A look at neurologic disorders
Complex and infinitely diverse, the nervous system is the body’s internal communication network. It coordinates all body functions and all adaptations to changes in the body’s internal and external environments. Because of the intricacy and complexity of the nervous system, neurologic impairments can manifest in many ways.
Anatomy and physiology
The nervous system is divided into the central nervous system (CNS), the peripheral nervous system, and the autonomic nervous system. Through complex and coordinated interactions, these three parts integrate all physical, intellectual, and emotional activities.
Central nervous system
The CNS includes the brain and the spinal cord, the two structures that collect and interpret voluntary and involuntary motor and sensory stimuli. (See The CNS, Image.)
A closer look : The CNS
This illustration shows a cross section of the brain and spinal cord, which together make up the central nervous system (CNS). The brain joins the spinal cord at the base of the skull and ends near the second lumbar vertebra. Note the H-shaped mass of gray matter in the spinal cord.
The brain consists of the cerebrum (cerebral cortex), the brain stem, and the cerebellum. It collects, integrates, and interprets all stimuli; in addition, it initiates and monitors voluntary and involuntary motor activity. I think; therefore, I am The cerebrum gives us the ability to think and reason. Within the skull, it’s enclosed in three membrane layers called meninges. If blood or fluid accumulates between these layers, pressure builds inside the skull and compromises brain function. The cerebrum has four lobes and two hemispheres. The right hemisphere controls the left side of the body, and the left hemisphere controls the right side of the body. Each lobe controls and coordinates specific functions. (See The lobes of the cerebrum.)
A closer look: The lobes of the cerebrum
The cerebrum’s four lobes — the parietal, occipital, temporal, and frontal lobes — are discerned by anatomic landmarks and functional differences. The name of each lobe is derived from the overlying cranial bone. This illustration shows the locations of the cerebral lobes and explains their functions. It also shows the location of the cerebellum.
A part of the cerebrum called the diencephalon contains the thalamus and hypothalamus. The thalamus relays sensory impulses and plays an important part in conscious pain awareness. The hypothalamus regulates many body functions, including temperature control, pituitary hormone production, appetite, thirst, and water balance.
Motoring up the path
The brain stem is beneath the diencephalon and is divided into the midbrain, pons, and medulla. The brain stem contains the nuclei for cranial nerves III through XII. It relays messages between the cerebrum and diencephalon and the spinal cord; it also regulates automatic body functions, such as heart rate, breathing, swallowing, and coughing.
At the back of the brain
The cerebellum is located below the occipital lobes at the back of the brain and consists of two hemispheres. It facilitates smooth, coordinated muscle movement and equilibrium. Spinal cord The spinal cord is the primary pathway for nerve impulses traveling between peripheral areas of the body and the brain. It also contains the sensory-to-motor pathway known as the reflex arc. A reflex arc is the route followed by nerve impulses to and from the CNS in the production of a reflex action. (See Understanding the reflex arc.)
Where it is and what it’s got
The spinal cord extends from the upper border of the first cervical vertebra to the lower border of the first lumbar vertebra. It’s encased by meninges, the same membrane structure as the brain, and is protected by the bony vertebrae of the spine. The spinal cord is made up of an H-shaped mass of gray matter, divided into the dorsal (posterior) and ventral (anterior) horns. White matter surrounds the horns. What matter, white matter? Dorsal white matter contains ascending tracts that transmit impulses up the spinal cord to higher sensory centers. Ventral white matter contains descending motor tracts that transmit motor impulses down from the higher motor centers to the spinal cord.
Mapping the nerves
Sensory (afferent) nerve fibers originate in the nerve roots along the spine — cervical, thoracic, lumbar, or sacral — and supply specific areas of the skin. These areas, known as dermatomes, provide a nerve “map” of the body and help when testing sensation to determine the location of a lesion.