S4 L1 Flashcards
What is final common pathway
It is The final output from the central nervous system to the effector muscles arises from alpha motor neurons (also called lower motor neurons) located
in the ventral horn of the spinal cord
and motor cranial nerve nuclei of the brainstem.
( Lower motor neurons )are the only neurons of the body that produce movements through the activation of muscles.( T/F)
T
Lower motor neurons are the only neurons of the body that produce movements through the activation of muscles.
Describe these movements or how these movements occur ?
● These movements can be reflexive in response to segmental inputs .
● or volitional as directed by higher centers of the CNS acting via upper motor neurons.
What are the kinds of Lowe motor neurons?
Two kinds :
1) alpha motor neurons ( a )
2) gamma motor neurons (Y)
How the activity of alpha motor neurons is controlled by?
The activity of alpha motor neurons is controlled by :
1) by segmental input (primary afferents) from the limbs
2) by descending inputs from supraspinal structures.
Define :
- alpha motor neurons
2. Gamma motor neurons
1• Alpha motor neurons: are neurons that arranged in the ventral horn in well-defined columns that innervate the individual skeletal muscle and they give rise to large type A alpha (Aa) motor nerve fiber , their diameter is 50-80 mm
2• Gamma motor neurons: are neurons that innervate the muscle spindles.
The alpha motor neurons give rise to large type A alpha (Aa) motor nerve fibers, Stimulation of a single alpha nerve fiber excites from three to several hundred skeletal muscle fibers, which are collectively called the motor unit.
through “much smaller” type A gamma (Ag) motor nerve fibers which go to “small”, special skeletal muscle fiber called ( intrafusal fibers) , these fibers constitute the middle of the muscle spindle, which helps control basic muscle “tone,”.
What is the motor unit?
Itis The alpha motor neuron, and its axon (traveling peripherally in a nerve),and its terminal arborizations, and all the muscle fibers it innervates constitute a motor unit.
What is the neurotransmitter of all motor neurons?
Acetylcholine
What are muscle spindles ?
Muscle spindles are proprioceptive organs that consist of specialized muscle fibers, called intrafusal fibers, which lie in parallel with the contractile ( extrafusal) fibers of the muscle.
Describe the innervation of muscle spindles or what are the two types of the afferent that innervats the muscle spindles?
Muscle spindles are innervated by two types of afferents:
☆ Primary, or type Ia, afferents innervate nuclear bag receptors and discharge vigorously to ( changes ) in length over time,
☆ and secondary, or type II, afferent endings innervate nuclear chain receptors and respond in proportion to the ( maintained ) length or stretch . ( statics change)
Define Golgi tendon organ , and when it stimulated ?
The Golgi tendon organ, is an encapsulated sensory receptor through which muscle tendon fibers pass. About 10 to 15 muscle fibers are usually connected to each Golgi tendon organ.
the organ is stimulated when small bundle of muscle fibers is “tensed” by contracting or stretching the muscle.
Note خليها ببالك
> Small spindles response to change in length
> Golgi tendon organ respons to change in tention ( contracting or stretching)
What is the major difference in excitation between the Golgi tendon organ and the muscle spindle ?
the major difference in excitation of the Golgi tendon organ versus the muscle spindle is that the spindle detects muscle length and changes in muscle length, whereas the tendon organ detects muscle tension as reflected by the tension in itself .
When the Golgi tendon becomes silent, and when the discharge increased ?
They are generally silent in relaxed muscles and in response to passive stretch. ( the same im muscle spindles * )
their discharge increases with the strength of muscle contraction.
Describe the mechanism that prevents the development of too much tension on the muscle by Golgi tendon ?
Or how we prevents the development of too much tension on the muscle ?
When the Golgi tendon organs of a muscle tendon are stimulated by increased tension in the connecting muscle, signals are transmitted to the spinal cord to cause reflex effects in the respective muscle.
• This reflex is entirely inhibitory. Thus, this reflex provides a negative feedback mechanism that prevents the development of too much tension on the muscle .
