Spinal cord and motor system Flashcards
(24 cards)
What type of neurons are found in the center of the spinal cord? (Hint: not motor neurons)
Interneurons. These connect between other neurons in the spinal cord. They allow motor neurons of antagonist muscles to be inhibited when other muscles are active
Where are sensory and motor tracts at their smallest?
Caudal end of the spinal cord
What type of neurons are in the ventral horn of the spinal cord? What about in the intermediate gray matter?
Mostly alpha motor neurons in the ventral horn.
Interneurons are in the intermediate gray matter
What is a motor pool?
All of the motor neurons innervating a single muscle
How are motor pools oriented along the spinal cord?
Vertically, spanning a number of spinal segments.
How are motor neurons organized within the ventral horn?
Distal muscles are more lateral. Proximal muscles are more ventral
What is a motor unit?
All of the muscle fibers innervated by a single motor neuron
Which is fast switch/slow twitch: type I muscle fibers vs type II muscle fibers?
Type I=slow twitch. Anaerobic with small fiber and neuron size.
Type II=fast twitch. Low aerobic metabolism, fatigues easily, with large fiber and neuron sizes
What determines the type of muscle fiber that it becomes?
The neuron which controls that muscle fiber
What are fast fatigue-resistant muscle fibers?
fast twitch muscle that is much more fatigue resistant
Describe the 3 classic spinal cord reflexes and what they are.
Myotatic muscle stretch: Stretching a muscle results in contraction. Inverse myotatic (golgi tendon organ reflex): Stretch to the point of muscle damage results in Relaxation of muscle Flexion reflex (withdrawal): Painful stimulus of a limb results in withdrawal
What are muscle spindles?
Modified muscle fibers, also called intrafusal fibers.
What are intrafusal muscle fibers innervated by?
gamma motor neuron.
Describe the structure of an intrafusal muscle fiber
Centrally located nucleus. Contractile elements on either side of the nucleus
What are annulospiral endings?
Sensory nerve process that wraps around the central portion of the muscle fiber. Activated when the muscle is stretched or gamma motor neuron is activated
How does the muscle restore its ability to detect stretch from a new position?
Gamma motor neuron activation resets a new length for the muscle
What do gamma loops do?
Stimulate gamma motor neurons which simultaneously activate agonist muscles while inhibiting corresponding antagonistic motor neurons
What is spasticity?
Overactivity of gamma motor neurons resulting in overactivity of the stretch reflex. Caused by damage to descending inhibitory projections that inhibit gamma motor neurons
What neuron is activated in golgi tendon organs?
Ib afferent neuron
During normal stretching, is the GTO activated? When is it activated?
No, because most of the muscle stretches (highly elastic) without building up any tension in the tendon (inelastic). ONly at the limits of muscle stretch are GTOs activated to prevent tearing of the muscle. However, can be highly active in patients with spasticity
Aside from extreme muscle stretching, when else is the GTO activated?
When muscle contracts–pulls on the tendons.
The babinski response is an example of:
Withdrawal reflex or physiological flexion.
What effect does physiologic flexion produce?
Flexion in the limb and extension in the contralateral limb
What are interneuron pattern reflexes?
Generates patterns of repetitive movements. Gait when running
