Alex r- Brain Mechanisms Flashcards
(30 cards)
Overview of nervous system
Upper motor neurones have motor cortex (planning, voluntary movement) and brain stem- basal ganglia and cerebellum feed into. Goes to local circuit neurones for reflexes (no cortex) and lower motor neurones in spinal and stem (both cns). Pns is sensory inputs and skeletal muscles W lower motor neurones
Basic types of movement
Reflexes, posture, locomotion, sensory orientation, species spec action and acquired skills
Voluntary to reflexive
Rhythmic movements can be voluntary but timing is from brain stem, produced by local spinal cord circuits called central pattern generators e.g. breathing
Pns and leprosy
Bacterial infection, peripheral nerves thicken which disrupt afferent (sensory input to local circuit neurones in spine and stem so no reflex) and efferent (lower motor neurones to skeletal muscles) signals. Thermal sensation goes first then pain and touch, limb damage from this
Muscle and movement
Striated/skeletal muscles are connected to bone or tendon apart from face, cardiac or smooth. Striated as sarcomere W actin and myosin. Myosin binds to actin and pulls along. Fibres stim but nerve impulse, AcH released at NMJ. Open ca+ channels to trigger contraction.
How muscles are controlled by neurones
Motor neurone sends signals via efferent connections, voluntary contraction from pns. Signal motor neurone will control many fibres (innervation) but a motor unit is the neurone plus fibres it controls. Signals go from upper to lower MN, proximal to distal (closer to centre of spine, the closer the body part it controls) At brain stem is crosses the midline (contralateral control)
AcH disruptions
Curare toxin: ach receptor blocked in muscle tissue. Made from plants, means inability of muscle to respond to motor nerve stim- reversible in some doses
Myasthenia gravis: abnormality in ach receptors, ppl are weak as can only activate some fibres, trouble smiling , ranges in extremeness
Sustained movement
Ap travels down lower motor neurone, single motor twitch, train is a sequence. If rapid, contractions get bigger. Multiple neurones activate many fibres, called tetanic contractions needed for sustained strong contraction. Motor pool requirement is bigger moment needs more neurones
Motor neuron problems
Lower neurones famished in motor neurone disease or trauma where peripheral nerves cut (polio)- hypotonia which is less muscle tone. Damage leads to motor neurone syndrome (paralysis, wasting, no reflexes and fasciculation/ contractions)
Motor programs
Set of commands to initiate movement, don’t depend on sensory info/ abstract representations of movements that centrally orgs. No feedback from limb/ equivalence means movements independent of muscle groups
Cortex
Supp motor cortex has learned actions, don’t monitor environment. Primary MC has execution of all voluntary. Posterior parietal is planning, attention. Premotor is sequences, intention, modulated pmc.
Somatotropic organisation
Body represented in cortex, contra lateral, more space for fine tuned moments (lips, tongue, hands), means phantom limb syndrome, Jacksonian March (seizure across brain affects body in order). Movements and not muscles represented. Brain achieves moments by averaging large pops of neurones
Evidence for cortical map
Mri and pet by lotze and graziano- move parts of body, see parts light up. Mushiake: monkeys activate promotors area in visual cue condition and supp motor not active but opposite in prior training condition (shift the more they learn. Apraxia is inability to move due to damage to ppc. Ideomotor is semantic (instruction), ideation all is inappropriate selection but no paralysis
Anticipatory firing
Premotor areas have planning. Libet 85: ppl looked at moving light and could make moments, looked at readiness potential in parietal. Expect decision then neural then activity but found RP, then will then action
Sea squirts
Larva form is more complex as need to navigate environment to find a new rock, then it becomes sessile, absorbs own brain
Graded and competitive goal selection
Roitman and shadlen 2002: monkeys see 2 targets, then shown stim W 0-50% motion coherence, hinting what direction to choose and then select correct target. 5% is enough for to guide monkeys. Activity in posterior parietal cortex has planning, found could tell condition from activity. If got variety of options, part of brain most active wins movement made
Sensorimotor transformation- reaching
When sensory stim is converted to motor actions. Responsible for trans visual info about object into direction of reaching (visuomotor trans). Everything happens quickly. Like grasping: dorsal cortex W anterior sulcus and ventral premotor - sensorimotor happens in parietal
Linking sequences
Supplementary motor area for learned movements, premotor cortex has cues moves. When Sam gone, monkeys can’t perform learn moves- tanji.
Background to cerebellum
Sometimes called the silent area- when run tms coil nothing seems to be effected
Hard to measure due to location in skull so understudied
Coordinates movement, balance, muscle tone and rapid movements
Error correction
Signals leaving the motor cortex go through cerebellum, also signals from what body is doing from spine
Compares 2 and adjusts what you to
E.g. of sensorimotor trans
Does comparator function with what done and what want to do, correct mistakes and operate smoothly. Motor cortex is planning and initiating, basal gang inhibits until appropriate
Motor learning and ballistic moves
Cerebellar neuronal circuits learn to make more accurate moves over time. After motor act done many times, steps become more precise. Once perfected, it establishes a spec motor program for each learned moves. Ballistic are rapid moves that can’t mod course by sensory feedback/can’t stop once started like running
Structure of cerebellum
Frontal motor and parietal cortex goes to pons, crosses midline to cerebellar cortex. Channels enter called inferior olive (vision and hearing), vestibular nucleus (head body and limbs) and spinal cord (body in space and time). If not match, sends info to deep cerebellar nuclei, crosses midline to ventrolatersl complex in thalamus to pmc. E.g. of reentrance circuit.
Cerebellar dysfunction
Vulnerable to heavy metals and strokes. Cerebellar ataxia (errros I’m direction of moves, uncontrolled eyes, slurred speech, can’t touch top of nose). Hypometria (response delay and moves short fo goal). Dysdiadocho kinesia (can’t do rapid alternating moves like a wavy line), one side of body can be affected
Alcohol
Cerebellum sensitive to ethanol, disrupts function. Field sobriety test allows to gauge extenet of alc, really tests cerebellum as tests walking in a line, touching tip on nose w eyes closed