Anatomy/Nervous System

The nervous system is a focus topic of the event Anatomy. It comes into rotation for the 2013 season. The nervous system consists of your brain and all the nerves throughout your body. It is responsible for regulating the body's response to external and internal stimuli. It can be divided into the central and peripheral nervous systems. The central nervous system or CNS includes the brain, cranial nerves, and the spinal cord; the peripheral nervous system or PNS, includes all nerves outside of the spinal region.


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Brain and Sense Organs
There are a wide variety and a vast number of parts in the Nervous System, but the major regions are the brain, nerves, and spinal cord, all of which contribute to the great capabilities of the human body.

The Brain
Your brain is arguably the most important organ in your body. It controls all actions, stores memory, and processes the 5 senses. It has many important parts, each with a unique and vital role.



The brain is divided into four main lobes: the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. Each has a specific function.

Frontal Lobe
The frontal lobe is responsible for conscious thought; damage to it can result in severe personality changes. It is positioned anterior to the central sulcus. It is generally responsible for recognizing future consequences resulting from current actions, choosing between good and bad actions (or better and best), overriding and suppressing socially unacceptable responses, and determining similarities and differences between things or events. In the posterior portion of the frontal lobe lies the precentral gyrus which is also known as the somatomotor or primary motor cortex. This is where voluntary motions are processed. The motor homunculus (little person) represents the portions of the body which the motor cortex controls. The foot lies inside the medial longitudinal fissure,the leg lies up against the medial longitudinal fissure, and traveling outward from there follow the arm and the head. While this cortex does control other regions of the body, there aren't enough controls in those regions to warrant a position in the homunculus. Different hemispheres of the brain control the body contralaterally.

In humans, the frontal lobe generally reaches maturity around 20 years old. This explains why, in most societies, people are considered to be an adult around this age.

Parietal Lobe
The parietal lobe is associated with spatial processing and navigation abilities. It is positioned posterior to the central sulcus and thereby the frontal lobe, anterior and superior of the parieto-occipital sulcus and superior of the lateral sulcus or sylvian fissure. It gets its name from the bone that lies above it, the parietal bone. In the anterior portion of the parietal lobe lies the somatosensory or primary sensory cortex which has nearly the same organization as the somatomotor cortex, just with more concentration in the genitalia and breasts.

Occipital Lobe
The occipital lobe is the section in which your brain processes visual images that come from your eyes. It is positioned in the back of the head, which gets it its name, since in Latin, 'oc' means back and 'caput' means head. It is positioned posterior and inferior of the parieto-occipital sulcus.

Temporal Lobe
The temporal lobe is responsible for visual memory/object recognition, processing sound and smell, and understanding language. It is located inferior to the lateral sulcus or sylvian fissure, and is positioned between the frontal and occipital lobe.

Other Divisions of the Brain

 * The Cerebrum- The Cerebrum controls perception, imagination, thought, judgement, and decision. The Cerebrum basically consists of the outer surface of the brain. It is the largest portion of the brain and encompasses about two-thirds of the brain mass. It consists of two hemispheres (right and left) divided by a fissure called the corpus callosum. It is further divided into lobes, such as the occipital lobe (processes vision) and the frontal lobe (processes voluntary movement and planning). It includes the cerebral cortex, the medullary body, and basal ganglia

The cerebral cortex is the layer of the brain often referred to as gray matter because it has cell bodies and synapses but no myelin (which makes other parts of the brain look white). The cortex covers the outer portion (1.5mm to 5mm) of the cerebrum and cerebellum. The cortex consists of folded bulges called gyri that create deep furrows or fissures called sulci. The folds in the brain add to its surface area which increases the amount of gray matter and the     quantity of information that can be processed.

The medullary body – is the white matter of the cerebrum and consists of myelinated axons

Basal ganglia – masses of gray matter in each hemisphere which are involved in the control of voluntary muscle movements

| General Psychology: Cerebrum


 * The Cerebellum- The Cerebellum is located under the Cerebrum, at the back of the brain. It controls balance, movement, and coordination. It is also involved in attention and language. | Neuroskills

| Brain Stem
 * The Brain Stem- The Brain Stem is located under the Cerebrum, and in front of the Cerebellum. It mainly controls involuntary functions such as respiration, digestion, circulation, sleep patterns, hunger and thirst, blood pressure, heart rhythms, and body temperature and moving involuntary muscles such as the heart. It helps to regulate the central nervous system. Basal ganglia connected to the brain stem function as switching centers. The brain stem houses the midbrain (mesencephalon), pons (part of the metencephalon), and medulla oblongata (myelencephalon). This is the area of the brain that attaches to the spinal cord. At the brain stem, information is sent back and forth between the cerebrum or cerebellum and the body. Cranial nerves 3-12 are located in the brain stem as well as significant processing centers.  Nerve fibers that are sent to the rest of the body from the brain must move through the brain stem. The motor and sensory systems that work along these nerves connections include the corticospinal tract (which includes motor skills), the posterior column-medial lemniscus pathway (this includes proprioception, vibration sensation and fine touch), and the spinothalamic tract (this is crude touch, pain, itch, and temperature). The cranial nerves that are located at the brain stem send the main motor and sensory feeling to the face and neck.


 * The Pituitary Gland- The Pituitary gland is responsible for controlling the release of hormones throughout the body. It is important in growth especially puberty. It can also be considered part of the Endocrine System. | U of Maryland Med. School


 * The Diencephalon- The diencephalon is made up of 2 parts (1) the thalamus and (2) the hypothalamus.

1. The Thalamus- The Thalamus is a dense nucleus. The thalamus receives sensory impulses from other parts of the nervous system. It receives all sensory impulses (except the sense of smell) and channels them to appropriate regions of the cortex for interpretation. In addition, all regions of the cerebral cortex communicate with the thalamus by descending fibers. The thalamus produces a general awareness of certain sensations such as pain, touch, and temperature.

2. The Hypothalamus- The Hypothalamus's most important function is to regulates your body's temperature using thermoreceptors and osmoreceptors. This is called homeostasis. If your body is too hot, the hypothalamus makes you sweat to lower your temperature. If your body is too cold, the hypothalamus makes you shiver to increase your body temperature. It also monitors and regulates food intake, water-salt balance, blood flow, sleep-wake cycle, and the activity of hormones secreted by the pituitary gland. It also mediates responses to emotions. It is a tiny cluster of brain cells that transmits messages from the body to the brain, and it links the autonomic nervous system, the limbic system, and the endocrine systems. | Biology: Hypothalamus

| UCSD: Limbic System
 * The Limbic System- The Limbic System is located in the middle of the brain. It consists of structures such as the hippocampus (processes short term memory into long term memory). It is important for memory, learning, and emotion. The limbic system is in charge of the expression of instincts, drives, and emotion. It mediates the effects of moods on behavior and influences interal changes in body function with their expression. It also associates feelings with sensations.


 * Broca’s area – located in the frontal lobe and is important in the production of speech


 * Wernicke’s area – comprehension of language and the production of meaningful speech


 * Cerebrospinal Fluid - cerebrospinal fluid is a colorless fluid that flows through the brain and spinal cord. It acts as a barrier to prevent wastes from damaging the brain and to maintain homeostatic conditions. When there is too much cerebrospinal fluid, hydrocephalus (or hydrocephaly) results, causing swelling in the head. This can be reversed to an extent by tubes draining the excess fluid.


 * Commisural fibers – conduct impulses between the hemispheres and form corpus callosum


 * Projection fibers – conduct impulse in and out of the cerebral hemispheres


 * Association fibers – conduct impulses within the hemispheres

The Nerves
The nerves are the body's messengers. The send the brain's messages and commands to the corresponding parts of the body. The spinal cord is the long bundle of nerves running through the back of your body. It connects with the brain, and all the other nerves. The spinal cord is supported by your backbone. The nerves are made of cells called neurons bound together in bundles called fascicles, nerves, peduncles, or tracts and surrounded by the endoneurium, perineurium, and epineurium membranes. Neurons connect with each other to communicate. Electrochemical waves travel along the axon of one neuron, then move across a gap called a synapse. Sodium and potassium ions are pumped across the synapse to the dendrite of another neuron in a nerve impulse.



Sense Organs
Sense Organs consist of the eye, ear, nose, tongue

Eye


Eye- the organ of vision. It consists of a transparent lens that focuses light on the retina. The retina is covered with light-sensitive cells-rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. These cells are located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The optic nerve is called the "blind spot" because it is insensitive to light. The occipital lobe of the brain maps the visual input from the eyes. The brain combines the input of our two eyes into a three-dimensional image. In addition, even though the image on the retina is upside-down because of the focusing action of the lens, the brain compensates and provides the right-side-up perception. In the dark, a substance produced by the rod cells increases the sensitivity of the eye so that it is possible to detect very dim light. In strong light, the iris contracts reducing the size of the aperture that admits light into the eye and a protective obscure substance reduces the exposure of the light-sensitive cells. The spectrum of light to which the eye is sensitive varies from the red to the violet. Lower electromagnetic frequencies in the infrared are sensed as heat, but cannot be seen. Higher frequencies in the ultraviolet and beyond cannot be seen either, but can be sensed as tingling of the skin or eyes depending on the frequency. The human eye is not sensitive to the polarization of light, i.e., light that oscillates on a specific plane.

Ear


Ear- the organ of hearing. The outer ear protrudes away from the head and is shaped like a cup to direct sounds toward the tympanic membrane, which transmits vibrations to the inner ear through a series of small bones in the middle ear called the malleus, incus and stapes. The inner ear, or cochlea, is a spiral-shaped chamber covered internally by nerve fibers that react to the vibrations and transmit impulses to the brain via the auditory nerve. The brain combines the input of our two ears to determine the direction and distance of sounds. The inner ear has a vestibular system formed by three semicircular canals that are approximately at right angles to each other and which are responsible for the sense of balance and spatial orientation. The inner ear has chambers filled with a viscous fluid and small particles (otoliths) containing calcium carbonate. The movement of these particles over small hair cells in the inner ear sends signals to the brain that are interpreted as motion and acceleration. The human ear can perceive frequencies from 16 cycles per second, which is a very deep bass, to 28,000 cycles per second, which is a very high pitch. The human ear can detect pitch changes as small as 3 hundredths of one percent of the original frequency in some frequency ranges. Some people have "perfect pitch", which is the ability to map a tone precisely on the musical scale without reference to an external standard.

Nose


Nose- the organ of smell. The nose is the organ responsible for the sense of smell. The cavity of the nose is lined with mucous membranes that have smell receptors connected to the olfactory nerve. The smells themselves consist of vapors of various substances. The smell receptors interact with the molecules of these vapors and transmit the sensations to the brain. The nose also has a structure called the vomeronasal organ whose function has not been determined, but which is suspected of being sensitive to pheromones that influence the reproductive cycle. The smell receptors are sensitive to seven types of sensations that can be characterized as camphor, musk, flower, mint, ether, acrid, or putrid. The sense of smell is sometimes temporarily lost when a person has a cold.

Tongue


Tongue- the organ of taste. The receptors for taste, called taste buds, are situated chiefly in the tongue, but they are also located in the roof of the mouth and near the pharynx. They are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue also can detect a sensation called "umami" from taste receptors sensitive to amino acids. Generally, the taste buds close to the tip of the tongue are sensitive to sweet tastes, whereas those in the back of the tongue are sensitive to bitter tastes. The taste buds on top and on the side of the tongue are sensitive to salty and sour tastes. At the base of each taste bud there is a nerve that sends the sensations to the brain. The sense of taste functions in coordination with the sense of smell. The number of taste buds varies substantially from individual to individual, but greater numbers increase sensitivity. The gouge is covered with papillae which makes the tongue have a rough texture.

CNS

 * astrocyte - named so because it resembles a star. These are the support cells of the CNS, they help form the blood-brain barrier, supply nutrients to neurons, and help regulate the extra cellular chemical environment most notably, removing potassium ions, in order to keep the concentration gradient. These are the most numerous of th CNS glial cells.
 * oligodendrocyte - these are similar to Schwann cells, but in the CNS. Like Schwann cells, they provide myelination to axons. However, they are able to myelinate many axons around they instead of just one.
 * microglia-these are the macrophages of the CNS. They protect the neurons from bacteria and viruses through phagocytosis. These are the least numerous of the CNS glial cells.
 * ependymal cells - also called ependymocytes. These line the walls of the ventricular and produce cerebrospinal fluid. They also have cilia that they beat in order to move CSF. Also, they make up the blood CSF barrier. Lastly, they also are believed to be neuronal stem cells.

PNS

 * schwann cells-these cells myelinate PNS axons. All cells-even the unmyelinated ones- in the PNS are surrounded by schwann cells. When myelinating, Schwann cells can only surround 1 axon, however, they can surround many unmyelinated axons at once. They also undergo a small amount of phagocytotic activity and they clear debris.
 * satellite cells-these cells are similar to astrocytes in that they regulate the extracellular chemical environment. They are different in that that is their only main job.

Spinal Cord
Along with the brain, the spinal cord makes up the central nervous system. It is divided into 31 pairs of nerves, making 62 nerves composed of sensory and motor neurons. The nerves are named off of where they leave the spine. They are divided into 5 groups, cranial, thoraic, lumbar, sacral, and coccygeal. The spinal cord itself in an adult usually ends around the L1 or L2 vertebra, while the remaining axons, formin the cauda equina, continue headin down through the spine and exit where they are supposed to. This happens because the spinal cord stops growing at 4 years of age, while the spine continues to grow. The spinal cord contains both white and gray matter. The white matter travels in tracts to and from the brain. The gray matter forms a sort of h, with 3 horns on either side of the spinal cord. The ventral horn contains somatic motor nuclei, the lateral horn contains autonomic motor nuclei. The dorsal horn is divided, with the farthest back being the somatic sensory portion and the other portion being the visceral sensory portion.
 * 8 pairs in the cervical region
 * 12 pairs in the thoracic region
 * 5 pairs in the lumbar
 * 5 pairs in the sacral
 * 1 pairs in the coccygeal.

Encephalography
A neural examination/radiography in which a small amount of cerebrospinal fluid is replaced with a gas.

Magnetic Resonance Imaging (MRI)
A scan of the brain which uses magnets to show images of the body with sharp contrast of soft tissue, air, and bone. This has advantages because it doesn't use radiation.

Neural Impulses
Ionic basis of the cellular membrane potential



When a neuron is not sending a signal, the inside of the neuron is negative relative to the outside. Although the concentrations of the different ions attempt to balance out on both sides of the membrane, they cannot because the cell membrane allows only some ions to pass through channels (ion channels). At rest, potassium ions (K+) can cross through the membrane easily. Also at rest, chloride ions (Cl-) and sodium ions (Na+) have a more difficult time crossing. The negatively charged protein molecules (A-) inside the neuron cannot cross the membrane. The sodium- potassium pump removes 3 sodium ions for every 2 potassium ions it lets in. When all forces balance out, and the difference in the voltage between the inside and outside of the neuron is measured. That is the resting potential. The resting membrane potential of a neuron is about -70 mV. At rest, there are more sodium ions outside the neuron and more potassium ions inside that neuron. Action Potential: Generation and Propagation

An action potential (spike/ impulse) occurs when a neuron sends information down an axon, away from the cell body.

1. Generation- A stimulus causes the resting potential to move toward 0 mV. When the depolarization reaches about -55 mV a neuron will fire an action potential. If the neuron does not reach this critical threshold level, then no action potential will fire. "ALL OR NONE" principle- The neuron either does not reach the threshold or a full action potential is fired. All sizes of action potentials are the same. Action potentials are caused when different ions cross the neuron membrane. A stimulus first causes sodium channels to open. Because of the concentration gradient, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Sodium has a positive charge, so the neuron becomes more positive and becomes depolarized. It takes longer for potassium channels to open. When they do open, potassium rushes out of the cell, reversing the depolarization. Sodium channels start to close. This causes the action potential to go back toward -70 mV (a repolarization). The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long. Gradually, the ion concentrations go back to resting levels and the cell returns to -70 mV.



2. Propagation- action potentials are carried from the axon of one neuron to the dendrite of another neuron by synapses and neurotransmitters. Positively charged ions in the fluid outside of the cell flood into the cell and the charge on the inside changes from negative to positive. The electrical impulse moves down the axon.



Impulses From Axon to Dendrite

Synapses- junctions where neurons pass signals to other neurons, muscle cells, or gland cells. When a charge reaches a synapse, it may trigger release of tiny bursts of chemicals called neurotransmitters. The synapse contains a small gap separating neurons. The synapse consists of: 1.a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles 2.a postsynaptic ending that contains receptor sites for neurotransmitters 3.a synaptic cleft or space between the presynaptic and postsynaptic endings. Neurotransmitters- used to restart impulse in the dendrite of the second neuron. They are chemicals in junctions.

For communication between neurons to occur, an electrical impulse must travel down an axon to the synaptic terminal. At the synaptic terminal, an electrical impulse will trigger the migration of vesicles containing neurotransmitters toward the presynaptic membrane. The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft. The neurotransmitter molecules diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message." Excess neurotransmitters are broken down by enzymes. If they are not, paralysis will occur. One example of a neurotransmitter is acetylcholine. The enzyme that breaks it down is acetylcholinesterase.



Central Nervous System
Consists of the Brain and Spinal Cord. Parts of the Brain- view above Organization of the Spinal Cord- view above

Peripheral Nervous System
Nerves and ganglia not including the CNS (see above) Split into afferent and efferent nervous systems The efferent nervous system is split into the autonomic and somatic nervous systems. The autonomic nervous system is split into the sympathetic and parasympathetic nervous systems.
 * afferent-sensory
 * efferent-motor.
 * autonomic-controlled by the subconscious. Happens "auto"matically. Can control all types of muscle
 * somatic-controlled by the conscious brain. Always effects skeletal muscle.
 * sympathetic-"fight or flight" response. Responds in times of stress.
 * parasympathetic-controls the body in times of rest.

Links

 * http://yucky.discovery.com/flash/body/pg000136.html


 * http://kidshealth.org/kid/htbw/brain.html


 * http://www.albany.edu/faculty/cafrye/apsy601/Ch.02cellsofthenervoussystem.html

Official Information 2013
These are all safe, downloadable files from http://www.soinc.org.

Official Training Handout 2013
http://www.soinc.org/sites/default/files/ANATOMY_HANDOUT_2013.doc

Official Training PowerPoint 2014
http://www.soinc.org/sites/default/files/uploaded_files/A%26P-2014.ppt