As indicated by its relative size (about 10% of the weight of the central nervous system), the cerebellum is essential to central nervous system function. However, it executes these responsibilities in unique ways. First, it receives extensive sensory input, but…
Brushing our teeth seems like a simple voluntary movement. The neural basis for this action is, in fact, richly complex. For example, muscles in the upper limb are used cooperatively with jaw muscles, whereas neck and back muscles provide postural…
Spinal anterior horn motor neurons whose axons innervate skeletal muscles are called lower motor neurons. These cells activate skeletal muscles to produce characteristic movements of a body part. The activity of these motor neurons is influenced by two sources. First,…
The telencephalon is the largest part of the human brain, constituting about 85% of total brain weight, and is that portion in which all modalities are represented. Various sensory inputs (such as vision and hearing) are localized in some areas,…
Although it is considered by some investigators to be part of the brainstem, the diencephalon is treated here as a portion of the forebrain. The diencephalon includes the dorsal thalamus, hypothalamus, ventral thalamus, and epithalamus, and it is situated between…
Although the brainstem is small, comprising only about 2.6% of total brain weight, the size of this structure belies its importance. First, all ascending and descending tracts linking the spinal cord and the forebrain traverse the brainstem. Second, there are…
The mesencephalon, or midbrain, is the most rostral portion of the brainstem. It gives rise to cranial nerves III and IV, conducts ascending and descending tracts, and contains nuclei that are essential to motor function. Caudally the midbrain is continuous…
The metencephalon consists of the pons and cerebellum. The pons is the middle segment of the brainstem, the caudal part being the medulla and the rostral portion being the midbrain. Although comprising only about 1.3% of the brain by weight,…
The medulla oblongata, or myelencephalon, is the most caudal segment of the brainstem. It extends from the level of the foramen magnum to the pons-medulla junction. The cavity of the medulla consists of a narrow, caudal part, which is the…
The term brainstem (sometimes written brain stem ) can mean either the portion of the brain that consists of the medulla oblongata, pons, and midbrain or the portion that consists of these structures plus the diencephalon. This book follows the…