Spinal Cord Reflexes Part 1

Question 1

-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

Answer 1

Myotactic Reflex

Question 2

-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

Answer 2

Monosynaptic Reflex Loop/DTR/Myotactic Reflex/Stretch Reflex

Question 3

Contains Alpha Motor Neurons and Gamma Motor Neurons

Answer 3

Anterior portion of the gray horn of the spinal cord

Question 4

Send out a signal via the ventral root to a muscle fiber
-Supplies extrafusal fibers.

Answer 4

Alpha Motor Neurons

Question 5

Neurons that supply intrafusal fibers.
2 Types of intrafusal fibers:
-Nuclear Bag
-Nuclear Chain

Answer 5

Gamma Motor Neurons

Question 6

1) Gamma Motor Neurons innervate the Intrafusal Fibers
2) Activation of the Afferent Limb
3) Efferent Limb of the Reflex (Alpha Motor Neurons)

Answer 6

Steps of the Myotactic Reflex

Question 7

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.

Answer 7

Gamma Motor Neurons

Question 8

Measure the rate of change of length of intrafusal fibers.
-Fibers end on a Plate Ending

Answer 8

Dynamic Gamma Motor Fibers

Question 9

Regulate the static length at any given moment of the intrafusal fibers.
-Fibers end on a Trail Ending

Answer 9

Static Gamma Motor Neuron

Question 10

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

Answer 10

Annulospiral Ending (Primary Ending)

Question 11

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

Answer 11

Flower Spray Ending (Secondary Ending)

Question 12

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

Answer 12

Activation of the Afferent Limb of the Monosynaptic Reflex

Question 13

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

Answer 13

Efferent Limb of the Monosynaptic Reflex

Question 14

-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

Answer 14

Increased Gamma Motor Neuron Excitability

Question 15

-Decreased Gamma Bias
-Causes the intrafusal fibers to relax

Answer 15

Decreases Gamma Motor Neuron Excitability

Question 16

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.

Answer 16

Control of Gamma Motor Neurons

Question 17

Balance between positive and negative influences determines the _______.
-Difference between high gamma bias and low gamma bias is what gives you your muscle tone.

Answer 17

Net Gamma Bias

Question 18

Net Gamma Bias determines the ______ Bias, which in turn determines the extrafusal fiber contractile state.
-Gives us muscle tone

Answer 18

Alpha Bias

Question 19

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

Answer 19

Muscle Tone

Question 20

If _____ is high, when stimulating the DTR, you will get a very rapid/brisk kick (more so than normal)

Answer 20

Muscle Tone is High

Question 21

Quadriceps tendon is stimulated, causing a knee-jerk
-Reflex is dependent on the intactness of L2-L4 spinal cord segments

Answer 21

Quadriceps Tendon DTR (Knee Jerk). L2-L4

Question 22

Push foot into dorsiflexion, and tap on Achilles tendon to elicit plantar flexion (pushes down on hand)
-Tests S1 and S2 spinal cord segments

Answer 22

Achilles Tendon DTR (Ankle Jerk). S1-S2

Question 23

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

Answer 23

Golgi Tendon Organ (GTO)

Question 24

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.

Answer 24

Inverse Myotactic Reflex

Question 25

-Ex: Burn finger on cooking utensil or step on a nail
The first thing you do is reflexively pull away from the stimulus.
-Bend at the knee and hip to escape the pain on one side, and extend the knee/ankle on the other side to provide support. Push against one extremity while you’re pulling away with the other extremity

Answer 25

Pain Withdrawal Reflex (polysynaptic reflex arc)

Question 26

Has both ipsilateral and contralateral components.
-Epicritic pain: can identify the location of the pain
-Excitatory fibers and inhibitory fibers involved
-Involves Reflexive Neurons that allow you to associate/judge pain, but not involved with the reflex part

Answer 26

Polysynaptic Reflex (Pain Withdrawal Reflex)

Question 27

Injured Side:
-Excitatory fibers (A Delta Fibers - fast pain) enter spinal cord, synapse, and a new neuron is originated that goes back to the Anterior Horn and then back out of the limb. It lands on the posterior thigh (hamstrings) to excite them (A Alpha Fibers), makes them contract (bends knee and flexes hip) to pull away from the object that is causing pain.
-Inhibitory fibers then inhibit the quadriceps, causing knee flexion to pull away from the injury

Opposite Side:
-Inhibition of Hamstrings
-Excitation of Quadriceps
Extends the knee so that we can push self away from stimulus. Need extension of hip to straighten lower limb out to push away from something painful to stand on one leg.

Answer 27

Polysynaptic Reflex Arch (Pain Withdrawal Reflex)

Question 28

Ipsilateral:
-Knee Flexors (Hamstrings) Contract (excited)
-Knee Extensors (Quadriceps Femoris) relaxes (inhibited)

Contralateral:
-Knee flexors (Hamstrings) Relax (inhibited)
-Knee Extensors (Quadriceps Femoris) contract (excited)

Sensory - A Delta (Fast pain)
Motor - A Alpha Fibers (fast response)

Answer 28

Polysynaptic Reflex Arch (Pain Withdrawal Reflex)

Question 29

Identified in the early 1950s by Bror Rexed to label portions of the gray matter of the spinal cord. A system of 10 layers of gray matter
-1-9 are very important
-Layer 10 is not important

Answer 29

Laminae of Rexed

Question 30

Laminae of Rexed 1-7 (I - VII)
-Neurons are located in the Dorsal Gray Horn

Answer 30

Sensory Neuron Cell Body Location

Question 31

Laminae of Rexed 8-9 (VIII - IX)
-Neurons are located in the Ventral Gray Horn and Lateral Gray Horn

Answer 31

Motor Neuron Cell Body Location

Question 32

Also called the Posterior Marginal Gyrus
-Present throughout the whole spinal cord
-Area where we see dorsal roots enter the cord
-Found in the Posterior Gray Horn

Answer 32

Layer 1

Question 33

Also called the Substantia Gelatinosa
-A modulator of pain; can inhibit pain in some ways. Painful stimuli travels through here, and connections are present to allow you to stop pain from going forward
-Located throughout the entire spinal cord
-Found in the Posterior Gray Horn

Answer 33

Layers 2 & 3

Question 34

Also called the Nucleus Proprius
-Located throughout the entire spinal cord
-Found in the Posterior Gray Horn

Answer 34

Layers 4 & 5

Question 35

Also called the Nucleus Dorsalis (Clarke)
-Axons originate here and receive input, then go off with spinal cord for a bit before taking a detour.
-NOT in entire spinal cord; only in C8 - L1
-Found in the Posterior Gray Horn on the medial side

Answer 35

Layer 6 (VI)

Question 36

Also called the Visceral Afferent Nucleus
-Stays in one area and then detours off of the spinal cord
-NOT in entire spinal cord, only in T1 - L3.
-Found in the Posterior Gray Horn on the medial side

Answer 36

Layer 7 (VII)

Question 37

Also called the Intermediolateral Call (or the Lateral Cell Column)
-Found in the Lateral Gray Horn
-Found only on T1-L2, L3
-Also has the Sacral Parasympathetic Nucleus that is only found on S2-S4
Receives input from thoracic and upper lumbar region for sympathetic stimulation, and sacral region for parasympathetic stimulation.
-Starting to get into Motor. Parasympathetic is motor area (no sensory)

Answer 37

Layer 8 (VIII)

Question 38

Called the Anterior Horn Cell Column
-Found in the Anterior Gray Horn
-Located throughout the entire spinal cord
-Has motor cells that are associated with intermediate and lateral cell columns
-Alpha and Gamma Motor Neurons

Answer 38

Layer 9 (IX)

Question 39

Located in the Gray Commissure. Not really important.
-Central Zone, gray matter surrounding the central canal. Has some unmyelinated neurons in there.

Answer 39

Layer 10 (X)