Visible Body 3d Brain
Hermila Farquhar
The cerebellum is the second largest part of the brain. It sits below the posterior (occipital) lobes of the cerebrum and behind the brain stem, as part of the hindbrain. Like the cerebrum, the cerebellum has left and right hemispheres. A middle region, the vermis, connects them. Within the interior tissue rises a central white stem, called the arbor vitae because it spreads branches and sub-branches through the hemispheres. The primary function of the cerebellum is to maintain posture and balance. When we jump to the side, reach forward, or turn suddenly, it subconsciously evaluates each movement. The cerebellum then sends signals to the cerebrum, indicating muscle movements that will adjust our position to keep us steady.
The brain stem connects the spinal cord to the higher-thinking centers of the brain. It consists of three structures: the medulla oblongata, the pons, and the midbrain. The medulla oblongata is continuous with the spinal cord and connects to the pons above. Both the medulla and the pons are considered part of the hindbrain. The midbrain, or mesencephalon, connects the pons to the diencephalon and forebrain. Besides relaying sensory and motor signals, the structures of the brain stem direct involuntary functions. The pons helps control breathing rhythms. The medulla handles respiration, digestion, and circulation, and reflexes such as swallowing, coughing, and sneezing. The midbrain contributes to motor control, vision, and hearing, as well as vision- and hearing-related reflexes.
The diencephalon is a region of the forebrain, connected to both the midbrain (part of the brain stem) and the cerebrum. The thalamus forms most of the diencephalon. It consists of two symmetrical egg-shaped masses, with neurons that radiate out through the cerebral cortex. Sensory data floods into the thalamus from the brain stem, along with emotional, visceral, and other information from different areas of the brain. The thalamus relays these messages to the appropriate areas of the cerebral cortex. It determines which signals require conscious awareness, and which should be available for learning and memory.
The hypothalamus is part of the diencephalon, a region of the forebrain that connects to the midbrain and the cerebrum. The hypothalamus helps to process sensory impulses of smell, taste, and vision. It manages emotions such as pain and pleasure, aggression and amusement. The hypothalamus is also our visceral control center, regulating the endocrine system and internal functions that sustain the body day to day. It translates nervous system signals into activating or inhibiting hormones that it sends to the pituitary gland. These hormones can activate or inhibit the release of pituitary hormones that target specific glands and tissues in the body. Meanwhile, the hypothalamus manages the autonomic nervous system, devoted to involuntary internal functions. It signals sleep cycles and other circadian rhythms, regulates food consumption, and monitors and adjusts body chemistry and temperature.
I've been told I have a weird way of looking at the body. I've likened the digestive system to a train route, the heart to a machine, and now I'm about to throw a bunch of computer jargon at you for the brain.
Here we go. Now we're in the "guts" of our computer, so to speak. The brain has two hemispheres. The largest part of the brain (what most people visualize when they think of the brain) is the cerebrum. In the image above I've highlighted sections of the four main lobes of the cerebrum: the frontal lobe, parietal lobe, temporal lobe, and occipital lobe; each are named for the bones with which they correspond.
The hindbrain, or rhombencephalon, is a large structure in the posterior region of the brain, inferior to the occipital lobe. It consists of the medulla oblongata, the pons, and the cerebellum. The cerebellum fine-tunes body movement and manages balance and posture. The medulla oblongata (which is just fun to say) acts as the conduction pathway between the spinal cord and the brain as it controls involuntary functions of the respiratory, digestive, and circulatory systems and contributes to hearing balance and taste. The pons bridges the two main function areas of the central nervous system, the "higher" brain centers and the spinal cord.
The midbrain also consists of the corpora quadrigemina: two large, paired nuclei that are divided into the superior colliculus (which controls visual reflexes) and the inferior colliculus (which controls hearing-related reflexes).
Surrounding the thalamus is the basal ganglia, a group of nuclei that regulate body movements by processing sensory and motor information coming from the cerebral cortex. Included in the basal ganglia are the caudate nucleus, the putamen, and the medial and lateral globus pallidi.
The cerebrospinal fluid, which is produced in the choroid plexus of each ventricle, travels through this system from the lateral ventricles to the spinal cord, transporting nutrients and wastes, providing support for the brain, and protecting the brain against trauma.
The nervous system must receive and process information about the world outside in order to react, communicate, and keep the body healthy and safe. Much of this information comes through the sensory organs: the eyes, ears, nose, tongue, and skin. Specialized cells and tissues within these organs receive raw stimuli and translate them into signals the nervous system can use. Nerves relay the signals to the brain, which interprets them as sight (vision), sound (hearing), smell (olfaction), taste (gustation), and touch (tactile perception).
The sense of smell is called olfaction. It starts with specialized nerve receptors located on hairlike cilia in the epithelium at the top of the nasal cavity. When we sniff or inhale through the nose, some chemicals in the air bind to these receptors. That triggers a signal that travels up a nerve fiber, through the epithelium and the skull bone above, to the olfactory bulbs. The olfactory bulbs contain neuron cell bodies that transmit information along the cranial nerves, which are extensions of the olfactory bulbs. They send the signal down the olfactory nerves, toward the olfactory area of the cerebral cortex.
Together, the central nervous system (CNS) and the peripheral nervous systems (PNS) transmit and process sensory information and coordinate bodily functions. The brain and spinal cord (the CNS) function as the control center. They receive data and feedback from the sensory organs and from nerves throughout the body, process the information, and send commands back out. Nerve pathways of the PNS carry the incoming and outgoing signals. Twelve pairs of cranial nerves connect the brain to eyes, ears, and other sensory organs and to head and neck muscles. Thirty-one pairs of spinal nerves branch out from the spinal cord to tissues of the thorax, abdomen, and limbs. Each nerve is responsible for relaying sensory information, sending motor commands, or both.
All nervous tissue, from the brain to the spinal cord to the furthest nerve branch, includes cells called neurons. Neurons are charged cells: they conduct electrical signals to pass information through the body. A typical neuron consists of a cell body, dendrites, and an axon with an axon terminal. The dendrites receive signals from body tissues or other neurons and pass them into the cell body. If an outgoing signal is produced, it zips down the axon to the axon terminal and passes to the next neuron or target cell. This conductive capability sends information up and down nerve pathways and through the central nervous system at incredible speed. Some 100 billion neurons give the brain its awesome processing power.
Nervous system messages travel through neurons as electrical signals. When these signals reach the end of a neuron, they stimulate the release of chemicals called neurotransmitters. Neurotransmitters travel across synapses, spaces between neurons or between neurons and other body tissues and cells. Neurotransmitters can be classified as two types: excitatory or inhibitory. Excitatory neurotransmitters stimulate electrical signals in other neurons and encourage responses from body cells. Inhibitory transmitters discourage signals and cellular responses. Through these chemicals, the nervous system regulates the activity of muscles, glands, and its own nerve pathways.
Structures of the nervous system, brain, spinal cord, peripheral nerves, and ganglia are formed from nervous tissue. At the cellular level, this tissue consists of neurons and neuroglia. Neurons are the message carriers. They transmit sensory signals and motor commands. Neuroglia support the neurons and other structures that supply and surround nervous tissue. Astrocytes, the most common neuroglia in the brain, surround capillaries, maintain a barrier between the bloodstream and the neurons, and actively control what gets through that barrier. Other neuroglia, including microglia, ependymal cells, and oligodendrocytes, maintain neuronal homeostasis, remove pathogens, circulate cerebrospinal fluid, protect neurons, and affect their signaling speed.
A typical neuron consists of a cell body, or soma, that has many branches called dendrites. Signals received by the dendrites affect the electrical charge of the cell body, determining the likelihood of an action potential. If the soma is depolarized enough then the axon hillock region initiates an action potential that travels down the tail-like axon. Most axons are short but some can be as long as 3 feet. Myelin sheaths protect them and increase their conductivity, or signal speed. The electric signal zips down to the axon terminal. The terminal branches then release neurotransmitters, which have an excitatory or inhibitory effect on their target (other neurons, glands, organs).
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