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Chapter 3
Neurophysiology
| Question | Answer |
|---|---|
| What two types of cells is the nervous system made up of? | Glia and neurons. |
| What is the function of glia? | They carry out support functions for the neurons. |
| What are the two types of glia? | Macroglia and microglia. |
| What are the types of macroglia? | Astrocytes, oligodendrocytes and Schwann cells. |
| What are the functions of astrocytes, oligodendrocytes and Schwann cells? | Astrocytes provide a variety of support functions to neurons. Oligodendrocytes and Schwann cells supply the myelin covering that insulates axon fibers. |
| What are some of the functions of astrocytes? | -Structural matrix for the neuron. -Connect with brain's capillary cells -> nutrients get to neurons, contribute to blood brain barrier -Keep neurochemicals within gap -Can clear synaptic gap -Remove excess potassium from extracellular fluid |
| How can astrocyte behaviour be harmful? | When CNS neurons are damaged, they form scar tissue to replace injured area and release chemicals that inhibit neural regrowth. Thus, it can also interfere with repairing of damaged connections. |
| Where can oligodendrocytes and Schwann cells be found? | In the CNS and the PNS respectively. |
| How are oligodendrocytes and Schwann cells similar and different? | They both supply myelin covering. Oligodendrocytes can myelinate axons from average of 15 different neurons, contributing to structural stability, while Schwann cells are able to guide the regrowth of damaged axons. |
| What do microglia do? | They are the brain's cleanup crew: they travel to the location of any neural injury, digesting the debris. |
| What are neurons made up of? | The soma (cell body) (+membranes and nuclei inside the soma), the axons (+ axon hillock and nodes of ranvier) and the dendrites |
| What is the purpose of the neural membrane? | It forms a boundary between the cell and its external environment. |
| What is the neural membrane made up of? | A double layer of phospholipids. |
| How is the fatty nature of the neural membrane suitable for its purpose? | It does not dissolve in water, and so is able to restrain the water-based fluids on either side. |
| What is the purposes of the ion pumps and ion channels? | They control the permeability of the membrane by providing pores which specific ions can move through. |
| What determines what ion passes through the ion pumps and channels? | The amino acid that make up the ion pump or channel. |
| What is the difference between ion pumps and channels? | Ion channels allow ions to move through passively without using up energy but ion pumps require energy. |
| What are the different types of ion channels? | Voltage-dependent channels and ligand-gated channels. |
| What are voltage-dependent channels? | They are ion channels that close and open in response to the electrical status of adjacent areas of membrane. |
| What are ligand-gated channels? | They are ion channels that open when they come in contact with specific ions. |
| What is a sodium-potassium pump? | Sodium-potassium pumps help maintain the differences in chemical composition between the intracellular and extracellular fluids by sending out three sodium ions out of the cell while collecting two potassium ions from the extracellular flluid |
| How much energy does all the sodium-potassium pump cost the brain? | 20 to 40 percent. |
| What is the difference between a sodium-potassium pump and a calcium pump? | Calcium pumps also perform the same function i.e send out calcium from the cell, but they do not collect another type of ion in exchange. |
| What provides the structural support for the neuron? | The cytoskeleton. |
| What are the three types of filament that make up the cytoskeleton? Largest first. | The microtubules (25 nm), the neurofilaments (10 nm), and the microfilaments (3-5 nm) |
| What is the role of the microtubules in the cytoskeleton? | They are responsible for the movement of various materials in the cell, including filled vesicles. |
| What is anterograde and retrograde transport in the microtubules? | Anterograde transport is the transport of materials away from the cell body. Retrograde transport is the transport of materials to the cell body. |
| How fast is the transport of materials in the microtubules? | It can vary from slow (<8 mm per day) to fast (400 mm per day), depending on the material being used. |
| What implications does transport in the microtubules have for pathogens? | Pathogens such as rabies which otherwise cannot enter the CNS because of the blood-brain barrier "hitchhike" via the retrograde transport system, travelling from the axon terminal to the brain and spinal cord |
| How does Alzheimer's disease affect transport in the microtubules? | Tau, a protein that connects adjacent microtubules and holds them in place, increases. The neuron then adds molecules of phosphate to the tau protein, causing it to disconnect. The tau forms tangles, hindering the cell's signalling. The cell collapses. |
| Which of the three filaments in the cytoskeleton are the most common? | The neurofilament. |
| What do neurofilaments in the cytoskeleton do? | They run parallel to the length of the axon and provide structural support. |
| What do microfilaments in the cytoskeleton do? | They might participate in changing the shape and length of the branches of the neuron during development and during learning. |
| What are the prominent organelles inside the soma? | The nucleus, the nucleolus (inside nucleus), the endoplasmic reticulum, the golgi apparatus and the mitochondria. |
| How are vesicles made in the neurotransmitter? | 1. Proteins are constructed by ribosomes on the rough endoplasmic reticulum 2. They are moved by the smooth endoplasmic reticulum to the Golgi apparatus. 3. The Golgi apparatus inserts the completed proteins into vesicles. |
| What does the nucleolus do? | It builds organelles known as ribosomes. |
| What do the rough and smooth portions of the endoplasmic reticulum do? | The rough portion has many ribosomes bound to its surface, which produce proteins. The smooth portions move the completed proteins to the Golgi apparatus. |
| How does mitochondria provide energy for the cell? | It extracts oxygen and pyruvic acid from sugar in the intracellular fluid and construct and release molecules of ATP which is the major energy source for the neuron. |
| What are dendrites and what do they do? | They are the branches of the neuron. They serve as locations at which information from other neurons is received. |
| What is the relationship between the surface area of dendritic membrane on a neuron and the amount of synapses it can form? | The greater the surface area of dendritic membrane a neuron has, the larger the number of synapses or connections it can form with other neurons. |
| Where are receptor sites located? What do they do? | They are located at the synapse on the dendrite. They are ligand-gated and thus interact with neurotransmitters released by the presynaptic neuron that have floated across the gap. |
| What are dendritic spines? | They are knobs on the dendrives. They provide additional locations for synapses to occur. |
| What are dendritic spines able to do? | They can change their shape based on the amount of activity occurring at the synapse, contributing to the processes of learning and memory. |
| What is an axon? | It is responsible for carrying messages to other neurons. |
| Where is the axon hillock? What does it do? | It is located at the junction of the axon and the cell body. Action potentials start in the axon hillock and are then reproduced down the length of the axon. |
| How large can axon diameters be? How does this affect transmission speed? | They can range from <1 micrometer to 25 micrometers. Large diameter axons are faster than smaller diameter axons. |
| Why are vertebrate axons much faster than invertebrate axons? | Vertebrate axons are insulated by myelin. |
| What local circuit neurons? | They are neurons that have axons that extend only a small bit from the cell body to communicate with adjacent cells. |
| What are projection neurons? | They are neurons with very long axons e.g. 3 feet or more long |
| What are axon collaterals? | The branches at the end of most axons |
| What are axon terminals? | The very end of each axon collateral. |
| What are axonal varicosities? | They are swellings that occur at intervals along the length of unmyelinated segments of axon. |
| What do axon terminals and axonal varicosities both contain? | Mitochondria and synaptic vesicles. |
| What are the neurons in the human body that are myelinated and non-myelinated? | Most of the CNS neurons and peripheral motor neurons are myelinated. Peripheral sensory nerves may or may not be myelinated, |
| Which parts of the neuron are not myelinated? | The axon hillock and the nodes of ranvier. |
| Describe the physical characteristics of the nodes of ranvier. | They are about 1 micrometer long and occur about once every 0.2 to 2.0 mm down the axon. Large diameter axons have thicker myelin and greater distances between nodes of Ranvier. |
| What are the advantages of myelin? | 1. It allows human axons to be smaller in diameter without sacrificing transmission speed. 2. It reduces the energy requirements of neurons by decreasing work done by Na-K pumps. |
| How does myelin decrease work done by pumps? | 1. Myelin wrap so tightly around axons - > no extracellular fluid bet. sheath and membrane 2. No ion channels under sheath; ion channels are concentrated at unmyelinated places During signalling less ions move in -> less ions need to be pumped out |
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