Structure and Function
Brainstem
The brainstem is located at the top of the spinal cord where the medulla connects to the pons. With control of many subconscious functions, such as breathing and swallowing, the brainstem plays a major role in the autonomic nervous system. In addition, the brainstem connects the spinal cord and brain by means of relaying messages between the two. Reticular formation is a group of neurons that connects to the cerebral cortex and thalamus with the purpose of carrying the messages for stimuli.
Spinal Cord
The spinal cord is a length of neural tissue that is enclosed in the vertebrae. Stretching from the lower back up to the brain, the spinal cord consists of segments of nerves with white and gray matter. With the purpose of meeting the most basic needs for survival, the brainstem has branches of nerves that diverge from the main cord and travel to muscles and organs throughout the body. One of the most prominent functions of the spinal cord is its involvement in the reflex arc, in which it receives signals from a harmful stimulus and creates a quick response to avoid danger, such as when a hot surface is touched and the hand is jerked away.
Thalamus
Found at the top of the brainstem, the function of the thalamus is act as a bridge for signals to cross to get to where they need to go. To do this, it takes sensory signals (except the olfactory system) and carries it to the the areas in the cerebral cortex that receive these signals. It also acts in the opposite direction in that it carries instructions for actions from the medulla and cerebellum to the brainstem to be dispersed throughout the body.
Cerebrum
Taking up about 85% of the brain’s weight, the cerebrum as a whole is by far the largest structure of the human brain. By achieving functions such as higher level thinking, decision making, and the ability to create and carry out plans, this region of the brain is said to be the cause of humanity. Since this is such a large section of the brain, it is further split into four lobes, the frontal, occipital, temporal, and parietal lobes, and a layer of neurons over the top, the cerebral cortex. These regions are then responsible for sensory functions, motor functions, and association areas.
Cerebral Cortex
The cerebral cortex is the thin layer of neurons covering the cerebrum that folds, giving the brain its telltale wrinkled appearance. With a lot of the cerebral cortex being gray matter, this is the site of connections between neurons. In fact, the average brain has over 300 trillion synapses in this region. As a result, the cerebral cortex is responsible for its role in thinking and controlling perceptions and consciousness.
Occipital Lobe
Split into the primary visual cortex and the secondary visual cortex, the occipital lobe specializes in interpreting vision. The primary visual cortex serves to take information taken in by the eyes and preserve the integrity of the image by keeping the proportion, space, and size accurate. The information is split so that everything on the left goes to the right hemisphere, activating neurons on the right side of the brain, and everything on the right side of the image goes to the left side of the brain, thus activating the neurons on the left. The secondary visual cortex consists of the neurons around the primary visual cortex and makes the image more specific by adding color and motion.
Cerebral cortex (dark purple outer layer)
Temporal Lobe
If vision is a projection of what is physically around someone and hearing is an auditory depiction, the temporal lobe is what takes that basic information and makes it something that would register with knowledge or memory. For example, the fusiform face area is the part of the brain that recognizes faces whereas other parts of the temporal lobe recognize objects, landscapes, images, or other sights. The primary auditory cortex has primary and secondary auditory areas which process sounds, including an area on the left side of the brain that takes heard words and sentences and processes them to give them meaning. Once these visual and auditory stimuli are processed, the hippocampus and amygdala, which are also located in the temporal lobe, stores them to memory so that, the next time a similar sight or sound is seen or heard, connections can be made from the previous memory.
Frontal Lobe
The frontal lobe is the part of the brain that gives an adult his or her maturity. As a person grows, the frontal lobe develops to form organized circuits of neurons located behind the forehead. Behaviors that society expects of someone who is “mature” come from this region of the brain including the ability to concentrate, plan, and follow societal norms. One subregion is the prefrontal cortex, which has a large portion of the functions. For example, it is in charge of directing and maintaining attention with the added job of blocking out background stimuli which may distract concentration. It creates and causes the body to carry out plans, and provides the basis for reception of and actions based on empathy and social norms. The orbitofrontal cortex, located behind the eyes, helps define personality by playing a role in emotions and impulse control. Finally, the primary motor cortex causes physical action based on decisions made in the other regions of the frontal lobe by sending messages down the brainstem to the muscles.
Parietal Lobe
The parietal lobe controls the continuation of the touch and sight senses. Stimuli from touch receptors are connected to the brainstem, which sends the message up to the primary somatosensory cortex, a strip of neurons that runs down the sides of the brain to receive touch stimuli. Receptors on this cortex correspond with where the stimulus touches, and parts of the body that are physically close are likewise close on the somatosensory cortex. Collectively, the entire body is represented with the somatosensory homunculus the ratio of amount of area dedicated to a particular region based on the level of sensitivity. For example, a sensitive area such as the lips would have more area than a less sensitive area, such as the leg. The other primary job of the parietal lobe is to establish spatial relationships. Although the eyes can create a projection of the objects around them, the parietal lobe is needed to process this and understand the concept of space that is open, space that is taken up, and the distance between objects.
Corpus Callosum
With the right hemisphere of the brain controlling the left side of the body and the left side of the brain controlling the right side of the body, a connection is needed to ensure communication between the two hemispheres. This connection is made by the corpus callosum, which consists of axon fibers across the space between the two hemispheres. Impulses can travel across the corpus callosum to facilitate the transportation of information between the two sides of the brain.
Cerebellum
The cerebellum is most commonly known as the part of the brain that enables balance and controlled motion. It is small, round, and extends off the back of the brainstem. In addition to coordinating movement, it houses certain cognitive processes that involve movement including planning, memory, and putting language into actions. Voluntary movement comes from collaboration with the pons to maintain balance and steadiness. The nervous system trains the cerebellum to work independently and without thought so that motion can be achieved while the brain is performing other tasks. Interestingly, all of the neurons throughout the cerebellum are identical, suggesting that all signals are identical, but the area that receives them is what differentiates the signals into different actions.
Limbic system
The limbic system is known as the animalistic part of the brain that functions to perform the basic needs for survival. Located between the hemispheres of the cerebrum, the system mostly consists of the amygdala and hypothalamus.
Hypothalamus
The hypothalamus is part of the animalistic section of the brain that is geared toward basic survival. Located just below the thalamus, the hypothalamus releases hormones to cause feelings according to what the body needs. For example, when glucose levels are low, a hormone will be released signaling that the person is hungry so that food will be eaten and glucose levels can return to normal. Other controls that are regulated include blood pressure, water levels, and blood pressure. In addition, the hypothalamus creates feelings of lust to drive reproduction so that the animal will produce offspring and pass on its genetics. The ability to regulate these functions comes from the ability of the hypothalamus to reward the body, also through hormones, so that it can have control over what needs are met.
Hippocampus
The hippocampus is the part of the brain in charge of creating and storing memories. Defined as connections between neural matter to form associations, memories are created by networks of neurons connecting via dendrites to enable the travel of impulses so that two ideas, objects, or events are linked and can easily trigger one another. In addition to memories of events, the hippocampus is responsible for remembering where places and objects are located, a direct connection to the sense of sight.
Amygdala
The amygdala works with the hypothalamus, hippocampus, and cerebral cortex to create connections that relate directly to emotions with an emphasis on fear. Physically just a pair of neural clusters that make up a part of the limbic system, the amygdala associates an event, object, or other stimulus with some emotion that goes with it. Evolutionarily, the connections that pertain to fear are especially important because of the use of fear to protect an animal from dangers to survival.
Basal Ganglia
The basal ganglia is a system made up of small structures located under the cerebral cortex with the purpose of assisting the thalamus by carrying information from the cerebral cortex to the motor centers of the brainstem. Another structure is the nucleus accumbens, a collection of neurons that release dopamine when something pleasurable is seen. This is known as part of the reward system as dopamine, a neurotransmitter to bring what is identified as relief and positive feelings.
