Question

Describe the pathway that transmits pain stimuli to the brain and the analgesic pathway that will lessen pain sensitivity.

Answer 1

THERE ARE PAIN RECEPTORS IN BODY .THE SENSITIVE NERVE ENDINGS AND ITS CORRESPONDING NERVE KNOWN AS PRIMARY AFFERENT NOCICEPTOR . THEY CONTACTS THE SECOND ORDER NEURONS OF SPINAL CHORD .THIS SECOND ORDER NEURONS TRANSMIT THE MESSAGE TO HIGHER CENTRES OF BRAIN .BRAIN CENTRES INCLUDES BRAINSTEM ,THALAMUS ,SOMATOSENSORY CORTEX AND LIMBIC SYSTEM

THERE ARE 4 STAGES IN PAIN PATHWAY

1 TRANSDUCTION - TISSUE DAMAGE STIMULI ACTIATING NERVE ENDINGS . THE HOST CHEICAL PROCESS ACTIVATE NOCICEPTOR

2 TRANSLATION - CARRYING OF THIS STIMULI TO BRAIN NOCICEPTOR TRANSMIT IT TO SPINAL CHORD NEURONS NOCICEPTOR  HAS CELL BODY IN DORSAL ROOT GANGLION AND LONG PROCESS ONE TO PERIPHERY AND OTHER TO S.CHORD .THUS BLOCKING BRANCH TO S.CHORD BLOCKS PAIN .IN SPINAL CHOD NOCICEPTORS RELEASE CHEMICAL TRANSMITTERS .THESE ACTIVATE SECOND ORDER PAIN TRANSMISSION CELLS .THE AXONS OF THIS NEURONS CROSS OVER TO OPPOSITE SIDE OF S.CHORD AND PROJECT TO BRAIN STEM AND THALAMUS .SPINAL CELLS PROJECTING TO THALAMUS ARE SPINOTHALAMIC TRACT CELLS .SPINOTHALAMIC PATHWAY IS FOR PAIN RECEPTION . OTHER PATHWAY IS SPINORETICULAR PATHWAY .THESE RECEIVES NEURONS FROM S. CHORD AND THALAMUS

IN THALAMUS VENROCAUDAL AND MEDIAL PART RECEIVES STIMULI . VENTROCAUDAL NEURONS DIRECTLY PROJECT TO CORTEX OF BRAIN ,MEDIAL THALAMUS RECEIVES INPUT FROM S.CHORD AND BRAIN STEM .IT PROJECTS TO FOREBRAIN INCLUDING CORTEX .SHARP WELL LOCALIZED PAIN PERCEIVED THROUGH VENTROCAUDAL THALAMUS .DEEP SOMATIC AD VISCERAL PAIN BY MEDIAL SPINORETICULOTHALAMIC PATHWAY

3 MODULATION -NEURAL PROCESS WHICH REDUCE ACTIVITY IN TRANSMISSION SYSTEM .PAIN RECEPTION IS DEPENDS ON NOCICEPTOR ACTIVITY .ELECTRICAL STIMULATION OF CERTAIN BRAIN REGIONS BLOCKS THIS TRANSMISSION .IT IS MEDIATED BY NEURONAL NETWORK RUNNING FROM MID BRAIN TO MEDULLA .STIMULATION OF BRAINSTEM SITES ALSO INHIBIT NOICEPTIVE SPINOTHALAMIC TRACT NEURONS . ANALGESIA CAN BE INDUCED BY DRUGS ALSO .MORPHINE BIND BRAINSTEM OPIATE RECEPTORS AND ACTIVATE SEROTONERGIC PATHWAY TO SPINAL CHORD

4 PERCEPTION SUBJECTIVE AWARENESS PRODUCED BY SENSORY SIGNALS