Proprioception is like a third sensory modality that supplies feedback to the solely on the status of the body internally, the first two senses being interoceptive and exteroceptive. The proprioceptive ability that one possesses is the sense that specifies whether the body is moving at the required effort , as well as other body parts are positioned in relation to each other. The ability to estimate weight of an object, the force and time at which our muscles must be contracted are examples of our proprioceptive ability.
Examples of proprioceptors are muscle spindles also called stretch receptors and their associated 1a axons. These receptors make up the somatic sensory system that is focus on body sense or proprioception. The muscle spindle consists of several types of speacialized skeletal muscle fibers that are contained within a fibrous capsule. In the middle region of this fibrous capsule group 1a axons are wrapped around the muscle fibre on the spindle. Group 1a axons are the fastest and largest of the group 1 axons, which are also the thickest myelinated axons in the body.
When a weight is placed on a muscle , the muscle lengthen and the muscle spindles are stretched. The stretching causes of the spindle causes depolarization of the 1a axons endings, this is caused by mechanosensitve ion channels. The 1a axons enter the enter the spinal cord through the dorsal root, from here they branch repeatedly and then form synapsese on both interneurons and alpha motor neurons of the ventral horns. The alpha motor neurons react by increasing its action potential frequency, this then causes the muscle to contract.
The Term Paper on Long Term Effects of Exercise on the Body
Chronic responses are very specific to the type of training performed. • The frequency, duration and intensity of the training undertaken – the greater these things, the more pronounced the adaptations • The individual’s capacities and hereditary factors (genetic make-up) Chronic Adaptations to Aerobic (endurance) Training: • Minimum period is 6 weeks • More evident over 12 weeks • Adaptations ...
The muscle spindle also contains intrafusal fibers and receive their motor innervation by a different type of lower motor neuron called Gamma motor neurons. When the extrafusal muscle contracts it becomes shorter, the intrafusal fiber also becomes shorter, this means that the 1 axons become silent and would no longer provide information about muscle length. However this is where the gamma motor neurons become activated at innervate the intrafusal muscle fibre at either end of the spindle. This causes contraction of the muscle spindle, therefore pulling on the noncontractile equatorial region and keep the 1a axons active.
Another source of proprioceptive input in the skeletal muscle is the golgi tendon organ, which monitors muscle tension or force of contraction. The golgi tendon organs are situated in series with the muscle fiber and spindle and is located at the junction of the muscle. A special feature about this source is that it is innervated by 1b sensory axons, which are a little bit smaller than 1a axons. The different anatomical arrangements between the muscle fiber and the golgi tendon organ is what distinguishes the type of information it provides.
The 1a axons from the muscle spindle offers muscle length information, the golgi tendon organ give muscle tension. The 1b axons enter the spinal cord, where they branch repeatedly and then synapse on interneurons in the ventral horn. Some of these interneurons connect with the alpha motor neurons which are inhibitory. This is usually called reverse myotatic reflex. There are certain factors that can influence our perception and sensation, this includes, alcohol, drugs and nerve damage. These factors can disrupt the proprioceptive ability by decreasing the feedback quality.
The Essay on Upper and Lower motor neurons
Upper motor neurons and lower motor neurons act to carry nerve impulses from the brain out to the muscles in the body. Upper motor neurons supply input to the lower motor neurons. They do this by either synapsing directly to lower motor neurons, or by synapsing with a local circuit neuron, which then synapses with a lower motor neuron. The upper motor neurons originate in the motor region of the ...
