Spinal Cord Motor Control
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| C1-C7 exit the spinal cord through the intervertebral foramen __________ the corresponding vertebrae. | Above. | |
| All spinal nerves except C1-C7 exit the spinal cord __________ the corresponding vertebrae. | Below. | |
| What are the types of neurons found in the spinal cord? | Alpha motor neurons, gamma motor neurons, and interneurons (Renshaw cells). | |
| Where are alpha motor neurons found? | The ventral (anterior) horn. | |
| Where are gamma motor neurons found? | The ventral horn. | |
| Where are interneurons found? | All areas of the gray matter. | |
| What are Renshaw cells? | A type of interneuron found in the ventral horn that is inhibitory, helps regulate and smooth movement. | |
| Define propriospinal fibers. | Nerve fibers that connect segments of the spinal cord and are involved in multisegmental reflexes, travel in the fasciculus proprius, synchronize function. | |
| The gray matter of the ventral horn is __________ organized. | Somatotopically. | |
| What is a neuromuscular junction? | The synapse between a muscle and a nerve. | |
| What is used to transmit the signal across the neuromuscular junction? | Acetylcholine, neurotransmitter. | |
| What is the function of the sarcoplasmic reticulum? | regulate calcium in the muscle cells, release of calcium triggers the formation of actin-myosin bonds for contraction. | |
| Define length-tension relationship. | Maximum tension is developed at the point where the myofilament overlap has the maximal cross bridge formation, the optimal length, can be observed on a graph. | |
| What type of receptor is a muscle spindle? | Sensory with motor components. | |
| What type of information does the muscle spindle provide? | Muscle length and the rate of change of muscle length. | |
| The muscle spindle is innervated by the __________afferent fibers. | Gamma. | |
| Group IA gamma afferent fibers innervate which portion of the bag and chain? | Sensory. | |
| Group II gamma afferent fibers innervate which parts of the muscle spindle? | The static bag fibers and all the chain fibers (flower spray). | |
| Extrafusal muscle fibers are innervated by __________ motor neurons. | Alpha. | |
| Intrafusal muscle fibers are innervated by __________ motor neurons. | Gamma. | |
| What is another name for gamma motor neurons? | Fusiform neurons. | |
| How do muscle spindles operate? | When a muscle is lengthened or contracted, tension is transferred to the intrafusal muscle, the tension causes the spindle to depolarize and initiates an action potential in group IA and group II axons. | |
| What is coactivation? | Signals sent to the alpha motor neurons also stimulate the gamma system and allows the extrafusal and intrafusal muscle fibers to contract at the same time. | |
| What activates the myotatic reflex? | Stretch. | |
| Which reflex is involved in reciprocal inhibition? | The myotatic stretch reflex. | |
| What is the crossed extension reflex? | When flexors are activated on one side, commissural spinal interneurons to the opposite side facilitate extensor motor neurons. | |
| Define fasciculus proprius. | A thin band of white matter that surrounds the gray matter which has short ascending and descending fibers which connect spinal segments, important for intersegmental reflexes. | |
| What are the reflexes of posture and locomotion? | Central pattern generators, positive support reaction, rhythmic stepping movement. | |
| Define central pattern generators. | Neuronal circuits (reflex) in the spinal cord and brainstem that generate stereotypical and rhythmical types of movement such as gait. | |
| Define positive support reaction. | pressure on the bottom of the foot causes the limb to extend against that pressure. | |
| The positive support reaction uses which tracts? | Vestibulospinal and reticulospinal descending tracts. | |
| Define rhythmic stepping movement. | Triggers from the sensory system from the bottom of the foot and position sensors activate the CPG (central pattern generators) and produce rhythmic stepping. |
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