ALS 2304 Week 4, Neurophysiology
ALS 2304 Week 4, Neurophysiology ALS 2304
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This 3 page Class Notes was uploaded by Mara DePena on Thursday February 11, 2016. The Class Notes belongs to ALS 2304 at Virginia Polytechnic Institute and State University taught by Dr. Cline in Spring 2016. Since its upload, it has received 72 views. For similar materials see Animal Physiology and Anatomy in Agricultural & Resource Econ at Virginia Polytechnic Institute and State University.
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Date Created: 02/11/16
ALS 2304 NEUROPHYSIOLOGY The cells of the nervous system are the neurons. Scenario for the exam (worth 80%): A horse is standing out in the pasture. Then, a snake comes up and bites it on its rear leg. This startles the horse, which kicks and then flees the scene. o Lectures will cover the circuitries in this and the physiology of the muscle. Neurons- Sit in circuits and work this way. They are essentially switches- either turned on or turned off. Sensory neuron- Receives sensory information from the external environment. Takes this info and sends it to the brain. Interneuron- The neuron that makes the decision of what is going to happen next, either by firing or not firing. o If it fires, there is a response to the stimulus. It will stimulate the motor neuron. Motor neuron- Leaves the brain and synapses on a skeletal muscle. THE NERVOUS SYSTEM Central nervous system- Brain and spinal cord itself. Peripheral nervous system- Everything else. o Sensory Sensory neurons carry signals into system. o Motor Take commands out of system. Autonomic nervous system- Involuntary. Conducts impulses from central nervous system to cardiac muscles, smooth muscles, and glands. Sympathetic division- Mobilizes body during emergency situations. Fight/flight. Parasympathetic division- Conserves energy, nonemergency functions. Somatic nervous system- Voluntary. Conducts impulses from the CNS to skeletal muscles. NERVE CELLS Neurons- Excitable cells that transmit electrical signal. o Soma- Center/bulk of neuron. o Axon- Very long process (arm) that comes off the neuron. It bulges where a synapse happens and forms an axon terminal. o Dendrites- Process, receptive region. Hundreds of terminals synapse on one dendrite, all sending out different neurotransmitters. Graded potential- Change in charge inside membrane. Appears mostly on dendrites. As it flows, it loses magnitude. EPSP- Type of graded potential that carries positive ions (Na) in. If it reaches the axon hillock, it causes an action potential to fire. IPSP- Type of graded potential that carries negative ions (Cl) in. This gets to the hillock and inhibits action potential. Whichever of these two predominates determines if the neuron fires or not. o Axon hillock- Where the axon connects to the soma. Sums all of the EPSP and IPSP and determines whether or not to fire an action potential (will fire if voltage is above 55 mV.) Voltage receptors- Open ion channels in response to change in charge (flow of positive ions.) Allows positive ions to flow in. If the first is triggered, they all open. This causes the creation of action potential, which does not lose magnitude as it goes down the axon. When the action potential gets down to the axon terminal, it activates voltage-gated calcium channels. Calcium sends out a neurotransmitter. o When a neuron is not doing anything, there is a slightly negative charge on the membrane known as resting membrane potential. This is formed by the sodium-potassium pumps located everywhere on the neuron. Neuroglia (glial cells)- “Neuron helpers.” Don’t transmit electrical impulses according to out current understanding. Chaperones for neurons, as neurons are extremely delicate. Neurons die without them. They surround and wrap neurons, insulate, promote health and growth, and guide young neurons to connections. o Astrocytes- Most abundant, cover capillaries. Control chemical environment. o Microglia- Phagocytes. Part of the immune system (as immune system is greatly suppressed within the brain itself.) Monitor neuron health. o Ependymal cells- Line cavities of the brain and spinal cavities. Entire brain is surrounded by blood-brain barrier, a collection of cells in a long line held together by tight junctions. This filters what gets in/out of the brain. Most drugs cannot cross this barrier. o Oligodendrocytes- Branched. Wrap CNS fibers. Insulate neurons. Makes up white matter. o Schwann cells- AKA neurolemmocytes. Surround PNS fibers. Insulate nerves. o Satellite cells- Surround neuron cell bodies with ganglia. TRANSPORT Neurotransmitters are released out of the terminal. They are made by transcription/translation in the soma and moved down to the terminal. Anterograde transport- Moving something (neurotransmitters) from the soma down to the terminal. Molecular motors are responsible for transport. Carry neurotransmitters to axon terminal. Retrograde transport- Moving something (waste) from the axon terminal to the soma. Myelin sheath- Made up of schwann or oligodendrocyte. Whitish, fatty, segmented sheath around most long axons.
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