Motor symptoms in MS are extremely variable and can range from slight weakness and a lack of coordination to loss of control over one or more muscle groups.
The Babinski reflex is a neurological sign in MS in which stroking the outside sole of the foot with a pointed object causes an upward (extensor) movement of the big toe rather than the normal (flexor) bunching and downward movement of the toes. This reflex is normal in younger children, but abnormal after the age of two.
Spasticity is a condition in which muscle tone becomes greatly increased. Muscle tone is what enables people to move limbs or hold a position. The term refers to the level of tension or resistance to movement in a muscle. For instance, to bend your arm, you must shorten or contract the biceps muscle at the front of the arm (increasing the tone) and at the same time lengthen or relax the triceps muscle at the back of the arm (reducing the tone).
When someone has spasticity in a limb, the signals from the brain are altered in such a way that opposing muscles, such as the biceps and triceps, may be simultaneously shortened or contracted. This causes the affected limb to feel stiff or tight and to be resistant to movement. Aching muscles and muscle spasms and cramps are also a common problem in MS.
Dysarthria refers to speech problems. In MS, dysarthria may be caused by decreased function of the nerves that control the muscles involved with speaking. Dysarthria may be characterized by slurred speech, lack or articulation, or altered rate of speech.
Paresis is the term used to describe muscle weakness, a common symptom of MS that is caused by lesions along the pathway of the nerves that control muscle movement. Muscle weakness can cause problems with walking and coordination.
Ataxia is the inability to coordinate voluntary muscle movements. A person with ataxia will appear to be unsteady when walking or off-balance when standing. There are three types of ataxia: Cerebellar ataxia is caused by lesions in the cerebellum and causes incoordination of extremity or eye movements or incoordination of speech. Vestibular ataxia is caused by lesions to the brain stem and can result in loss of balance or dizziness. Sensory ataxia is caused by damage to position-sensing nerves and causes the brain to be confused as to the positioning of the limbs.