Neural Control of Human Movement

EP 4703 Neural Control of Human Movement Study Guide for Exam Three

These notes are organized according to the topics and questions presented in the study guide for Exam Two. They encompass the primary concepts regarding the neural control mechanisms involved in human movement as discussed in class.

Cerebral Cortex Review

• Primary Functions:
    - Perception
    - Conscious decisions
    - Planning
    - Execution and accuracy of movement

• Two Primary Types of Cells:
    - Pyramidal cells: Large, multipolar neurons that are the primary excitatory cells of the cerebral cortex.
    - Stellate cells: Smaller cells involved in local circuit functions.

• Layers of the Cerebral Cortex:
    - Layer II (External Granular Layer): Involved in intracortical communication.
    - Layer III (External Pyramidal Layer): Functions in further intracortical communication.
    - Layer IV (Internal Granular Layer): Acts as the main input layer, receiving sensory information from the thalamus.
    - Layer V (Ganglionic Layer): Contains large pyramidal cells, which serve as the major output layer of the cortex.

• Brodmann Areas and Their Functions:
    - Primary Motor Area: Major control for motor output of limbs and trunk musculature.
    - Premotor Cortex: Transforms visual signals into motor signals for arm transport and grasping.
      - Dorsal Premotor Cortex: Encodes position of targets and specifies movement amplitude, direction, and speed.
      - Ventral Premotor Cortex: Involved in planning high-level goals; contains mirror neurons aiding in the decision of which object to reach for.
    - Supplementary Motor Area: Involved in sequencing movements, initiation, and motor execution.
      - Pre-supplementary Motor Area: Engages in higher-level motor planning and response inhibition to sudden task changes.
    - Primary Somatosensory Area: Responsive to tactile information and proprioception related to joint movement.
    - Parietal Association Cortex: Guides sensory motor behavior and spatial awareness.
    - Temporal Association Cortex: Involved in recognition and storage of factual information (semantic knowledge).
    - Frontal Association Cortex: Associated with organization of behavior and working memory.
    - Limbic Association Cortex: Concerned with complex functions related to emotion and episodic memory.

• Information Flow:
    - Ascending Information Sources: Primary sources include thalamus and other cortical areas.
    - Descending Information Destinations: Include striatum, brainstem nuclei, spinal cord, basal pons, and thalamus.

• Convergence and Divergence:
    - Convergence: Different cortical cells activate the same group of motor units, resulting in similar actions.
    - Divergence: One or more similar cortical cells activate different groups of motor units enabling movement of different body parts.

Basal Ganglia Review

• Disorders and Diseases:
    - Disorders of the basal ganglia lead to excessive involuntary movements (e.g., Huntington's disease) or movement poverty/slowness (e.g., Parkinson's disease).

• Five Paired Nuclei:
    - Caudate nucleus
    - Putamen
    - Globus pallidus
    - Subthalamic nucleus
    - Substantia nigra

• Input Sources:
    - Input comes from the cerebral cortex and thalamus. The caudate nucleus and putamen (striatum) primarily receive this information.

• Pathways:
    - Direct Pathway: Facilitates initiation of voluntary movement; considered excitatory.
    - Indirect Pathway: Suppresses competing motor plans; considered inhibitory.

• Symptoms of Diseases:
    - Parkinson's Disease: Characterized by hypokinetic symptoms due to loss of dopamine in the substantia nigra.
    - Huntington's Disease: Characterized by hyperkinetic symptoms due to atrophy of the striatum.

• Primary Functions:
    - Facilitates the selection and initiation of voluntary movements.

Cerebellum Review

• Input to Output Ratio:
    - The cerebellum has a ratio of 40:1 concerning inputs to outputs.

• Common Symptoms of Cerebellar Disorders:
    - Hypotonia: Diminished resistance to passive limb displacement, resulting in muscle weakness.
    - Astasia Abasia:
      - Astasia: Loss of the ability to maintain a steady limb or body posture across multiple joints.
      - Abasia: Loss of ability to maintain an upright stance against gravity.
    - Ataxia: Lack of coordination in movements.
    - Tremor: Involuntary muscle movement when attempting to stop (either action or intention tremor).

• Cerebellar Neurons:
    - Stellate Cells: Inhibitory neuron located in the molecular layer, inhibits Purkinje cells.
    - Basket Cells: Inhibitory neuron in the molecular layer, inhibits Purkinje cells.
    - Purkinje Cells: Sole excitatory output from the cortex, inhibiting deep cerebellar nuclei.
    - Golgi Cells: Inhibitory neuron in granular layer, inhibits granule cells.
    - Climbing Fibers: Excitatory input neuron to the cerebellum, powerfully excites Purkinje cells.
    - Mossy Fibers: Provide excitatory input to the cerebellum, targeting granule cells.
    - Granule Cells: Located in the granular cortex, excitatory neurons that target Purkinje, Golgi, stellate, and basket cells.

• Types of Information Entering the Cerebellum:
    - Motor Information: Received from the cortex, indicating intended actions.
    - Sensory Information: Proprioceptive input from muscles/joints via the spinal cord, and balance information from the vestibular system.

• Output Pathways:
    - Generally travels through deep cerebellar nuclei targeting the thalamus, red nucleus, and vestibular/reticular formation.

• Primary Functions:
    - Ensures smooth and harmonious movement.

Brainstem and Pathways Review

• Brainstem Anatomy and Functions:
    - Red Nucleus: Large group of cells in the rostral midbrain involved in motor control of upper extremities, communicates with the cerebellum through the inferior olive.
    - Reticular Formation: Collection of nuclei throughout the brainstem, involved in motor function, oculomotor control, autonomic functions, sensory processing, circadian rhythms, and mood regulation; plays a role in posture and balance.
    - Vestibular Nuclei: Composes four major nuclei in the medulla and pons; integrates vestibular, somatosensory, and cerebellar information, essential for equilibrium and postural control.
    - Superior Colliculus: Transforms sensory input into motor output, directing eye movements towards visual stimuli in a process called orienting.

• Hierarchy of Neurons:
    - First Order Neurons: Carry somatosensory information into the spinal cord; cell bodies in dorsal root ganglia.
    - Second Order Neurons: Relay between first order neurons and thalamus.
    - Third Order Neurons: Relay information from thalamus to the somatosensory cortex.

• Ascending Pathways and Brain Targets:
    - Dorsal Column Pathway:
      - Carries sensory information (fine touch, vibration, conscious proprioception) to the primary somatosensory cortex (medulla and thalamus).
    - Spinothalamic Tract:
      - Carries information on pain, temperature, and crude touch to the somatosensory cortex (via thalamus).
    - Spinocerebellar Tract:
      - Carries unconscious proprioception/coordination to the cerebellum:
        - Dorsal Spinocerebellar Tract: Proprioceptive info for the lower extremities.
        - Cuneocerebellar Tract: Proprioceptive info from the upper extremities.
        - Ventral Spinocerebellar Tract: Carries FRA information to the lower extremities.
        - Rostral Spinocerebellar Tract: Carries FRA information to the upper extremities.

• Descending Pathways and Origins:
    - Pyramidal Tract:
      - Corticospinal Tract: Originates in motor cortex, controls limb and trunk movements, passes through internal capsule and medulla.
      - Corticobulbar Tract: Arises from motor cortex face area, synapsing on motor nuclei of cranial nerves.
    - Rubrospinal Tract: Originating in the red nucleus of the midbrain, it controls flexor muscles primarily in the upper extremities.
    - Vestibulospinal Tract: Originates in vestibular nuclei, important for postural control in response to sensory information.
    - Reticulospinal Tract: Begins in reticular formation of brainstem; modulates involuntary movements and assists with posture.
    - Tectospinal Tract: Originates in superior colliculus, involved in head-eye coordination in response to visual/auditory stimuli.

• Cranial Nerve Functions:
    - I. Olfactory Nerve: Smell
    - II. Optic Nerve: Vision
    - III. Oculomotor Nerve: Eye movement
    - IV. Trochlear Nerve: Eye movement
    - V. Trigeminal Nerve: Facial sensation
    - VI. Abducens Nerve: Eye movement
    - VII. Facial Nerve: Facial expressions
    - IX. Glossopharyngeal Nerve: Swallowing, taste, salivation
    - X. Vagus Nerve: Parasympathetic control of thoracic/abdominal organs, swallowing, and speaking (sensory/motor for viscera).
    - XI. Spinal Accessory Nerve: Muscles of head, neck, and shoulders.
    - XII. Hypoglossal Nerve: Muscles of head, neck, and throat for speech.

Memory Review

• Theories of Memory:
    - Dualism: Concept that the mind and brain are distinct entities.
    - Reductionism: The view that the mind is exclusively the outcome of physical and chemical processes in the brain.
    - Neodualism: A hybrid view positing that the brain is hardware, while the mind is software.

• Types of Memory:
    - Declarative (Explicit): Conscious recollection of facts (semantic) and events (episodic).
    - Non-declarative (Implicit): Automatic recollection of tasks, skills, and habits such as motor skills and conditioning.

• Behavioral Responses:
    - Habituation: Decrease in behavioral response to a non-threatening stimulus upon repeated exposure; e.g., no longer feeling a shirt after wearing it for a while.
    - Sensitization: Increase in behavioral response due to exposure to a noxious or intense stimulus first, making one hyper-responsive to environmental stimuli; e.g., a loud car backfire causing a heightened response to a door slam.
    - Dishabituation: Sudden recovery of a previously habituated response, such as recognizing background noise when it suddenly interrupts.

• Conditioning Types:
    - Operant Conditioning: Associating behavior with consequences (reward or punishment).
    - Classical Conditioning: Associating two stimuli, such as in Pavlov’s experiments with dogs.

• Memory Stages:
    - Encoding: The process of attending to and processing new information.
    - Consolidation: The stabilization of memory traces after initial acquisition transitioning from short-term to long-term.
    - Storage: The retention of information across time.
    - Retrieval: The process of accessing and utilizing stored information.

• Short-term Memory Capacity:
    - Typically limited to approximately 7 ± 2 items.

• Consolidation Mechanism:
    - Memories are formed through repeated synapsing and transfer of information from the hippocampus to various cortical areas.

• Synapse and Memory:
    - Current thinking suggests that memory is not solely located at synapses but is a large-scale, distributed function involving multiple neural networks throughout the brain.

• Types of Amnesia:
    - Retrograde Amnesia: Memory loss for events occurring before brain trauma.
    - Anterograde Amnesia: Inability to form new memories post-injury.
    - Korsakoff's Syndrome: Resulting from alcohol abuse and thiamine deficiency; marked by severe anterograde amnesia and confabulation (the creation of false memories).

• Hippocampus and Cerebellum in Memory:
    - Hippocampus: Crucial for forming new declarative memories and effective spatial navigation.
    - Cerebellum: Engages in the learning and storage of non-declarative motor skills and classical conditioning.

Motor Control/Motor Synergies Review

• Perception of Skeletal Muscles by Engineers:
    - Engineers might see skeletal muscles as slow due to the inherent delays in force production post-neural signal and susceptibility to fatigue, contrasting mechanical or electrical systems.

• Inverse Kinematics vs. Inverse Dynamics:
    - Inverse Kinematics: Determining joint configurations required to reach a specified point in space.
    - Inverse Dynamics: Calculating the necessary patterns of joint torques to achieve a specific movement.

• Force-Control Approach:
    - Proposes that the brain sends specific commands intended to generate exact forces necessary to move limbs towards a target, treating the body like a mechanized system controlled by the brain.

• Generalized Motor Program:
    - Suggests a universal program for movements like throwing, with variations in parameters (speed, power) without changing the fundamental movement formula.

• Internal Models:
    - Direct (Forward) Model: Predicts motor outcomes before executing movement based on the action taken (e.g. reaching for an object).
    - Inverse Model: Calculates the requisite commands necessary for desired outcomes.

• Internal Model Experiments:
    - (Additional examples and support for internal models can be added as needed.)

• Challenges with Internal Models:
    - Difficulties arise as real-time physics calculations can be complex; the brain may not be sufficiently fast to manage these computations efficiently. Additionally, response times may vary significantly for different stimuli.

• Equilibrium Point Hypothesis:
    - Suggests that the brain does not simply exert force on an arm but instructs muscles to find a new balance point, resulting in movement towards a new equilibrium.

• Principle of Reafference:
    - (Definition needed as this point is unclear in original transcript.)

• Motor Redundancy and Bernstein's View:
    - Motor Redundancy: The presence of multiple ways to achieve the same motor outcome. Bernstein considered this a problem because it can complicate movement efficiency.
    - Optimization: The process of selecting the most effective way to organize motor outputs to achieve desired goals efficiently.
    - Drummer's Example and Alternative Approaches: Illustrating different solutions to redundancy issues.
    - Bernstein's Blacksmith Study Conclusions: Reflections on movement coordination and variability in skilled tasks.

• Abundancy vs. Redundancy:
    - Abundancy is proposed as a preferable concept due to its emphasis on flexibility and adaptability in motor coordination rather than fixed redundant paths.

• Coordination of Motor Units:
    - (Elaboration on coordination mechanisms needed for completeness.)