Central Nervous System

The Central Nervous System:

The Central Nervous System comprises of the Brain and the Spinal cord:

1. The Brain plays a central role in the control of most bodily functions, which includes awareness, movements, sensations, thoughts, speech, and memory. The brain takes in sensory information, organizes and synthesizes this input, then provides instructions for motor output to the rest of the body. The brain is the main data center of the body, consisting of the cerebrum (which regulates Cognitive functions) and the cerebellum (which regulates coordination and muscular skeletal functions).
2. The Spinal cord consists of nerves that carry incoming and outgoing messages between the brain and the rest of the body. Spinal cord acts as the center for reflexes.

Brain:

The human brain is the command center for the human nervous system. It receives input from the sensory organs and sends output to the muscles. The Human Brain weighs about 1.5 kilograms, it makes up about 2 percent of a human’s body weight. The cerebrum makes up 85 percent of the brain’s weight composing of nearly 86 billion neurons. The neurons are the structural and functional unit of the nervous system.

The brain develops from 3 sections, they are as follows.

1. Forebrain: also known as prosencephalon, is the anterior part of the brain, includes the cerebral hemispheres, the thalamus forebrain develops into the cerebrum and underlying structures.
2. Midbrain: also known as mesencephalon becomes part of the brainstem, serves important functions like motor activity and sensory functions.
3. Hindbrain: the lower part of the brain stem, comprising the cerebellum, pons cerebelli, and medulla oblongata.

Parts of the Brain and functions:

• AMYGDALA: Lying deep in the center of the limbic emotional brain, this powerful structure, the size, and shape of an almond, is constantly alert to the needs of basic survival.
• BRAIN STEM: The part of the brain that connects to the spinal cord. The brain stem controls function basic to the survival of all animals, such as heart rate, breathing, digesting foods, and sleeping. It also plays a role in learning.
• CEREBRUM: This is the largest brain structure in humans and accounts for about two-thirds of the brain’s mass. The two hemispheres of the cerebrum are connected by long neuron branches called the corpus callosum. The cerebrum control most of our body functions such as the state of consciousness, the senses, the body’s motor skills, reasoning, and language.
• CEREBELLUM: Two peach-size mounds of folded tissue located at the top of the brain stem. It controls most of the learning pathways and coordinated skilled movements.
• The Frontal Lobe is the most recently-evolved part of the brain. The frontal lobe is dorsolateral prefrontal circuit is the brain’s top executive. It organizes responses to complex problems, plans steps to an objective, searches memory for relevant experience, adapts strategies to accommodate new data, guides behavior with verbal skills and houses working memory.

• The Temporal Lobe controls memory storage area, emotion, hearing, and, on the left side, language.

• The Parietal Lobe receives and processes sensory information from the body including calculating location and speed of objects.
• The Occipital Lobe processes visual data and routes it to other parts of the brain for identification and storage.
• HIPPOCAMPUS: located deep within the brain, it processes new memories for long-term storage. If you didn’t have it, you couldn’t live in the present, you’d be stuck in the past of old memories. It is among the first functions to falter in Alzheimer’s.

• HYPOTHALAMUS: Located at the base of the brain where signals from the brain and the body’s hormonal system interact, the hypothalamus maintains the body’s status quo. It monitors numerous bodily functions such as blood pressure and body temperature, as well as controlling body weight and appetite.
• THALAMUS: Located at the top of the brain stem, the thalamus acts as a two-way relay station, sorting, processing, and directing signals from the spinal cord and midbrain structures up to the cerebrum, and, conversely, from the cerebrum down the spinal cord to the nervous system.

Spinal Cord:

The spinal cord is a long, fragile tube-like structure that begins at the spinal cord extends from the foramen magnum where it is continuous with the medulla to the level of the first or second lumbar vertebrae. Spinal Cord is a vital link between the brain and the body, and from the body to the brain, which is 40 to 50 cm long and 1 cm to 1.5 cm in diameter. Two consecutive rows of nerve roots emerge on each of its sides, these nerve roots join distally to form 31 pairs of spinal nerves. The spinal cord is a cylindrical structure of nervous tissue composed of white and gray matter, is uniformly organized and is divided into four regions: cervical (C), thoracic (T), lumbar (L) and sacral (S). The spinal cord consists of nerves that carry incoming and outgoing messages between the brain and the rest of the body. It is also the center for reflexes, such as the knee jerk reflex. The spinal nerve roots are formed by the union of dorsal and ventral roots within the intervertebral foramen, resulting in a mixed nerve joined together and forming the spinal nerve.

The arterial blood supply to the spinal cord in the upper cervical regions is derived from two branches of the vertebral arteries, the anterior spinal artery, and the posterior spinal arteries. At the level of the medulla, the paired anterior spinal arteries join to form a single artery that lies in the anterior median fissure of the spinal cord. The posterior spinal arteries are paired and form an anastomotic chain over the posterior aspect of the spinal cord. A plexus of small arteries, the arterial vasocorona, on the surface of the cord constitutes an anastomotic connection between the anterior and posterior spinal arteries. This arrangement provides uninterrupted blood supplies along the entire length of the spinal cord.

Functions:

1. conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain, the spinal nerves carry sensory information (sensations) from the body and some from the head to the central nervous system (CNS) via afferent fibers, and it performs the initial processing of this information.

1. Motor neurons in the ventral horn project their axons into the periphery to innervate skeletal and smooth muscles that mediate voluntary and involuntary reflexes. The spinal nerves conduct motor information from the brain to various effectors such as
   1. skeletal muscles
   2. cardiac muscle
   3. smooth muscle
   4. glands
2. the neurons of the spinal cord’s descending axons mediate autonomic control for most of the visceral functions.
3. The spinal cord is of great clinical importance because it is a major site of traumatic injury and the locus for many disease processes
4. Spinal cord also serves as a reflex center.