Spinal Cord Reflexes Part 1 Flashcards
-Deep tendon reflex (DTR)
-Stretch reflex. Applying stretch to muscle and it’s reflexively contracting
-Tap right underneath patella, achilles tendon, or on cubital fossa at the biceps tendon to elicit response
-Missing reflex = neurological problem
Myotactic Reflex
-Ex: Tap on Patella Tendon
Tapping on the tendon puts stretch on the muscle fibers, which sends a signal all the way up to the dorsal root and into the spinal cord.
When in the spinal cord, it synapses with an internuncial neuron, then goes to a motor fiber.
Exits spinal cord via motor fiber, goes to Quadriceps m., which reflexively contracts and kicks out, extending the knee.
-Afferent limb tendon is stimulated to elicit the reflex
Monosynaptic Reflex Loop/DTR/Myotactic Reflex/Stretch Reflex
Contains Alpha Motor Neurons and Gamma Motor Neurons
Anterior portion of the gray horn of the spinal cord
Send out a signal via the ventral root to a muscle fiber
-Supplies extrafusal fibers.
Alpha Motor Neurons
Neurons that supply intrafusal fibers.
2 Types of intrafusal fibers:
-Nuclear Bag
-Nuclear Chain
Gamma Motor Neurons
1) Gamma Motor Neurons innervate the Intrafusal Fibers
2) Activation of the Afferent Limb
3) Efferent Limb of the Reflex (Alpha Motor Neurons)
Steps of the Myotactic Reflex
Two types:
-Dynamic Motor Fibers
-Static Motor Fibers
Can cause a muscle to contract or relax.
Measured by two sensory endings:
-Annulospiral Ending (Primary Ending)
-Flower Spray Ending (Secondary Ending)
Spinal cord and afferent branches interface with these.
Gamma Motor Neurons
Measure the rate of change of length of intrafusal fibers.
-Fibers end on a Plate Ending
Dynamic Gamma Motor Fibers
Regulate the static length at any given moment of the intrafusal fibers.
-Fibers end on a Trail Ending
Static Gamma Motor Neuron
Group 1A fibers that curl around an intrafusal fiber (around the nuclear bag and the nuclear chain)
-Very high velocity fibers
-Fibers project up through the sensory system to take info from Gamma Motor Neurons back to the spinal cord
-Attaches to the Nuclear Bag and the Nuclear Chain
Annulospiral Ending (Primary Ending)
Sensory ending that sends its influence back upon stimulation through spinal cord via Group 2 Sensory Axons
-Takes info from the Gamma Motor Fibers back to the spinal cord
-Attaches to the Nuclear Bag and the Nuclear Chain
Flower Spray Ending (Secondary Ending)
Consists of:
-Dynamic Sensory Fibers (1A fibers) that measure rate of change of intrafusal fiber length
-Static Sensory Fibers (2 fibers) that measure the static length of intrafusal fibers
Our ability to get the measurement of the intrafusal fibers back to the spinal cord
Activation of the Afferent Limb of the Monosynaptic Reflex
Groups 1A and 2 fibers enter the spinal cord via the dorsal root and synapse with A Alpha Motor Neurons.
A Alpha Motor fibers leave the spinal cord over the ventral root and travel to the extrafusal fibers.
Extrafusal fibers contract, and you need several of them all contracting together to move a joint
Efferent Limb of the Monosynaptic Reflex
-Called Increased Gamma Bias
-Can occur with lesion in the spinal cord that knocks out inhibitors
-Causes the intrafusal fibers to contract permanently, except they tend to relax when you go to sleep
-Go into abnormal contraction and stay there
Increased Gamma Motor Neuron Excitability
-Decreased Gamma Bias
-Causes the intrafusal fibers to relax
Decreases Gamma Motor Neuron Excitability
Positive (excitatory) and negative (inhibitory) influences come down from the motor areas of the cerebral cortex, feed into the brainstem and spinal cord, and project to Gamma Motor Neurons that then project to the Intrafusal fibers of a muscle.
-If you have a lot of Gamma Bias, there will be an excitatory influence
-If you have a reduced amount of Gamma Bias, there will be an inhibitory influence (IF fiber relaxes)
-Positive or negative influence will come down on the gamma motor neurons, causing the intrafusal fiber to contract or relax
-Contraction is picked up by a Primary or Secondary sensory ending, and is shipped out over the ventral roots to the muscle fibers. If there’s enough EF fibers getting influence, they will contract.
Control of Gamma Motor Neurons
Balance between positive and negative influences determines the _______.
-Difference between high gamma bias and low gamma bias is what gives you your muscle tone.
Net Gamma Bias
Net Gamma Bias determines the ______ Bias, which in turn determines the extrafusal fiber contractile state.
-Gives us muscle tone
Alpha Bias
Continuous and passive contraction of muscles at rest.
-Even if totally relaxed, should still have a little resistance against extension when muscle tone is normal and Gamma Bias is normal
Muscle Tone
If _____ is high, when stimulating the DTR, you will get a very rapid/brisk kick (more so than normal)
Muscle Tone is High
Quadriceps tendon is stimulated, causing a knee-jerk
-Reflex is dependent on the intactness of L2-L4 spinal cord segments
Quadriceps Tendon DTR (Knee Jerk). L2-L4
Push foot into dorsiflexion, and tap on Achilles tendon to elicit plantar flexion (pushes down on hand)
-Tests S1 and S2 spinal cord segments
Achilles Tendon DTR (Ankle Jerk). S1-S2
Limitations of the DTR. Keeps it from over-contracting.
-Projects to the spinal cord over 1B Fibers.
-Gives us the Inverse Myotactic Reflex. Interrupts contraction that was produced by the Myotactic Reflex.
-A Pressure receptor found in the tendon of a muscle that is very sensitive to tension. When the muscle contractions, tension is placed on the tendon to pull the joint into position.
-Pulling motion excites the ________ , sending an inhibitory message back to the spinal cord to say stop contracting
Golgi Tendon Organ (GTO)
GTO gives off 1B fibers to inhibit motor neurons. Goes into the Dorsal Root Ganglion, then into the spinal cord, and then runs into inhibitory internuncial neurons that tell the downstream neuron to stop contracting. Sends an inhibitory message back to the muscle via Alpha Motor Neurons. Stops contraction.
Inverse Myotactic Reflex
