Term
| Basic mechanism for a spinal reflex |
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Definition
| Receptor organ receives stimulus information and converts the information to an electrical signal that travels through afferent nerve fibers to the CNS. The CNS processes the information and sends a command through the efferent nervous system to an effector organ which responds. |
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Definition
Ia fibers sense the velocity of stretch and relay this information monosynaptically to the homonymous alpha motorneuron. So, the alpha motorneuron causes the muscle to contract.
The stimulus is primarily rapid stretch which excites the nuclear bag and therefore Ia afferents.
Monosynaptic excitation of synergistic muscles.
Ia afferents synapse on inhibitory interneurons (disynaptic) to inhibit antagonist muscles. |
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Definition
| excitation and contraction of agonist muscles at the same time as relaxation or inhibition of antagonist muscles |
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Definition
Definition: resistance of a muscle to active or passive stretch
Hypotonia: decrease in resistance to passive manipulation of limb- can be caused by a decrease in excitatory influences on the motorneurons. Voluntary movements require more effort.
Hypertonia: increasein resistance to passive manipulation of limb- results from increased sensitivity of muscle spindles caused by an increase in gamma motoneuron activity
Under normal conditions, the muscle spindle fires tonically to maintain activation of the motoneuron pool resulting in muscle tone. |
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Definition
| If the dorsal root is cut, input from the spindles is removed so motoneuron activity decreases and the muscle becomes flaccid. |
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Term
| How can you change the response of the knee jerk reflex? |
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Definition
| Increasing fusimotor activity (gamma motorneuron activity), increases the response to a stretch reflex. This can be achieved by doing the Jendrassik's maneuver (having the patient pull his hands apart). |
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Term
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Definition
This is the opposite of the stretch reflex. When the muscle contracts, the golgi tendon detects the contraction. It sends the information to the spinal cord via Ib afferents. It uses disynaptic connections. It synapses onto an inhibitory interneuron which then synapses on the homonymous alpha motorneuron. This decreases the activity and causes the homonymous muscle to relax.
Disynaptic pathway also excites antagonist muscles. |
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Term
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Definition
| If one tries to stretch a hypertonic limb, there would be resistence to the stretch due to the oversensitive spindles. Eventually the muscle tension resisting the stretch will trigger the golgi tendon organ setting off a rapid inverse myotatic reflex. The muscle would suddenly relax and the joint would flex. |
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Term
| Flexor Reflex (withdrawal reflex) |
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Definition
Afferents can be group II (touch), III(temp), or IV(pain) fibers.
All flexor muscles on that limb are excited and the extensors on that limb are inhibited causing the limb to withdraw from the stimulus.
There will be an opposite effect on the opposite side of the body; extensors will be excited and flexors inhibited in order to maintain posture.
This is a complex reflex involving multiple interneurons so it is considered polysynaptic.
After discharge: after the stimulus is over the muscle begins to relax but does not fully relax immediately- this is due to recurrent circuits (persistent neural activity) |
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Definition
projection of many fibers onto a single cell
Example: a single motorneuron received input from practically all the muscle spindle afferents that originiate from the homonymous muscle |
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Definition
single to many projections
example: each Ia affarent that originates from a given muscle spindle project to practically all the motneurons that innervate that muscle |
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Term
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Definition
| When two motorneuron pools have overlapping subliminal fringe regions, there is a summation of the stimulus in the region of overlap. So, you will get more than the sum of the responses. |
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Definition
| When two cells have an overlap of discharge zones and are fired simultaneously the result may be less than the sum of the two individual cells. |
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Definition
| responsible for recurrent inhibition- self inhibition |
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