Neuroscience Module 5: Central Motor Control and Movement

Flashcards covering the neural control of movement, brain motor areas, cerebellum, basal ganglia functions, neuromuscular junction, and spinal reflexes.

Prefrontal cortex ($PFC$)

Initiates long term planning or cognitive aspects of movements, weighs consequences of motor actions, and determines if a motor action is appropriate for a specific situation.

Posterior parietal cortex

An associative area that processes sensory information by integrating visual, tactile, and proprioceptive information to determine an appropriate motor action.

Premotor area ($PM$)

An area anterior to the primary motor cortex that helps plan and organize movement and makes decisions about which actions should be used for a situation.

Primary motor cortex ($M1$)

A major motor control center required for deliberate, voluntary movements made in response to a command, containing cells referred to as upper motor neurons.

Frontal eye field ($FEF$)

A region that communicates with the extraocular muscles and mediates saccadic eye movements.

Broca’s area

Located in the inferior frontal gyrus, this area contributes to motor processes related to language.

Upper motor neurons ($UMNs$)

Motor cortex cells that send signals to the brain stem or spinal cord to trigger lower motor neurons.

Lower motor neurons ($LMNs$)

Neurons located in the brain stem or spinal cord that fire whenever an upper motor neuron sends a signal.

Somatotopic map

An organizational principle of the motor cortex where different populations of neurons communicate with specific muscle groups, such as dorsal $M1$ activating hip and trunk muscles.

Motor homunculus

A graphical representation of the somatotopic map where body parts with larger representations in the brain are shown with much larger size.

Population coding

A mechanism where $UMNs$ are broadly tuned to a certain movement in a certain direction, with the firing rate being highest when moving in that specific direction.

Corticobulbar tract

A descending communication route where axons terminate in brainstem motor nuclei and communicate with cranial nerves including $CN\,V$, $CN\,VII$, $CN\,IX$, and $CN\,XII$.

Corticospinal tract

The major output of $M1$ that runs down the spinal cord through white matter; $90\%$ of these axons form the lateral tract that controls contralateral distal limbs.

Central pattern generators ($CPGs$)

Networks of cells capable of producing intrinsic, repetitive motor responses (such as respiration or walking) even in the absence of sensory or brain inputs.

Pre-Botzinger complex

A population of medullary cells suspected to be a central pattern generator that contains cells which change their activity in a cyclic pattern.

Phrenic nerve

The major nerve that innervates the diaphragm for respiration.

Cerebellar cognitive affective syndrome ($CCAS$)

A condition characterized by executive dysfunction, impaired visual spatial memory, personality changes, and language production problems due to cerebellar damage.

Deep cerebellar nuclei

Three pairs of nuclei including the Fastigial nucleus, Interposed nuclei, and Dentate nucleus located within the internal core of cerebellar white matter.

Vestibulocerebellum

Composed of the flocculonodular lobe, it integrates visual and vestibular inputs to relay information about head and body position in space.

Spinocerebellum

Includes the vermis and intermediate regions of the hemispheres; it receives somatosensory and proprioceptive inputs for locomotion and extremity movement.

Cerebrocerebellum

Lateral portions of the cerebellar hemispheres that communicate with the cerebral cortex and target nonmotor associative areas like the $PFC$.

Granule cells

Small, densely packed excitatory neurons in the granular layer of the cerebellar cortex that are the main unit receiving mossy fiber inputs.

Purkinje cells

The output layer cells of the cerebellar cortex characterized by giant cell bodies and a broad dendritic arbor that fans in a single plane.

Basal ganglia

A series of subcortical brain structures (including the striatum and substantia nigra) involved with voluntary motor activity, habit learning, and action selection.

Spiny projection neurons ($SPNs$)

Also known as medium spiny neurons ($MSNs$), these GABAergic cells make up the majority of neurons in the striatum.

Dorsal striatum

Made up of the caudate nucleus and putamen; it contributes to learning habitual behaviors and goal-directed actions.

Direct pathway

A basal ganglia pathway involving $D1$ receptors that projects to the internal globus pallidus ($GPi$) and increases motor activity.

Indirect pathway

A basal ganglia pathway involving $D2$ receptors that projects to the external globus pallidus ($GPe$) and decreases motor activity.

Alpha motor neurons

Lower motor neurons located in the ventral horn of the spinal cord that directly command muscle contraction.

Motor unit

A functional unit consisting of one alpha motor neuron and all the individual muscle fibers it innervates.

Fast fatiguable motor units

Motor units that are quickest to contract and generate the most force, but are prone to tire quickly due to a decreased number of mitochondria.

Nicotinic $Ach$ receptors

Ligand-gated non-selective cation channels in the muscle fiber's postjunctional folds that allow the influx of $Na^+$ for depolarization.

Sarcomeres

The functional units of muscle contraction where actin (thin filaments) and myosin (thick filaments) slide to shorten and contract the muscle.

Monosynaptic reflex arc

A neural circuit where a sensory neuron synapses directly onto a motor neuron in the spinal cord, as seen in the knee-jerk reflex.

Crossed-extensor reflex

A reflex that activates contralateral interneurons and alpha motor neurons to extend the opposite leg and provide stability during a withdrawal reflex.