Introduction to Neurophysiology Neuroanatomy The Neuron the Brain and the Nervous Systems Basic Structure and Function Neuron they do the work of processing information neurons do the work of the nervous system Brain where all behavior feeling and thought originate a brain with no active neurons is feeling and thinking nothing and its impossible to behave Structure of an Interneuron Soma Dendrites and Axon Three Types of Neurons 1 Sensory Neurons specifically designed to take physical energy from the environment and transform it into neuro chemical impulses that gets passed on to other neurons located throughout our body 2 Motor Neurons specialized function of causing some kind of action by the body takes neuro chemical impulses and transforms them into motion ex skeletal muscle movement heart rate hunger thirst all these things involve motor neurons that receive messages from the brain telling the body what to do 3 Interneurons communicates with other neurons sensory neurons motor neurons interneurons three types of neurons There is a biochemical set of processes that is carried out by the cells of the nervous system Nothing else works unless the neurons in the brain are functioning In the brain there are 100 150 billion neurons talking on an order of complexity we can t wrap our minds around These billions are interconnected to thousands of the other neurons Interneurons will have 1 Dendrites branch like projections that protrude outward from the body or soma theyre like antennae they pick up signals from someplace else nucleus 2 Axon purpose is to transmit the electrochemical impulse from this neuron to the next one in the network its like a long tail 3 Soma cell body Electrochemical message is received by a neuron and will be transmitted to the dendrites in the next neuron Electrochemical impulse is a change in the charge of a neuron if it exceeds the cell s threshold it gets sent down to the next one Presynaptic neuron it s before the synapse Postsynaptic neuron after the synapse Axon is covered by a fatty substance myelin sheath it makes it more reliable and allows faster conductivity its like protection over a wire like insulated wires in cars and computers so the current does not jump from the wire to something else which makes it more unreliable and slows it down Young children don t have this yet they do not have mature neurons so their impulses are slower and less reliable myelination when neurons become covered with this substance Resting Potential and Action Potential in a Neuron Action potential the electrochemical impulse how the nervous system takes care of everything what hunger or thirst is made of up how we see The resting charge 70 millivolts of a neuron Principles of action potentials are the same in every living thing What happens when inputs exceed the threshold of excitation A neuron is like a light switch its on or off the action potential either fires or it does not if the threshold is achieved by the inputs then the neurons charge will change from 70 to 35 millivolts this takes a few milliseconds neurons can fire very rapidly and many times within a second or slowly several times a second Speed of neural firing is an important thing If the threshold of excitation is reached there is a radical change in the charge of neuron and then within a millisecond or less it will return back to its original charge When the threshold of excitation is reached the sodium channels in the cell membrane which are normally close will open up this allows sodium ions which are positively charged to rush into the neuron which changes the polarity of the ion positive ions rushing into the cell drive the cell from the negative seventy millivolts to the positive 35 The electrical force pulls them into the cell negative attracts positive the other force is the diffusion force things of higher concentration will move to areas of lower concentration the concentration of ions inside the neuron is lower than outside the neuron Potassium channels open up also and the sodium channels close and many potassium ions leave the cell which will make the charge drop to below 70 hyperpolarization Hyperpolarization charge of the neuron moves more negative than the resting potential below a 70 millivolts eventually returns to 70 and then will fire again For 2 3 milliseconds the neuron cannot fire because it just did and needs to return to its resting potential before it can fire again How fast neurons fire somewhat relies on the intensity of the stimulus we can look at how many neurons are firing and how fast they re being fired this will help us determine stimulus intensity A low intensity light will cause the neurons to fire more slowly Depolarization its moving from negative to positive the charge of the neuron the peak of the neuron is 35 millivolts this all happens within a thousandth of a second The negative charge is maintained by the concentration of ions there is a higher concentration of chloride ions on the inside and those are negative Synapse the axon terminals don t actually make contact with the dendrites of the postsynaptic neuron the neuro chemical is transferred from presynaptic and pos Release of neurotransmitters by the presynaptic neuron which is caused by the change in polarity of it Neurotransmitters are chemicals that are released at the axon terminal they will change the polarization of the postsynaptic neuron they will change the polarity of the postsynaptic neuron Some of them are excitatory driving the postsynaptic neuron towards the threshold of excitation inhibitory neurotransmitters drive the postsynaptic neuron away from the threshold of excitation hyperpolarization There are enzymes in the brain for breaking down neurotransmitters Drugs that held your mood and stuff target this idea they keep the firings from happening or help them happen etc psychotropic drugs act at the syntax How an Excitatory Neurotransmitter Works When the action potential reaches the end of the axon terminal it causes the release of neurotransmitters The sodium channels open as a result of an excitatory neurotransmitter NOTES FROM THE BOOK Axon tail like part of neuron that transmits information to other neurons and cells Dendrite branch like structures that are the part of a neuron that are specialized to receive the information Neurons individual cells of the nervous system that receive integrate and transmit information Myelin sheath cells make up a white fatty substance that
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