Transcript PPT
Neuroscience: An Overview Introduction to Cognitive Science Lecture 4: Neuroscienc e: An Overview September 17, 2009 A Quick Tour of Neuroscience The Nervous System The Neuron The Action Potential Synaptic Transmission Methods of Studying Neuronal Activity Basic Neuroanatomy The Nervous System Central & Peripheral Nervous Systems CNS: brain & Spinal Cord Autonomic Nervous System (part of PNS) PNS: nervous system outside CNS SUBDIVISIONS: •Somatic: nerves innervate skin, joints, and muscles (axons in PNS while somas in CNS) •Autonomic Unconscious, e.g., heart rate, sweating The Neuron: Basic Structure Santiago Ramón y Cajal (1852-1934) “The Neuron Doctrine” Neurons are the most basic functional units in the brain which communicate with one another via contact and not continuity. Basic Structure of a Neuron Soma: Cell Body Dendrites: Receive signals from other neurons (sometimes the same neuron!) Axon Hillock: Electrical trigger zone at the Collateral Axon beginning of the axon Schwann Cells: Make myelin Terminal Arbor: Branches at end of the axon that terminate in the same region of the nervous system Myelin Sheath: Axon Nucleus: Cellular organelle that contains DNA Membraneous wrapping around axons made by Schwann cells (PNS) or oligodendroglia (CNS) Node of Ranvier: Saltatory Conduction: Space between two In myelinated myelin-sheaths where neurons, the action axon is exposed potential skips along the nodes of Ranvier resulting in faster conduction Ways of Describing Neurons By Neurite Shape or Number (axons and dendrites) Bipolar Unipolar Multi-polar Pyramidal By Connections • Primary Sensory Neurons: receive information from neurites in sensory surfaces such as skin or retina • Motor Neurons: send messages from central nervous system to other areas • Interneurons: neurons that are neither sensory or motor neuron; can also describe CNS neurons whose axons do not leave the structure in which they reside By Neurotransmitter •Amino Acids: e.g. glutamate, Gammaaminobutyric acid (GABA) Neurotransmitter: A chemical released by a presynaptic area at axon terminii upon stimulation and activates postsynaptic dendrites •Monoamines: e.g. Serotonin: Acetylcholine Epinephrine (Adrenaline) Norepinephrine (Nor-Adrenaline) •Others: Acetylcholine Adenosine Nitric Oxide Peptides AND LOADS MORE!! The Action Potential A Brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels. Action potentials sweep down axons to transfer information from one place to another in the nervous system. Neuronal Firing Patterns • Tonic: some neurons are always active and fire constantly • Phasic: neurons fire in bursts Synaptic Transmission Methods for Studying Neurons Neuronal Firing: Intracellular Recordings • Impale neuron or axon with a microelectrode (very challenging) • Measure potential difference between the tip of the intracellular electrode and another electrode in the solution bathing the neuron. • Intracellular electrode is filled with KCl salt solution which has high electrical conductivity • Electrode connected to an amplifier; can view potential differences on an oscilloscope (voltmeter). Voltage changes can be heard as a popping sound. Movie: http://www.youtube.com/watch?v=IgUMdwa1_Us Fluorescent Proteins: Study Neuron Shape & Development • Get neurons to express Green Fluorescent protein (GFP) as a marker • Can study neuron shape and growth • If GFP is spliced (entered) into DNA near where a specific gene of interest resides: Both the gene product and GFP are expressed together Electroencephalogram (EEG) Electroencephalography (EEG) is a non-invasive technique for detecting and localizing electrical activities of the central nervous system. EEG systems measure the electric potentials induced on the surface of the scalp using electrodes. USES •Clinical: localization of focal epilepsy sources, psychiatry •Research: to analyze sensorimotor or cognitive functions of the brain. Functional Magnetic Imaging (fMRI) • Type of MRI that studies blood flow responses to neuronal activity • Can study responses to specific visual or auditory stimuli or performance of a cognitive task. • Here are areas where neural activation was greater when listening to sentences using incorrect syntax vs correct syntax (blue) • And when the auditory recordings were intelligible vs untintelligible Obesler, et. Al. Disentangling Syntax and Intelligibility in Auditory Language Comprehension, Human Brain Mapping (2009) Major Brain Regions Left and Right Hemispheres The human brain consists of two hemispheres that are more or less mirror images of each other in terms of their physical shape. Functionally, however, there are some symmetries but also asymmetries. Symmetries exist in the processing of low-level sensory input and motor control, where the left hemisphere is responsible for the right half of the body and vice versa. One striking asymmetry is that the ability to understand and produce language is much more pronounced in the left than in the right hemisphere. Left and Right Hemispheres Decades ago, a common treatment of epilepsy was to cut the corpus callosum, which is the main connection between the hemispheres, in order to limit the spreading of epileptic activity. These split-brain patients typically behaved and felt like healthy people in everyday life situations. In laboratory experiments, however, the consequences of the functional separation of their hemispheres can be demonstrated. Split-Brain Patients If the image of an object is presented in their left visual field, they cannot tell the experimenter the identity of the object. This is because this visual information is processed only in the right hemisphere, which cannot produce language. They could pick that object from a set of items placed outside their visual field using their left hand (controlled by the right hemisphere) but not their right one. Patients can name objects presented in their right visual field and pick them with their right hand, but not with their left one.