1.Definition of cervical spondylosis
Cervical spondylosis is a syndrome, also known as cervical spine syndrome. It is common in middle and old age. It is a set of comprehensive symptoms stimulated or caused by the gradual degeneration of human cervical intervertebral discs, cervical spine osteophytes, or changes in the normal physiological curve of the cervical spine. These patients often feel numbness in the head, neck, shoulders and arms, and in severe cases, it can lead to limb weakness and even urinary and fecal incontinence and paralysis.
2.Physiological characteristics of cervical spondylosis
The cervical vertebrae are small and carry a large volume and weight of the head, while the cervical vertebrae have a large range of motion such as extension and flexion, rotation and lateral flexion, thus forming an unstable skeletal structure mechanically, and in the physiological state, they are kept in balance by the strong bones and soft tissues of the cervical vertebrae. In adulthood, due to increased physical work intensity, excessive head and neck movement and poor posture, the muscles and ligaments in the back of the neck and shoulders are strained or injured, causing injury to the cervical spine and its surrounding soft tissues. With the increase of age, the intervertebral discs, joint capsule and ligaments of the cervical spine undergo degenerative pathological changes one after another.
3.Physiological role of the intervertebral disc
The cervical intervertebral disc accounts for 20%-40% of the total length of the cervical spine, it is the main linkage structure between the vertebrae, and is extremely elastic, so it can make the pressure on the lower vertebrae equal, play the role of cushioning external forces, and slow down the external forces transmitted by the foot, so that the head from shock. The cervical intervertebral disc also participates in cervical spine activities and can increase the amplitude of movement. Its high front and low back structure makes the cervical spine have the physiological bending of forward projection.
4.Motion of the head and neck
Although the range of motion between two adjacent vertebrae is small, the range of motion of the entire spine is large and can be carried out along three axes, namely flexion and extension along the frontal axis, lateral flexion on the sagittal axis and rotation on the vertical axis. The range of motion of the cervical spine is greatest due to the oblique superiority of the superior cervical articular surface. The range of flexion and extension of the neck is large, with an average amplitude of 100-110, and the amplitude of forward flexion is the largest in the spine, with the mandibular chin touching the chest wall when fully forward flexed. The rotational range of motion of the neck is 75 for both left and right, and the lateral flexion of the neck is accompanied by rotational motion.
At the head-neck junction, the atlanto-occipital joint and atlanto-axial joint are formed due to the special differentiation of the first and second cervical vertebrae, allowing the head to move freely in all directions. Rotational movements of the head are mainly in the atlanto-occipital joint and the atlanto-axial joint, which account for about half of the rotational movements of the neck.
The axis of cervical spine motion, which passes through the vertebral body, corresponds to the central point of the nucleus pulposus. As a result, the vertebrae are elongated when the cervical spine is flexed forward. When the cervical spine is fully flexed, the anterior edge of the spinal canal can be elongated by 1.5 cm, while its posterior edge can be elongated by 5 cm, and the spinal cord in the spinal canal is also elongated, thinned and strained. In posterior extension, the spinal canal becomes shorter and the spinal cord is relaxed and slightly thicker. Fourth, the physiological curvature of the cervical spine
When the human body is sitting or standing, the human neck seems to be straight from the side, but the cervical spine is not straight, but has a forward projecting curve in its middle section. This forward curved projection is known medically as the physiological curvature of the cervical spine. The normal value is 12±5mm. The measurement method is to start from the posterior upper edge of the dentate process and connect the posterior edge of each vertebra to become an arc, then make a straight line from the posterior upper edge of the dentate process to the posterior lower edge of the seventh cervical vertebra. The maximum distance from the highest point of the above arc to this line is the value reflecting the size of cervical curvature.
The formation of cervical curvature is caused by the thick front and thin back of the cervical 4 to 5 intervertebral discs, which is required by human physiology. It can increase the elasticity of the cervical spine, play a certain role in cushioning oscillations and prevent damage to the brain. At the same time, it is also necessary for the normal physiology of the cervical spinal cord, nerves, blood vessels and other important tissues. Changes in the physiological curvature of the cervical spine can cause corresponding pathological changes.
5.The basic function of the cervical spinal cord
The activities of the spinal cord are controlled by the brain. Various sensory impulses from the extremities and trunk are transmitted to the brain through the upstream fiber tracts of the spinal cord for advanced comprehensive analysis; the activities of the brain, in turn, adjust the activities of spinal cord neurons through the downstream fiber tracts of the spinal cord. The spinal cord itself performs many reflex activities, but is also influenced by brain activity.
6.Transmission of sensory perception in the spinal cord
The sensory analyzer consists of three parts: the peripheral apparatus, i.e., the receptors, the intermediate conveying ventricular conduction tracts and the cortical sensory cells. In the spinal cord, the intermediate conduction tracts of sensation, there are shallow sensory conduction tracts, deep sensory conduction tracts and essential sensory conduction tracts.
(1) The superficial sensory conduction tract, the thalamic tract of the spinal cord, conducts nociceptive temperature and gross tactile sensations other than those of the face.
(2) The deep sensory transmission pathway is a bundle that conducts proprioceptive and fine tactile sensations and is located in the posterior cord of the spinal cord.
(3) The cerebellar proprioceptive pathway, the cerebellar tract of the spinal cord, is located in the superficial layer of the lateral cord of the spinal cord.
(4) Its fibers come from cells in the dorsal nucleus and the medial medial nucleus of the gray matter and travel up to the cerebellum.
7.Motor function of the spinal cord
Motor function is the response after receiving sensory stimulation, which is divided into “random” and “non-random” movements. Random movement, refers to the conscious execution of a certain action, mainly the function of the conus, by the transverse muscle contraction to complete. Non-random movements are “spontaneous” movements that are not controlled by the conscious mind, and are activities that maintain normal posture under normal conditions, and are mainly functions of the extrapyramidal system and the cerebellar system.
It is generally believed that the cortical impulses to random movements are transmitted along two neural pathways.
(i) upper motor neurons, which send fibers from cortical pyramidal cells in the precentral gyrus of the brain, terminating in the anterior horn cells of the spinal cord and motor cells of the cranial nucleus of the brainstem.
(ii) lower motor neurons, starting from the anterior horn cells of the spinal cord and the motor cells of the cranial nucleus, whose fibers nerve the anterior spinal roots and peripheral nerves to reach the muscles.
Corticospinal tract.
Also known as the pyramidal tract, it is composed of axonal fibers from large pyramidal cells in the cerebral cortex. Most fibers cross at the pyramidal crossings to the lateral cords of the contralateral spinal cord, forming the lateral corticospinal tract, which terminates in the anterior horn cells of the spinal cord; a small proportion of fibers do not cross and enter the anterior cords of the spinal cord, forming the anterior corticospinal tract.
Extrapyramidal system.
It is the downstream pathway outside the pyramidal system, which is a poorly differentiated motor system with specific primitive functions, including the reticulospinal tract, red nucleus spinalis tract, parietal spinalis tract, vestibular spinalis tract and olivary spinalis tract. The function of the extrapyramidal system is to adjust the activity of the pyramidal system and adjust muscle tone to coordinate muscle activity, maintain posture such as habitual movements, and make movements coordinated, accurate, and free from vibration and unnecessary collateral movements.
8.Spinal reflex
Reflex, the basic form of neural activity, is the body’s internal and external environmental stimuli to make a regular response.
The simplest spinal cord reflex arc consists of only one afferent neuron and one efferent neuron, forming a monosynaptic reflex, which is generally confined to one or adjacent spinal cord segments, also known as intrasynaptic reflex. Most reflex arcs are multisynaptic reflexes consisting of more than two neurons, i.e., there is an intermediate neuron between the afferent neuron and the efferent neuron, and the axon of the intermediate neuron travels up or down several spinal cord segments within the intrinsic tract before terminating in the anterior horn cell, which is called the intersegmental reflex. The detrusor reflex or extensor reflex is an intrasegmental reflex whose physiological function is to maintain skeletal muscle tension and is particularly important for maintaining upright posture. The knee reflex, Achilles reflex, and other tendon reflexes are all detrusor reflexes. The detrusor reflex has a fairly simple reflex arc, but it is also controlled by higher centers. When the spinal reflex arc is interrupted, the reflex disappears; however, when control of the higher centers is lost, the reflex is hyperactive.
The so-called superficial reflex, which is a reflex activity elicited by stimulation of the skin or mucous membranes, is a skin-muscle reflex, not a pull reflex, but a protective reflex. The reflex arc of the superficial reflex is long and the reflex impulse may reach the motor or premotor areas of the parietal lobe of the cerebral cortex.