Human Body Systems: Hearing, Touch, Bones, and Joints Explained

The Human Ear and Hearing Process

The ear consists of three main parts:

• Outer Ear: Formed by the auricle (pinna) and the ear canal. The canal is protected by auditory wax and ends at the eardrum (tympanic membrane).
• Middle Ear: Contains three tiny bones called ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup).
• Inner Ear: The deepest part, formed by the membranous labyrinth, which is contained within the bony labyrinth. Between these two labyrinths is perilymph, and within the membranous labyrinth is endolymph. The membranous labyrinth includes the cochlea (a snail-shaped structure responsible for detecting sounds) and the vestibular apparatus (involved in balance).

How Sound Perception Occurs

When sound waves reach the eardrum, it begins to vibrate. This vibration is transmitted through the ossicles. The stapes then sends this vibration to the oval window, leading to the excitation of certain existing cells that constitute the organ of Corti. This process generates a nerve impulse that travels to the brain, where it is interpreted as sound.

Understanding Body Balance

Balance relies on two different types of information:

• Static Equilibrium (Knowledge of Body Position): This occurs in the utricle and saccule, which contain sensory cells that transmit impulses related to changes in position to the brain.
• Dynamic Equilibrium (Perception of Movement): This is performed by the semicircular canals. When the head moves, the inner ear also moves. However, the endolymph within the semicircular canals remains momentarily motionless, creating a relative movement between it and the existing sensory cells in the vestibular apparatus. This relative movement generates impulses that inform the brain about head motion.

The Skin: Our Organ of Touch

The sense of touch, facilitated by the skin, can perceive various types of information:

• Texture and surface characteristics of objects.
• Pressure, ranging from light touch to intense tactile sensations.
• Heat (temperatures higher than usual).
• Cold (temperatures lower than usual).
• Pain.

Understanding Human Bones

Bones are organs composed of mineral salts (primarily calcium phosphate), which provide their hardness, and organic cells that enable their growth and repair.

Bones are primarily formed by:

• Spongy (Cancellous) Bone Tissue: Characterized by a porous, lattice-like structure with cavities.
• Compact Bone Tissue: Dense, solid, and without visible internal spaces, providing strength and rigidity.

Joints: Connecting Bones

Joints are the connections between bones. They are classified based on the amount of movement they allow:

• Fixed (Fibrous) Joints: Also known as sutures (e.g., in the skull), these joints allow no movement of the bones.
• Movable (Synovial) Joints: These joints allow significant movement between bones. They contain a lubricating synovial fluid that reduces friction. Ligaments are present to hold the bones together, as seen in the elbow and knee joints.
• Semi-movable (Cartilaginous) Joints: These joints allow limited movement of the bones, as is the case with the vertebrae in the spinal column.