The Back Muscle Groups Lecture Flashcards
Describe the classification of back muscle groups.
- Superficial Back Muscles
These muscles are primarily involved in movements of the shoulder and upper limb and are typically larger and more superficial.
Trapezius:
Function: Elevates, retracts, and rotates the scapula; extends the neck.
Innervation: Accessory nerve (CN XI) and cervical nerves.
Latissimus Dorsi:
Function: Extends, adducts, and medially rotates the arm; assists in deep breathing and shoulder movement.
Innervation: Thoracodorsal nerve.
Rhomboid Major and Minor:
Function: Retracts and elevates the scapula.
Innervation: Dorsal scapular nerve.
Levator Scapulae:
Function: Elevates the scapula and assists in neck movements.
Innervation: Dorsal scapular nerve and cervical nerves.
2. Intermediate Back Muscles
These muscles are mainly involved in respiratory movements and are not as prominent as the superficial muscles.
Serratus Posterior Superior:
Function: Elevates the ribs during inhalation.
Innervation: Intercostal nerves (T2-T5).
Serratus Posterior Inferior:
Function: Depresses the ribs during exhalation.
Innervation: Intercostal nerves (T9-T12).
3. Deep Back Muscles
These muscles are primarily responsible for the movements and stabilization of the vertebral column. They are deeper and include several groups:
Erector Spinae Group:
Comprises three columns:
Iliocostalis: Lateral group; extends and laterally flexes the vertebral column.
Longissimus: Intermediate group; extends and rotates the head and vertebral column.
Spinalis: Medial group; primarily extends the vertebral column.
Innervation: Dorsal rami of spinal nerves.
Transversospinalis Group:
Includes:
Semispinalis: Extends and rotates the spine; spans 4-6 vertebrae.
Multifidus: Stabilizes the spine; spans 2-4 vertebrae.
Rotatores: Stabilizes and rotates the spine; spans 1-2 vertebrae.
Innervation: Dorsal rami of spinal nerves.
Other Deep Muscles:
Quadratus Lumborum:
Function: Laterally flexes the lumbar spine and stabilizes the pelvis.
Innervation: Lumbar plexus.
Describes the main intrinsic muscle group (e.g., erector spinae) of the back.
Erector Spinae Group
The erector spinae is divided into three main columns, each with specific functions and innervation:
Iliocostalis
Location: The most lateral column.
Subdivisions: Iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis.
Function:
Extends the vertebral column.
Laterally flexes the spine to the same side.
Innervation: Dorsal rami of the spinal nerves.
Longissimus
Location: The intermediate column, situated between the iliocostalis and spinalis.
Subdivisions: Longissimus thoracis, longissimus cervicis, and longissimus capitis.
Function:
Extends the vertebral column.
Rotates the head and laterally flexes the spine.
Innervation: Dorsal rami of the spinal nerves.
Spinalis
Location: The most medial column, closest to the spinous processes of the vertebrae.
Subdivisions: Spinalis thoracis, spinalis cervicis, and spinalis capitis (though the last is often considered part of the semispinalis capitis).
Function:
Extends the vertebral column.
Stabilizes the spine.
Innervation: Dorsal rami of the spinal nerves.
General Functions of the Erector Spinae
Extension: The erector spinae group plays a key role in extending the spine when the torso is bent forward or when returning to an upright position.
Lateral Flexion: They assist in bending the spine laterally to the same side.
Rotation: They contribute to rotation of the spine, especially when working with other muscles.
Clinical Relevance
Back Pain: Dysfunction or strain of the erector spinae can lead to lower back pain or stiffness, which is common in individuals with poor posture or those who engage in repetitive lifting.
Posture: Strong and well-functioning erector spinae muscles contribute to better posture and spinal alignment, helping to reduce the risk of injury.
Know the function of the main intrinsic back muscle group (e.g., erector spinae) on the vertebral column movement.
Functions of the Erector Spinae Group
Extension of the Spine:
The erector spinae muscles are primarily responsible for extending the vertebral column. This action occurs when you move from a flexed position (such as bending forward) back to an upright position. The extension helps maintain an erect posture.
Lateral Flexion:
When contracting unilaterally (one side at a time), the erector spinae allows for lateral flexion of the spine. This means that if you bend to one side, the erector spinae on that side contracts to facilitate the movement.
Rotation:
The erector spinae muscles assist in the rotation of the vertebral column. Although they are not the primary muscles for rotation, they support and stabilize the spine during movements that involve turning the torso.
Stabilization:
The erector spinae group helps stabilize the vertebral column during various activities, such as lifting or carrying heavy objects. By maintaining proper alignment of the vertebrae, these muscles contribute to balance and posture.
Support During Activities:
Activities such as running, walking, and jumping involve coordinated movements of the spine. The erector spinae contracts to provide stability and control during these dynamic movements, helping to absorb impact and prevent injury.
Understand the interrelationship of the main intrinsic back muscle groups (e.g., erector spinae) and the functional component of the spinal nerve.
Interrelationship of Erector Spinae and Spinal Nerves
Muscle Innervation:
The erector spinae muscles are innervated by the dorsal rami of the spinal nerves. Each segment of the spinal cord corresponds to a specific pair of spinal nerves that exit the vertebral column.
The dorsal rami provide motor innervation to the muscles of the back, enabling them to contract and produce movement.
Functional Components of Spinal Nerves:
Each spinal nerve is composed of sensory and motor fibers, and it typically has three functional components:
Motor Component: Innervates the intrinsic back muscles (like the erector spinae), enabling voluntary movements such as extension and lateral flexion of the spine.
Sensory Component: Carries sensory information from the skin and proprioceptors (muscle spindles and Golgi tendon organs) back to the spinal cord. This information helps the brain understand the position of the body and coordinate movements.
Sympathetic Component: Provides autonomic innervation to structures such as blood vessels and sweat glands in the back, but this component is less directly related to the function of the erector spinae.
Muscle Coordination and Movement:
The erector spinae work in conjunction with other intrinsic muscles, such as the transversospinalis group (semispinalis, multifidus, and rotatores), to stabilize the spine during movement. This coordination is essential for activities requiring balance and posture.
During complex movements, such as twisting or lifting, the spinal nerves provide feedback about the position and tension in the muscles, allowing for adjustments to maintain stability and prevent injury.
Reflex Arcs:
The intrinsic back muscles are also involved in reflex arcs. For example, if the spine is suddenly loaded or if there is a risk of injury, sensory receptors in the muscles and joints can trigger reflex contractions to protect the spine.
