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Chapter 12 The Central Nervous System

Terms in this set (48)

- Ascending Pathways: Usually a chains of 3 neurons, 1st, 2nd, and 3rd order.
- 1st order neurons: impulse form cutaneous receptors and proprioceptors
- their cell bodies are in ganglia (PNS)
- Impulse to spinal cord or brain stem (CNS)
- Synapse with 2nd order neurons
- Spinal nerves conduct somatic sensory impulses from everywhere, but the facial area.
- Cranial nerves transmit in this area.
- 2nd order neurons (interneurons)
- Cell bodies are in the dorsal horn or in medullary nuclei (CNS)
- Transmit impulses to the Thalamus or Cerebellum
- 3rd order neurons (interneurons)
- cell bodies are in the thalamus (CNS)
- relay impulses to sometosensory cortex
- No 3rd order neurons in cerebellum.
- (there are no third order neurons in the cerebellum)
- information expressways:
- Spinocerebellar pathways (terminate at cerebellum): info about muscle and tendon stretch (proprioceptors), no conscious sensation/sensory perception (proprioceptive info.)
- Dorsal column-medial lemniscal pathways, via thalamus, mediate precise, straight transmission of sensory input (touch receptors and joint stretch proprioceptors), we can tell exactly where the input is coming from; provide discriminative touch and conscious proprioception
- Spinothalamic pathway: via thalamus, pain and temperature ( and coarse touch and pressure) receptors, we have a hard time figuring out where these sensations are precisely cominig from.
- Descending Pathways:
- Direct (pyramidal) system, lateral & ventral corticospinal pathways.
- mostly from the pyramidal neurons in the precentral gyri (+ subcortical motor nuclei), upper motor neurons initiate direct pathways
- pyramidal neurons (axons) do not synapse until reaching the spinal cord, they snynapse with interneurons or ventral horn neurons (lower motor neurons)
- Activating skeletal muscle, fast & fine (skilled) voluntary movements, ex. writing and needle work.
- Indirect (extrapyramidal) system, ex rubrospinal tract, originates from red nucleus (midbrain), include brain stem motor nuclei and all motor pathways, except for the pyramidal pathways.
- complex and muti-synaptic
- help regulate muscle tone and axial muscles involved in balance and posture
- Ascending pathways take sensory input up to the brain, while descending pathways take motor output away from the brain.