Neuropsychology Lecture 3 PDF

Quiz! Please come down and get a notecard. Name Student ID Write your NAME on the top left of the card and your STUDENT ID on the top right of the card.  Quiz! Complete the following sentence: Ionotropic r...

Quiz! Please come down and get a notecard. Name Student ID Write your NAME on the top left of the card and your STUDENT ID on the top right of the card.  Quiz! Complete the following sentence: Ionotropic receptors are _______________ and ______________ in their action than metabotropic receptors and more likely to be involved in ______________ than _______________. A. Slower, longer, signaling, modulation B. Faster, shorter, signaling, modulation C. Slower, longer, modulation, signaling D. Faster, shorter, modulation, signaling  Quiz! Complete the following sentence: Ionotropic receptors are _______________ and ______________ in their action than metabotropic receptors and more likely to be involved in ______________ than _______________. A. Slower, longer, signaling, modulation B. Faster, shorter, signaling, modulation C. Slower, longer, modulation, signaling D. Faster, shorter, modulation, signaling Human Neuropsychology Lecture 3 BIO N173 / PSY 163/ PSYCH 162 Brain Cell Communication and Measuring Brain Activity Cellular Membrane Cellular Membrane Resting Potential Resting membrane potential (-70mV) There is a larger concentration of positive ions outside the membrane compared to inside. Forces affecting this potential: Diffusion Electrostatic pressure Sodium (Na+)/Potassium (K+) pump Cellular Membrane Opposing forces K+ is higher inside the cell than outside so diffusion forces it outside, but electrostatic pressure moves it inside. Cl- has the opposite situation but is also kept in balance. Na+ is higher outside the cell than inside, so diffusion forces it inside AND electrostatic pull ALSO moves it inside. BUT why isn’t the membrane potential positive then??? The Sodium/Potassium pump pumps Na+ outside the cell and K+ into the cell (against their concentration gradients) to keep membrane potential negative. This pump requires energy (ATP). The Action Potential When a threshold is reached (-55 mV), voltage gated Na+ channels open and Na+ rushes into the cell causing depolarization. Voltage gated K+ channels open but much more slowly, reaching peak permeability only after depolarization has occurred. They allow K+ to exit the cell. Together with voltage gated Na+ channels being closed, this causes repolarization. Voltage gated K+ channels eventually close but after a lag inducing a brief hyperpolarization. Membrane returns to rest by the action of the Na+/K+ pump  The Action Potential All-or-none law—the strength of the action potential is independent of the intensity of the stimulus that elicits it. Action potential is always the same size. Coding of intensity (a minor ache vs. a broken bone) is by the firing rate (rate law) of a neuron and by the number of neurons firing.  Action Potentials Are Unitary Action potentials are the same height at axon terminals as they are at the axon hillock. Every action potential is the same height. A neuron can generate a greater number of action potentials but it cannot generate bigger or smaller action potentials.  Saltatory Conduction In myelinated axons, action potentials appear to jump from one node of Ranvier to the next. That’s because the myelinated segment has no voltage-gated Na+ channels. Na+ entering at a previous node sets up a current that flows passively along the myelinated segment until it reaches the next node. Synaptic Transmission Release of aqueous neurotransmitter molecules is the principal means by which one neuron communicates with other neurons. This requires fusion of synaptic vesicles with the presynaptic membrane (requires calcium influx). Transmitter molecules then diffuse across the synaptic cleft and bind to protein receptors in the postsynaptic membrane. Terminating neurotransmitter action Termination of neurotransmitter effects can be done in one of three ways: Diffusion (passive) Enzymatic degradation Reuptake Remember that these are potential drug targets e.g. Acetylcholinesterase inhibitor (Aricept) or Selective Serotonin Reuptake Inhibitor (Prozac) Electroencephalography (EEG) Discovered by Hans Berger in the 1930s, EEG records electrical potentials or “brain waves” in the brain. It has very low spatial resolution but high temporal resolution. It is typically used for sleep studies, anesthesia monitoring and recording seizure activity. Event-Related Potentials (ERPs) Brief change in a slow-wave EEG signal in response to a discrete sensory stimulus is classified as an ERP. Stimulus is presented repeatedly and the recorded responses are averaged. Different types of stimuli can be subtracted from each other to see if they have different ERP signals → different cognitive processes.  Transcranial Magnetic Stimulation Stimulation of the brain using a small wire coil in the shape of a Figure 8. Largely noninvasive but can cause seizures in rare cases. It can be used to temporarily knock out or enhance function in certain regions of the brain (demonstrate causality). Now being used as a treatment for movement disorders, chronic pain, and depression.  Computerized Tomography (CT) Produces an image of the brain by shooting a narrow beam of x-rays from all angles to produce a cross-sectional image. CT scanning of the head is typically used to detect infarction, tumors, calcifications, hemorrhage and bone trauma.  CT Cerebral Angiography Substance that absorbs X-rays (iodine) is injected into the bloodstream through a catheter. This produces an excellent image of the blood vessels, but it’s pretty invasive. Can help diagnose vascular abnormalities, aneurysms, clots, and strokes.  Magnetic Resonance Imaging (MRI) a b c d Produces an image of the brain by passing a strong magnetic field through the brain, followed by a radiofrequency pulse, then measuring the energy emitted from hydrogen atoms (protons) as they return (precess) to their original orientation. Magnetic Resonance Imaging (MRI)  Functional MRI fMRI capitalizes on two important facts: Neural activity is metabolically demanding and requires oxygen to move from the blood into active neurons Oxygenated and deoxygenated hemoglobin have different magnetic properties, and the contrast between the two can be used as a proxy for neural activity (blood-oxygenation-level- dependent i.e. BOLD) signal. Positron Emission Tomography  How PET is used to study pathology? Amyloid PET Tau PET Alzheimer’s Healthy Alzheimer’s Healthy Radioactively labeled tracers bind to different proteins in the brain. Regional uptake is measured and compared against a reference region (e.g. cerebellum) How is FDG-PET used to study function? Fluoro-deoxyglucose (FDG) PET can be used to measure metabolic function in the brain. Can be done in the basal state or during a stimulation (e.g. a cognitive task) condition. FDG-PET tracer uptake can be averaged across individuals to generate a mean difference image (stimulation minus control).  Diffusion Tensor Imaging (DTI) Water molecules in your body are constantly in motion in random directions. Whenever there’s structure (e.g. axons) that constrains the movement, movement become more directional (anisotropic). DTI measures the directionality of water diffusion along these “highways”. Information can be used to reconstruct white matter pathways (tractography).