Archive for June, 2011

The point of contact between a motor neuron and a skeletal muscle cell is called a what?

June 10th, 2011
Jocelyn asked:


A) tendon
B) neuromuscular junction
C) periosteum
D) cross-bridge site

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The Costs of Paralysis

June 10th, 2011
Joseph Devine asked:




Paralysis is a type of catastrophic injury that results in the complete loss of muscle function in one or more muscle groups. Common causes of paralysis include herniated disks, fractured vertebrae, and nerve impingement. These types of injuries result from incidents such as automobile accidents, sports-related accidents, industrial or construction accidents, disease in the spinal column, and tumor growth on the spinal cord. Spinal cord injuries are classified as either complete or incomplete. Complete spinal cord damage means the person experiences a complete loss of feeling and movement below the site of injury. Incomplete spinal cord injuries occur when a person retains some motor control and feeling below the point of damage.

Different types of paralysis exist. Paraplegia, quadriplegia, and tetraplegia describe the extent of injuries. In paraplegia, functioning of the lower extremities, such as the legs and feet, is damaged. The ability to walk or run is usually lost. Quadriplegia, also known as tetraplegia, describes impairment affecting all four limbs, although this effect does not imply a complete loss of utility or sensation. Like paraplegics, quadriplegics are unable to walk or run, and often have additional complications including sexual functioning, bowel control, digestion, and torso movement problems.

Paralysis is a serious medical condition that has negative effects extending outside of restricted mobility. Muscle atrophy from discontinued use, low blood pressure, difficulty breathing, sensation loss, and a shortened life expectancy are all complications related to paralysis. As one could imagine, the associated medical costs of caring for a person who has major spinal damage are enormous. Round-the-clock medical care and assistance from doctors and nurses is often necessary. In extreme cases where the patient has trouble breathing as a result of their injury, ventilator use might be required for the remainder of their life.

If paralysis resulted from someone else’s negligent actions, a legal right exists for the injured to pursue damages through a lawsuit. Damages which are available for recovery include medical costs, lost wages, and other compensation, such as pain, suffering, and mental anguish. Over a decade ago, the annual medical costs for a quadriplegic totaled about $1 million. This high cost of medical attention should not be paid by the person who suffered the injury, which just adds a fiscal burden to already negatively affected health and prognosis for the patient.

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Age-Related Muscle Changes

June 9th, 2011
Yuri Elkaim asked:




One of the hallmark features of aging is the loss of muscular mass and strength. Much of this loss can be explained by changes to the neuromuscular system such as decreased number of motor neurons, decreased number of muscle fibers, and decrease muscle fiber size. But it is important to ask whether these changes are a consequence of aging or simply a result of an inactive lifestyle.

Age-Related Changes to Muscle

The age related decline in muscle mass appears to occur in 2 phases. The first or “slow” phase of muscle loss, in which 10% of muscle mass is lost, occurs between the ages of 25 and 50. The majority of muscle loss occurs thereafter where an additional 40% is lost from the ages of 50 to 85. Overall, the human body loses 50% of its muscle mass by the age of 80. This muscle atrophy can be explained by significant decreases in both the total number of muscle fibers, as well as in muscle fiber size.

It has been shown that aging results in a loss of the power and speed producing fast twitch fibers (particularly IIb) and an increase in the more aerobic slow twitch fibers. This seems to make sense since movements that demand a high velocity of contraction (such as jumping and sprinting) tend to be less in the older years.

Mechanisms of Strength Loss

The problems with decreasing strength can be seen in its contribution to osteoporotic decline in bone density, arthritic joint pain, and an overall reduced functional capacity.

With the loss in muscle mass evidently comes a decrease in muscular strength. However, as with muscle loss, most strength losses are not significant until the sixth decade. As briefly mentioned, this loss in strength can be attributed to a decrease in the number of motor units (nerve-muscle fiber complex), the decreased number of muscle fibers and the reduction in muscle fiber size. It is also known that a decline in leg strength precedes upper extremity strength loss in the elderly. This is important due to the fact that strength, rather than cardiovascular function, is considered to be the most physically limiting factor in the elderly. This is apparent when considering strength-limiting activities faced by many seniors such as getting up from a seated position or walking up stairs.

Encouraging is the finding that aging does not seem to effect eccentric strength. This phase of contraction is an important consideration for the elderly due to the possible linkage between poor eccentric strength and the incidence of falls in the elderly.

The Importance of Active Living

Regular exercise is the most effective way to slow and counteract the effects of age-related muscle and strength loss. Comparisons between active and sedentary older adults suggest that much of the strength loss with aging is due lifestyle factors. For example, individuals who continue to use certain muscles on a regular basis do not show the same age-related decreases in strength. In general, muscle atrophy, and thus strength loss, will occur any time the muscles are not required to work against a given load. The result will be a decrease in protein synthesis accompanied by an increase in protein breakdown. Overall, the muscle atrophies and loses much of its strength, characteristics commonly seen in astronauts during space flight. Incorporating regular resistance training is the most effective means of attenuating this effect.

Encouraging Findings

Studies have consistently shown that regular exercise can improve muscular endurance and strength in the elderly in a manner similar to that observed in young people. One of the largest studies in this field was done at McMaster University several years ago. The researchers looked at the effects of 2 years of twice/weekly strength training (80-85% 1RM) across 114 subjects between the ages of 60-80 years. The results indicated steady increases in strength in each of the muscle groups tested with no evidence of plateauing. There were also significant increases in muscle mass accompanying the gains in strength and, perhaps more importantly, there was evidence that these strength gains translated into improved function (as measured by walking and stair climbing performance).

Although there are certain unavoidable changes that occur with aging, it is possible to delay or attenuate the losses muscle mass and strength normally accompanying these changes. Since so many daily living activities such as walking, climbing stairs, and standing up from a chair are so dependent on strength it is imperative to minimize the age-related loss in strength as much as possible. The muscles in older adults maintain their ability to adapt; therefore, regular resistance training (2-3x/week) should be implemented into the lifestyle of such individuals. Moreover, a similar strength training protocol needs to be employed in younger adults as means of prevention and staying healthy into the golden years!

Written by Yuri Elkaim, BPHE, CK. Do not reprint without permission
Copyright 2006