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Neurosciences - Lecture Notes

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University of Ottawa
Kenneth Campbell

th September 29 : McGills: 20% given a placebo, 35% psychiatrists prescribed meds below minimal recommended dose Action Potentials: If the level excitation is not enough (the critical threshold is not reached) the depolarization will reverse (the neuron will return to the resting potential). The depolarization will not travel down the axon. The action potential will travel down the length of the axons; long axons are mylineated (they have a myelin sheath). They myelin sheath is not continuous. At places the axon (called the “nodes”) is exposed. (Message is like telephone) This allows the action potential to “jump from node to node. Thus, transmission is much faster in mulineated axons. Short axons are not mylineated. Thus, transmission is slower in short neurons. (Ex stepping on someone foot, fast reaction but pain stays. Or hand on burner – pain will continue) Synaptic transmission: under the influence of the action potential, neurotransmitters are released in the synaptic gap. The synaptic gap is the “intercellular space”. Excitatory – depolarization, that the post- synaptic cell will fire, possibility of action potential, inhibitory neurotransmitter – decreases likely that cell will fire, more negatively charged, needs a stronger stimulation to fire, hyperpolarisation, and increase critical threshold for the firing of action potential. Neurotransmitter – long-term effect until its action are terminated. Remove neurotransmitter with enzymes. Reuptake mechanism (recycling...) Drugs may affect synaptic transmission: 1. Block release of neurotransmitter 2. Block storage of neurotransmitter in pre-synaptic membrane 3. Cause release of excessive neurotransmitter 4. Stimulate or block receptor on post synaptic membrane 5. May attack enzymes that break down neurotransmitter 6. Block re-uptake of neurotransmitter Cannot observe the change with acetylcholine (ACh). Nerve gas = used during WWII so they inhale the gas and cannot exhale it. Black Widow spider venom = muscle convulsions, result death. Nicotine releases more ACh. Cone snail (relatively bigger ones) releases venom that can kill 8 humans. NE/NA: important role in alertness and mood, increase alertness in brain, fast heart rate, fight or flight (cocaine, antidepressants inhibit effects of NE enzymes). GABA: sleep and anti- anxiety medications – stimulate GABA receptors. DA: missing in Parkinson’s disease – need to inhibit muscles that aren’t functioning. There are an unknown number of neurotransmitters (around 100). The Brain and Nervous System: Read in Myers. Imaging Techniques: Anatomical techniques (slicing the human brain) – appropriate for cadavers. MRI: see where the oxygen is going, no microstructures. Functional Techniques (observing the active brain). What are areas responsible for functions? Observe functions that are lost because of brain injury (trauma, stroke, tumours, etc.) – very old method, brain injuries are often widespread and not specific. Higher mental states differ between species – makes experimenting hard. PET: measures blood flow (requires glucose), where does it go? fMRI: where oxygen is being carried. th October 4 : If patient is conscious, won’t take off life support – how do you know if they are or not if they are non-responsive? The patient would be told to imagine them playing tennis, action will be detected on the MRI. Adian Owen. Imaging Techniques - EEG/Evoked Potentials: (rough indication) changes in the electrical activity of the brain, thinking. (trace faster than the MRI) - Electrodes attached to the scalp. Provides an indication of the electrical activity of the brain. - When a stimulus is presented the changes in the electrical activity (The evoked potentials) can be measured. Advantages: RAPID – Processing in the brain can be determined every 1 ms. Very inexpensive. Disadv: poor spatial resolution. The Nervous System: - The Peripheral nervous system o Central nervous system (CNS) - (the spinal cord, the brain) The Peripheral Nervous System - Sensory receptors: in the body and also, specialized receptors in the head. (Do not shine light in ear – receptors aren’t sensitive to light) - Sensory “nerves”: afferent input front he sensory receptors to the C.N.S., in the body (soma), in the head (specialized “senses”) - Motor nerves: efferent output
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