Introduction to the Muscular System

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Questions and Answers

What is the role of the origin in muscle anatomy?

It is the end of the muscle attached to a stabilizing bone. (correct)

It is the thickened portion of the muscle.

It describes the action of the muscle when it relaxes.

It is the end of the muscle attached to the moving bone.

Which type of lever is most commonly found in the human body?

Second-class lever

Third-class lever (correct)

Quaternary-class lever

First-class lever

In a second-class lever, where is the load positioned in relation to the effort and fulcrum?

To the side of the effort

At the opposite end from the effort

Between the effort and the load

Between the fulcrum and effort (correct)

What distinguishes a third-class lever from a second-class lever?

Effort is located between the fulcrum and the load in third-class levers. Signup and view all the answers

Why are third-class levers frequently used in the body despite producing a mechanical disadvantage?

They enable faster movement of the load. Signup and view all the answers

What is the role of fixators in the muscular system?

They stabilize one end of the bone so the other end can move. Signup and view all the answers

Which of the following accurately describes the function of the biceps brachii?

Permits flexion at the elbow joint. Signup and view all the answers

What occurs when both the biceps brachii and triceps brachii contract simultaneously?

Stabilization of the elbow joint. Signup and view all the answers

What is the primary action of the external obliques?

To protect the abdominal viscera and move the vertebral column. Signup and view all the answers

Which muscle is primarily responsible for elevating the mandible?

Temporalis Signup and view all the answers

What is the role of synergists in muscle action?

They stabilize intermediate joints during movement. Signup and view all the answers

How does the arrangement of fascicles in the abdominal muscles contribute to their function?

It creates a mesh network providing additional protection. Signup and view all the answers

Which statement accurately represents the function of facial muscles?

They permit facial expressions and other functions such as speech. Signup and view all the answers

What happens during the action of the occipitofrontalis when its frontal belly contracts?

It raises the eyebrows and wrinkles the forehead. Signup and view all the answers

Which muscle acts primarily as an antagonist to the biceps brachii?

Triceps brachii Signup and view all the answers

Study Notes

Introduction to the Muscular System

All skeletal muscles are under voluntary control.
Functions of the muscular system include supporting body movement and generating heat.
Origin: End of the muscle attached to a stabilized or stationary bone, usually proximal.
Insertion: End of the muscle attached to a moving bone, usually distal.
Muscle belly is the thickened portion between tendons.
Actions are the movements possible when the muscle contracts.
Reverse muscle actions (RMAs) result when the origin and insertion are reversed.
Bones act as levers moved by the effort of muscle action.
A load is resistance against effort.
Effort is the force required to move a load.

Levers

First-class levers: Fulcrum is between effort and load.
- Examples include a see-saw or pair of scissors.
- Rare in the human body.
- Example: Looking up at the ceiling.
  - Effort: Posterior neck muscles.
  - Fulcrum: Atlanto-occipital joint.
  - Load: Weight of the anterior portion of the skull.
Second-class levers: Load is between effort and fulcrum.
- Examples include a wheelbarrow.
- Produce a mechanical advantage.
- Little effort is needed to move a load a short distance.
- Example: Standing on your toes.
  - Effort: Gastrocnemius (calf) muscles.
  - Load: Body weight.
  - Fulcrum: Metatarsophalangeal joints (ball of the foot).
Third-class levers: Effort is between the fulcrum and the load.
- Examples include forceps.
- Most common levers in the body.
- Always produce a mechanical disadvantage.
- A lot of effort is needed to move small loads a short distance.
- Example: Bending your elbow.
  - Fulcrum: Elbow joint.
  - Effort: Biceps brachii muscle.
  - Load: Weight of the distal upper limb.

Muscle Actions

Muscles typically work in opposing pairs.
Example: Flexion at the elbow joint.
- Biceps brachii contracts, triceps brachii relaxes.
- Biceps brachii is the agonist (exerts effort to move the lever).
- Triceps brachii is the antagonist (muscle action opposes the agonist).
Synergists stabilize intermediate joints when contracted, allowing movement around only one joint.
Fixators stabilize one end of the bone so the other end can move.
- The proximal end of the bone is held fast by fixators.
- The distal end is moved by contraction of the agonist.
Muscles are organized into compartments, which are groups of skeletal muscles, their nerves, and blood vessels with specific functions.

Naming Muscles

Muscles are named based on:
- Direction: Example: Transversus abdominis muscles run perpendicular to the midline.
- Size: Example: Latissimus dorsi muscles are the widest of the back.
- Shape: Example: Serratus anterior muscles have a saw-shape at the anterolateral portion of the chest.
- Action: Example: External anal sphincter decreases the diameter of the anus.
- Number of origins: Example: The biceps brachii has two origins.
- Location: Example: The occipitofrontalis has a frontal and occipital belly.
- Origin and insertion: Example: The sternocleidomastoid originates on the sternum and inserts on the mastoid process of the temporal bone.

Muscles of the Face

Facial muscles permit facial expressions, including expression of emotions, speech and vocalization, and chewing or mastication.
Orbicularis oculi closes the eyelid.
Orbicularis oris closes the lips and purses the lips.
Occipitofrontalis:
- Frontal belly: Raises eyebrows and wrinkles the forehead.
- Occipital belly: Raises hair (pulls the scalp posteriorly).
- Bellies are connected by the epicranial aponeurosis.
Platysma pulls the corners of the mouth laterally and inferiorly, permitting frowning and depressing the mandible.
Masseter and temporalis elevate the mandible.

Muscles of the Neck

Two sternocleidomastoid muscles, one on each side of the neck:
- Originates anteriorly (manubrium) and inserts posteriorly (temporal bone).
- Rotates the head and can extend the head at the atlanto-occipital joint.
- Capable of RMAs, including elevation of the sternum.
- Unilateral contraction causes the head to tilt to the side of the contracted muscle and rotate to the opposite side.

Muscles of the Abdomen

Functions include protecting the abdominal viscera and moving the vertebral column.
External obliques are the most superficial.
Internal obliques are intermediate to external obliques and transversus abdominis.
Transversus abdominis is the deepest muscle.
The fascicles of the abdominal muscles are arranged at angles to one another, creating a mesh network for better protection of abdominal viscera.
- External obliques extend medially and inferiorly.
- Internal obliques extend medially but superiorly.
- Transversus abdominis extend transversely to the abdominal cavity.
Rectus abdominis runs longitudinally along the anterior of the abdominal cavity, parallel to the midline.
- Divided by tendinous intersections.
- Responsible for the "6-8 pack" definition.
Diaphragm permits breathing.
- Bounds the thoracic cavity inferiorly.
- Circular muscle with origins on many bones and tissues.
- Inserts on the central tendon (aponeurosis at the center of the diaphragm).
- Contraction moves the diaphragm down, expanding the lungs.

Muscles that Move the Pectoral Girdle

Functions include moving the clavicle and scapula, or stabilizing the scapula during movement of the humerus.
Serratus anterior:
- Fan-shaped muscle that originates on ribs and inserts on the scapula.
- Abducts the scapula.
- RMA: Elevation of ribs.
- Assists in pushing and punching.
Trapezius muscle:
- Originates on the occipital bone and inserts on the scapula.
- Permits rotation, adduction, depression, and stabilization of the scapula.

Muscles that Move the Upper Limb

Function is to move the humerus.
Pectoralis major:
- Permits adduction, medial rotation, and flexion of the arm.
Deltoid muscles wrap the shoulder posteriorly, laterally, and anteriorly.
- Permits abduction, medial/lateral rotation, flexion/extension of the arm.
Latissimus dorsi:
- The strongest and widest muscle of the back, triangular posterior and lateral muscle.
- "Swimmer's muscle"
- Muscle actions include extension, adduction, medial rotations of the arm.
- RMA includes elevation of the vertebral column and torso.
- Originates on the spinal column.

Muscles that Move the Forearm

Function is to move the radius and ulna.
Biceps brachii:
- Two heads, both originate on the scapula and insert on the radius.
- Permits flexion of the arm at the elbow joint and supination of the hand.
Triceps brachii:
- Originates on the scapula and humerus.
- Inserts at the olecranon of the ulna.
- Permits extension of the forearm at the elbow joint.
Brachioradialis:
- Flexes the arm at the elbow joint.
- Controls speed of movement.
- Supinates and pronates the hand.

Muscles that Move the Lower Limb

Gluteal muscles function to move the femur.
Gluteus maximus:
- One of the largest muscles in the body.
- Originates on the pelvis and inserts on the fascia of thigh muscles.
- Muscle action permits extension of the leg at the hip joint and lateral rotation of the femur at the hip joint.
- RMA: Extension of the torso.
Gluteus medius:
- Deep to the gluteus maximus.
- Originates at the ilium and inserts on the femur.
- Permits abduction and medial rotation of the femur.
Flexor compartment of the thigh (includes the "hamstrings"):
- Three muscles: biceps femoris, semitendinosus, and semimembranosus.
- Flex the distal lower limb at the knee joint and extend the leg at the hip joint.
Extensor compartment of the thigh (includes the "quads"):
- Four muscles: vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris.
- Anterior to the flexor compartment of the thigh.
- Permits extension of the distal lower limb at the knee joint and flexion of the leg at the hip joint (rectus femoris only).
Medial compartment of the thigh:
- Gracilis originates on the pubis and inserts on the tibia.
- Permits adduction of the thigh at the hip, medial rotation of the thigh, and flexion of the leg around the knee joint.

Muscles that Move the Foot

Soleus and gastrocnemius belong to the superficial posterior compartment of the leg.
Soleus:
- Originates at the fibula and tibia and inserts onto the calcaneal (Achilles) tendon.
- Permits plantar flexion of the foot at the ankle joint.
Gastrocnemius:
- Originates on the femur and inserts at the calcaneal tendon.
- Permits plantar flexion of the foot at the ankle joint and flexion of the lower limb at the knee joint.
Tibialis anterior:
- Originates on the tibia and inserts on the metatarsals and tarsals.
- Permits dorsiflexion of the foot at the ankle joint and supination (inversion) of the foot at intertarsal joints.

Homeostatic Imbalances of the Muscular System

Muscle injuries are often activity-related.
Regular, moderate-intensity exercise helps protect against injury.
Stretching, good nutrition, and sleep also help.
Minor injuries include spasms, cramps, and muscle soreness.
Spasms are involuntary contractions of a muscle or group of muscles.
- Painful spasms are called cramps.
- Most common cause is dehydration.
- Other causes include injury, overuse, prolonged periods in one position, and inadequate blood flow to muscle(s).
Muscle soreness is often due to microscopic damage to muscles (e.g., torn sarcolemmas, Z-discs).
- May be accompanied by swelling or inflammation.
- May be delayed (24-48 hours following high-intensity exercise).
Minor injuries (e.g., strains) should be treated with PRICE:
- Protection, Rest, Ice, Compression, and Elevation.

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Description

This quiz covers essential concepts of the muscular system, including its functions, components, and the mechanics of muscle contraction. It also explores the role of levers in muscle actions, particularly the different classes of levers found in the human body. Test your understanding of skeletal muscles and their interactions with bones.