Cortical Sensorimotor Systems

Question 1

how is the cerebral cortex organised?

Answer 1

through hierarchal sensory-motor organisation, that focuses on planning and programming in the premotor and motor complex, that provides sensory feedback into cortical areas

Question 2

two main areas of the cerebral cortex

Answer 2

basal ganglia and cerebellum

Question 3

basal ganglia

Answer 3

initiates movements

Question 4

cerebellum

Answer 4

is important for fine-motor control

Question 5

how is the cerebral cortex divided?

Answer 5

into four main lobes (motor regions within the frontal lobe)

forms the outer surface of the forebrain

Question 6

layers of the cerebral cortex

Answer 6

has 6 distinct layers of laminae which define different regions of the cortex by their different cell types

Question 7

example of layer-specific inputs and outputs of the cerebral cortex

Answer 7

5 and 6 are both involved in sending outputs to the muscles and spinal cord

Question 8

brodmann (1868-1918)

Answer 8

defined 52 areas of the cortex based on their distinct laminae profiles, to identify different relevant functions of different anatomic cortical areas

Question 9

where is the primary cortex located?

Answer 9

the frontal lobe, and this is one of the primary areas involved in motor function

Question 10

what does the primary motor cortex (M1/BA4) contain?

Answer 10

betz cells in layer 5, which project from motor cortex to the spinal tract

95% of these cells instead reach spinal interneurons and project to the brainstem

Question 11

what is the purpose of betz cells along the corticospinal tract?

Answer 11

initiate, regulate, and control voluntary movement by innervating alpha/gamma motor neurones in the spinal cord to cause muscle contractions

Question 12

where does the corticospinal tract cross?

Answer 12

at the medulla, hence limb movements are controlled by contralateral M1

Question 13

how can M1 be mapped?

Answer 13

by somatotopic representations

Question 14

somatotopic representations

Answer 14

different parts of the motor cortex send motor signals to different parts of the human body

• related to how much fine-motor control is required

Question 15

penfield (1940)

Answer 15

discovered electrical stimulation causes simple movements

Question 16

what do cortical motor maps reflect?

Answer 16

sensory-motor specialisation, seen in changes based on what is used most

• humans have big representations of hand/face as we have most fine-motor control of these

Question 17

overlap between cortical motor maps

Answer 17

between these areas based on how much the muscles work together

Question 18

what was initially believed the motor cortex represents?

Answer 18

simple contractions of contralateral muscles, seen in brief micro-stimulation of 50ms

Question 19

sustained stimulation longer than 500ms results in…

Answer 19

complex goal-directed actions, such as defence, climbing, and reach-to-grasp in monkeys, but these results have not been shown in humans

Question 20

precision grip in M1…

Answer 20

requires more M1 activity than power grip, but muscle activity remains the same

Question 21

motor lesions result in…

Answer 21

loss of individuated fine movements, and result in ‘gross’ trunk movements

Question 22

what are frontal eye fields connected to?

Answer 22

the superior colliculus, which is a somatotopic area in the frontal lobe important for volitional control of eye movements

Question 23

what is FEF connected to?

Answer 23

the occipital cortex and frontal regions important for decision making

Question 24

why are there dense connections between sensory motor areas and M1?

Answer 24

secondary sensory motor areas are involved in executing actions vs M1 sends out motor commands

Question 25

secondary motor areas

Answer 25

supplementary motor area premotor cortex - dorsal PM - ventral PM posterior parietal cortex

Question 26

what does PPC link?

Answer 26

frontal cortex decision-making with premotor planning areas, as it receives information from sensory regions

Question 27

what is PPC important for?

Answer 27

determining potential actions given the environment - the frontal cortex then decides which action to perform, and secondary areas plan for these

Question 28

SMA regions

Answer 28

SMA proper learning preSMA for execution

Question 29

what is SMA involved in?

Answer 29

postural stability and planning and executing complex sequential movements

Question 30

what does SMA initiate?

Answer 30

internally generated movements, that are not stimulus-driven

Question 31

what is PMd important in?

Answer 31

preparation of movement and learning conditional actions in response to external cues, e.g., red traffic light – foot on brake

Question 32

what is PMv important in?

Answer 32

sensory guidance of movement, such as responding to tactile, visual, and auditory stimuli involved in visuomotor control during grasping and contains mirror neurones

Question 33

mirror neurons

Answer 33

were first reported in the PMC these show similar activity when performing and observing the same action – important for observation learning and understanding intention

Question 34

neuroplasticity

Answer 34

ability of the brain to form and reorganise synaptic connections, in response to learning, experience, or following injury. This can occur in all brain areas, but clear in M1.

Question 35

rapid changes in the somatosensory or somatotopic maps after change in inputs:

Answer 35

- training expands map - denervation/amputation reduces the map - co-activation fuses the maps

Question 36

how do changes in maps reflect neuroplasticity?

Answer 36

- long-term changes in functional connectivity - branching of dendritic connections - neurons compete for space in the cortex

Question 37

what is synapse efficacy an example of?

Answer 37

learning-based neural changes, as synapses enable neurons to communicate with each other

Question 38

presynaptic

Answer 38

increase vesicle volume, availability of vesicles, and increase release probabilitysy

Question 39

synaptic cleft

Answer 39

reduce reuptake mechanisms and gap dimensions

Question 40

postsynaptic

Answer 40

increase receptor density and area

Question 41

growth

Answer 41

make new synapses

Question 42

what causes long-term synaptic changes?

Answer 42

specific timed patterns of neuronal activity

Question 43

LTP

Answer 43

activity-dependent strengthening of synapses, which produces a long-lasting increase in signal transmission between two neurons

Question 44

LTD

Answer 44

activity-dependent reduction in the efficacy of neuronal synapses, producing a long-lasting decrease in signal transmission between two neurons

Question 45

associative LTD induction involves...

Answer 45

1. NMDA channel is normally blocked by Mg+ and concurrent voltage channel drives this out a. Achieved by glutamate binding to nearby AMPA receptors 2. Glutamate binds to NMDA and AMPA receptors a. Temporary change in shape of channel which opens it up b. Calcium enters through the open, unblocked NMDA channel 3. Ca+ entry triggers intra-cellular signalling cascade which results in… a. Migration of AMPA receptors from intracellular stores to the cell membrane b. Synthesis of more AMPA receptors

Question 46

what does increasing AMPA receptors result in?

Answer 46

greater communication between neurones due to more output

Question 47

key principles of LTP and importance to learning and memory

Answer 47

cooperation associative synapse specific

Question 48

cooperation

Answer 48

LTP requires simultaneous activation of large number of axons due to large depolarisation Ensures only events of high significance that activate inputs will result in memory storage

Question 49

associative

Answer 49

Pairing weak synaptic input with large depolarisation can cause LTP at synapse Allows an event with little significance to have meaning, when associated with a significant event

Question 50

synapse specific

Answer 50

If particular synapse is not activated, then LTP will not occur even with strong post-synaptic depolarisation Inputs that convey information not related to an event will not be strengthened in memory

Question 51

where was LTD first identified?

Answer 51

hippocampus and believed to be a major component of motor learning in the Cerebellum. Involves decrease in AMPA receptors, however this is not NMDA-dependent

Question 52

how can LTP and LTD-like mechanisms be measured in humans?

Answer 52

with TMS by stimulating shallow brain regions as a result of pulses caused by magnetic coils placed on the scalp, which cause muscle contractions.