Nervous Systems
Vertebrate brains
Human brain
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These "homunculus" diagrams are based on experimental recordings of anesthetized subjects. The "motor homunculus" was determined by electrical stimulation of locations in the primary motor cortex to see what muscles responded. Notice that the lips and fingers are over-represented, indicating fine motor control of those structures. The "sensory homunculus" was determined by gently stroking parts of the body surface to see what locations in the primary somatosensory cortex responded electrically. Notice that the face and hands, which are very sensitive, are over-represented, while the body trunk is relatively insensitive.  Autonomic nervous system  Sense organs: Human Ear   Sense organs: Vertebrate Eye  Endocrine System Hormones belong to several different classes of chemicals  Overall diagram of the endocrine glands and their locations   The pituitary is really two glands: Posterior pituitary hormones are produced by cells whose cell bodies are really in the hypothalamus.  The many hormones of the anterior pituitary are controlled by "releasing hormones" secreted over a short distance by the hypothalamus.  Sexual structures in young embryos are "indifferent"-- male and female fetuses look the same. Hormones cause these structures to develop either as male or female.  |