Identification and Function of Human Muscles: Anatomy & Physiology I Study Guide

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Muscle Identification and Classification

Introduction to Human Muscles

The human muscular system consists of various muscles that enable movement, maintain posture, and support bodily functions. In Anatomy & Physiology I, students are required to identify major muscles, understand their origins and insertions, and describe their specific actions.

Muscle Naming Conventions: Muscles are named based on location, size, shape, direction of fibers, number of origins, and action.
Key Terms:
- Agonist: The primary muscle responsible for movement.
- Antagonist: Muscle that opposes the action of the agonist.
- Synergist: Muscle that assists the agonist.
- Fixator: Muscle that stabilizes the origin of the agonist.
Examples of Naming:
- Transverse – lying across; crosswise
- Oblique – slanting, diagonal
- Minimus – small
- Longus – long
- Biceps – 2 origins
- Triceps – 3 origins

Muscles of the Face and Neck

Major Muscles and Their Actions

Facial and neck muscles are responsible for facial expressions, mastication, and head movement.

Muscle	Figure Reference	Action
Epicranius (Frontalis)	#1, #20	Raises eyebrows, wrinkles forehead
Occipital	#10, #21	Pulls scalp posteriorly
Orbicularis oculi	#2, #25	Closes eyelids
Orbicularis oris	#6, #28	Closes and protrudes lips
Buccinator	#35	Compresses cheek (as in blowing)
Zygomaticus major and minor	#5 major, #31 major, #32 minor	Raises corners of mouth (smiling)
Masseter	#39	Elevates mandible (chewing)
Temporalis	#38	Elevates and retracts mandible
Platysma		Tenses skin of neck
Sternocleidomastoid	#11, #41	Flexes and rotates head
Sternohyoid	#12, #42, #43, #45	Depresses hyoid bone
Sternocleidomastoid	#11	Flexes neck, rotates head

Muscles of the Back and Thorax

Intrinsic Back Muscles

These muscles stabilize and move the vertebral column.

Erector Spinae Group: Includes Iliocostalis, Longissimus, and Spinalis. Responsible for extension and lateral flexion of the spine.

Thorax and Abdomen Muscles

Muscle	Figure Reference	Action
External intercostal		Elevates ribs during inspiration
Internal intercostal		Depresses ribs during forced expiration
Diaphragm		Prime mover of inspiration; flattens on contraction
Rectus abdominis	#22	Flexes vertebral column, compresses abdomen
External abdominal oblique	#21	Compresses abdomen, flexes and rotates trunk
Internal abdominal oblique		Compresses abdomen, flexes and rotates trunk
Transverse abdominis		Compresses abdomen

Muscles of the Shoulder and Arm

Shoulder Joint Muscles

Muscle	Figure Reference	Action
Deltoid	#18, #7	Abducts arm
Pectoralis major	#20, #8	Flexes, adducts, and medially rotates arm
Latissimus dorsi	#16, #5	Extends, adducts, and medially rotates arm
Teres major	Not labeled, #3	Extends, adducts, and medially rotates arm

Rotator Cuff Muscles

Muscle	Figure Reference	Action
Supraspinatus	#15, #2	Abducts arm
Infraspinatus	#3	Laterally rotates arm
Teres minor	#4	Laterally rotates arm
Subscapularis	#6	Medially rotates arm

Muscles of the Forearm and Hand

Elbow Joint Muscles

Muscle	Figure Reference	Action
Biceps brachii	#25, #9	Flexes elbow, supinates forearm
Brachialis	Not labeled, #10	Flexes elbow
Triceps brachii	#24, #11	Extends elbow
Brachioradialis	#30, #20	Flexes forearm

Forearm and Hand Muscles

Muscle	Figure Reference	Action
Flexor carpi radialis	#13	Flexes and abducts wrist
Flexor carpi ulnaris	#15	Flexes and adducts wrist
Palmaris longus	#14	Flexes wrist
Extensor carpi radialis longus	#26, #19	Extends and abducts wrist
Extensor carpi ulnaris	#16	Extends and adducts wrist
Extensor digitorum	#27, #17	Extends fingers

Additional info: The flexor retinaculum is a fibrous band involved in carpal tunnel syndrome.

Muscles of the Hip, Thigh, Knee, Leg, and Foot

Gluteal Region

Muscle	Figure Reference	Action
Gluteus maximus	#17, #3	Extends and laterally rotates thigh
Gluteus medius	Not labeled, #4	Abducts and medially rotates thigh
Gluteus minimus		Abducts and medially rotates thigh

Anterior and Medial Hip and Thigh

Muscle	Figure Reference	Action
Iliopsoas	#1	Flexes thigh
Tensor fasciae latae	Not labeled, #9	Abducts and medially rotates thigh
Rectus femoris	#32, #11a	Extends knee, flexes thigh
Vastus lateralis	Not labeled, #11c	Extends knee
Vastus medialis	Not labeled, #11b	Extends knee
Vastus intermedius	Not labeled, #11d	Extends knee
Sartorius	#31, #10	Flexes, abducts, and laterally rotates thigh; flexes knee
Adductor longus	#35, #13	Adducts thigh
Adductor magnus	Not labeled, #14	Adducts and medially rotates thigh
Gracilis	#34, #15	Adducts thigh, flexes knee
Pectineus	#33, #12	Adducts and flexes thigh

Posterior Hip and Thigh

Muscle	Figure Reference	Action
Biceps femoris	#36, #18 a,b	Extends thigh, flexes knee
Semimembranosus	#38, #17	Extends thigh, flexes knee
Semitendinosus	#37, #16	Extends thigh, flexes knee

Muscles of the Leg and Foot

Muscle	Figure Reference	Action
Tibialis anterior	#43, #19	Dorsiflexes and inverts foot
Extensor digitorum longus	#42, #21	Extends toes, dorsiflexes foot
Peroneus (fibularis) longus	#45, #22	Plantar flexes and everts foot
Gastrocnemius	#39, #24 a,b	Plantar flexes foot, flexes knee
Soleus	#40	Plantar flexes foot
Calcaneal (Achilles') tendon	#41, #24 d	Attaches gastrocnemius and soleus to calcaneus

Summary Table: Muscle Actions and Locations

The following table summarizes the main muscle groups, their locations, and primary actions.

Region	Muscle Group	Primary Action
Face/Neck	Facial muscles, Sternocleidomastoid	Facial expression, head movement
Thorax/Abdomen	Intercostals, Abdominals	Breathing, trunk movement
Shoulder/Arm	Deltoid, Rotator cuff, Biceps, Triceps	Arm abduction, rotation, flexion, extension
Forearm/Hand	Flexors, Extensors	Wrist and finger movement
Hip/Thigh	Gluteals, Quadriceps, Hamstrings	Thigh movement, knee extension/flexion
Leg/Foot	Tibialis anterior, Gastrocnemius, Soleus	Foot movement, walking

Key Concepts and Equations

Muscle Contraction: Muscles contract via the sliding filament mechanism, where actin and myosin filaments slide past each other.
Equation for Muscle Force:

Where F is force, m is mass, and a is acceleration. This basic physics equation applies to muscle-generated force in biomechanics.

Additional Info

Muscle models in lab may use different figures for head, torso, arm, and leg muscles. Refer to the provided figure numbers for identification.
Some muscles (e.g., intrinsic back muscles) may not be visible on models and require diagram study.
Be specific when describing muscle actions (e.g., "knee flexion" rather than just "flexion").