Heidi A. Everett
The basic structures of the neuron are dendrites, the cell body, and the axon. Dendrites are described as multiple branches that typically protrude from the cell body. These branches act as channels for incoming information from other neurons. The dendrites send this information as an electrical signal to the cell body where it is then sent to an additional process called the axon (Beatty, 1995). The nucleus and other organelles are located in the cell body or the soma of the neuron. The axon is one long continuous extension from the cell body. These basic components of the neuron can be found in various arrangements depending on the location of the neuron in the body (Beatty, 1995).
The axon sends information received from the cell body to the next neuron by the continuation of the electrical signal. Once this electrical signal reaches the terminal end of the axon, structures at this end of the axon called terminal buttons release chemicals called neurotransmitters (Hopson, 2006). The axons of sensory neurons can be found in a variety of places in the body such as muscles, the skin, the blood, and connective tissues (tendons and ligaments) (Grabowski, 2000).
The gap that exists between two neurons is called the synapse or the synaptic cleft. This is the point at which neurotransmitters are passed from one neuron's terminating axon to the dendrites of neighboring neurons. The synapse is the point of communication between two or more nerve cells and can also include other types of cells (Hopson, 2006). The mechanism behind the electrical impulse generated and then carried through the neuron is not covered in this unit due to the focus being on the gross anatomy of the brain.
The brain and spinal cord receive information from organs and tissues through the peripheral nervous system. Depending on the function of the neuron they are classified as receptors, interneurons, and effectors. The receptor and effector neurons are the two categories that are focused on in this unit. The motor neurons are effector neurons that can cause the contraction of voluntary muscles as well as the contraction of involuntary muscles found in blood vessels. These motor neurons also stimulate glandular cells to secrete hormones (Grabowski, 2000). The receptors of sensory neurons transmit their information through the dorsal root ganglion that then enters the central nervous system.
The brain stem, cerebrum, and the cerebellum are the three structures that compose the brain matter. The greatest portion of the brain resides within the cerebrum as it makes up the top outer layer of the brain. The cerebrum is the most recognizable anatomical structure of the brain being composed of large grooves and fissures. The cerebrum is divided into two main sections, the left and right cerebral hemispheres. The corpus callosum connects the left and right hemisphere through a thick band of axons that allow for communication to take place between the two hemispheres (Hopson, 2006). The left hemisphere is largely responsible for processing speech and language while the right hemisphere is responsible for processing reasoning and spatial information (Hopson, 2006).
The brain is then further subdivided into four lobes called the frontal lobe, occipital lobe, parietal lobe, and the temporal lobe (Hopson, 2006). The frontal lobe houses the brain's multiple processing centers for motor function, speech, and intellectual function (Johnson, 2004). The temporal lobe houses the brain's centers for smell and hearing. The occipital lobe houses the brain's centers for vision, and the parietal lobe houses the brain's centers for sensory function (Johnson, 2004). These are the major regions of the brain that the students will learn to identify and describe their function.
The cerebrum is responsible for the higher levels of functioning regarding the storage of memories, the ability to learn, and for intelligence. The cerebral cortex will be a key anatomical structure for the students to be able to identify as it is area that is easily identifiable composing the most superficial layer of the cerebrum composed of gray matter (Grabowski, 2000). This area serves a critical role in the brain's ability to process motor and sensory information. The cerebral cortex contains the largest surface area in the brain as it the outermost layer being only 2-4 millimeters thick (Hopson, 2006).
The cerebellum is another key brain structure as it serves to regulate the timing associated with skeletal muscles as they control our movement and aid posture and balance (Hopson, 2006). This structure will be highlighted throughout the unit as students perform various motor activities. It will also be mentioned that this brain structure must be intact and developed for individuals to be successful in various activities that athletes, musicians, and artists take part in.
The brain stem will not be covered in depth but its location and function will be briefly reviewed to acquaint the students with its importance. Its location is at the base of the brain connecting to the spinal cord. It serves a vital role in maintaining the internal
balance of the body's vital functions such as heart rate, sleep, breathing, temperature, and body temperature will be covered (Hopson, 2006). In addition, the brain stem acts as a relay station for sensory information intended for the cerebral cortex, and also for motor information intended for the head and body (Grabowski, 2000).
