Types of Cells and Tissues - AP Biology

The sarcoplasm in muscle cells is comparable to the cytoplasm in other types of cells. The sarcoplasm is specialized in the high amount of myoglobin present. Its specialized regulation of calcium ion concentrations controls muscle contractions.

The resting potential of a cell is the relatively static membrane potential that serves as the baseline voltage of a cell, which is about in neurons. The resting potential stands in opposition to the action potential.

The threshold potential of a cell is a specific membrane potential that is needed in order to initiate action potential. Therefore, threshold potential precedes action potential. Note that reaching the threshold potential triggers a positive feedback loop, causing more sodium to rush into the cell, further depolarizing the membrane potential.

The axon hillock is the area of a neuron that connects the soma and axon. This is also the area of the of the neuron that "decides" whether an action potential would be initiated or not, depending on whether the cell has reached threshold or not.

In the presynaptic terminal, the action potential causes an influx of calcium. Rising calcium levels stimulates exocytosis of neurotransmitters, which bind to post-synaptic receptors. Unused neurotransmitters are recycled by the pre-synaptic cell or degraded in the synaptic cleft.

The connective tissue is found throughout the body in between other tissues and cell types. Connective tissue functions to both connect and separate the different tissue types.

Connective tissue has three main components: fibers, ground substance, and cells (fibroblasts, adipocytes, macrophages, mast cells, and leukocytes). Typically, connective tissue contains a relatively low proportion of cells, and a very high proportion of ground substance and fibrous proteins, such as collagen. Blood and lymph is sometimes considered a component of connective tissue as well.

Cells are also a critical component of connective tissue and are typically suspended in the ground substance. Cells that are a part of connective tissue include fibroblasts (cells that produce fibers), mast cells (involved in histamine-mediated inflammatory response), and adipocytes (fat cells). Staining methods can show these cell types within the connective tissue. Other connective tissue cells include osteocytes (bone cells), and chondrocytes (cartilage cells).

In connective tissues, ground substance is an extracellular matrix that suspends and supports cells. Ground substance does not contain fibers and is composed mostly of water and glycoproteins.

The connective tissue includes fibers that act as a matrix and support structure for cells suspended in ground substance. These fibers are categorized as collagenous fibers, elastic fibers, and reticular fibers. Collagenous fibers are the most abundant in the extracellular matrix, comprise tendons and ligaments, where play structural roles. Elastic fibers are present in areas of the body that undergo cycles of stretching and recoiling, such as arteries. Reticular fibers form meshlike networks that provide the base for other support structures.

Collagenous fibers are composed primarily of collagen. Collagenous fibers bind bones together and connect different tissues to one another. Examples of collagenous fibers include tendons, cartilage, and blood vessels.

Collagenous fibers connect tissue types and bind elements of the musculoskeletal system to one another. Types of collagenous fibers in connective tissue include blood vessels, ligaments, and tendons. Stratified epithelium is comprised of layers of epithelial cells, which function as a covering/lining to a body structure that is subject to lots of friction.

Elastic fibers are a type of fiber within the connective tissue category. These types of fibers are made up of the protein elastin and they allow tissues and organs to recoil and oppose tearing forces.

Reticular fibers are composed of collagen and form thin mesh networks that supports cells, tissues, and organs. The reticular meshwork also acts as a scaffold for other structures to anchor into.

In the human body, connective tissue has a variety of functions that allows proper function and survival. These functions include elasticity to resist tearing and stretching forces, loose tissue and ground substance that allow for the diffusion of nutrients and oxygen, and immune cells that can activate to protect the body.

In the human body, not all types of connective tissue contain fibers. Examples of non-fibrous connective tissues are blood, adipose tissue, and bone which are made of plasma and cells, fat, and mineralized extracellular matrix, respectively.

Cartilage also performs a structural function, but it is more flexible than bone. Furthermore, it doesn't have nerves or blood vessels. This explains why a broken bone heals quite well (sometimes the broken bone becomes stronger than it was before) while cartilage does not heal/regenerate nearly as fast. They both secrete matrices, and are made up of collagen and calcium salts.

Squamous cells are flat and wide. Both stratified and simple squamous epithelia will form smooth and flat surfaces that are specialized for the simple diffusion across the layer. Squamous cells are found in lung epithelia, the lining of blood vessels, and in the lining of body cavities.

Cuboidal epithelial cells are one category of epithelial cell types. These cells have equal height and width; therefore, they are cube-shaped. They possess round nuclei and are typically involved in secretion and absorption. Cuboidal epithelial cells are located in the exocrine system.

Epithelial cuboidal cells are involved in secretion and absorption in the exocrine system in the lining of glands.