Sensory Systems and Musculoskeletal Anatomy
Sensory Receptors
Sensory receptors are specialized nerve cells that capture stimuli and convert them into nerve impulses. Different types of receptors respond to various stimuli:
- Chemoreceptors: Sensitive to chemical changes.
- Mechanoreceptors: Sensitive to mechanical stimuli like friction and pressure.
- Photoreceptors: Sensitive to light.
- Thermoreceptors: Sensitive to temperature changes.
- Nociceptors: Sensitive to intense pressure, responsible for pain.
Based on their location, receptors are classified as:
- Interoceptors: Located inside the body, collecting information from internal organs.
- Exteroceptors: Located on the body’s surface, collecting external stimuli.
Vision
The eye, responsible for receiving light stimuli, resides in the eye socket. It consists of:
- Eyeball: Composed of three layers: sclera, choroid, and retina. Aqueous humor and vitreous humor fill the eyeball.
- Adnexa: Protective structures that allow eye movement: eyebrows, eyelids, eyelashes, lacrimal apparatus, and eye muscles.
Light enters the eye through the cornea, which directs the rays to a focal point. The pupil controls the amount of light entering. Light passes through the cornea and aqueous humor, reaching the lens. The lens adjusts its curvature to focus the image (accommodation). Photoreceptors on the retina capture the image and convert it into nerve impulses, which are then transmitted to the cerebral cortex via the optic nerve. Human vision is binocular.
Hearing and Balance
The ears are the sensory organs responsible for hearing and balance. They capture sounds and transform them into nerve impulses. The ear is divided into three parts: external, middle, and inner ear.
Touch
Touch receptors are located in the skin, which has two layers:
- Epidermis: The outer layer, formed by layers of epithelial cells containing keratin, which waterproofs the skin.
- Dermis: The inner layer, formed by connective tissue, providing elasticity to the skin. It contains blood vessels and numerous tactile receptors.
Smell
Smell receptors are located in the nasal cavity. The nostrils are lined with a mucous membrane called the pituitary, which has two parts:
- Red pituitary: Occupies the bottom part and contains blood vessels that warm the inhaled air.
- Yellow pituitary: Occupies the upper part and contains olfactory receptors connected to the olfactory bulb.
Taste
Taste receptors are located in the taste buds on the tongue. Sensitive cells within the taste buds detect four basic tastes: sweet, salty, sour, and bitter. Substances must be dissolved to be perceived.
Musculoskeletal System
The musculoskeletal system carries out motor responses produced by the nervous system. It provides support, facilitates internal movements, and enables displacement.
- Skeletal System (Passive): Composed of bones, joints, and ligaments. It supports body movement, provides shape, supports body weight, and protects internal organs.
- Muscular System (Active): Composed of muscles and tendons. It produces movements for vital functions, maintains posture, and allows for facial expressions.
Bones
Bones are living organs that grow and require nourishment. They are composed of calcium, phosphorus, and collagen. The outer layer consists of compact bone tissue, while the inner layer is spongy bone tissue. A thin membrane of connective tissue called the periosteum surrounds each bone.
Joints
Joints are structures where adjacent bones meet, preventing separation. There are three types of joints:
- Stationary Joints: Do not allow movement between bones, such as the skull bones.
- Semi-Mobile Joints: Allow limited movement. Cartilage and ligaments connect the bones, such as the intervertebral discs.
- Mobile Joints: Allow a wide range of motion. Articular cartilage covers the bone ends, enclosed by a joint capsule and ligaments. Synovial fluid lubricates the joint.
Muscles
Muscles are made up of elongated cells called muscle fibers. They contract and relax, changing their length and enabling movement. There are three types of muscles:
- Smooth Muscle: Slow, involuntary contractions.
- Cardiac Muscle: Rapid, involuntary contractions.
- Skeletal Muscle: Rapid, voluntary movements. Part of the locomotor apparatus.
Skeletal muscle fibers are wrapped in endomysium, grouped into bundles surrounded by perimysium. Muscles are categorized by shape (annular, flat, orbicular, fusiform) and function (flexors, extensors, abductors, adductors, pronators, supinators, elevators, depressors, sphincters, dilators).
Common Musculoskeletal Injuries
- Fractures: Broken bones, which can be split or splintered.
- Sprains and Strains: Injuries involving inflammation. Sprains affect ligaments, while strains affect muscles and tendons.
- Dislocations: Displacement of a bone from its normal position in a joint.
- Muscle Contractures: Involuntary and sustained muscle contractions due to overuse.
Injury Prevention
- Regular Exercise: Strengthens muscles, joints, and ligaments.
- Balanced Diet: Calcium, phosphorus, and vitamin D contribute to bone health.
- Proper Footwear: Supports the foot’s arch and distributes body weight.
- Correct Posture: Proper posture protects the spine.
- Avoid Excessive Weight: Carrying heavy backpacks can lead to spinal curvature.