Section 6: Motor functions of spinal cord Flashcards
What kind of reflex applies to putting your hand on a hot burner?
Withdrawal reflex
Where are sensory neurons and their synapse located?
In the dorsal root ganglion and they synapse at the spinal cord level to elicit motor reflexes
Tue or false: Sensory neurons transmit signals to higher centers
True
Define motor neurons (anterior horn)
- Directly innervate skeletal muscle fibers
- Alpha MNs (a-alpha axons) excite extrafusal muscle fibers
- Gamma MNs (A-gamma axons) excite intrafusal fibers (muscle sensory receptors)
What are interneurons?
Local neurons that have connections with sensory and motor neurons
Are interneurons inhibitory or excitatory?
They can be both
What are sensory receptors of the muscles?
Mechanoreceptors
Define muscle spindle
- Mechanoreceptors
- Are distributed throughout the muscle belly
- Sense muscle length and rate of change of length
- Sensory signals are transmitted through 1a fibers and II fibers
Golgi tendon organs are:
- Located in the muscle tendon
- Sense tendon tension and rate of change of tension
- Sensory signals are transmitted through 1b fibers
What is the function of muscle spindles?
To provide information on the position of body parts (proprioception)
What type of fibers terminate on the nuclear bag AND on the nuclear chain?
Type 1a fibers
Type 1a fibers respond to what in the muscle spindle?
The rate of change in the muscle length (dynamic) and to the degree of stretch of the muscle
Type II fibers terminate where?
Nuclear chain fibers
Type II fibers respond to what?
The degree of stretch of the muscle (static)
What is the purpose of Alpha-Gamma Coactivation?
To maintain the tension in the muscle spindles as the muscle shortens, the sensitivity to stretch is maintained
True or false: Signals are still sent to the CNS even if the muscle spindles are not stretched
False: they must be stretched
What are GTO’s?
Golgi tendon organs: they are encapsulated sensory receptors through which the muscle tendon fibers pass
GTO’s are stimulated when?
When the muscle fibers are tensed by the contraction or the stretching of the muscle (sensitive to muscle tension)
When do GOT’s react intensively?
when the muscle tension suddenly increases (dynamic) or when it settles down rapidly to a lower level of steady state tension (static)
What is the role of Ib fibers in the GTO?
To inhibit indirectly, through interneurons, alpha motor neurons at the spinal cord to allow the muscle to relax and relieve tension in the tendon
What are spinal cord reflexes?
A mechanism by which sensory impulses are automatically converted into a motor effect, a protective mechanism to the body
Are reflexes voluntary?
No, they are rapid and controlled by the spinal cord integration center
Define stretch reflex
- Sudden stretch of the muscle activates the muscle spindle
- Associated sensory fibers transmit impulses at the spinal cord level
- Type 1a and II fibers synapse directly with alpha motor neurons causing the muscle to contract to oppose the stretch
- Inhibitory interneurons sends efferent signal to antagonist
Define the Golgi tendon reflex
- Serves to relieve excess tension on the muscle
- Sensory neurons synapse with inhibitory interneurons that inhibit alpha motor neurons and cause the contracted muscle to relax
- Sensory neurons synapse with excitatory neurons of antagonist muscles and cause the muscle to contract
How is the Golgi tendon reflex activated?
By the contracting of a muscle that creates tension on the tendon attached to the same muscle and thus activates the GTO
What is the flexion reflex?
- Also known as the withdrawal reflex
- Is initiated by a painful stimulus that causes an automatic withdrawal of the threatened body part
Describe the process of the flexion reflex
Sensory neurons synapse with interneurons that:
- Excite motor neurons of the flexor muscle and cause muscle to contract
- Inhibit motor neurons of the extensor muscles and cause the muscle to relax
