The human cerebral cortex

Brain researches have mapped much of the cerebral cortex into área that serve know functions.

We can now pinpoint accurately the sites of the cortex concerned with voluntary movement, bodily sensations (such as touch, pain, and temprature), hearing, visión, smell, taste, and the processing and interpretation of incoming information.

The cerebral cortex is also the seat of all higher human functions, such a intellect, memory, talent, and emotion.

Areas of cortex adjacent to sites of known function are called association areas.

These areas occupy more tan three fourths of the cortex. The association areas interpret the various types of information (such as touch and vision) received by primary areas in the cortex and traslate these stimuli into voluntary motor responses.

Association areas also regulate the complex processes that underlie higher mental functions, such as memory.



The cerebral cortex is divided into right and left hemispheres. It encompasses about two-thirds of the brain mass and lies over and around most of the structures of the brain.

It is the most highly developed part of the human brain and is responsible for thinking, perceiving, producing and understanding language. It is also the most recent structure in the history of brain evolution.

Most of the actual information processing in the brain takes place in the cerebral cortex. The cerebral cortex is divided into lobes that each have a specific function.

For example, there are specific areas involved in vision, hearing, touch, movement, and smell. Other areas are critical for thinking and reasoning.

Although many functions, such as touch, are found in both the right and left cerebral hemispheres, some functions are found in only one cerebral hemisphere. For example, in most people, language abilities are found in the left hemisphere.  

WHAT IS A CELL?

Cells are the structural and functional units of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, or have many cells—an estimated 100,000,000,000,000 cells! Each cell is an amazing world unto itself: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Even more amazing is that each cell stores its own set of instructions for carrying out each of these activities.

Prokaryotic Organisms It appears that life arose on earth about 4 billion years ago. The simplest of cells, and the first types of cells to evolve, were prokaryotic cells—organisms that lack a nuclear membrane, the membrane that surrounds the nucleus of a cell. Bacteria are the best known and most studied form of prokaryotic organisms, although the recent discovery of a second group of prokaryotes, called archaea, has provided evidence of a third cellular domain of life and new insights into the origin of life itself. Prokaryotes are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of our bodies. Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions.                                  Eukaryotic Organisms Eukaryotes include fungi, animals, and plants as well as some unicellular organisms. Eukaryotic cells are about 10 times the size of a prokaryote and can be as much as 1000 times greater in volume. The major and extremely significant difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, a membrane-delineated compartment that houses the eukaryotic cell’s DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name. Eukaryotic organisms also have other specialized structures, called organelles, which are small structures within cells that perform dedicated functions. As the name implies, you can think of organelles as small organs. There are a dozen different types of organelles commonly found in eukaryotic cells. In this primer, we will focus our attention on only a handful of organelles and will examine these organelles with an eye to their role at a molecular level in the cell. The origin of the eukaryotic cell was a milestone in the evolution of life. Although eukaryotes use the same genetic code and metabolic processes as prokaryotes, their higher level of organizational complexity has permitted the development of truly multicellular organisms. Without eukaryotes, the world would lack mammals, birds, fish, invertebrates, mushrooms, plants, and complex single-celled organisms. Thanks..

                     The vertebrate nervous system

The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish.
The CNS contains the majority of the nervous system and consists of the brain and the spinal cord. It is contained within the dorsal cavity, with the brain in the cranial cavity, and the spinal cord in the spinal cavity. In vertebrates, the brain is protected by the skull, the spinal cord is protected by the vertebrae, and both are enclosed in the meninges. The brain receives sensory input from the spinal cord as well as from its own nerves (e.g., olfactory and optic nerves). It devotes most of its volume (and computational power) to processing its various sensory inputs and initiating appropriate — and coordinated — motor outputs.
The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body. However, it also contains neural circuits that can independently control numerous reflexes and central pattern generators. The spinal cord has three major functions:

1. To serve as a conduit for motor information, which travels down the spinal cord.
2. To serve as a conduit for sensory information, which travels up the spinal cord.
3. To serve as a center for coordinating certain reflexes.

                                  THE REFLEX ARC

A reflex arc is a neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs.
A reflex is a rapid automatic response to a stimulus. When you accidentally touch a hot object and automatically jerk your hand away, this is a reflex action. It happens without you having to think about it.
Animals automatically blink when an object approaches the eye and cats twist their bodies in the air when falling so they land on their paws. The classic example of reflex reaction is the knee-jerk reaction when the patellar tendon is tapped just below the knee (Figure 1). Swallowing, sneezing, and the constriction of the pupil of the eye in bright light are also all reflex actions.

                                THE SPINAL CORD

The vertebrate spinal cord is divided into different segments running down the dorsal side of the body
At every segment, right and left pairs of spinal nerves (mixed; sensory and motor) form. Each segment of the spinal cord is associated with a pair of ganglia, called dorsal root ganglia, which are situated just outside of the spinal cord. These ganglia contain cell bodies of sensory neurons. Axons of these sensory neurons travel into the spinal cord via the dorsal roots.
Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies within the CNS. Dorsal roots and ventral roots come together and exit the intervertebral foramina as they become spinal nerves.
During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens as ridges on either side of the groove (the neural folds) become elevated and ultimately meet, transforming the groove into a closed tube. This tube develops into the central nervous system. The hollow center of the tube becomes the central canal of the spinal cord. This canal and the hollow ventricles within the developing brain at the anterior (superior) end of the tube become filled with cerebrospinal fluid.

                        WHITE AND GRAY MATTER

The vertebrate nervous system can also be divided into areas called gray matter and white matter. Gray matter contains a high proportion of cell bodies of neurons. White matter is composed mainly of myelinated axons, and takes its color from the myelin sheathing that surrounds and insulates the axons.
White matter includes all of the peripheral nerves and much of the interior of the brain and spinal cord. Gray matter is found in clusters of neurons in the brain and spinal cord, as well as in cortical layers that line their surfaces.
There is an anatomical convention that a cluster of neurons in the brain or spinal cord is called a nucleus, whereas a cluster of neurons in the periphery is called a ganglion (Figure 3) . The white matter provides tracts or pathways for rapid transmission of neural impulses. Therefore, the white matter provides the common link between the CNS and the peripheral nervous system (PNS).

How the Vertebrate Nervous System is Organized

Many neurons play a role in the reflex. In order to simplify the diagram, only a few neurons are shown. Step 1: An artificial reflex is generated by tapping the tendon which is connected to the quadriceps muscle. Step 2: The sudden stretch in the quadriceps is detected by the sensors. Step 3: Sensory neurons then carry the message to the spinal cord. Step 4: Incited to action by the signals coming in from the sensory neurons, the motor neurons carry the signals to the quadriceps. As a result the quadriceps contract, extending the leg forward. Step 5: The sensory neurons communicate with interneurons in the spinal cord. Step 6: Inhibition of the motor neurons that lead to the hamstring muscle by the interneurons prevents the hamstring from contracting (hamstring offers resistance to the action of the quadriceps).

 

The spinal cord, enclosed inside the spinal column and running down the entire length of the back, carries signals back and forth from the brain to all the parts of the body. It is also involved in the regulation of our limbs and movement.

 

One function the spinal cord acts upon independently, without any input from the brain, is the regulation of the body's instinctive response to particular stimuli, a process known as réflex  action (reflexes).

The spinal cord is positioned dorsally and its neural network is arranged in a compartmental manner; they are within the spinal cord, and the spinal nerves and ganglia are on the outside of the spinal cord.

The functions of the cerebrospinal fluid are to nourish the brain, carry a supply of hormones to the brain, and carry waste away from the brain and drain it into the veins. It offers support, lubrication and protection for the connective tissues surrounding the brain and spinal cord of mammals.

Along with the cerebrospinal fluid, the brain is made of gray and white matter.

The gray matter is made of tightly packed dendrites, neurons and axons that are not insulated with myelin sheathing. On the other hand, the white matter comprises myelinated axons, which give it its white appearance.

cerebrospinal fluid

Abbreviated CSF. A clear bodily fluid in the form of a very pure saline solution with microglia that occupies the subarachnoid space in the brain (between the skull and the cerebral cortex), and which acts as a cushion or buffer for the cortex.

The central canal is the cerebrospinal fluid-filled space that runs longitudinally through the length of the entire spinal cord.

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. Some people use the term "reflex" to mean a behavior that is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.

 

 

 

 

 

 

 

 

 

 

 

 

 

What is a nervous system?

Your nervous system is an interconected network of nerve cell,or neurons, that coordinates your actions.
I
t senses the environment and helps you react to external stimuli by thinkng, moving, and speaking. Your nervous system also regulates your internal, involuntary function, such as breathing and heart rate.

All nerve pass information from one part of your body to another. To perform this function, some of the nerve cells are enlongate so that they can connet all parts of your body.
Simpler organisms have more elementary nervous system. A simple animal such as a jellyfish, with a limited range of actions, possesses a nervous system that operates almost entirely by means of simple reflex (see below).

Through such a system, the jellyfish is able to avoid danger, such as a poisonous subtance, or move toward desirable objects, such as food.

More advance animals developed the ability to learn from prvious experience. Because the simple reflexis too basic for this puspose, it must be augmented by an entire network of nerve cells that can analyze information from many sources, store the data, and coordinate the organism's responses.