Neuro Ch 7

• comprises a collection of muscle fibres arranged in fascicles 
• each fibre has myofibril, each myofibril have sarcomeres

some work as opposing pairs (one contract, other relax). Flexors vs extenders

sense contraction and load

somatosensory receptors embedded in the body of muscles; sense the length of muscles and prevent them from being overstretched

somatosensory receptors embedded in tendons, sense changes in muscle tension and prevent excessive tension from damaging the muscle

• specialised for endurance
• type 1

• specialised for speed and power
• type 2

place where endplates of muscle fibres are contracted by motor neurons

• when action potentials in motor neuron will release acetylcholine into the synapse
• summation of enough miniature endplate potentials will cause muscles contraction

paralyses muslce by preventing vesicles filled with ACh from fusing with the presynaptic membrane, so motor neurons can't activate muscles

originate in the ventral horn of the spinal chord

stimulate contractions in skeletal muscle to cause movements of the body

maintain tension in muscle spindles

• consist of a single alpha motor neuron and all the muscle fibres that innervate
• different motor = different number of muscle fibres, more MF are innervated, stronger muscle contraction

• consist of all the motor units that work together within a single muscle 
• each pool can produce variety of contraction forces by recruiting different motor units, recruited from smallest to largest
• smallest = weak contraction and precise control 
• largest = strong contractions and courser movement

• polio - virus that attacks motor neurons in the spinal cord causing flaccid paralysis 
• west nile virus - damage ventral horn of the spinal cord and can sometimes cause severe, long lasting muscle weakness

automatic movements mediated by the spinal cord (don't require input from the brain)patellar tendon reflex

• inhibitory mechanism prevent severe muscle spasms and injuries (both extensors and flexors activated at the same time)
• tetanus and strychnine poisoning - causes severe muscle spasms all over the body (death by asphyxiation)

• most important for fine motor control in humans 
• from the brain

from primary motor cortex, can modulate lower motor neurons in the spinal chord

• name of somatotopic map of the body in the primary motor cortex
• electric simulation of different parts of motor cortex elicit movement in different parts of the body

other motor areas exists important for guiding more complex movements, including voluntary eye movement

• upper motor neurons (originate in PMC) connect to lower motor neurons (originate in SC) at all levels of the spinal cord
• also connect to interneurons in the spinal chord, enabling modulation of spinal reflexes

• upper motor nueronce influence movement via PC. 
• Each neuron has coarse directionl preference and the summation of activity across the population determines the movement. 
• high firing for fowards and left movement, no firing for backward and right movements

• hierarchy of control 
• primary motor cortex: simple movements
• premotor cortex: complex movements, actions 
• dorsolateral/ventrolateral prefrontal cortex: cognition, rule-guided behaviour
• frontopolar cortex: long term goals, multitasking

• premotor neurons that fire when an animal performs a particular action of when the animal witnesses someone else perform a similar action
• fire in response to goal-directed actions no just any movement
• respond even when part of motion is not seen, or when a consequence of the movement is heard

critical for many forms of motor control, including smoothness and accuracy of motor trajectories, and correction of movements

• projects to the frontal cortical regions involved in cognition, emotion, motivation, and judgement 
• cognitive affective syndrome - when damaged cerebellum, leads to impairments in cognitive and emotional functions

• Grey matter structures buried deep in the brain 
• works closely with the cortex to coordinate movement including intitating and maintaininig cortical activity
• every cortical area except low level sensory cortices is served by loop circuits through the basal ganglia

• genetic disorder in which abnormal huntingtin proteins cause the caudate and putamen to degenerate
• initially affects the inhibitory circuitry of the basal ganglia leading to chorea

parkinson's disease: result of degeneration of dopinergetic neurons in the substantia nigra

motor regions in lateral areas are primarily influenced by external stimuli motor regions in medial areas are primarily influenced by internal states and motivations

• damage to the medial motor: impairs internally generated movements but leaves externally cued movements intact 
• damage to lateral motor areas impairs externally cued movements but leaves internally generated movements in tact