Motor Control and Skill Acquisition

• Understanding how the neuromuscular system activates and coordinates muscles and limbs during motor skill performance defines motor control.
• Coordination involves patterning body and limb motions relative to each other and to the surrounding environment.
• Motor behavior involves exerting muscular forces that affect the limbs or other body parts.
• Goal directed motor behavior produces a particular outcome despite obstructions or changing conditions.
• The study of processes involved in acquiring and refining motor skills is motor learning.
• Motor learning can either promote or inhibit skill acquisition.
• Skill is an action or task with a specific goal to achieve.
• An activity is a skill if directed toward a goal, performed voluntarily, and acquired through experience/practice.
• Motor skill requires voluntary body/limb movement.
• Levels of skillfulness vary, such as comparing novice to NFL player.
• Skillfulness is defined by adaptability, consistency, and efficiency.
• Components of a skill are movements, which are specific behavioral characteristics of limbs.

Skill Classification

• Gross motor skills use large musculature and are less precise. Examples include lifting a heavy box or jumping.
• Fine motor skills involve the control of small muscles with hand-eye coordination, such as writing, typing, or sewing.
• Discrete movements have a clearly specified beginning and end, like hitting an elevator button.
• Serial movements involve a series of discrete movements, such as typing or playing the piano.
• Continuous movements have an arbitrary start and end, exemplified by swimming.
• Low cognitive demand skills are automatic with little thinking, for example walking.
• Moderate cognitive demand skills require some thought, such as walking on an icy sidewalk.
• High cognitive demand skills place less significance on motor components than cognitive elements, like chess.
• Closed skills have a stable environment. -The environment does not change, is self-paced, like a free throw.
• Open skills involve a changing environment.
• The environment changes during performance, requiring constant adjustment, like a layup during defense.

Skillful Behavior

• Skillful behavior is characterized by the attainment of a goal, voluntary performance, acquisition through experience/practice, adaptability, consistency, and efficiency.
• Ability is a stable trait or capacity of an individual, generally hereditary/genetically determined.
• Individual differences in ability include body type, cultural background, and emotional makeup.
• Abilities are stable, inherited traits that are limited in number.
• Skills are modified through practice, developed, and numerous.
• Being good at one skill does not guarantee proficiency in another.
• Identifying abilities helps practitioners determine the source of a problem in rehabilitation.

Motor Actions

• Discrete motor actions have clearly identifiable start and end points.
• Serial movements build on discrete actions, for example, the actions to pick up a cup: reach, grasp, and lift.
• Motor fit describes achieving the same motor outcome despite different circumstances.
• Motor equivalence is the equality of outcome of two or more movements, movement patterns, or muscle contractions that may be different in other respects.
• Adaptability is the ability to change motor behavior depending on the circumstances.
• Voluntary motor control involves goal-directed actions performed deliberately.
• Involuntary motor control is performed without conscious awareness.
• Involuntary motor control can reveal issues with neurologic control of movement.
  • Parkinson's disease involves too little movement due to loss of dopamine neurons.
  • Huntington's disease involves too much movement, is genetic, and involves reduced brain tissue.
• Adaptability and persistence in response to failure determine if a behavior is goal directed.

Movement Feedback & Errors

• Movement errors occur when the plan and the actual outcome do not align.
• The internal model is a preprogrammed basis of movement contained in the brain. It can be small or large.
• Open loop control involves pre-set commands where adjustments cannot be made until the next movement. Throwing darts uses open loop control.
• Closed loop control uses feedback during movement to reduce errors as much as possible. Constantly adjusting when driving a car uses closed loop control.
• Disturbance, controller mistakes, and changes to the requirements cause movement errors.

Neurophysiological Perspective

• The subsystems that the nervous system uses to control and coordinate the musculoskeletal system.
• The structures and processes through which body movement is controlled.
• The brain and spinal cord are the CNS.
• The PNS consists of nerves and ganglion, which are critical for communication between the CNS and other organ systems.

Neuron Structure

• The neuron is the nervous system's functional unit, receiving electrical impulses from other neurons, and either transmitting electrical impulses or not.
• Neuron structure varies considerably.
• The soma contains a single centrally located nucleus and is responsible for neurotransmitter production and transportation.
• Dendrites are projections from the soma that receive signals/inputs from neighboring neurons.
• The axon is a single projection from the soma that varies in thickness, and many axons are covered by myelin.
• Axons send signals/inputs to other neurons or a "target" tissue.
• Dynamic polarization governs the electrical activity within a neuron, allowing for unidirectional flow of information.

Neuron Electrical Activity

• Information flows from the dendrites, through the axon, to the axon terminals; it will not flow in the opposite direction, and is called the action potential.
• Action potential is a brief change from negative to positive transmembrane potential.
  • It is an all-or-none response. -AP is from the influx and efflux of sodium and potassium across the membrane.
  • Depolarization is when membrane potential is more positive than resting potential. -Repolarization returns to resting potential. -Hyperpolarization is more negative than resting potential. Threshold is the potential a membrane must be depolarized to initiate the action potential.
• Connectional specificity means neurons make precise connections rather than random connections.

Synapses & Axons

• Electrical and chemical synapses are the two synapse types (neurotransmitters are considered chemical messengers).
• Axon diameter and myelin presence determine the speed of conduction.
• Nodes of Ranvier increase the speed of axon transmission, as action potentials jump from one node to the next (saltatory conduction).
• Neuronal firing rate (rate at which a neuron generates an action potential).
• Neurons directly connected are monosynaptic.
• Polysynaptic connections include more than two interneurons.
• Convergence is when many neurons connect to a few neurons.
• Divergence is when few neurons connect to many neurons.

Functional Classes of Neurons

• Sensory neurons detect environmental changes (stimuli) and transmit information to the CNS (afferent).
• Motor neurons send signals to target tissues to elicit a response.
  • Signals are sent away from the CNS to the PNS (efferent).
• Serving an integrative function, interneurons connect incoming sensory and outgoing motor information. They make up 90% of neurons.

Cerebral Cortex Organization

• Neural organization changes with experience.
• Plasticity is experience-dependent and is thought to be the neurophysiological mechanism that underlies learning.

Nervous System Components

• Critical components/structures of the nervous system in motor control and learning. -Spinal cord, brain, frontal lobe, parietal lobe, occipital lobe, temporal lobe, primary motor cortex (M1).
• Spinal cord: dorsal horn receives incoming afferent sensory information, and ventral horn sends out outgoing efferent motor information.
• Frontal lobe: Executive functions, cognitive processes, and decision-making for motor control
• Parietal lobe: Sensory and vestibular information and the integration of sensory and motor information
• Occipital lobe: Processing visual information
• Temporal lobe: Hearing, olfaction, and object recognition
• Primary motor cortex (M1): Execution of movement
• Primary somatosensory cortex (S1) processes sensory information such as touch, pain, and proprioception.

Somatotopic Organization

• M1 and S1 have somatotopic organizations.
  • Neural representations directly correspond to body parts.
  • Adjacent cortical regions correspond to adjacent body areas.
• Body parts with fine control/higher sensation have a larger cortical representation.
• Motor actions: basal ganglia, premotor cortex, motor cortex, basal ganglia.
• Basal ganglia initiate movement plans, send it to the premotor cortex which selects motor plan, sends message from brain to spinal cord to muscles.
• Basal ganglia: Movement initiation and completion, scaling movement parameters, and adding motor sequencing information, and act as motor "breaks”
• Cerebellum: Posture, balance, motor learning and coordination, and cerebellar outputs. Cerebellar outputs: Cerebrocerebellum, spinocerebellum, and vestibulocerebellum Cerebrocerebellum: Motor planning. Spinocerebellum: Motor execution. Vestibulocerebellum: motor neurons in spinal cord and brainstem

Ascending Tracts

• Ascending tracts communicate sensory information.
• Dorsal column medial lemniscus pathway relays proprioceptive information to cortex.
  • This pathway facilitates conscious refined touch, proprioception, vibration, and fast conduction. Spinocerebellar tract relays proprioceptive information to both the cerebellum and cortex. -Path 1 travels through the spinal cord, medulla, and cerebellum. -Path 2 runs through the spinal cord, medulla, thalamus/cortex. -This tract includes non-conscious proprioceptive information and facilitates fast conduction.
• Spinothalamic tract -Relays information from the spinal cord to the somatosensory cortex. -Includes information about touch, pain, and temperature. -Decussates the midline at the level of the spinal cord. -Involves spinal cord, brainstem, thalamus, and somatosensory cortex.
• In comparison to the previous tract, this one facilitates slow conduction.
• Vestibulospinal tract regulates head position in response to rotational accelerations.
• Tectospinal tract coordinates audiovisual information critical for eye movements and orientation responses.
• Corticospinal tracts arise from the cortex; they are involved in fine motor movements and have fast conduction.
• Rubrospinal tracts: involved in gross movements and motor coordination.

Motor Skill Impairments

• Parkinson's disease: Trouble initiating movement
• Cerebellar ataxia:Genetic neurodegenerative disorder; Affects ability to walk, talk, use fine motor skills

Studying the Living Brain

• Recording electromagnetic activity(EEG,MEG) -Electroencephalography(EEG)
• Electrodes placed on the skull detect and record “brain waves” or the electrical patterns created by the rhythmic oscillation of neurons -Technique 1:Electrical peaks that are related to specific stimulus (ERP) -Technique 2:Coherence functional communication between brain areas of interest -Pros: Cheap,easy to transport,silent, easy to use, direct measure -Cons: Poor spatial resolution,set up time,can only record activity from outermost portions of the brain
• Record the magnetic fields produced by the electrical activity of the brain
• Recording metabolic activity(fMRI, PET): Positron emission tomography (PET_ -Use computed tomography and radioactive markers injected into bloodstream -Indirect measure of brain activity- identifies areas of where brain is working based on fuel intake
• The study of magnetic recordings of neural activity; fMRI_ -Aligns atomic particles in tissue by magnetism then bombards them with radio waves. Different tissues return different radio signals. -Determines what areas in the brain where there are the most oxygenated hemoglobin

Receptor Properties

• Adequate stimulus: Receptors are built to respond only or primarily to one kind of stimulus energy.
• Modality: Stimulation of a receptor (with adequate stimulus) causes a consciously perceived sensation. Adaptation: Response slows with sustained stimulation.
• Mechanoreceptors for touch adapt slowly to size and shape and fast to direction of movement. Intensity coding: Receptors detect and code stimulus strength/magnitude.
• Graded response: The greater the stimulus, the greater the response.
• Spatial summation: The larger the number of receptors stimulated, the stronger the perceived stimulus.
• Temporal summation: A strong stimulus elicits a higher frequency firing pattern than a weak stimulus. Receptive field: Stimulation modulates the activity of a neuron over the sensory surface.
• Specialized cells or subcellular structures transduce an environmental stimulus into electrical impulses that can be interpreted.

Classes of Receptors

• Exteroceptors sense stimuli outside the body.
• Proprioceptors sense from the body itself.
• Interoceptors sense from inside the body.
• Photoreceptors respond primarily to light.
• Mechanoreceptors respond to mechanical energy.
• Chemoreceptors respond to certain chemical substances.
• Thermoreceptors respond to thermal energy.

JND

• Individual receptor cells convey information about stimulation characteristics: strength, timing, type, and location.
• Weber's law describes the Just Noticeable Difference (JND).
  • It is the minimum amount that the strength or intensity of a stimuli must be to produce a perceived difference.
• Two point discrimination: ability to discern points as being distinct is a quality of tactile sensation
• Functions of the vestibular system=Perception of self position, head position, and spatial orientation
• Semicircular canals; arranged perpendicularly- covers all possible rotational head movements
• Endolymph displacement: A fluid that allows for the stimulation of nerves in the inner ear.
• Otholith organs two organs responsible for detecting linear accelerations and gravity; are connected Uticle and saccule

Postural Control

• Movement in horizontal SC canals; movement of the head is accompanied by a compensatory movement of the eyes in the opposite direction
• Vestibular information communicated to the muscles contributing to posture and balance
• Vestibular information communicated to the nuclei of the extraocular muscles: eye movement
• The nuclei of extraocular coordinate eye movement to maintain a stable image on the retina.
• Somatosensory system: Alpha motor nerons and Propioception

Somatosensory & Proprioception

• Sensations originate from free and encapsulated receptors.
• Encapsulated endings primarily act as mechanoreceptors; the free endings primarily act as nocireceptors.
• Proprioception consists of sensations from the musculoskeletal system.
• Mechanoreceptors give the cortex information about the movement and position, they detect stretch. Alpha motor neurons innervate the extrafusal muscle fibers causing muscular contraction
• Perception occurs on the left side of the brain
• Somasensory system and cutaneous organization: -Pacini, messiner, Merkel and ruffini give touch and pressures
• Mechanoreceptors detect information about objects: they help adjust grip strength.
• Spindles stretch to covey information about muscle length/ stretch
• Alpha neurons contaction muscle fiber; gamma cause contraction of the sprindle
• Gamma Motor Neuron is smaller and slower then alpha and contributes to efferent to Gamma
• Golgi is touch to applied force; locate passive stretch and Active
• Ruffini like Receptors- located slow adaptation
• Paciniform Receptors- Rapidly Receptors

Muscle Spindles

• Muscles spindles are located inside of the muscle fibers and is used to Detect muscle
• Golgi is located in the endo and acts as a muscle and detects force