Cellular Biology - AP Biology

White matter is a component of the central nervous system that contains myelinated axons and is located in the deep parts of the brain and superficial spinal cord. The term “white” matter comes from the white color of the area due to the fatty myelin that surrounds the axons. White matter is involved in communication between the gray matter and other parts of the central nervous system.

Light enters the eye through the pupil and is focused at the back of the eye to form an image on the retina. The retina contains rods and cones that can convert the image to nerual signals for the brain to interpret.

The iris is the muscle around the pupil that allows it to dilate or constrict. Changing the size of the pupil will alter the amount of light entering the eye.

The ciliary muscles attach the lens to the scelera (the outer white part of the eye). Contracting or relaxing these muscles will change the focal point of the lens, allowing the eye to properly focus the image on the retina. The ciliary muscles and lens do not affect the amount of light to enter the eye.

The ciliary body is adjacent to the ciliary muscles and produces aqueous humor, a liquid that fills the space between the cornea and the lens.

The CNS includes the brain (including white matter and gray matter) and the spinal cord. The CNS coordinates and controls all activity within the body.

Three layers of connective tissue surround peripheral nervous system (PNS) neurons: the endoneurium, perineurium, and epineurium. This connective tissue encloses the neurons and offers protection and support.

Ganglia are clusters of nerve cells that are a part of the autonomic nervous system, which controls the function of organs.

The colloquial term “nerve” refers to a neuron—a nerve cell—that can transmit electrical signals throughout the human body. Nerves can be grouped into two categories: motor neurons and sensory neurons.

The peripheral nervous system (PNS) is the part of the nervous system that connects the central nervous system (CNS) with the rest of the human body. The PNS includes ganglia, nerves, and certain cranial nerves. The PNS does not include the brain and spinal cord, which are components of the CNS.

After neurotransmitters bind to the post-synaptic neuron, ion gated channels open. This allows for depolarization and the generation of another action potential.

Epithilial tissue is usually classified in two ways: by the shape of the cells and by their organization. Cell shape can be flat and polygonal (squamous), elongated and rectangular (columnar), or short and rectangular (cuboidal). Cells can be found in a single layer (simple) or multiple layers (stratified). Pseudostratified epithelium is usually columnar in shape and consists of a single cell layer that has the appearance of multiple layers.

Sprilli is a classification of spiral-shaped bacteria.

Epithelial tissue lines the blood vessels, organs, and cavities in the human body. The primary function of epithelial tissue is to regulate secretion, absorption, and transport across surfaces. Epithelial tissue additionally plays a role in protection and detection of signals; therefore, the role of the epithelial tissue is to act as a regulatory barrier.

Epithelial tissue acts as a barrier in the human body. The functions of epithelial tissue are broad and include selective absorption, secretion, transport, and protection.

Epithelial cells can be categorized by morphology, or shape. Epithelial cells exist in the following morphologies: squamous, columnar, or cuboidal.

Epithelial cells have three distinct morphologies: squamous, cuboidal, and columnar. Squamous cells are wider than they are tall. In other words, they are flat.

Swallowing involves both skeletal muscle and smooth muscle. While skeletal muscle is voluntary (somatic), smooth muscle is involuntary (autonomic). Swallowing involves both of these systems. One can voluntarily induce swallowing, but will also swallow involuntarily, such as while sleeping.

Most of the muscles in the esophagus are smooth muscle; these will be the muscles largely responsible for counter-acting gravity in the example. The upper region of the esophagus (the pharynx) and the tongue are composed of skeletal muscle, allowing us to induce the swallowing motion voluntarily.

The three types of muscle in the body are smooth, skeletal, and cardiac muscle. The type of muscle lining artery walls is smooth muscle, which is also present in many organs such as the intestines and the urinary bladder. Unlike skeletal muscle, smooth muscle control is involuntary and, unlike both skeletal and cardiac muscle, it is non-striated. Smooth muscle around the arteries and arterioles is important for regulating blood pressure and directing blood flow in the body.

A muscle consists of millions of tiny subunits called sarcomeres. This is the functional unit of the muscle cell responsible for shortening and causing contractile force. Sarcomeres combine to form myofibrils, which form together to become a single muscle fiber, or muscle cell. Multiple muscle fibers form a muscle belly, the macrostructure of the muscle.

The autonomic nervous system is a part of the peripheral nervous system that controls the function of internal organs including the heart, lungs, and gastrointestinal organs. This is done through the use of nerves that activate and/or inactivate glands and muscles.

Calcium ions facilitate the translocation of the troponin-tropomyosin complex, which inhibits cross-bridge formation between the myosin head (thick filament) and actin (thin filament). In order to inhibit muscle contraction, the troponin-tropomyosin must slide back into its original position, thereby inhibiting physical and chemical contact between the thick and thin filaments. In order to accomplish this, the calcium ions must be actively pumped out of the cytoplasm and into the sarcoplasmic reticulum (SR). It is important to remember that in a muscle fiber, the SR acts as a reservoir to store calcium ions. In order for them to be stored in a concentration greater than that in the cytoplasm, active transport must be involved to pump the ions against their gradient.

The somatic nervous system is a part of the peripheral nervous system and controls voluntary body movements. The central nervous system involves only the brain and spinal cord. The autonomic nervous system is not under voluntary control.