Anatomy and physiology of coordination
For a person to perform precise and smooth voluntary movements, continuous interaction between the cerebral cortex, basal ganglia, and cerebellum is necessary. At the same time, maintaining balance and normal walking are impossible without the intact function of the visual analyzer, muscle tissue proprioceptors, and the labyrinth.
The main coordination center is the cerebellum, consisting of the vermis and two hemispheres. Within the hemispheres, the cortex and deep nuclei are distinguished: the dentate, emboliform, globose, and fastigial nuclei.
The key movement control mechanism is the feedback loop. The signal follows this pathway:
- From the cerebral cortex via the corticopontine tracts.
- To the pontine nuclei, from where it proceeds via the pontocerebellar tracts.
- Into the cerebellar cortex, then via the dentatorubrothalamic and dentatothalamic pathways.
- To the thalamus.
- Returning to the cerebral cortex via thalamocortical pathways.
Impact of hyperkinesia on motor activity
Various involuntary movements (hyperkinesias) can severely disrupt gait and the execution of purposeful actions.
- Chorea: accompanied by disorderly, chaotic, and jerky contractions of the muscles of the face, trunk, and limbs. Movements constantly succeed one another. The patient staggers when walking, produces noisy breathing, and involuntarily grimaces. In the periods between hyperkinesias, muscle tone is decreased.
- Dystonia: characterized by slow and sustained muscle contractions. They cause rotation, flexion, or extension of body parts, forming changing pathological postures. It can be focal, segmental, multifocal, generalized, or manifest as hemidystonia.
- Ballism: a rare form, similar to chorea, but manifesting as sweeping, flinging movements in the proximal segments (shoulder and pelvic girdles). Hemiballism (unilateral lesion) is more common. It occurs with damage to the subthalamic nucleus, often as a result of a stroke.
- Athetoid movements (athetosis): slow, "worm-like" movements involving the distal parts of the limbs. Muscle tone constantly fluctuates.
- Myoclonus: sudden, shock-like jerks of limb segments. It can be active (due to muscle contraction) and negative (due to a sharp drop in postural muscle tone).
Clinical tests for assessing gait and balance
To detect coordination disorders, the physician uses a number of specific tests.
Gait assessment The patient is asked to walk in a straight line, first with eyes open and then with eyes closed. The physician evaluates step speed, the distance between the feet, overall stability, and the ability to turn quickly. Additionally, tandem gait is used—walking strictly in a line, placing the heel directly against the toe.
Assessment of static coordination
- Simple Romberg test: the subject places their feet closely together, slightly raises the head, and extends their arms horizontally forward. Stability is assessed with eyes open and closed.
- Advanced Romberg test: the feet are placed in a single line (heel-to-toe). Allows for the detection of minimal deviations.
Assessment of trunk asynergy
- Babinski's trunk test: the patient lies supine on a flat surface without a pillow, with arms crossed over the chest. They are asked to sit up without bending their legs at the knee joints.
Assessment of limb coordination
- Heel-shin test: performed in the supine position. The patient must lift the straightened leg, place the heel on the opposite knee, and smoothly slide it down along the anterior surface of the shin.
Briefly: answers to topical questions
Which pathways connect the cerebellar cortex to the thalamus?
The cerebellar cortex is connected to the thalamus by the dentatorubrothalamic pathway, the dentatothalamic pathway, and cerebellothalamic fibers.
- Dentatothalamic pathway (tractus dentatothalamicus) — runs from the dentate nucleus of the cerebellum to the thalamus (ventral intermediate nucleus and ventral oral posterior nucleus).
- Dentatorubrothalamic pathway — participates in the feedback loop from the cerebellar cortex to the thalamus.
- Cerebellothalamic fibers — run from the cortex of one cerebellar hemisphere to the contralateral thalamus, undergoing the first decussation.
Feedback loop: Cortex → Pons → Cerebellum → Thalamus → Cortex.
Class and exam questions
How is the advanced Romberg test performed?
The patient places their feet in a single line so that the heel of one foot touches the toe of the other. The head is slightly raised, arms extended forward. This test helps reveal even minimal balance disorders.
What is the difference between chorea and ballism?
Chorea manifests as disorderly, jerky movements and muscle hypotonia during pauses. Ballism is characterized by sweeping, flinging movements that occur predominantly in the proximal parts of the limbs (shoulder and pelvic girdles).
What is evaluated during gait examination?
The physician analyzes the patient's stability, movement speed, the width of the base of support, and the ability to make rapid turns. The test is performed with both eyes open and closed.
What else to study on this topic
- Pharmacotherapy of primary tics: dosages of neuroleptics and tranquilizers.
- Specific hand posture in athetosis and fluctuations in muscle tone.
- Etiology, injury prevention, and surgical treatment of acute hemiballism.
- Classification of myoclonus by level of generation (cortex, basal ganglia, brainstem, spinal cord).
- Technique for performing the finger-to-nose test and the diadokinesis test.
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Other topics in Chapter 2. Movement Disorders
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