Chapter 14: Brain Control of Movement Flashcards
The( ) influences motor activity of the spinal cord -> Initiates voluntary movements
brain
Hierarchy of controls
Highest level: strategy (1) -> deciding what to do; deals with complex information to decide the course of action
Middle level: tactics (2) -> which muscles to use, how much force to use; how to move the muscles of the body to achieve the course of action
Lowest level: execution (3)
- Association area of neocortex, basal ganglia
- Motor cortex, cerebellum
- Brain stem, spinal cord
(): Sensory information used by all levels of the motor system
sensorimotor system
Axons from brain descend along two major pathways:
Lateral pathways
Ventromedial pathways
axon pathway from brain that mediates Voluntary movement— originates in cortex
lateral pathways
components of lateral pathways
- corticospinal (pyramidal) tract
- rubrospinal tract
lateral pathway component: Motor cortex neurons directly innervate spinal cord; originates directly from motor cortex
corticospinal stract (direct)
the corticospinal tract passes through (lateral/medial) side of midbrain and (2), where the decussation occurs
- lateral
- medulla
lateral pathway component: indirectly control spinal cord neurons; suggested purpose: controls fine fractionated movements of arms and hands (not present in monkeys)
rubrospinal tract
the rubrospinal tract originates from () in the midbrain, which are governed by neurons in the motor cortex
red nucleus neurons
The effects of experimental corticospinal lesions
Deficit in fractionated movement of arms and hands
Both lateral pathways can (1) for the other if the other has a lesion -> allows for recovery after some time; subsequent (2) in the other pathway reverses recovery
- compensate
- lesion
() in human can affect (cause lesions) in motor cortex or corticospinal tract -> causes paralysis on contralateral side, with possibility of recovery over time
strokes
() pathways mediate balance and posture; originate in the brain stem
ventromedial
4 components of ventromedial pathways
- vestibulospinal tracts
- tectospinal tract
3-4. pontine/medullary reticulospinal tract
ventromedial pathway component: manages muscles to maintain head balance and head turning
vestibulospinal tracts
ventromedial pathway component: manages muscles for the orienting response -> Turning your head and moving your eye when you focus on an object
tectospinal tract
vestibulospinal tracts originate from (), which is the projection site of info from vestibular organs in inner ear -> combines sensory (proprioception) and motor info
vestibular nucleus
the vestibular spinal tracts pass near the (ventral/dorsal) side of the spinal cord
ventral
the tectospinal tract originates from the (1) and receives info from the (2) -> processing center for visual info and motor execution
- superior colliculus (optic tectum)
- retina
reticulospinal tract: enhances antigravity reflexes -> muscles resist effect of gravity to maintain standing position
pontine reticulospinal tract
reticulospinal tract: liberates and relaxes antigravity muscles from reflex control
medullary reticulospinal tract
motor cortex comprises areas () of the frontal lobe
4 and 6
area 4 of motor cortex: ()
primary motor cortex, M1
(): “higher” motor area (Penfield)
Area 6
area 6 consists of ()
Lateral region -> premotor area (PMA)
Medial region -> supplementary motor area (SMA)
Body areas that require more sensitive motor movements correspond to (narrower/wider) areas in motor cortex
wider
the posterior parietal cortex consists of areas () of the frontal cortex
5 and 7
- Area (): inputs from areas 3, 1, and 2 (S1) (from somatosensory cortex and combines info for deciding output)
5
Area (): inputs from higher-order visual cortical areas such as MT
7
Represent highest levels of motor control -> Decisions made about actions and their outcome
posterior parietal cortex
Contributions of Posterior Parietal and Prefrontal Cortex: () -> abstract thought, decision making, and anticipating consequences of action
Anterior frontal lobes
(): Actions converted into signals specifying how actions will be performed. (PMA neurons vs SMA neurons)
Area 6
() neurons were shown by Evarts to be active during the planning of a muscle movement (“Ready”)
PMA
some neurons in cortical area 6 respond when movement is only imagined -> May be part of extensive brain system for understanding actions and intentions of others
mirror neurons
(): Selection and initiation of willed movements; Important source of inputs towards area 6 and motor cortex
basal ganglia
the basal ganglia consists of: ()
striatum (caudate nucleus + putamen), globus pallidus, subthalamic nucleus
midbrain structure that is reciprocally connected with the basal ganglia; important for stimulating striatum thru dopaminergic innervation
substantia nigra
most of the inputs from basal ganglia pass through the () of the thalamus
ventral lateral (VL) nucleus
target of the cortical input to the basal ganglia
striatum
2 major points of the motor loop
basal ganglia, cortex
the basal ganglia provides major input to area ()
6
Excitatory connection from cortex to putamen (basal ganglia striatum neurons)
direct motor loop
cortical activation of the direct motor loop:
excites putamen, inhibits globus pallidus (GPI), and releases VLo from inhibition
activity in VLo boosts activity in ()
SMA neurons
(): trouble initiating willed movements due to increased inhibition of the thalamus by basal ganglia
Parkinson’s disease
Organic basis of Parkinson’s : degeneration of () -> (lack of stimulation via dopamine)
dopaminergic substantia nigra inputs to striatum
(): facilitates production of dopamine to alleviate some Parkinson’s symptoms
l-dopa treatment
Loss of neurons in caudate nucleus, putamen, globus pallidus; Consequent loss of inhibitory output to the thalamus -> motor systems can’t be suppressed properly (overactivation of motor loop)
Huntington’s Disease
in Huntington’s disease, () is primarily responsible for dementia and personality changes
cortical degeneration
Electrical stimulation of () causes contraction of small group of muscles.
area 4
(): pyramidal cells in cortical layer 5
Betz cells
Two sources of input to Betz cells
Cortical areas
Thalamus
Extensor motor neurons are innervated by ()
Betz cells (excitatory)
Flexor motor neurons are connected to ()
inhibitory interneurons
Movement of direction encoded by () of neurons
collective (populational) activity
direction of movement is determined by () - a tally (and averaging) of votes; activity of each cell represents a single “vote”.
population vectors
Motor map is easily changed -> adapts to changes such as ()
loss of connection to certain muscles
function of cerebellum
mediates sequence of muscle contractions
(): uncoordinated and inaccurate movements; caused by cerebellar lesion
Ataxia
(): decomposition of synergistic multi-joint movements (e.g. catching a ball); caused by cerebellar lesion
Dyssynergia
(): overshoot or undershoot target; caused by cerebellar lesion
Dysmetria
() – increases surface area in cerebellum (similar to gyri and sulci)
Folia and lobules
Relay cerebellar cortical output to brain stem structures
deep cerebellar nuclei
(): axial musculature; connection between left and right cerebellar hemispheres; contributes to ventromedial pathways
Vermis
cerebellar hemispheres mediate ()
limb movements
Most abundant cells in cerebellum
Very densely packed (blue)
Located in inner side of cerebellum
Excitatory neurons
granule cells
granule cells have () that are projected in molecular (outer) layer -> connects Purkinje cells
parallel fibers
Very large cells (one of the largest cells in CNS)
Many dendrites and processes
Packed in outer molecular layer of cerebellum
Collect info from granule cells via the granule cell parallel fibers
Inhibitory neurons -> project inhibitory axons towards deep cerebellar nuclei
Purkinje cells
Cerebellum is the center for the proper execution of ()
planned, voluntary, multijoint movements
Axons from layer V pyramidal cells in the sensorimotor cortex form massive projections to pons.
Pontine nuclei
the corticopontocerebellar tract 20 times larger than the () tract;
pyramidal
