Second Half Flashcards
What are the 3 types of movement?
Reflexive –> peripheral stimuli produces involuntary coordinated pattern of muscle contraction/relaxation (stretch reflex)Rhythmic –> can be spontaneous or due to peripheral stimuli; repetitive (chewing, scratching)Voluntary–> goal directed movement, improves with practice
How is the spinal cord nerves organized?
31 nerves: cervical, thoracic, lumbar, sacral, coccygealCervical: controls upper limb musclesThoracic: controls trunk and chest musculatureLumbar: controls lower back and leg musclesSacral: controls bowel and bladder muscles
What are the 4 types of spinal cord neurons
Local –> axons confined to adjacent spinal segmentsMotor –> axons innervate muscle fibres; organized in a distal (lateral) to proximal (medial) fashionPropriospinal –> axons connect distal spinal segmentsProjection –> axons reach higher brain centres
Describe motor units
One motor unit = motor neuron + all fibres it innervatesone motor neuron integrates multiple fibres, each fibre innervated by one neuronunits can be fast or slow twitchsize of motor units relates to amount of control needed (finer selection of motor fibres to contract if smaller units)Number of motor units recruited related to force generated
Describe how a muscle is innervated
Axons loses myelin sheath, branches into multiple extensions called synaptic boutons. It connects to a portion of the muscle membrane called the endplate. Boutons are positioned over junctional folds (deep depression in the post-synaptic muscle fiber) that have Ach receptors. Depolarization of axon causes Ca2+ to enter boutons, causes release of Ach. Ach crosses synaptic cleft, binds to the Ach receptors and depolarizes end plate to create potential. Ach receptors equally permeable to Na and K, but potential activates the voltage-gated Na+ receptors, which creates an action potential.
How is muscle force increased
recruit more motor unitsincrease frequency of action potentials, results in complete tetany (twitch–> summation–> incomplete tetany–> complete tetany)
What are spinal reflexes?
neuronal networks in spinal cord integrating responses to produce coordinated pattern of muscle contraction through divergent and convergent connections
Explain the withdrawal and crossed-extension reflex
Nocioceptor (in foot) senses painful stimulus, sensory neuron relays signal to spinal cord. Neuron diverges, one pathway goes up to higher brain centres, another activates flexion reflex (excites flexors in leg, inhibits extensors). Crossed-extension reflex also occurs (extensors excited) to shift weight onto that side to maintain balance
How does the spinal region control reflexes?
There is a resting membrane potential, and a threshold needed to produce action potential. Spinal cord changes resting membrane potential. Can have tonic excitatory input to raise resting potential, means that stimulus input will be more likely to generate potential. Can also be modulated to decrease reflex sensitivity.
How are postural reflexes organized?
SLR, MLR, LLR –> short, medium, long latency responseintegrates response at different regionsSLR=spinal cord, nonfunctionalMLR = cerebellum, brain stemLLR = cortex (functional) modulates response, knows more about body state
Describe task dependent reflexes
depends on task. Table vs. holding cup, amount of extensor activity changes
Describe 7 neonatal reflexes and why we don’t see them with age, and the study showing off the smart spinal cord
1) Babinski= touch bottom of foot, toes fan out, big toe raised. test for spinal cord injury2) STARtle reflex = star response due to sudden visual/auditory stimulus, arms/legs outwards, upwards, inwards, fists/feet open and clench3) Tonic neck reflex = head turned to side –> fencer’s pose, arm and leg to side that head faces is extended, other side flexes4) Grasp reflex = pressure on palm/fingers, results in grasping action5) Swimming reflex = belly touches water/ground = rhythmic alternating contraction/extension of arms/legs6) walking reflex = feet in contact with surface = lift and plant feet7) Righting reflex = when sit baby up, attempt to keep head uprightStop seeing because cortical regions develop, start to have descending pathway modulation, also start to have more control over movement so no need for reflexFrog experiment –> apply stimulus to one area, spinal cord cut, spinal cord can still control muscle to wipe that area –> shows spinal integration and control of movement
What is a CPG, how is it controlled
neuron network in the spinal cord that generates rhythmic pattern of reciprocal flexion and extension in absence of sensory inputInitiated by MLR (mesoencephalic locomotor region). walking initiated. see hip proprioception, hip flexor is stretched, causes burst of flexion (swing phase). when foot lands, GTO senses load, sends signal through 1b afferents to maintain extensor activity through positive feedback loop, creates flexor stretch in opposite leg.Proven through cat –> flexion/extension alternate, sudden stretch of hip flexor causes abortion of extension, flexion triggered early
How do neurons project to the spinal cord?
medial or lateral pathwaysmedial=control basic posture, axial/proximal musclesreticulospinal, vestibulospinal, tectospinallateral = goal directed, voluntary movements, limb musclesrubrospinal, corticospinal
Describe 3 pathways
reticulospinal –> maintains posture and muscle tonevestibulospinal –> maintains balance, orientation of head/bodyrubrospinal –> excites neurons innervating proximal upper limb flexors
What is the function of the cerebellum?
Receives feedback, comparison of motor plan with actual responseInvolved in learning new motor skillsProduce smooth motion (timing)Coordinates groups of muscles with cerebral cortexMaintains equilibriumFine-tunes locomotor pattern by regulating timing/intensity of descending signals
How is the basal ganglia organized?
5 nuclei: substantia nigra, striatum caudate nucleus, putamen, subthalamic nuclei, globus pallidus No direct input to spinal cordReceives input to cerebral cortex, inputs to cerebral cortex through indirect pathways
List name and function of 4 basal loops
Occulomotor loop –> controls eye movementsMotor loop –> movement, links to primary motor cortex, premotor cortesxPrefrontal loop –> decision making, linked to DLPCLimbic loop –> related to emotions
What does the thalamus do?
connects regions
What is the function of the PPC?
Sensorimotor transformations –> integrate sensory input from different coordinate systems and convert to motor coordinates, reference frame suitable for motor centrePlanning, on-line control of movementSpatial maps/working memory
What are the different PPC regions and their function?
Parietal arm field –> retinotopic locations of spaces that can actually be reachedParietal eye field –> retinotopic location of objects, responds to auditory and visual inputparietal face field –> represents ultra near space of mouth/face through visual and tactile inputparietal grasp field –> shape information required to grasp objects
When are neurons in the PPC active?
During foreperiod –> planning movementMemory delay task –> PPC heavily active between cue and reach to plan movement
How does the cortex project to the motor neurons?
corticobulbar and corticospinal fibrescorticobulbar –> controls motor nuclei in brainstem for facial musclescorticospinal –> controls motor nuclei in spinal cord for voluntary control of trunk/distal limb muscles–> acts on spinal pathway or motoneuronsmost fibers cross at pyrimidal decussation for contralateral control
What is the function of the SMA?
supplementary motor area selects movement trajectories based on internal cuesinvolved with memoryimportant for bimanual movementsrole in learning sequences