Chapter 10: Control of Body Movement

A complete set of vocabulary flashcards covering the motor control hierarchy, local reflexes, sensory receptors, descending motor pathways, and motor disorders.

Forebrain

The major brain division consisting of the cerebrum and diencephalon.

Brainstem

The brain division consisting of the midbrain, pons, and medulla oblongata.

Highest Level of Motor Control Hierarchy

The organizational level that generates the intention to move, consisting of command neurons including the sensorimotor cortex and brain areas involved with memory, emotions, and motivation.

Middle Level of Motor Control Hierarchy

The organizational level comprising the sensorimotor cortex, basal nuclei, thalamus, brainstem, and cerebellum that specifies individual postures and movements by establishing a motor program.

Local Level of Motor Control Hierarchy

The structures including brainstem and spinal cord interneurons, afferent neurons, and motor neurons that relay sensory information and adjust motor output to muscle fibers.

Voluntary Movements

Motor actions accompanied by conscious awareness, characterized by attention directed toward the action or purpose.

Involuntary Movements

Motor actions characterized as unconscious, automatic, or reflexive.

Local Pattern Generator Circuits

Interneuronal circuits that provide intrinsic coordination to local excitatory and inhibitory interneurons to drive repetitive motor patterns.

Muscle Spindle

A stretch receptor capsule embedded in muscle tissue containing intrafusal muscle fibers wrapped by afferent endings that monitors muscle length and the rate of change in muscle length.

Intrafusal Muscle Fibers

Modified skeletal muscle fibers enclosed within the muscle spindle capsule that are innervated by gamma motor neurons.

Alpha Motor Neurons

Motor neurons that innervate extrafusal muscle fibers to cause muscle contraction and generate force.

Gamma Motor Neurons

Motor neurons that innervate intrafusal muscle fibers to maintain tension in muscle spindles during contraction.

Alpha-Gamma Coactivation

The simultaneous activation of alpha and gamma motor neurons that prevents intrafusal fibers from going slack, ensuring that information about muscle length is continuously available during contraction.

Stretch Reflex

A muscle contraction elicited in response to passive stretching within that same muscle.

Knee-Jerk Reflex

A monosynaptic reflex initiated by tapping the patellar tendon, which stretches extensor muscle spindles and produces a rapid extensor muscle contraction accompanied by flexor relaxation.

Golgi Tendon Organ

A tension receptor wrapped around collagen bundles in tendons that fires action potentials in response to the tension generated by a contracting or passively stretched muscle.

Withdrawal Reflex

A protective reflex triggered by painful stimuli to nociceptors, resulting in ipsilateral flexor contraction and ipsilateral extensor relaxation to pull the limb away from harm.

Sensorimotor Cortex

All the parts of the cerebral cortex that act together to plan and control muscle movement, including the primary motor cortex, premotor area, supplementary motor cortex, and somatosensory cortex.

Somatotopic Map

The mapped topographical organization of body regions such as the leg, trunk, arm, and head across the primary motor and somatosensory cortices.

Substantia Nigra

A brainstem nucleus that projects axons into the basal nuclei to deliver dopamine.

Parkinson Disease

A disorder characterized by reduced movement, slow movement, rigidity, and resting tremor, resulting from degeneration of dopamine neurons in the substantia nigra.

Cerebellum

A hindbrain structure that provides timing signals for precise execution of motor programs, coordinates movements, and is involved in muscle memory.

Corticospinal Pathways

Descending motor pathways that originate directly in the cerebral sensorimotor cortex and cross over in the brainstem to synapse on motor neurons and interneurons in the spinal cord.

Brainstem Pathways

Descending motor pathways that originate within the brainstem to control posture and coordinate movement.

Muscle Tone

The baseline resistance to stretch exhibited by a relaxed muscle, produced by passive elastic forces and partial contraction due to slight motor neuron activity.

Hypertonia

A motor condition marked by abnormally high muscle tone due to increased motor neuron activity.

Hypotonia

A motor condition marked by abnormally low muscle tone caused by disorders of motor neurons, neuromuscular junctions, or muscle fibers themselves.

Center of Gravity

The point on the body whose vertical line of action must remain within the base of support provided by the feet to maintain balance and upright posture.

Motor Program

An integrated pattern of neural activity established by the middle level of the motor control hierarchy that specifies the individual postures and movements needed to carry out an intended action.

Extrafusal Muscle Fibers

Standard skeletal muscle fibers forming the bulk of the muscle that generate contractile force under the innervation of alpha motor neurons.

Sensory Inputs to Local Interneurons

Afferent signals converging from the active muscle, surrounding muscles, tendons, joints, and skin to continuously adjust motor neuron firing.

Crossed-Extensor Reflex

A postural reflex occurring alongside the withdrawal reflex, causing contralateral extensor contraction and contralateral flexor relaxation to support body weight when the injured limb withdraws.

Monosynaptic Reflex Arc

A neural pathway where an afferent sensory fiber directly synapses on an efferent motor neuron without intervening interneurons, as seen in the patellar stretch reflex.

Polysynaptic Reflex Arc

A neural pathway containing one or more interneurons situated between the sensory afferent input and the motor efferent output, as seen in the withdrawal reflex.

Cortical Areas of the Sensorimotor Cortex

The cerebral regions that plan and control movement, consisting of the primary motor cortex, premotor area, supplementary motor cortex, somatosensory cortex, and parietal-lobe association cortex.

Primary Motor Cortex

A precentral gyrus region that contains a somatotopic representation of the body and provides major descending drive to execute voluntary motor commands.

Supplementary Motor Cortex

A medial premotor cortical area involved in planning and organizing complex, sequential motor programs.

Premotor Area

A lateral cortical region anterior to the primary motor cortex that coordinates muscle groups in response to sensory cues and postural adjustments.

Parietal-Lobe Association Cortex

A cortical structure that integrates visual, somatosensory, and spatial information necessary for targeted, visually guided movements.

Basal Nuclei Motor Function

Subcortical structures that interact with the cerebral cortex to establish motor programs, facilitate desired movements, and suppress unwanted muscle activity.

Basal Nuclei Dysfunction in Parkinson Disease

The loss of dopaminergic input from the substantia nigra, which unbalances facilitatory and inhibitory pathways and decreases the activation of the motor cortex.

Pharmacological Treatments for Parkinson Disease

Therapies aimed at restoring dopamine signaling, including dopamine precursors, dopamine receptor agonists, and inhibitors of dopamine-metabolizing enzymes.

Sensory Inputs to the Cerebellum

Afferent signals converging from the sensorimotor cortex, vestibular system, visual pathways, skin, joints, and muscle spindles to continuously update and coordinate motor execution.

Mechanisms of Hypertonia

Abnormally high resistance to passive stretch caused by elevated motor neuron activity, often secondary to upper motor neuron lesions and loss of descending inhibition.

Causes of Hypotonia

Abnormally low muscle resistance resulting from damage to lower motor neurons, impairment of neuromuscular transmission, or intrinsic skeletal muscle disorders.

Decussation of Corticospinal Tracts

The anatomical crossing over of descending pyramidal fibers in the medulla oblongata, enabling the sensorimotor cortex of one hemisphere to control skeletal muscles on the contralateral side.

Initiation of Locomotion

The onset of walking, which is mechanically triggered by leaning forward so that the center of gravity shifts beyond the base of support.

Postural Stability Requirement

The biomechanical condition requiring the vertical line extending through the center of gravity to remain within the boundary formed by the feet.