Neuroscience in Neuroscience in the Classroomthe Classroom

Hands-On Activities Using Weakly Hands-On Activities Using Weakly Electric Fish as a Model for the Electric Fish as a Model for the Study of NeurologyStudy of Neurology

November 8th, 2003

Project Background – 21Project Background – 21stst Century Biology Century Biology(Est. 1991)

Students have completed and designed experiments

on projects such as:

Allows students to work cooperatively

Weakly Electric fishZebrafish

ThigmomorphogenesisTelemicroscopy

Tomography

Brain Awareness Week

Project BackgroundProject BackgroundProject ObjectiveProject Objective

Introductory Neuroscience• Muscle Physiology• Anatomy• Biochemistry• Membrane Potential• Sensory Physiology• Behavior• Evolution• Electrical Physics

Scientific Procedure• Scientific Method• Experimental Thought/Scientific Reasoning• Protocol Writing• Scientific Equipment and Techniques• Data Analysis

Project BackgroundProject BackgroundThe Electric Fish ModelThe Electric Fish Model

Historical Applications

• Electric Rays to cure health problems• Studied as possible source of electricity• Aided in studies of motor neuron transmissions and

electric potential gradients

Current and Possible Applications

• Military• Biosensors• Medical

Electric Fish BackgroundElectric Fish BackgroundEvolution and HabitatEvolution and Habitat

Above: Electroreceptor Evolution.

Below: Habitat of Weakly Electric Fish. Both orders (mormyriforms and gymnotiforms) live in shallow, murky waters and hide in aquatic vegetation.

Electric Fish BackgroundElectric Fish BackgroundEigenmannia virescensEigenmannia virescens

Habitat • Member of the Gymnotiform class in South America• Resides principally in the Magdalena and Amazon Rivers• Nocturnal, generally timid• Live in areas of low water flow• Can grow in length to 45 cm

Diet •Generally, the diet for this species is the larvae of small insects

Electric Organ Characteristics• Myogenic electric organ• Emits a wave-type frequency of 300 Hz (low frequency)

Electric Fish BackgroundElectric Fish BackgroundOrganization of the Nervous SystemOrganization of the Nervous System

The nervous system is composed of two parts:

• Central Nervous System (CNS) • Peripheral Nervous System (PNS)

The nervous system has three functions: • Sensory Input • Integration • Motor Output

Electric Fish BackgroundElectric Fish BackgroundA view of a NeuronA view of a Neuron

Above: Neurons are made up of three parts: cell body, axons, and dendrites.

Below: A computer representation of a neuron. The three types of neurons are sensory neurons, interneurons, and motor neurons.

Electric Fish BackgroundElectric Fish BackgroundPhysics Review: Electricity and the Physics Review: Electricity and the Circuit BoardCircuit BoardElectrical Physics

Circuit: path of an electric current Coulomb: unit of electrical chargeVoltage: electrical difference, potential between two poles; volts (joule per coulomb)Current: flow of electrical charge; amperes (coulomb per second)Resistance: conductivity of a material; ohms (volt per amp)

The Circuit Board

Series: circuit where current through each resistor is the same and voltage is proportional to the resistanceParallel: circuit where voltage through each resistor is the same and current is proportional to the resistance.

Electric Fish BackgroundElectric Fish BackgroundPhysics Review: Circuit BoardPhysics Review: Circuit Board

Left: Capacitors and resistors are used to demonstrate key concepts of electrical physics.

Right: Light bulbs are used to show electrical flow and intensity in a series or parallel circuit. They are also considered resistors.

Electric Fish BackgroundElectric Fish BackgroundThe Electric Organ and the EODThe Electric Organ and the EOD

Below: Anatomy of an electric organ.

Left: Location of electric organ in the posterior of the fish. Usually has gelatinous texture with a large volume of cellular space. Composed of multinucleated cells myogenically or neurogenically derived.

Electric Fish BackgroundElectric Fish BackgroundThe Electric Organ and the EODThe Electric Organ and the EOD

Right :

Electroreceptor

located on fish body.

Interprets

information from the

electric field. The

two types of

electroreceptors are

ampullary and

tuberous.

Electric Fish BackgroundElectric Fish BackgroundThe Electric Organ and the EODThe Electric Organ and the EOD

Below: Weakly electric fish create a dipole electric field to locate objects, communicate, and navigate.

Electric Fish BackgroundElectric Fish BackgroundThe Electric Organ and the EODThe Electric Organ and the EOD

Above: The electrical field generated by the fish is distorted by nearby objects. A good conductor (i.e. a living organism) is conducive to the electric force. A non-conductor (i.e. a rock) blocks it. The fish decides how to react to an object based on the distortion pattern it creates in the electric field.

Electric Fish BackgroundElectric Fish BackgroundHummers vs. ClickersHummers vs. Clickers

Above: All weakly electric fish emit either “hums” or “clicks” as a means of exploring their environment. Clickers emit a short, pulse-like EOD in bursts.Hummers emit a constant, wave-like EOD.

Electric Fish Electric Fish BackgroundBackgroundThe Jamming Avoidance Response The Jamming Avoidance Response (JAR)(JAR)• When two fish with nearly the same frequency meet, one

fish shifts its frequency slightly higher and the other fish shifts its frequency slightly lower. • The shifts are simultaneous and reflexive. • The process prevents the two frequencies from interfering and jamming each other’s electrical signals, allowing the fish to operate in the same area.

Electric Fish Electric Fish BackgroundBackgroundVestibular and Acostico-Lateralis Vestibular and Acostico-Lateralis SystemSystem

Left: Section of nervous system in inner-ear that controls balance by maintaining the orientation of body. Processes orientation, acceleration, and movement information.

The Acostico-lateralis system in fish is housed in the lateral line canal along the sides of the head and body. Electroreceptors are located there as well. Detects water movements.

Electric Fish Electric Fish BackgroundBackgroundSources and LinksSources and Links

•http://www.life.edu/faculty/wilkinson/BSCI338/L11electrosense/ACL11-electro.ppt•http://soma.npa.uiuc.edu/labs/nelson/electric_fish.html•http://www.apta.org/Education/Continuing_Education/onLine_ceu_List/Vestib_Intro/Page_2•http://www.sdsc.edu/~marty/cmda/jeol4000.jpg •http://www.people.virginia.edu/~mk3u/mk_lab/electric_fish_E.htm•“Echolocation in Fish: The Electric Organ Discharge.” Grass Instrument Company, 1993. •www.enchantedlearning.com/.../•anatomy/brain/gifs/Neuron.GIF •http://faculty.washington.edu/chudler/gif/spiback1.gif•http://www.easi.org/nape/apslides/26_cns.gif•www.monkeytime.com/sciencemaster/galleries/brain/images/01.jpg•http://www.psy.jhu.edu/~fortune/data.html

Coming Next…Coming Next…Outline of Workshop ActivitiesOutline of Workshop Activities

• Hummers and Clickers

• Circuit Board Activity

• Model presentation/anatomy

• Ice Cube/Vestibular System

• Neuron Activity

Contact Us!E-mail: 21bio@sidwell.edu

Website: http://www.21bio.org