Although the nervous system functions as a coordinated whole, it is divided into anatomical and functional divisions as an aid in understanding this complex organ system. Anatomical Divisions The nervous system has two major anatomical divisions. The central nervous system (CNS) consists of the brain and spinal cord. The CNS is the body's neural integration [...]
Several types of sensory receptors provide information to the brain for the maintenance of equilibrium. The eyes and proprioceptors in joints, tendons, and muscles are important in informing the brain about equilibrium and the position and movement of body parts. However, unique receptors in the internal ear are crucial in monitoring two types of equilibrium. [...]
The nervous system consists of organs composed primarily of nervous tissue supported and protected by connective tissues. There are two types of cells that compose nervous tissue: neurons and neuroglia. Neurons Neurons, or nerve cells, are the structural and functional units of the nervous system. They are delicate cells that are specialized to generate and [...]
Vision is one of the most important senses supplying information to the brain. The sensory receptors for light stimuli are located within the eyes (or eyeballs), the organs of vision. The eyes are located within the orbits, where they are protected by seven skull bones Connective tissues provide support and protective cushioning for the eyes. [...]
A synapse is a junction of an axon with either another neuron or an effector cell. At a synapse, the terminal bouton of the presynaptic neuron fits into a small depression on the postsynaptic neuron's dendrite or cell body or on a cell within a muscle, a gland, or adipose tissue. There is a tiny [...]
Mastication, or chewing, mixes food with salivary mucus. This action subdivides food and exposes ingested starch to salivary amylase to begin the digestive process. Mastication is not essential for normal GI function but facilitates the process. Swallowing propels food from the mouth into the esophagus. The initiation of swallowing is voluntary, but once started, the [...]
The brainstem is the stalklike portion of the brain that joins higher brain centers to the spinal cord. It contains several nuclei that are surrounded by white matter. Ascending (sensory) and descending (motor) axons between higher brain centers and the spinal cord pass through the brainstem. The components of the brainstem include the midbrain, pons, [...]
Stomach The stomach is anatomically and functionally divided into the fundus, body, and antrum. The fundus and body are highly distensible and act as reservoir for the ingested meal. A 1.5 L volume increase causes only a small increase in pressure in the lumen of the stomach. The esophageal swallowing reflex promotes release of NO [...]
There are four interconnecting ventricles, or cavities, within the brain. Each ventricle is lined by ependymal cells and is filled with cerebrospinal fluid (CSF). The largest ventricles are the two lateral ventricles (first and second ventricles), which are located within the cerebral hemispheres. The ihird ventricle is a narrow space that lies on the midline [...]
The small intestine is divided into duodenum, jejunum, and ileum, with the duodenum and jejunum being the major site of digestion and absorption. Chyme takes 2 to 4 hours to move through the 5 m of the small intestine. Segmentation, which mixes intestinal contents and enhances contact of the chyme with the intestinal microvilli, is [...]