Essay On Neurologic
1. Mechanism that result in a patient showing hyperreflexia and hypertonia
Hypertonia is muscle stiffness. It can also be associated with the increased muscle tone. Reflexes (such as a knee-jerk reflex) in hypertonia are stronger or increased. Hypertonia may hinder walking, movement or speech of a man. Muscles are strained and tight to the touch. Tonus is increased by the spastic type; muscle tone in the study of the resistance is felt at the beginning of the movement (a symptom of ‘folding knife’). The obvious hypertonia is characterized by contracture. In hemiplegia (hemiparesis) in hand, tone increases in adductor muscles of the shoulder, in the flexors of the hand, fingers and forearm, in hemiplegia in foot - mainly in the extensor femur and tibia, adductor muscles of the thigh.
Hypertonia is usually caused by damage of the part of the brain that is involved in the controlling process of movement. It can also develop as a result of damage of the nerves that run from the brain to the spinal cord.
The symptoms of muscle hypertonia include:
curvature of the shoulder, arm, wrist and fingers under the angle does not conform because of muscle tightness;
acquisition of deep tendon reflexes;
repetitive jerky movements (muscle twitching), especially when the person moves or touches anything;
crossing legs as ‘scissors.’
Hypertonia can also affect the speech. Serious, long-term hypertonia can result in muscle contractures. It can reduce the range of motion or affect the flexibility of the joints.
Causes that result in hypertonia are the followings:
brain damage caused by lack of oxygen, as it can occur the suffocation;
child cerebral palsy;
traumatic brain injury;
neurodegenerative diseases, which in the course of time damage the brain and nervous system;
spinal cord injury.
Thus, hypertonia is one of the manifestations of various diseases of the nervous system. The cause of hypertonia is an imbalance in the nerve impulses, which are sent by the nervous system to muscles. The changes in muscle tone can be caused by diseases and injuries at different levels of the nervous system. To a lesser extent muscle tone is affected by mental and emotional state, ambient temperature (cold increases, and the heat reduces muscle tone), the rate of passive movements.
Treatment of hypertonia
For the treatment of muscle hypertonia in adults it is most commonly used muscle relaxants in combination with physical therapy. In the treatment of local muscle spasms in certain cases it can be applied botulinum toxin. For the treatment of certain forms of hypertonia (e.g., muscle rigidity in Parkinson's disease) it is used drugs, which affect the dopamine receptors. Young children with signs of hypertonia are prescribed with therapeutic massage, in some cases - with physiotherapy.
Hyperreflexia is an increase of segmental reflexes due to the weakening of the inhibitory influences of the cerebral cortex in the segmental reflex apparatus. It occurs, for example, after the defeat of the pyramidal tract.
An increase of reflexes indicates increased reflex activity of the segmental apparatus (spinal cord, brain stem). The most common cause of the increase of reflexes is the defeat of the pyramidal tract - the system that sends the inhibitory effect of the cerebral cortex to the spinal segmental reflex mechanisms. Symmetrical reflexes increase in the absence of other pathological symptoms are not always indicates the presence of organic disease; high reflexes may be obvious in healthy individuals, in neurotics, under certain intoxications, etc.
Extreme manifestation of increase of tendon reflexes is so-called clonuses. Clonuses are the rhythmic contractions of muscle, resulting from the sprain. In essence, clonus is a chain of one after the other tendon reflexes, caused by an uninterrupted stretch the tendon. The most common are clonuses of kneecap and foot.
Thus, mechanism of hyperreflexia is the following. Normally, reflex is activated as soon as there is a sharp stretching of muscles. This reflex causes the muscles to contract, resisting the tensile force. However, with the normal movement, this reflex should be ‘turned off.’ For this, the brain sends a signal to the overwhelming corticospinal tract cells of the spinal cord, which suppress the reflex. In case of any damage of the corticospinal tract (it is predominantly in the spinal cord and the small part of the brain) or corrupted signal generating cells of the brain, there is the inability to suppress the stretch reflex.
The methods of treatment include mostly physiotherapy and drug therapy. Physiotherapy is mainly used for muscle strain and to preserve joint mobility, reducing the risk of damage. For very inactive muscles it is used to gradually stretching. Sometimes it is needed a surgical procedure to cut the muscle or extension cords. Drug therapy includes drugs that reduce the tension reflex. Drugs differ by the mode of action; some influence on receptors in the brain, the other drugs influence on the spinal cord. Botulinum toxin is also an effective means for the short-term relaxation of spastic muscles.
2. How a loss of motor neurons leads to muscle atrophy
One of the causes of muscle atrophy is motor neurone disease, which is a progressive neurodegenerative disease that affects motor neurons in the brain and spinal cord. The gradual destruction of the cells of the nervous system leads to a steadily increasing muscle weakness, covering all muscle groups.
Neurons in the brain, which are responsible for movement (upper motor neurons), are located in the cerebral cortex, their processes (axons) descend to the spinal cord, there is a contact with spinal cord neurons. This contact is called the synapse; in synaptic area neuron of the brain extracts the chemical substance (neurotransmitter) that transmits a signal to the neurons of spinal cord.
Neurons of the spinal cord (lower motor neurons) are located in the lower regions of the brain (the bulbar separated) and the cervical, thoracic or lumbar spinal cord depending on the muscles to which they send their signals. These signals reach the muscles and control them. Bulbar department neurons are responsible for the contraction of the muscles responsible for speech, chewing and swallowing; cervical spine neurons - for the contraction of the diaphragm, the movement of the hands; thoracic neurons - for the movement of the body; lumbar neurons - for foot traffic. Therefore, the damage of neurons leads to the muscle atrophy.
The damage of spinal cord neurons increases muscle weakness, muscles lose weight (atrophy), it appears involuntary twitching (fasciculations). The damage of neurons in the brain causes the state when the muscles become weak, but it appears stiffness (spasticity), that is increased the muscle tone, it becomes difficult for muscles to relax.
With the defeat of both the neurons of the brain and spinal cord, these symptoms may occur in various combinations at the same time. That is, muscle weakness may be accompanied by fasciculations, muscle losing weight and stiffness. Depending on which areas of the brain and spinal cord are affected, these symptoms may occur in the muscles responsible for the movement of the arms, legs, for breathing or swallowing. Spinal motoneurons by their processes are in direct contact with the muscles and transmit signals to reduce them. In conditions of the damage of motor neurons muscles atrophy (die).
Progressive muscular atrophy is characterized by a gradual death of motor neurons of the spinal cord, so the muscles become weaker and decreases in volume, which causes problems with movement in that part of the body. As a result, there comes a progressive muscle weakness, muscle twitching, loss of muscle mass and weight loss.
When choosing a method of treatment of muscle atrophy, it is required to take into account the following important factors: age of the patient, the severity and form of the disease. The treatment focused on the underlying disease, which led to the development of muscle atrophy. It should be provided the medical treatment and, additionally, physiotherapy, electrotherapy, therapeutic massage and gymnastics. Strict adherence to all of the recommendations and requirements of the physician allows many patients to regain lost motor skills and slow down the process of atrophy.
3. The organization of the motor neuron pools in the ventral horn that serve the paraspinal and abdominal muscles
Neuron pool (biological neural network) is a set of neurons that are connected or functionally integrated in the nervous system, perform specific physiological functions, as it could be seen in the motor neuron pools in the ventral horn that serve the paraspinal and abdominal muscles. The neural pool consists of a group or groups of chemically or functionally related neurons. A motor neuron pools may be connected to many other neurons, and the total number of neurons and connections in the pool can be quite large.
Each motor neuron is connected to a particular muscle. Motoneurons of the intercostal muscles and the abdominal muscles are located in the thoracic segments of the spinal cord. In the anterior horns there are neurons that give their axons to the paraspinal and abdominal muscles. All descending pathes of the central nervous system, causing the motor reactions, end in neurons of the anterior horn. In this regard, they are called ‘final common path.’
The ventral horns contain motor neurons. Each motor neuron is connected to a particular muscle. Here are those muscles that can be consciously controlled by a person, and those that are reduced by reflexes. In the ventral horns there are neurons, in-unnerving muscles. Starting with I thoracic segment of the spinal cord and to the first lumbar segments, in the lateral horns of gray matter it is located the sympathetic neurons.
Motor neuron axon by its terminals innervates the hundreds of the muscle fibers, forming a motor neuron unit. The less muscle fibers innervate one axon (i.e. the less quantitatively motor neuron unit is), the more differentiated, precise movements are performed by muscle.
Several motor neurons can innervate a muscle; in this case, they form the so-called motor neuron pool (in case of motor neuron pools in the ventral horn that serve the paraspinal and abdominal muscles). Excitability of motoneurons of one pool is different, so the different intensity of stimulus causes the different number of fibers one muscle, involved in the reduction. At the optimum strength stimulus, all the fibers of the muscles shrink; in this case it develops the maximum muscle contraction.
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