Structure of the Brain
The brain consists of many different parts. All these parts are divided into five main categories: the cortex, the hindbrain, the limbic system, the neocortex, and the corpus callosum.
Cortex
The cortex is the layer of the brain that is often referred to as gray matter. The cortex is gray because nerves in this area lack the insulation that makes most other parts of the brain appear to be white. The cortex covers the outer portion of the cerebrum and cerebellum. The portion of the cortex that covers the cerebrum is called the cerebral cortex. The cerebral cortex consists of folded bulges called gyri that create deep furrows or fissures called sulci. The folds in the brain add to its surface area and therefore increase the amount of gray matter and the quantity of information that can be processed. 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.
The Hindbrain
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Having evolved hundreds of millions of years ago, the hindbrain (the reptilian brain) is the oldest part of the human brain. This part of the brain is in charge of our primal instincts and most basic functions. Things like the instincts of survival, dominance, mating and the basic functions of respiration, heartbeats all come from this area of the brain. The parts of the hindbrain are:
- The Spinal Cord – The spinal cord runs down the middle of your back and ends around the pelvis. The spinal cord allows the brain to interact with the rest of the body. The spinal cord carries signals from sensors around the body up to the brain. Depending on these signals, the brain sends instructions back down the spinal cord to the right sensor.
- The Medulla Oblongata – The medulla oblongata helps control the body's autonomic functions like respiration, digestion and heart rate. The medulla oblongata aslo acts like a relay station. Nerve signals going to and from the brain pass through here.
- The Pons – The pons has roles in your level of arousal or consciousness and sleep. Like the medulla oblongata, the pons relays sensory information to and from the brain, and it is also involved in controlling autonomic body functions.
- The Cerebellum – The cerebellum mostly deals with movement. The cerebellum also regulates coordinates posture and balance. The cerebellum is involved in learning various movements as well.
Limbic System
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The limbic system is sometimes called the "emotional brain" or "Old Mammalian Brain." This is where our emotions reside, where memory begins and where these two functions combine together to mark behaviors with positive or negative feelings. It's where mostly unconscious value judgments are made. Information going through the limbic system is filed under "agreeable or disagreeable". It also plays a role in salience (what grabs your attention), spontaneity and creativity. The limbic system is made up of:
- The Amygdala – The amygdala helps in storing and classifying emotionally charged memories. It plays a large role in producing our emotions, especially fear. It's been found to trigger responses to strong emotions such as sweaty palms, freezing, increased heart-beat, increased respiration and stress hormone release.
- The Hippocampus – The hippocampus's primary role is in memory formation, classifying information, and long-term memory. It processes and stores new and temporary memory for long-term storage. It's also involved in interpreting incoming nerve signals and spatial relationships.
- The Hypothalamus – It's linked closely with the pituitary gland to control many of the body's functions. It monitors and controls your circadian rhythms (your daily sleep/wake cycle), homeostasis (making sure your body is running smoothly), appetite, thirst, other bodily urges and also plays a role in emotions, autonomic functions and motor functions.
- The Thalamus – Most of the sensory signals including auditory, visual, and somatosensory signals go through this organ on their way to other parts of the brain for processing. It also plays a function in motor control.
- The Archicortex – The archicortex is categorized under allocortex. The archicortex is necessary for the hippocampus to develop.Categorized under allocortex.
- Olfactory bulb – The olfactory is useful in the perception of various smells, fragrances, and odors.
Neocortex
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The last and most advanced brain to evolve to date is called the neocortex, neo-mammalian or rational brain. It takes up 2/3's of the human brain. This is where we find the brain power to develop language, abstract thought, consciousness and imagination. Let there be no doubt, this is what grants us our status on the food chain and allows us to be human. The Neocortex is divided into two hemispheres, right and left. The right side of the brain controls the left side of the body and vice versa. Also the hemispheres are divided in terms of what kind of thought they process or produce. The right being more concerned with the artistic, spatial and musical while the left is more concerned with the colder, linear, rational and verbal aspects. Located in the neocortex are:
- The Frontal Lobe – It is the center for command and control in your body. The frontal lobe is responsible for functions such as reasoning, problem solving, judgment, and impulse control and is the last part of the brain to develop. The frontal lobe forms when we are young adults. It also manages our higher emotions such as empathy and altruism. This lobe is also involved in motor control and memory.
- The Parietal Lobe – The parietal lobe is involved in processing sensations related to touch. It's where the somatosensory cortex resides. It's also associated with cognition (including calculating location and speed of objects), movement, orientation, recognition and speech.
- The Temporal Lobe – The temporal lobe is involved in auditory sensation and is where the primary auditory cortex and on the left hemisphere, Wernicke's Area (language recognition) are located. This lobe is also involved in emotion, memory and speech.
- The Occipital Lobe – The occipital lobe controls visual sensation and processing. The visual cortex is resides here.
- Broca's Area – This part of the cortex controls speech, language recognition, and facial nerves.
Corpus Callosum
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The corpus callosum is a thick band of nerve fibers that divides the cerebrum into left and right hemispheres. It connects the left and right sides of the brain allowing for communication between both hemispheres. The corpus callosum is located underneath the cerebrum at the center of the brain. The corpus callosum transfers motor, sensory, and cognitive information between the brain hemispheres.
The corpus callosum is involved in several functions of the body including:
The corpus callosum is involved in several functions of the body including:
- Communication between brain hemispheres
- Eye movement
- Maintaining the balance of arousal and attention
- Tactile localization
Neuron Structure
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Your brain is made of approximately 100 billion nerve cells, called neurons. Neurons have the ability to gather and transmit electrochemical signals. Neurons share the same characteristics and have the same makeup as other cells, but the electrochemical aspect lets them transmit signals over long distances (up to several feet or a few meters) and send messages to each other. Neurons have three basic parts:
- Cell body (soma) – This main part has all of the necessary components of the cell, such as the nucleus (which contains DNA), endoplasmic reticulum and ribosomes (for building proteins) and mitochondria (for making energy). If the cell body dies, the neuron dies.
- Axon – This long projection of the cell carries the electrochemical message (nerve impulse or action potential) along the length of the cell. Depending upon the type of neuron, axons can be covered with a thin layer of myelin sheath, like an insulated electrical wire. Myelin is made of fat and protein, and it helps to speed transmission of a nerve impulse down a long axon. Myelinated neurons are typically found in the peripheral nerves (sensory and motor neurons), while non-myelinated neurons are found in the brain and spinal cord.
- Nerve endings (dendrites) – These small, branchlike projections of the cell make connections to other cells and allow the neuron to talk with other cells or perceive the environment. Dendrites can be located on one or both ends of a cell.