Fundamental Definitions and Characteristics of Motor Control and Learning Definitions - Areas of Study ❖ Motor Control ➢ Understanding how the neuromuscular system functions to activate and coordinate the muscles and limbs involved in the performance of a motor skill ➢ Coordination: the patterning of body and limb motions relative to each other and to the environmental objects and events ❖ Motor Learning ➢ Study of the processes involved in acquiring and refining motor skills that promote or inhibit the acquisition ➢ Difference between just practicing & practicing correctly ➢ Ex: bike riding → once learned, can always do ❖ Motor Behavior ➢ Behavior that involves exerting muscular forces that affect the limbs or other body parts ❖ Goal-Directed Motor Behavior ➢ Movements producing a particular outcome despite the presence of obstructions or changing conditions ➢ Ex: shooting basketball Skills, Movements, and Abilities ❖ Skill: an action or task that has a specific goal to achieve ❖ Are All Activities Skills? ➢ An activity is a skill if it: ■ Is directed toward the attainment of a goal ■ Is performed voluntarily ■ Has been acquired by experience/practice ❖ Motor Skill: required voluntary body/limb movement ➢ Differs from cognitive skills (born with these, ex → suckling) ❖ Levels of Skillfulness ➢ EXPERTS VS NOVICES ➢ Additional characteristics of skilled performance: adaptable, consistent, efficient ❖ Movements: behavioral characteristics of specific limb(s) that are components of a skill ➢ MOVEMENTS ARE BUILDING BLOCKS OF A SKILL ❖ Classifying Skills ➢ Why classify? ■ Simplifies discussion ■ Allows comparison across research ■ Provides context for coaches/therapists ➢ One dimensional continuum: range between two ends on a given variable ■ Ex: hot ← → cold ➢ Skill commonalities ■ All require concentration ■ All must focus attention on a specific point/thing ■ Coordination ➢ Skill differences ■ Some have stable, predictable environment in which skill is performed, some do not ■ Some use the whole body, some just hands/arms ■ Some are continuous, some are sporadic ■ Some involve fast movements, some involve slow movements ■ Some involve standing posture, some seated ➢ CLASSIFICATION 1: SIZE OF MUSCULATURE USED ■ Prime movers used in surgery and long jumping are clearly not the same ■ Gross ← → Fine ■ Gross: use large musculature, involve less movement precision ● Fundamental motor skills (jumping, locomotion, etc) ■ Fine: requires control of small muscles; hand-eye coordination ● Writing, typing, sewing, etc ➢ CLASSIFICATION 2: TYPE OF MOVEMENT ■ Discrete: have clearly specified beginning and end (ex: hitting a switch) ■ Serial: involve a series of discrete movements (ex: playing piano, hammering nail) ■ Continuous: have arbitrary start and end (ex: swimming) ● Where does stroke start and end in the circle? ➢ CLASSIFICATION 3: MOTOR-COGNITIVE DIMENSION ■ Low Cognitive Demand: actions are automatic, with little thinking ■ Moderate Cognitive Demand ■ High Cognitive Demand: motor component is less significant than the cognitive element ➢ CLASSIFICATION 4: STABILITY OF THE ENVIRONMENT ■ Environment refers to the characteristics of objects/people the skill is performed with ■ Closed ← → Open ■ Closed: environment does not change while performing skill ● Tend to be self-paced ● Object waits for your action Open: environment is changing during performance of the skill ● Usually not self-paced ● Require constant adjustments ■ Abilities VS. Skills ❖ Ability: stable trait or capacity of the individual that is a determinant of a person’s potential for the performance of a specific skill ➢ Abilities are generally thought to be hereditary/genetically determined, and by large unmodified by experience ❖ Individual Differences: stable enduring differences among people that contribute to differences in task performance ➢ Height, body type, cultural background, emotional make-up, developmental stage ➢ ABILITIES is a category ❖ Ability vs Skill ➢ A: stable, inherited traits, few in number, underlie performance of many skills ➢ S: modified by practice, developed, many in number, depend on different subsets of abilities ❖ Generalized Motor Ability: abilities are highly related and can be characterized by a single, global ability ➢ Minimal empirical evidence ❖ Specificity of Motor Ability: abilities are relatively independent; the “all around” athletes had a high number of abilities ➢ CORRELATION DOES NOT EQUAL CAUSATION (typing doesn’t equate to piano playing ➢ Research evidence for specificity of motor abilities ❖ Rehabilitation ➢ Identifying abilities allows the practitioner to get to the source of the problem ➢ Can be achieved by task analysis ➢ Many identify areas for compensation ❖ Genetics Equal Ability ➢ Eero Antero Mantyranta (Finnish) ■ PFCP → primary familial and congenital polycythemia ■ 50% INCR in oxygen-carrying capacity ■ This led to development of EPO drugs ❖ Orthopedics VS Endocrinology ➢ Tommy John Surgery ➢ Tendon tighter → throw faster Motor Fit, Equivalence, Error, and Feedback Control Understand and Identify examples of motor fit, adaptation, motor equivalence, voluntary/involuntary movements ❖ Motor Components ➢ Elemental motor action (aka discrete actions): motor action in which the goal outcome is achieved by executing just one goal-directed action ➢ Discrete Action: a motor action whose execution has clearly identifiable start and end points ■ BUILDING BLOCKS OF ACTION ■ Ex: hitting a baseball, picking up coffee ❖ Motor Fit: achieving the same motor outcome despite different circumstances ➢ Ex: opening door (normal, push to open, heavy door, arms full) ❖ Adaptation: the ability to change motor behavior depending on circumstances ➢ Ex: driving different cars; walking on different surfaces ❖ Motor Equivalence: equality of outcome of two or more movements, movement patterns, or muscle contractions that may be different in other respects ➢ All lead to the same outcome ❖ Voluntary vs. Involuntary Motor Control ➢ Voluntary: goal-directed behavior that is performed deliberately and with the conscious intention to achieve a goal ■ The performer is aware of having the choice of whether or not to carry it out ■ Ex: open door, throw ball ➢ Involuntary: behavior that is not voluntary; performed without conscious intention, and the person is not aware of having a choice about whether it is produced or not ■ Ex: blinking, digestion, pupil restriction, knee jerk reflex ➢ Parkinson’s Disease ■ Hypokinetic disorder → too little movement ■ Loss of dopamine neurons in the Substantia Nigra (SN) ● Part of basal ganglia Symptoms: ● Tremor; bradykinesia; freezing/shuffling of gait; impaired posture/balance; muscular rigidity ■ ● Video in class → trouble walking, could easily ride bike (cyclical motions help) ➢ Huntington’s Disease ■ Hyperkinetic disorder → too much movement ■ ■ ■ ■ Genetic neurodegenerative disorder Disease onset at ~40 ATROPHY OF BASAL GANGLIA Symptoms: ● Chorea (dance-like movements); lack of coordination; emotional and cognitive impairments (tail-end of disease) ❖ How to decide if behavior is goal-directed? ➢ 1. Adaptability ■ The same outcome can be achieved in different conditions using different motor behavior ➢ 2. Persistence in response to failure ■ When possible, if an outcome is not achieved on first attempt, further attempts may be made until the outcome is achieved Understand the ideas of movement feedback and movement errors for production of movement, and be able to identify different forms of feedback that are used in movement ❖ Movement Error: when what we plan and what we do DO NOT align ➢ The difference between desired action and the actual performance ➢ Internal Model: pre-programmed basis of movement contained in the brain ■ Thought to “live” in the cerebellum ■ Ex: allows us to be able to drive any car ➢ Errors can be small or large!! ■ Overcorrecting steering by 2 in vs 2 ft ➢ Correct movement errors via loop control ■ 1. Open-loop control → commands are preset ● ● ■ Have to wait until next movement to make a correction Ex: shooting basketball 2. Closed-loop control → uses feedback to continue to improve movement ● Can make corrections to movements along the way ● Purpose of using feedback is to reduce errors as much as possible ● Ex: air conditioning, maintaining position driving ❖ Causes of Movement Errors ➢ 1. Disturbances ■ Inputs external to the control system could affect the controlled variable(s) and produce errors ■ Ex: getting your elbow bumped; ice when walking; strong wind; hole in ground ➢ 2. Controller Mistakes ■ Controller could make a change in the control variable when it is not needed, or response to an error with an inappropriate change of the control variable ■ Ex: pick up empty suitcase thinking it’s heavy ➢ 3. Changes to the Requirements ■ If the required value of the controlled variable changes, an error is likely to be created ■ Ex: biking over different terrain; drop in speed limit Neuromechanical Foundations - Intro to Neuroscience Name and describe the function of the components of a neuron ❖ Neurophysiological Perspective: the subsystems which the NS (CNS & PNS) controls and coordinates the musculoskeletal system ❖ Functional Perspective: the structures and processes through which we control body movements (ie integration and regulation) → theoretically based!! ➢ Theory of behaviors that control ❖ Nervous System Overview ➢ PNS: nerves, ganglion ■ PNS critical for communication between CNS and other organ systems ➢ CNS: brain, spinal cord ➢ Neurons ■ Functional unit of the NS ■ Receive electrical impulses from other neurons which cause them to either transmit electrical impulses or not ❖ Divisions of the Neuron ➢ 1. Soma (cell body) → contains single, central nucleus; responsible for production and transportation of neurotransmitters ➢ 2. Dendrites → projections from soma that receive signals/inputs from neighboring neurons ➢ 3. Axon → single projection from soma (but can branch); sends signals/inputs to other neurons or “target” tissue ■ Can vary in length and thickness ■ Covered in myelin sheaths (white fatty substances) ➢ Structure/morphology of individual neurons varies considerably ■ Function can be inferred from morphology ❖ Properties of Neurons ➢ 1. Synapses → the region of contact where a neuron transfers information to another cell ■ ■ Electrical: direct connections between neurons (gap junctions) Chemical: communication between synapses via the release of neurotransmitters ● Neurotransmitters are chemical messengers ◆ Produced in the soma ◆ Stored in the terminal ends of axons ◆ Released when an action potential reaches the ends of the axon ➢ 2. Synaptic Cleft → the region separating the presynaptic and postsynaptic membranes ➢ 3. Synaptic Vesicle → a membrane-enclosed structure that contains neurotransmitters ➢ 4. Neurotransmitter → a chemical that is released by a presynaptic element upon stimulation and activates postsynaptic receptors ❖ Properties of Axons ➢ Axon diameter and the presence of myelin determine the speed of conduction ■ Myelinated: propagation speed faster as axon diameter INCR ■ Unmyelinated: propagation speed levels out as diameter INCR ➢ Myelination ■ Nodes of Ranvier → important for INCR speed of axon transmission (spaces between sheaths) ● Saltatory Conduction → APs jump from one node to the next ■ Myelinated axons are twice as fast as unmyelinated axons!! ➢ Multiple Sclerosis ■ Damage to the myelin sheath ■ Symptoms: vision problems; sensory problems (tingling, numbness); motor problems (muscle weakness, poor coordination) ■ Video in class: weighted vest helps stabilize movements Explain the principles that govern the flow of electrical activity within a neuron, as well as between two neurons ❖ Principle of dynamic polarization → unidirectional flow of information (ex: dendrites to axons) ➢ 1. Concerned with the flow of information (electrical signals) within a neuron ➢ 2. Information flows from the dendrites to the axon terminals ➢ 3. Due to characteristics of the neuron, information will not back-propagate (flow in opposite direction) ❖ Principle of connectional specificity ➢ No cytoplasmic connection between neurons (connect directly) ➢ Neurons make precise connections (not random) ❖ Action Potential → flow of information refers to propagation of an action potential (electrical activity) ■ 1. Brief change from negative to positive in transmembrane potential ■ 2. All-or-none response: amplitude of AP does not change based on magnitude of stimulus ➢ Result of the influx and efflux of sodium and potassium ions across the membrane ■ 1. Depolarization → membrane potential more positive than resting membrane potential ■ 2. Repolarization → return of membrane to resting potential ■ 3. Hyperpolarization → membrane potential more negative than resting membrane potential ■ 4. Firing threshold → potential to which a membrane must be depolarized to initiate an AP ❖ Neuronal Firing Properties ➢ Firing rate → rate at which a neuron generates action potential (aka spikes) ➢ Refractory period → after firing, a short time period where the neuron is unable to fire ➢ PATTERNS ■ Convergence: many neurons connect to small number of neurons ■ Divergence: few neurons connect to many neurons ❖ Patterns of Neuronal Connectivity ➢ Monosynaptic: neurons directly connected (ex: patellar reflex) ➢ Polysynaptic: more than two interneurons connecting (ex: crossed extensor reflex) Identify and distinguish between functional classes of neurons ❖ Sensory Neurons ➢ Detect changes in the environment referred to as stimuli (ex. light, touch, pain, etc) and transmit information to the CNS ➢ Afferent information → TO CNS ❖ Motor Neurons ➢ Send signals to target tissues (ex. muscles, glands) in order to elicit a response to a particular stimulus ➢ Efferent information → AWAY FROM CNS ❖ Interneurons ➢ Neither sensory or motor ➢ Serve as integrative function – connect incoming sensory and outgoing motor information ➢ 90% of neurons Describe the organization of the cerebral cortex and how this organization is altered based on experience ❖ Gray vs White Matter ➢ White matter → myelin surrounding axons ■ Important for electrical impulse transmission ➢ Gray matter → soma and dendrites ■ Important for synaptic activity ❖ Cerebral Cortex ➢ Brodmann’s areas: studied the structure and cerebellar composition of the cerebral cortex ■ ID’d 52 distinct areas ➢ Neural Organization ■ Topographic maps of information are maintained throughout the nervous system ■ Proximal areas in the middle of the cortex, distal areas in the outer part of cortex ■ Area of brain dedicated to how innervated area of body is ■ Motor Homunculus ➢ Plasticity → experience dependent and is thought to be the neurophysiological mechanism that underlies learning ■ ■ Study: mapped out brain, removed monkey finger, brain compensated and removed area Video in class: man learned to pick up a can due to the stimulus from practicing it Neuromechanical Foundations - Neuroanatomy and Neuroscience Methodology Name and describe components/structures of the nervous system and their functions critical for motor control and learning ❖ Spinal Cord Cross-Section (WHITE MATTER = MYELIN; tracts mostly in white matter) ➢ Dorsal Horn: incoming afferent sensory information ➢ Ventral Horn: outgoing efferent motor information ❖ Descending Tracts → communicate efferent/motor information (END AT SPINAL) ➢ Ventromedial Spinal Pathways (proprioceptive/balance) ■ 1. Reticulospinal tract (MOTOR) → starts in pons ● ■ 2. Vestibulospinal tract (MOTOR) → balance ● ■ Function: voluntary movements, muscle tone, and variety of spinal reflexes Functions ◆ Regulates head position in response to rotation ◆ Facilitates limb extensor muscles in response to otolith organs (postural control) ◆ Facilitates control of eye movements (vestibular ocular reflex/VOR) 3. Tectospinal tract (MOTOR) → survival skills (look to where sound came from etc) ● Functions ◆ Coordinates audiovisual information - critical for eye movements and orientation responses ◆ Originates in the superior colliculus (nucleus important for eye movement) ➢ Lateral Spinal Pathways (voluntary skilled action) ■ 1. Corticospinal/pyramidal tract (MOTOR) → CONTRALATERAL ● Function: involved in fine motor movements (fast conduction at 4m/s) ● Arises from cortex ■ 2. Rubrospinal tract (MOTOR) → originates in red nuclei ● Function: involved in gross movements, motor coordination (conduction at 100 m/s) ❖ Ascending Tracts → communicate sensory information (START AT SPINAL) ➢ 1. Dorsal Column Medial Lemniscal Tract/DCML (SENSORY) → CONTRALATERAL ■ Path: spinal cord → medulla (crosses) → thalamus → somatosensory cortex ■ ■ Function: conscious refined touch, proprioception, vibration ● Proprioception: awareness of body’s position in space Conduction: fast direct path ➢ 2. Spinocerebellar tract (SENSORY) → HALF CONTRALATERAL ■ Path 1: spinal cord → medulla → cerebellum ■ Path 2: spinal cord → medulla → thalamus/cortex (crosses) ■ Function: relay non-conscious proprioceptive information from muscles to the cerebellum and cortex Conduction: fast ■ ➢ 3. Spinothalamic tract (SENSORY) → CONTRALATERAL ■ Path: spinal cord (crosses) → brainstem → thalamus (connects) → somatosensory cortex ■ Function: relays information about touch, pain and temperature from spinal cord to somatosensory cortex Conduction: slow ■ Name and describe areas of the brain and their importance ❖ Brain Lobes/Areas ➢ Frontal lobe: executive functions, cognition, decision making for motor control ➢ Parietal lobe: sensory information, vestibular information, integration of sensory and motor information ➢ Occipital lobe: visual information ➢ Temporal lobe: hearing, olfaction, object recognition ➢ M1 (primary cortex) → execution of movement ➢ S1 (primary somatosensory cortex) → processing sensory information (touch, pain, proprioception) ➢ Premotor Cortex → planning of movements ➢ SMA (supplementary motor area) → learning movement sequences, bimanual motor activities ➢ *Pre-SMA → learning sequential movement patterns, voluntary actions in response to conflict (role is fuzzy) ➢ FEF (frontal eye fields) → important for eye movements ➢ Broca’s Area → speech production (disorder = aphasia) ❖ M1 and S1 Somatotopic Organizations ➢ Neural representation directly corresponds to parts of the body ➢ Adjacent cortical regions correspond to adjacent body areas ➢ Body parts with fine control (motor)/ higher sensation (sensory) have a larger representation ❖ Basal Ganglia ➢ Important for the control of voluntary movements: ■ Movement initiation and completion ■ Activates and retrieves movement plans ■ Scales movement parameters (power, speed, direction, amplitude) ■ Adds motor sequencing information ■ Acts as motor “brakes” ➢ Substantia Nigra!! ❖ How do they all work together?? ➢ 1. Basal ganglia controls initiation of familiar movement by triggering pre-motor cortex ➢ 2. Pre-motor cortex passes “move it” message onto motor cortex ➢ 3. Motor cortex sends message to spinal cord telling appropriate musicals to contract ❖ Cerebellum ➢ Important for: posture/balance, motor learning, motor coordination ❖ Cerebellar Outputs ➢ 1. Cerebro-cerebellum → dentate nucleus → premotor cortex (motor planning) ➢ 2. Spino-cerebellum → interposed and fastigial nuclei → motor cortex and brainstem (motor execution) ➢ 3. Vestibulo-cerebellum → vestibular nuclei → motor neurons in spinal cord and brainstem Name and describe disorders/impairments of the nervous and muscular systems that impact motor skill execution ❖ Parkinson’s Disease ➢ On their own: steps very small, slow, shuffled ■ Turning is difficult ➢ When given targets: can easily walk ■ Visual input helps initiate movements ❖ Cerebellar Ataxia ➢ Genetic neurodegenerative disorder ➢ Affects ability to: ■ Walk; talk; use fine motor skills ➢ Video: no balance, needs a ton of support, uncoordinated, no coordination in arms ❖ Transcranial Magnetic Stimulation (TMS) ➢ A non-invasive experimental technique, induction of large-scale cortical plasticity ■ Can deliver stimulation to the brain; can deliver inhibition to the brain ➢ Potential therapy for stroke, parkinsons, major depression, etc ➢ Perinatal stroke causes most hemiplegic cerebral palsy (stroke before birth) ■ Results in a variety of motor problems ● Poor coordination ● Impaired movement ● Sensory problems ● 30-50% of children have cognitive impairment with CP ❖ Cerebral Palsy ➢ Often specialized rehabilitation camps that are fun for kids ■ Focus on play, intensive regular therapy, everyday skills ➢ TMS combined with rehabilitation can lead to greater improvements for some children ■ Improved participation in daily activities and school activities List different methodologies to study the brain ❖ Recording electromagnetic activity (EEG, MEG) ➢ direct ❖ Recording metabolic activity (fMRI, PET) ➢ Indirect ❖ Electroencephalography (EEG) ➢ Electrodes placed on skull detect and record brainwaves (electrical patterns) ➢ Techniques used: ■ Event-related potentials (ERPs): electrical peaks that are related to specific stimulus ■ Coherence-functional communication between brain areas of interest ➢ Pros: ■ Directly measures brain ■ Good temporal resolution ■ Cheap ■ Easy to transport ■ Silent ■ Easy to use for many behavioral paradigms ■ Easy to use for many populations ➢ Cons: ■ Poor spatial resolution (general ideas, no specifics) ■ Set-up time ■ Can only record activity from the outermost portions of the brain ❖ Positron Emission Tomography (PET) ➢ Uses computed tomography and radioactive markers injected into the bloodstream ➢ Indirect measure of brain activity: IDs areas of where the brain is working, based on “fuel intake” (ie glucose and O2 providing energy to firing neurons) ❖ Magnetoencephalography (MEG) ➢ Records the magnetic fields produced by the electrical activity of the brain ➢ Pros: ■ Excellent temporal resolution (order of milliseconds) ■ Good spatial resolution (millimeter precision) ■ Less set-up time ■ Direct measure of brain activation ➢ Cons: ■ Orientation of MEG (upright position) ■ Less readily available ■ $$$ ❖ Functional Magnetic Resonance Imaging (fMRI) ➢ Indirect measure ➢ Aligns atomic particles in tissue by magnetism, then “bombards” them with radio waves ■ Different tissues return different radio signals ➢ Determines areas of the brain where there is the most oxygenated hemoglobin ➢ Pros: ■ Excellent spatial resolution ➢ Cons: ■ Poor temporal resolution ■ Indirect measure of brain activity ■ Susceptible to movement artifacts ■ Use of templates and atlases ❖ HUMAN CONNECTOME PROJECT IS ONGOING → study of the brain and compilation of data Receptors for Sensorimotor Control Explain the five general properties of a receptor ❖ Perception: our ability to recognize an input and its relative importance ➢ Selection of specific inputs necessary for action ➢ Integration of separate, different types of information into a meaningful whole ❖ Receptors: specialized cells or subcellular structures that transduce an environmental stimulus into electrical impulses that can be interpreted by the nervous system ➢ 1. Photoreceptors → primarily responsive to light ➢ 2. Mechanoreceptors → respond to mechanical energy (touch, vestibular receptors) ➢ 3. Chemoreceptors → response to certain chemical substances (taste and smell receptors) ➢ 4. Thermoreceptors → primarily response to thermal energy (hot/cold) ❖ Receptor origin of stimulus ➢ Exteroreceptors → outside the body ➢ Interoceptors → inside the body (NOT AS IMPORTANT) ➢ Proprioceptors → from the body itself (arise from movement of the body) ❖ Five General Properties of Receptors ➢ 1. Intensity Coding: receptors can detect and code strength or magnitude of stimulus ■ Graded response → the greater the stimulus, the greater the response (ex: dim vs bright light) ● Spatial summation: larger the number of receptors that are stimulated, the stronger the perceived stimulus (ex: pinpoint prick vs holding orange) ● Temporal summation: a strong stimulus causes receptors to fire at a higher frequency than a weak stimulus (ex: candle vs bonfire flame) ■ Both summations above can happen at the same time!! ➢ 2. Adequate Stimulus: most receptors are built to respond only or preferably to one kind of stimulus ■ Will focus on the one that is more pressing ➢ 3. Modality: when a specific receptor is stimulated (with an adequate stimulus) to cause a consciously perceived sensation, you get the same modality of sensory experience ■ Every time you see the same light, you get the same experience ➢ 4. Adaptation: response slows with sustained stimulation ■ Ex: mechanoreceptors in hand for touch ● Slow adapting: info about size and shape ● Fast adapting; info about direction of movement ➢ 5. Receptive Field: the region of a sensory surface that, when stimulated, modulates the activity of a neuron ■ Ex: areas in cat retina, light shown in each, cell responded differently in each area ❖ Individual receptors cells convey information about stimulation ➢ Strength, timing, type, location Describe the nature and be able to compute Just Noticeable Differences (Weber’s law) for receptor-based, sensory information ❖ Weber’s Law of Just Noticeable Difference (JND) ➢ The minimum amount that the strength or intensity of a stimuli must be to produce a perceived difference in the sensory experience ➢ Determines how intense the difference needs to be between two stimuli to notice a difference ❖ Two-point discrimination (type of JND) ➢ Our ability to discern points as being distinct (used for sensation of touch) ➢ Place two points apart on the body and see if you can determine if they are separate or one ■ Fingers can determine ~0.6cm ■ Foot ~ 3cm → not as important to determine here compared to fingers ➢ Individuals with neuropathy often have larger values for TPD!! Vestibular System Describe the components of the vestibular apparatus and identify the stimuli to which each component responds ❖ Functions of the Vestibular System ➢ Perception of self-motion ➢ Perception of head position ➢ Spatial orientation (orienting head to sound stimulus) ➢ Afferent information is used to stabilize gaze, head, and posture ❖ Semicircular Canals → arranged perpendicularly, covers all possible rotational head movements ➢ Rotations: ■ X-axis → anterior and posterior canals ■ Y-axis → anterior and posterior canals ■ Z-axis → horizontal canal ➢ The three canals lie in different planes (right angles to each other) ■ Labyrinths are mirror images of one another (parallel planes) ■ Nodding the head stimulates anterior and posterior (but not horizontal) ➢ Endolymph in the semicircular canal displaces the cupula – hair cells within the canals – to bend ■ Excitation or inhibition of the hair cells, depending on the direction of the bend ➢ Head rotation deforms the cupula in opposing directions for the two canals – result in opposite changes in their firing rate ■ For turning your head right… (OPPOSITE FOR LEFT TURN) ● Right canal = depolarized = INCR firing rate ● Left canal = hyperpolarized = DECR firing rate ➢ Movement of head turns the tube – not the fluid!! ■ Fluid is stationary and creates resistance (deflecting the hair cell) Describe the sensory receptors of the vestibular system and explain how these receptors detect and code different stimuli ❖ Otolith organ: two organs (utricle and saccule) responsible for detecting linear accelerations and gravity ➢ Utricle → responsible for detecting linear accelerations and horizontal head-tilt ➢ Saccule → responsible for detecting linear accelerations and vertical head-tilt ➢ These organs allow us to perceive changes in linear acceleration and gravity!! ➢ Otolith = ear stones ❖ Utricle and Saccule ➢ Contain hair cells embedded in a jelly like substance (similar to semicircular canals) ➢ Substance contains small calcium carbonate crystals called otoconia ■ Otoconia have a higher specific weight which allows them to be influenced by gravity ➢ A change in position of the head alters the pattern of hair cells bending due to the effect of the gravity on the otoliths ❖ Fundamental Ambiguity of Otolith Signal ➢ 1. Head back → INCR firing rate; depolarize ➢ 2. Head forward → DECR firing rate; hyperpolarize ➢ 3. Forward acceleration → INCR firing rate; depolarize ➢ 4. Backward acceleration → DECR firing rate; hyperpolarize ➢ LINEAR ACCELERATION = HEAD TILT!! ■ Can cause sensations of movement ➢ Sudden changes during flight (climbing to going horizontal) may stimulate otolith organs ■ Give illusion that plane is pulling up → INVERSION ILLUSION ■ Pilot perceives plane is ascending still and will overcorrect by pushing plane downwards Explain the effects of the vestibular system on the control of movements ❖ Influence of Vestibular Information ➢ Vestibular information is communicated to the nuclei of the extraocular muscles to coordinate eye movements that maintain a stable image on the retina ■ VOR → vestibulo-ocular reflex ➢ Vestibular information is also communication to the muscles contributing to equilibrium and posture via the vestibulospinal tract ❖ VOR ➢ CNS must integrate the following information to control eye movements: ■ Vestibular and proprioceptive inputs about head position ■ Visual inputs about movement of an image across the retina ■ Proprioceptive inputs about eye movements relative to head position ➢ VOR maintains eye fixation on an object as the head turns ■ 1. Movement in hair cells in the horizontal SC canals ■ 2. Leads to action potentials in the vestibular nerve (CN 8) ■ 3. Axons in vestibular nucleus → contralateral abducens nucleus ■ 4. Abducens = CN 6 (innervate lateral rectus muscle) ■ 5. Other CN 7 axons → lateral vestibular nucleus → relay ipsilateral oculomotor nucleus (CN 3 → innervates medial rectus muscle) ❖ Oscillopsia ➢ No VOR; can’t make compensatory eye movements when head moves; very shaky vision Somatosensory System Compare and contrast cutaneous sensations and proprioception ❖ Somatosensation and Movement ➢ Cutaneous sensation ■ Basic modalities include touch, pressure, heat, cold, and pain ■ Sensations such as itch, tickle, dampness, texture, and firmness ● Don’t have receptors for; these are perceptions ● Modalites above work together to create such sensations ■ Encapsulated endings → primarily mechanoreceptors that inform about object movement and friction ● Regulated structures ■ Free endings → primarily act as nociceptors ● Float in space ➢ Proprioception ■ Sensations form the musculoskeletal system (muscles, tendons, joint capsules, ligaments) ■ Low threshold mechanoreceptors that inform the CNS about movement and position by detecting stretch of the tissue in which they lie ■ Three types: ● 1. Muscle spindles → detect muscle stretch ● 2. Golgi tendon organs → detect applied force ● 3. Joint receptors (type 1-4) → act as limit detectors ● First two are for muscle, last one is for joints Describe the neural organization of the cortical areas involved in somatosensory processing ❖ Neural organization: topographic maps of information are maintained throughout the nervous system ➢ Have one for sensory and motor ❖ Somatosensory Processing - CONTRALATERAL ➢ Sensory information detected from one side of the body is perceived by the opposite side of the brain ❖ Movement Production ➢ Alpha motor neurons innervate the extrafusal muscle fibers, causing muscular contraction Explain the effects of cutaneous information on the control of movement Describe the proprioceptive receptors and explain how they detect and code adequate stimuli ❖ Muscle spindle: cigar-shaped (fusiform) structures that run parallel to regular (extrafusal) muscle fibers ➢ Spindle stretches to convey information about muscle length/stretch ➢ Density of spindles vary from muscle to muscle ■ Muscles used for precision movements have higher density of spindles ➢ Difference Between Alpha and Gamma Motor Neurons: ■ Alpha-motor neurons → innervate extrafusal muscle fiber ● ■ Cause contraction of the muscle Gamma-motor neurons → innervate intrafusal muscle fiber ● ● Smaller, slower than alpha Cause contraction of spindle and responsible for keeping the spindle taut!! ➢ Efferent vs Afferent Fibers ■ Each muscle spindle is innervated by an efferent fiber and one or more afferent fibers ● Efferent → axons of gamma motor neurons ◆ Two types: ➢ 1. Gamma static ➢ 2. Gamma dynamic ● Afferent ◆ Two types: ➢ 1. Type Ia afferent ➢ 2. Type II afferent ➢ Muscle Spindle – Afferents ■ Type Ia Afferents (faster) ● Sensitive to speed and length of stretch ◆ When we change speed of stretch, firing of afferent matches the speed ■ Type II Afferents (slower) ● Sensitive to length of stretch, insensitive to speed ➢ Stretch Reflex – Reciprocal Inhibition ❖ Golgi Tendon Organs → located in the myotendinous junction ➢ Both passive stretch and active contraction of the muscle INCR tension of the tendon, which activates the GTO ■ Detects force – muscle tension!!! ➢ Type Ib afferent fibers ❖ Joint Receptors ➢ Four types: ■ Type 1 → ruffini-like receptors ● ● ■ Type 2 → paciniform receptors ● ● ■ Rapidly adapting nerve fibers Signal joint movement, particularly movement velocity Type 3 → golgi endings ● ● ● ■ Slowly adapting nerve fibers Signal static joint position, movement, direction, and speed of movement Slowly adapting receptors (resemble GTO) Only found in ligaments Functional role unknown Type 4 → free nerve endings ● Signal tissue damage ● Located in fibrous capsule and ligaments ➢ Different receptors fire at different ranges of joint angles ■ MOST fire near extreme joint angles: ● Thought to play protective role ● Limited involvement in proprioception Compare and contrast the muscle spindle and the golgi tendon organ reflexes ❖ Stretch Reflex – Reciprocal Inhibition MUSCLE SPINDLE ➢ Ex: tendon reflex ❖ Vibration Illusions – Proprioception MUSCLE SPINDLE ➢ Selectively stimulates type 1a spindle afferents and produces a proprioceptive illusion ■ Type 1a → stretch and speed ➢ Amount of stretch is too small to activate type II afferents ➢ If applied to biceps tendon → will give illusion that biceps are extending ➢ The percept is in the direction of muscle lengthening (stretch!) ■ Due to muscle spindles being selectively activated ❖ Pinocchio Illusion ➢ Addition of tactile information ➢ Two pieces of sensory information ■ 1. Percept that arm is moving ■ 2. Sensation that fingertip is on nose ➢ Vibration of biceps tendon gives illusion that arm is moving away from face ➢ Perception that the nose is growing! ➢ SENSORY DOMINANCE ■ Proprioceptive dominant; dominates over the touch sensation ❖ Proprioceptors and Sensory Illusions ➢ Two target lights (only visual information seen) ➢ Vibrate both biceps - both arms feel like they are extending ➢ SENSORY DOMINANCE ■ Visual information is dominant and it appears the lights move apart!! ❖ Rubber Hand Illusion ➢ Visual dominance over proprioception ➢ Visual Capture → proprioceptive awareness is “captured” by a visual location ■ Felt position of hand is referred to a new visual location
