Remodelling neurons during metamorphosis

The lifestyle and behaviour of the adult moth are quite different from those of the larva, and the two stages have completely different locomotory and sensory systems. The larva moves by crawling movements involving stubby pro-legs on the abdomen and thorax, and these legs and their muscles disappear during the pupal stage. Almost all of the larval muscles die during metamorphosis, and are replaced by new muscles that move adult structures such as wings and thoracic legs. The adult has more...

Scope and limitations of neuroethology

As might be expected, neuroethology has been most successful in tackling those elementary components of behaviour with which ethology itself began. The simple kinds of behaviour that first caught the attention of the founders of ethology are often also the kinds of behaviour most readily analysed in terms of the underlying neural events. One good example is intraspecific communication, which requires both that the sender delivers a clear signal and that the receiver has the appropriate sensory...

Summary of pathways in crayfish startle behaviour

The startle response of crayfish is a simple behaviour, which is initiated with the least possible delay. Nevertheless, the neuronal circuit underlying this behaviour is quite sophisticated and involves complexities that could hardly be predicted from the behaviour itself. The main pathways involved in linking the response to an adequate stimulus are shown in Fig. 3.7. The initial tail flip is triggered by sensory information, which is fed with minimal processing on to the lateral giant, which...

Development of song nuclei

Nuclei lMAN, DLM and Area X are required for a bird to acquire the normal adult song pattern (Bottjer, Meisner & Arnold, 1984), but not for an adult bird to sing. If lMAN is removed from a fledgling bird, the bird will produce an incomplete pattern of song, and if Area X is removed, song remains plastic. In the adult, neurons in Area X and lMAN, like those in HVc, respond specifically to tape recordings of the bird's own song. This selectiv ity arises gradually. Neurons in lMAN and Area X of...

The role of an identified neuron in conditioning

A bee's brain must be able to form associations between a sucrose reward and many different other stimuli, including a variety of odours. We could, therefore, expect that a neuron that plays a key role in conditioning would have branches distributed in many different regions of the brain. One such neuron is VUMmxl (Fig. 9.4b), an unpaired neuron which has branches that are arranged symmetrically on both the left and right sides of the sub-oesophageal ganglion and brain, and Martin Hammer (1993)...

Proprioceptors and the flight motor pattern

Locusts have a large array of sensors that report back to the central nervous system on the mechanical effects which the commands it issued slightly earlier caused. This is necessary because the effects of muscle contraction are not totally predictable. A flying locust might, for example, experience a gust of wind which causes its course to deviate. When it deviates, the wings on one side of the body might move up and down more than those on the other side for a few wing-beat cycles. A large...

Generation of the flight rhythm

An influential paper in the study of the neuronal control of movement was by Donald Wilson, published in 1960. This challenged the prevailing view that sequential activation of reflex loops generated rhythmical movements, such as locust flight and walking in vertebrates. Locust wings bear a large number of sense organs that report details of their movements. However, Wilson showed that when he removed the wings and destroyed the sense organs of the wing bases, a locust could still generate a...

Neuronal pathways and conditioning

Taste-sensitive sensory neurons that detect sucrose project from the proboscis into the suboesophageal ganglion, which is the first ganglion in the nerve cord after the brain and is also the ganglion that contains the motor neurons of the proboscis muscles. Odours are detected by sensilla on the antennae, which project into antennal lobes of the brain. After processing in the brain, information about odours is carried to the suboesophageal ganglion by neurons that originate in the forebrain, or...

Triggering and maintaining escape swimming in Tritonia

Some of the first intracellular recordings from nerve cells in an animal behaving in a more-or-less normal pattern were made from Tritonia (Willows, Dorsett & Hoyle, 1973). By exposing the brain through a small incision and then fastening it to a support platform, intracellular recordings can be made from single neurons. The animal is suspended in a tank of seawater and can perform normal muscular movements. This experimental technique allowed identification of motor neurons and...

Excitation and inhibition in the Mauthner neuron

The Mauthner neuron is excited by a wide range of sensory modalities as a result, a large number of sensory neurons converge on this neuron, either directly or indirectly, and this is reflected in the great size of the two main dendrites (Fig. 3.8c and Fig. 3.10a). The cell body and the dendrites sum the synaptic potentials which are generated by inputs from the sensory neurons, and this summed signal is conducted passively to the initial part of the axon. The membrane of the Mauthner neuron...

Basic receptor mechanisms the campaniform organ

Campaniform organs detect strains in the cuticular exoskeleton of insects and so provide information about loading on different parts of the body. They occur in groups at those parts where stresses are most likely to be felt, particularly near joints between segments (Fig. 4.1a, b). Mechanoreceptors that detect the relative positions of, or stresses and strains in, different parts of the body are known collectively as proprioceptors. The muscle receptor organ in the crayfish abdomen (see...

Steering and initiating flight

Flying animals require sensory mechanisms both for maintaining a certain flight course and for altering it so that they avoid collisions or predators. The DCMD neuron (see section 5.8) might be responsible for the ability of locusts to avoid colliding with each other in dense swarms and locusts, like some other insects, possess neurons which respond to the high-frequency calls of insect-eating bats and which can probably cause a locust to steer its flight path away from a hunting bat (Robert,...

Neuronal coding in the insect lamina

The large monopolar cells are specialised to respond to changes, or contrasts, in the visual signal. Like the photoreceptor cells, they convey signals as small, graded changes in membrane potential and do not generate trains of spikes. They are, therefore, particularly sensitive to small fluctuations in light intensity about an average value. Their responses also depend on the contrast between light received by their own photoreceptors and those of neighbouring cartridges. Characteristic...

Neural implications of ethological results

The behaviour of an animal is to a large extent the product of activity in its nervous system. The patterns of behaviour that are recognised in ethological studies must therefore reflect the underlying organisation of the nervous system. In the case of the elementary components of behaviour studied by the early ethologists, this correspondence may be fairly close. Consequently, a careful study of behaviour patterns at the level of the intact organism will often produce results that provide...

Neuroethology of a releasing mechanism

As with other vertebrates, early visual processing in amphibians takes place in the neuronal circuits of the retina. The neurons of the vertebrate retina (see Fig. 2.4, p. 25, and Box 5.1, p. 107) are arranged in a way that provides for both lateral interaction and through transmission. The through route of the visual pathway is made up of receptors, bipolar cells and ganglion cells. Recording with microelectrodes shows that the receptors respond in a simple way to changes in the intensity of...

The insect visual system

Motor Neurons Insect

The interneurons that process visual information in insects are arranged as a series of neuropiles that lie beneath a compound eye and make up an optic lobe of the brain (Fig. 5.1). Most interneurons connect two layers of neuropile, with their cell bodies and input synapses in one layer and an axon that conducts information towards the brain into the next layer of neuropile. Information, therefore, tends to flow sequentially through different layers of neuropile. But there are also circuits...

Design features of eyes

Www Ommatidium Photo Grasshopper Com

The lens of an eye gathers light from the environment and usually focuses it as a crisp image onto photoreceptor cells. The greater the amount of light that one photoreceptor receives, the easier it is for it to provide an accurate measure of light intensity. This is particularly important for animals that are active in dim lighting conditions, when the amount of light available is small. There are two main ways of maximising the amount of light that a photoreceptor receives one is for the eye...

Executive functions of the lateral giant neuron

A lateral giant not only initiates a tail flip, but also extensively co-ordinates the sequence of events involved. This executive function is achieved by a massive and widely distributed array of inhibitory effects that follow a spike in the giant axon. Pathways lead away from the lateral giant to exert inhibition at almost every point in the neuronal circuit generating a tail flip. The IPSPs produced at these points in the circuit differ from one another, in the delay to their onset and in...

Sign stimuli in amphibians

The way in which frogs and toads recognise their prey provides another example of a releasing mechanism. In this case, the ethological results are even more compelling because they have been combined with a neuro-physiological study of the same system. This combined approach clearly shows how the selective properties of nerve cells (neurons) are involved in releasing particular patterns of behaviour (Ewert, 1985, 1987). In the visual world of a frog or toad, just a few, simple criteria serve to...

Photoreceptors and the receptor potential

Within an ommatidium, the lens focuses light onto the tips of photoreceptor cells, which are called retinula ('little retina') cells (see Fig. 4.5). There are usually eight or nine retinula cells per ommatidium. A retinula cell is elongated, with its longitudinal axis parallel to that of the ommatidium. Outermost is the cell body, and it includes a specialised structure, the rhab-domere, where phototransduction occurs. The cell membrane is folded into very regular finger-like projections, or...

Outputs and executive functions of the Mauthner neuron

Interneuron

The Mauthner neuron has monosynaptic connections with many of the spinal motor neurons that it excites a short collateral of the Mauthner axon makes contact with a special region of the motor axon several micrometres from the cell body (see Fig. 3.8b). A spike in the Mauthner axon produces an EPSP in the motor neuron with a synaptic delay of about 0.6 ms, so the transmission is probably chemical. The excitation of a substantial number of other motor neurons is relayed by way of a premotor...

A mechanism for directional selectivity

In sensory systems, there are many examples of neurons that act as filters, responding most vigorously to one particular stimulus configuration. The selectivity of these neurons for their preferred stimulus must arise from the way in which their presynaptic neurons are arranged, and study of fly lobula plate neurons has enabled insights into the way in which one particular kind of selectivity - directional selectivity - arises. The neurons are considered to be driven by an array of local...

Auditory interneurons and sound localisation

The fact that a barn owl can localise sounds accurately under open-loop conditions implies that its auditory system can recognise each point in space from a unique combination of the cues that specify azimuth and elevation. Interneurons that respond to such complex combinations of stimulus features are found among higher-order neurons in the midbrain. The main auditory region of the midbrain in owls is situated on the inner edge of the optic tectum (Fig. 6.4a) and is divided functionally into...

Prey localisation by hearing in owls

Elevation Azimuth Barn Owl

Adult owls hunt within a well-defined territory, which they know well and patrol regularly at night. During its patrol, an owl visits a number of observation perches, from which it can survey the ground round about. If it hears potential prey, the owl swiftly turns its head so that it directly faces the object of interest. Then, after adequate scrutiny, it flies down to capture the prey in its outspread talons (Fig. 6.1). An owl listening from a perch or in low-level flight must be able to...

Interneurons of the flight generator

None of the motor neurons contributes to the generation of the flight rhythm, and one good functional reason is that motor neurons, and there fore muscles, can be used independently of each other. This is important during steering, and during some movements of the legs in which muscles that also move the wings are involved. The regular waves of depolarisation that occur in motor neurons during flight must, therefore, originate in interneurons and be communicated to the motor neurons by synaptic...

Swimming by young Xenopus tadpoles

The most complex patterns of behaviour occur in vertebrates, and understanding the neuronal basis of these behaviours must involve unravelling the circuits of the spinal cord. One approach, which has been particularly fruitful, is to examine very simple behaviours in lower vertebrates, particularly swimming in lampreys (Grillner et al., 1995) and in tadpoles. The pattern of swimming in newly hatched tadpoles of the clawed frog Xenopus, turns out to be especially simple (Roberts, 1990). For the...

Overall view of locust flight

The overall picture we now have of the flight control system of the locust is of a series of intermeshed, overlapping neuronal loops (Fig. 7.8). It contains Figure 7.8 A flow diagram to show the relationships between some of the elements involved in generating the flight motor program in a locust. Some, but not all, of the thoracic interneurons included here are involved in generating the rhythm. Rhythmic input to motor neurons and interneurons is also derived from wing proprioceptors and brain...

The echolocation sounds of bats

Whereas owls locate prey by listening passively to the noises produced by the prey, insectivorous bats actively interrogate the environment using the technique of echolocation (Fig. 6.7). For this purpose, a flying bat produces a succession of loud calls, each of which consists of a brief pulse of sound. These sounds are often described as ultrasonic because they contain frequencies (20-200 kHz) beyond the range of human hearing. The sound pulses travel out in front of the bat and, when they...

The auditory system and echolocation

Inner Ear Muscle Bat

When echolocation sounds return as echoes to a bat, they are received by an auditory system that conforms to the general mammalian pattern. The sounds are collected by the external ear and enter the ear canal, where they impinge on the tympanum (Fig. 6.10). The vibrations of the tympanum are Figure 6.10 The middle and inner ear of a bat diagram based on a horizontal section. The external ear opening is off picture to the right. Structural elements of the middle and inner ear are shown in solid...

Auditory specialisations for Doppler shift analysis

All echolocating bats need to be able to analyse sound frequencies accurately. With FM signals, fine frequency analysis yields accurate range measurement and detailed description of the target, and with CF signals it yields an accurate measure of the Doppler shift. Frequency analysis is certainly excellent in bats that use only FM signals, such as Myotis, but their abilities are not so very different from those of other mammals. However, in bats that use long CF signals, such as Rhinolophus,...

Circuit reconfiguration in the stomatogastric ganglion of the lobster

Gastric Mill Crustaceans

In crustacea, movements of the foregut are achieved by contraction of discrete striated muscles, very similar to the muscles that move limbs during movements of the body. Quite complex, regularly repeating patterns of activity occur in these muscles. A major reason for investigating their control is that the neurons responsible for generating these movements are contained in four discrete, small ganglia and the nerves that connect them (Fig. 7.11a). The most intensively investigated is the...

Auditory specialisations for echo ranging

The mechanisms of attenuation outlined above are particularly important in facilitating accurate measurement of the echo delay, and hence of distance, because they prevent the auditory system from being overloaded by the outgoing sound pulses. In order to measure echo delay, the bat's auditory system must be capable of resolving very small time intervals. Most mammals are unsuited to this task because their auditory systems take too long to recover between successive sound stimuli - usually...

Local bending reflexes in the leech

If you touch a small area of the skin of a leech, it will bend its body away from the touch, a movement caused by contraction of longitudinal muscles in a few segments close to the site of the touch. The body of the leech locally assumes a U shape. Touching the top of the body causes a downward bend, whereas touching the left side causes a bend towards the right, and so on (Fig. 8.2a). The main sensory neurons involved in triggering these local reflex movements are pressure-sensitive P neurons....

Giant neurons and the crayfish tail flip

Crayfish escape from the strike of a predator by means of a rapidly executed tail flip, produced by flexing and re-extending the whole abdomen. The abdomen is able to act as an effective locomotory organ because the last two (sixth and seventh) abdominal segments are modified to form the tail fan (Fig. 3.1a). A single flip of the tail fan is capable of moving the animal several centimetres through the water. The power for this movement is provided by the fast flexor muscles, which occupy much...

Neuronal activity during different behaviours in Aplysia

Aplysia is a shell-less gastropod mollusc that spends most of the time grazing on seaweed near or just below the low-tide mark. It breathes by drawing currents of water over a delicate gill, which is normally partially extended from under a fleshy shelf of the body wall, but is retracted for defence if nearby skin is touched lightly (Fig. 8.1a). The gill is also strongly retracted in time with respiratory pumping movements. Some species of Aplysia grow in excess of 30 cm long and have attracted...

Synthesising a neuronal map of auditory space

Auditory Pathway Mso

Each space-specific neuron in the owl's midbrain responds to stimuli delivered via the earphones only when both the time difference and the intensity difference fall within the range to which it is tuned. It is not excited by either the correct time difference alone or the correct intensity difference alone. Evidently, the receptive fields are formed by tuning of the neurons to specific combinations of time differences and intensity differences, which are coded separately by lower-order...

Collision warning neurons in the locust

Optomotor responses help to stabilise an animal when it is stationary or proceeding along a straight course, and they do this by referring to movements that occur in the background. The animal also needs to be able to respond to individual objects, such as potential predators, mates or perching sites. Like many animals, locusts and grasshoppers will escape from rapidly approaching objects. This is apparent to anyone who has tried to catch one of these insects they respond to approach by a...

The lateral giant interneuron input and output

Undoubtedly the most striking feature of the initial tail flip is its speed. Within 50 ms, abdominal flexion is completed and the animal has usually moved some distance through the water. The mean delay between the stimulus and the onset of flexor muscle potential is 6 ms (see Fig. 3.1 b). This speed is required because the tail flip is probably a response to a predator that is extremely near to or touching a crayfish. Physiologically, the speed is partly achieved by extensive use of large...

Neuron physiology and action potentials

Action Potential Neurons

Neurons are specialised in their physiology to receive, sort out and pass on information. The signals that neurons deal with involve small changes in the electrical voltage between the inside and outside of the cell, and integration is the process by which these voltage changes are combined together to determine the neuron's output signal. This is essentially how neurons make decisions. The most conspicuous of these voltage changes are action potentials, which are the signals that neurons use...

Integration of postsynaptic potentials

Neurons Png

Integration involves weighing up the balance of EPSPs and IPSPs within a cell and the outcome determines how excited the neuron is at any given moment. In order to sort out all the PSPs that it receives, a neuron needs to have a way of combining them together. In general, the dendrites of a neuron function to combine PSPs as well as to receive them and this function is made possible by their passive cell membrane. This contrasts with the membrane of an axon, which is described as being active...

Local reflex movements of a locusts leg

Jointed limbs, such those of a mammal or an insect, are used in a wide variety of ways. Besides being involved in locomotion, they are capable of finely controlled movements such as grooming, in which the end of the limb is brought precisely to a particular spot on the animal's surface. Since the 1970s, Malcolm Burrows and colleagues have investigated in detail the neurons responsible for controlling local movements of a locust's hind leg, providing a very complete description of the links...

Associative learning and the proboscis extension reflex in honey bees

Www Digram Honey Bee Brain Com

Some of the most interesting behaviour patterns amongst insects are found in the social hymenoptera, bees, wasps and ants. These animals are capable of memorising landmarks, which they use for navigation Dyer, 1996 Judd amp Collett, 1998 , and they have elaborate systems for communication amongst individuals, such as the waggle dance of honey bees Lindauer, 1967 . The disposition of bees to learn to associate colours and shapes of flowers with a good source of food was recognised by one of the...

Basic organisation of nerve cells

Arthropod Circulatory System

The very title of this chapter would have been contentious in the nineteenth century, when detailed scientific study of the nervous system got underway. For it was then not generally agreed that the nervous system is composed of many individual nerve cells. This was mainly due to the fact that nerve cells are difficult to visualise with routine histological methods. Many cells are packed tightly together in nervous tissue there are 100000 nerve cells in 1mm3 of human brain and they give off...