The brain and spinal cord make up the central nervous system. They process information presented by sensory receptors located all over the body and execute appropriate responses. Different regions of the brain are responsible for integrating specific types of information. The adult brain consists of three major regions: the forebrain, midbrain and hindbrain.
Forebrain: Cerebrum
The major structures of the forebrain include the cerebrum, the thalamus, hypothalamus and epithalamus. The cerebrum is the largest structure in the brain, accounting for 90 percent of its volume. It is divided into 2 hemispheres and 4 lobes. Each lobe is named after the cranial bone that overlies it--frontal, parietal, temporal and occipital. The most superficial layer of the cerebrum is called the cerebral cortex. The frontal lobe holds the language center, responsible for recognizing and understanding words; a motor area, responsible for the motions associated with speech; a premotor area, responsible for planning movements; and a behavior/personality area. The parietal lobe contains tactile sensory centers, a taste center and a speech center that allows you to recognize spoken words. The temporal lobe is the major center for auditory information and balance. The occipital lobe contains the brain's visual center.
Forebrain: Thalamus, Hypothalamus and Epithalamus
The thalamus is the first place in the brain to receive information coming in from sensory receptors, and it acts as a filter and routing center to convey that information to the cerebrum. Additionally, it routes visual information to the occipital lobe and auditory information to the temporal lobe. The thalamus is also involved in emotion and memory. Beneath the thalamus is the hypothalamus, which is responsible for regulating body temperature, sleep/wake cycles, food and water intake, sex drive, emotions and autonomic nervous system function. It also communicates with the pituitary gland, which is directly below it, to influence the secretion of hormones. The mammillary bodies are small lumps of tissue behind the hypothalamus that play an important role in memory. Finally, the epithalamus is a small mass of tissue behind the thalamus that contains the pineal gland--an endocrine gland involved in sleep cycles.
Midbrain
The midbrain is a short segment of brain stem connecting the forebrain and hindbrain. The midbrain contains centers for visual motor output and motor response to auditory input. The superior colliculi are responsible for the former and the inferior colliculi for the latter. Collectively, these areas are called the corpora quadrigemina; it is located in an area of the midbrain called the tectum. In front of the tectum is a midbrain structure called the tegmentum. This area contains a motor control structure called the red nucleus, a somatic pain processing center called the periaqueductal gray, and an inhibitory motor structure called the substantia nigra. Deterioration of neurons in the substantia nigra is responsible for the muscle tremors of Parkinson's disease. Finally, the cerebral aqueduct lies between the tectum and tegmentum and is responsible for transporting cerebral spinal fluid, or CSF, to the brain's ventricles.
Hindbrain: Medulla Oblongata
The hindbrain consists of the medulla oblongata, cerebellum and pons. The medulla contains the medullary pyramids, which are involved in controlling voluntary movement. It also houses some areas involved in auditory pathways, known as the cochlear nuclei and the superior olive. Below the superior olive lies the inferior olive, a motor control center. The mid-section of the medulla contains the medial lemniscus, which conveys somatic sensory information to the thalamus. Some aspects of balance are served by the vestibular nuclei of the medulla, and aspects of taste by the gustatory nucleus of the medulla. Also found in the medulla is the raphe nucleus, important in modulating pain, mood and wakefulness.
Hindbrain: Cerebellum and Pons
The cerebellum is a wrinkly ball of brain tissue located directly under the occipital lobe. Movement often involves the use of several muscles that must be activated sequentially for the desired action to be carried out. The cerebellum is the part of the brain responsible for coordinating motor signals so that movement is smooth. Deficits in cerebellar function are evident in the clumsy actions exhibited under the influence of alcohol. The information processed by the cerebellum is received by the pons, which also contains centers involved in sleep, respiration and posture.
References
- "Anatomy and Physiology: The Unity of Form and Function (5th Edition)"; Ken Saladin; 2010
- "Neuroscience: Exploring the Brain (3rd Edition)"; Mark Bear, Barry Connors and Michael Paradiso; 2007
