The nervous system of the dog is evaluated beginning with the medical history of the animal. Thorough physical and neurologic examinations follow, which may include various tests designed specifically to assess the workings of the different nervous system components. The veterinarian may assess the reflex reactions of the dog as well as its motor control and function, observing its gait and posture at rest and during various activities.
Analysis of the blood and urine, and cerebrospinal fluid testing, are two of the routine lab tests conducted. X-rays may be taken and CT scans or MRI scans may be done too. The electrical activity of different parts of the nervous system such as the brain, spinal cord, and the different nerves of the peripheral nervous system, as well as that of muscles, are measured. Specific lab tests may follow to detect particular problems.
The Neurologic Examination Of Dogs
It includes the evaluation of the following:
- the gait of the dog while walking
- the cranial nerve and its functioning
- the neck and the forelimbs
- the torso, hind limbs, anus and tail
- the reflex reactions of the dogs
Evaluation of Gait
The gait of the dog while it performs various actions like walking, running, stepping to a side, turning and backing up is evaluated by the veterinarian. Weakness in any of the limbs, stumbling or falling, rolling or circling movements, and any type of uncoordinated motions are indicative of nervous system dysfunction.
Evaluation of the Cranial Nerves In Dogs
Twelve pairs of cranial nerves arising from the brain stem enervate specific regions and sense organs on the two sides of the dog’s head. These nerves have different functions which are specific to each pair. While some of them are involved in sensory functions such as sensing scents, sounds, or sights, others control the movement of the facial muscles as well as the muscles controlling the eye movements. The dog’s barking and muscular actions of the tongue, chewing of food and swallowing are all directed by the cranial nerves. The veterinarian may be able to locate the damage by observing their reflexes and by conducting specific tests to identify their dysfunction, if any.
The cranial nerves and their functions
- Olfactory nerves – transmission of scents
- Optic nerves – the sense of vision and the certain reflex actions of the eyes
- Oculomotor nerves – most of the movements of the eye
- Trochlear nerves – other eye movements
- Trigeminal nerves – have several functions such as the muscular movements of the jaw, sense of taste and smell, sense of pain from the cornea of the eyes
- Abducent nerves – some muscular movements of the eye
- Facial nerves – muscular movements of the face including the movements of the ears, nose, mouth and the eyelids
- Vestibulocochlear nerves – sensing of sounds by the cochlear branch and the maintaining balance and posture by the vestibular nerve
- Glossopharyngeal nerves – control of the vocal chords and throat movements
- Vagus nerves – movements of the internal organs such as the heart and the gastrointestinal tract
- Spinal accessory nerves – muscular movements of the head and the neck
- Hypoglossal nerves – movement of the tongue
The mental activity of the dog, the posture of its head, level of coordination and reflex responses are measured as part of the evaluation of the cranial nerves. The various symptoms observed during these tests reflect the site and extent of the disease or injury affecting the brain. A typical head tilt, tremors or bobbing of the head are symptoms of the involvement of cerebellum. A deterioration of mental faculties, depression, seizures and coma indicate damage to the brain stem and cerebrum. It may also result in repetitive actions like pacing, circling or turning the head in the same direction.
Evaluation of the Neck and Forelimbs
The neck and forelimbs are evaluated by a physical examination. The veterinarian looks for signs of pain and loss of muscle mass and muscle tone. If these symptoms are detected, it indicates some damage to the upper part of the spinal cord. There are some specific tests to determine spinal cord damage too.
Wheel barrow test is one such test conducted to evaluate the functioning of the forelimbs and the neck. The hind limbs are slightly lifted and the dog is made to walk on the forelimbs. Another test is the righting test done to evaluate how the dog rights itself when it is made to lie upside down or on its side. In the positioning test, the positions of the limbs are changed, and the veterinarian observes how fast the dog corrects their positions and how accurate those positions are. The voluntary muscular movements and the reflex actions are evaluated too.
Evaluation of the Torso, Hind Limbs, Anus, and Tail
The torso, or the body of the dog, can be evaluated by conducting a few tests besides doing a thorough physical examination to detect pain and loss of muscle mass. Muscle dystrophy in the legs and on the body usually indicates damage to the related nerves. Feeling the different areas manually may help the veterinarian locate areas that have lost sensation as well as those that have become oversensitive. Both indicate neurologic involvement. Reflexes to pinpricks can estimate the sensitivity.
The righting and positioning tests conducted for evaluating the neurologic function of the neck and forelimbs are useful in the evaluation of the trunk and hind limbs too. The posture of the dog and positioning of the limbs are closely observed for abnormalities of the vertebral column. Testing the different reflexes may help in locating the injury since damage to different areas of the nervous system precipitate typical symptoms characteristic of such injuries.