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#Muscletone

Also look into reflex arc and stretch reflex -    • #Reflex #deeptendonreflex #DTR #Monosynapt...   MUSCLE TONE - SPINAL REFELXES Muscles are always at least partially contracted. Even seemingly relaxed muscles possess a small degree of tension called resting muscle tonus or tone. This tone is ultimately controlled by impulses from the brain, though special receptors in the muscles themselves are also instrumental in its regulation. The brain relies on input from these receptors as well as those in tendons and joints to give it the information it needs to direct smooth and coordinated muscle movements. They constantly supply the brain with necessary information concerning the ever-changing tone in muscles as well as the present position of muscles at any time during a movement. Many aspects of posture and movement depend on appropriately controlled and subsequently monitored tone in the large postural muscles. Here, we will examine how muscle tone is regulated both by the brain and spinal cord and how the brain is kept informed of the ever-changing status of this tone. A second objective will be to examine spinal reflexes. It is easy for the beginner to treat reflexes lightly, associating them only with visible activities such as the knee jerk. In fact, the vast majority of reflex actions are unseen and unnoticed and yet are vitally important to normal function. Reflexes operating though the spinal cord are responsible for the smooth functioning of the gastrointestinal tract and bladder as well as all of the skilled movements of the trunk and limbs and the often-taken-for-granted activities of standing erect, walking, and running. OVERVIEW OF MUSCLE TONE The muscle tone exhibited by otherwise relaxed muscles is necessary for these muscles to produce effective movements. If muscles relaxed completely (no resting tone), they would overlengthen, and too much time would be required to take up slack when a contraction was called for. On the other hand, too much tone would not allow for sufficient rest and recovery. The principal regulator of muscle tone is the small stretch-sensitive intramuscular unit called the muscle spindle. Muscle spindles are encapsulated units within the belly of a muscle that lie parallel to the muscle fibers, stretching when the muscle is stretched and shortening when the muscle contracts. Thus they are uniquely situated to detect slight changes in muscle tone. When stretched, muscle spindles become activated, causing an increase in the impulse firing rate of afferent nerve fibers from the spindles to the spinal cord. Some of these spindle afferents synapse on second-order neurons which conduct the stretch information up the spinal cord to the cerebellum and even the cerebral cortex. Since the firing rate of these neurons varies with the degree and velocity of stretch, the CNS is continually informed of the ever-changing status of muscle tone and movement. Other spindle afferents directly excite large alpha motor neurons innervating skeletal muscle fibers. This reflex activation causes contraction (and short­ening) of the muscle via the simple myotatic or stretch reflex. This reflex functions as a servo-mechanism to maintain muscle tone at a preset level. If tone in a particular muscle decreases, allowing the muscle to lengthen, the spindles become stretched and trigger increased impulse firing in the spindle afferents, thereby increasing the firing rate of the alpha motor neurons to that same muscle and causing it to contract. The stretch sensitivity of the spindles can be adjusted by action of the small gamma motor neurons in the anterior horn (lamina IX) of the spinal cord. This is an important capability, allowing the CNS to keep the spindles "in tune" with the muscles. These and other functions of the muscle spindles, as well as the tension-sensitive organs in tendons, will be discussed. Click on to the link below PArt 1 - Corticospinal tract (LMN vS UMN)    • Part1 #UMNvsLMN #NeuroAnatomy #Pyramidalce...   Part 2 - Cortico Bulbar tract    • Part 2 #Corticobulbar#tract #UMN #LMN #BEL...   Part 3 - Extrapyramidal system - Rubrospinal Tract    • Part 3 #Neuro Class room #extrapyramidalsy...   Part 4 - Vestibulo spinal tract - extrapyramidal system    • Part 4 Neuro class room #Vestibulospinal #...   Part 5 - Reticulo spinal tract - Extrapyramidal    • Neuro class room 5 #Reticulospinal #tract ...   Part 6 - Tectospinal And olivospinal tract    • #ExtraPyramidal #Tectospinal #olivospinal ...