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03.02 Nervous System

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Bugs 101: Insect-Human Interactions

Universidade de AlbertaUniversidade de Alberta

4.8 (17 classificações) | 5.3K alunos inscritos

Of all the animals on earth, which are the strongest for their size? What about the fastest? Who were the first animals to evolve flight? Insects take all of these titles and more! As the most abundant animals on the planet, insects and other arthropods affect our lives in so many ways. From beneficial interactions like pollination and biological pest control, to the transmission of life threatening diseases; this course will teach you about the big ways that these little arthropods impact our lives. In Bugs 101: Insect-Human Interactions, you will be plunged into the diverse (and sometimes alien) world of arthropods to learn how they work, what they do, and how insects and humans interact every day. After completing this course, you will be able to: Describe the evolutionary relationships between insects and their arthropod relatives Inventory major groups of insects and their diversity Demonstrate evolutionary adaptations that make insects successful Discuss insect biology and human-insect interactions Evaluate positive and negative interactions between insects and humans Propose practical and symbolic roles insects play in human societies

Visualizar o programa do curso

Habilidades que você aprenderá

Biology, Entomology, Science, Ecology

Avaliações

4.8 (17 classificações)

5 stars
16 ratings
2 stars
1 ratings

VI

Aug 13, 2019

A study which is highly enjoyable and useful for professionals

CS

Aug 15, 2019

Overall a great course. Would, and have, recommend to others.

Na lição

Module 03: The Business of Being an Insect Part 2

Building on the previous module, we continue to explore insect biology through an overview of the major physiological systems of insects. We look at the nervous and reproductive systems, and highlight some of the ways insects court, seduce, and reproduce.

03.02 Nervous System11:11

Ministrado por

Dr. Maya Evenden
Professor of Entomology

Transcrição

[MUSIC]

The next biological system we will examine is the nervous system.

The sophistication of the nervous system is one of the adaptations

that has contributed to the success of insects.

The insect nervous system is similar to that of other animals in that it is

characterized by the presence of special cells called neurons.

Neurons are cells that receive and send out electrochemical impulses.

These impulses travel along neurons due to an electrochemical gradient across

the cell membrane, this transmission is called an action potential.

There are three major types of neurons.

Sensory neurons receive stimuli from the environment and

send this information to the Central Nervous System.

Motor neurons receive stimuli from the Central Nervous System and

transmit signals that stimulate muscles.

Finally, there are interneurons,

bridging cells which connect to our motor neurons of any type.

The neuron itself has three main parts, the dendrite, the cell body, and the axon.

The dendrites receive stimuli from the environment or other cells.

The stimulus is then transmitted as an action potential from the dendrite through

the cell body, which contains the cell's nucleus.

From here the signal travels along the axon to another neuron or

the target tissue.

The space between neurons where a dendrite and an axon meet is called a synapse.

At the synapse neural signals are passed from one neuron to

the next via chemical messengers known as neurotransmitters.

These chemicals can either stimulate or inhibit other neurons and muscles.

An important excitatory neurotransmitter in insects is acetylcholine,

an organic chemical released by neurons to stimulate other neurons and tissues.

The insect nervous system has two main components.

The Peripheral Nervous System perceives information from the environment.

And sends action potentials to the Central Nervous System,

where information is processed and behaviors are initiated.

The Central Nervous System contains the brain and the ventral nerve cord.

The Peripheral Nervous System registers stimuli from the environment.

Most insects can detect visual, olfactory, auditory, and

mechanical cues, some can even sense heat cues from a distance.

For example, Fire Chaser Beetles, in the genus Melanophila,

lay eggs in freshly burned trees that they sense with sensory organs on their legs.

These receptors can detect infrared radiation produced by hot objects

from up to 130 kilometers away.

Neurons in the Peripheral Nervous System that detect external environmental stimuli

are enclosed in sensory structures, called sensory receptors,

that are located on various parts of the insect's body.

They can be present in large concentrations on sensory structures,

like the antennae, the compound eyes, or the mouthparts.

They are also located on an insect’s tarsi, or feet, and even on a female's

ovipositor so that she can sense the environment before laying eggs.

Sensory receptors come in many forms.

A common one is the Trichoid Sensillum,

which has a single hair like seta that is associated with a neuron.

Neurons within most Trichoid Sensillum register physical movement,

a process known as mechanoreception.

During mechanoreception movement of the seta stimulates

the neuron within the sensillum and generates an action potential.

This is transmitted to the Central Nervous System,

which allows the insect to register physical cues in its vicinity.

Some trichoid sensilla sense chemical stimuli,

a process known as chemoreception.

Chemoreceptive trichoid sensilla have one or more microscopic pores along

the length of the seta, which allow liquid or gaseous chemicals to enter.

The compounds dissolve in a fluid within the seta and bind to the sensory neuron,

which in turn sends a signal to the insect’s Central Nervous System.

There are two types of trichoid sensilla that receive chemical cues.

Contact chemoreceptors, which detect substances dissolved in fluids and

olfactory chemoreceptors, which detect volatile substances in the air.

Let's move on to the Central Nervous System,

which you'll remember receives signals from the Peripheral Nervous System and

is made up of the brain and the ventral nerve cord.

In insects the nerve cord is located along the ventral side of the body,

unlike vertebrates in which the nerve cord is dorsally located.

Within the Central Nervous System the nerve cells are bundled into

interconnected masses of neurons known as ganglia.

These neural bundles located along the length of the nerve cord are joined by

connectives giving the insect's Central Nervous System

a distinctive ladder like appearance.

Ancestrally, each insect body segment had a pair

of ganglia that received stimuli from receptors.

And transmitted signals to muscles and other organs within each segment.

This is why if a primitive insect, like a cockroach,

is beheaded it can continue to function as long as water balance is maintained.

In most insects today fusion of ganglia has

resulted in a reduction in the overall number of ganglia.

This mirrors the reduction of the number of segments that we also see in

derived insects The insect's brain is

formed by the fusion of three pairs of ganglia located in the head.

Each pair of ganglia forms a distinct part of the brain with different functions.

The brain, as it does in vertebrates, integrates and

transmits information that controls behavior.

In adult insects the largest and most anterior part of the brain receives

stimuli from the compound eyes and the oscilla.

It also receives and processes messages from other parts of the brain.

It contains dense neural structures, known as mushroom bodies,

that sorts and coordinate information,

enabling some insects to learn, particularly from olfactory cues.

The mushroom bodies are most highly developed in social insects,

like the honeybee.

The second part of the insect's brain receive signals mainly from

receptors on the antennae.

Olfactory signals are processed here and interneurons transmit this

information to higher brain centers to influence insect behavior.

Finally, the third part of the brain receives information from

the rest of the body, primarily the foregut and labra.

Posterior to the brain lies the subesophagael ganglion,

which communicates with muscles that control movements of the mouthparts.

And is the bridge between the insect's brain and the rest of the nervous system.

Neurosecretory cells are found throughout the insect nervous system,

but occur in especially large concentrations in the brain.

These neurosecretory cells are responsible for the production

and release of insect hormones and neurohormones.

Neurohormones may promote further hormone production in other non-neural

tissues like the endocrine glands.

Examples of hormones that are regulated by neurohormones include Ecdysteroid and

Juvenile hormones, which influence physiological processes in other tissues.

Remember, Ecdysteroids are important in the molting process of insect growth and

development.

Neurohormones produced and released by the Corpora Cardiaca and

sometimes the Corpora Allata in Lepidopterans,

stimulate the production and release of ecdysteroids by prothoracic glands.

Another important hormone released by endocrine glands is juvenile hormone,

an important regulator of metamorphosis and reproduction.

Juvenile hormone is produced by the Corpora Allata.

The insects nervous system is often the target of chemical insecticides.

Some chemical insecticides, called axonic poisons,

inhibit the neurons ability to transmit an action potential along the axon.

Insects affected by these poisons exhibit tremors and

have a general loss of control of their motor functions.

A very well known and controversial axonic poison widely used

in North America after the Second World War is DDT.

DDT, or Dichlorodiphenyltrichloroethane, don't worry we

won't be testing you on this, is a colorless and odorless chemical.

That was developed for its insecticidal properties during World War II.

Widespread use of DDT against agricultural pests in the years following

the war resulted in environmental poisoning and human toxicity issues.

DDT was considered the major cause of sharp declines in Bald Eagle and

Peregrine Falcon populations in the United States in the 1940s and 50s.

Fortunately, the use of DDT has since been banned in most developed countries.

It is still used against insect vectors to reduce malaria in some parts of the world.

We will discuss how DDT affects insects in detail when we discuss pest

control in a future module.

Insecticides that act at the synapse between nerve cells are called

synaptic poisons.

These poisons result in rapid nerve firing in the affected insects,

which often results in restlessness, tremors, paralysis, and, finally, death.

The neurons of insects and humans function in the same way.

As such, most insecticides that target the insects nervous system can also

affect people and other non-target animals.

We hope you enjoyed this lesson on the remarkably complex insect nervous system.

The next biological system we'll look at may be even more remarkable and

sometimes downright bizarre, the reproductive system.

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