Chapter 5 (3)

• Nervous and Muscular Tissues are known as Excitable Tissues. Excitability means the ability to respond to stimuli by changing membrane potential, and it is developed to the highest degree in nervous and muscular tissues.
• Membrane potential is the electrical charge difference (voltage) that occurs across the cell membrane. In nerve cells, changes in voltage result in rapid transmission of signals to other cells. In muscle cells, changes in voltage result in the contraction/shortening of the cell.
• Nervous tissues are specialized for communication by electrical and chemical signals. There are Neurons, Neuroglia (also known as glial cells that are the dotted nucleus-looking things), Neurosoma, Dendrites, and Axons.
• Neurons (nerve cells) detect stimuli, respond quickly, and transmit coded information rapidly to other cells. Neuroglia (glial cells) protect and assist neurons, and are the “housekeepers” of the nervous system.
• The 3 parts of the Neuron are: The Neurosoma, the Dendrites, and the Axon.
• Neurosoma (cell body) houses the nucleus and other organelles; it controls protein synthesis. Dendrites are short, branched processes that receive signals from other cells and transmit messages to the neurosoma. Axon (nerve fiber) sends outgoing signals to other cells, and it can be more than a meter long!
• Muscular tissue are elongated cells that are specialized to contract in response to stimulation. They create movements involved in body and limb movement, digestion, waste elimination, breathing, speech, and blood circulation. Their Primary job is to exert physical force on other tissues and organs and they are an important source of body heat.
• There are three types of muscle/muscle tissues: Skeletal, cardiac, and smooth muscles.
• Skeletal muscles are made of muscle fibers—long thin cells. Most skeletal muscles attach to bone. They have striations that alternate between dark and light bands, And they are voluntary(conscious control over skeletal muscles).
• Cardiac muscle is limited to the heart wall. Cardiomyocytes are short and branched with one centrally located nucleus (and they resemble a bunch of eyes). Intercalated discs join cardiomyocytes end-to-end(This provides electrical and mechanical connection). And these muscles are striated and involuntary (not under conscious control)
• Smooth muscles are made of fusiform cells that lack striations. These cells are relatively short and have one central nucleus. They are involuntary. And most are visceral muscles which means they make up parts of the walls of hollow organs (e.g. the walls of the intestine).
• Cell/cellular junctions are connections between two cells.
• Tight junctions are like a zipper that interlocks adjacent cells using transmembrane cell-adhesion proteins. They seal off the intercellular space, making it difficult for substances to pass between cells.
• Desmosomes are patches that hold cells together, similar to clothing snaps. They resist mechanical stress and prevent cells from pulling apart. J-shaped proteins arise from the cytoskeleton.
• Hemidesmosomes are half-desmosomes that anchor basal cells of an epithelium to an underlying basement membrane. This structure ensures that the epithelium does not easily peel away from underlying tissues.
• A Gap Junction, which is a type of intercellular junction, is formed by ring-like structures called Connexons. A Connexon is made up of six transmembrane proteins that are arranged in a circular pattern around a water-filled pore. This channel allows ions, nutrients, and other small solutes to pass between cells. Gap junctions are typically found in cardiac and smooth muscle, embryonic tissue, as well as the lens and cornea of the eye.
• Collagen is a protein fiber that provides strength and flexibility to connective tissues such as skin, tendons, ligaments, cartilage, bone, and blood vessels. It consists of three polypeptide chains twisted into a triple helix shape.