THE NERVOUS SYSTEM AND SENSES

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BrokenWing Chronicles
THE NERVOUS SYSTEM AND SENSES


 Birds are highly visual animals; they have to be to be able to fly. The importance of birds' eyes is implied by their size - they are the largest relative to the body of all animals. Some hawks and owls have eyes as large as human eyes. The eyes of the ostrich, at 50 mm in diameter are the largest of any land vertebrate. In some owls, the eyes comprise up to 1/3 of the total weight of the head. In the Starling, the eyes comprise 15% of the head weight; in humans it is only about 1%. In most aspects, the avian eye structure resembles that of mammals.

The eyes of a bird are able to adjust to the light about 2x as well as that of a 20 year old human. The lens is very flexible in most birds and can change shape readily - birds need to focus near and far and change rapidly. The entire eye also varies in shape form flat to round to tubular (hawks and owl); the shape is maintained by a ring of overlapping bony plates.

The retina is the sensitive layer of the eye that absorbs the incoming light, senses it, integrates the information in it, and sends this information to the brain. The entire retina is thicker than that of mammals and the rods and cones are more abundant. Cones are for color and rods are for black and white and dim light. The distribution and density and proportion of rods to cones varies with the species of bird. Diurnal birds have retinas dominated by cones while nocturnal birds have mostly rods. Many hawks and owls have more sensory cells in the upper half of the eye that receives more light when the birds look down.Color vision varies among birds; some, but not all, see color. Hummingbirds, like insects, can see ultraviolet light.



http://www.ornithology.com/lectures/Senses.html

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BrokenWing Chronicles
Nervous System: Brain & Senses



The Avian Nervous System consists of

    * central nervous system, including the brain & spinal cord
    * peripheral nervous system, including cranial & spinal nerves, autonomic nerves & ganglia, & sense organs

The functions of the avian nervous system are to

    * obtain (via sensory receptors) information about the internal & external environment
    * analyze &, as needed, respond to that information
    * store information as memory & learning
    * coordinate outgoing motor impulses to skeletal muscles & the viscera (smooth muscle, cardiac muscle, & glands)


http://people.eku.edu/ritchisong/birdbrain.html



Accumulation of testosterone in the spinal cord of a bird with an elaborate courtship display -- Elaborate courtship displays are common features of the reproductive behavior of male birds. However, little is known about their neural and hormonal control. One bird that performs such a display is the Golden-collared Manakin (Manacus vitellinus) of Panamanian forests. Adult males, but not females, perform a display requiring substantial neuromuscular control of the wings and legs. Schultz and Schlinger (1999) tested the hypothesis that steroid sensitivity is a property of neurons in the manakin spinal cord. Males and females were captured from active courtship leks, treated with drugs to block steroidogenesis, injected with 3H-labeled testosterone, and the spinal cords were removed and processed for autoradiography. Most sex steroid-accumulating cells were found in the cervical and lumbosacral enlargements. Because motor neurons in these areas control muscles of the wings and legs, these cells may have multiple behavioral functions, perhaps innervating muscles controlling the elaborate dancing and wing-snapping of these birds. This evidence indicates that sex steroids may control diverse behaviors in male birds in part by acting directly on the spinal neural circuits.



http://people.eku.edu/ritchisong/birdbrain.html



The avian brain includes:

    * medulla - part of the brainstem; includes neurons that help control heart rate, respiration, & blood pressure
    * optic lobe - part of the midbrain; relatively large in birds compared to other vertebrates (reflecting the importance of vision for most birds)
    * cerebellum - involved in the coordination of skeletal muscle activity; relatively large (reflecting the need for precise coordination of muscle activity during flight)
    * cerebrum - consisting of 2 cerebral hemispheres plus olfactory lobes; the olfactory lobes are relatively small in most birds (suggesting a poor sense of smell, but some birds do have a well-developed sense of smell)



http://people.eku.edu/ritchisong/birdbrain.html



The cerebral hemispheres of birds, like those of other vertebrates, consists of 2 regions:

    * a dorsal PALLIUM &
    * a ventral SUBPALLIUM (including the basal ganglia, which are areas important in coordinating muscular activity)

All vertebrates have a cerebrum based on the same basic plan; major phylogenetic changes are due to loss, fusion, or enlargement of the various regions.

Simply a must see site

http://people.eku.edu/ritchisong/birdbrain.html

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