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What are the three Parts of the Nervous System? Central Nervous System (CNS): brain and spinal cord. 1. Peripheral Nervous System (PNS): nerves of the body 2. Autonomic Nervous System (ANS): has parts of the CNS and PNS. Controls autonomic function (blood pressure, digestion, etc). a. Sympathetic division b. Parasympathetic division Which system is made up of more cell than any other system? Nervous System About how many cells does the brain have? A trillion cells What is the main and most important cell type of the nervous system? Neuron What are three things that all neurons do? 1. Receive a signal. Can be any type of stimulus (change in environment, signal from another neuron, etc). 2. Transmit a signal to another location. E.g. finger touching something signal to spinal cord or brain. 3. Stimulate another cell a. Another neuron transmit signal b. Muscle contraction c. Gland secretion What are some other special characteristics of neurons? • • • Longevity – can live and function for a lifetime Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose How many types of neurons exist? There are hundreds of different types of neurons. What is the function of each type of neuron? Each one is specialized for a particular task (e.g. sensory nerves receive and transmit sensory information, and there are several different types of them, with receptors for touch, light, smell, etc). Motor neurons transmit signals for muscle contraction, etc. What characteristics do all neurons share? They all share certain characteristics. They have longevity (can last a lifetime), they have a high metabolic rate, they cannot divide to reproduce, and they cannot survive without oxygen. Neuron Describe the function of DENDRITES? They function to receive the signal and carry the nerve conduction toward the cell body. What is the CELL BODY? It’s where the nucleus, ribosomes, and most organelles are located Describe the function of an AXON? The function of an axon is to transmit signals. Some cells have many axons, some have one, some are short, and some are long. Describe the function of SYNAPTIC KNOBS? They function to stimulate another cell. Neurons may have a couple of synapses, or hundreds. Axon of presynaptic neuron SYNAPTIC CLEFT dendrite of post synaptic neuron How does the signal go through the space? By a chemical transmission. The synaptic knob has vesicles filled with a neurotransmitter that carries the signal. Each type of neuron used particular types of neurotransmitters, so there are 100’s of types. What is a type of cell in the nervous system other than neurons, that are supporting cells of the nervous system? Most tumors of the brain originate from these cells. GLIA (neuroglia) These are found in the CNS, and are very large and complex cells. They form myelin sheaths. OLIGODENDROCYTES (“few branches”) This sheath is a covering around an axon to speed up the nerve conduction. MYELIN SHEATHS Describe myelin sheaths. A sheet of paper is like one of these cells, and it wraps itself around a pencil (axon), so there are many layers. The myelin sheath is an electrical insulator. BETWEEN the sheaths are nodes = NODES OF RANVIER; these are BARE regions of axonal membranes only found in myelinated axons. What are the bare regions of axonal membranes only found in myelinated axons? NODES OF RANVIER Describe the function of myelinated axons and Nodes of Ranvier. The action potential jumps from one Node of Ranvier to the next Node of Ranvier, speeding up the overall nerve conduction. Therefore, a myelinated axon conducts impulses faster than an unmyelinated axon. An unmyelinated axon can travel 1-20 meters per second. A myelinated axon can travel 20-100 meters per second. Why would you want any unmyelinated axons? They are not necessary for things like digestion to start at 1/10 of a second rather than one second, or start sweating in 1/20 of a second rather than 1 second. Walking and thinking are things that need to be quick. An oligodendrocyte can wrap around one nerve cell in many locations, and nerve cells can have many oligodendrocyes on their axons. Describe MULTIPLE SCLEROSIS. It is an autoimmune disease where the oligodendrocytes (the myelin sheaths) are destroyed, interfering with the neuron functions in the CNS and brain. It is the most common neurological disease of young adults. Starts to manifest in late teens and early 20’s. It progresses to paralysis and sometimes death. One in 1000 people get it. There are treatments, but no cure. Which type of cell is another cell that forms myelin sheaths, but in the PNS? Each cell only forms one myelin sheath. SCHWANN CELL What is another very large, complex cell, in the CNS, whose function is to wrap around capillaries while it also is physically supporting and wrapping around neurons? ASTROCYTE Describe the function of astrocytes. a. Physically supports the neurons b. Transmits materials from capillaries to neurons c. Forms blood-brain barrier (BBB) Describe the blood brain barrier. The BBB prevents a lot of certain types of materials from leaving the blood and entering the brain (e.g. hormones, drugs). The brain still gets its nourishment from the blood, without the toxins. The continuous capillaries have leakage, but are surrounded by astrocytes, so not everything can leak out. Certain antibiotics can’t cross the BBB, so they can’t be used for brain infections. The only function of the blood-brain barrier is to help protect the central nervous system. What is the only function of the blood brain barrier? To help protect the central nervous system. These are not micro, nor are they glia. They are macrophages, the same size as everywhere else in the body. They are called micro because they are much smaller than real glia cells. They pick up bacteria and dead cell, etc. MICROGLIA (one word, two errors!). What is the portion of the CNS that is unmyelinated (cell bodies of neurons, glia, and dendrites)? GREY MATTER What is the portion of the CNS with myelin (axons)? WHITE MATTER What makes the white matter look white? Myelin A collection of axons in the PNS. No cell bodies, dendrites, or synapses; just axons. NERVE A collection of axons in the CNS e.g. conveys information (axons) from the left to the right side of the brain. TRACT Where information is processed. Most synapses are in the CNS. SYNAPSES A collection of cell bodies in the PNS. GANGLION A network of nerves (nerves don’t run by themselves, they go in groups). NERVE PLEXUS Nerves that leave the CNS to effect a muscle or gland. MOTOR NEURON This type of cell goes from body to CNS, carrying sensory information. SENSORY NEURON This is a small neuron found only in the CNS; it connects two other neurons. There are a large number of interneurons in the CNS; this is what makes the CNS complex. INTERNEURON