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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?
Medial --> neurons projecting to AXIAL and GIRDLE muscles

Lateral --> neurons projecting to DISTAL LIMBS and EXTREMITIES
Within which segments of the spinal cord are the cervical and lumbar enlargements located?
Cervical--> C4 - T1
Lumbar --> L2 - S3
Within the ventral horn, are flexor motoneurons located more dorsally or ventrally?
Flexor motonoeurons are located more DORSALLY

(extensor motoneurons are located more ventrally)
Which motoneurons innervate the force generating (extrafusal) muscle fibers?
alpha-motoneurons
Which motoneurons innervate the non-force generating (intrafusal) muscle fibers within the muscle spindle?
gamma-motoneurons
All of the motoneurons that innervate a muscle is called ______?
Motoneuron pool
A motoneuron and all of its muscle fibers is known as...?
Motor unit
All of the muscles innervated by a single nerve root is known as...?
Myotome
Describe, in general, how more force is obtained for muscle contractions
First, more motor units are recruited. Then, if additional force is necessary, the frequency of action potentials also is increased
What is the size principle for motoneuron recruitment?
Smaller motoneurons are recruited first, then large ones
Why are small motoneurons more excitable than large motoneurons?
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
What kind of motor units do small and large motoneurons form?
Small motornuerons --> slow motor units

Large motoneurons --> fast motor units
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
Lesions to the dorsal and ventral roots are called __________.
Radiculopathies
All of the spinal nerves have a dorsal root and a ventral root except one. Which spinal nerve is this?
C1 spinal nerve

*Has ventral root, but no dorsal root
The dorsal and ventral roots join together to form spinal nerves, and then exit the vertebral canal through the....?
Neural (intervertebral) foramina
All but one of the cervical roots exit the vertebral canal above their corresponding numbered vertebra, except which roots?
C8 roots
(There is no C8 vertebrae, so C8 roots exit below C7 and above T1 vertebra).
Do the thoracic, lumbar, and sacral roots exit above or below their corresponding named vertebrae?
BELOW

*Remember, cervical roots exit ABOVE their corresponding named vertebrae
Describe the relative length of cervical and lumbosacral roots and whether they travel vertically or horizontally
Cervical roots are relative SHORT and travel HORIZONTALLY
Lumbosacral roots are relatively LONG and travel VERTICALLY
If the disc between the C4 and C5 vertebrae herniates, which roots are most commonly damaged?
C5 roots
If the disc between L3 and L4 herniates, which roots are most commonly affected?
L4 roots
Where are muscle spindles generally located within a muscle?
Close to the tendon
Extrafusal fibers are innervated by which motoneurons?
alpha-motoneurons
List two types of intrafusal fibers
1. Nuclear bag
2. Nuclear chain
Describe the functions of Bag1 and Bag2 in nuclear bag fibers
Bag1 (dynamic) --> sense RATE OF CHANGE in length

Bag2 (static) --> sense MAGNITUDE of length
Which sensory endings are termed "annulospiral" endings and surround the center region of the muscle spindle?
Ia primary endings
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
Which fibers are located lateral to secondary endings in the muscle spindle?
gamma-efferents
Describe the innervations of "dynamic" and "static" g-motoneurons, and what type of endings they form
"Dynamic" g-motoneurons --> Bag1 fibers, forming PLATE endings

"Static" g-motoneurons --> Bag2 fibers, forming TRAIL endings
What are "skeletofusimotor" neurons?
Beta motoneurons
Which motoneurons are both extrafusal and intrafusal fibers?
Do these neurons innervate Bag1 or Bag2 fibers?
Beta-motoneurons

*Bag1 fibers
List the sensory fibers that interact with Bag1 fibers in the muscle spindle.
1. Ia primary sensory
2. Beta-motoneurons
3. "Dynamic" g-motoneurons
List the sensory fibers that interact with Bag2 fibers in the muscle spindle.
1. Ia primary sensory
2. II secondary sensory
3. "Static" g-motoneurons
What do nuclear chain fibers sense?
Magnitude of length
Which sensory endings innervate the center region of all the chain fibers in the muscle spindle?
Ia primary endings
Which gamma-motoneurons form trail endings lateral to the II endings on nuclear chain fibers?
"static" g-motoneurons
Which nuclear chain fibers do B-motoneurons innervate?
Only the long chain fibers that exit the spindle capsule
Which motoneurons do NOT innervate any of the nuclear chain fibers?
"dynamic" g-motoneurons
Which fibers are the only ones to signal rate of change of length?
Bag1 (dynamic) fibers
Which fibers signal magnitude of length?
1. Bag2 (static) fibers
2. All nuclear chain fibers
Which sensory fibers signal both rate of change in length and magnitude of length?
Ia fibers
(innervate Bag1 and Bag2 fibers)
Which sensory fibers signal magnitude of length, but not rate of change of length?
Group II fibers
(innervate Bag2, but not Bag1)
Which B-motoneurons innervate long chain fibers only?
"Static" B-motoneurons

("dynamic" B-motoneurons innervate Bag1 fibers)
What determines the sensitivity (or gain) of a muscle spindle?
Spindle stretch
(g- and B-motoneurons change the sensitivity)
How do sensory Group Ia and II contribute to signaling phasic and tonic changes in length?
Group Ia --> both phasic and tonic changes

Group II --> only tonic changes
Information from golgi tendons is transmitted in which fibers?
Group Ib fibers
Describe the difference effects of contraction (with shortening) on Spindle fibers and GTOs.
Spindle (Ia fibers) --> inhibited
GTO (Ib fibers) --> excited
Which sensory fibers signal both rate of change in length and magnitude of length?
Ia fibers
(innervate Bag1 and Bag2 fibers)
Tendon tapping activates which sensory fibers?
Ia (muscle spindle) fibers

*Dose NOT activate Ib (GTO) fibers
Which sensory fibers signal magnitude of length, but not rate of change of length?
Group II fibers
(innervate Bag2, but not Bag1)
Which B-motoneurons innervate long chain fibers only?
"Static" B-motoneurons

("dynamic" B-motoneurons innervate Bag1 fibers)
"Deep tendon reflexes" exhibits what kind of reflex?
Stretch reflex
If the biceps stretch reflex is lost, which nerve root is involved and which muscles are affected?
C5 root

1. Biceps
2. Deltoid
What determines the sensitivity (or gain) of a muscle spindle?
Spindle stretch
(g- and B-motoneurons change the sensitivity)
How do sensory Group Ia and II contribute to signaling phasic and tonic changes in length?
Group Ia --> both phasic and tonic changes

Group II --> only tonic changes
Information from golgi tendons is transmitted in which fibers?
Group Ib fibers
Describe the difference effects of contraction (with shortening) on Spindle fibers and GTOs.
Spindle (Ia fibers) --> inhibited
GTO (Ib fibers) --> excited
Tendon tapping activates which sensory fibers?
Ia (muscle spindle) fibers

*Dose NOT activate Ib (GTO) fibers
"Deep tendon reflexes" exhibits what kind of reflex?
Stretch reflex
If the biceps stretch reflex is lost, which nerve root is involved and which muscles are affected?
C5 root

1. Biceps
2. Deltoid
What is the function of gamma-motoneurons?
Set the sensitivity of the stretch reflex
If the triceps stretch reflex is lost, which nerve roots are involved and which muscles are affected?
C7 roots

1. Triceps
2. Wrist extensors
3. Finger extensors
If the knee jerk reflex is lost, which nerve roots are involved and which muscles are affected?
L2-L4

*Quadriceps
If the ankle jerk reflex is lost, which nerve roots are involved and which muscles are affected?
S1

1. Gastrocnemius
2. Plantar flexors
The tendon reflex is elicited when there is activity in which fibers?
Ib fibers


(Remember: Ia fibers --> stretch reflexes (muscle spindles))
How many synapses are involved in the stretch and tendon reflexes?
Stretch reflex --> monosynaptic
Tendon reflex --> disynaptic
What causes GTOs to stretch?
Increased muscle TENSION

(Change in muscle length causes muscle spindles to stretch.)
Describe the sequence of events that occur in the tendon reflex
1. Increased muscle tension
2. GTO stretches
3. Ib fibers activate
4. Inhibitory interneurons discharge
5. a-motoneurons inhibited
6. Muscle relaxes

*Autogenic inhibition
Which reflex is involved in autogenic inhibition?
Tendon reflex
The clasped-knife response occurs in people which what disorder?
Hyperreflexia
What elicits the flexor (withdrawl) reflex?
Nociceptive stimulus
Describe the sequence of events involved in the flexor (withdrawl) reflex.
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
Describe the sequence of events involved in the stretch reflex
1. Muscle lengthens
2. Spindles stretch
2. Ia fibers activated
3. alpha-motoneurons activated
4. Muscle contraction
What is the function of the crossed extensor reflex?
Support a limb during withdrawl
Recurrent inhibition is mediated by which cells?
Renshaw cells
(unique type of inhibitory interneuron)

*Inhibit the alpha-motoneuron that excited it