Flexor- Crossed Extensor Reflex (Sheridan 1900). Reflex Circuits With Inter-neurons. Painful Stimulus. A Simple model or Minimum Circuit:. HIGHER LEVEL CONTROL. Pain Stimulus. MotoNeuron. +. +. +. Sensory Neuron. Inter Neuron. Inter Neuron. Flexor. MotoNeuron. -. -. - PowerPoint PPT Presentation
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HIGHER LEVEL CONTROL
Gaits of the cat: an informal computational model
In humans, during the 3rd week, this mesoderm begins to segment. The neural plate folds to form a neural groove and folds.
The neural groove fuses dorsally to form a tube at the level of the 4th somite and "zips up” cranially and caudally and the neural crest migrates into the mesoderm (somites differentiate to form vertebrae, muscles).
BRAIN DEVELOPMENT. The human brain and nervous system begin to develop at three weeks’ gestation as the closing neural tube (left). By four weeks, major regions of the human brain can be recognized in primitive form, including the forebrain, midbrain, hindbrain, and optic vesicle (from which the eye develops). Irregular ridges, or convolutions, are clearly seen by six months.
Axons locate their target tissues by using chemical attractants (blue) and repellants (orange) located around or on the surface of guide cells. Left: An axon begins to grow toward target tissue. Guide cells 1 and 3 secrete attractants that cause the axon to grow toward them, while guide cell 2 secretes a repellant. Surfaces of guide cells and target tissues also display attractant molecules (blue) and repellant molecules (orange). Right: A day later, the axon has grown around only guide cells 1 and 3.
Cat Striate Cortex Layer IV
Monkey Striate Cortex Area 17 (V1) Layer IV
The brain has an amazing ability to reorganize itself through new pathways and connections rapidly.
When nerve stimulation changes, as with amputation, the brain reorganizes. In one theory, signals from a finger and thumb of an uninjured person travel independantly to separate regions in the brain's thalamus (left). After amputation, however, neurons that formerly responded to signals from the finger respond to signals from the thumb (right).
Cognition and Language