The brain co-ordinates homeostasis within the body.
At any given time it contains 15 percent of the body’s blood supply and consumes 20 percent of the body’s oxygen and glucose.
The medulla oblongata
The medulla oblongata, attached to the spinal cord at the base of the brain, has a number of major functions, each of which is related to a particular structure.
The cardiac centre controls heart rate and the force of the heart’s contractions.
The vasomotor centre adjusts blood pressure by controlling the diameter of blood vessels, and the respiratory centre controls the rate and depth of breathing.
The medulla oblongata also contains reflex centres for vomiting, coughing, hiccupping, and swallowing.
The cerebellum controls muscle co-ordination.
Although the cerebellum makes up only 10 percent of the volume of the brain, it contains 50 percent of the brain’s neurons.
The thalamus is a sensory relay centre.
It receives sensations of touch, pain, heat, and cold, as well as information from the muscles.
If the sensations are mild, the thalamus relays the information to the appropriate part of the cerebrum.
However, if the sensations are strong, the thalamus triggers a more immediate reaction while, at the same time, transferring the sensations to the homeostatic control centre — the hypothalamus.
The hypothalamus is an incredibly complex and important bundle of tissues that acts as the main control centre for the autonomic nervous system.
The hypothalamus enables the body to respond to external threats by sending impulses to various internal organs via the sympathetic nervous system.
It re-establishes homeostasis after the threat has passed by stimulating the parasympathetic nerves.
The hypothalamus also controls the endocrine hormone system.
The pituitary gland
Attached to the hypothalamus is the pituitary gland, which is sometimes called the master gland.
The pituitary gland is only about 1/3 of an inch in diameter (that’s about as large as a pea).
The pituitary gland produces hormones that control many of the other endocrine glands.
For example, the pituitary gland produces the thyroid stimulating hormone (TSH) that stimulates the thyroid gland to make and release its hormone, thyroxine.
The pituitary is actually two glands, both of which are controlled by the hypothalamus.
The back, or posterior lobe of the pituitary is formed from the cells of the hypothalamus during fetal development. The hormones released from this lobe of the pituitary — ADH and oxytocin — are produced in the hypothalamus.
The front, or anterior, lobe of the pituitary is controlled by stimulating factors — chemicals produced by the hypothalamus.
The hypothalamus also monitors body temperature and can trigger responses that increase or decrease that temperature.
The hypothalamus maintains a biological clock as well.
The cerebrum is the part of the brain in which all the information from our senses is sorted and interpreted.
Voluntary muscles that control movement and speech are stimulated from this part of the brain.
Memories are stored and decisions are made in this region as well.
The cerebral cortex, the thin layer that covers each hemisphere of the brain, contains over one billion cells.
It is this layer that enables us to experience sensation, voluntary movement, and all the thought processes we associate with consciousness.
The surface of the cerebral cortex is made up of gray matter, composed primarily of cell bodies and dendrites packed closely together for maximum interaction.
The two hemispheres are joined by the corpus callosum, a layer of white matter made up of axons. The corpus callosum transfers impulses from one hemisphere to the other.
The cerebrum is also divided into four lobes, each associated with different functions.
The frontal lobe is involved in the control of muscles (motor areas) and the integration of information from other parts of the brain to help us reason. This area allows us to think critically and plan our actions.
The parietal lobe receives sensory information from the skin and skeletal muscles, and is associated with our sense of taste.
The occipital lobe receives information from our eyes, and the temporal lobe receives information from our ears.
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