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12 Cards in this Set
- Front
- Back
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Muscle spindle
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Special sensory organ in skeletal muscle that provides info about LENGTH. (senses stretch)
Arranged in PARALLEL w/ muscle. Associated afferents: Group Ia & II |
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Muscle spindle
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Special sensory organ in skeletal muscle that provides info about LENGTH.
Associated afferents: Group Ia & II |
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Golgi tendon organ
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Receptor located in muscle tendons that provides info about muscle TENSION. (senses force)
Arranged in SERIES w/ muscle. Associated afferents: Group Ib |
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How does the muscle spindle stay "on-line" to provide sensory input when the muscle shortens (contracts) to a point where there is slack in the spindle?
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GAMMA motoneurons activate the INTRAFUSAL FIBERS within the muscle spindle.
This keeps the spindle taut, allowing it to maintain sensitivity to changes in length during contraction. ** Therefore, the alpha-MN is usually co-activated simultaneously w/ the gamma-MN. |
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Deep Tendon Reflex
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aka Stretch or Myotactic Reflex
MONOSYNAPTIC: 1. Stretch of a muscle's spindles by an external force (eg hammer)--> 2. Synchronous activity in Ia&II afferents--> 3. Excitatory activation of that muscle's motoneurons -Also usually leads to activation of synergist muscles Effect on antagonist muscles: "RECIPROCAL INHIBITION" DISYNAPTIC - The same Ia & II afferents also make an excitatory synapse w/ Ia inhibitory interneurons--> they make INHIBITORY synapse w/ antagonist MNs |
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Hoffman Reflex
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Allows quantitative assessment of the deep tendon reflex. More sensitive than a reflex hammer.
Measures the amplitude & latency of the H reflex elicited by electrical stimulation. |
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Golgi tendon circuit
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Organ acts in a negative feedback system to regulate muscle tension.
Functions: - Protects muscle from damage by decreasing its activation when generated force is too large. - Maintains a steady level of force at reduced levels, by counteracting small changes in muscle tension. 1) Various sensors, including the golgi tendon organ, sense excessive force production in a muscle--> 2) Ib afferents from G.T.O., together w/ axons from descending pathways and other sensory fibers all synapse onto the muscle's Ib inhibitory interneuron--> inhibits/decreases alpha-MN activity in the muscle. Ib afferents also synapse on interneurons that activate the antagonst muscle. |
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Renshaw cells
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Component of recurrent inhibition:
- a motoneuron gives off collaterals from main axon that activate Renshaw Cells. - Renshaw cells are inhibitory interneurons that then synapse back onto the same MN, allowing the MN participate in self-inactivation. * Renshaw cells can also connect to SYNERGIST muscles, simultaneously reducing their activity. * Renshaw cells can also synapse on INHIBITORY INTERNEURONS of antagonist muscles, therefore making them easier to activate. |
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Recurrent inhibition
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A type of negative feedback; activity in a population of neurons (alpha MNs) excites a 2nd population (Renshaw cells) that in turn inhibits the activity of the 1st.
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Flexor Reflex/
Crossed Extensor Reflex |
A cutaneous polysynaptic reflex that coordinates activity on both sides of the spinal cord.
Ex: "Stepping on a Tack" 1) Painful stimulus activates A-delta nociceptor afferent--> 2) Excitatory synapses on: i. Flexor muscle (hamstring) ii. Inhibitory interneuron of extensor (quadriceps)--> inhibits extensor iii. Excitatory commisural interneurons that cross the spinal cord--> synapse on inhibitory interneuron of flexor, and excite the extensor ** note the opposite response in other leg to counterbalance. |
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Intra-spinal connections
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Coordinate activity between different levels of the spinal cord.
ex. The lumbar enlargement has locomotion circuitry, which connects to--> - locomotion circuitry in the cervical enlargement - via the fasciculus proprius. - Allows for coordination of arm swing and stepping, etc. |
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Central Pattern Generators (CPGs)
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Made up of:
1) Rhythm generator interneurons (initiation & modulation of speed) 2) Patterning Network Interneurons **#1 & #2 may be influenced by descending signals, afferent signal, and/or drugs. 3) Motoneurons - Current research is being done using Afferent Drive to CPG Circuitry to improve gait recovery after stroke or spinal cord injury. |
