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ASCENDING TRACTS. LEARNING OBJECTIVES. • • • • • • • • At the end of lecture, students should be able to know: Sensory pathways and receptors. Spinothalamic pathway. Spinothalamic damage. Dorsal column pathway. Dorsal column damage. Spinocerebellar pathway. Spinocerebellar tract damage. Sensory pathways • Sensory systems allow us to detect, analyze and respond to our environment • “ascending pathways” • Carry information from sensory receptors to the brain • Conscious: reach cerebral cortex • Unconscious: do not reach cerebral cortex • Sensations from body reach the opposite side of the brain Sensory receptors A: Free nerve endings (pain, temperature) A B C D B: Pacinian corpuscle (pressure) C: Meissner’s corpuscle (touch) D: Muscle spindle (stretch) Sensory pathways: 3 neurons • 1st: enters spinal cord from periphery • 2nd: crosses over (decussates), ascends in spinal cord to thalamus • 3rd: projects to somatosensory cortex Spinothalamic pathway • • • • Carries pain, temperature, touch and pressure signals 1st neuron enters spinal cord through dorsal root 2nd neuron crosses over in spinal cord; ascends to thalamus 3rd neuron projects from thalamus to somatosensory cortex Spinothalamic damage Left spinal cord injury spinothalamic pathway Spinothalamic Pathway Spinothalamic damage spinothalamic pathway Left spinal cord injury Loss of sense of: • Touch • Pain • Warmth/c old in right leg Dorsal column pathway: • Carries fine touch, vibration and conscious proprioception signals • 1st neuron enters spinal cord through dorsal root; ascends to medulla (brain stem) • 2nd neuron crosses over in medulla; ascends to thalamus • 3rd neuron projects to somatosensory cortex Two-Point Discrimination dorsal cloumn pathwa y • Sensory ataxia • Patient staggers; cannot perceive position or movement of legs • Visual clues help movement dorsal column pathway. \ Dorsal column damage Dorsal column damage Sensory ataxia Patient staggers; cannot perceive position or movement of legsVisual clues help movement . Spinocerebellar pathway • • • • • Carries unconscious proprioception signals Receptors in muscles & joints 1st neuron: enters spinal cord through dorsal root 2nd neuron: ascends to cerebellum No 3rd neuron to cortex, hence unconscious Spinocerebellar tract damage • Cerebellar ataxia • Clumsy movements • Incoordination of the limbs (intention tremor) • Wide-based, reeling gait (ataxia) • Alcoholic intoxication produces similar effects. Somatosensory cortex Located in the postcentral gyrus of the human cerebral cortex. THAT'S ALL!!!