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What is a Sensory System?

What is a Sensory System?

Sensory systems detect stimuli—such as light and sound waves—and transduce them into neural signals that can be interpreted by the nervous system. In addition to external stimuli detected by the senses, some sensory systems detect internal stimuli—such as the proprioceptors in muscles and tendons that send feedback about limb position.

Somatosensation

Somatosensation

The somatosensory system relays sensory information from the skin, mucous membranes, limbs, and joints. Somatosensation is more familiarly known as the sense of touch. A typical somatosensory pathway includes three types of long neurons: primary, secondary, and tertiary. Primary neurons have cell bodies located near the spinal cord in groups of neurons called dorsal root ganglia. The sensory neurons of ganglia innervate designated areas of skin called dermatomes.

Neurulation

Neurulation

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior...

Cranial Nerves: Overview and Anatomy

Cranial Nerves: Overview and Anatomy

The cranial nerves are an important part of the complex network of nerves in the human body. These nerves emerge directly from the brain and are responsible for transmitting essential information between the brain and various parts of the head and neck. There are 12 pairs of cranial nerves, systematically numbered using Roman numerals from I to XII, beginning from the anterior and moving to the posterior of the brain. Each cranial nerve is uniquely identified by names that reflect its function...

Sensory Perception: Organization of the Somatosensory System

Sensory Perception: Organization of the Somatosensory System

The somatosensory system is the central and peripheral nervous system component that senses and processes touch, pressure, pain, temperature, and body position or proprioception. The process of sensation takes place at three levels:
The receptor level:
The receptor level is the first stage of sensation. It involves the detection of a stimulus by specialized sensory receptors. The stimulus must arrive within the receptor's receptive field. Next, the receptor converts the energy of the stimulus...

Overview of Somatic Sensory Pathways

Overview of Somatic Sensory Pathways

Somatic sensory or somatosensory pathways refer to the neural pathways that carry information related to touch, pressure, pain, temperature, and proprioception from the skin, muscles, tendons, and joints to the brain. These pathways involve several stages of processing and integration of sensory information.
The somatosensory system is divided into three main pathways: the dorsal (or posterior) column-medial lemniscus, spinothalamic (or anterolateral), and spinocerebellar pathways.
The dorsal...

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Related Experiment Video

Updated: Jul 16, 2026

A Large Lateral Craniotomy Procedure for Mesoscale Wide-field Optical Imaging of Brain Activity

A Large Lateral Craniotomy Procedure for Mesoscale Wide-field Optical Imaging of Brain Activity

Published on: May 7, 2017

Sensory system evolution at the origin of craniates.

¹Krasnow Institute for Advanced Study and Department of Psychology, George Mason University, Fairfax, VA 22030, USA. abbutler@gmu.edu

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences

|November 18, 2000

Summary

The evolution of craniates involved significant changes in sensory systems. A serial transformation hypothesis suggests paired eyes and an enlarged brain preceded the development of neural crest sensory systems.

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Area of Science:

Evolutionary developmental biology
Neuroscience
Comparative anatomy

Background:

The transition from invertebrates to craniates involved key innovations like migratory neural crest and neurogenic placodes.
These tissues are crucial for developing peripheral sensory neurons and the central nervous system.
The timing of these peripheral and central nervous system developments is debated.

Purpose of the Study:

To investigate the temporal relationship between the evolution of central nervous system structures (brain, eyes) and peripheral sensory systems (neural crest, placodes).
To test the serial transformation hypothesis, which posits a specific order of evolutionary events.

Main Methods:

Comparative analysis of sensory system organization across different taxa (craniates, cephalochordates, arthropods).
Examination of the distribution of visual system components versus neural crest-placodal sensory systems within the neuraxis.
Inference of evolutionary pathways based on conserved and divergent features.

Main Results:

Evidence suggests that large, paired eyes and an enlarged brain evolved independently in multiple lineages, including craniates.
The diencephalon is primarily associated with visual processing, while neural crest-placodal systems are more broadly distributed.
This pattern supports a scenario where central visual pathways were established first.

Conclusions:

A serial transformation, with the brain and eyes evolving before neural crest-placodal sensory systems, is a plausible model for early craniate evolution.
This sequence explains the conserved organization of central sensory pathways, with visual systems establishing a foundational "beachhead".