Muscle Types and Arrangements

Muscle Structure

• Muscles with a circular pattern of fascicle arrangement surround external body openings and act as sphincters (e.g. orbicularis oris muscle).
• Convergent muscles have a broad origin and fascicles that converge towards the insertion (e.g. pectoralis major muscle).
• Parallel muscles have fascicles with long axes parallel to the long axis of the muscle, can be fusiform or strap-like (e.g. biceps brachii and sartorius muscles).

Motor Unit

• A motor unit consists of a motor neuron and all muscle fibers it controls.
• The number of muscle fibers in a motor unit varies from one to several hundred, depending on the precision of the produced movements.
• An impulse from a motor neuron generates a simultaneous contraction of all muscle fibers supplied by its axon.

Muscle Names

• Skeletal muscles are named based on location, shape, size, and other characteristics.
• Understanding the Latin and Greek roots of anatomical terms is crucial for learning muscle names (e.g. adductor pollicis brevis muscle).

Axial Muscles

• Axial muscles can be divided into two groups: muscles of the head, neck, and trunk.
• Aponeuroses transmit forces and length changes from muscle fascicles to the skeleton and modulate muscle shape changes during contraction.

Fascia

• Fascia is a thin layer of connective tissue outside the epimysium that surrounds individual muscles.
• Fascia can be classified as superficial and deep, with superficial fascia found under the skin and deep fascia surrounding and subdividing muscular compartments.

Patterns of Fascicle Arrangement in Muscles

• Fascicle arrangement and the number of fascicles affect range of motion and muscle power.
• Different skeletal muscles have different patterns of fascicle arrangement, including circular, convergent, and parallel patterns.
• Examples of muscles with different fascicle arrangements include multipennate, convergent, and parallel muscles.

Muscle Structure and Function

• Muscles with a circular pattern of fascicle arrangement surround external body openings and act as sphincters (e.g. orbicularis oris muscle)
• Muscles with a convergent pattern of fascicle arrangement have a broad origin and fascicles that converge towards the insertion (e.g. pectoralis major muscle)
• Muscles with a parallel pattern of fascicle arrangement have fascicles that are parallel to the long axis of the muscle, and can be either fusiform or strap-like (e.g. biceps brachii muscle and sartorius muscle)

Motor Unit

• Every skeletal muscle fiber is supplied by the axon branch of a somatic motor neuron, which signals the fiber to contract
• The functional unit of a muscle is called the motor unit, which consists of a motor neuron and all muscle fibers it controls
• An impulse from a motor neuron generates a simultaneous contraction of all muscle fibers supplied by the branching terminals of its axon

Muscle Names

• Skeletal muscles are named according to several criteria, including location, shape, size, and other characteristics
• Understanding the Latin and Greek roots of anatomical terms helps in learning muscle names (e.g. adductor pollicis brevis muscle)

Axial Muscles

• Axial muscles include the main groups of muscles that are attached to the axial skeleton (e.g. head, neck, and trunk muscles)
• Axial muscles include muscles that move the eyeballs, tongue, and larynx, as well as muscles that flex, extend, and rotate the neck and trunk

Fascia

• Fascia is a thin layer of connective tissue that surrounds individual muscles and is classified as superficial and deep
• Superficial fascia is found directly under the skin and within the superficial adipose layers, while deep fascia surrounds and subdivides the muscular compartments

Patterns of Fascicle Arrangement in Muscles

• Different skeletal muscles have different patterns of fascicle arrangement, which affect range of motion and muscle power
• Examples of fascicle arrangements include circular, convergent, parallel, and multipennate patterns

Skeletal Myofibre Structure

• A skeletal muscle cell (myofiber) is a long, cylindrical cell with multiple peripherally located nuclei
• A myofiber is composed of many myofibrils, which are the contractile elements of a myofiber
• A myofibril is composed of bundles of myofilaments (thick and thin filaments), which are arranged in repetitive units called sarcomeres

Sarcomere

• A sarcomere is the basic functional contractile unit of a myofiber
• A sarcomere is composed of overlapping thick and thin filaments and has several regions

Blood Supply and Innervation of Skeletal Muscle

• Skeletal muscles have an extensive network of blood vessels and nerves traveling through the epimysium and perimysium connective tissue layers
• The innervation of skeletal muscle is voluntary, and large motor units are found in trunk or thigh muscles, while small motor units are found in hand muscles

Origins and Insertions

• A skeletal muscle has at least two attachments, called an origin and an insertion
• The origin is the end of the muscle attached to a fixed, or stabilized, bone, while the insertion is the end of the muscle attached to the bone being pulled during muscular contraction
• In the anatomical position, the origin is usually the proximal attachment and the insertion is usually the distal attachment

Muscle Structure

• Muscles with a circular pattern of fascicle arrangement surround external body openings and act as sphincters (e.g. orbicularis oris muscle).
• Convergent muscles have a broad origin and fascicles that converge towards the insertion (e.g. pectoralis major muscle).
• Parallel muscles have fascicles with long axes parallel to the long axis of the muscle, can be fusiform or strap-like (e.g. biceps brachii and sartorius muscles).

Motor Unit

• A motor unit consists of a motor neuron and all muscle fibers it controls.
• The number of muscle fibers in a motor unit varies from one to several hundred, depending on the precision of the produced movements.
• An impulse from a motor neuron generates a simultaneous contraction of all muscle fibers supplied by its axon.

Muscle Names

• Skeletal muscles are named based on location, shape, size, and other characteristics.
• Understanding the Latin and Greek roots of anatomical terms is crucial for learning muscle names (e.g. adductor pollicis brevis muscle).

Axial Muscles

• Axial muscles can be divided into two groups: muscles of the head, neck, and trunk.
• Aponeuroses transmit forces and length changes from muscle fascicles to the skeleton and modulate muscle shape changes during contraction.

Fascia

• Fascia is a thin layer of connective tissue outside the epimysium that surrounds individual muscles.
• Fascia can be classified as superficial and deep, with superficial fascia found under the skin and deep fascia surrounding and subdividing muscular compartments.

Patterns of Fascicle Arrangement in Muscles

• Fascicle arrangement and the number of fascicles affect range of motion and muscle power.
• Different skeletal muscles have different patterns of fascicle arrangement, including circular, convergent, and parallel patterns.
• Examples of muscles with different fascicle arrangements include multipennate, convergent, and parallel muscles.

Learn about different types of muscle arrangements, including circular, convergent, and parallel patterns. Understand their functions and examples.