In the inner part of the forebrain sits the thalamus, hypothalamus, and pituitary gland :. The midbrain, underneath the middle of the forebrain, acts as a master coordinator for all the messages going in and out of the brain to the spinal cord. The hindbrain sits underneath the back end of the cerebrum. It consists of the cerebellum, pons, and medulla.
The cerebellum — also called the "little brain" because it looks like a small version of the cerebrum — is responsible for balance, movement, and coordination. The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates the brain's messages. It also controls many of the body's automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.
The basic workings of the nervous system depend a lot on tiny cells called neurons. The brain has billions of them, and they have many specialized jobs. For example, sensory neurons send information from the eyes, ears, nose, tongue, and skin to the brain.
Motor neurons carry messages away from the brain to the rest of the body. All neurons relay information to each other through a complex electrochemical process, making connections that affect the way you think, learn, move, and behave.
Intelligence, learning, and memory. As you grow and learn, messages travel from one neuron to another over and over, creating connections, or pathways, in the brain. It's why driving takes so much concentration when someone first learns it, but later is second nature: The pathway became established.
In young children, the brain is highly adaptable. In fact, when one part of a young child's brain is injured, another part often can learn to take over some of the lost function.
But as you age, the brain has to work harder to make new neural pathways, making it harder to master new tasks or change set behavior patterns. That's why many scientists believe it's important to keep challenging the brain to learn new things and make new connections — it helps keeps the brain active over the course of a lifetime. Memory is another complex function of the brain. The things you've done, learned, and seen are first processed in the cortex. Then, if you sense that this information is important enough to remember permanently, it's passed inward to other regions of the brain such as the hippocampus and amygdala for long-term storage and retrieval.
As these messages travel through the brain, they too create pathways that serve as the basis of memory. The autonomic nervous system Autonomic nervous system The peripheral nervous system consists of more than billion nerve cells neurons that run throughout the body like strings, making connections with the brain, other parts of the body, and After the autonomic nervous system receives information about the body and external environment, it responds by stimulating body processes, usually through the sympathetic division, or inhibiting them, usually through the parasympathetic division.
An autonomic nerve pathway involves two nerve cells. All thoughts, beliefs, memories, behaviors, and moods It is connected by nerve fibers to the other cell, which is located in a cluster of nerve cells called an autonomic ganglion. Nerve fibers from these ganglia connect with internal organs. Most of the ganglia for the sympathetic division are located just outside the spinal cord on both sides of it.
The ganglia for the parasympathetic division are located near or in the organs they connect with. Fat tissue has a lower percentage of water than lean tissue and women tend to have more fat, so the percentage Doctors think about the body's water as being restricted to various spaces, called fluid compartments.
The three main compartments are Many organs are controlled primarily by either the sympathetic or the parasympathetic division. Sometimes the two divisions have opposite effects on the same organ. For example, the sympathetic division increases blood pressure, and the parasympathetic division decreases it.
Overall, the two divisions work together to ensure that the body responds appropriately to different situations. Thus, the sympathetic division increases heart rate and the force of heart contractions and widens dilates the airways to make breathing easier. It causes the body to release stored energy. Muscular strength is increased. This division also causes palms to sweat, pupils to dilate, and hair to stand on end.
It slows body processes that are less important in emergencies, such as digestion and urination. Generally, the sympathetic division prepares the body for stressful or emergency situations—fight or flight. For example, it increases heart rate and the force of heart contractions and widens dilates the airways to make breathing easier. Generally, the parasympathetic division conserves and restores.
It slows the heart rate and decreases blood pressure. It stimulates the digestive tract to process food and eliminate wastes. Energy from the processed food is used to restore and build tissues. The parasympathetic division regulates body process during ordinary situations. Generally, it conserves and restores. For example, it slows the heart rate and decreases blood pressure. Both the sympathetic and parasympathetic divisions are involved in sexual activity, as are the parts of the nervous system that control voluntary actions and transmit sensation from the skin somatic nervous system Somatic nervous system The peripheral nervous system consists of more than billion nerve cells neurons that run throughout the body like strings, making connections with the brain, other parts of the body, and Two chemical messengers neurotransmitters are used to communicate within the autonomic nervous system:.
Nerve fibers that secrete acetylcholine are called cholinergic fibers. Fibers that secrete norepinephrine are called adrenergic fibers. Generally, acetylcholine has parasympathetic inhibiting effects and norepinephrine has sympathetic stimulating effects. However, acetylcholine has some sympathetic effects. Sympathetic neurons are frequently considered part of the peripheral nervous system PNS , although there are many that lie within the central nervous system CNS.
Sympathetic neurons of the spinal cord which is part of the CNS communicate with peripheral sympathetic neurons via a series of sympathetic ganglia.
Within the ganglia, spinal cord sympathetic neurons join peripheral sympathetic neurons through chemical synapses. Spinal cord sympathetic neurons are therefore called presynaptic or preganglionic neurons, while peripheral sympathetic neurons are called postsynaptic or postganglionic neurons.
At synapses within the sympathetic ganglia, preganglionic sympathetic neurons release acetylcholine, a chemical messenger that binds and activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus, postganglionic neurons principally release noradrenaline norepinephrine. These include pupil dilation, increased sweating, increased heart rate, and increased blood pressure. Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in the intermediolateral cell column or lateral horn , beginning at the first thoracic segment of the spinal cord and are thought to extend to the second or third lumbar segments.
These neurons then tag a second set of nerve cells into the relay, signaling them with help from the chemical messenger acetylcholine. Having picked up the baton, the second set of neurons extends to smooth muscles that execute involuntary muscle movements, cardiac muscles and glands across the body.
Often, the parasympathetic nervous system communicates with the same organs as the sympathetic nervous system to keep the activity of those organs in check. The sympathetic and parasympathetic nervous systems rest on either side of a wobbling scale; each system remains active in the body and helps counteract the actions of the other.
If the opposing forces are mostly balanced, the body achieves homeostasis and operations chug along as usual. But diseases can disrupt the balance. The sympathetic nervous system becomes overactive in a number of diseases, according to a review in the journal Autonomic Neuroscience.
These include cardiovascular diseases like ischemic heart disease, chronic heart failure and hypertension. A boost of sympathetic signaling raises the blood pressure and enhances tone in smooth muscles, which may cause hypertension. Beyond cardiovascular ailments, sympathetic dysfunction has been associated with kidney disease, type II diabetes, obesity , metabolic syndrome and even Parkinson's disease.
Changes in sympathetic nervous activity are evident in the skin, pupils and especially the heart.
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