ByAdjat S. Rasyad

General Structure of the Spinal CordThe spinal cord gives rise to 31 pairs of spinal nerves. Spinal cord has cervical and lumbar enlargements where nerves of the limbs enter and leaveThe spinal cord is shorter than the vertebral column. Nerve from the end of the spinal cord form the cauda equina.

Spinal Cord and Spinal Nerve RootsThe spinal cord extend from the foramen magnum to the level of the second lumbar vertebra, composed of cervical, thoracic, lumbar, and sacral segments

The spinal cord communicates the brain and the PNS inferior to the headThe spinal cord integrates incoming information and produces responses through reflex mechanismGeneral Function of Spinal Cord

Cross Section of the spinal cordThe cord consists of peripheral white matter and central gray matterWhite matter is organized into funiculi, which are subdivided into fasciculi, or nerve tract, which carry potentials to and from the brainGray matter is divided into horns: dorsal horn contain sensory axon that synapse with interneurons, ventral horn contain the neuron cell bodies of somatic motor neurons, and lateral horns contain the neuron cell bodies of autonomic neuronsThe dorsal root coveys sensory input into spinal cord, and the ventral root conveys motor output away from the spinal cord

Cross Section of the Spinal CordRelationship of sensory and motor neurons to the spinal cord

ReflexesA reflex is the functional unit of the nervous system: sensory receptors, sensory neurons, interneurons, motor neurons, and effector organsReflexes dont require conscious thought, and they produce a consistent and predictable resultReflexes are homeostasisReflexes are integrated with the brain and spinal cord. Higher brain centers can suppress or exaggerate reflexesKind of reflexes: (1) Stretch reflex, (2) Golgi tendon reflex, (3) Withdrawal reflex (4) Withdrawal reflex with reciprocal interneuron, and (5) Withdrawal reflex with crossed extension reflex

Reflex ArcThe parts of reflex arc are labeled in the order in which action potentials pass through them. The five components are the (1) sensory receptor; (2) sensory neuron, (3) interneuron, (4) motor neuron, and (5) effector organ

Stretch reflexMuscle spindle detect stretch of the skeletal muscles and cause the muscle to shorten reflexively

Golgi Tendon ReflexGolgi tendon organs respond to increased tension within tendons and cause skeletal muscles to relax

Activation of pain receptors causes contraction of the muscles and the removal of some part of the body from a painful stimulusWithdrawal Reflex

Withdrawal reflex with reciprocal innervationReciprocal innervation causes relaxation of the muscle that would oppose the withdrawal movement

Withdrawal reflex with crossed extensor reflexIn the crossed extension reflex, during flexion of one of the limb caused by the withdrawal reflex, the opposite limb is stimulated to extent

Spinal reflex, with ascending and descending axonsConvergent and divergent pathways interact with reflexes