BIO 342
Comparative Vertebrate Anatomy
Lecture Notes 11 - Nervous System

The Vertebrate Nervous System:

    1 - receives stimuli from receptors & transmits information to effectors that respond to stimulation

    2 - regulates behavior by integrating incoming sensory information with stored information (the results of past experience) & translating that into action by way of effectors

    3 - includes billions of nerve cells (or neurons), each of which establishes thousands of contacts with other nerve cells

    4 - also includes neuroglia cells that support, nourish, & insulate neurons

Subdivisions of the Vertebrate Nervous System:

  1 - Central Nervous System - including the brain & spinal cord

  2 - Peripheral Nervous System - including cranial nerves, spinal nerves, & all branches of cranial & spinal nerves


Neurons (or nerve cells):

Multipolar neuron

Bipolar neuron

Unipolar neuron

Nerves = bundles of nerve cell processes; may be sensory, motor, or mixed

Spinal cord:

Used with permission of G. Mandl
Spinal nerves:




     Myelencephalon - consists of the medulla oblongata & its major functions include:

    Metencephalon - consists of the pons & cerebellum:     Mesencephalon - consists of the tectum which includes the optic lobes & auditory lobes:     Diencephalon - consists of the epithalamus, hypothalamus, & thalamus:


    Telencephalon - consists of the cerebrum which, in turn, consists of  2  cerebral hemispheres



 Cranial nerves - agnathans, most fish, & living amphibians have 10 cranial nerves; crossopterygians & amniotes have 12:

Possibly useful mnemonics to aid in memorization of cranial nerves: “On Old Olympus Towering Top A Finn And German Viewed A Hop” or “Oh, Once One Takes The Anatomy Final, A Good Vacation Appears Heavenly.”

Sensory Organs

Sensory receptors:

Special Somatic Receptors

Shark lateral line system

The ampullae of Lorenzini are small vesicles that form part of an extensive subcutaneous sensory network system.  These vesicles are found around the head of the shark.  They detect weak magnetic fields produced by other fish at short ranges. This enables a shark to locate prey buried in the sand or to orient to nearby movement.  Each ampulla is a bundle of sensory cells innervated by several nerve fibers.  These fibers are enclosed in a jelly-filled tubule that has a direct opening to the surface through a pore.  These pores on the head of the shark are visible to the naked eye, and appear as dark spots. 

 Semicircular canals:

Functions of the labyrinth:

 1 - Equilibrium

 2 - Hearing - function of ORGAN OF CORTI located in lagena (enlargement of sacculus); lagena tends to be longer in terrestrial vertebrates &, in most mammals, it’s coiled into the cochlea. The organ of Corti contains a specialized strip of neuromasts connected to the nervous system via the auditory nerve.

1-Inner hair cell, 2-Outer hair cells, 3-Tunnel of Corti, 4-Basilar membrane, 5-Reticular lamina,
6-Tectorial membrane, 7-Deiters' cells, 8-Space of Nuel, 9-Hensen's cells, & 10-Inner spiral sulcus

[Drawing by Stephan Blatrix, from "Promenade around the cochlea"  by R Pujol, S. Blatrix, T. Pujol and V. Reclar-Enjalbert, CRIC,
University Montpellier 1 - INSERM. URL:]


How do pressure or sound waves become ‘sound?’

 (Also: check out &

Pit receptors of reptiles = infrared receptors:

 1 - Labial pits

 2 - Loreal pits

Light receptors (or photoreceptors) - vertebrates can perceive only a narrow band of electromagnetic radiation between about 350 & 760 nm; 2 types include the epiphysis (already described) & the eye

Structure of a vertebrate eye:

Accommodation is the process of focusing light on the retina & this can occur in several different ways:

Special visceral receptors - olfactory (smell) & gustatory (taste):

General Somatic Receptors - come in two categories: cutaneous receptors & proprioceptors General Visceral Receptors:

Useful links:

Comparative Anatomy of the Chordate Nervous System

Comparative Anatomy Topic 19: The Nervous System

Coordination and Integration

Evolution of the Amniote Brain

Sensory Mechanisms

The Evolution of the Vertebrate Brain

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