This laboratory will explore several basic mechanisms involved in information processing in the nervous system. The cricket cercal sensory system will be used as a model to study these mechanisms.
Structure-function relationships in the nervous system:
One of the most basic concepts involved in the organization of neural
systems is the relationship between the anatomical structure of
neurons and their functional properties. These structure function
relationships can be studied at many different levels. At a
macroscopic level, the location a particular neuron in the brain,
determines what behaviors that neuron will participate in. For
example, a motor neuron in the spinal cord is involved in controlling
the movements of a particular muscle. A ganglion cell in the retina is
involved in processing visual stimuli. At the microscopic level the
location of the dendritic and axonal processes of an neuron within a
neural structure, determines the inputs it receives from other neurons
and the neurons it transmits information to. At the ultrastructural
level the distribution of synapses and ion channels over branches of a
neuron determine how that cell integrates information. The structure
of a neuron, at all of these levels, is tightly linked to its
functional properties.
Topographic maps in sensory systems:
Sensory systems are organized anatomically to represent certain
features of the sensory environment in the central nervous
system. This anatomical organization is called a neural map. Your
brain contains many such maps of the external world, including maps of
the visual world, the auditory world and your body surface. These
neural maps have evolved as an efficient means of organizing the
massive amount of sensory information that comes in to the brain in a
way that is easy to access and analyze by the rest of the nervous
system. For example, in the auditory system there exists a map of
sound frequency. Neurons sensitive to low sound frequencies are
located at one location in the map and those sensitive to higher
frequencies are located at another location of the map. Cells
sensitive to intermediate frequencies are located in a stepwise
fashion through the map. Thus there is a continuous representation of
sound frequency within the auditory system. In general, cells
that are sensitive to similar stimuli (like the same sound frequency)
are located near each other in a map, and cells sensitive to different
stimuli are spatially separated in the map.
Topographic mapping of receptor direction in the cricket cercal
sensory system:
In this laboratory you will examine the relationship between the
functional properties of individual sensory receptors, sensory
interneurons and their location within a neural map. The system you
will study is an insect sensory system, the cricket cercal sensory
system. This system allows the animal to detect air currents in its
local environment, such as those produced by an approaching predator.
The system analyzes the direction and velocity of the air currents,
which tells the cricket the location of the approaching predator.
With this information, the cricket can then turn away from the
predator and make its escape.
This laboratory will use anatomical data from the cricket cercal system and anatomical reconstruction and imaging techniques to address these questions.
The images that will be used in this laboratory have been assembled into a series of web pages. For each activity, use one or more sets of images (slides) to answer the questions on your lab handout.