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Unformatted text preview: Touch & Proprioception Touch & Proprioception Cutaneous Receptors: “of the skin”
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(thermoreceptors) (nociceptors) (Merkel’s vs. Pacinian) Sensitivity is not equal on all areas of the body. Depends on the # of receptors in area. Proprioception: Proprioception:
Knowledge of body position in space. Sensory receptors in: Muscles, Tendons, Joints Muscle Spindles Sensitive to changes in muscle length – activated when muscle is stretched. Sensitive to changes in muscle force/tension activated when muscle is contracted Firing rate ↑ with greater tension Golgi Tendon Organs: “GTO’s” Crosssection of Spinal Cord
Dorsal roots carry afferent AP’s to CNS via dorsal horn. Ventral roots carry efferent AP’s to effector organs. soma of alpha motorneurons in ventral horn. Key Sensory Areas in the Brain Key Sensory Areas in the Brain Primary Somatosensory Cortex (S1) Proprioceptive and cutaneous Proprioceptive and cutaneous information ascends in afferent tracts in spinal cord and projects to sensory and parietal cortex. Somatotopic Organization: Amount of cortical tissue devoted to each body surface proportional to sensitivity of that part. Reflexes and Reflexes and Spinal Circuits Reflex Properties Reflex Properties Reflexes – rapid, involuntary, and predictable responses to stimuli Reflex Arc – direct route from sensory neuron to an effector organ Reflex Arcs Reflex Arcs
Latency (time of expression) app. 75 ms Factors affecting latency: 1. length of pathway 2. number of synapses (more synapses = more time*) 3. myelin 4. axon diameter; bigger axons conduct action potential faster than smaller axons Spinal Stretch Reflex Spinal Stretch Reflex
Function: 1. Regulate muscle length 2. Help maintain posture Sensory Receptor? Muscle spindle Simplest Reflex: Monosynaptic Golgi Tendon Reflex
Function: Protective mechanism Helps prevent excessive muscle contraction Sensory Receptor? GTO FlexionWithdrawal & Crossed Extensor Reflexes
Polysynaptic Function: Maintain balance during flexion withdrawal Reciprocal Inhibition?? occurs when one muscle is excited and other is inhibited Central Pattern Generators Rhythmical movements (e.g. locomotion) occur as the result o the activation of central pattern generators residing in the spinal cord. Transecting spinal cord does not completely abolish ability to make locomotor movements ...
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- Spring '08