Comparative Vertebrate Neuroanatomy

Nervous systems

The nervous system manages, stores, creates, and directs the flow of information.In the process behavior is initiated, defined, controlled, and expressed according to the basic scheme: "Sense - Decide - Act". Properties such as mind, consciousness, emotion or "free will" are emergent properties dependent on the structure of the nervous system and thus may vary greatly between species.

Vertebrates

• dorsal, centralized brain
• Central nervous system (CNS)–brain & spinal cord
• Peripheral nervous system (PNS) — ganglia & peripheral nerves
• Typically small cells, fast action potentials, myelinated axons
• Advantages: Show more complex behaviors.Results are more directly related to human medical conditions

Invertebrates

• ventral, distributed
• Ganglia and connectives
• Ganglion — cluster of neurons with a central neuropile
• Advantages: Typically large neurons, slow action potentials, non-myelinated axons, Generally simpler, larger elements, hardier and more accessible, Often have identifiable neurons.

Basic Organization of the Vertebrate Nervous Systems

The vertebrate nervous system forms as a hollow, ectodermally derived, cyllindrical tube, dorsal to the notochord. Along its entire length this neural tube consists of a dorsal (roof) section which processes afferent sensory information, and a ventral (floor) section for motor control. The brain forms at the rostral end as a series of bulges containing 4 connected, cerebrospinal fluid-filled ventricles. These differentiate into five distinct neural compartments. The forebrain features a central unpaired diencephalon. It consists of the thalamus as a relay and processing center for sensory information, the hypothalamus which controls neuroendocrine systems and autonomic functions, and the retina that forms the primary visual sensory epithelium of the eye. Paired telencephalic hemispheres emerge dorsally from the diencephalon and play a primary role in conscious thought processes, intellectual functions, memory processing and storage, and control of voluntary somatic motor activity. The dorsal (sensory) roof of the mesencephalon integrates sensory input for vision (i.e., superior colliculus, optic tectum) and hearing (i.e., inferior colliculus) towards a production of adaptive behavioral output. The Metencephalon contains centers for motor control and for the autonomic regulation of visceral functions such as cardiovascular, breathing and digestion. The cerebellum forms an unpaired dorsal lobe, receives input from vestibular and other sensory systems, and coordinates motor control systems.

a. b. c.

The rostral component of the vertebrate neural tube differentiates into a series of brain structures © 2004 lobsterman. a. Cross section through the neural tube and schematic locations of sensory (blue) and motor (red) areas. The teleost (fish) brain (b. top view, c. side view ) featuring from left to right: paired olfactory nerves and bulbs (ob) attached to telencephalic hemispheres (t), diencephalic region with optic nerves (on), optic tectum (ot) and hypothalamus (h), cerebellum (cb), and medulla oblongata (mo) with dorsal bulges housing sensory nuclei (sn) of cranial nerves, and spinal cord (sc)

• Myelencephalon (i.e., Medulla oblongata)