Lecture 4 - Stimulus evoked responses and simple reflexes PDF

Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience  Outline – Stimulus evoked responses / Reflexes KIN 255 – Fundamentals of Neuroscience 1. Automatic vs reflexive...

Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience  Outline – Stimulus evoked responses / Reflexes KIN 255 – Fundamentals of Neuroscience 1. Automatic vs reflexive 2. Characteristics of stimulus-response (S-R) transformation – measurement, timing, task difficulty, S-R compatibility, predictability 3. Monosynaptic reflex – mechanisms, characteristics  Stimulus evoked responses and simple reflexes 3 Stimulus evoked responses (or behaviours) automatic Stimulus evoked behaviour – behaviour evoked as an involuntary and relatively immediate consequence of sensory stimulation KIN 255 – Fundamentals of Neuroscience Involuntary meaning compulsory, done without will Types: ❖ Stimulus driven – where stimulus defines the characteristics of response ❖ Stimulus released – characteristics of response can be independent of some of the stimulus characteristics Automatic occurring spontaneously, without Many stimulus evoked behaviours are examples of reflexes. conscious thought or intention automatic Reflex – is produced as a direct, involuntary and relatively immediate response to stimulation of specific sensory inputs Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 4 Exercise: Push the professor KIN 255 – Fundamentals of Neuroscience Consider my response when being pushed in different contexts to explain why I replaced “involuntary” with “automatic” Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 5 Stimulus evoked responses KIN 255 – Fundamentals of Neuroscience Stimulus Response motoneuron Central nervous system We can measure different elements of the stimulus/response transformation using: ❖ Behavioral measures of the stimulus-response process ▪ Timing, accuracy, stimulus-response characteristic, response modifiability ❖ Electrophysiology assessment of the stimulus-response pathways ▪ H-reflex, evoked potentials, brain hemodynamics, non-invasive brain stimulation Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 6 Stimulus evoked responses: Timing The elapsed time between different points of the stimulus to response KIN 255 – Fundamentals of Neuroscience process can provide information about each specific part of the process Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 7 What time period captures the amount of time it takes the nervous system to relay the afferent signal, turn the stimulus into a response and relay that “motor command” to the muscles? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 8 Stimulus evoked responses: Timing Time within the nervous system is KIN 255 – Fundamentals of Neuroscience comprised of Conduction time and Synapse time. Conduction time is the time it takes to conduct the signal along the axons of afferent (and efferent) pathways. Synapse time is the time it takes for information to be exchanged by neurons (e.g. processing time) Reaction time is the time between the stimulus onset and the motor system response. Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 9 What measurement should be used to define “Reaction Time”, why? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 10 Stimulus evoked responses: Timing Response time is the time between stimulus onset and the movement KIN 255 – Fundamentals of Neuroscience outcome ▪ Response time is sometimes called “Response reaction time” Reaction time is the time between the stimulus onset and the motor system response. ▪ Reaction time is sometimes called “premotor time” or “latency” Movement Time is the time between the onset of the motor system response and the movement outcome Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 11 What measurement should be used to define “Reaction Time”, why? Reaction Movement Time Time Response Time = Reaction Time + Movement Time Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 12 Factors that influence reaction time: Task Complexity/Difficulty More response choices → Longer the reaction time KIN 255 – Fundamentals of Neuroscience Hick’s Law (1952) captures the cost of increasing the The Keep It Simple Stupid (KISS) number of stimulus response alternatives principle is a manifestation of Hick’s Law 𝑅𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑇𝑖𝑚𝑒 = 𝑎 + 𝑏[𝐿𝑜𝑔2 𝑁 ] Hick’s Law is prevalent in our lives. Even when ordering a meal from a new restaurant. The simpler the menu the quicker we choose our meal! Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 13 Factors that influence reaction time: Task Complexity/Difficulty Task complexity can be studies in the lab using “choice reaction time” KIN 255 – Fundamentals of Neuroscience tasks. ❖ When you see the green dot, press the “F” key with your left index finger x Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 14 Factors that influence reaction time: Task Complexity/Difficulty Task complexity can be studies in the lab using “choice reaction time” KIN 255 – Fundamentals of Neuroscience tasks. ❖ If you see the green dot, press the “F” key with your left index finger ❖ If you see the red dot, press the “J” key with your right index finger x Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 15 Factors that influence reaction time: Stimulus-response compatibility On average, reaction time is quicker the more straightforward it is to relate KIN 255 – Fundamentals of Neuroscience the stimulus to the response Quicker response time Slower response time Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 16 Factors that influence reaction time: Stimulus modality Stimulus modalities take different amounts of time to be identified, and KIN 255 – Fundamentals of Neuroscience associated to the appropriate response (even if the response is the same) Slower = More time spent in the nervous system V – visual H – haptic (tactile) A – auditory Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 17 The experiment on the preceding slide used a button press to quantify reaction time. What is the big assumption the experimenters made? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 18 Factors that influence reaction time: Stimulus intensity & predictability The more intense the stimulus energy (relative to ambient stimuli) the KIN 255 – Fundamentals of Neuroscience quicker the reaction time Watch track and field running events and you will notice the crowd gets quiet just before the starter begins their process Knowing when a specific response will be required (predictability) leads to quicker response times ❖ Can preload a particular response --- a preloaded response reduces response time since the expected stimulus is already related to the response Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 19 Why do 100 m runners false start more frequently than 800 m runners? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 20 Simple reflexes: Key terminology Monosynaptic arc KIN 255 – Fundamentals of Neuroscience ❖ Sensory neuron synapses (communicates) Monosynaptic arc directly with the motor neuron Disynaptic arc Disynaptic arc ❖ Sensory neuron acts on the motor neuron via an intermediary neuron Polysynaptic arc Polysynaptic arc ❖ A pathway involving multiple interneurons An interneuron is a neuron that between the sensory and motor neurons transmits impulses between other neurons. Interneurons can transmit or ❖ Polysynaptic arcs can also include a mix of modify the nature of the incoming monosynaptic, disynaptic and signal. An inhibitory interneuron is a neuron polysynaptic arcs that, when excited, exerts a suppressive effect on the next neuron Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 21 Simple reflexes: Monosynaptic reflex Overview KIN 255 – Fundamentals of Neuroscience Stimulus Response motoneuron Central nervous system Stimulus? Receptor (and afferent)? Transformation – where? Effector? Can you go through each step? – from stimulus to response? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 22 Simple reflexes: Monosynaptic reflex Example: The myotatic reflex (stretch reflex) KIN 255 – Fundamentals of Neuroscience What is the stimulus? What is the sensory receptor? Where does the transformation occur? What is the effector/response? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 23 Simple reflexes: Monosynaptic reflex There are substantially more extrafusal compared to intrafusal fibers in a KIN 255 – Fundamentals of Neuroscience muscle ❖ Therefore, the afferent nerve diverges to act on many motor neurons, innervating different extrafusal fibers, when the muscle is stretched Extrafusal muscle fibers are the muscle fibers responsible for generating contractile force Intrafusal muscle fibers are the specialized muscle spindle fibers that detect muscle stretch Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 24 Simple reflexes: Monosynaptic reflex The monosynaptic reflex requires KIN 255 – Fundamentals of Neuroscience coordinated action across the agonist as well as synergist and antagonist muscles ❖ The pathways involving the agonist and synergist muscles are monosynaptic ❖ The pathway involving the antagonist muscle is disynaptic Can you explain the role of the inhibitory interneuron in the antagonist disynaptic pathway? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 25 Simple reflexes: Key terminology Homonymous reflex pathway KIN 255 – Fundamentals of Neuroscience ❖ The afferent excitation of the sensory neuron acts to excite a motor neuron that projects back to the same muscle from which the sensory neuron originates Heteronymous ❖ The afferent excitation of the sensory neuron acts to excite/inhibit a motor neuron that projects to a different muscle The agonist monosynaptic pathway is a homonymous reflex pathway The synergist monosynaptic pathway is a heteronymous reflex pathway The antagonist disynaptic pathway is a heteronymous reflex pathway Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes KIN 255 – Fundamentals of Neuroscience 26 Muscle spindle fibers run parallel to extrafusal skeletal muscle fibers. However, spindle fibers do not contribute to contractile force. Do you foresee a problem in detecting the muscle length when the muscle is getting shorter? Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 27 Monosynaptic reflexes: Alpha & Gamma motor neurons Together the muscle spindle fibers and Alpha motor neurons innervate extrafusal the gamma motor neurons are known as the fusimotor system. The effect of fibers to shorten (more action potentials) or KIN 255 – Fundamentals of Neuroscience the gamma motor neuron on the lengthen (fewer action potential) the fiber spindle fiber is known as the fusimotor drive. Gamma motor neurons innervate special segments at each end of the intrafusal fibers to keep them taught as the muscle contracts Remember, a receptor potential is generated by stretching forces that pull ion channels open If the spindle fiber folds on itself, these ion channels will not open, even if the muscle is lengthening, until after the fiber becomes taught again Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 28 Monosynaptic reflexes: Alpha-Gamma coactivation Coordinated activity of alpha and gamma motor neurons is required for healthy KIN 255 – Fundamentals of Neuroscience motor control Alpha-gamma coactivation is the coordinated action of alpha and gamma motor neurons during muscle contraction Tonic bias or fusiomotor bias is the increase in spindle fibre tension through the coordinated action of alpha and gamma motor neurons during muscle contraction Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Stimulus evoked responses and simple reflexes 29 Monosynaptic reflexes: Involuntary or Automatic Involuntary meaning Simple reflexes are initiated by a sensory input and do not require a compulsory, done without conscious decision to move KIN 255 – Fundamentals of Neuroscience will However, the stimulus-response relationship of a simple reflex can be Automatic occurring modified by several mechanisms spontaneously, without conscious thought or 1. Change gamma motor neuron activity intention ▪ Changes muscle spindle receptor sensitivity ▪ Changing alpha-gamma relationship will alter the tautness of the spindle → same stretch will result in weaker afferent response 2. Inhibit the reflex ▪ Decrease the strength of the effect of the sensory afferent on the motor neuron (called gain) 3. Facilitate the reflex ▪ Increase the gain at the sensory to motor synapse Department of Kinesiology and Health Sciences, University of Waterloo https://uwaterloo.ca/kinesiology/  Summary – Stimulus evoked responses / Reflexes KIN 255 – Fundamentals of Neuroscience 1. Automatic vs reflexive 2. Characteristics of stimulus-response (S-R) transformation – measurement, timing, task difficulty, S-R compatibility, predictability 3. Monosynaptic reflex – mechanisms, characteristics