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75 Cards in this Set
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Describe the organization of neurons in the ventral horn--which neuron groups are located medially, and which are located laterally?
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Medial --> neurons projecting to AXIAL and GIRDLE muscles
Lateral --> neurons projecting to DISTAL LIMBS and EXTREMITIES |
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Within which segments of the spinal cord are the cervical and lumbar enlargements located?
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Cervical--> C4 - T1
Lumbar --> L2 - S3 |
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Within the ventral horn, are flexor motoneurons located more dorsally or ventrally?
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Flexor motonoeurons are located more DORSALLY
(extensor motoneurons are located more ventrally) |
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Which motoneurons innervate the force generating (extrafusal) muscle fibers?
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alpha-motoneurons
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Which motoneurons innervate the non-force generating (intrafusal) muscle fibers within the muscle spindle?
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gamma-motoneurons
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All of the motoneurons that innervate a muscle is called ______?
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Motoneuron pool
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A motoneuron and all of its muscle fibers is known as...?
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Motor unit
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All of the muscles innervated by a single nerve root is known as...?
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Myotome
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Describe, in general, how more force is obtained for muscle contractions
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First, more motor units are recruited. Then, if additional force is necessary, the frequency of action potentials also is increased
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What is the size principle for motoneuron recruitment?
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Smaller motoneurons are recruited first, then large ones
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Why are small motoneurons more excitable than large motoneurons?
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Small motoneurons have increased resistance because they have fewer ion channels.
Think about the equation V = IR *Since R is higher in small motoneurons, the same current will produce a larger voltage in smaller motoneurons than larger ones |
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What kind of motor units do small and large motoneurons form?
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Small motornuerons --> slow motor units
Large motoneurons --> fast motor units |
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Describe the muscle types are that are innervated by slow and fast motor units.
Are these muscles resistant or susceptible to fatigue? |
Slow motor units --> "slow" muscle (red, Type I); RESISTANT to fatigue
Large motor units--> "fast" muscle (pale or white, Type II); susceptible to fatigue |
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Lesions to the dorsal and ventral roots are called __________.
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Radiculopathies
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All of the spinal nerves have a dorsal root and a ventral root except one. Which spinal nerve is this?
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C1 spinal nerve
*Has ventral root, but no dorsal root |
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The dorsal and ventral roots join together to form spinal nerves, and then exit the vertebral canal through the....?
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Neural (intervertebral) foramina
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All but one of the cervical roots exit the vertebral canal above their corresponding numbered vertebra, except which roots?
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C8 roots
(There is no C8 vertebrae, so C8 roots exit below C7 and above T1 vertebra). |
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Do the thoracic, lumbar, and sacral roots exit above or below their corresponding named vertebrae?
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BELOW
*Remember, cervical roots exit ABOVE their corresponding named vertebrae |
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Describe the relative length of cervical and lumbosacral roots and whether they travel vertically or horizontally
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Cervical roots are relative SHORT and travel HORIZONTALLY
Lumbosacral roots are relatively LONG and travel VERTICALLY |
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If the disc between the C4 and C5 vertebrae herniates, which roots are most commonly damaged?
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C5 roots
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If the disc between L3 and L4 herniates, which roots are most commonly affected?
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L4 roots
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Where are muscle spindles generally located within a muscle?
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Close to the tendon
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Extrafusal fibers are innervated by which motoneurons?
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alpha-motoneurons
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List two types of intrafusal fibers
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1. Nuclear bag
2. Nuclear chain |
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Describe the functions of Bag1 and Bag2 in nuclear bag fibers
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Bag1 (dynamic) --> sense RATE OF CHANGE in length
Bag2 (static) --> sense MAGNITUDE of length |
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Which sensory endings are termed "annulospiral" endings and surround the center region of the muscle spindle?
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Ia primary endings
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What is another term for II secondary endings and where are they located in the muscle spindle?
Do they innervate Bag1 or Bag2 fibers? |
"flower spray" endings
Located a short distance from the center region *Innervate Bag2 fibers |
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Which fibers are located lateral to secondary endings in the muscle spindle?
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gamma-efferents
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Describe the innervations of "dynamic" and "static" g-motoneurons, and what type of endings they form
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"Dynamic" g-motoneurons --> Bag1 fibers, forming PLATE endings
"Static" g-motoneurons --> Bag2 fibers, forming TRAIL endings |
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What are "skeletofusimotor" neurons?
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Beta motoneurons
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Which motoneurons are both extrafusal and intrafusal fibers?
Do these neurons innervate Bag1 or Bag2 fibers? |
Beta-motoneurons
*Bag1 fibers |
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List the sensory fibers that interact with Bag1 fibers in the muscle spindle.
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1. Ia primary sensory
2. Beta-motoneurons 3. "Dynamic" g-motoneurons |
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List the sensory fibers that interact with Bag2 fibers in the muscle spindle.
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1. Ia primary sensory
2. II secondary sensory 3. "Static" g-motoneurons |
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What do nuclear chain fibers sense?
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Magnitude of length
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Which sensory endings innervate the center region of all the chain fibers in the muscle spindle?
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Ia primary endings
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Which gamma-motoneurons form trail endings lateral to the II endings on nuclear chain fibers?
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"static" g-motoneurons
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Which nuclear chain fibers do B-motoneurons innervate?
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Only the long chain fibers that exit the spindle capsule
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Which motoneurons do NOT innervate any of the nuclear chain fibers?
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"dynamic" g-motoneurons
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Which fibers are the only ones to signal rate of change of length?
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Bag1 (dynamic) fibers
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Which fibers signal magnitude of length?
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1. Bag2 (static) fibers
2. All nuclear chain fibers |
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Which sensory fibers signal both rate of change in length and magnitude of length?
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Ia fibers
(innervate Bag1 and Bag2 fibers) |
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Which sensory fibers signal magnitude of length, but not rate of change of length?
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Group II fibers
(innervate Bag2, but not Bag1) |
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Which B-motoneurons innervate long chain fibers only?
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"Static" B-motoneurons
("dynamic" B-motoneurons innervate Bag1 fibers) |
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What determines the sensitivity (or gain) of a muscle spindle?
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Spindle stretch
(g- and B-motoneurons change the sensitivity) |
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How do sensory Group Ia and II contribute to signaling phasic and tonic changes in length?
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Group Ia --> both phasic and tonic changes
Group II --> only tonic changes |
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Information from golgi tendons is transmitted in which fibers?
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Group Ib fibers
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Describe the difference effects of contraction (with shortening) on Spindle fibers and GTOs.
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Spindle (Ia fibers) --> inhibited
GTO (Ib fibers) --> excited |
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Which sensory fibers signal both rate of change in length and magnitude of length?
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Ia fibers
(innervate Bag1 and Bag2 fibers) |
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Tendon tapping activates which sensory fibers?
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Ia (muscle spindle) fibers
*Dose NOT activate Ib (GTO) fibers |
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Which sensory fibers signal magnitude of length, but not rate of change of length?
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Group II fibers
(innervate Bag2, but not Bag1) |
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Which B-motoneurons innervate long chain fibers only?
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"Static" B-motoneurons
("dynamic" B-motoneurons innervate Bag1 fibers) |
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"Deep tendon reflexes" exhibits what kind of reflex?
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Stretch reflex
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If the biceps stretch reflex is lost, which nerve root is involved and which muscles are affected?
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C5 root
1. Biceps 2. Deltoid |
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What determines the sensitivity (or gain) of a muscle spindle?
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Spindle stretch
(g- and B-motoneurons change the sensitivity) |
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How do sensory Group Ia and II contribute to signaling phasic and tonic changes in length?
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Group Ia --> both phasic and tonic changes
Group II --> only tonic changes |
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Information from golgi tendons is transmitted in which fibers?
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Group Ib fibers
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Describe the difference effects of contraction (with shortening) on Spindle fibers and GTOs.
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Spindle (Ia fibers) --> inhibited
GTO (Ib fibers) --> excited |
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Tendon tapping activates which sensory fibers?
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Ia (muscle spindle) fibers
*Dose NOT activate Ib (GTO) fibers |
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"Deep tendon reflexes" exhibits what kind of reflex?
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Stretch reflex
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If the biceps stretch reflex is lost, which nerve root is involved and which muscles are affected?
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C5 root
1. Biceps 2. Deltoid |
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What is the function of gamma-motoneurons?
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Set the sensitivity of the stretch reflex
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If the triceps stretch reflex is lost, which nerve roots are involved and which muscles are affected?
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C7 roots
1. Triceps 2. Wrist extensors 3. Finger extensors |
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If the knee jerk reflex is lost, which nerve roots are involved and which muscles are affected?
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L2-L4
*Quadriceps |
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If the ankle jerk reflex is lost, which nerve roots are involved and which muscles are affected?
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S1
1. Gastrocnemius 2. Plantar flexors |
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The tendon reflex is elicited when there is activity in which fibers?
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Ib fibers
(Remember: Ia fibers --> stretch reflexes (muscle spindles)) |
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How many synapses are involved in the stretch and tendon reflexes?
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Stretch reflex --> monosynaptic
Tendon reflex --> disynaptic |
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What causes GTOs to stretch?
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Increased muscle TENSION
(Change in muscle length causes muscle spindles to stretch.) |
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Describe the sequence of events that occur in the tendon reflex
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1. Increased muscle tension
2. GTO stretches 3. Ib fibers activate 4. Inhibitory interneurons discharge 5. a-motoneurons inhibited 6. Muscle relaxes *Autogenic inhibition |
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Which reflex is involved in autogenic inhibition?
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Tendon reflex
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The clasped-knife response occurs in people which what disorder?
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Hyperreflexia
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What elicits the flexor (withdrawl) reflex?
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Nociceptive stimulus
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Describe the sequence of events involved in the flexor (withdrawl) reflex.
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1. Activation of pain fibers
2. Excitation of excitatory interneurons innervating flexor alpha-motoneurons and inhibition of extensor alpha-motoneurons 3. Limb flexes away from stimulus |
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Describe the sequence of events involved in the stretch reflex
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1. Muscle lengthens
2. Spindles stretch 2. Ia fibers activated 3. alpha-motoneurons activated 4. Muscle contraction |
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What is the function of the crossed extensor reflex?
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Support a limb during withdrawl
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Recurrent inhibition is mediated by which cells?
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Renshaw cells
(unique type of inhibitory interneuron) *Inhibit the alpha-motoneuron that excited it |
