Midterm 1: Introduction To Nervous System PDF

UNIT 1 INTRO TO NERVOUS SYSTEM what is motor control? - movement produced by complex neural networks - activation and coordination of the muscles and limbs - reflexive/reactive components and voluntary mechanisms involves: - sensory — afferent - cortical processing — information processing -...

UNIT 1 INTRO TO NERVOUS SYSTEM what is motor control? - movement produced by complex neural networks - activation and coordination of the muscles and limbs - reflexive/reactive components and voluntary mechanisms involves: - sensory — afferent - cortical processing — information processing - motor/action — efferent - coordination simple behaviours use many parts of the brain — tennis example A. tennis ball coming over - visual cortex: process visual information - premotor cortex: planning actions - amygdala and hypothalamus: motivation, alert B. tennis ball is over - motor cortex: movement > sends signals to spinal cord to act - posterior parietal cortex: integrate sensors to understand surroundings - basal ganglia: execute motor task - cerebellum: error correction > perform task accurately 1 nervous system has central and peripheral components - cns — central nervous system brain & spinal cord - pns — peripheral nervous system peripheral nerves and ganglia - cns & pns separated anatomically functionally interconnected - constant communication to a.} sense the world we are in or b.} act on it through motor plans cellular components of nervous system - 2 major types of cells 1. neurons 2. glia - human brain contains approx. 100 billion neurons that makes 100 trillion ‘connections’ neurons - 4 main components 1. dendrites - branch looking structures that come off cell body - recieve inputs from multiple areas - giver information to cell body 2. cell body - gives rise to dendrites - sums up the information and sends to axon 3. axon 2 - myelinated or un-myelinated - aids in conduction velocity - longer than dendrites allows for transmission of information over long distances within the nervous systems 4. presynaptic boutons axon terminals/presynaptic terminals attachment zone where axon branches transmit information to the next neuron neuron — functional classification - sensory - motor - interneurons - work together to transmit information from the periphery into the nervous system or towards each-other to create reflexive movements or to creates updates for voluntary movement - building blocks of motor control networks senosry neurons - function — provide cns with information about our world - cell bodies are found in the dorsal root ganglia, just outside of the spinal column - also called ‘afferent’ neurons - approx. 5 million - information comes from a receptor in the periphery (ie. muscle, joint, skin, etc.) projecting to cns (spinal cord) - ‘connect’ with motor neurons, interneurons & ascend to the higher brain centres 3 motor neurons - function — control muscle contraction - start with other neurons and project to muscle - cell bodies in spinal cord — ventral horn - input — sensory neurons, interneurons in the spinal cord & higher brain centres - also called ‘efferent’ neurons - approx. several 100 thousand in cns interneurons - function —receive multiple inputs, integration of these inputs, pass on ‘processed’ information signals to multiple locations - vastly outnumber sensory and motor neurons central nervous system (cns) - consists of several main regions including: 1. spinal cord 2. brainstem 1. medulla 2. pons 3. midbrain 4 3. cerebellum 4. thalamus (part of diencephalon - ‘between brain’) 5. cerebral hemisphere (forebrain) structure of spinal cord - grey matter: cell bodies, un-myelinated axons. in the spinal cord, grey matter is on the inside dorsal horn — sensory neurons/inputs ventral horn — motor neurons - white matter: nerve fibres/tracts (axons ascending (relaying information) and descending (relaying motor information) ), in the spinal cord, white matter is on the outside dorsal, lateral and anterior columns myelinated axons appear white grey/white matter differences across spinal sections - cervical has a lot of white matter - segments in lower spinal cord has less relative white matter organization of the spinal cord - dorsal horn heavily related to sensory inflow - ventral horn heavily related to motor output/commands somatotopic organization of ventral horn - medial to lateral goes proximal to distal - dorsal to ventral goes flexor to extensor - same goes for lower limbs 5 brainstem - made up of medulla, pons, and midbrain - midbrain: extension of the spinal cord for the neck and head; regulates critical life support systems - pons: functions as a connection (relay) between higher brain regions, cerebellum, and spinal cord - midbrain: control of (reflexive) eye movements, as well as auditory and visual reflexes cerebral cortex - deeply convoluted (multiple folds and crevices) this way, we can fit many neurons in the same volume - gyri (gyrus): convolution or bumps - sulci (sulcus): valleys between gyri that appears as surface lines - fissure: very deep sulcus, can separate lobes subdivisions of the cerebral cortex - frontal lobe - parietal lobe - occipital lobe 6 - temporal lobe - central sulcus separates frontal and parietal lobe - lateral fissure separates temporal and frontal lobe occipital lobe - visual system - houses primary visual cortex, responsible for processing visual information temporal lobe - hearing - smell - taste - visual perception - speech (left hemisphere) parietal lobe - bodily (somatic) sensation - spatial processing - integration of visual and bodily sensation frontal lobe - movement - planning - reasoning 7 cerebral cortex cnt’d - many areas are concerned primarily with processing either sensory information or motor commands (unimodal) known as primary or secondary (sensory or motor) areas depending upon the complexity of the signal they process - examples: primary somatosensory cortex - localize and identify sensory stimuli primary motor cortex - trigger and execute movement commands - these areas are surrounded by even higher order regions called association areas (multimodal; systems coming together within the cortical region and processed together) - association area — integrate diverse information for purposeful action and are responsible for perception, movement and motivation 8 grey/white matter — cortex - white matter is on the inside - grey matter on the outside - un-myelinated axons coming from the outside inwards - once the axons become myelinated, they become white matter and project down through the brain stem into the spinal cord and into individual segments peripheral nervous system (pns) - 2 subdivisions — somatic & autonomic 1. somatic information to/from cns about muscle and limb position & the external environment 2. autonomic nervous system for viscera, smooth muscle & exocrine glands sympathetic / parasympathetic terms used to ‘navigate’ the nervous system - when in the cortex dorsal is superior (up) rostral is anterior (towards the nose/forwards) caudal is posterior (towards the tail/backwards) ventral is inferior (down) - when in the spinal cord rostral is superior caudal is inferior 9  dorsal is posterior (towards the back/dorsal fin) ventral is anterior (towards the chest) - medial is closer is midline - lateral is away from midline - distal is muscle or joints further away from the midline - proximal is muscle or joints closer to the midline - ipsilateral is two structures on the same side - contralateral is two structures on the opposite side - 3 planes 1. horizontal/transverse: separates top and bottom half 2. coronal: forward and back 3. sagittal: left and right INTRODUCTION TO MOTOR CONTROL 1 2 3 5 4 membrane potential - difference in distribution of ions (charged atoms) inside and outside the cell - INSIDE the cell: lots of negatively charged molecules (A-) & potassium (K+) 10  some sodium (Na+) and chloride (Cl-) - OUTSIDE the cell: lots of Na+ and Cl- some K+ - this imbalance of ions across the cell membrane results in a difference in electrical charge between the inside and outside the cell - usually more negative ions inside than outside the neuron - most neurons have a membrane potential of about -70 mv called resting membrane potential 1. deformation of the receptor membrane and generation of the action potential - when sensory information is detected, resting potential reaches threshold - if membrane voltage reaches a threshold, triggers an action potential caused by opening of sodium channels (depolarization) — channels close when membrane potential reaches about 30+ mv - membrane potential re-polarizes, coming towards resting state - membrane potential will go past the resting potential (hyper-polarization) membrane and action potentials - an action potential (AP) is a very rapid change in the membrane potential that occurs when a neuron is stimulated - due to sodium channel opening to allow an influx of Na+ ions inside the cell (depolarization) - potassium channels open, allowing positive K+ ions to flood out making the inside more negative again (re-polarization) - it will hyper-polarize, going past the resting membrane potential in which K+ channels will close and membrane potential will go back to -70 mv state 11 action potential - all or none principal - generated at inital segment of axon and travel down the axon to the axon terminal (presynaptic boutons) - voltage dependent: voltage-gated ion channels - comes from summation of all the inputs on the cell body - can cause neurotransmitter release 2. propagation of action potential - myelin: fatty substance covering the axons, allowing faster conduction of nerve impulses - ranvier nodes: breaks in the myelin sheath, action potentials ‘jumps’ from node to node 3. depolarization of presynaptic membrane and release of neurotransmitters - synapse to control behaviour, information must be passed amongst nerve cells electro-chemical mechanisms at synpase involves 3 main components 1. presynaptic neuron 2. synaptic cleft 3. postsynaptic neuron (dendrites or cell body itself will be affected) - neurotransmitter release vesicles release neurotransmitters across synaptic cleft onto other neurons released neurotransmitter bind to post synaptic receptors, which in turn open ion- channels - can either cause membrane potential to increase, excitatory 12  - or membrane potential to decrease, inhibitory - channels open on post synaptic neuron 4. stimulation of receptors on postsynaptic membrane and generation of synaptic (local) potential - postsynaptic potentials can have a positive or negative influence on membrane potential of post synaptic neuron 1. depolarize (closer to threshold) producing an excitatory postsynaptic potential (EPSP) 2. hyper-polarize (farther from threshold) producing an inhibitory postsynaptic potential (IPSP) membrane and local potentials - small amplitude, spread small distances - must summate to produce action potential summation of signals - spatial summations: inputs from multiple presynaptic neurons at once - temporal: a single presynaptic neuron sending input quick successions, over and over - potential at a given post synaptic neuron = sum of (+/depolarization) and (-/hyper- polarization) neurotransmitters affecting it - a given neuron may have 1000’s of other neurons synapsing on it convergence/divergence - spatial / convergence - divergence: one neuron talking to multiple 13 5. generation of action potential - propagation of action potential - depolarization of presynaptic membrane - release of neurotransmitters terminating the postsynaptic potential - postsynaptic potential is terminated by having the neurotransmitter destroyed or taken back to the axonal terminal that released it (re-uptake) - some drugs can influence the processes affecting the postsynaptic potential (for example, less uptake or more stimulation effects of drugs - drugs that affect behaviour can do so by affecting synaptic transmissions neurotransmitters are the gate-keepers, they open and close ion-channels to allow positive or negative ions to enter the postsynaptic membrane drugs can interfere with the opening/closing of these ion channels can block or inhibit the postsynaptic effect or can facilitate them - ethanol (alcohol) facilitates postsynaptic (GABA) stimulation GABA binds to receptors causing inhibitory channels to open keeps inhibitory channels open for longer periods of time - ie., larger or longer IPSP - cocaine blocks re-uptake of dopamine (a type of neurotransmitter) allowing the dopamine to remain in the synapse for longer post-synaptic transmission increases which causes euphoric feeling, increased energy level 14 summary 1. deformation of receptor membrane 2. generation of the action potential 3. propagation of action potential 4. depolarization of presynaptic membrane 5. release of neurotransmitters 6. stimulation of receptors on post synaptic membrane 7. ion channels open 8. generation of synaptic (local) potentials 9. generation of action potential 10. propagation of action potential 11. depolarization of presynaptic membrane 12. release of neurotransmitters CONTROL OF MUSCLE inputs to motor neurons - cell body within ventral horn - summation of local potentials - afferent — dorsal - efferent — ventral - direct connection EPSP - indirect connection IPSP - alpha/low motor neurons 15 - response to synaptic input depends on size due to surface area & axon diameter smaller m.n larger m.n conduction velocity slow fast communication w/ muscle fibers few many postsynaptic potential larger smaller motor units - a motor neuron and all the extrafusal muscle fibers it innervates the number of fibers innervated by a motor neuron: innervation ratio - the number of muscle fibers innervated by a motor neuron varies depending on the muscle: gastrocnemius; approx. up to 2000 eye muscles; as few at 5 fibers - each individual muscle fiber is innervated by only one motor neuron one motor neuron may innervate several muscle fibers - the muscle fibers of a single motor unit are distributed throughout the muscle mixed with fibers innervated by other motor neurons — not grouped together motor unit (mu) recruitment - important to get the right amount of force during a movement - size of the m.u is related to force ex; bigger m.u produce more force >> due to more muscle fibers being active - ratio of motor neurons to muscle fibers affects the precision of control ex; the control of fine movements relies on smaller m.u (smaller innervation ratio) 16 - during muscle contraction, small m.u are recruited before the large ones this is known as the size principle, it allows for gradation of muscle force - increase force increase the number of active motor units increase the firing rate (code) of active motor units - the level of force where all motor units affiliated with a muscle are recruited, differs between muscles ex; hand muscle has all motor units recruited at 60% max slow contraction; 85% in biceps motor neuron pool and motor units - motor neuron pool: all the individual motor neurons innervating a single muscle - motor neurons innervating one muscle are clustered in the spinal cord - can extend 1 to 4 spinal segments motor neuron > muscle fiber > motor unit > motor neuron pool 17 muscle fibers - type types of muscle fibers 1. extrafusal muscle fibers regular muscle fibers contraction of these fibers allows for movement responsible for the power-generating component of muscle innervated by alpha/low motor nuerons MOVERS 2. intrafusal muscle fibers fewer of them, located deep within most skeletal muscles along side extrafusal muscle fibers 4-7 in a group and wrapped in capsule separating them from the rest of the muscle: muscle spindle change in length just like the extrafusal muscle fibers, but not to generate force involved in detecting changes in muscle length specialization for proprioception which informs us about how our body is positioned or moving in space SENSORS motor neuron types - two types of motor neurons (for the 2 types of muscle fibers) 1. alpha motor neurons - innervates extrafusal muscle fibers - control muscle contraction - “lower motor neurons’” 18 2. gamma motor neurons - innervates muscle spindles (intrafusal muscle fibers) - controls the sensitivity of muscle spindles changes in control - DEPENDING ON THE STATE OF THE MUSCLE, THE LEVEL OF CONTROL CHANGES - muscle force is influence by: force-length relationship: degree of overlap & non contractile element properties influence force output force-velocity relationship: the faster the shortening rate, the lower the force (concentric contractions) - the same neural activation does not produce the same output need a different command to produce the same force at different limb positions and speeds - nervous system must account for muscle properties when making brain-output to force-output calculations during motor learning & performance 19  UNIT 2 INTRODUCTION TO SKILLED PERFORMANCE AND MOTOR LEARNING human movement - types of movements we can make reflexes stereotyped movements self-expression/goal-directed behaviours accuracy skilled performance - learned ability to achieve predetermined results (a well defined goal) by: these maximizing the certainty of goal achievement three requirements minimizing the physical and mental energy costs of performance vary depending minimizing the time used on tasks speed energy spent features of skilled performance 1. quality of performance that does not depend solely on a person’s innate abilities, but it is developed through training, experience, and practice. (i.e learning is crucial; long hours of practice) — this is the distinction between ability and skill 2. skill depends on learning, but goes beyond it to include efficiency and economy of performance (i.e. quality of learning, smooth and tireless 3. flexibility of operation with which a skilled performer can reach the same end results depending on circumstance (i.e. many strategies and procedures) 20 components of skills - three elements are critical to almost any skills 1. perceptual - perceiving the relevant environmental features - discriminate between sensor stimuli important for the skill vs noise 2. cognitive - deciding what to do, where and when to perform the skill - quality of the performer’s decisions regarding what to do is important 3. motor - producing organized muscular activity to generate movements that achieve the goal - quality of movement is important classifying skills 1. level of environmental predictability — open >closed 2. movement initiation — self paced > forced 3. task organization — discrete > serial > continuous 4. importance of physical and cognitive components — motor > cognitive 5. primary muscles required — gross > fine motor level of environmental predicitabilty - closed skill a skill performed in an environment that is stable and predictable during the action allows performers to plan their movements in advance stereotyped movements can be used: habitual repetition of same movements with as little variability as possible 21 - open skill a skill performed in an environment that is variable and unpredictable during the action requires performers to adapt their movements in response to dynamic properties of the environment an absence of stereotyped movements movement initiation - self paced performers set pace with respect to the initiation of movement - forced paced pace set by outside stimulus task organization - discrete discrete skills usually have an easily defined beginning and end, often with a very brief duration of movement - serial a serial skill is a group of discrete skills strung together to make up a new more complicated skilled action the word ‘serial’ implies that the order of the elements is usually critical for successful performance 22 - continuous continuous skills have arbitrary (not defined) beginning and end points, the behaviour flowing for minutes or hours series of actions strung together importance of physical and cognitive compoentns - cognitive high decision making requirement - knowing what to do - sensorimotor low decision making requirements - doing it correct primary muscles required - gross motor skill = large muscle groups used - fine motor skills = small muscle groups (hands and fingers primarily) SKILLED PERFORMANCE AND INFORMATION PROCESSING a model for information porcessing - to analyze skilled performance and skill acquisition (learning), some questions arise 1. how do humans process information and control movement? 23 2. what are the difference between skilled and unskilled performers? input: information/signals > processing mechanisms > output: action a more detailed infromation processing model a simple sensorimotor model 24 factors affecting the flow of information processing a. limited capacity b. speed-accuracy characteristic c. response time d. limiting principle limited capacity - humans can only process a limited amount of information at a time without becoming overloaded a. information is either: i. lost or ii. filtered out by the system b. information takes time to be processed by each function (stage). processing time for each stage is cumulative and adds up to response time speed-accuracy characteristic - if insufficient time is allowed for ideal processing, then accuracy suffers, i.e. the information is distorted - when a task requires both speed and accuracy, performers must make a choice between the two criteria 25 fitts’ law - predicts the movement time for a task requiring speed and accuracy in which one must move to a target as quickly and as accurately as possible - knowledge of the distance required to move and the size of the targets allows us to predict the time it will take to perform the task —equation— T = a + b log2 (2D/W) > termed the index of difficulty (ID). higher ID = more difficulty - t = movement time - a + b are constants - d is the distance moved - w is the size of the target speed/accuracy & skilled performers - skilled performers are faster and more accurate than unskilled performers (the speed-accuracy characteristic has shifted to the left) - this means skilled performers have increased their information processing capacity - this increase in capacity is due to the storage of past experience (information) in long term memory - using this information to solve present problems by-passes time-consuming information transformations — the problem does not have to be solved each time - this process is reflected by the third stage of learning — autonomous stage - when dealing with a lot of information, action is automated and unconscious (becomes like a reflex, so its faster). this process is also called chunking 26 response time - response time is the sum of separate times for each function/mental operation - understanding that response time is a composite of different stages and has important practical consequences for learning/improving activities limiting principles - cannot determine form the end result of an action the reasons for successful or unsuccessful performance - must analyze the action in order to determine which stage produced the problem definition of learning - a relatively permanent improvement (change) in performance as a result of practice or experience - implies a change from unskilled to skilled performance characteristics of learning - four characteristic of performance that indicate learning 1. improvement — is the action faster, more accurate? 2. consistency — are the improvements in the action repeatable? 3. persistence — can the actions be maintained over time? 4. adaptability — can the characteristic of the action change based on task/environment demands stages of learning - people go through distinct stages as they acquire skills - two conceptualization of learning stages during skill acquisition - descriptors of different levels of skill development 27  fitts and posner: identified stages of learning according to how the cognitive process involved in motor performance change as a function of practice bernstein: identified stages of learning from a combined motor control and biomechanical perspective fitts and posner 1. cognitive stage - ‘understand’ task, gross errors, disconnected performance, learn strategies - learner is concerned with goal identification, performance evaluation, what to do, when to do it - this stage is MAINLY characterized by information that can be verbalized: demonstrations, film clips, discussions between teacher/learner, self talk - very rapid and large gains in proficiency in this stage, indicating that more effective strategies for performance are being discovered 2. associative stage - connect stimuli to motor response and connect parts of task into a whole, gross errors drop out, refinement of performance - the learner’s focus shifts to organizing more effective movement patterns - in skills requiring quick movements, such as a tennis stroke, the learner begins to build a motor program to accomplish the movement requirements - in slower movements, such as balancing, the learner constructs ways to use movement- produced feedback - inconsistency gradually decreases closed skill movements become stereotypic open skill movements become adaptable - enhanced movement efficiency reduces energy costs, self talk is less important - learners begin to monitor their own feedback and detect errors 28 3. autonomous stage - constant monitoring of performance unnecessary, becomes automatic; speed increases and variability decrease; error drop out; ‘skilled performer’; takes months to years - learner attained expert performance - decreased attention demanded by both perceptual and motor processes frees the individual to perform simultaneously higher-order cognitive activities eg. making higher level decisions about strategies in sport, expressing emotion and affect in music and dance - self confidence increases and capability to detect and correct one’s own errors become more fine tuned stage process characteristics other name cognitive gathering inforamtion large gains, inconsistent verbal-motor stage performance associative putting actions together small gains, disjointed motor stage performance, conscious effort autonomous much time and practice performance seems automatic stage unconscious, automatic, smooth MEASURING PERFORMANCE performance ≠ learning - performance and learning describe different concepts - performance = an observable behaviour e.g. hitting a ball - learning = a relatively permanent change (improvement) in performance as a result of practice or experience 29 measuring performance - performance production measures production refers to measuring behaviour (performance) required to achieve goal - performance outcome measures outcome refers to measuring the goal of performance - ex. archery drawing the bow and releasing the arrow i production accuracy of shot is outcome assessing production - production is generally difficult to measure compared to outcome but is important to be able to analyze production directly because it controls outcome 1. human judgement - usually used to assess production. this is satisfactory up to a point but will be unsatisfactory where high speed complex movements are involved or where there is a need to understand relationships between movements 2. video recording - assists human judgement by slowing down movement and removing memory load 3. high speed filming and computer analysis - slows movement down so that position (location), velocity, and acceleration of body parts can be calculated 30 4. electromyogram (EMG) - body movement produced by muscles. emg measures electrical activity of muscles so that the size and timing of contractions can be analyzed 5. brain activity measures - eeg: electroencephalogram ‘brain waves measures electrical activity in the brain using small, metal discs (electrodes) attached to the scalp - fmri: functional magnetic resonance imaging - measures blood flow to actives brain areas assessing outcome - response magnitude refers to absolute size of response - ex; number of laps run during track practice - reaction time (speed) (rt) time from appearance of stimulus to beginning of movement - fractional reaction time (frt) premotor time (prmot) = stimulus until first emg activity motor time (mot) = first change in emg until movement begins 31 - accuracy / error refers to performance with respect to criteria - shots in hoop in basketball (spatial accuracy) - distance from bullseye in dart throwing (spatial accuracy) - pressing a button on your controller to shoot (temporal/timing accuracy) - hitting a ball with a racquet or landing an aircraft (combination of spatial accuracy and temporal accuracy) four measures of error: constant error - constant error (ce): a measure of accuracy and considers the difference between the score and the target (keeping +ve and -ve values) - by keeping the values you can quantify the magnitude and direction of error scores: 10, 4, -1, -5 target = 0 cm ce = trial score - target = (xi -t); means ce = sum(xi-t)/n ce = sum of scores/number of scores ce = (10 + 4 - 1 - 5) / 4 =8/4 = 2 cm - interpretation: average distance of scores from criterion is +2cm - MAGNITUDE AND DIRECTION OF ERROR ON AVERAGE 32 four measures of error: variable error - variation error ve: standard deviation of scores (gives the variability of inconsistency of performance around the mean) xi = each point n = number of tries E = sum mean = (10+4-1-5) / 4 = 2 cm ve = 5.6 - interpretation: ve reflects the variability/consistency in movement relative to one’s own average performance four measures of error: total variability - total variabilty (E) or root mean square error (RMS) — measure of overall error similar to calculation for VE T = target or criterion value - interpretation — spread of scores about the target and viewed as an overall measure of success/error relative to the target e / rms = 5.96 33 four measures of error: absolute error - absolute error (ae): measure of overall accuracy (mean of the scores ignoring the sign) mean AE = sum |(xi - t)| / n - interpretation: measure of overall accuracy of performance (the absolute deviation between movement and the target - magnitude of error without particular direction summary — measures of error 34  UNIT 3 SENSORY SYSTEMS somatosensory system - to detect the position and motion of our body parts - reception of signals from periphery send to central nervous system for integration and interpretation - convey information about posture and movement of the body - modulates/change descending commands in the spinal cord - information ascends to cerebral and cerebellar areas - proprioception — sense of position of the limbs in space and relative to body; sense of oneself kinaesthesia — (conscious) sense of movement - exteroception — sense through interaction with the external environment general components - receptor encodes stimulation thermal, mechanical or chemical - action potential along peripheral axon to dorsal root ganglion and into spinal cord - sensory processing: spinal reflexes ascends to brainstem, cerebellum and cerebral areass 35 peripheral receptors - cutaneous receptors touch, stretch, vibration, pain, temperature - joint receptors joint angles and range of motion - muscle spindles muscle length and change in muscle length - golgi tendon organs muscle tension or force muscle spindles - encapsulated spindle shaped located in muscle parallel with skeletal (extrafusal) muscle fibers - gamma motor neuron innervates contractile component - there are two types of intrafusal fibres: nuclear bag nuclear chain - wrapped with sensory axons type Ia and type II sensory fibers - signal muscle length and change in muscle length - when at rest extra and intrafual fibres remain at resting length firing rate is active and consistent at a neutral rate - when muscle is stretching (lengthening) extr and intrafusal fibres stretched 36  firing rate is quicker - when muscle is shortening extra and intrafusal fibers contract firing rate is slower/longer spindle afferents - sensory neurons wrapped around the intrafusal fibres include type Ia afferent - signal the length of the muscle (static) as well as changes in length during movement (dynamic) - innervates nuclear bag and chain intrafusal muscle fibres type II afferent - signal the length of the muscle (static) and less so the change in length - innervates mainly nuclear chain intrafusal muscle fibres dynamic: rate of change in muscle length static: change in muscle length golgi tendon organs - in series with skeletal muscle: muscle-tendon junction - innervated by Ib afferent fiber - sensitive to tension (active or passive) ex; when tension generated by the muscle increases, Ib afferents are activated — increasing the firing rate - homonymous (same muscle) muscle inhibition via an inhibitory interneuron precise spinal control of muscle force in activities such as grasping a delicate object 37 cutaneous receptor - 4 main types - classified into slow adapting and fast adapting slow = merkle disks and ruffini endings fast = pacinian and meissner corpuscles - measure skin deformations - ex; used in balance (feet) and object manipulation (hand) - only happens when theres a change in stimulus - if stimulus remains on, only slow adapting will tell you that - fast acting gives more detail regarding change in stimulus — vibration, acceleration joint receptors - located within joint capsule - sensitive to extreme ranges of movement — protective role - thought to be active for a specific range of motion 38 reflexes: spinal control of movement - many motor tasks are performed without thinking - automatic but adaptable response to a sensory stimulus - considered the basic units of movement; elementary form of motor coordination sensory information is the main driver of motor response - ex; flexion withdrawal reflex: limb withdrawn from a painful stimulus stretch reflex: monosynaptic reflex from a stretch of a muscle - communicates with synergistic muscles (same action) - communicates with interneuron that turns off antagonistic muscle (opposite action) crossed extension reflex: stimulated limb withdraws opposite limb extends to support (eg. balance) 1. ipsilateral activation of flexor 2. deactivation of extensor 3. contralateral activation of extensor 4. inhibition of flexor - reflexes: involuntary: happens without conscious planning, although modifiable stereotyped: roughly the same response to the same simple stimulus fast-responding main ascending pathways - dorsal column-medial lemniscus pathway vibration, proprioception, light touch information - discriminative touch and conscious proprioception important for: recognizing object by touch, controlling & coordinating movement 39 - anterolateral pathway pain, temperature, crude touch information important for: localizing noxious sensation, distinguishing between warm & cold VISUAL AND VESTIBULAR SYSTEMS visual system — function - exteroceptive sense identify objects in space determine movements in objects - visual proprioception body in space relation of body segments motion of the body in space the eye - receptors for vision located on back of the eyeball, on the retina - concentration of receptors providing high resolution (clear image) = fovea - need to move eyes so that images (or visual target) fall on fovea pathway for visual information - ganglion cell axons exit through optic disk - axons bundle together to form optic nerve - travel to optic chiasm, where nerves from both eyes comes together left information goes to right side of brain right information goes to left side of brain - when it leaves the chiasm it forms optic tract, which terminates at several locations 40  relays information to multiple different areas related to visual function visual system — central visual pathway - from the optic tract, information goes two 3 different areas 1. superior colliculus eye (and head) movement 2. pretectal region pupillary reflex 3. lateral geniculate nucleus relays information/visual processing through v1 - primary visual cortex (v1) striate cortex visual system — higher order visual cortex - from visual cortex, information goes to different places of the brain - separate ‘streams’ for processing visual information - two visual systems (pathways) 1. dorsal (parietal) stream (where) spatial visual cues to posterior parietal region 2. ventral (temporal) stream (what) pattern discrimination and recognition to temporal cortex 41 pathway deficits - optic ataxia (with parietal lobe damage) — damage pointing to or grasping object, but no problems with recognition - visual agnosia (with temporal lobe damage) — problems recognizing or naming objects, but no problems reaching and grasping object vestibular system — function - involved in the control of balance (vestibulo-spinal) - position of head and neck (vestibulo-colic reflexes) - controls eye muscles/reflexes (i.e. vestibulo-ocular reflex) vestibulo-ocular reflex (vor) - eyes go opposite to head movement allowing gaze to remain on target when its head is moving compensates for head rotation vestibular system - bony ‘labyrinth’ filled with perilymph fluid peri = around - membraneous inner structure filled with endolymph fluid endo = inside bone > perilymph fluid > membraneous structure > endolymph fluid vestibular appartus: 5 sensory structure - 3 semicircular canals - 2 otolith organs 42 semicircular canals - orthogonal oriented 1. anterior 2. posterior 3. horizontal - three co-planar pairs 1. right and left horizontal canals - increase sensitivity to detect accelerated changes 2. left anterior and right posterior 3. right anterior and left posterior - excite one, inhibit the other - one end of each semi-circular canal bulges to form ampulla - ampulla houses this gelatinous material: cupula - cupula has hair cell celia extend up into iot from the ‘floor/base’ of the ampulla - hair cells have axons projecting to brainstem and go into vestibular nuclei semicircular canals: hair cells - hair cells can be excited or inhibited - kino cilia: really tall cilia (medial side) - if bent towards kino cilia you depolarization and increase in firing rate - if bent away from kino cilia you get inhibition and decrease in firing rate 43 semicircular canals — detect angular acceleration - the way the cupula bends is due to its interaction with endolymph fluid - angular acceleration of the head endolymph fluid lags (due to inertia) - cupula and cilia deflect otolith organs - detect linear acceleration 1. utricle 2. saccule - hair cell cilia extend into gelatinous layer: otolithic membrane - calcium crystals embedded on the surface of the membrane: otoconia/otoliths - hair cell receptors have axons that project into brainstem to the vestibular nuclei otoliths — detect linear acceleration and static orientation relative to gravity - otoconia lags in opposite direction as the body if accelerating, lags move backwards if decelerating, lags move forwards - otoconia moves in the same direction as the head when tilting (due to gravity) if tilting backwards, otoconia move backwards if tilting forwards, otoconia move forwards - the movement of otoconia causes the bending of gelatinous material, bending the cilia, therefore changing the firing rate 44 vestibular sensory neurons - vestibular signals carried via vestibulo-cochlear nerve (CN VIII/8) to ipsilateral vestibular nuclei: - 4 vestibular nuclei 1. lateral vestibular nucleus (LVN) 2. medial vestibular nucleus (MVN) 3. superior vestibular nucleus (SVN) 4. inferior vestibular nucleus (IVN) 45