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Transcript
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) 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 rd • 3 neuron projects from thalamus to somatosensory cortex Spinothalamic damage 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 column damage Dorsal column damage • Sensory ataxia • Patient staggers; cannot perceive position or movement of legs • Visual 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!
