Muscle Identification, Structure, and Function: Study Guide for Anatomy & Physiology

Muscle Identification and Classification

Overview

This section provides a comprehensive list of muscles required for identification in Anatomy & Physiology. Students are expected to know the location, origin, insertion, and action of selected muscles, as well as their classification by region.

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point where the muscle exerts its action.

• Action: The movement produced when the muscle contracts.

Muscles of the Head and Neck

• Facial Expression:

  • Frontalis

  • Occipitalis

  • Orbicularis oculi

  • Zygomaticus major and minor

  • Orbicularis oris

  • Buccinator

• Mastication:

  • Masseter

  • Temporalis

• Moves Head and Neck:

  • Sternocleidomastoid

  • Trapezius (upper fibers)

  • Splenius group

Muscles of the Trunk

• Vertebral Column:

  • Erector spinae group

• Respiration:

  • Diaphragm

  • External intercostal

  • Internal intercostal

• Abdominal Wall:

  • Rectus abdominis

  • External oblique

  • Internal oblique

  • Transverse abdominis

  • Linea alba

• Act on Pectoral Girdle:

  • Trapezius (again)

  • Serratus anterior

Muscles of the Upper Limb

• Moves the Arm:

  • Pectoralis major

  • Latissimus dorsi

  • Deltoid

  • Teres major

  • Subscapularis

  • Supraspinatus

  • Infraspinatus

  • Teres minor

• Moves the Forearm:

  • Biceps brachii

  • Brachialis

  • Triceps brachii

• Moves Wrist, Hand, and Digits:

  • Flexor carpi radialis

  • Flexor carpi ulnaris

  • Palmaris longus

  • Flexor digitorum superficialis

  • Extensor carpi radialis longus

  • Extensor carpi ulnaris

  • Extensor digitorum

Muscles of the Lower Limb

• Moves the Thigh:

  • Iliopsoas

  • Adductors

  • Gluteus maximus

  • Gluteus medius

• Moves the Leg:

  • Quadriceps group (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius)

  • Tensor fasciae latae

  • Gracilis

  • Sartorius

  • Hamstrings group (Biceps femoris, Semitendinosus, Semimembranosus)

• Moves Ankle, Foot, and Digits:

  • Tibialis anterior

  • Extensor digitorum longus

  • Fibularis longus

  • Gastrocnemius

  • Soleus

  • Tibialis posterior

  • Flexor digitorum longus

Muscle Structure and Function

Overview

Understanding the microscopic and macroscopic structure of muscle tissue is essential for grasping how muscles contract and produce movement. This section covers the basic anatomy and physiology of skeletal muscle.

• Muscle: A tissue composed of fibers capable of contracting to produce movement.

• Muscle cell/fiber: The basic cellular unit of muscle tissue, also called a myocyte.

• Myofibril: Rod-like units within muscle fibers, composed of repeating sarcomeres.

• Myoglobin: Oxygen-binding protein found in muscle cells.

• Myosin: Thick filament protein involved in muscle contraction.

• Perimysium: Connective tissue surrounding bundles of muscle fibers (fascicles).

• Sarcolemma: The cell membrane of a muscle fiber.

• Sarcomere: The functional contractile unit of a muscle fiber, defined by Z-disks.

• Sarcoplasm: The cytoplasm of a muscle cell.

• Striations: Alternating light and dark bands seen in skeletal muscle due to the arrangement of actin and myosin filaments.

• Z-disks: Structures that define the boundaries of a sarcomere.

Basic Muscle Functions

• Produce movement by contracting and pulling on bones.

• Maintain posture and stabilize joints.

• Generate heat as a byproduct of contraction.

Features of Skeletal Muscles

• Origin

• Insertion

• Action

• Epimysium (outer connective tissue covering)

• Fascicles (bundles of muscle fibers)

• Endomysium (connective tissue surrounding individual muscle fibers)

• Innervation (nerve supply)

• Blood supply

Muscle Naming Conventions

Muscles are named based on characteristics such as size, shape, location, direction of fibers, number of origins, and function.

• Size: Maximus (largest), Minimus (smallest), Longus (long), Brevis (short)

• Shape: Deltoid (triangle), Trapezius (trapezoid)

• Location: Temporalis (temporal bone), Tibialis anterior (front of tibia)

• Direction of fibers: Rectus (straight), Oblique (angled)

• Number of origins: Biceps (two), Triceps (three), Quadriceps (four)

• Function: Flexor, Extensor, Adductor, Abductor

Table: Major Muscles by Region and Function

Region	Muscle Name	Primary Action
Head/Neck	Frontalis	Raises eyebrows
Head/Neck	Masseter	Elevates mandible (chewing)
Trunk	Rectus abdominis	Flexes vertebral column
Upper Limb	Biceps brachii	Flexes forearm
Upper Limb	Triceps brachii	Extends forearm
Lower Limb	Quadriceps femoris	Extends leg at knee
Lower Limb	Gastrocnemius	Plantar flexes foot

Key Equations and Concepts

• Sliding Filament Theory: Muscle contraction occurs as actin and myosin filaments slide past each other within the sarcomere.

• Force of Muscle Contraction: $F = m \cdot a$ Where F is force, m is mass, and a is acceleration. Additional info: This equation is a general physics principle; in muscle physiology, force depends on cross-sectional area and number of fibers recruited.

Example: Biceps Brachii

• Origin: Scapula

• Insertion: Radius

• Action: Flexes forearm at elbow

Example: Gastrocnemius

• Origin: Femur

• Insertion: Calcaneus (via Achilles tendon)

• Action: Plantar flexes foot

Additional info: Students should be able to identify muscles on models and diagrams, and describe their anatomical features and functions.