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Structure and Functions of the Brain

By Tjs2dance Sep 15, 2013 1555 Words
Structures and Functions of the Brain

“Until recently, scientists could gather information about the human brain only by removing it from cadavers, slicing it, staining it, and taking pictures of the sliced sections. This method has many limitations, including the inability to study the brain in action. Technological advances, however, have enabled scientists to use advanced imaging methods to learn more about the function and anatomy of the brain” (BSCS, 2005, p. 1). The brain is one of the two main organs of the central nervous system. The central nervous system is made up of the brain and spinal cord. The brain lies within the cranial cavity of the skull and is surrounded by meninges, bone, and fluid for protection. “The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second” (Serendip, 2012, p. 1). The brain is a very complex organ composed of about one hundred billion multipolar neurons and innumerable nerve fibers. There are three major portions of the brain. Those portions include the cerebrum, cerebellum, and brain stem. Each one of these portions has many functions and different structures.

The cerebrum is the largest portion of the brain. It is involved in motor and sensory functions, and is concerned with higher mental functions such as memory and reasoning. The cerebrum is divided into two hemispheres that are connected by the corpus collasum and separated by a layer of dura mater. The surface is marked by numerous ridges called convolutions, also known as gyri, and separated by grooves. Shallow grooves called sulcus divide each hemisphere into lobes. Deep grooves called fissures separates the right and left cerebral hemispheres. The bulk of the cerebrum is made up of white matter. The functions of the cerebrum include interpreting sensory impulses, initiating voluntary muscle movements, storing information for memory and reasoning, and determining intelligence and personality. The cerebral hemisphere is made up of several lobes, and each lobe is named after the skull bones they underlie. The frontal lobe forms the anterior portion and is separated from other lobes by a central and lateral sulcus. The parietal lobe is posterior to the frontal lobe and is separated from it by the central sulcus. The temporal lobe lies below the frontal lobe and is separated from it by the lateral sulcus. The occipital lobe is the posterior portion of the cerebrum. It is separated from the cerebellum by a shelf-like extension called the tentorium cerebelli. The insula is located deep within the lateral sulcus and hidden by lobes, and separated from them by the circular sulcus. The cerebral cortex is a thin layer of gray matter that constitutes the outermost portion of the cerebrum. It covers convolutions and dips into sulci and fissures. The cerebral cortex contains 75% of the neuron cell bodies in the nervous system. “Note that the cerebral cortex is highly wrinkled. Essentially this makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it” (Serendip, 2012, p. 1). There are functional regions of the cerebral cortex that include motor areas, sensory areas, and association areas. The motor areas of the cerebral cortex lie in the frontal lobes. The right cerebral hemisphere controls left skeletal movements and vice versa. The broca’s area coordinates muscular actions of the tongue, mouth and larynx. The frontal eye field controls voluntary movements of the eye and eyelids. The area in front of the frontal eye field controls muscular movement of the hands and fingers. The sensory areas of the cerebral cortex interpret sensory impulses that give rise to feelings and sensations. The parietal lobes deal with skin sensations. The posterior part of the occipital lobe deals with vision. The temporal lobes deal with hearing, and the central and lateral sulci deal with taste. Centers deep within the cerebrum deal with smell. Association areas of the cerebral cortex function in analysis and interpretation of sensory experiences. They are also involved with memory, reasoning, verbalization, judgment, and emotional feelings. The frontal lobes are concerned with higher intellectual processes such as concentration, planning, and complex problem solving, and judging possible consequences of behavior. The parietal lobes aid in understanding speech and choosing words needed to express thoughts and feelings. The temporal lobes aid in understanding speech and in reading printed words. They are also involved in memory of visual scenes, music and other complex sensory patterns. The occipital lobes aid in analyzing visual patterns and combining visual images. Both hemispheres of the brain are involved with basic functions. These functions include receiving and analyzing sensory impulses, controlling skeletal muscles, and storing information. In most people one side acts as a dominant hemisphere for certain functions. However, in some people the hemispheres are equally dominant. The left hemisphere controls speech, writing, reading, verbal, analytical and computational skills. The right hemisphere controls motor tasks, interpreting musical patterns, nonverbal visual experiences, and emotional and intuitive thought processes. The corpus collosum allows for the dominant side to control the motor cortex of the non-dominant side, and the non-dominant side to send sensory information to the dominant. The brain stem is never tissue that connects the cerebrum to the spinal cord. The parts of the brain stem include the diencephalon, the midbrain, pons, medulla oblongata, and the reticular formation. The diencephalon is located between the cerebral hemisphere and above the midbrain. There are four main parts to the diencephalon which include the thalamus, hypothalamus, limbic system, and pineal gland. The thalamus is the central relay station for sensory impulses to the cerebral cortex. This does not include the sense of smell however. The cortex can communicate with the thalamus through descending fibers. The thalamus can’t pinpoint sensory stimulation but produces general awareness of pain, touch, and temperature. The hypothalamus maintains homeostasis by serving as a link between the nervous and endocrine system. The hypothalamus also regulates activities such as heart rate and arterial blood pressure, body temperature, water and electrolyte balance, body weight and controls hunger, and control of movements and glandular secretions of stomach and intestines. The limbic system is involved in emotional experience and expression. It modifies the way a person acts by producing such feelings as fear, anger, pleasure, and sorrow. The pineal gland is a small cone-shaped endocrine gland attached to the thalamus. The midbrain is located between the diencephalon and pons. It serves as a reflex center for vision and hearing. The midbrain contains nerve fibers that serve as a motor pathway between cerebrum and lower parts of the nervous system. “Sensory axons, including those of the spinothalamic tract also ascend, along the front of the midbrain behind the motor tracts” (McCaffrey, 2008, p. 1). Pons is located on the underside of the brain stem that separates the midbrain from the medulla oblongata. The dorsal portion consists of longitudinal nerve fibers that relay impulses to and from medulla oblongata and cerebrum (BSCS, 2005). The ventral portion consists of transverse nerve fibers that transmit impulses from cerebrum to centers within cerebellum. The medulla oblongata enlarged continuation of spinal cord extending from the pons to foramen magnum. All ascending and descending nerve fibers connecting brain and spinal cord pass through it due to its location. “Because the nuclei of the vagus nerve are found in the medulla, it is a center for circulation and respiration. It is also quite important to swallowing. It controls muscles of the pharynx, larynx and velum” (McCaffrey, 2008, p. 1). The reticular formation is a network of nerve fibers scattered throughout to medulla oblongata, pons and midbrain. It signals the cerebral cortex with sensory impulses activating it into a state of wakefulness. Without this the cortex remains unaware and cannot interpret sensory information or carry on thought processes. Sleep results from decreased activity in reticular formation. If it ceases to function because of injury a person remains in a comatose state.

The cerebellum is a large mass of tissue located below occipital lobes of the cerebrum and behind the medulla oblongata and pons. There are two hemispheres of the cerebellum. These hemispheres are connected by the vermis, separated by a layer of dura mater, and covered by a thin layer of gray matter called the cerebellar cortex. The cerebellum functions as a reflex center in control of skeletal muscle movements and helps maintain posture. The cerebellum is made mainly of white matter which is due to the presence of an insulating material called myelin. There are three main parts of the cerebellum which are the cerebrocerebellum, vestibulocerebellum, and spinocerebellum. The cerebrocerebellum receives signals from cerebrum. The vestibulocerebellum receives input from the brain stem. The spinocerebellum receives electrical signals from the spinal cord. Damage to the cerebrum may cause tremors, inaccurate movements of voluntary muscles, loss of muscle tone, or a distorted walk.

References
BSCS. Information about the Brain. Retrieved (September 6, 2013) from http://science.education.nih.gov/supplements/nih4/self/guide/info-brain.htm McCaffrey, Patrick. Chapter 6. The Midbrain, Pons, Medulla and Reticular Formation. Retrieved (September 6, 2013) from http://www.csuchico.edu/~pmccaffrey/syllabi/CMSD%20320/362unit6.html Morris, Charles G. Maisto, Albert A.. (2001). Understanding Psychology. River: Pearson Education Inc. Serendip. Brain Structures and Their Functions. Retrieved (September 6,2013) from http://serendip.brynmawr.edu/bb/kinser/Structure1.html

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