Chapter 11: Muscular System – Axial and Appendicular Muscles Study Guide

Muscular System: Axial and Appendicular Muscles

Overview

This chapter explores the structure, organization, and function of the muscular system, focusing on both axial and appendicular muscles. Key concepts include muscle attachments, fascicle organization, muscle actions, and the identification and classification of major muscle groups throughout the body.

Muscle Attachments and Organization

Superior (Proximal) vs. Inferior (Distal) Attachments

• Superior (Proximal) Attachment: The end of the muscle that is typically closer to the center of the body or the point of origin. Often remains stationary during contraction.

• Inferior (Distal) Attachment: The end of the muscle farther from the center of the body or the point of insertion. Usually moves during contraction.

• Example: In the biceps brachii, the proximal attachment is at the scapula, and the distal attachment is at the radius.

Organizational Patterns in Muscle Fascicles

• Parallel: Fascicles run parallel to the long axis of the muscle (e.g., sartorius).

• Pennate: Fascicles organized as if part of a large feather. Fibers pull at an angle to the tendon. (e.g., rectus femoris).

• unipennate (on the same side of tendon, extensor digitorum), bipennete (on both side of tendon, most common, rectus femoris), multipennate (branches of tendon within muscle and fascicles on both sides, deltoid)

• Convergent: Fascicles converge from a broad area to a single tendon (e.g., pectoralis major).

• Circular: Fascicles are arranged in concentric rings (e.g., orbicularis oris).

• Additional info: Organizational pattern affects muscle strength and range of motion.

Agonists, Antagonists, and Synergists

• Agonist (Prime Mover): Muscle primarily responsible for a specific movement. Triceps brachii agonist for forearm extension

• Antagonist: Muscle that opposes the action of the agonist. Biceps brachii is antagonist for forearm extension

• Synergist: Muscle that assists the agonist in performing its action.

• Example: During elbow flexion, biceps brachii is the agonist, triceps brachii is the antagonist, and brachialis annd biceps brachii acts as a synergist.

Muscle Naming and Classification

Characteristics Contributing to Muscle Names

• Action: Indicates the movement produced (e.g., flexor, extensor, flexor digitorium longus will flex digits).

• Body Region: Location in the body (e.g., brachii for arm, rectus femoris near femur)

• Attachments: Points of origin/insertion (e.g., sternocleidomastoid).

• Orientation of Fibers: Direction of muscle fibers (e.g., rectus for straight, rectus abdominis).

• Shape: Physical shape (e.g., deltoid for triangular, abductor pollicis).

• Size: Relative size (e.g., maximus for largest).

• Number of Heads: Number of tendons of origin (e.g., biceps for two heads, triceps has 3 heads).

Examples of Muscle Names

• Action: Flexor carpi radialis (flexes wrist).

• Region: Tibialis anterior (located on the anterior tibia).

• Attachments: Sternocleidomastoid (attaches to sternum, clavicle, and mastoid process), intercostal, subscapularis, fibularis longus, zygomaticus major

• Orientation: Transversus abdominis (fibers run transversely). Rectus abdominis, rectus= straight, obilique, orbicularis

• Shape: Trapezius (trapezoid-shaped), longus, brevis, deltoid, quadratus (rectangle)

• Size: Gluteus maximus (largest gluteal muscle). Pectoralis major,

• Heads: Triceps brachii (three heads), biceps brachii, quadriceps femoris (bk of calf)

Muscles of the Head and Neck

Facial Expression Muscles (11.1 table it’s more than just these muscles)

• Include orbicularis oculi blink eye, orbicularis oris mouth, zygomaticus major smile, frontalis, corrugating supercilii (eyebrows together) and buccinator.

• Responsible for movements such as smiling, frowning, blinking, and puckering lips.

Extrinsic Muscles of the Eye: insert onto the outer surface of the eye and moves it.

4 rectus and 2 oblique 11.2 table

Six muscles:

• superior rectus, pulls eye superior and medial. CN III

• lateral rectus, pulls eye laterally, CN VI, 6

• medial rectus, pulls the eye laterally, CN III

• inferior rectus, pulls eye inferior and media, CN III

• superior oblique, pulls eye superior and lateral, CN IV, 4

• inferior oblique. pulls eye inferior and lateral, CN III

• Control eye movement in various directions.

Innervation of Extrinsic Eye Muscles

• Three cranial nerves: Oculomotor (III), Trochlear (IV), Abducens (VI).

• Each nerve innervates specific eye muscles.

Muscles of Mastication

• Masseter, most powerful, pulls and elevate mandible anteriorly

• Temporalis elevate and pulls mandible posteriorly

• medial pterygoid, lateral pterygoid. Protraction and side to side movement of mandible

• Responsible for movements of the mandible: elevation, depression, protrusion, and lateral movement.

Muscles of the Tongue

• Intrinsic muscles: Change the shape of the tongue.

• Extrinsic muscles: Move the tongue in various directions (e.g., genioglossus, hyoglossus, styloglossus, palatoglossus).

Muscles of the Pharynx

• Primary muscles: superior, middle, and inferior pharyngeal constrictors.

• Function in swallowing by constricting the pharynx.

Suprahyoid and Infrahyoid Muscles

• Suprahyoid: Located above the hyoid bone; elevate the hyoid and larynx (e.g., digastric, mylohyoid).

• Infrahyoid: Located below the hyoid bone; depress the hyoid and larynx (e.g., sternohyoid, omohyoid).

Neck Muscles

• Anterolateral: Flex the neck (e.g., sternocleidomastoid).

• Posterior: Extend the neck (e.g., splenius capitis).

Muscles of the Back and Trunk

Deep Back Muscles

• Move and stabilize the vertebral column (e.g., erector spinae group).

Muscles of Respiration

• Diaphragm: Main muscle of inspiration.

• Intercostal muscles: Assist with breathing by moving the rib cage.

Muscles of the Abdominal Wall

• Include rectus abdominis, external oblique, internal oblique, transversus abdominis.

• Function in trunk movement and abdominal compression.

Muscles of the Pelvic Region

Pelvic Floor Muscles

• Support pelvic organs and control openings of the urethra and anus.

Perineum Boundaries

• Diamond-shaped area between the thighs, bounded by pubic symphysis, ischial tuberosities, and coccyx.

Muscles of the Pectoral Girdle and Upper Limb

Thoracic Muscles Moving the Pectoral Girdle

• Anterior: Pectoralis minor, serratus anterior.

• Posterior: Trapezius, rhomboids, levator scapulae.

Muscles Acting on the Arm (Glenohumeral Joint)

• Include deltoid, pectoralis major, latissimus dorsi, teres major.

• Actions: extension, flexion, adduction, abduction.

Rotator Cuff Muscles

• Four muscles: supraspinatus, infraspinatus, teres minor, subscapularis.

• Stabilize the shoulder joint and assist with rotation.

Arm Compartments

• Anterior compartment: Flexes the forearm (e.g., biceps brachii).

• Posterior compartment: Extends the forearm (e.g., triceps brachii).

Forearm Muscles: Pronation and Supination

• Pronation: Pronator teres, pronator quadratus.

• Supination: Supinator, biceps brachii.

Forearm Muscles Moving Wrist, Hand, and Fingers

• Anterior: Flexor carpi radialis, flexor digitorum superficialis.

• Posterior: Extensor carpi ulnaris, extensor digitorum.

Intrinsic Muscles of the Hand

• Responsible for fine motor movements of the fingers and thumb.

Muscles of the Lower Limb

Thigh Muscles Moving the Hip Joint

• Include iliopsoas, adductors, gluteus maximus, gluteus medius.

• Actions: flexion, extension, abduction, adduction, rotation.

Gluteal Region Muscles

• Include gluteus maximus, gluteus medius, gluteus minimus.

• Responsible for movement and stabilization of the hip.

Thigh Muscles Moving the Knee Joint

• Anterior compartment: Quadriceps femoris (extends knee).

• Posterior compartment: Hamstrings (flex knee).

Leg Compartments and Actions

• Anterior: Dorsiflexion of foot (e.g., tibialis anterior).

• Lateral: Eversion of foot (e.g., fibularis longus).

• Posterior: Plantarflexion of foot (e.g., gastrocnemius).

Muscle Groups and Actions

• Each compartment contains muscles with similar actions and innervation.

Summary Table: Muscle Compartments and Actions

Region	Compartment	Main Muscles	Primary Action
Arm	Anterior	Biceps brachii, brachialis	Flexion of forearm
Arm	Posterior	Triceps brachii	Extension of forearm
Thigh	Anterior	Quadriceps femoris	Extension of knee
Thigh	Posterior	Hamstrings	Flexion of knee
Leg	Anterior	Tibialis anterior	Dorsiflexion of foot
Leg	Lateral	Fibularis longus	Eversion of foot
Leg	Posterior	Gastrocnemius, soleus	Plantarflexion of foot

Key Equations

• Muscle Force Equation:

$F = m \cdot a$

• Torque Produced by Muscle:

$\tau = F \cdot r$

• Additional info: These equations relate to the mechanical principles of muscle contraction and movement.