The ears contain structures for both the sense of hearing and the sense of balance.
Tuesday, May 18, 2010
The nervous system is your body's decision and communication center. The central nervous system (CNS) is made of the brain and the spinal cord and the peripheral nervous system (PNS) is made of nerves. Together they control every part of your daily life, from breathing and blinking to helping you memorize facts for a test. Nerves reach from your brain to your face, ears, eyes, nose, and spinal cord... and from the spinal cord to the rest of your body. Sensory nerves gather information from the environment, send that info to the spinal cord, which then speed the message to the brain. The brain then makes sense of that message and fires off a response. Motor neurons deliver the instructions from the brain to the rest of your body. The spinal cord, made of a bundle of nerves running up and down the spine, is similar to a superhighway, speeding messages to and from the brain at every second.
The brain is made of three main parts: the forebrain, midbrain, and hindbrain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The midbrain consists of the tectum and tegmentum. The hindbrain is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem.
The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Here is a visual representation of the cortex:
What do each of these lobes do?
Note that the cerebral cortex is highly wrinkled. Essentially this makes the brain more efficient, because it can increase the surface area of the brain and the amount of neurons within it. We will discuss the relevance of the degree of cortical folding (or gyrencephalization) later. A deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. The two hemispheres look mostly symmetrical yet it has been shown that each side functions slightly different than the other. Sometimes the right hemisphere is associated with creativity and the left hemispheres is associated with logic abilities. The corpus callosum is a bundle of axons which connects these two hemispheres.Nerve cells make up the gray surface of the cerebrum which is a little thicker than your thumb. White nerve fibers underneath carry signals between the nerve cells and other parts of the brain and body.The neocortex occupies the bulk of the cerebrum. This is a six-layered structure of the cerebral cortex which is only found in mammals. It is thought that the neocortex is a recently evolved structure, and is associated with "higher" information processing by more fully evolved animals (such as humans, primates, dolphins, etc).
The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance.The cerebellum is assumed to be much older than the cerebrum, evolutionarily. What do I mean by this? In other words, animals which scientists assume to have evolved prior to humans, for example reptiles, do have developed cerebellums. However, reptiles do not have neocortex. The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old.This system contains the thalamus, hypothalamus, amygdala, and hippocampus. Here is a visual representation of this system, from a midsagittal view of the human brain:Click on the words to learn what these structures do:
Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. Scientists say that this is the "simplest" part of human brains because animals' entire brains, such as reptiles (who appear early on the evolutionary scale) resemble our brain stem. The brain stem is made of the midbrain, pons, and medulla. Click on the words to learn what these structures do:
The Brain
The brain is the most complex organ in the body. It is the organ that allows us to think, have emotions, move, and even dream. Given this complexity, it should not be surprising that there are many ways to separate brain parts. Brain parts can be separated on the basis of what they look like to the naked eye, under a microscope, or by what certain brain parts do. The brain and spinal cord make up the central nervous system and all of the nerves found in our body make up the peripheral nervous system. When you see a picture of the brain you probably think of a wrinkled gray blob. Well, the wrinkles are called cortex and it is where the majority of brain cells or neurons reside. The cortex can be divided into four main lobes. The frontal lobe, where you do your heavy thinking, pondering and planning your actions; temporal cortex, where you process sounds and form memories; occipital cortex, where you process all the things that you see; and parietal cortex, where you integrate or makes sense of all of the different bits of information that are bombarding your brain.
The Hindbrain
Having evolved hundreds of millions of years ago, the Hindbrain or the Reptillian Brain is the oldest part of the human brain. As you might guess from it's name, it's a piece of brain anatomy that we share with reptiles and is the most primitive. Likewise it's in charge of our primal instincts and most basic functions. Things like the instincts of survival, dominance, mating and the basic functions of respiration, heartbeat all come from this area of the brain. Located in the Hindbrain are:· The Spinal Cord
This is the infomation superhighway of the body. It carries information up to the brain and instructions back down.· The Medulla Oblongata
Helps control the body's autonomic functions (things you don't need to think about to perform) like respiration, digestion and heart rate. Also acts as a relay station for nerve signals going to/from the brain· The Pons
Has roles in your level of arousal or conciousness and sleep. Relays sensory information to/from the brain. Also involved in controlling autonomic body functions.· The Cerebellum
Mostly deals with movement. It regulates and coordinates movement, posture and balance. Also involved in learning movement.The Limbic System
The Limbic System sometimes called the "emotional brain" or "Old Mammalian Brain" is the next brain to have evolved in the more primitive mammals about 150 million years ago. This is where our emotions reside, where memory begins and where these two functions combine together to mark behaviours with positive or negative feelings. It's where mostly unconcious value judgements are made. Information going through the Limbic System are filed under "agreeable or disagreeable". It also plays a role in salience (what grabs your attention), spontaneity and creativity. Located in the Limbic System are:· The Amygdala
It's name is latin for almond which relates to its shape. It helps in storing and classifying emotionally charged memories. It plays a large role in producing our emotions, especially fear. It's been found to trigger responses to strong emotion such as sweaty palms, freezing, increased heart-beat/respiration and stress hormone release.· The Hippocampus
This guy is all about memory and a little about learning. It's primary role is in memory formation, classifying information, long-term memory. Like the RAM in your computer it processes and stores new and temporary memory for long term storage. It's also involved in interpreting incoming nerve signals and spatial relationships.· The Hypothalamus
It should be called the Hyperthalamus because it does so much. It's linked closely with the pituitary gland to control many of the body's functions. It monitors and controls your circadian rhythms (your daily sleep/wake cycle), homeostasis (making sure your body is running smoothly), apetite, thirst, other bodily urges and also plays a role in emotions, autonomic functions and motor functions.· The Thalamus
The Thalamus is THE relay station in the brain. Most of the sensory signals, auditory (sound), Visual, Somatosensory (from your skin and internal organs), go through this organ on their way to other parts of the brain for processing. It also plays a function in motor control.The Neocortex
The last and most advanced brain to evolve to date is called the Neocortex, neomammalian or rational brain. We share this part of our brain with other higher level mammals like the primates and dolphins, although in humans the neocortex is the largest. It takes up 2/3's of the human brain. This is where we find the brain power to develop language, abstract thought, conciousness and imagination. Let there be no doubt, this is what grants us our status on the food chain and allows us to be human.The Neocortex is divided into two hemispheres, right and left. The right side of the brain controls the left side of the body and vice versa. Also the hemispheres are divided in terms of what kind of thought they process or produce. The right being more concerned with the artistic, spatial and musical. While the left is more concerned with the colder, linear, rational and verbal aspects. Located in the Neocortex are:· The Frontal Lobe
This is the most recent evolutionary addition to the brain. If the brain had a White House it would be here. It is the true center for command and control in your body. The Frontal lobe is responsible for functions such as reasoning, problem solving, judgement, impulse control. This coupled with the fact that it's the last to develop when we are young adults, probably answers a lot of questions for many parents out there. It also manages our higher emotions such as empathy and altruism. This lobe is also involved in motor control and memory.· The Parietal Lobe
The Parietal Lobe is involved in processing pain and touch sensation. It's where the Somatosensory (from your skin and internal organs) Cortex resides. It's also associated with cognition (including calculating location and speed of objects), movement, orientation, recognition and speech.· The Temporal Lobe
The Temporal Lobe is involved in auditory (sound) sensation and is where the Primary Auditory Cortex and on the left hemisphere, Wernicke's Area (language recognition) are located. This lobe is also involved in emotion, memory and speech.· The Occipital Lobe
The Occipital Lobe controls visual sensation and processing. The Visual Cortex is resides here.· Broca's Area
This part of the cortex controls speech, language recognition and facial nerves.· The Corpus Callosum
This is the neural bridge that connects the two hemispheres to each other, located centrally in brain.
The Lungs
The lung is a magnificent organ that performs a multitude of vital functions every second of our lives. Breathing is the most essential of these functions. With each breath, the lungs take in oxygen and remove carbon dioxide.
The air (oxygen) we breathe enters the lungs via the main windpipe (trachea), which branches into two main tubes supplying the right and left lung, respectively. These tubes progressively branch 22 additional times to form more than 100,000 smaller tubes (bronchi, bronchioles) and more than 300 million air sacs (alveoli), which are only about 0.3 mm in diameter.
Thus, the surface area of the lungs is huge -- larger than the surface of a person's skin. In fact, if all the airways and air sacs of a person's lungs were laid flat on the ground, they would cover more than 100 square yards, which is larger than the size of a tennis court. Because the walls of these air sacs are 1/50th the thickness of tissue paper and are bathed with millions of tiny blood vessels called capillaries, there is an easy and efficient exchange of oxygen and carbon dioxide between the body and the environment.
The lungs are also important in the body's defense against infection and other harmful environmental factors. While the nose is the first line of defense against inhaled harmful materials, the lungs provide the second line of defense. Inhaled particles (smoke, pollution) or infectious agents (bacteria, viruses) pass through the mouth or nose and lodge in the lungs.
Mucus, a sticky fluid produced in the lungs, can trap these inhaled agents and aid the lungs' protective white blood cells (macrophages, neutrophils) in the engulfment and destruction of bacteria and other harmful materials. Coughing is the best way to clear mucus and other materials from the lungs; however, the larger airways have tiny hairlike cells called cilia that aid in this process. The cilia beat with a rhythm fast enough, and a force sufficient enough, to propel mucus and cells up the airways to be coughed out or swallowed. When a person smokes, the cilia are inactivated or destroyed, allowing thick mucus to accumulate and compromise lung defense.
The Teeth
Teeth (singular tooth) are small, calcified, whitish structures found in the jaws (or mouths) of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness.
Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing.Carnivores, on the other hand, need canines to kill prey and to tear meat.
Mammals are diphyodont, meaning that they develop two sets of teeth. In humans, the first set (the "baby," "milk," "primary" or "deciduous" set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months is known as teething and can be painful.
Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth.Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Many rodents such as voles (but not mice) and guinea pigs, as well as rabbits, have continuously growing molars in addition to incisors.
Section of a human molar
The Skin
The skin forms a protective coating over the whole body and act as a mechanical barrier against the entry of bacteria. It consists of two layers, the Epidermis and the Dermis.Functions of SkinSkin performs the following functions:1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.2. Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory system and haptics.3. Heat regulation: the skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals.4. Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss.5. Storage and synthesis: acts as a storage center for lipids and water6. Absorption: Oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts, some animals using their skin for their sole respiration organ (contrary to popular belief, however, humans do not absorb oxygen through the skin).7. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.
The Epidermis
The upper or outer layer of the two main layers of cells that make up the skin. The epidermis is mostly made up of flat, scale-like cells called squamous cells. Under the squamous cells are round cells called basal cells. The deepest part of the epidermis also contains melanocytes. These cells produce melanin, which gives the skin its color.
The Dermis
The other main layer of the skin is the dermis, the inner layer of skin, that contains blood and lymph vessels, hair follicles, and glands. These glands produce sweat, which helps regulate body temperature, and sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin's surface through tiny openings called pores.
The Blood
Blood is a specialized bodily fluid that delivers necessary substances to the body's cells – such as nutrients and oxygen – and transports waste products away from those same cells.The average adult has about five liters of blood living inside of their body, coursing through their vessels, delivering essential elements, and removing harmful wastes. Without blood, the human body would stop working.Blood is the fluid of life, transporting oxygen from the lungs to body tissue and carbon dioxide from body tissue to the lungs. Blood is the fluid of growth, transporting nourishment from digestion and hormones from glands throughout the body. Blood is the fluid of health, transporting disease fighting substances to the tissue and waste to the kidneys.
Blood circulation
Red = oxygenated
Blue = deoxygenated
Because it contains living cells, blood is alive. Red blood cells and white blood cells are responsible for nourishing and cleansing the body. Since the cells are alive, they too need nourishment.Vitamins and Minerals keep the blood healthy. The blood cells have a definite life cycle, just as all living organisms do. Approximately 55 percent of blood is plasma, a straw-colored clear liquid. The liquid plasma carries the solid cells and the platelets which help blood clot. Without blood platelets, you would bleed to death.When the human body loses a little bit of blood through a minor wound, the platelets cause the blood to clot so that the bleeding stops. Because new blood is always being made inside of your bones, the body can replace the lost blood. When the human body loses a lot of blood through a major wound, that blood has to be replaced through a blood transfusion from other people.But everybody's blood is not the same. There are four different blood types. Plus, your blood has Rh factorswhich make it even more unique. Blood received through a transfusion must match your own. Patients who are scheduled to have major surgery make autologous blood donations (donations of their own blood) so that they have a perfect match.
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