According to Harvard professor Dr. J. Kimball, there are approximately one-hundred-billion neurons in the brain, and each one can have about ten thousand connections. That results in major complexity. However, the brain has several ridges, fissures, lobes, distinctive cell clusters and other visible landmarks that make the process of attributing function to specific locations within the brain much easier.
Cerebrum
In humans, the cerebrum is the largest and most obvious part of the brain. It is here where thought occurs and where deliberate actions become triggered. The cerebrum consists of two hemispheres, each with four lobes. From front to back, they include the frontal, temporal, parietal and occipital lobes. Each lobe has characteristic responsibilities. The frontal lobe has responsibilities that include problem solving, reasoning and planning. Movement initiates from here, as well as emotion and personality. This lobe contributes to the process of speaking. The temporal lobe perceives and recognizes auditory and visual information. It has heavy involvement in memory formation and speech comprehension. The parietal lobe's involvement includes movement and spatial orientation of the body, perception and recognition. The occipital lobe is the primary center for vision. The right and left hemispheres do differ somewhat in their function. For example, the left temporal lobe is involved in the comprehension of speech, while the right temporal lobe deals with non-verbal sounds such as music and the recognition of shapes and faces.
Cerebellum
The cerebellum hangs below the cerebrum and in back of the brain stem. Structurally it resembles the cerebrum in that it has two hemispheres and appears highly folded. The incoming information received by the cerebellum from the brain, spinal cord and sensory organs enable it to coordinate smooth voluntary movement while maintaining balance and posture.
Limbic System
The limbic system is buried deep within the cerebrum. It includes the thalamus, the hypothalamus, the amygdala and the hippocampus.
The thalamus relays information from most sensory systems to the cerebrum, the olfactory system being the only exception.
The hypothalamus mediates thirst, hunger and emotion, contributes to the maintenance of homeostatis, regulates circadian rhythms and helps to control the autonomic nervous system and the pituitary gland.
The amygdala is buried within the temporal lobe. It becomes active in fear responses, emotion and memory.
The hippocampus also lies in the temporal lobe. It promotes learning and long-term memory.
Brain Stem
The brain stem links the brain and the spinal cord. Sensory information from the body travels through to the higher brain. Regulatory and motor instructions head back down. But the brainstem is more than a highway for travelling nerve signals. According to Dr. Hendelman from the University of Ottawa, of the twelve pairs of cranial nerves, only the optic and olfactory nerves do not relay information through the midbrain, pons and medulla, the structures that comprise the brainstem. Through its cranial nerve connections, the brainstem is involved with motor control of the eyes, face, tongue, throat, chest and abdomen. It receives sensory information pertaining to touch, hearing and balance. It also connects to sensors that monitor blood pressure, blood gas concentrations and blood acidity. It regulates the heart rate, respiration and digestion. And within the brainstem lies the reticular formation which regulates the sleep cycle and plays a critical role in maintaining consciousness through its connections to the cerebrum. If those connections are severed, a deep coma results.
References
- Kimball's Biology Pages; C; Central Nervous System
- University of Maryland Medical Center; Medical Reference; English Medical Encyclopedia; Cerebellum
- "Atlas of Functional Neuroanatomy," 2nd ed. Walter J. Hendelman. 2006
- The Merck Manuals Online Medical Library, Home Edition; Brain, Spinal Cord and Nerve Disorders; Cranial Nerve Disorders
