Lecture 9 280 - Sensory Components 2025 PDF

Review from last class alpha muscl e A motor unit is the (blank) motor neuron and all of the (blank) fibres it innervates. Hennema Small Large n’s (Blank) s...

Review from last class alpha muscl e A motor unit is the (blank) motor neuron and all of the (blank) fibres it innervates. Hennema Small Large n’s (Blank) size principle states that motor units are recruited from (blank) to (blank). Recruitm Rate Coding ent Muscular contraction force can be varied by motor unit (blank) and by (blank-blank-ing). 1  KIN 280 – Motor control and Learning Sensory Components Faculty of Kinesiology and Health Studies University of Regina, Regina, SK January 27, 2025 2 Sensory Components How do you move if you can’t feel anything? Think about how much you move without watching yourself Your non-visual senses play an enormous role in motor control 3 Sensory Components Learning Outcomes: Identify and describe the neural pathways that make up the ascending tract Describe sensory receptors that provide proprioceptive information and how they impact movement Describe sensory receptors in the skin that provide tactile sensory feedback and consider how they impact movement 4  Sensory components Types of neurons: Sensory (afferent) Send neural impulses to the CNS Motor (efferent) Send neural impulses from the CNS Interneurons Transmit information within the CNS 5  Sensory components Somatosensory information (i.e., originating from the body) is sent to and processed in the primary somatosensory cortex of the parietal lobe 6 Neuromotor Basis for Motor Control Spinal cord: Gray matter (gray area, cell bodies, dendrites, axon terminals) White matter (white area, axons) Ventral horn and ventral column (1 and 4, motor) Dorsal horn and dorsal column (2 and 6, sensory) Sensory pathway (12), Motor pathway (11) Many different tracts running up and down the white matter: Ascending: Spinothalamic, spinocerebellar Descending: corticospinal, rubrospinal, reticulospinal. Vestibulospinal, tectospinal 7 Neuromotor Basis for Motor Control Brain and spinal cord (ascending): Into the dorsal horn Sensory signals travels up the dorsal column Crosses over at the medulla Through the pons and the midbrain Through the hypothalamus and thalamus Up to the cerebrum (somatosensory cortex) A second pathway goes through the cerebellum on its way to the cerebrum 8 Sensory Components Receptors: A receptor is a specialized neuron that can transduce a stimulus into an electrical signal i.e., a stimulus is converted into a change in membrane potential in the receptor The stimulus opens ion channels Four main stimulus characteristics: Modality – nature of the stimulus (temperature, pressure, pain) What type of receptor is activated? Location – where is the stimulus Which neurons fire? Carried to different CNS regions. Intensity How many receptors activated? How often (i.e., frequency?) Duration How long is the stimulus applied? 9 Sensory Components Proprioception: The “6th sense” - refers to an individual’s sense of where their body is in space 3 components: Position sense Kinaesthesia – sense of movement Sense of effort Mechanoreceptors providing proprioceptive info: Muscle spindles Golgi tendon organs Ligament and joint capsule receptors Cutaneous Rosie MacLennan, Olympic Gold Medal Trampolinist 10 Sensory Components Muscle spindles are the primary joint position sensor Detect changes in muscle length and velocity - mechanoreceptor 1) Muscle lengthens Intrafusal muscle 2) Sensory endings fibres detect stretch capsule 3) Mechanical 1a sensory endings stimulus converted to electrical signal 1a afferent axons 4) Travels up 1a afferent axons to efferent axons notify CNS Bigger stretch = gamma motor increased spindle neuron endings firing rate Gamma motor neurons contract intrafusal fibres so Extrafusal spindles still work in 11 muscle fibres contraction Sensory Components Muscle spindles 12 Sensory Components Muscle spindles 13 Sensory Components Muscle spindles Take a moment and explain all this back to yourself. What do muscle spindles sense? Describe the steps by which a muscle spindle is activated and then transmits information to the CNS. Explain what alpha-gamma co-activation is and why it is important. 14 Sensory Components Muscle spindles Stretch reflex 15 Sensory Components Golgi tendon organs (GTOs) are found within skeletal muscle near tendons GTOs are poor detectors of muscle length, they detect muscle tension or force 1) Muscle contracts 2) Collagen fibrils in the tendon are pulled tight 3) Sensory nerve endings of the GTO afferent (1b) are activated 4) Mechanical stimulus converted to electrical signal 5) Travels up 1b 16 afferent axons to Sensory Components Golgi Tendon Organs Inverse stretch reflex 17 Sensory Components Muscle spindle activity > GTO activity during passive stretch GTO activity > muscle spindle activity during concentric muscle contraction (you still get some b/c of alpha gamma co- activation though) 18 Sensory Components Ligament and joint capsule receptors are not well understood, but it is generally agreed that they exist and are likely free nerve endings (similar to a GTO) 19 Sensory Components Proprioceptive sensory information influences: Movement accuracy www.trendhunter.com Timing of onset of motor commands movement in one muscle cues another Coordination control www.threatpost.com 20  Sensory Components Proprioception is very important in the context of closed- loop motor control Athletes’ concept of “feel” rooted in proprioception 21  Sensory Components Deafferented individual is a drastic example, but proprioception also commonly impaired in less severe injuries to a lesser degree (e.g., ligament injuries, joint replacements) www.sbnation.com/nba Photo by Mitchell Leff/Getty Images www.betterbraces.com 22 Sensory Components Tactile: Mechanoreceptors – specialized endings of sensory nerves which transduce mechanical stimuli Mechanoreceptors in the skin (cutaneous) provide sensory inputs that create the sensation of touch (e.g., gripCutaneous force) receptors for tactile sensation 1. Meissner’s corpuscle (touch) 2. Pacinian corpuscle (pressure, vibration) 3. Merkel’s disk (touch) 4. Ruffini ending (pressure, skin stretch) 23 Sensory Components Cutaneous Receptors Flexor Withdrawal Reflex 24 Sensory Components Tactile sensory information influences: Movement accuracy www.trendhunter.com Movement consistency Movement timing Movement force adjustments www.threatpost.com See: “A closer look” pg 115 – Magill 25 Sensory Components Summary of Learning Outcomes: Identify and describe the neural pathways that make up the ascending tract Dorsal column, dorsal horn, medulla, pons, midbrain, hypothalamus, thalamus, primary somatosensory cortex Describe sensory receptors that provide proprioceptive information and how they impact movement Muscle spindles, GTOs, joint receptors Describe sensory receptors in the skin that provide tactile sensory feedback and consider how they impact movement Meissner’s corpuscle, Pacinian corpuscle, Merkel’s disk, Ruffini endings 26 Sensory Components Wednesday Jan 29 – Sensory Components continued 27