Spinal Cord Physiology

Spinal Cord Physiology

The spinal cord is a vital part of the central nervous system, located within the vertebral canal. It is divided into 32 segments: 8 cervical, 12 thoracic, 5 lumbar, 4 sacral, and 1 coccygeal. Each spinal segment has a pair of spinal nerve roots (spinal nerves, or dorsal roots), consisting of an anterior root and a posterior root, which combine to form a spinal nerve.

• Anterior root, also known as the motor root: contains alpha and gamma motor neurons, controlling the contraction of skeletal muscles.

• Posterior root, also known as the sensory root: receives sensory axons, with cell bodies in the posterior root ganglion.

Cross-section diagram of the spinal cord:

• Gray matter: located in the center, divided into 3 horns:

• Anterior horn: motor horn

• Posterior horn: sensory horn

• Lateral horn: intermediate horn, only present in some locations: cervical segments C8 to L2 and sacral segments S2-S4.

• Lateral horn in cervical segments C8 -L2: contains neurons of the sympathetic ganglion.

• Lateral horn in sacral segments S2-S4: contains parasympathetic neurons.

• White matter: surrounds the gray matter, divided into 3 columns:

• Anterior column: contains the anterior corticospinal tract (direct pyramidal tract).

• Lateral column: contains the spinothalamic tract, lateral corticospinal tract (crossed pyramidal tract) and spinocerebellar tract.

• Posterior column: contains the gracile fasciculus and cuneate fasciculus.

Functions of the spinal cord:

• Transmission:

• Sensory:

• Touch: anterior spinothalamic tract.

• Pain, temperature: lateral spinothalamic tract.

• Conscious proprioception: gracile fasciculus and cuneate fasciculus.

• Unconscious proprioception: spinocerebellar tract.

• Motor:

• Voluntary: corticospinal tract (direct pyramidal tract and crossed pyramidal tract).

• Involuntary: extrapyramidal system (rubrospinal tract, reticulospinal tract, tectospinal tract, vestibulospinal tract, olivospinal tract).

Spinal reflexes:

The spinal cord is the center for spinal reflexes, following general reflex laws and anatomical arrangement. Specific rules of spinal reflexes:

• Unilateral rule: weak stimuli only produce reflexes at the site of stimulation.

• Symmetrical rule: increased stimulus intensity causes reflexes on the opposite side.

• Diffusion rule: further increasing stimulus intensity, the reflex will spread from posterior to anterior on the same side of stimulation.

• Holistic rule: stimuli with excessive intensity will cause reflexes to spread throughout the body, causing all muscles to contract.

Spinal reflex arc: consists of 5 components:

• Sensory receptor

• Afferent nerve

• Neural center

• Efferent nerve

• Effector organ

The spinal reflex arc can be:

• 2-neuron reflex arc (monosynaptic reflex): sensory receptors in the periphery enter the posterior root, synapse with motor neurons in the anterior horn of the spinal cord -> control effector organs.

• 3-neuron reflex arc (polysynaptic reflex): includes interneurons.

Basic spinal reflexes:

• Stretch reflex:

• Golgi tendon reflex: affects receptors in the tendon.

• Muscle spindle reflex: stimulation of muscle spindle receptors causes muscle contraction to protect against excessive muscle tension.

• Flexor reflex (withdrawal reflex): flexes muscles to move the body part away from danger.

• Crossed extensor reflex: controls the contralateral limb, extending the limb to prevent falling.

• Cutaneous reflex: produced by stimulating receptors in the skin.

• Tonic reflex: helps maintain balance, posture, and body alignment.

• Autonomic reflexes:

• Diffusely localized: sweating reflex, goosebumps reflex, vasomotor reflex.

• Localized: bladder reflex, genital reflex, eye blink reflex.

Examination of spinal reflexes: helps locate the region of spinal cord injury.

Spinal shock:

• Spinal cord transection: the part below the lesion is paralyzed, loses sensation, loses muscle tone, loses reflexes, and blood pressure drops rapidly.

• Spinal shock period: about 2-3 weeks.

• Post-spinal shock: increased reflexes, increased muscle tone, due to loss of inhibition of the central nervous system on the spinal cord.

Spinal animal: an animal with a spinal cord transection below the medulla oblongata, its muscles do not relax completely but are slightly contracted -> spinal tone.

Tabes dorsalis: damage to the gracile fasciculus and cuneate fasciculus, causing loss of pressure sensation, weight sensation, and uncoordinated walking.

Unconscious proprioceptive pathway: controlled by the cerebellum, helps maintain balance and coordinate automatic movements.

Motor transmission pathways:

• Pyramidal tract: transmits voluntary movements (corticospinal tract, corticobulbar tract).

• Extrapyramidal tract: transmits involuntary movements (rubrospinal tract, reticulospinal tract, tectospinal tract, vestibulospinal tract, olivospinal tract).

Note:

• This text has been rewritten from the provided data, but may be missing some details or have unclear details.

• To understand spinal cord physiology better, refer to specialized literature.