GAP Ch11 The Muscular System Default

Overview of the Muscular System

The muscular system is a complex network of skeletal muscles that plays a crucial role in movement and support of the body. It not only facilitates voluntary movements but also contributes to various bodily functions like posture maintenance, joint stability, and thermogenesis.

Focus on Skeletal Muscle Organization and Naming

The organization of skeletal muscles aids in efficient movement. Muscles are arranged such that they can assist with opposing movements; this is particularly evident in the way certain muscles are classified as antagonists, working against primes to balance motion.

Examination of Muscle Actions

• Muscle actions are categorized from head to toe, highlighting how muscle contractions influence specific regions of the body.

• Understanding these actions is vital for diagnosing and treating musculoskeletal injuries and conditions.

Interaction of Skeletal Muscles

• Origin: This is the fixed attachment point of a muscle, typically located on a non-moving bone, which serves as the anchor for muscle contraction.

• Insertion: The movable end of a muscle, attached to the bone being acted upon during muscle contraction, plays a significant role in the muscle’s function.

• Prime Mover (Agonist): The principal muscle responsible for carrying out a specific action— for instance, the biceps brachii is the prime mover when lifting a cup.

• Synergists: These muscles assist the prime mover in executing its action. For example, the brachioradialis and brachialis both support the biceps brachii in flexing the elbow.

• Antagonists: Muscles that oppose the action of the prime mover, allowing controlled movement and flexibility. This opposition minimizes injury risk during rapid movements.

Muscle Fascicle Arrangements

• Parallel Muscles: Fascicles aligned in the same direction as the muscle's long axis, maximizing range of motion (e.g., most skeletal muscles like the rectus abdominis).

• Fusiform Muscles: Spindle-shaped muscles featuring a thick central belly that tapers at both ends (e.g., biceps brachii), which enable powerful movements.

• Circular Muscles (Sphincters): Fascicles arranged in concentric circles control the size of openings, aiding in functions such as eating and seeing (e.g., orbicularis oris around the mouth).

• Convergent Muscles: These have widespread fascicles that converge at a single attachment point, allowing for powerful movements that pull at multiple angles (e.g., pectoralis major).

• Pennate Muscles: Fascicles attach to a central tendon and are classified into types based on their arrangement:

  • Unipennate: Fascicles on one side of the tendon (e.g., extensor digitorum).

  • Bipennate: Fascicles inserted on both sides of the tendon (e.g., rectus femoris).

  • Multipennate: Fascicles attach to a tendon from multiple angles, creating strength (e.g., deltoid).

Muscle Naming Criteria

Muscles are named according to several criteria, highlighting their unique characteristics:

• Shape: For example, the deltoid muscle is named for its triangular shape.

• Size: Muscles may be categorized by their relative size, such as gluteus maximus (largest) and gluteus minimus (smallest).

• Location in the body: The anatomical position often describes where the muscle is located (e.g., rectus femoris, located in the thigh).

• Locations of attachments: Often muscles are named according to their origin and insertion points (e.g., sternocleidomastoid).

• Number of origins: For example, biceps (two origins) vs. triceps (three origins).

• Action performed: Muscles may be named based on their function (e.g., flexor carpi radialis, which flexes the wrist).

Muscular System Overview by Region

Superficial vs. Deep Muscles

Superficial muscles are located closer to the skin surface, while deeper muscles lie beneath the superficial layer and contribute significantly to body function and stability.

Facial Expression Muscles

Facial muscles insert into the skin rather than bones, allowing for facial expressions and movements. Key muscles include:

• Orbicularis Oris: Encircles the mouth.

• Orbicularis Oculi: Found around the eyes, enabling blinking and squinting.

Jaw Muscles

Primarily located in the cheeks, jaw muscles are essential for mastication (chewing). The masseter muscle, in particular, is instrumental in this process.

Neck and Back Musculature

Neck Muscles: Responsible for moving the head and cervical vertebrae, important muscles include:

• Splenius Capitis: Supports head extension.

• Sternocleidomastoid: Facilitates head rotation and flexion.

• Trapezius: Aids in shoulder elevation and head movement.

Back Muscles: The longissimus muscle supports movement and stability of the head, shoulders, and vertebral column.

Abdominal Musculature

The anterior abdominal region features critical muscles:

• Rectus Abdominis: Known as the "six-pack," it runs parallel to the midline, essential for core stability.

• Three Layers of Abdominal Muscles:

  • External Oblique (outermost layer, crucial for trunk rotation)

  • Internal Oblique (middle layer, aids in trunk flexion and rotation)

  • Transversus Abdominis (innermost layer, crucial for stabilizing the pelvic region).

Pelvic and Thoracic Muscles

• Diaphragm: A dome-shaped muscle crucial for respiration, separating the thoracic and abdominal cavities and enabling inhalation and exhalation patterns.

• Intercostal Muscles: Important for respiratory mechanics; external intercostals serve to raise the ribs, while internal intercostals lower them during forced exhalation.

Muscles of the Pectoral Girdle and Upper Limbs

Muscles in this region are generally positioned anteriorly and primarily function to move the humerus:

• Pectoralis Major: Major mover of the humerus anteriorly.

• Muscles from the scapula (e.g., deltoid and infraspinatus) facilitate movements that lift or rotate the humerus superiorly or posteriorly.

Hip and Thigh Muscles

Major muscles typically originate from the pelvic girdle:

• Quadriceps Group: Comprising rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius, crucial for knee extension and mobility.

• Adductor Muscles: Assist in bringing the thigh back toward the midline, crucial for stabilizing walking and running.

Muscles of the Lower Leg

Muscle functions involve two primary movements: dorsiflexion and plantar flexion

• Dorsiflexion: Primarily performed by anterior muscles (e.g., tibialis anterior), involved in lifting the foot upwards.

• Plantar Flexion: Done by posterior muscles (e.g., gastrocnemius and soleus), essential for standing on tiptoes and walking.

• Important Lower Leg Muscles include tibialis anterior, gastrocnemius, soleus, and popliteus, each integral to ankle and foot movement and stability.

Conclusion of Overview

A comprehensive understanding of muscular organization is essential for effectively identifying, labeling, and training muscles in practical settings, aiding in educational advancements and rehabilitative practices in the field of health and fitness.