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Cell and Systems Biology
Francis Bambico

 Circuitry underlying basal ganglia motor complex  Extra pyramidal system because it modulates the pyramidal pathway (main voluntary pathway)  Main voluntary pathway: originated from pyramidal neurons in the primary motor cortex down the brainstem (upper motor neurons) these axons go down spinal cord and synapse with lower motor neurons (innervate muscles)  Outside of this pathway is this extrapyramidal system consisting of striatum (interior of brain)  Direct pathway versus indirect pathway  Procedural learning takes place when you rehearse a seq of motor output: analogous to inducing a reverberatory signaling along this pathway  This BG pathway eventually projects to the primary motor cortex that controls your movement  If a reverberatory activity of this pathway, which originates from the axons coming from diff regions  Premotor area contains the program of motor output  That information could be relayed through cortical striatal pathway  Axons forming this pathway can directly come from primary motor cortex  If you do behavioural sequence over and over again – analogous to inducing presynaptic stimulation (overstimulation of cortical striatal pathway -> induce LTP -> increase in synaptic efficacy -> stronger synaptic output)  Late phase LTP will result in structural changes -> synaptogenesis created by cortical striatal pathway  Increase in synapses -> easier to do the behavior the next time, almost automatic (not a lot of energy, don’t have to recruit diff sensory modalities and integrate them)  That’s how procedural learning takes place  So this pathway is subdivided between direct and indirect  Direct: originates from striatum-> directly relay info to GPi -> efferent to thalamus -> cortex  End product of stimulation via this pathway -> excitation from primary motor cortex  Indirect: travel to GPe and makes a detour -> subthalamic nucleus (glutamergic)  Net effect of indirect: inhibition of cortex  Balance of direct and indirect (excitation and inhibition) -> well coordinated execution of movements  This is disrupted/disturbed in movement disorders  Parkinsons – slow movements, tremors -> hypokinesis  Huntington – uncontrollable involuntary movements -> disturbance in transmission of dopamine in striatum  Destruction dopamergic neurons in SN -> decrease in dopamine (dorsal striatum usually) -> under activity of the direct and overactivity of indirect (inhibition of primary motor cortex)  ______ is characterized by destruction of GABAergic medial spiny neurons which are the primary neurons located in the striatum that is going to lead into an overactivity of the direct pathway and underactivity of the indirect pathway leading to overexcitation of the primary motor cortex  Last slide in lecture 19  Think of your own personal experiences that exemplify the diff types of explicit and implicit memory  Nootropics and cognitive enhancers: drugs that help cognitive functions  Used to treat disorders  Can boost synaptic plasticity and even promote LTP and synaptic efficiency signaling  Critical period: If some changes induced by ext stimuli is employed during the first phases of your development (critical period: until adolescence) interfering with normal synaptic changes in the first 15 years -> results in disturbance and changes in structure and function  If these events happen after critical period (early/late adulthood), it’s not going to affect your behavior much  Examined the limbic system sensitivity to cannabanoids and another against of CB1R  In rats; 2 groups; 1 group got THC from birth to end of adolescence and the other group got cannabanoids in adulthood  Examined anxiety and depressive-like behaviour  We observed that those that received chronic admin of THC during adolescence -> dramatic impairness of emotional activity -> more depressed  Cannabanoids admin during adulthood -> emotional behavior was okay  This is one experiment that pinpointed and conclude that interfering with synaptic transmission in diff system in the brain is dependent upon the time the drug was administered  Studies of critical period have been conducted in the sensory systems: easier to examine and control (esp. visual system)  Kittens and monkeys: As soon as they’re born, suture one of the eyes and take it off after adulthood and examine changes in synaptic structures in the neurons as well as function  Similar conclusion: sensory deprivation early on -> loss of vision and impairments in synaptic structures  But if that experiment was done after critical period, in adulthood, no change  Slide 6  Diff types of sensory receptors  Sensory receptors are the structures, coatings of the cell that are responsible in transducing external stimuli into electrical impulses that can be understood by the brain  Diff shape and sizes  Mechanoreceptor: temp  Proprioception – ability to locate our diff parts of the body  2 groups: short and long  Short receptors: photoreceptors (cones and rods), ear cells, gustatory  No long axon, don’t produce APs  Receptor is a diff structure altogether  Spec
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