Cell Structure, Function, and Skin & Muscular System Key Terms

Nucleus

The control center containing genetic material, responsible for growth, metabolism, and reproduction.

Mitochondria

The powerplant that breaks down nutrients to produce ATP via cellular respiration.

Ribosomes

Small particle found in the cytoplasm or on the rough ER that assembles amino acids into proteins.

Rough ER

Network covered in ribosomes that modifies and transports proteins.

Smooth ER

Produces lipids, phospholipids, and steroids, and detoxifies harmful substances.

Golgi apparatus

Acts as the packaging and shipping center modifying, sorting, and packaging proteins and lipids for secretion or delivery.

Lysosomes

Garbage disposal containing digestive enzymes that break down waste, old cell parts, or foreign invaders.

Vacuoles

Sacs that store water, nutrients, or waste; large in plants to maintain turgor pressure, smaller in animal cells.

Chloroplasts

A network of fibers that gives the cell its shape, provides mechanical support, and aids in movement.

Cell membrane

Phospholipid bilayer that controls what enters and exits the cells.

Centrioles

Found in animal cells, they assist in organizing microtubules during cell division.

Pinocytosis

Continuously takes in surrounding extracellular fluid and dissolved solutes by invaginating the membrane to form small vesicles.

Receptor-mediated endocytosis

Highly specific process where extracellular molecules bind to specialized receptor proteins on the cell surface.

Pseudopod formation

The extension of cytoplasm, or 'false feet' used by amoebas and white blood cells for movement and feeding.

Transcytosis

An active, energy-dependent (ATP) transport mechanism where macromolecules are engulfed in vesicles on one side of a cell, transported across the cytoplasm, and released on the opposite side.

Keratin

Found in the outermost layer of skin, hair, and nails; it is present in epithelial cells lining many internal organs and glands.

Tight junctions

Form a watertight seal between adjacent cells, preventing leakage of fluids and molecules, particularly in epithelial cell sheets like the gut or bladder.

Adherens junctions

Connect actin filaments between adjacent cells.

Desmosomes

Act like spot welds connecting intermediate filaments of neighboring cells, providing high structural strength to tissues like skin and heart.

Hemidesmosomes

Anchor intermediate filaments of a cell to the basal lamina.

Gap junctions

Forms channels that connect the cytoplasm of adjacent cells, allowing ions, nutrients, and signaling molecules to pass directly.

Plasmodesmata

Specialized channels in plant cells that connect the cytoplasm of adjacent cells, serving a similar function to gap junctions.

Epidermis

Waterproof, topmost layer that provides a protective barrier and skin tone; it contains no blood vessels.

Stratum corneum

Top layer of dead keratin that protects against abrasions and pathogens.

Stratum lucidum

A thin, clear layer found only in the thick skin of palms and soles.

Stratum Granulosum

Where keratinocytes produce keratin and lipids, strengthening the skin.

Stratum Spinosum

Gives the skin strength and flexibility.

Stratum Basale

The deepest layer that produces new keratinocytes and contains melanocytes.

Dermis Layer

Located beneath the epidermis, packed with collagen and elastin, providing strength and elasticity.

Hypodermis

Insulates the body, cushions muscle and bones, and stores energy.

Merkel Discs (Tactile Discs)

Located in the basal epidermis; they are slow-adapting, detecting sustained light touch, edges, and textures.

Meissner's Corpuscles

Found in the upper dermis (dermal papillae), especially in hairless skin; they are rapidly adapting, sensing light touch, vibration, and slipping objects.

Pacinian Corpuscles

Located deep in the dermis or hypodermis; they are rapidly adapting, detecting deep pressure and high-frequency vibration.

Ruffini Endings (Bulbous Corpuscles)

Located in the dermis; they are slow-adapting, responding to skin stretch and sustained pressure.

Free Nerve Endings

Located throughout the epidermis; they detect pain (nociceptors), temperature (thermoreceptors), and light touch.

Arrector pili muscles

A tiny band of smooth muscle that connects the hair follicle to the upper dermis, responsible for causing goosebumps.

Functions of the skeletal system

Support, movement, protection, mineral storage, and blood cell production.

Osteoclasts

Cells that break down bone tissue.

Osteocytes

Mature bone cells that maintain bone tissue.

Osteoblasts

Cells that build new bone tissue.

Fibrous

Immovable or fixed; bones held together by dense connective tissue, such as sutures in the skull.

Cartilaginous

Slightly movable; bones connected by cartilage, like the vertebrae.

Skeletal muscle fibers/cells

Long, cylinder, multinucleated cells that act as the individual contractile units of muscles, responsible for voluntary movement, posture, and heat generation.

Myosin

A motor protein that drives muscle contraction by converting chemical energy ATP into mechanical force. It forms thick filaments in sarcomeres, binding with actin filaments to pull them inward during contraction.

Sarcoplasmic reticulum

A specialized type of smooth endoplasmic reticulum found in muscle cells that acts as the primary storage and release site for calcium ions.

T tubules

Deep invaginations of the sarcolemma that penetrate striated muscle cells, enabling rapid, synchronized contraction.

ACH

Initiates skeletal muscle contraction by transmitting signals from motor neurons to muscle fibers at the neuromuscular junction.

Agonist

Muscle primarily responsible for producing a specific movement at a joint, it contracts and shortens to create the movement.

Antagonist

A muscle that opposes or reverses true action of the agonist, it stretches and yields to movement, but acts to control or stop the motion, preventing injury.

Synergist

Muscles that assist the prime mover (agonist) in performing an action, they help provide additional force, stability, or control, making the movement more efficient.

Hemoglobin

Iron rich protein in RBC that transports O2 from the lungs to tissues and returns carbon dioxide to the lungs.

General characteristics of a red blood cell

Biconcave, lacking a nucleus and organelles to maximize hemoglobin capacity. Lifespan of approximately 120 days.

Rh incompatibility

When Rh negative mother carries a positive baby.

Thalassemia

Inherited blood disorders caused by genetic mutations that reduce the production of normal hemoglobin, leading to fewer RBCs and anemia.

Anemia

Blood condition characterized by insufficient, healthy red blood cells or low hemoglobin, reducing O2 delivery to tissue.

Leukemias

Cancer of the blood and bone marrow, where abnormal, immature white blood cells multiply uncontrollably and crowd out healthy blood cells.

Monocytes

A type of white blood cell that acts as the immune system's first line of defense, fighting infections, destroying germs and repairing tissue by turning into macrophages.

Arrhythmias

Irregular, too fast, or too slow heartbeat caused by faulty electrical signals.

Lub

Heart sound at the start of systole, signaling the closure of atrioventricular (mitral/tricuspid) valves.

Dub

Heart sound at the start of diastole, signaling the closure of semilunar (aortic/pulmonary) valves.

Tunica media

Middle layer of blood vessels, containing smooth muscle and elastic fibers.

Tunica intima

Innermost layer of blood vessels, consisting of endothelial cells.

Tunica externa

Outer layer of blood vessels, providing structural support and protection.

Elastic arteries

Nearest the heart, expands to receive blood from the heart and recoil to maintain blood pressure.

Muscular arteries

Contain more smooth muscles and distribute blood to various parts of the body and control regional blood flow.

Arterioles

Smallest arteries, regulate blood pressure through constriction and dilation, known as resistance vessels.

Venules

Tiny vessels that collect blood from capillaries and merge to form veins.

Interneurons

The most abundant neurons, acting as central, mainly inhibitory 'middlemen' within the central nervous system to connect sensory and motor neurons.

Glial cells

Specialized cells that support, nourish, and protect neurons in the nervous system.

Oligodendrocytes

Create the myelin sheath that insulates axons, significantly speeding up nerve impulse conduction in the brain and spinal cord.

Astrocytes

Star-shaped cells that regulate the chemical environment, provide nutrients, maintain the blood-brain barrier, and support synaptic function.

Neuroglial cells

Non-neuronal support cells in the central and peripheral nervous systems that, unlike neurons, can divide and do not produce electrical impulses.

Microglial cells

The resident immune cells of the CNS constituting 5-10% of brain cells.

Neurolemma

The thin, outermost nucleated cytoplasmic layer of a Schwann cell that surrounds the axons and myelin sheath of peripheral nerve fibers.

Reflex arc

The neural pathway mediating an involuntary near-instantaneous response to a stimulus, essential for protection and homeostasis.

Sciatic nerve

Runs from the lower back through the hips, buttocks, and down each leg, typically caused by nerve compression from a herniated disc or bone spur.

Microglia

Acts as the immune system's first line of defense, removing debris via phagocytosis.

Ependymal cells

Line brain ventricles and produce cerebrospinal fluid (CSF).

Schwann cells

Myelinate axons in the peripheral nervous system (PNS).

Satellite cells

Surround peripheral neuron cell bodies and support their health.

Somatic nervous system

Voluntary control of skeletal muscles.

Autonomic nervous system

Involuntary control of smooth muscle, cardiac muscle, and glands.

Enteric nervous system

The brain of the gut, regulating digestive tract activity.

Preganglionic neuron

Cell body in the CNS; axon extends to an autonomic ganglion.

Postganglionic neuron

Cell body in the ganglion; axon extends to the effector.

Sympathetic division

Key part of the autonomic nervous system responsible for the fight or flight response, preparing the body for stress and action.

Parasympathetic division

Division of the autonomic nervous system that acts as the body's rest and digest system, conserving energy and regulating bodily functions during calm states.

Sympathetic stimulation

Activation of the body's fight or flight response, part of the autonomic nervous system, to handle stress, danger, or exercise.

Acetylcholine

Released by both sympathetic and parasympathetic preganglionic neurons.

Norepinephrine (NE)

Released by sympathetic postganglionic neurons, acting on alpha and beta-adrenergic receptors on target organs.

Alpha receptors

Cause vasoconstriction.

Beta receptors

Manage cardiac stimulation, muscle relaxation, and metabolic function.

Dual innervation

The process where organs receive instructions from both the sympathetic and parasympathetic divisions of the autonomic nervous system.

Exteroceptors

Detect stimuli from the outside world.

Interoceptors

Detect internal stimuli such as blood pressure, pH, oxygen levels, and organ stretch.

Proprioceptors

Located in muscles, tendons, and joints, they provide information on body movement, position, and balance.

Ruffini Endings

Slow-adapting receptors that detect skin stretch and sustained pressure.

Retina

Contains photoreceptors (rods and cones) that convert light into nerve signals

Retinal Pigment Epithelium

Supports the photoreceptors and prevents light scattering

Lens

A transparent structure behind the iris that changes shape to focus light