Human Anatomy - Lecture Notes - Savchuk O.I. 2017

Evolution of the Nervous System

Lecture Outline

1. Differentiation of the Nervous System

2. Comparative CHARACTERISTICS OF THE nervous system in Roundworms

3. Characteristics of The Nervous System in Arthropods

4. Characteristics of the nervous system in amphibians

5. Structure OF THE nervous system in mammals

Animals in which the first Nerve Cells appeared (Coelenterates). The type of nervous system in coelenterates (hydras, jellyfish, corals).

Disadvantages of the diffuse nervous system.

Nervous System of the flatworm type (ganglia in the anterior part of the body and two nerve cords extending from them). The initial stage of concentration and Organization of nerve cells in Flatworms (emergence of ganglia, nerve cords, chemoreceptors, and visual Organs).

Differentiation of the nervous system in roundworms (a circumpharyngeal nerve ring with 4 nerve cords: 2 lateral, one ventral, and one dorsal—a diffuse-ganglionic type of nervous system). The nervous system in Annelids (ganglionic type of nervous system) consists of a circumpharyngeal ring with 2 ganglia and 2 ventral nerve cords with segmental ganglia connected by commissures. Mollusks share a similar type of nervous system.

The nervous system of arthropods: concentration of nerve cells increases, forming a single supraesophageal ganglion (a primitive brain); classes: crustaceans, arachnids, insects.

Differentiation of the nervous system in Chordates.

Formation of the brain, divided into three divisions: the Forebrain, Diencephalon, Midbrain, Cerebellum, and Medulla Oblongata, as well as the Spinal Cord with its nerve branches.

Tubular type of nervous system.

Features of the nervous system in fish: a well-developed cerebellum and midbrain, highly developed olfactory and gustatory systems, and underdeveloped eyes (spherical lens).

Tactile and chemical receptors of the lateral line. Taste receptors are located not only in the Mouth but also across the entire body. Behavioral responses are based on unconditioned Reflexes; conditioned ones are difficult to form and quickly fade.

Features of the nervous system in amphibians: similar to fish, but Vision is improved (due to the transition to land). Eyelids and a lens controlled by Muscles appear. Organ of Hearing: a tympanic membrane and a Middle ear with auditory ossicles emerge.

The nervous system of reptiles: the spine is divided into 4 regions, and the Cerebral Cortex appears. The cerebellum and diencephalon are highly developed. Smell and Taste are well-developed. The eye has a third eyelid. Behavior is primarily based on unconditioned reflexes.

The nervous system of birds: body mass increases, the brain undergoes further differentiation, and the relative size of the cortex and cerebellum increases. The relative size of the olfactory brain decreases slightly, while vision and hearing are highly developed.

Conditioned reflexes are formed and reinforced more easily, providing better adaptation to changing environmental conditions.

Class Mammalia: differentiation and specialization of the Central nervous system and receptors. Complex behavior based on conditioned reflexes. Smell, hearing, and Higher Nervous Activity are highly refined. The Emergence of the second signaling system represents the highest stage of nervous system specialization.

The Morphology/3.html">MAIN DIRECTIONS OF nervous system evolution: concentration and specialization.

The nervous system first appears in the phylum Coelenterata and consists of scattered nerve cells that form a nerve net. This type of nervous system is called diffuse (hydra, jellyfish, coral polyps).

Phylum Flatworms (classes Turbellaria, Trematoda, Cestoda).

Their nervous system is represented by ganglia in the HEAD region and two nerve cords extending from them. Some species possess visual organs as well as chemoreceptors.

PHYLUM ROUNDWORMS or Pseudocoelomate worms.

The nervous system is represented by a circumesophageal ring, from which nerve cords extend: dorsal, ventral, and 2 lateral. The nervous system of annelid worms is more complex: a circumesophageal ring consisting of suprapharyngeal and subpharyngeal ganglia. On the ventral side, there are thickenings—ganglia connected by commissures (ladder-like nervous system). The head possesses Sensory Organs; many have eyes, organs of smell, balance, and chemical sense.

Phylum Mollusca: the circumesophageal ring consists of 2 pairs of interconnected ganglia (radial); many have eyes, and all possess organs of balance and chemical sense.

Phylum Arthropoda: suprapharyngeal ganglion, brain, and ventral nerve cord (ganglionated nervous system)

Phylum Chordata: internal Axial Skeleton (retained throughout life in acraniates), which is replaced by a Vertebral Column in vertebrates.

Craniates (vertebrates)—formation of the brain and its division into 5 regions: forebrain, diencephalon, midbrain, medulla oblongata, and cerebellum:

- formation of the axial skeleton in the form of a vertebral column;

- division of the body into head, trunk, and tail.

Class Reptilia: THE VERTEBRAL COLUMN is divided into regions: cervical, thoracolumbar, sacral, and caudal. Nervous system: the cerebral cortex emerges from the Gray matter of the forebrain. The diencephalon forms the parietal organ, and the cerebellum is highly developed, which accounts for the variety of movements. The basis of behavior is the unconditioned reflex. The eyes have 3 eyelids. Organ of hearing: middle and Inner ear. Olfaction is well developed.

Class Aves: the vertebral column consists of 5 regions, but only the neck is mobile. The brain is larger, with a more developed CEREBRAL CORTEX AND cerebellum. The olfactory brain occupies a smaller portion. Conditioned reflexes are more easily formed and consolidated, providing better ADAPTATION TO ENVIRONMENTAL changes.

Class Mammalia: they give birth to live young and nurse them with milk. The cerebral cortex is highly developed, and stable conditioned reflexes are formed and consolidated.

References:

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