INSPIRATION. The Neuron Doctrine...Henriech Wilhelm. The neuron is the anatomic, genetic, system.

Transcription

1 Denver Ncube 2010

2 INSPIRATION The Neuron Doctrine...Henriech Wilhelm Waldeyer (1891). The neuron is the anatomic, genetic, trophic and functional unit of the nervous system.

3 BACKGROUND The differences that exist between the vertebrates are at neuron level. Differences of neuronal structure translate to behavioural differences. Examinining neuronal complexity across the vertebrates aids in gaining a better appreciation how different vertebrates behave.

4 LEARNING OBJECTIVES To outline the anatomic differences in the nervous systems of different vertebrates; To elaborate how these differences translate into the different behaviours across the spectrum of vertebrates.

5 APPROACH Compare the basic structure of the nervous systems through detailed dissections of animals from representative vertebrate classes; Compare behaviour of different vertebrates and examine the extent to which they are determined by the structure of the nervous systems.

6 VERTEBRATE TAXONOMY Brief outline 1. Jawless/Agnathans(cyclostomes-round stoma) Two main classes exist namely myxinoids(hagfish) and the petromyzontia (lamperys). 2. Jawed/Gnathostomes 5 main classes exist: I)Fishes II) Amphibians III) Reptiles IV)Birds IV)Mammals From the reptiles onwards the remaining vertebrates can be called Amniotes because this special membrane first appears in reptiles.

7 DIVISIONS OF THE NERVOUS SYSTEM

8 VERTEBRATE NERVOUS SYSTEM

9 SPINAL CORD STRUCTURE

10 SPINAL CORD General trends across vertebrates: 1. Decrease in the length of the cord relative to the vertebral canal. 2. Union of dorsal and ventral roots to form single spinal nerves. 3. The appearance of cervical and lumbar enlargements as the scale is ascended. 4. Plexiform arrangement of nerves at the proximal portions of the limbs. 5. The appearance of extra coverings for the spinal cord from 1 in fishes, 2 in amphibians, reptiles and birds to 3 in mammals. 6. White and gray matter become more distinct and clearly delineated. 7. More complex neuronal circuits are observed from the transition from quadrupedal to bipedal as inter-neurons start to appear in higher vertebrates.

11 REVIEW What do you think is the significance of the cervical and lumbar enlargements that appear as the evolutionary scale is ascended? What is the significance of the plexiform arrangement of nerves at the proximal aspect of the limbs?

12 BRAIN Basic observations: The primitive segmental arrangement disappears in the higher vertebrates Cranial nerves 1. There is an increase in the number of cranial nerves from 10 in Anamniotes to 12 in Amniotes. Why? The spino-occipital nerves of lower vertebrates are believed to have been approximated rostrally to form the Accessory and Hypoglossal nerves, thus the higher vertebrates have an addition of 2 nerves to make it 12 cranial nerves. 2. In lower vertebrates the facial (VII), glossopharyngeal (IX) and vagus (X) nerves have sensory branches related to the lateral-line system(acousticolateralis system), in higher vertebrates this system is absent but its functions are represented by the vestibulocochlear VIII nerve.

13 LATERAL LINE SYSTEM

14 MAIN DIFFERENCES IN BRAINS

15 SUMMARY OF DIFFERENCES HINDBRAIN Basically not much difference in the extent of development of the hindbrain regions; Exceptionally well developed across all vertebrates. MIDBRAIN Major differences are on the dorsal aspect of the midbrain. In lower vertebrates only a pair of colliculi develop and these constitute the optic lobe. In higher forms (reptiles onwards) 2 pairs appear and these are the superior and inferior colliculi serving as relay centres for vision and audition, respectively. DIENCEPHALON Regression of the pineal body as a visual organ to a largely neuroendocrine structure. TELENCEPHALON

16 TELENCEPHALON Site of the greatest differences. As the scale is ascended there is a greater tendency of the cells to migrate to the superficial layers. General regression of the olfactory bulb as it fuses almost imperceptibly with the cerebral hemispheres In fishes the brain is no more than a meshwork of cells surrounding the ventricles-pallium. In amphibians only two regions can be recognised namely the Archipallium and Paleopallium. Neopallium (neocortex) first appears in reptiles and reaches its greatest development in mammals particularly man. The corpus callosum first appears in marsupials (e. g kangaroo) thus facilitating hemispherical interchange.

17 TELENCEPHALON In all vertebrates below mammals the brain lacks convolutions (lissencephalic- smooth brained ) and this is believed to be an index of information processing capacity. Gyrencephalic (convoluted) brains exist in mammals contributing to an increase in the cortical surface area.

18 GYRENCENCEPHALIC AND LISSENCEPHALIC BRAINS

19 REVIEW What do you think is the effect on gyrencephaly/lissencephaly on integrative ability? The cerebral hemispheres play a greater integrative role in higher ranked vertebrates. It ceases to be a small reflex co-ordinating ordinating region to a complex manager of the nervous system. Thought: why is it the cortical association areas are larger than the primary sensory areas?

20 AREAS OF THE CORTEX

21 CONCLUSIONS Differences in the nervous system of vertebrates can be attributed to different neuronal organisation. As the spectrum of vertebrates is traversed there is an increase in function of the nervous system from a mere informative system to a complex integrating system. The neuronal repertoire of an organism is the substrate of its behaviour.

22 THE END THANK YOU,TATENDA,SIYABONGA!!