The Nervous System Neuron Nucleus Cell body Dendrites they are part of the cell body of a neuron that collect chemical and electrical signals from other neurons at synapses and convert them into electrical activity along the thin membrane that encloses the cell. Axon (maybe mylinated) Synapses junction between two neurons: Chemical Synapses Electrical Synapses The Synapse: The Processor A synapse is where two neurons communicate electrically or chemically. A chemical synapse is a small gap that exists between the terminals of one neuron and the dendrites of another, into which neurotransmitters are released. At an electrical synapse, two neurons are physically connected to one another via gap junctions. Gap junctions make it possible for an electrical signal in one neuron to pass directly to another. Chemical synapses are far more common than the electrical ones. Electrical synapses in mammalian CNS, are mainly found in specialized locations where normal functions requires highly synchronized activity between the neighboring neurons. Although gap junctions are relatively rare between adult mammalian neurons, they are very common in a large variety of non-neural cells, including smooth cardiac muscle cells, epithelial cells, some glandular cells, glia, etc. They are also common in many invertebrates. 1
Types of Synapses (from functional view point) Inactive Excitatory Inhibitory Simple Neural Network What would happen if inputs from axons 1 & 2 was excitatory? What would happen if inputs from axons 1 & 2 was inhibitory? What would happen if input from axon 1 was excitatory and from axon 2 was inhibitory? Neurotransmitter It is a chemical substance that is released by one neuron and binds to a receptor of another neuron, altering the flow of electrical current or internal biochemical events within the 2 nd cell. There are many kinds of receptors for a single neurotransmitter. Neurotransmitter It's not the structure of the compound that makes it a neurotransmitter. It's really its function. For example, glutamate, which is a simple amino acid, is the main excitatory neurotransmitter in the brain. Obviously it's not an excitatory neurotransmitter when it s incorporated into other proteins. And the same substance might be a neurotransmitter in the brain and a hormone elsewhere in the body. can become quite confusing! http://cvlab.epfl.ch/research/medical/neurons/ 2
Neurotransmitters & Hormones Neurotransmitters and hormones are chemicals secreted inside our brain, and are largely responsible for our behaviour and attitude but they are not the same! The most notable difference between a neurotransmitter and a hormone pertains to the point of its release inside the body. Also they are different depending on their release mechanism. A hormone is a compound produced by endocrine gland and is released directly into the bloodstream where it easily finds its target cells at a small distance from the point of release. Neurotransmitter is a compound released by a nerve terminal when the nerve is triggered by an electrical impulse. Hormones can be synthesized, whereas it is impossible to make neurotransmitters. They are made inside the body only. Important Neurotransmitters Neurotransmitter Usual action Secreted by: Associated with: Acetycholine Excitatory Cells of the motor cortex, the motor neurons to skeletal muscles, some neurons in the basal ganglia. Glutamate Excitatory Cells in the sensory pathways into the CNS, cortex Muscle contraction, arousal, aggression Learning, memory Norepinephrine Excitatory Cells in the brain stem Levels of activity, arousal Glycine Inhibitory Cells in the spinal cord. Joint movement, arthritis, depression Dopamine Inhibitory Cells in the substantia nigra of the midbrain, target is cells in the basal ganglia. GABA (gammaaminobutyric Inhibitory Cells in the spinal cord, cerebellum, basal ganglia, acid) cortex. Control of movement and posture, mood, dependency. Motor control, regulates anxiety. Serotonin Inhibitory Cells in the core of the brain stem Pain pathways, mood. Simple Processing in the Spinal Cord Complex Processing in the Spinal Cord Simple Reflex Arc Input from skin receptor Processed in spinal cord by interneuron - or Output to muscle 3
Processing at Higher Levels Processing at Higher Levels Sensory Pathways periphery brain stem cerebellum thalamus primary cortex association cortex Motor Pathways supplemental and premotor cortex primary motor cortex basal ganglia thalamus cerebellum brain stem Learning and Memory Classification of Memory Sensory Memory Working Memory (htt (shot-term memory) 474-1899 Long-Term Memory X6L40DR2MZS8 4
Classification of Memory Sensory Memory Very short in duration ( <1 s) Acts like buffer for sensory stimuli (5 senses) Cannot be maintained like other types of memory by rehearsing. http://www.human-memory.net/types.html Short-Term (working) Memory Classification of Long-Term Memory Duration: 10-15s, <1 min Ability to remember and process information at the same time. By attention and repetition and association it can convert to long-term memory. Involves prefrontal lobe of the brain. 474-7023 R3T-5V6 Short-term working memory appears to operate phonologically. For instance, whereas English speakers can typically hold seven digits in short-term memory, Chinese speakers can typically remember ten digits. This is because Chinese number words are all single syllables, whereas English are not. 5
Episodic vs Semantic Memory Semantic Memory Semantic memory is for facts, while episodic memory is the memory for events/experiences. Episodic memories are very dynamic. Interesting to know! Females consistently perform better than males on episodic long term memory tasks, especially those involving delayed recall and recognition. However, males and females do not differ significantly on working memory and semantic memory tasks. There is also evidence for a negative recall bias in women, which means that females in general are more likely than males to recall their mistakes. Studies have shown that attention significantly affects memory during the encoding phase, but hardly at all during recall. Thus, distractions or divided id d attention ti during initial learning may severely impair subsequent retrieval success, whereas distractions at the time of recall may slow down the process a little, but has little to no effect on its accuracy. Construction of Memory 6
Memory Storage Areas Working Memory Prefrontal Lobe Construction of Long-term Memory Hippocampal Area Construction of Long-term Memory Hippocampal Area Gatekeeper for semantic and episodic memory which are stored in diffuse areas of cortex Location of spatial memory (GPS unit) 7
New Findings/Research about Memory Retrieving memory is a creative process; there is no fixed exact of memory of anything that just needs to be recalled; every time we have to recreate the memory. Memories are prone to error. General comment: Be aware of the difference between association and causal relationship. Conclusions from Case Study HM: a patient who had bilateral destruction of his hippocampus (in the medial temporal lobe) and had lost short term memory 1. The ability to acquire new memories is a distinct cerebral function that is located in the medial portion of the temporal lobes. 2. The medial temporal lobes were not required for immediate memory. He could retain some new information as longas he didn t get interrupted. 3. The medial lobes and the hippocampus can t be the ultimate storage sites for long term memory, because he still had his longterm memory from before the injury. 4. There is another kind of memory besides the kind that we normally think of, which is like memories of events. (He became better from day to day even without a conscious memory of doing it. Methods used to study Brain Lesion studies EEG ERP Imaging Studies Animal Studies Neuropsychological Studies Lesion Studies Damage to a particular part of the brain can result in specific behavioral effects Examples Amygdala (emotion) Hippocampus (memory) Visual cortex (blindsight) Parietal cortex (attention) Left hemisphere (language) 8
Electroencephalography (EEG) Measures brain waves Gross measure of integrity of the brain as a system Can be used as a very low level indicator (is this person alive) Can also be used to measure behavior Depression Electroencephalography (EEG) How does it work? Brains produce electricity Neurons do their business basically by acting like wires Electrodes placed on scalp record brain electrical activity Measures include the amount of activity in particular frequency bands Power Activation Activation in a particular frequency range Event related Potentials (ERP) Definition: Brain electrical activity that comes from simultaneous firing of synapses, and is related to a specific event. How do you measure them? Electrodes placed on the scalp record brain activity Activity is recorded in response to a specific discrete event. Averaging over enough trials gets rid of the noise of the background EEG. Imaging Computed Tomography (CT or CAT Scans) Uses Xray, Useful for describing overall brain structure P E T h (PET) Positron Emission Tomography (PET) Scans Good measure of blood flow in brain Poor resolution Involves radiation usually used to compliment rather than replace the information obtained from CT or MRI scans. 9
Imaging (continued) Imaging (continued) Magnetic (Nuclear) Resonance Imaging (MRI) Excellent resolution for structure of the brain fmri Excellent resolution Provides image of blood flow in the brain Example - Working Memory Neuropsychology Behavioral method derived from lesion and animal studies These behaviors are associated with parts of the brain from lesion, animal, or imaging studies You can measure the function of the brain indirectly Example: Autism All of the above? There are advantages to combining these methods. What might these be? Look at behavior to determine what you re really measuring converging measures What if an imaging study shows something different than lesion studies or animal studies always have? Complementary resolution advantages 10
Sleep Electrical Activity of Neurons Recording of Electrical Activity of Neurons Classification of EEG Waves 11
Interpretation of EEG Waves EEG Waves in Sleep Beta waves: frequency range from 13-15 to 60 Hz, amplitude of about 30 μv. Beta waves occur when the subject is awake, alert, and actively processing information. Alpha waves: frequency range from 8 to 12 Hz, amplitude of 30 to 50 μv. Alpha waves are typically found in people who are awake but have their eyes closed and are relaxing or meditating. Theta waves: frequency range from 3-4 to 7-8 Hz, amplitude of 50 to 100 μv. Theta waves are associated with memory, emotions, and activity in the limbic system. Delta waves: frequency range from 0.5 to 3 or 4 Hz, amplitude of 100 to 200 μv. Delta waves are observed when individuals are in deep sleep or in a coma. Stages of Sleep Patterns of Sleep Stages Stage 1 eyes are closed relaxed heart rate, respiration normal easily aroused Stage 2 arousal more difficult Stage 3 sleep is deeper heart rate, respiration slower Stage 4 arousal difficult heart rate, respiration slowest seen in sleepwalkers REM most skeletal muscles inhibited eye movements heart rate, respiration increased dreaming 12
The End!! 13