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| Basic structures of the midbrain complex |
The Midbrain Complex
To simplify the discussions, the term ‘midbrain complex’ has been coined to include the midbrain along with the thalamus and the limbic system.
The midbrain is cylinder shaped, about 2 centimetres (cm) in height and 2 cm in diameter. It sits on top of the hindbrain in the middle of the head; approximately level with the bridge of your nose. The midbrain is associated with the pathways for voluntary muscle control, visual system reflexes, and hearing.
The thalamus consists of two plum sized lobes just above the midbrain. These leftright lobes provide a system for relaying neural signals between the midbrain and the hemispheres of the forebrain, and act as the brain’s main filter of sensory input. The thalamus is also associated with regulating sleep, wakefulness, consciousness, and mental arousal.
The limbic system is an important series of left-right nerve pathways located around the midbrain and under the forebrain. The limbic system is involved in emotional responses such as fear and aggression, mood in general, appetite, and emotional responses to food. The limbic system is also involved in the processing and storage of short-term memory. From an evolutionary point of view, the limbic system is an old structure that can also be found in fish, amphibians, and reptiles – as well as mammals. The limbic system is highly connected with the frontal lobes (see section 1.1.4) and may be the source of emotional satisfaction that can be derived from clear thinking. There is no universal agreement on exactly which organs should be listed as part of the limbic system, but its main components are the hypothalamus, the hippocampus, and the amygdala.
The hypothalamus consists of two small left-right structures, each about the size of a bean. The two parts of the hypothalamus reside under the two parts of the thalamus.
The primary function of the hypothalamus is to maintain the body’s status quo. It regulates blood pressure, temperature, fluid levels, electrolyte balance, body weight, and appetite. Your hypothalamus sends you a signal to let you know when you are hungry, thirsty, tired, mad, or sad. The hypothalamus is also connected to the pituitary gland, the master regulator of the body’s endocrine (hormone) system.
Your hypothalamus works much like the thermostat on a furnace, maintaining key body parameters at appropriate levels. In the short run you may gain or lose a few pounds, but the setting for body weight established in your hypothalamus will eventually bring your body weight back to its former setting. Similar corrective measures initiated in your hypothalamus maintain your body temperature and blood pressure.
To simplify the discussions, the term ‘midbrain complex’ has been coined to include the midbrain along with the thalamus and the limbic system.
The midbrain is cylinder shaped, about 2 centimetres (cm) in height and 2 cm in diameter. It sits on top of the hindbrain in the middle of the head; approximately level with the bridge of your nose. The midbrain is associated with the pathways for voluntary muscle control, visual system reflexes, and hearing.
The thalamus consists of two plum sized lobes just above the midbrain. These leftright lobes provide a system for relaying neural signals between the midbrain and the hemispheres of the forebrain, and act as the brain’s main filter of sensory input. The thalamus is also associated with regulating sleep, wakefulness, consciousness, and mental arousal.
The limbic system is an important series of left-right nerve pathways located around the midbrain and under the forebrain. The limbic system is involved in emotional responses such as fear and aggression, mood in general, appetite, and emotional responses to food. The limbic system is also involved in the processing and storage of short-term memory. From an evolutionary point of view, the limbic system is an old structure that can also be found in fish, amphibians, and reptiles – as well as mammals. The limbic system is highly connected with the frontal lobes (see section 1.1.4) and may be the source of emotional satisfaction that can be derived from clear thinking. There is no universal agreement on exactly which organs should be listed as part of the limbic system, but its main components are the hypothalamus, the hippocampus, and the amygdala.
The hypothalamus consists of two small left-right structures, each about the size of a bean. The two parts of the hypothalamus reside under the two parts of the thalamus.
The primary function of the hypothalamus is to maintain the body’s status quo. It regulates blood pressure, temperature, fluid levels, electrolyte balance, body weight, and appetite. Your hypothalamus sends you a signal to let you know when you are hungry, thirsty, tired, mad, or sad. The hypothalamus is also connected to the pituitary gland, the master regulator of the body’s endocrine (hormone) system.
Your hypothalamus works much like the thermostat on a furnace, maintaining key body parameters at appropriate levels. In the short run you may gain or lose a few pounds, but the setting for body weight established in your hypothalamus will eventually bring your body weight back to its former setting. Similar corrective measures initiated in your hypothalamus maintain your body temperature and blood pressure.
The amygdala has a left-right structure with almond shaped components residing just below the hypothalamus. The amygdala is involved with the emotions of aggression, fear, and pleasure. Persons with a large amygdala tend to be more aggressive.
Anxiety, autism, depression, narcolepsy, phobias, and schizophrenia are often linked to a malfunctioning amygdala.
The hippocampus has a left-right structure in the shape of elongated beans curving towards the back of the brain from the amygdala. The hippocampus plays an essential role in our ability to create new memories of daily events and also influences our ability to access old memories. Research also suggests that the hippocampus plays a role in our ability to form mental maps of our surroundings and to perform spatial tasks.
The nucleus accumbens is sometimes considered part of the basal ganglia of the forebrain and sometimes as part of the limbic system. It has sensitive dopamine receptors that respond to intense stimuli, novel stimuli, and pheromones. The nucleus accumbens has been called the pleasure centre of the brain.
Many of the structures in the midbrain are connected by an extended loop called the fornix.
Anxiety, autism, depression, narcolepsy, phobias, and schizophrenia are often linked to a malfunctioning amygdala.
The hippocampus has a left-right structure in the shape of elongated beans curving towards the back of the brain from the amygdala. The hippocampus plays an essential role in our ability to create new memories of daily events and also influences our ability to access old memories. Research also suggests that the hippocampus plays a role in our ability to form mental maps of our surroundings and to perform spatial tasks.
The nucleus accumbens is sometimes considered part of the basal ganglia of the forebrain and sometimes as part of the limbic system. It has sensitive dopamine receptors that respond to intense stimuli, novel stimuli, and pheromones. The nucleus accumbens has been called the pleasure centre of the brain.
Many of the structures in the midbrain are connected by an extended loop called the fornix.
