Neuroscience- motor systems- weeks 5+6

Primary Motor Cortex

Located in the precentral gyrus (Brodmann's area 4), it controls voluntary movement on the opposite side of the body.

Primary Somatosensory Cortex

Located in the postcentral gyrus (Brodmann's areas 3, 1, 2), it processes sensory information from the opposite side of the body.

Motor Association Areas

Includes the supplementary motor area (SMA) and premotor area (Brodmann's area 6); these are involved in higher-order motor planning.

Somatotopically Organized

The anatomical arrangement where adjacent body parts are represented in adjacent regions of the cortex or white matter pathways.

Motor and Sensory Homunculus

The "little man" map representing the distorted proportions of the body on the motor and sensory cortices based on the level of control or sensitivity.

Dorsal Horn

The posterior part of the central gray matter involved primarily in sensory processing.

Ventral Horn

The anterior part of the central gray matter containing lower motor neurons (LMNs).

Central Gray Matter

The butterfly-shaped center of the spinal cord containing cell bodies.

Dorsal Root Ganglia

Clusters of sensory neuron cell bodies located just outside the spinal cord.

White Matter Columns

The dorsal columns carry vibration, proprioception, and fine touch; lateral and ventral columns contain descending motor and other ascending sensory tracts.

Cerebellum

Coordinates ongoing movements and participates in motor planning.

Basal Ganglia

Deep gray matter nuclei involved in automated movement patterns.

Thalamus

The major relay station for sensory and motor information en route to the cerebral cortex.

Alpha Motor Neurons

Large LMNs that innervate skeletal muscles for contraction.

Gamma Motor Neurons

Smaller LMNs that innervate muscle spindles to help control stretch reflexes.

Lateral Motor Systems

Travel in the lateral columns (e.g., lateral corticospinal tract, rubrospinal tract) to control movement of the extremities.

Medial Motor Systems

Travel in the anteromedial columns (e.g., anterior corticospinal, vestibulospinal, reticulospinal, and tectospinal tracts) to control proximal axial and girdle muscles for posture and balance.

Ataxic Gait

A wide-based, unsteady, staggering gait seen in cerebellar lesions.

Vertiginous Gait

Similar to ataxic gait, but often associated with vestibular dysfunction and a positive Romberg sign.

Frontal Gait

Slow, shuffling, and "magnetic" (feet barely leave the floor), often caused by frontal lobe lesions.

Parkinsonian Gait

Characterized by a slow, shuffling, narrow-based pattern with difficulty initiating movement and "en bloc" turning.

Dyskinetic Gait

Features involuntary dancelike (choreic) or flinging (ballistic) movements while walking.

Ataxia

A "lack of order" resulting in uncoordinated, wavering movements and disordered contractions of agonist/antagonist muscles.

Vermis

The midline region involved in proximal limb and trunk coordination.

Hemispheres

Divided into intermediate (distal limb coordination) and lateral (planning motor programs for extremities) parts.

Lobes

Includes the anterior, posterior, and flocculonodular lobes (the latter handles balance and eye movements).

Truncal Ataxia

Unsteady gait and proximal instability caused by midline vermis lesions.

Appendicular Ataxia

Incoordination of the limbs caused by lateral cerebellar lesions.

Sensory Ataxia

Incoordination caused by loss of proprioceptive input, typically worse when the patient's eyes are closed.

Dysmetria

Inability to judge the distance or range of a movement (overshooting or undershooting).

Dysrhythmia

Abnormal timing of movements.

Dysdiadochokinesia

Impaired ability to perform rapid alternating movements.

Intention Tremor

A tremor that occurs during voluntary movement and increases as the limb nears its goal.

Movement Disorders

Can be hyperkinetic (excessive involuntary movement) or hypokinetic (paucity of movement).

Basal Ganglia Nuclei

Composed of the caudate, putamen, globus pallidus, subthalamic nucleus, substantia nigra, and nucleus accumbens.

Parkinson's Disease

Characterized by a resting tremor, bradykinesia (slowness), and rigidity.

Akinesia

The absence of movement.

Cogwheel Rigidity

Ratchet-like interruptions in resistance felt during passive limb movement.

Postural Instability

Includes retropulsion (rapid steps to regain balance when pushed backward).

Festinating Gait

A "hurried" gait with difficulty starting and stopping.

Chorea

Sudden, rapid, involuntary jerky movements.

Athetosis

Slow, twisting, "wormlike" involuntary movements.

Ballismus/Hemiballismus

Large-amplitude, violent thrashing or flinging movements.

Dystonia

Sustained muscle contractions resulting in twisted, abnormal postures.

Tics

Brief, rapid, repetitive movements or sounds.

Myoclonus

Fast, brief, shock-like muscle jerks.

Apraxia

The inability to follow a motor command despite having intact strength and comprehension, caused by a deficit in higher-order planning.

Ideomotor Apraxia

Specifically, the inability to carry out an action in response to a verbal command (e.g., "pretend to comb your hair").

Decorticate

Flexor posturing (upper extremity flexion), typically seen with lesions above the red nucleus.

Decerebrate

Extensor posturing (often associated with more caudal brainstem damage).

Motor Control

The ability of the CNS to direct the musculoskeletal system in purposeful activity.

Neuroplasticity

The CNS's ability to reorganize, such as through neural sprouting (forming new connections).

Rigidity

A non-velocity-dependent increase in tone affecting both agonist and antagonist muscles simultaneously.

Spasticity

A velocity-dependent increase in muscle tone.

Praxis

Higher-order motor planning; the ability to conceptualize and perform tasks.

Dressing Apraxia

Visuospatial difficulty specifically related to getting dressed.

Constructional Disorder

Difficulty with drawing or constructing complex figures.

Primary Motor Cortex (Location & Function)

Located in the precentral gyrus of the frontal lobe (Brodmann's area 4). It is responsible for the execution of voluntary movements on the contralateral side of the body.

Primary Somatosensory Cortex (Location & Function)

Located in the postcentral gyrus of the parietal lobe (Brodmann's areas 3, 1, 2). It processes tactile and proprioceptive information from the contralateral side of the body.

Supplementary Motor Area (SMA) & Premotor Cortex

Both are located in Brodmann's area 6, just anterior to the primary motor cortex.

Motor Association Cortex Function

These areas are involved in higher-order motor planning. They integrate multimodal sensory and limbic information to formulate the "motor program" for complex actions involving multiple joints.

Primary Areas Lesions

Cause severe, basic deficits in movement (weakness/paralysis) or sensation (numbness).

Association Areas Lesions

Do not produce severe basic movement or sensory loss. Instead, they cause deficits in higher-order analysis or planning, such as apraxia (motor planning deficit) or agnosia (inability to recognize objects despite intact primary sensation).

Homunculus Definition

A "little man" map where body parts are represented somatotopically on the motor and sensory cortices.

Homunculus Clinical Significance

Body parts are represented by size relative to their functional importance (level of motor control or sensory sensitivity) rather than actual physical size. It is a fundamental tool for clinical neuroanatomical localization (e.g., hand weakness maps to the lateral convexity).

Gray Matter

Butterfly-shaped center composed of cell bodies. It is divided into the dorsal horn (sensory processing), intermediate zone (interneurons), and ventral horn (lower motor neurons).

White Matter

Surrounding area composed of myelinated axons organized into dorsal, lateral, and ventral columns. Most axons transmit signals over greater distances.

Lateral Motor Systems

Travel in the lateral columns of the spinal cord and synapse on lateral ventral horn motor neurons to control distal limb movements.

Medial Motor Systems

Travel in the anteromedial columns and synapse on medial ventral horn motor neurons to control proximal axial and girdle muscles for posture, balance, and orienting movements.

Lateral Corticospinal Tract

Originates in the primary motor cortex; decussates at the cervicomedullary junction; descends in the contralateral lateral spinal cord to control contralateral limb movement.

Rubrospinal Tract

Originates in the red nucleus of the midbrain; decussates in the midbrain; controls contralateral limbs (function is uncertain in humans but may support corticospinal recovery).

Anterior Corticospinal Tract

Originates in the motor cortex/SMA; descends ipsilaterally to the cervical/upper thoracic cord; controls bilateral axial and girdle muscles.

Vestibulospinal Tracts

Originate in vestibular nuclei; control head/neck positioning (medial) and balance (lateral).

Reticulospinal Tracts

Originate in the reticular formation; handle automatic posture and gait-related movements.

Tectospinal Tract

Originates in the superior colliculus; coordinates head and eye movements.

Corticospinal Tract Primary Difference

The lateral tract crosses at the pyramids and controls distal extremities, while the anterior tract remains ipsilateral and controls proximal trunk muscles.

Corticospinal Tract Axon Distribution

About 85% of fibers form the lateral tract, while 15% form the anterior tract.

Cortex/Internal Capsule/Brainstem Lesion

Results in contralateral weakness (above the pyramidal decussation).

Spinal Cord Lesion

Results in ipsilateral weakness (below the pyramidal decussation).

Upper Motor Neuron (UMN) Signs

Weakness, hyperreflexia, and spasticity.

Lower Motor Neuron (LMN) Signs

Weakness, atrophy, fasciculations, and hyporeflexia.

Paresis

Partial weakness.

Plegia/Paralysis

Complete loss of movement.

Hemiparesis

Weakness on one side of the body.

Monoparesis

Weakness of only one limb.

Decorticate Rigidity (Flexor)

Characterized by upper extremity flexion and lower extremity extension; indicates a lesion above the red nucleus (e.g., midbrain/forebrain).

Decerebrate Rigidity (Extensor)

Characterized by extension of all four limbs; indicates more caudal brainstem damage.

Ataxic Gait

Wide-based, unsteady, staggering gait; typically indicates a lesion in the cerebellar vermis or vestibular pathways.

Parkinsonian Gait

Slow, shuffling, narrow-based gait with difficulty starting/stopping; caused by basal ganglia dysfunction.

Vestibular Impact

A lesion in the vestibular system causes vertigo and unsteadiness, severely impacting functional mobility and balance.

Cerebellum Function

Acts as an error-correcting device that integrates massive sensory and motor inputs to smoothly coordinate movement, maintain posture, and regulate balance.

Cerebellum Role in Motor Movement

It compares intended movement with actual performance and sends corrective signals back to the motor cortex via the thalamus.

Cerebellar Inputs

Arrive via the cerebellar peduncles; mossy fibers come from numerous CNS regions, and climbing fibers come exclusively from the contralateral inferior olive.

Cerebellar Outputs

All cortical output is through inhibitory Purkinje cells to the deep cerebellar nuclei, which then send excitatory outputs to the thalamus (VL nucleus) and cortex.

Dorsal Spinocerebellar & Cuneocerebellar

Convey afferent proprioceptive information about limb movements to the cerebellum.

Ventral Spinocerebellar & Rostral Spinocerebellar

Carry information about the activity of spinal cord interneurons, reflecting activity in descending pathways.

Ataxia Characteristics

Irregular, uncoordinated movements featuring disordered agonist/antagonist contractions, dysrhythmia (abnormal timing), and dysmetria (overshooting/undershooting).

Truncal Ataxia

Midline vermis lesion; affects proximal musculature and gait.

Appendicular Ataxia

Lateral hemisphere lesion; affects limb coordination ipsilateral to the lesion.

Sensory Ataxia

Caused by posterior column disruption; unsteadiness that worsens in the dark or with eyes closed.