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41a - March 19 2013 Basal Ganglia 1. Intro to Motor Systems.doc

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Mac Burnham

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BASAL GANGLIA 1: INTRODUCTION TO THE MOTOR SYSTEMS Readings for the Basal Ganglia section: Carlson: Chapter 8: 272-278, 264-269, 285- 289, 277-282 (motor systems), Chapter 15: 537-543, 533-540 (BG disorders); Olanow (therapy); Dunnett et al. (early transplant article); Bergman et al. (early DBS/surgery article) Outline Definitions Functions of the Motor System Cortical Motor Areas Descending Motor Pathways Further Terms / Definitions Progress of the Course 1. DEFINITIONS Motor system – produces movement • We’re going to focus on voluntary movementthrough striate muscles. Motor neuron i) neuron in ventral horn of spinal grey that attaches to the muscles (“primary” motor neuron) • Motor neurons are down in ventral horn of spinal cord. Motor neurons can be defined in two ways. Strictest definition is a neuron in the ventral horn of spinal grey that attaches to the muscles. So runs from cell body in ventral horn of spinal the muscle. This would also be called the primary motor neuron: the end of motoron pathway. ii) neuron within three synapses of the ventral horn neuron – that yields motor evoked potentials • Used in a freer sense, it’s a neuron within 3 synapses or so of this primary motor neuron in the ventral horn. • If you want to define it he says 3 synapses. But perhaps a better definition is that had evoked potentials used to measure velocity of the nerves, the peripheral, we nerves, so called compound potential. And we talked about evoked potentials registered in primary centres of the brain (visual, auditory etc). Those are ways you can watch the receptors in periphery of body recording into brain of sensory systems. And when they’re looking for brain damage would use somatosensory evoked potentials to see whether if they stimulate your legs would find evoked potential in areas 3 1 or 2. • We have sensory evoked potentials, also intracranial evoked potentials (left cortex stimulationevoked potential in right cortex). Motor evoked potential – moving the body by stimulating the brain • Finally term evoked potential is applied in stimulating motor centre in brain and observe body movement. Moving body by stimulating the brain. And a number of places in the brains that can do this. o mganglia (thought to be wired in a circuit with neocortex), red nucleus in brain stem, and throughout reticular core of brain stem. When talked about reticular core in arousal, talked about its ascending effects, but also has descending which can move the body 2. FUNCTIONS OF THE MOTOR SYSTEMS • Talked about nature of life as being self producing molecule, and behaviour exists because it interacts with environment to reverse entropy and maintain structure. So teleological point of view is to act on… Teleological – to act on the environment to maintain life (to reverse entropy) Engineering – to adjust muscle tension in relation to sensory input – to adjust sensory input • muscle tension to change sensory input. Now if you listen to neuroscientists argue, ones that do sensory systems argue that whole brain is extended sensory systems. And others argue the opposite. Probably the proper formation is including both. Essentially what motor systems do is to change sensory input (hunger etc). Let’s work on that thought more. - reflex – preset change - with a reflex it’s a fixed change. If you you’re your arm out, sensory input is saying gravity is trying to pull it down, and monosynaptic response is to keep it in place: a simple reflex. Essentially it’s a preset change; if you stick a needle in your hand, it will move away. Once again, a preset change. In each case, changing sensory input. We’ve given you defensive reflexes that move you from harm, but what your muscles will do is take you away from a bad stimulus. If you look at swallowing, this would be a good thing, will swallow involuntarily, once again an approach behaviour, a preset, changing sensation in your mouth to your stomach. So reflexes are simple preset changes and their job is to change sensory input. - Instinctinve patterns are approach/avoidance behaviours designed to maximize… - instinctive pattern – maximize (minimize) a sensation or perception - in out of the cold. Behaviour will change sensory input. Andl come when dealing with instinctive patterns change it in a way that is predictable in other members of your species. - purposive pattern – adjust input to match an image of a non-present thing - Finally purposive pattern, in terms of discussion in this course as thinking of imaging non-present objects. Imaging it and then you will approach or avoid those non-present objects. If you’re hungry, visualize what you’ll have for lunch and walk over there and get it. Change sensory input to what will be good for you in the long run. - So simple idea of engineering approach is we make movements to change sensory input and the meaning of that is to get things in environment that keep us alive! 3. CORTICAL MOTOR AREAS (Figs. 8.8 and 8.13 in Carlson) - all “pre- central” - motor cortex (M 1, Brodmann’s 4, precentral gyrus, motor homunculus): - “movements not muscles” • Diagram of human brain: have central culcus, and precentrally have motor strip. That’s brodmann’s 4, and then you’ll have supplementary motor area, and then premotor area. • B4 is motor strip specifically, also called M1 or precentral gyrus or motor homunculus. Stimulating towards the top moves the toes or legs, lowerarms etc. • It produces movements not muscles, meaning several muscles will move together. If you want to move a muscle individually, go down to spinal cord, but in the brain, will move as a group. • The premotor areas and SMA are playing down on the M1. Some books will call these areas Broadmann’s area 6. If m1 is a keyboard, B6 is playing the keyboard. - supplementary motor cortex (medial) (“motor association cortex”) • Moving on here which is more medial. It will be called motor association cortex. Supplementary and premotor are called motor association cortex, area in front of them is frontal association cortex. Part of frontal lobe specifically occupied with movement but not the motor strip is motor association cortex. • Looked this up on Wikipedia because prof was confusing: The premotor cortex occupies the part of Brodmann area 6 that lies on the lateral surface of the cerebral hemisphere. The medial extension of area 6, onto the midline surface of the hemisphere, is the site of the supplementary motor area, or SMA. - ouputs to M 1 - behavioural sequences • What does this do? Produce a series of movements, sequence is important. Incidentally the stimulus for the next movement is the last movement. - premotor cortex (lateral) (“motor association cortex”) – inputs to M 1 • something that’s probably fairly specific to human beings. Its is means that if he says would you look up, everyone would look up. That’s arbitrary stimulus because it will depend on language you use. Words are arbitrary stimuli and
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