Detailed Notes on Human Physiology: Locomotion and Movement

1. Skeletal System:

a. Organization of the Skeletal System:

• The human skeletal system consists of 206 bones that provide structural support, protection, and facilitate movement.
• The bones are organized into two main divisions: the axial skeleton and the appendicular skeleton.

b. Types of Bones:

• Long bones: These are long and cylindrical in shape, such as the femur (thigh bone) and humerus (upper arm bone).
• Short bones: These are roughly cube-shaped, such as the carpal bones in the wrist.
• Flat bones: These are thin and flattened in shape, such as the sternum and scapula (shoulder blade).
• Irregular bones: These have an irregular shape, such as the vertebrae in the spine.
• Sesamoid bones: These are small, round bones that are embedded within tendons, such as the patella (kneecap).

c. Structure and Functions of the Axial and Appendicular Skeleton:

Axial Skeleton:

• The axial skeleton consists of the skull, vertebral column, and ribcage.
• It protects vital organs, supports the head, and facilitates movement.

Appendicular Skeleton:

• The appendicular skeleton includes the bones of the limbs (arms and legs) and the shoulder and hip girdles.
• It provides support and allows for a wide range of movements.

d. Joints: Types, Structures, and Functions:

Types of Joints:

• Fibrous joints: These joints are tightly connected by fibrous connective tissue, allowing little or no movement. Example: Sutures between skull bones.
• Cartilaginous joints: These joints have a layer of cartilage between the bones, allowing limited movement. Example: Joints between vertebrae.
• Synovial joints: These joints are freely movable and have a joint cavity filled with synovial fluid. Examples: Knee, shoulder, and hip joints.

Structures of Synovial Joints:

• Synovial membrane: Lines the joint cavity and produces synovial fluid.
• Articular cartilage: Covers the ends of bones within the joint, reducing friction during movement.
• Synovial fluid: Lubricates the joint, reducing friction and providing nutrients to cartilage.
• Ligaments: Tough connective tissue bands that connect bones and provide stability to the joint.
• Tendons: Connect muscles to bones, transmitting forces generated by muscle contractions.

2. Muscle Structure and Contraction:

a. Ultrastructure of Skeletal Muscles:

• Skeletal muscles are striated, meaning they have a repeating pattern of light and dark bands.
• Each muscle cell (myocyte) contains numerous myofibrils, which are bundled together by connective tissue.
• Myofibrils are made up of smaller units called sarcomeres, which are the basic units of muscle contraction.
• Sarcomeres consist of thick (myosin) and thin (actin) filaments, arranged in a repeating pattern.

b. Mechanism of Muscle Contraction (Sliding Filament Theory):

• Muscle contraction occurs when thick and thin filaments slide past each other, causing sarcomeres to shorten.
• The sliding movement is initiated by the release of calcium ions from the sarcoplasmic reticulum, which triggers the binding of calcium to troponin, a protein associated with actin filaments.
• This allows myosin heads to bind to actin filaments, forming cross-bridges.
• The myosin heads undergo power strokes, pulling the thin filaments towards the center of the sarcomere, resulting in muscle contraction.
• The energy for muscle contraction comes from ATP hydrolysis by myosin.

c. Role of ATP and Calcium in Muscle Contraction:

• ATP is required for the myosin heads to bind to actin and undergo power strokes.
• Calcium ions act as triggers for muscle contraction by binding to troponin and allowing the cross-bridge formation between myosin and actin filaments.

d. Muscle Twitch and Tetanus:

• Muscle twitch refers to a single contraction and relaxation cycle of a muscle in response to a single stimulus.
• Tetanus occurs when a muscle contracts continuously without relaxing due to rapid and repeated stimulation.

3. Types of Muscle Fibers:

• Slow-twitch fibers (Type I): These are fatigue-resistant and have a relatively slow contraction speed. They are involved in sustained, low-intensity activities like endurance exercises.
• Fast-twitch oxidative fibers (Type IIA): These are also fatigue-resistant but have a faster contraction speed than Type I fibers. They are involved in activities requiring both endurance and speed.
• Fast-twitch glycolytic fibers (Type IIB): These fibers have the fastest contraction speed but are also the most easily fatigued. They are involved in high-intensity, short-duration activities like sprinting.

4. Organization of Skeletal Muscles:

• Motor units: A motor unit consists of a motor neuron and all the muscle fibers it innervates. The size of the motor unit can vary, with larger motor units having more muscle fibers.
• Recruitment: Recruitment refers to the activation of additional motor units to increase the force of muscle contraction. Smaller motor units are recruited before larger ones.
• Skeletal muscle arrangement: Skeletal muscles can be arranged in parallel (more fibers contract simultaneously) or pennate (fibers are arranged diagonally, allowing for greater force production).

5. Joints:

• Synovial joints: These are the most common type of joints and are freely movable. They are classified into several types based on their shape and structure:
  • Ball-and-socket joints: Allow for a wide range of movements, such as the hip and shoulder joints.
  • Hinge joints: Allow only bending and straightening movements, such as the knee and elbow joints.
  • Pivot joints: Allow rotation around a single axis, such as the joint between the first and second cervical vertebrae.
  • Condyloid joints: Allow both bending and straightening and some rotation, such as the wrist and ankle joints.
• Structure of a synovial joint:
  • Articular cartilage: Covers the ends of the bones within the joint to reduce friction during movement.
  • Synovial membrane: Lines the joint cavity and produces synovial fluid.
  • Synovial fluid: Lubricates the joint and provides nutrients to the articular cartilage.
  • Ligaments: Tough connective tissue bands that connect bones and provide stability to the joint.
  • Tendons: Connect muscles to bones, transmitting the forces generated by muscle contractions.

6. Mechanics of Movement:

• Levers: Levers are simple machines that facilitate movement by reducing the amount of force required. The human body uses three classes of levers:
  • First-class levers: These levers have the fulcrum (pivot point) between the force and the load, such as the see-saw. Examples include the head and the spine.
  • Second-class levers: These levers have the load between the fulcrum and the force, such as the wheelbarrow. Examples include the calf muscle and the foot while standing on one leg.
  • Third-class levers: These levers have the force between the fulcrum and the load, such as the tweezers. Examples include the forearm and the elbow joint.
• Calculation of mechanical advantage: The mechanical advantage of a lever is the ratio of the output force (the load) to the input force (the effort). A higher mechanical advantage means that less force is required to move the load.

7. Muscle Mechanics and Energy:

• Work, power, and efficiency of skeletal muscles:
  • Work: The work done by a muscle is the product of the force generated and the distance through which the force is exerted.
  • Power: The power of a muscle is the rate at which work is done, measured in watts.
  • Efficiency: The efficiency of a muscle is the ratio of the work done by the muscle to the total energy consumed by the muscle.
• Factors affecting muscle strength and endurance:
  • Muscle strength is influenced by factors such as muscle size, muscle fiber type composition, and neural factors like motor unit recruitment and synchronization.
  • Muscle endurance is determined by the availability of energy substrates, oxygen supply, and the resistance of muscles to fatigue.
• Fast and slow muscle fibers: Fast-twitch fibers have a higher power output but fatigue quickly, while slow-twitch fibers have a lower power output but are more fatigue-resistant.

8. Posture and Balance:

• Maintaining body posture and equilibrium: The body maintains its upright posture and equilibrium through a combination of sensory input from the proprioceptors, vestibular system, and visual system, and the coordination of various muscles and joints.
• Role of proprioceptors and the vestibular system: Proprioceptors are sensory receptors present in muscles, tendons, and joints, providing information about body position and movement. The vestibular system in the inner ear senses changes in head position and contributes to maintaining balance.

9. Locomotion:

• Different modes of locomotion: Humans use various modes of locomotion, including walking, running, jumping, swimming, climbing, and flying.
• Analysis of gait cycle (stance and swing phases): The gait cycle refers to the sequence of events that occur during one complete step. It consists of the stance phase (foot in contact with the ground) and the swing phase (foot off the ground).
• Factors affecting speed and efficiency of locomotion: Factors such as muscle strength, endurance, coordination, and energy efficiency influence the speed and efficiency of locomotion.

10. Exercise and Muscle Adaptation:

• **Effects of regular exercise on the