=Paralysis= (_Akinesis_) is loss of voluntary or involuntary muscular
movement through defective innervation.
=Paresis= is a paralysis which is partial in degree; power of motion is
impaired but not completely lost.
=Hemiplegia= is the loss of voluntary motion in many muscles on one side
of the face or body. In general hemiplegia, the following muscles are
usually excepted: muscles of the tongue, of mastication, of the eye, of
respiration, of the neck and trunk, generally and of the proximal part
of the limbs. The hind limbs are usually most affected, and muscles that
are most exclusively under the control of the will those dominated by
the cortical centres of the brain. When due to a clot on the brain or
degeneration it occurs on the side opposite to that occupied by the
clot, on account of the motor fibres crossing at the anterior pyramids
of the medulla. Hemianæsthesia is a rare attendant and when present is
often on the side opposite to the hemiplegia. Sensory fibres cross in
the spinal cord, and the lesion is probably spinal.
=Crossed Hemiplegia= is motor paralysis of certain cephalic nerves (3d,
7th, 5th, 6th, and 8th,) on the same side with the clot or lesion, and
of the muscles of the trunk on the other side. The cranial nerves
proceed to muscles on the same side as their origin, while filaments
going to the trunk through the spinal cord, cross in the pyramids
(motor), or spinal cord (sensory). In crossed hemiplegia, hemianæsthesia
is common with both forms of paralysis on one side.
=Spinal Hemiplegia= has the face and head sound (except sometimes the
iris), and half the body paralyzed on the side opposite to that on which
the spinal lesion (clot) exists. If anæsthesia exists it is on the side
opposite to the lesion and posterior to it—the sensory filaments
crossing just before leaving the cord.
=Paraplegia= is loss of voluntary power of one transverse half of the
body; usually the posterior, and affects the tail, and has coincident
anæsthesia, being due to a spinal lesion. Anal and vesical sphincters
may or may not be paralyzed according as the lesions implicate their
respective spinal centres or not. If there is neither anæsthesia nor
vesical paralysis the lesion may be cerebral, in the paracentral lobes
of both hemispheres (meso-vertix at the fissure of Rolando).
=Monoplegia= is a circumscribed paralysis, as of one limb, or on one
side of the face, one group of muscles or a single muscle. It may be due
to cerebral, spinal or nervous lesion. _Cerebral monoplegias_ are
distinguished by: 1st, initial spasm; 2nd, absence of anæsthesia; 3d,
persistence of nutrition; 4th, paralysis greatest in the distal portion
of the member.
=Localized Paralysis= is usually due to lesion of a nerve, and is both
motor and sensory. If due to a spinal lesion it usually affects one or
more groups of muscles. In case the lesion is in the nerve, be guided,
in investigating it, by Van der Kolk’s law, that the sensory fibres are
usually distributed in the skin corresponding to the muscles which
receive the motor fibres.
=Pseudo-paralysis= occurs from muscular disease, injury, inflammation or
degeneration and has no appreciable central nor nervous lesion nor
anæsthesia.
=Spasm= (_Hyperkinesis_); abnormal violent muscular contractions with or
without loss of consciousness.
=Tonic= (_tetanic_) =Spasm= is violent and continuous.
=Clonic Spasm= is rapidly intermittent:—Contractions and relaxations.
=Tremor= (_trembling_) consists in small, intermittent, involuntary
contractions.
=Hemispasm= affects the face, or limbs, or both, on one side of the body
and may precede hemiplegia.
=Monospasm= affects one limb, one group of muscles or a single muscle.
It may be due to lesion of the brain, of the spinal cord or of the
nerves. Thus it may imply commencing disease of the motor centres or
tracts.
=Spasms of the Eyeballs= (rolling of globe to one side), and =Spasms of
the Eyeballs and Head=, are important indications of apoplexy. They
imply disorder (commencing irritation) of the cerebral motor areas.
Advanced disease would probably determine hebetude, coma, drowsiness, or
palsy. If epileptiform it turns away from the lesion. If hemiplegic it
turns toward the lesion and away from the paralysis. If lesion of the
pons it turns away from the lesion.
=Paraplegic Spasm= is a tonic spasm, partial in degree, causing stiff,
tetanoid (spastic) walk. In all four extremities there may be mixed
paresis and contraction. This often attends on hemorrhage into the
meninges.
=General Spasms=, convulsions as in Eclampsia, Epilepsy, Chorea,
Tetanus.
=Local Spasms= may be rhythmic or not, in slight cases to be seen only
in the eyelids or superficial muscles as twitching, and occur in
neurasthenia, or in poisoning by strychnia, brucia and other motor nerve
poisons.
=Incoördination= (_Dyskinesis_) is the lack of the harmonious balanced
movement of the various groups of muscles. Coördination of movement is
due to a special mechanism in the spinal cord, and extending forward
through the medulla oblongata, pons, and crura cerebri to the floor of
the third ventricle. In the form of _ataxia_ (lack of power of muscular
control) it is usually the result of degeneration (sclerosis) of the
superior columns of the cord, of the medulla, pons or crura. It may
occur from degeneration or destructive change in the cerebellum, or from
disease or section of the posterior roots of spinal nerves, or finally
from the action of certain narcotic poisons (ptomaines, toxins).
=Staggering= (_titubation_) occurs from lesions of the cerebellum,
medulla or pons; also from alcohol, opium, and other narcotics.
=Reflex Action.= The normal stimulation of different functions, motor,
secretory, circulatory, etc., depends on the nerve centres in the spinal
cord, which are roused into action by a centripetal impulse derived from
a distant part. Thus the balanced contraction of the different muscles
which preserves the equilibrium of the body, depends on the apprehension
by the nerve centres, consciously or subconsciously, of such
contractions (muscular sense), and it is largely under the control of
the will. Here three impulses act coördinately: 1st, the afferent
impulse from the muscle to the nerve centre; 2d, the efferent impulse
from the nerve centre to the muscle; and 3d, the inhibitory or
controlling, voluntary impulse from the sensorium to the nerve centre
involved. In another case, savory odors, sapid flavors and masticatory
movements cause a free secretion from the salivary glands. Again, the
scratching of a dog’s breast causes him to move his hind limb as if he
were himself doing the scratching. Again, the pricking of a limb causes
the prompt, even if involuntary, contraction of its muscles to withdraw
it from the source of irritation.
=Morbid Reflex.= Reflex action may be modified in various ways as the
result of disease or injury. It may become excessive from irritability
of the organ from which the centripetal impulse starts, or of the reflex
centre in the spinal cord, or of the muscle or other organ to which the
centrifugal impulse is directed, or, finally, from impairment of, or
separation from the inhibitory centre in the cerebrum. It may be
impaired or abolished from degeneration or destruction of any of the
tissues just named, or of the conducting nerves which connect them to
each other.
The contraction and closure of the pupil under light is a reflex act
from the retina on the optic lobes, etc., and from these through the
motor oculi to the iris. This reflex is lost and the iris fails to
contract in: anæsthesia of the retina; atrophy of the optic nerve;
disease of the optic lobe; superior (posterior) spinal sclerosis;
disease of the motor oculi; or disease of the iris.
The lumbar reflex is lost in many febrile states in the horse, so that
pinching of the loins fails to produce wincing, and this becomes a test
of the active persistence of the disorder.
=Encreased Reflex= is often noticed when the parts, including the spinal
reflex centre, are disconnected from the brain: as in lesions or disease
of the cord in front (cephalad) of its reflex centre. Here the cerebral
or voluntary inhibition is lost.
=Reflex Tonic Spasm= of muscles around a diseased or dislocated joint,
or of those controlling its action, often affords a valuable means of
diagnosis, the possibility of nervous, muscular and tendinous disease
being excluded.