Exam #6: Introduction to Motor Systems Flashcards
What is an alpha motoneuron?
This is a lower motor neuron that innervates skeletal muscle; the cell body is located in the anterior (or ventral) horn of the spinal cord
What is the motoneuron pool?
All of the motor neurons that innervate a single skeletal muscle
*****Note that these motor units are recruited from smallest to largest
What is the motor unit?
One alpha motor neuron and all of the skeletal muscle fibers it innervates
What is a fibrillation?
Spontaneous activity within a single muscle fiber
What is a fasciculation?
Visible twitches of muscles that can be seen as ripples under the skin
What is the difference between a fibrillation & a fasciculation?
- Size: fibrillations involve a single muscle fiber vs. a fasciculation that involves a muscle
- Presentation: cannot see a fibrillation, can see a fasciculation
What size (large, small) motor units are expected in the extra ocular muscles?
Small
What size (large, small) motor units are expected in the muscles controlling individual fingers?
Small
What size (large, small) motor units are expected in the large postural muscles?
Large
What size (large, small) motor units are expected in the limb muscles that have been affected by polio?
Large
What is a lower motor neuron?
A motor neuron that directly innervates a skeletal muscle
- Originates from the brainstem or spinal cord
What is an upper motor neuron?
A neuron in a higher motor area that synapses with a lower motor neuron or its interneuron
What are the effects of lower motor neuron damage i.e. describe the presentation of a lower motor neuron lesion?
1) Paresis or paralysis
2) Muscle atrophy/ decreased muscle tone
3) Hyporeflexia or absent reflexes
4) Fibrillations or fasciculations
*****Note that there is an increase in post-synaptic ACh receptors when there has been LMN damage
What are the effects of upper motor neuron damage i.e. describe the presentation of an upper motor neuron lesion?
1) Hypertonia
2) Hyperreflexia & clonus
3) Resurgence of primitive reflexes i.e. Babinski sign
4) Spasticity i.e. velocity-dependent increase in muscle tone
Generally, what happens if the spinal cord is transected?
- Permanent total paralysis for all muscles innervated by spinal segments below the level cut
- Anesthesia below the level cut
When the spinal cord is transected, what effects are seen immediately? What is spinal shock?
Initially there is “spinal shock” which is characterized by:
1) Flaccid paralysis
2) Areflexia
3) Loss of ANS function
**Note that loss of ANS function below the transected level can lead to HYPOTENSION that can be life-threatening
When the spinal cord is transected, what effects are permanent?
1) Paralysis below the level
2) Anesthesia below the level of the injury
How would a patient’s condition change over time in response to transection of the spinal cord?
1) The type of paralysis changes over time
- Transition from FLACCID paralysis to SPASTIC paralysis
2) Transition from hypotonia to hypertonia with time
3) Areflexia–>hyperreflexia
What is the difference between voluntary muscle movement and reflex activity following spinal cord transection?
- Patient will have total loss of voluntary muscle movement
- Reflexes e.g. patellar tendon reflex will not only be intact, it will be HYPERREFLEXIVE if enough time has passed since the injury–this is NOT a voluntary movement
What is Babinski’s sign? What is the difference between the extensor plantar response and the normal plantar (flexor) response?
Babinski= upward movement of the great toe in response to stroking of the foot
- Extensor Plantar Response= Babinksi Sign
- Flexor Plantar Response= downward movement of the great toe in response to stroking of the foot
What is the difference between paralysis and paresis?
Paralysis= complete loss of voluntary contraction Paresis= partial loss of voluntary contraction
