Study Notes on Locomotion and Support Systems

39.1 Diversity of Skeletons

• Support Systems for Animals
  • Functions:
  • Provide rigidity, protection, and surfaces for muscle attachment.
  • Range of types from fluid-filled cavities to tough external skeletons and hard skeletons made of bones and cartilage.

Hydrostatic Skeleton

• Functions:
  • Supports body form.
  • Provides resistance for muscle contraction, allowing mobility.
• Examples of organisms:
  • Hydra and planarians use their fluid-filled gastrovascular cavity.
  • Annelids utilize their fluid-filled coelom.
• Muscle Functions:
  • Each compartment comprises its own set of longitudinal and circular muscles that have their own nerve supply.
  • Forward movement is caused by alternating contractions of circular and longitudinal muscles.

## Use of Muscular Hydrostats

• Activities like movement in animals with exoskeletons and endoskeletons.
• The fluid within muscle cells aids in movement.
  • Case Study:
• Movement of an elephant’s trunk is an example of a muscular hydrostat.

39.2 The Human Skeletal System

Functions of the Skeletal System

• Primary Functions:
  • Support the body.
  • Protect vital internal organs.
  • Serve as sites for muscle attachment.
  • Act as storage reservoirs for ions.
  • Produce blood cells.

Bone Growth and Removal

• Process:
  • Cartilaginous structures in early development serve as models for future bones,
  • These models are converted to bone as calcium salts are deposited in the matrix, initiated by cartilage cells followed by bone-forming cells.
  • This process is termed endochondral ossification: the conversion of cartilage to bone that starts at the primary ossification center, where cartilage is broken down, invaded by blood vessels, and transformed by osteoblasts into bone.
  • Secondary ossification centers form, with a cartilaginous growth plate in between allowing for growth.

Key Bone Cell Types

• Osteoblasts:
  • Function: Bone-forming cells that synthesize new matrix.
• Osteoclasts:
  • Function: Bone-resorbing cells that break down bone, remove worn cells, and deposit calcium into the blood, contributing to calcium homeostasis.
• Osteocytes:
  • Mature bone cells originating from osteoblasts that become trapped in the matrix, existing in lacunae within osteons, affecting bone remodeling’s timing and location.

Long Bone Anatomy

• Structure:
  • Medullary cavity at the center, bordered by compact bone on the sides and spongy bone at the ends.
• Compact Bone:
  • Structure is based on osteons (Haversian systems), comprising osteocytes in lacunae surrounded by blood vessels and nerves in a central canal, separated by collagen fibers and mineral matrix.
• Spongy Bone:
  • Runs as a network of bars and plates with irregular spaces, filled with red bone marrow that produces blood cells, assisting in blood oxygen homeostasis through red blood cell generation, and hosting white blood cells for immune response.

The Axial Skeleton

• Components:
  • Consists of the skull, vertebral column, thoracic cage, sacrum, and coccyx.

The Vertebrate Endoskeleton

• Provides a rigid internal structure allowing for growth alongside the organism, supporting the weight of large animals, protecting vital organs, being safeguarded by outer tissues, and permitting complex movements.

Human Skeleton Overview

• Types of Bones:
  • Skull (frontal, zygomatic, maxilla, mandible, parietal, temporal, occipital), Pectoral girdle (clavicle, scapula), Thoracic cage (sternum, ribs, costal cartilages), Pelvic girdle (coxal bones), and limb bones including humerus, ulna, radius, femur, tibia, and others.

Skull Anatomy

• Structure:
  • Comprised of cranial and facial bones, with prominent facial bones: mandible, maxillae, zygomatic bones, nasal bones.
• Foramen Magnum:
  • An opening at the base of the skull where the spinal cord connects to the brain (becomes the brainstem).

The Vertebral Column

• Roles:
  • Supports the head and trunk while protecting the spinal cord and surrounding nerves.
• Segments:
  • Cervical (neck), Thoracic (thorax), Lumbar (lower back), Sacral (sacrum), Coccyx (tailbone).
• Intervertebral Disks:
  • Composed of fibrocartilage, act as padding allowing movement and shock absorption as vertebrae bend.

The Rib Cage

• Comprises thoracic vertebrae, ribs, costal cartilages, and the sternum, protecting the heart and lungs.
• Rib Functionality:
  • Flexible structure that expands and contracts during breathing. Contains 12 pairs of ribs classified as:
  • True Ribs: 7 pairs directly attaching to the sternum.
  • False Ribs: 5 pairs that do not connect directly (three pairs attach via common cartilage; two pairs are floating ribs).

The Appendicular Skeleton

• Composed of bones in the pectoral girdle and pelvic girdle, supporting limbs specialized for flexibility (upper) and strength (lower).
• Pectoral Girdle Components:
  • Connects arms and hands, supporting mobility with bones like clavicle and scapula.
  • Upper limb structure includes humerus, ulna, radius, carpals, metacarpals, and phalanges.

Pelvic Girdle and Lower Limb

• Pelvic Girdle:
  • Ono two coxal (hip) bones anchoring to the sacrum form the pelvic cavity, transmitting weight to the legs. Specialized for strength.
• Lower Limb Composition:
  • Includes femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Classification of Joints

• Fibrous Joints:
  • Immovable joints found between cranial bones.
• Cartilaginous Joints:
  • Slightly movable joints located between vertebrae.
• Synovial Joints:
  • Freely movable joints where bones are separated by a cavity and bound by ligaments.
• Types of Synovial Joints:
  • Hinge Joints: Allow movement in one direction (e.g., knee, elbow).
  • Pivot Joint: Allows rotary movement (e.g., joint between the first two cervical vertebrae).
  • Ball-and-Socket Joint: Allows movement in all planes (e.g., hip joint).
  • Arthritis: Joint inflammation treatable with anti-inflammatory medication.

39.3 The Muscular System

Muscle Characteristics

• Composition:
  • Muscles are made of contractile tissue that alters length through contraction and relaxation.
  • Most animals rely on muscles for movement; few are nonmotile (primarily aquatic).
• Muscle Tissue Types:
  • Smooth Muscle: Involuntary muscle found in internal organs.
  • Cardiac Muscle: Involuntary muscle specific to the heart.
  • Skeletal Muscle: Voluntary muscle responsible for body movement.

Macroscopic Muscle Anatomy and Physiology

• Skeletal Muscles:
  • Attached to bones via tendons, arranged in pairs that work antagonistically (one flexes while the other extends).
  • Muscle tone is present at rest (minimal contraction) crucial for posture.

Microscopic Muscle Structure

• Skeletal Muscle Fiber:
  • Composed of bundles of myofibrils, each myofibril consists of repeated units called sarcomeres, the primary contractile units, which include:
  • Thick Filaments: Composed of myosin.
  • Thin Filaments: Composed of actin.
  • The Sliding Filament Model describes how actin slides past myosin for contraction to occur.
  • Muscle contraction process requires ATP and calcium.

Muscle Contraction Mechanism

• ATP Role:
  • Provides energy for muscle contraction through ATP hydrolysis, while creatine phosphate regenerates ATP.
• Neuromuscular Junction:
  • Connection between motor nerve fibers and muscle fibers, where acetylcholine (ACh) is released to initiate muscle contraction.
• Calcium Ions:
  • Critical for muscle contraction, facilitating the sliding of actin and myosin filaments and ultimately leading to movement.
  • Calcium binds to troponin, shifting tropomyosin to expose myosin-binding sites.
• Power Stroke:
  • Myosin heads pull on actin filaments, leading to shortening of the sarcomere, producing movement.

Components of Muscle Contraction

• Various components involved in contraction:
  • Actin filaments slide past myosin based on calcium’s presence and ATP’s hydrolysis which drives the binding, pulling, and resetting cycle of myosin heads to enhance contraction efficiency.