Muscle Anatomy and Physiology Overview

Overview of Chicken Muscles

Chickens have primarily white muscle fibers.
- These muscle fibers provide strength but lack endurance.
- Chickens are not strong fliers; they can flap their wings but cannot sustain flight.
The muscle that accounts for the chicken's ability to run quickly is the pectoral muscle (breast meat).
Comparison to Human Muscle
- Humans do not have distinct classifications of red and white meat like chickens.
- Muscle histology in humans shows a blend of red, pink, and white fibers.
- Red fibers are associated with endurance (marathon runners).
- White fibers are associated with short-term strength (sprinters).
- Ethical concerns exist regarding muscle sampling from living athletes.

Key arrangements of fascicles in muscles:
- Strap Muscles:
- Fascicles run parallel, resulting in uniform width along the length.
- Example: Sternocleidomastoid (named based on attachment locations).
- Importance of anatomical understanding: knowing bone locations (e.g., sternum, clavicle) is critical for recognizing muscle attachment.

Rectus Muscles:
- Generally have parallel fibers; may often include the term "rectus" in their name (e.g., rectus abdominis, rectus femoris).
Fusiform Muscles:
- Classic shape: wider belly and tapering ends, e.g., biceps brachii has two bellies.
Bipennate Muscles:
- Example: Rectus femoris, having fibers running in two directions.
Circular Muscles (Sphincters):
- Named "orbicularis" indicating circling action, e.g., orbicularis oculi (around the eye).

Muscles must cross at least one joint to cause movement; those that cross two joints can perform complex actions.
- Example: Sartorius muscle, crossing both the hip and knee joints.
Old terminology (origins and insertions) is shifting toward "attachments."
- Proximal attachment generally refers to the muscle's origin, while distal refers to the insertion.
Knowing muscle function and action is essential for identifying muscles by their names:
- Prime movers/Agonists: Muscles that mainly produce a movement.
- Antagonists: Muscles that oppose the action of prime movers.
- Synergists: Assist prime movers in their actions.
- Approximately 700 muscles exist in the human body, which can be reduced to about 350 pairs due to bilateral symmetry.

Rectus: Generally indicates fibers oriented up and down.
Transverse: Refers to horizontal orientation.
Oblique: Indicates slanted fibers.
- External obliques have fibers traveling inferior medially, while internal obliques travel superior medially.

Muscle names often indicate location (e.g., frontalis is located in the forehead area, tibialis anterior is the front of the tibia).
Size descriptors in muscle names:
- Maximus: Largest muscle.
- Medius: Middle size.
- Minimus: Smallest muscle.
Additionally, terms such as longus and brevis denote length (long and short, respectively), and names may reflect the number of attachment heads (e.g., biceps, triceps).

Flexors: Decrease the angle between attachment points (e.g., flexor carpi radialis).
Extensors: Increase the angle between attachment points (e.g., extensor carpi radialis longus).
Abductors: Move a limb away from the midline (e.g., abductor pollicis).
Adductors: Move a limb toward the midline.
Levator: Lifts a structure (e.g., levator scapulae).
Depressor: Lowers a structure.

Understanding muscle fiber arrangements, actions, and attachments enhances the ability to correctly name and locate muscles.
The study of muscle anatomy serves as a foundational aspect of understanding human physiology and anatomy in more advanced fields.