Neuroscience of Sensorimotor Function

Sensorimotor Spinal Circuits

• Spinal circuits control fundamental movements without input from the brain, enabling reflexes and basic actions.

Central Sensorimotor Programs and Learning

• Initial motor tasks require conscious effort, but become automated with practice, resulting in smooth and efficient movements.

Sensorimotor Association Cortex

• Integrates sensory and motor information to guide behavior and attention.

Posterior Parietal Cortex

• Combines spatial information.

Dorsolateral Prefrontal Cortex

• Involved in planning and decision-making.

Disorders of Sensorimotor Function

• Apraxia is difficulty carrying out voluntary movements independent of motor deficits.
• Contralateral neglect involves failure to respond to stimuli on the side opposite a brain lesion.

Secondary Motor Cortex

• Receives input from the association cortex and transmits signals to the primary motor cortex, playing a pivotal role in movement planning and coordination.

Mirror Neurons

• Fire both when someone performs an action and when they observe the same action taking place, contributing to the understanding of others' movements.

Primary Motor Cortex

• Located in the precentral gyrus of the frontal lobe.
• Directs voluntary movements.

Motor Homunculus

• A map depicting the motor control of different body parts within the cortex.

Effects of Primary Motor Cortex Lesions

• Widespread damage may result in less significant impairment than expected, suggesting redundant motor control pathways.

Cerebellum

• Coordinates and refines movements based on sensory feedback.
• Involved in timing, motor learning, and cognitive and emotional processing.

Basal Ganglia

• Regulates motor output and is crucial for habit learning and cognitive functions due to connections with the prefrontal cortex.

Descending Motor Pathways

• Dorsolateral pathways control fine movements (e.g., hand and finger movements).
• Ventromedial pathways manage posture and whole-body movements.

Types of Muscle Fibers

• Fast muscle fibers contract quickly and generate high force but fatigue rapidly.
• Slow muscle fibers sustain contractions for longer durations, suitable for endurance activities.

Types of Muscle Contraction

• Isometric contraction: Muscle tension increases without shortening (e.g., holding a weight).
• Dynamic contraction: Muscle shortens while exerting force (e.g., lifting an object).

Receptor Organs of Tendons and Muscles

• Muscle spindles detect changes in muscle length; they trigger reflexes to prevent overstretching.
• Golgi Tendon Organs sense muscle tension; They prevent excessive contraction to protect muscles.

Muscle Reflexes

• Stretch reflex: Automatic response to sudden stretching (e.g., knee-jerk reflex).
• Withdrawal reflex: Rapid response to painful stimuli, involving immediate muscle contraction.

Reciprocal Innervation

• Coordination mechanism for smooth movements where opposing muscles work in tandem; One muscle contracts while the opposing muscle relaxes.

Hierarchy of Central Sensorimotor Programs

• The sensorimotor system operates hierarchically, with higher levels coordinating complex actions and lower levels functioning autonomously.

Characteristics of Central Sensorimotor Programs

• Motor equivalence: Programs can adapt to different movements to achieve the same goal.
• Sensory feedback: Programs can develop without practice and improve with experience.

Functional Brain Imaging of Sensorimotor Learning

• PET scans show increased activity in sensorimotor areas during learning, with a decrease in activity as tasks become practiced.