The structures in the limbic system include the hippocampus, the amygdala, and
the hypothalamus. The hippocampus is the part of the brain that is involved in
memory forming, organizing, and storing. It is particularly important in forming
new memories (especially about personal experiences and facts) and with connecting
emotions and senses, such as smell and sound, to memories. The hippocampus ceases
to play a crucial role in the retention of the memory after a period of consolidation,
eg. when we've mastered a new skill. Damage to the hippocampus usually results
in profound difficulties in forming new memories, however, it does not affect
some aspects of memory such as the ability to learn new skills (e.g., playing
a musical instrument).
The amygdala is linked to responses like fear,
pleasure, feelings of punishment, and awareness of behavior. The amygdla receives
input from the sensory systems and attaches emotional meaning to these sensations.
It signals other parts of the brain when there is danger and sends outputs to
the hypothalamus for activation of the sympathetic nervous system. It is also
important in the activation of dopamine, norepinephrine, and epinephrine. Conditions
such as anxiety, autism, depression, narcolepsy, post-traumatic stress, and schizophrenia
are suspected of being linked to the functioning of the amygdala owing to damage,
developmental problems, or neurotransmitter imbalance.
is also considered to be part of the limbic system. The hypothalamus mediates
between the nervous system and the endocrine system. It helps to regulate blood
pressure, heart rate, hunger, thirst, sexual arousal, and the sleep/wake cycle.
The hypothalamus secretes releasing hormones to the nearby pituitary in response
to nervous system stimuli including smell, taste, pain, and emotions. Thus, stress,
cold, heat, and other stimuli cause a release of CRF, or corticotropic hormone-releasing
factor, from the hypothalamus. CRF travels to the pituitary, called the "Master
Gland" because it produces hormones that regulate a wide variety of bodily
activities, including growth, blood pressure, pregnancy, sexual function, metabolism,
and water balance in the body. CRF stimulates the pituitary to produce ACTH (adrenocorticotropic
hormone) which in turn causes the adrenal cortex to produce cortisol.
Cortisol, has become known as the "stress hormone", yet it is necessary
in the functioning of almost every part of the body. Cortisol is a steroid hormone
made in the adrenals, which are small glands next to the kidneys. Cortisol secretion
increases in response to any stress in the body, whether physical (such as illness,
trauma, surgery, or temperature extremes) or psychological. It acts as an antagonist
to insulin and promotes the breakdown of carbohydrates, fatty acids, and proteins
to immediately increase the body's energy levels in response to a life threat
and ensure that the brain receives adequate energy sources.
the early stages of adrenal stress, cortisol levels will be too high during the
day and continue rising in the evening. This is called "hyperadrenia".
In the middle stages, cortisol may rise and fall unevenly as the body struggles
to balance itself despite the disruptions of caffeine, carbs, and other factors,
but levels are not normal and are typically too high at night. In advanced stages
of prolonged stress, when the adrenals are exhausted from overwork, cortisol will
never reach normal levels ("hypoadrenia"). Medically adrenal dysfunction
may only show up in its extreme stages.e.g. Cushings Disease or Addisons Disease.
However, sustained high cortisol destroys healthy muscle and bone, slows down
healing and normal cell replacement, co-opts biochemicals needed to make other
vital hormones, impairs metabolism, increases blood sugar levels, storage of abdominal
fat, diabetes, heart disease, interferes with healthy endocrine function, and
suppresses the immune system. By products of Cortisol depress brain activity and
act as sedatives and cortisol itself blocks seratonin, contributing to feelings
of depression. Adrenal dysfunction may also be a factor in many related conditions,
including fibromyalgia, hypothyroidism, chronic fatigue syndrome, arthritis, and
menstrual difficulties. Additional red flags of adrenal fatigue include insomnia
and using caffeine and carbohydrates as "pick-me-ups." (Many of these
same sequelae can also arise from long-term use of glucocorticoid drugs.) Long-term
exposure to cortisol has also been found to result in damage to cells in the hippocampus.
This damage results in impaired learning and mood dysregulation. However, short-term
exposure of cortisol helps to create memories, called "flashbulb memories".
It can also damage other parts of the brain which control emotions, impulse control,
arousal, and attention.