Muscular System PowerPoint AS111

Muscular System - AS111 Anatomy & Physiology

Basic Functions of the Muscular System

• Movement
  • Muscles enable movement by using bones as levers, allowing mobility and manipulation.
• Heat Production
  • Skeletal muscles generate heat through shivering when body temperature drops, helping to warm the body.
• Glucose Storage
  • Unused glucose is converted into glycogen and stored in muscles and the liver for later use.

Terminology

• Tendon
  • Definition: A cord of connective tissue that attaches muscle to bone.

Muscle Types

• Agonist
  • Defined as "prime movers," these are the muscles directly responsible for producing the desired action during movement.

Basic Muscle Movements

• Flexion
  • The act of bending at a joint (or spine) resulting in a decrease of the angle of the joint.
• Supination
  • The action of turning the palm upwards.

Types of Muscle

Skeletal Muscle

• Characteristics
  • Striated appearance
  • Multinucleated
  • Exhibits extensibility and elasticity
• Functions
  • Provides motion
  • Maintains posture
  • Generates heat
• Control
  • Skeletal muscles are controlled consciously, moving the bones of the skeleton.
• Structure
  • Muscle fibers are arranged in bundles surrounded by connective tissues; these fibers contain threads known as myofibrils.
• Cellular Components
  • Sarcoplasm holds the inside of the muscle cell together, while the outer layer is the epimysium (covering).

Skeletal Muscle Attachment

• Tendons
  • Connective tissue bands that attach muscles to bones.
• Aponeuroses
  • Definition: A sheet of pearly white fibrous tissue that acts in place of a tendon for flat muscles with a wide attachment area.

Important Skeletal Muscles

• Muscles of the Head, Neck, and Shoulders
  • Masseter Muscle: Main muscle of chewing
  • Temporal Muscle: Involved in mouth closure
  • Trapezius Muscle: Elevates the front limb
  • Latissimus Dorsi Muscle: Adducts the front limb and pulls it caudally
  • Deltoids: Primary shoulder muscle, comprised of three parts, responsible for flexing and abducting the arm.
• Muscles of Respiration
  • Diaphragm: Main muscle of respiration
  • External Intercostal
  • Internal Intercostal
• Muscles of the Abdomen
  • External Abdominal Oblique
  • Internal Abdominal Oblique
  • Transversus Abdominus
  • Rectus Abdominus
  • Linea Alba: Connective tissue, not a muscle; common site for surgical incisions.
• Muscles of the Front Limb
  • Supraspinatus Muscle: Extends the shoulder
  • Infraspinatus Muscle: Assists with shoulder flexion
  • Triceps Brachii Muscle: Extends the forearm
  • Brachialis Muscle: Advances the forelimb and extends the shoulder.
• Superficial Muscles of the Hind Leg
  • Gluteals: Extends the hip
  • Sartorius: Flexes the hip and knee joint
  • Semimembranosus: Extends the hip and flexes the knee
  • Biceps Femoris: Extends the hip and flexes the knee
  • Semitendinosus: Flexes the knee.
• Hamstring Muscles
  • Includes semimembranosus, biceps femoris, and semitendinosus; crucial for running and jumping and prone to injury in active animals.
• Deep Muscles of the Hind Leg
  • Rectus Femoris
  • Vastus Lateralis: Extends the knee
  • Cranial Tibial: Flexes the tarsus and rotates the paw laterally
  • Adductor: Adducts and extends the hip
  • Gastrocnemius: Extends the tarsal joint.
• Medial Muscles of the Hind Leg
  • Gracilis: Adduction of the limb
  • Semitendinosus
  • Sartorius: Also flexes the hip and knee.

Cardiac Muscle

Type 2

• Characteristics
  • Striated appearance
  • Involuntary control
  • Comprises intercalated disks that facilitate communication between cells
  • Mononucleated cells
• Location
  • Found only in the heart, performing autonomously without external nervous stimulation.

Cardiac Muscles

• Intercalated Disks
  • Edge structures of individual muscle cells that allow impulses to propagate.
• Sinoatrial (SA) Node
  • Acts as the pacemaker of the heart, initiating contractions.
• Purkinje Fibers
  • Special conducting fibers composed of electrically excitable cells, pivotal in heart contraction.

Smooth Muscle

Type 3

• Characteristics
  • Involuntary with a non-striated appearance
  • Mononucleated
  • Elasticity and flexibility.
• Visceral Smooth Muscle
  • Comprising 99% of smooth muscles, found in internal organs.
• Locations
  • Gastrointestinal system (stomach, intestines)
  • Urinary system (bladder)
  • Vascular system (veins, arteries)
  • Found in most internal organs such as liver, pancreas, etc.

Sphincters

• Definition
  • Circular smooth muscles that control entry or exit of materials in the body.
• Types
  • Pyloric sphincter: Prevents intestinal contents from re-entering the stomach.
  • Anal sphincter: Controls bowel movements.
  • Cardiac sphincter: Controls entry of food into the stomach.

Comparison of Muscle Types

Muscle Functioning

• Synaptic Junctions
  • Where motor neurons contact muscle fibers, also known as Neuromuscular Junction. Motor neurons originate in the spine.
• Neurotransmitter Action
  • Acetylcholine is released by motor neurons to initiate muscle contraction; it binds to receptors in the muscle fiber, setting off an Action Potential that depolarizes muscle fibers, releasing calcium to lead to contraction.
• Relaxation Process
  • Achieved by the release of Acetylcholinesterase, which deactivates acetylcholine, allowing the muscle to relax.
• All or None Principle
  • States that each striated muscle fiber cell must be sufficiently stimulated by a nerve in order to contract; if it contracts, it does so maximally, otherwise, it does not contract at all.
• Physiological Responses
  • Rigor mortis occurs due to a lack of ATP following death, preventing calcium pumps from functioning, resulting in muscle stiffness.
  • Abnormal contractions may occur during events such as grand mal seizures causing continuous nerve firing.

Intramuscular Injection

• Definition
  • Injection directly into an animal's muscle, often used for pre-medications or sedating aggressive pets.
• Common Sites for Injection
  • Epaxial or Lumbar muscle is preferred; other sites include the hamstrings (caution with sciatic nerve), and triceps brachii in the shoulder.

Conclusion

• These notes encapsulate the detailed functions, classifications, characteristics, control mechanisms, and implications of the muscular system as discussed in the transcript, providing a comprehensive reference for anatomy and physiology.