Biology Chapter on Nervous and Epithelial Systems

Stem Cells and Tissues

• Stem cells are undifferentiated cells capable of differentiating into specialized cell types.
• Stem cells have the ability to self-renew almost unlimitedly.
• Stem cells can differentiate into multiple cell types.
• Totipotent stem cells can form any cell type in the developing embryo and placenta. They can replicate indefinitely without losing potency.
• Pluripotent stem cells can differentiate into almost any cell type in the body, but their potency diminishes over time. They can only become certain types of cells.
• Multipotent stem cells can self-renew for long periods and differentiate into specialized cells with specific functions. Their differentiation abilities are limited.
• Induced pluripotent stem cells are biologically engineered to resemble pluripotent stem cells.

Types of Stem Cells

• Totipotent stem cells are formed soon after egg and sperm fuse. They have an almost unlimited differentiation capacity without losing potency and are derived from early embryonic tissue.
• Pluripotent stem cells can differentiate into nearly any cell type. They are derived from the inner cell mass of early embryos. Also, they have huge therapeutic value and limited availability.

Ethical Considerations

• Multipotent stem cells have very limited differentiation capacity but are advantageous because stem cells can be isolated directly from adult tissue. Obtaining stem cells from adult tissue is less difficult than obtaining them from embryos.
• Haematopoietic stem cells are found in bone marrow and differentiate into all different cell types in the blood.
• Induced pluripotent stem cells are derived from adult tissues, like fibroblasts, and can be grown in a mix of growth factors, allowing them to turn into pluripotent stem cells.
• IPSCs have similar functions to embryonic stem cells but without ethical issues. They represent a significant therapeutic value.

Tissues

• A tissue is a group of cells that function together.
• Tissues perform specific functions in a multicellular organism.
• There are four main types: connective, epithelial, muscle, and nervous
• Connective tissue provides support and connects different tissues and organs. This tissue type is found throughout the body.
• Epithelial tissue covers surfaces, lines cavities, and forms glands. This tissue type is found on the surface and lining of body parts and organs.
• Muscle tissue allows movement in the body. Different types of muscles are responsible for movements like voluntary and involuntary motions.
• Nervous tissue transmits and processes information throughout the body. The nervous system is responsible for how the body functions from a cellular level.

Epithelial Tissues

• Epithelial tissue forms sheets or structures that cover body surfaces, line body cavities, and form glands.
• Functions of epithelial tissue include protection, secretion, absorption, transport, filtration, and detection of sensations.
• Types of epithelial tissues include simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal, and pseudostratified columnar.

Connective Tissues

• Connective tissue cells are scattered throughout an extracellular matrix.
• Connective tissue supports and connects different tissues and organs.
• Types of connective tissue include loose connective tissue, dense connective tissue, cartilage, bone, and blood.
• Loose connective tissue supports organs and is found beneath epithelial tissues. It contains collagen protein for support.
• Dense connective tissue has densely packed collagen fibers, giving it strength and flexibility, and is found in ligaments and tendons
• Cartilage provides cushioning and support and is found in joints.
• Bone is a hard material that supports and protects the body.
• Blood is a fluid connective tissue that transports substances throughout the body.

Glands

• Glands are formed via infolding of epithelial tissues.
• Exocrine glands secrete their products into ducts (tubular or acinar).
• Endocrine glands secrete their products directly into the bloodstream.

Muscle Tissues

• Muscle tissue is comprised of muscle cells and enables movement of the body.
• The three main types of muscle are skeletal, cardiac, and smooth.
• Skeletal muscles are voluntary and attached to bones. Cardiac muscle is involuntary and found in the heart. Smooth muscle is involuntary and found in internal organs.
• Skeletal muscle cells are striated. Cardiac muscle cells are connected via intercalated discs, a type of junction. Smooth muscle cells are not striated.

Nervous Tissues

• Nervous tissues transmit information to all parts of the body.
• The basic cells of nervous tissue are neurons, which transmit electrical signals.
• Many cells help with support of the nervous system. Glial cells include astrocytes, microglia, oligodendrocytes, and ependymal cells.

Nervous System

• The peripheral nervous system (PNS) includes nerves and ganglia.
• The spinal cord is part of the central nervous system (CNS).
• The central nervous system (CNS) includes the brain and spinal cord.
• The peripheral nervous system (PNS) carries sensory information from the body to the central nervous system and transmits motor signals from the CNS to effectors.
• Neurons consist of a cell body, dendrites, and an axon.
• Neuron classifications are based on function and morphology. The morphology of a neuron includes multipolar, bipolar, and unipolar types.