Limbic system

The Limbic System is a biological system comprised of functionally related neural structures in the brain that are involved in emotional behavior. It provides fantastic confirmation of the great complexity and creativity of the Creator God. The Limbic System can cause everything from a fearful reaction to an unrestrained fit of laughter. With its many intertwined organs and multiple tasks it is essential to life, the Limbic System allows the human body to feel everything as simple as hunger to even associating memories to things such as smell, pain, or another stimuli. The Limbic System is our gateway into our feelings, emotions, and the way we associate ourselves with the people and places around us. Although it is still very mysterious as to exactly how this system functions, it cannot be denied that we cannot live without it.

Functions

The Limbic System is of absolute importance when generating emotions in the creation we call the human body. The limbic system is a grouping of different organs just under the cerebrum of the brain and is on both the left and right hemispheres. These organs all work together to create emotions, memories, pleasures, and even addictions. The Limbic System is also essential to human survival; allowing the body to have a drive to find food and protect itself. Its different organs have very important roles in human life. They control how we distribute our love, friendship, anger, and other emotions towards different people or things. They control some of our movement and can even be traced to loud, irrepressible laughter.

Hypothalamus

The hypothalamus is located below the thalamus of the brain on both sides and is about the size of a pearl.. It is in between the two tracts of the optic nerve and above the pituitary gland. The Hypothalamus completes many jobs both within and outside of the Limbic System. Its main function is homeostasis. Homeostasis is the happy-medium of the body. You hypothalamus will try to create that happy-medium for things such as hunger and thirst, pain, pleasure, anger, and sexual matters. It also wakes you up in the morning by getting your adrenaline flowing.

Autonomic nervous system:
The hypothalamus also has control over the autonomic nervous system. This system controls blood pressure, heart rate, breathing, digestion, perspiration, and the sympathetic and parasympathetic functions. The sympathetic and parasympathetic systems trigger fight or flight and survival techniques such as feeding, breeding, and resting.[1] The hypothalamus receives input on the state of the body from many organs and systems to maintain homeostasis.

• The nucleus of the solitary tract collects all the visceral information from the vagus and relays it to the hypothalamus and other organs. This input gives information about blood pressure and the fullness of the stomach.
• The Reticular formation in the brainstem receives input from the spinal cord. The main information from this input is about skin temperature. The retina send input from the optic nerve directly to a nucleus in the hypothalamus called the superchiasmatic nucleus. This regulates circadian rhythms and pairs these rhythms to light/dark circles.
• Nuclei located in the circumventrical organs have no blood-brain barrier allowing them to monitor substances in the blood that would normally be blocked from neuron tissue. Organs such as the OVLT, which is also sensitive to changes in osmolarity and the area postrema, is sensitive to blood toxins and can induce vomiting both send information to the hypothalamus.
• The olfactory system and the limbic system use structures such as the amygdala, the hippocampus, and the olfactory cortex send signals to the hypothalamus which affect eating and reproduction.

Once a problem is sighted, the hypothalamus will fix the problem either by neural signs to the autonomic system or by sending endocrine signals to the pituitary gland. [2]

Hippocampus

Main Article: Hippocampus

Hippocampus literally means “sea horse” due to its shape. It has two “horns” that curve back to the amygdala. The hippocampus is deep in the limbic lobe. It’s important for the forming and possibly long-term storage of collateral and sporadic memories. It has been recognized for being involved in deciphering face-name associations, retrieving of face-name associations, the understanding of events, and the reminiscence of memories in reaction to smell. It may also be used in organizing memories during sleep. In the brain structure, the hippocampus lies under the medial temporal lobe, It is sometimes grouped together with other structures such as the denate gyrus creating what is known as the hippocampal formation. It may serve the function as a gateway through which memories must travel before entering permanent storage. [3]

Amygdala

The amygdala of a human is slightly larger than an almond. The amygdala’s name actually came from the Greek word for almond. The amygdala lies beneath the parahippocampus and actually causes it to elevate. The amygdala is consisted of three collections of nuclei. These different nuclei are connected by a strand of fibers called the stria terminalis to a part of the hypothalamus called the bed nucleus of the stria terminalus. Some of the nuclei are connected to olfactory sensors and is a large part of the humans ability to connect scent to memory.

The amygdala, through the stria terminalis, it will connect primarily to the hypothalamus and will influence hormonal and somatomotor (touch recognizing) aspects of behavior and emotional states. This means the amygdala can have influence on whether or not we eat, drink, or participate in sexual activities. Other nuclei in the amygdala also receive visual information which will help us remember primarily faces. The amygdala can also recognize sound, taste, smell, somatosensory (touch), and visual stimuli.

The lateral (outer) portion of the amygdala is considered as inhibitory and reflective of the outside environment, while the medial (more center) amygdala is seen as facilitatory and reflective of the internal environment. Stimulation of the basolateral amygdala reduces hunger and arouses the person, while stimulation of the corticomedial amygdala increases hunger. The amygdala’s outputs normally originate in the central nucleus, the most peptide-rich section of the brain. They are then transported by peptide-containing fibers in the stria terminalis and ventral amygdalofugal pathway. There are many projections from the amygdala to the hippocampus, many more than from the hippocampus to the amygdala. The strongest projection is from the lateral nucleus to what is called the entorhinal cortex which is where the hippocampus receives most sensory input. [4]

Other Structures and Functions

There are also more specific areas related to the limbic system such as:

• The cingulate gyrus is a part of the cerebrum that lies closest to the limbic system, just above the corpus collosum. This structure makes a connection from the thalamus to the hippocampus. It is responsible connecting memories, especially from emotionally significant events, to smells and pain.
• The ventral tegmental area of the brain stem, just posterior to the thalamus, holds dopamine pathways which are responsible to pleasure. People with damage to these areas often have problems finding pleasure in life and will often turn to things such as: alcohol, drugs, gambling, or sweet foods.
• The basal ganglia (includes the caudate nucleus, the putamen, the globus pallidus, and the substantia nigra) lie on the sides and over the limbic system. They are tightly connected with the cortex above them and are responsible for recurring behavior, reward experiences, and focusing attention.
• The prefrontal cortex is a part of the frontal lobe which lies anterior to the motor area; it is closely linked to the limbic system. It is believed to be connected to thinking about the future and planning the future. It may also help us take action in completing these plans. It is also connected to the dopamine pathways as the ventral tegmental system and is involved in pleasure and addiction.

Diseases

Injuries to the limbic system can cause abnormal communication of information and cause inappropriate responses. Injuries to the temporal lobe will cause problems with recalling memories. Ways to injure the limbic system can be falls, car accidents, hits to the head, concussions, etc. Lack of oxygen can also cause damage. A lack of oxygen can occur during surgery, strokes, overexertion at high elevations, seizures, childbirth, etc. Meningitis, encephalitis, or a severe ear or sinus infection can damage the limbic system. Stress, lack of sleep, certain foods, and weather changes make the limbic system more susceptible to dysfunction. Also someone who is sensitive to chemicals can be sent messages by the limbic system telling them they are ill. Symptoms include a feeling of a loss of balance, gastrointestinal issues, insomnia, being very emotional, a sense of being overwhelmed, poor sleep, and impaired memory. [5]

If a human has an amydala lesion or wound, it will be shown that they have damaged immediate visual recognition, while visual memory remains regular. In a person who is also exposed to prolonged stress it will impair the long-term potentials (LTP) in the hippocampus and will smooth the progress of the LTP in the amygdala. An LTP is a long lasting signal transmission between two neurons that results from stimulating them simultaneously. Humans who have any abrasions on the amygdala normally show a reduction in emotional anxiety. If anyone experiences electrical stimulation of the amygdala this increases plasma levels of cortisone causing most people to experience fear. If there is damage to the lateral hypothalamus, when a person is afraid they may still experience the “freeze state” however the persons heart rate would not increase as is expected when someone is afraid. However damage to the central gray will stop the “freeze state” but the heart rate will still increase. Also, brains of human schizophrenics show a significant reduction of the hippocampus and amygdala. People who suffer from depression or subjects experiencing anxiety prior to a mild shock normally have an increased blood flow to the amygdala.[6]