Kalat Ch. 1: Nerve Cells and Nerve Impulses

Kalat Ch. 1: Nerve Cells and Nerve Impulses Experience Neuropsychology of Religious Nerve Cells and Nerve Impulses 1. Cells of the Nervous System a. Neurons i. Receive, process, transmit information. 1. Neurons receive information and transmit it to other cells. ii. Neuronal structure 1. Neural membranesa. a structure that separates the inside of the cell from the outside environment; protein molecules embedded b. semi-permeable- some stuff can and cannot get through. c. embedded in cell membrane: ion channels made of proteins and can change shape to open or close. 2. Cell body- Known as the Soma, contains the nucleus, ribosomes, and mitochondria. Most of a neuron’s metabolic work occurs here. In many Neurons, the cell body is like dendrites- covered with synapses on its surface. 3. Dendritesa. Branching Fibers that get narrower near their ends. Their surface is lined with specialized synaptic receptors, at which the dendrite receives information from the other neurons. The greater the surface area, the more information the dendrite can receive. b. Branches that come off the cell body c. Branch off the soma d. Receive information from other neurons. e. Dendritic Spines- short outgrowths that increase the surface area available for synapses. i. Actual points of communication, receive information at the spines. 4. Axona. a thin fiber of constant diameter. The axon conveys an impulse toward other neurons, an organ, or a muscle. They can be more than a meter in length. b. Only ever one axon c. Comes off the neuron at the axon hillock. d. Transfer, process, or communication information within the neuron e. The axon has myelin, fatty insulation, allows information processing to happen faster- facilitates info. Processing. f. Ends in a branched-out fork- axon terminals or terminal buttons g. Spaces without myelin: nodes of Ranvier- important for the transfer of information 5. Synapse a. Communication point between neurons- where neurons are talking to each other. b. Presynaptic terminali. the swelling at the end of a branch on an axon. Also known as an end bulb or bouton. At that point, the axon releases chemicals that cross the junction between that neuron and another cell. ii. Terminal button of the neuron, sends message (end of axon of neuron that is sending info) c. Synaptic cleft i. Space between neurons d. Postsynaptic terminal i. The receiving end of another neuron (usually the dendrite of the next neuron b. Glia- broad, and categorized based on their size macroglia and microglia. i. Macroglia 1. Astrocytesa. Star shaped. Wrap around the synapses of functionally related axons. By surrounding a connection between neurons, an astrocyte shields it from chemicals circulating in the surrounding. Also, by taking up the ions and transmitters released by axons and then releasing them back, an astrocyte helps synchronize closely related neurons, enabling their axons to send messages in waves. They also dilate blood vessels to bring more nutrients into brain areas that have heightened activity. b. Central nervous system (CNS) brain and spinal cord c. Participate in chemical signaling between neurons. d. Actively send chemical signals to influence activity. e. Participate in the blood-brain barrier. f. Provide structural and nutritional support for neurons. ii. Microglia1. Function as a part of the immune system, removing viruses and fungi from the brain. They proliferate after brain damage, removing dead or damaged neurons. They also contribute to learning by removing the weakest synapses. 2. CNS 3. Inactivate viruses. 4. Clean up debris in the brain. a. Neuron dies and microglia can clean up the bits. b. c. Blood-brain barrieri. the mechanism that excludes most chemicals from vertebrate brain. ii. Helps to keep stuff in our blood out of our brain. iii. Cells in capillary walls are closer together in the brain than they are in the rest of the body- harder for substances to get to brain. iv. Glial cells surround the capillary walls as another layer of protection for blood vessels in your brain. v. What gets across? – 1. Any substance to change the activity of your brain- medication. 2. Small uncharged molecules-oxygen, carbon dioxide 3. Fat soluble substances- vitamin a and d 4. Actively transported substances- amino acids, glucose 2. The Nerve Impulse a. Ionic composition of intracellular and extracellular fluid i. Mostly extracellular: 1. Na+: Sodium positive 2. Cl-: Chloride negative ii. Mostly intracellular: 1. K+: potassium positive 2. Protein ions (anions) negative b. The resting potential i. The charge when a neuron is at rest. ii. Difference in electrical charge between the inside and the outside of a neuron 1. Averages -70mV iii. Neuron is polarized. iv. Reason for polarization: 1. Location of ions v. Maintained by controlling movements of ions. c. Membrane potentials i. No activity: 1. At resting potential and cell is polarized ii. Apply positive charge: 1. Depolarization- a decrease in membrane potential- going towards zero, decrease difference from inside to outside. 2. Inside becomes more positive. iii. Apply negative charge: 1. Hyperpolarization 2. Increase in membrane potential- inside and outside are even further apart from each other. 3. Inside becomes more negative (goes below -70mV) iv. Depolarizations and hyperpolarization’s vary in size- small or large hyper or depolarization. 1. Depending on intensity of incoming stimulus. d. Action potential- how we measure individual neurons in the brain. i. Represent neuronal activity. ii. Neuron is depolarized to -65mV- this starts an action potential. 1. The threshold of excitation 2. Starts at axon hillock. iii. Properties of action potentials 1. Equal in size or shape (within each neuron) 2. All-or-nothing process- never half an action potential 3. Active- caused by ions moving across cell membrane, channel proteins opening and closing. iv. Propagation of action potentials 1. AP is regenerated down length of axon. 2. Propagates in one direction.