperextension - Body Movement

• occurs when a join is extended beyond its normal range (past 180 degrees) is part of the body’s normal range of motion but…

• examples - raising the back of your hand with your palm down or looking up at the ceiling

• can sometimes lead to injury, especially in joints like the knees, elbows, or wrists.

Abduction - Body Movement

• “move away” a lateral movement of a body part away from the body midline

• example - arm or the thigh is moved laterally away from the body midline, the fingers or the toes as you spread them apart, away from the longest digit that acts as the midline.

• always refers to movement of appendicular skeleton

Adduction - Body Movement

• opposite of abduction, “move toward” the medial movement of a body part towards the body midline

• examples - raised arm or thigh is brought back toward the body midline, or in the case of the digits, toward the midline of the hand.

• always refers to movement of appendicular skeleton

Circumduction - Body Movement

• movement where the proximal end of a limb stays stationary while the distal end moves in a circular motion “cone shape”

• examples - the shoulder stays fixed while the hand moves, combines a continuous sequence of flexion, abduction, extension, and adduction.

Rotation - Body Movement

• pivoting movement where a bone turns along its own longitudinal axis

• examples - rotation occurs at the atlantoaxial joint when you shake your head to say "no."

• lateral rotation - moves the front of the femur or humerus away from the body's midline.

• medial rotation - moves the front of the femur or humerus toward the midline.

Special Movements

• protraction and retraction, depression and elevation, dorsiflexion and plantar flexion, inversion and eversion, and opposition and reposition.

Pronation - Body Movement

• medial rotation of the forearm so that the palm of the hand is directed posteriorly or inferiorly

• radius and ulna are crossed to form an X

Supination - Body Movement

• forearm rotates laterally so that the palm faces anteriorly or superiorly

Depression - Body Movement

• the inferior movement of a part of the body

• examples - downward movement of the mandible while opening the mouth and movement of your shoulders in an inferior direction

Elevation - Body Movement

• the superior movement of a body part

• examples - the upward superior movement of the mandible while closing the mouth and the movement of the shoulders in a superior direction

Dorsiflexion - Body Movement

• limited to ankle joints

• movement at the ankle joint where the top of the foot moves toward the leg

• examples - when you lift your toes while walking to prevent them from scraping the ground or when positioning your foot above the brake pedal.

Plantar Flexion - Body Movement

• occurs when the foot points downward, away from the leg

• examples - like pressing on a gas pedal or standing on your tiptoes

Inversion - Body Movement

• occurs at the intertarsal joints of the foot only

• the sole of the foot turns medially

Eversion - Body Movement

• occurs at the intertarsal joints of the foot only

• the sole of the foot faces laterally

Protraction - Body Movement

• the forward movement of a body part from its anatomical position.

• examples - pushing your jaw forward (jutting it out) at the temporomandibular joint, moving your shoulders forward by crossing your arms, which involves movement at the acromioclavicular and sternoclavicular joints.

Retraction - Body Movement

• the backward (posterior) movement of a body part, returning it to the anatomical position.

• examples - pulling your jaw back after it has been protracted, or drawing your shoulders back after they've been pushed forward

Opposition - Body Movement

• occurs when the thumb is brought over to touch another digit

• It involves movement at the first carpometacarpal and metacarpophalangeal joints.

• Opposition enables you to grasp and hold objects between your thumb and palm.

Reposition - Body Movement

• the movement that returns the thumb and fingers from opposition

General Rules for Naming Skeletal Muscles

• size - Terms such as maximus (largest), minimus (smallest), longus (long), and brevis (short) are often used in muscle names.

• fiber direction and orientation - rectus (straight) fibers run parallel to that imaginary line (axis). Transversus (straight across) muscle fibers run at right angles to that line, oblique (slanted) fibers run obliquely to it

• Some muscles are named according to their points of origin and insertion. The origin is always named first.

• shape - There are four main fascicle patterns: circular, parallel, convergent, and pennate.

• can be named after muscle action

Circular Muscle Shape

• fibers arranged in rings that surround body openings

• muscles act as sphincters that close openings when they contract.

• example - the orbicularis oris, the muscle that encircles the mouth and allows you to pucker your lips or close your mouth tightly

Convergent Muscle Shape

• have a wide origin and fibers that converge toward a single tendon

• fan-shaped structure allows the muscle to pull from different directions

• example - pectoralis major, the broad, fan-shaped muscle in the chest that helps you push or lift heavy objects

Parallel Muscle Shape

• have fibers that run in line with the long axis of the muscle

• These muscles can be strap-like

• examples - the sartorius or fusiform, where the muscle has a thicker middle and tapers at the ends like biceps brachii.

• These muscles are known for endurance, though they are not as strong as other muscle types

Pennate Muscle Shape

• have fibers that attach at an angle to a central longitudinal tendon, resembling the structure of a feather

• unipennate (fibers on one side of the tendon, like the extensor digitorum longus),

• bipennate (fibers on both sides, like the rectus femoris)

• multipennate (with several tendons, like the deltoid).

• Pennate muscles produce more force than parallel muscles but have less range of motion

Muscles of the Scalp

• Frontalis - forehead muscle part of the occipitofrontalis group, responsible for elevating the eyebrows and draws the scalp anteriorly, making it possible to raise your eyebrows and wrinkle your forehead.

• Occipitalis - Located at the back of the skull, the occipitalis muscle draws the scalp posteriorly and assists the frontalis muscle in elevating the eyebrows. This muscle is also part of the occipitofrontalis group.