The document discusses the differences between vertebrate and invertebrate nervous systems. It examines examples from various phyla of invertebrates including cnidarians, echinoderms, nematodes, platyhelminthes, annelids, molluscs, arthropods, and compares them to typical vertebrate systems. Key differences include the level of centralization, important neural structures like ganglia or the brain, and physiological properties. Invertebrates range from very decentralized nerve nets to centralized brains, while vertebrates have advanced centralized brains and spinal cords for rapid information processing.
Invertebrates are not ‘simple animals’, but they are indeed
masters of economy: their small nervous systems contain
many fewer nerve cells than those of even the tiniest
vertebrates, yet these animals solve all of the same survival
problems, can live in highly organized societies and can
communicate complex messages. The goal of this article is
to outline general features of the nervous systems of
invertebrates, and to begin to ask how these tiny
information-processing systems drive such diverse behaviour.
The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
The basic fundamental plan of the aortic arches is similar in different vertebrates during embryonic stages.
But in adult the condition of the arrangement is changed either being lost or modified considerably.
The number of aortic arches is gradually reduced as the scale of evolution of vertebrates is ascended.
The embryonic aortic arches were basically six pairs.
But with progressive evolution , there has been consequent reduction in numbers of aortic arches.
In the basic pattern the major arterial channels consists of
A ventral aorta emerging from the heart and passing forward beneath the pharynx
A dorsal aorta paired above the pharynx and passing caudal above the digestive tract.
Six pairs of aortic arches connecting ventral aorta to with the dorsal aorta.
1st aortic arch= Mandibular aortic arch
2nd Aortic arch= hyoid aortic arch
3rd ,4th ,5th and 6th aortic arches in case of aquatic animal , known as branchial aortic arches.
Invertebrates are not ‘simple animals’, but they are indeed
masters of economy: their small nervous systems contain
many fewer nerve cells than those of even the tiniest
vertebrates, yet these animals solve all of the same survival
problems, can live in highly organized societies and can
communicate complex messages. The goal of this article is
to outline general features of the nervous systems of
invertebrates, and to begin to ask how these tiny
information-processing systems drive such diverse behaviour.
The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body.
In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
The basic fundamental plan of the aortic arches is similar in different vertebrates during embryonic stages.
But in adult the condition of the arrangement is changed either being lost or modified considerably.
The number of aortic arches is gradually reduced as the scale of evolution of vertebrates is ascended.
The embryonic aortic arches were basically six pairs.
But with progressive evolution , there has been consequent reduction in numbers of aortic arches.
In the basic pattern the major arterial channels consists of
A ventral aorta emerging from the heart and passing forward beneath the pharynx
A dorsal aorta paired above the pharynx and passing caudal above the digestive tract.
Six pairs of aortic arches connecting ventral aorta to with the dorsal aorta.
1st aortic arch= Mandibular aortic arch
2nd Aortic arch= hyoid aortic arch
3rd ,4th ,5th and 6th aortic arches in case of aquatic animal , known as branchial aortic arches.
Central nervous system: The central nervous system consists of the brain and spinal cord. The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures. The spinal cord is connected to a section of the brain called the brainstem and runs through the spinal canal.
Peripheral Nervous System: Nerve fibers that exit the brainstem and spinal cord become part of the peripheral nervous system. Cranial nerves exit the brainstem and function as peripheral nervous system mediators of many functions, including eye movements, facial strength and sensation, hearing, and taste.
The autonomic nervous system: The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
The autonomic nervous system comprises two antagonistic sets of nerves, the sympathetic and parasympathetic nervous systems. The hypothalamus is the key brain site for central control of the autonomic nervous system, and the paraventricular nucleus is the key hypothalamic site for this control.
Divisions of Nervous System:
The vertebrate nervous system has three divisions:
(i) A central nervous system comprising the brain and spinal cord. Its function is to receive the stimulus from the receptors and transmit its response to the effectors. Thus, it coordinates all the functions of the body.
(ii) A peripheral nervous system consisting of cranial and spinal nerves arising from the brain and spinal cord respectively. It forms a connecting link between the receptors, central nervous system (CNS) and effectors.
(iii) An autonomic nervous system made of two ganglionated sympathetic nerves, ganglia in the head and viscera, and their connecting nerves. The autonomic nervous system is often regarded as a part of the peripheral nervous system because the two are connected. But all the three divisions of the nervous system are connected intimately both structurally and functionally.
Sense organs are the specialized organs composed of sensory neurons, which help us to perceive and respond to our surroundings. There are five sense organs – eyes, ears, nose, tongue, and skin.
External receptors (exteroceptors): sense organs for touch, smell, taste, sight and hearing.
Internal receptors (interocepyors): these sense organs found in the body which detect the temperature, pain, hunger, thirst, fatigue and muscle position.
Why do animals need to breathe?
Breathing is important to organisms because cells require energy (oxygen) to move, reproduce and function. Breath also expels carbon dioxide, which is a by-product of cellular processes within the bodies of animals.
Respiration is the process of releasing energy from food and this takes place inside the cells of the body.
The process of respiration involves taking in oxygen (of air) into cells, using it for releasing energy by burning food, and then eliminating the waste products (carbon dioxide and water) from the body.
Respiration is essential for life because it provides energy for carrying out all the life processes which are necessary to keep the organisms alive.
The energy produced during respiration is stored in the form of ATP (Adenosine Tri- Phosphate) molecules in the cells of the body and used by the organism as when required.
KEY POINTS
Life started in an anaerobic environment in the so called ‘primodial broth’ (a mixture of organic molecules.
Subsequently, oxygen strangely enough became an crucial factor for aerobic metabolism especially in the higher life forms.
The rise of an oxygenic environment was an important event in the diversification of life.
It evoked a dramatic shift from inefficient to sophisticated oxygen dependent oxidizing ecosystems.
Anaerobic fermentation, the metabolic process that prevailed for the first about 2 billion years of the evolution of life, was a very inefficient way of extracting energy from organic molecules. Ex: A molecule of glucose, e.g., produces only two molecules of ATP (≈ 15 kCal) compared with 36 ATP molecules (≈ 263 kCal) in oxygenic respiration.
Aerobic metabolism must have developed at a critical point when the partial pressure of oxygen rose from an initial level to one adequately high to drive it passively across the cell membrane.
Respiration is a complex and highly integrated biomechanical, physiological, and behavioral processes.
The transfer of O2 occurs through a flow of tissue barriers and compartments by diffusion down a partial pressure gradient, which drops to about zero at the mitochondrial level.
Acquisition of molecular oxygen (O2) from the external fluid media (water and air) and the discharge of carbon dioxide (CO2) into the same milieu is the primary role of respiration.
The respiratory system is a biological system consisting of specific organs and structures.
The vertebrate brain
The vertebrate brain is the main part of the central nervous system. The brain and the spinal cord make up the central nervous system,
In most of the vertebrates the brain is at the front, in the head. It is protected by the skull and close to the main sense organs.
Brains are extremely complex and the part of human and animal body. The brain controls the other organs of the body, either by activating muscles or by causing secretion of chemicals such as hormones and neurotransmitters.
Muscular action allows rapid and coordinated responses to changes in the environment.
The brain of an adult human weights about 1300–1400 grams .
In vertebrates, the spinal cord by itself can cause reflex responses as well as simple movement such as swimming or walking. However, sophisticated control of behaviour requires a centralized brain.
The structure of all vertebrate brains is basically the same.
At the same time, during the course of evolution, the vertebrate brain has undergone changes, and become more effective.
In so-called 'lower' animals, most or all of the brain structure is inherited, and therefore their behaviour is mostly instinctive.
In mammals, and especially in man, the brain is developed further during life by learning. This has the benefit of helping them fit better into their environment. The capacity to learn is seen best in the cerebral cortex.
Three principles
The brain and nervous system is essentially a system which makes connections. It has input from sense organs and output to muscles. It is connected in several ways with the endocrine system, which makes hormones, and the digestive system and sex system. Hormones work slowly, so those changes are gradual.
The brain is a kind of department store. It has, all inter-connected, departments which do different things. They all help each other gather senses.
Much of what the body does is not conscious. Basically, much of the body runs on automatic (breathing, heart beat, hungry, hair growth) adjusted by the autonomic nervous system. The brain, too, does much of its work without a person noticing it. The unconscious mind refers to the brain activities which are hardly ever noticed.
DENTITION IN MAMMALS
The study of arrangement structure and number of types of teeth collectively is called as dentition. Teeth are present in the foetal as well as in adults of mammals, based on the presence of teeth Mammals are two types.
Edentata : In some animals teeth are absent hence called as edentate. e.g., Echidna or spiny ant-eater (Tachyglossus) the teeth are absent in all stages of life.
Dentata : Teeth are present in all mammals though a secon¬dary toothless condition is found in some mammals. Modern turtles and birds lack teeth. The adult platypus (Ornithorhynchus) bears epidermal teeth but no true teeth are present. In platypus embryonic teeth are replaced by horny epidermal teeth in adult.
Classification According to the Shape and Size of the Teeth:
Homodont:
Homodont or Isodont type of teeth is a condition where the teeth are all alike in their shape and size in the toothed whales e.g., Pinnipedians. Fishes, amphibians, reptiles and in the extinct toothed birds.
Heterodont
Heterodont condition is the usual feature in mammals, i.e. the teeth are distinguished according to their shape, size and function. The function is also different at different parts of the tooth row.
According to the Mode of Attachment of Teeth:
Thecodont : The teeth are lodged in bony sockets or alveoli of the jaw bone and capillaries and nerves enter the pulp cavity through the open tips of the hollow roots e.g., mammals, crocodiles and in some fishes.
Acrodont: The teeth are fused to the surface of the underlying jawbone. They have no roots and are attached to the edge of the jawbone by fibrous membrane e.g., fishes, amphibians and some reptiles.
Pleurodont:
The teeth are attached to the inner-side of the jawbone. The tooth touches the bone only with the outer surface of its root. In acrodont and pleurodont types of dentition, there are no roots, and nerves and blood vessels do not enter the pulp cavity at the base, e.g., Necturus (Amphibia) and some reptiles.
According to the Succession or Replace¬ment of Teeth:
Phylum Mollusca-my report..
sorry for some overlapping of texts... i was not able to edit it..it is actually because of the animations that i put it..... i just uploaded it directly :)
Central nervous system: The central nervous system consists of the brain and spinal cord. The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. Some reflex movements can occur via spinal cord pathways without the participation of brain structures. The spinal cord is connected to a section of the brain called the brainstem and runs through the spinal canal.
Peripheral Nervous System: Nerve fibers that exit the brainstem and spinal cord become part of the peripheral nervous system. Cranial nerves exit the brainstem and function as peripheral nervous system mediators of many functions, including eye movements, facial strength and sensation, hearing, and taste.
The autonomic nervous system: The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.
The autonomic nervous system comprises two antagonistic sets of nerves, the sympathetic and parasympathetic nervous systems. The hypothalamus is the key brain site for central control of the autonomic nervous system, and the paraventricular nucleus is the key hypothalamic site for this control.
Divisions of Nervous System:
The vertebrate nervous system has three divisions:
(i) A central nervous system comprising the brain and spinal cord. Its function is to receive the stimulus from the receptors and transmit its response to the effectors. Thus, it coordinates all the functions of the body.
(ii) A peripheral nervous system consisting of cranial and spinal nerves arising from the brain and spinal cord respectively. It forms a connecting link between the receptors, central nervous system (CNS) and effectors.
(iii) An autonomic nervous system made of two ganglionated sympathetic nerves, ganglia in the head and viscera, and their connecting nerves. The autonomic nervous system is often regarded as a part of the peripheral nervous system because the two are connected. But all the three divisions of the nervous system are connected intimately both structurally and functionally.
Sense organs are the specialized organs composed of sensory neurons, which help us to perceive and respond to our surroundings. There are five sense organs – eyes, ears, nose, tongue, and skin.
External receptors (exteroceptors): sense organs for touch, smell, taste, sight and hearing.
Internal receptors (interocepyors): these sense organs found in the body which detect the temperature, pain, hunger, thirst, fatigue and muscle position.
Why do animals need to breathe?
Breathing is important to organisms because cells require energy (oxygen) to move, reproduce and function. Breath also expels carbon dioxide, which is a by-product of cellular processes within the bodies of animals.
Respiration is the process of releasing energy from food and this takes place inside the cells of the body.
The process of respiration involves taking in oxygen (of air) into cells, using it for releasing energy by burning food, and then eliminating the waste products (carbon dioxide and water) from the body.
Respiration is essential for life because it provides energy for carrying out all the life processes which are necessary to keep the organisms alive.
The energy produced during respiration is stored in the form of ATP (Adenosine Tri- Phosphate) molecules in the cells of the body and used by the organism as when required.
KEY POINTS
Life started in an anaerobic environment in the so called ‘primodial broth’ (a mixture of organic molecules.
Subsequently, oxygen strangely enough became an crucial factor for aerobic metabolism especially in the higher life forms.
The rise of an oxygenic environment was an important event in the diversification of life.
It evoked a dramatic shift from inefficient to sophisticated oxygen dependent oxidizing ecosystems.
Anaerobic fermentation, the metabolic process that prevailed for the first about 2 billion years of the evolution of life, was a very inefficient way of extracting energy from organic molecules. Ex: A molecule of glucose, e.g., produces only two molecules of ATP (≈ 15 kCal) compared with 36 ATP molecules (≈ 263 kCal) in oxygenic respiration.
Aerobic metabolism must have developed at a critical point when the partial pressure of oxygen rose from an initial level to one adequately high to drive it passively across the cell membrane.
Respiration is a complex and highly integrated biomechanical, physiological, and behavioral processes.
The transfer of O2 occurs through a flow of tissue barriers and compartments by diffusion down a partial pressure gradient, which drops to about zero at the mitochondrial level.
Acquisition of molecular oxygen (O2) from the external fluid media (water and air) and the discharge of carbon dioxide (CO2) into the same milieu is the primary role of respiration.
The respiratory system is a biological system consisting of specific organs and structures.
The vertebrate brain
The vertebrate brain is the main part of the central nervous system. The brain and the spinal cord make up the central nervous system,
In most of the vertebrates the brain is at the front, in the head. It is protected by the skull and close to the main sense organs.
Brains are extremely complex and the part of human and animal body. The brain controls the other organs of the body, either by activating muscles or by causing secretion of chemicals such as hormones and neurotransmitters.
Muscular action allows rapid and coordinated responses to changes in the environment.
The brain of an adult human weights about 1300–1400 grams .
In vertebrates, the spinal cord by itself can cause reflex responses as well as simple movement such as swimming or walking. However, sophisticated control of behaviour requires a centralized brain.
The structure of all vertebrate brains is basically the same.
At the same time, during the course of evolution, the vertebrate brain has undergone changes, and become more effective.
In so-called 'lower' animals, most or all of the brain structure is inherited, and therefore their behaviour is mostly instinctive.
In mammals, and especially in man, the brain is developed further during life by learning. This has the benefit of helping them fit better into their environment. The capacity to learn is seen best in the cerebral cortex.
Three principles
The brain and nervous system is essentially a system which makes connections. It has input from sense organs and output to muscles. It is connected in several ways with the endocrine system, which makes hormones, and the digestive system and sex system. Hormones work slowly, so those changes are gradual.
The brain is a kind of department store. It has, all inter-connected, departments which do different things. They all help each other gather senses.
Much of what the body does is not conscious. Basically, much of the body runs on automatic (breathing, heart beat, hungry, hair growth) adjusted by the autonomic nervous system. The brain, too, does much of its work without a person noticing it. The unconscious mind refers to the brain activities which are hardly ever noticed.
DENTITION IN MAMMALS
The study of arrangement structure and number of types of teeth collectively is called as dentition. Teeth are present in the foetal as well as in adults of mammals, based on the presence of teeth Mammals are two types.
Edentata : In some animals teeth are absent hence called as edentate. e.g., Echidna or spiny ant-eater (Tachyglossus) the teeth are absent in all stages of life.
Dentata : Teeth are present in all mammals though a secon¬dary toothless condition is found in some mammals. Modern turtles and birds lack teeth. The adult platypus (Ornithorhynchus) bears epidermal teeth but no true teeth are present. In platypus embryonic teeth are replaced by horny epidermal teeth in adult.
Classification According to the Shape and Size of the Teeth:
Homodont:
Homodont or Isodont type of teeth is a condition where the teeth are all alike in their shape and size in the toothed whales e.g., Pinnipedians. Fishes, amphibians, reptiles and in the extinct toothed birds.
Heterodont
Heterodont condition is the usual feature in mammals, i.e. the teeth are distinguished according to their shape, size and function. The function is also different at different parts of the tooth row.
According to the Mode of Attachment of Teeth:
Thecodont : The teeth are lodged in bony sockets or alveoli of the jaw bone and capillaries and nerves enter the pulp cavity through the open tips of the hollow roots e.g., mammals, crocodiles and in some fishes.
Acrodont: The teeth are fused to the surface of the underlying jawbone. They have no roots and are attached to the edge of the jawbone by fibrous membrane e.g., fishes, amphibians and some reptiles.
Pleurodont:
The teeth are attached to the inner-side of the jawbone. The tooth touches the bone only with the outer surface of its root. In acrodont and pleurodont types of dentition, there are no roots, and nerves and blood vessels do not enter the pulp cavity at the base, e.g., Necturus (Amphibia) and some reptiles.
According to the Succession or Replace¬ment of Teeth:
Phylum Mollusca-my report..
sorry for some overlapping of texts... i was not able to edit it..it is actually because of the animations that i put it..... i just uploaded it directly :)
Objective of the study:- Structure of a typical Neuron, Classification of Neuron based on Polarity, on conduction direction, on neurotransmitters released, on their shape, Glial cells, major type of Glial cells present in CNS and PNS and their functions.
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For more information, visit-www.vavaclasses.com
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This will be used as part of your Personal Professional Portfolio once graded.
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Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
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2. VERTEBRATE AND INVERTEBRATE NERVE PHYSIOLOGY
What are the major differences between vertebrates and invertebrates?
3. Typical examples of vertebrates and invertebrates
The differences mentioned above account for the nerve physiology in
the mentioned example of these categories given below
8. Illustration of invertebrate nerves
• How are invertebrate able to be sentient (responsive, sensitive, feel,
emotions, perceptive)?. The answer to this question require an
understanding of their nerve structure and function.
• The most important is the organization of their nervous system
(centralization of their nervous systems and presence of structure that
enables sentience to arise) and the size of the nervous systems
9. Phylum: Cnidaria
Examples Jellyfish, sea anemones, coral
• The nervous system size may be of approximately 5,000-
20,000 nerve cells in a jellyfish. contain diffuse nerve nets,
which transmit information bi-directionally (signals can travel
in either direction through the network)
Centralization
• The nervous system consists of one or more nerve nets.
Information is likely to be integrated in the sensory ganglia.
• These animals possess a central nerve net rather than a body
concentrating neurons.
• Diffuse and/or through-conduction nerve nets.
Important structures
Sensory ganglia.
Comparative physiology
Seems that among invertebrates with nervous systems, these
have some of the most decentralized ones.
10. Phylum: Echinodermata
Examples
• Starfish, sea urchins, sea cucumbers
Centralization
• These animals have a circumoral nerve ring, which may be analogous
to a brain.
• However, it may be that most sensory input is integrated peripherally
and that there is no need for a central brain structure.
• Ectoneural subsystem, containing the circumoral nerve ring and outer
part of the radial nerve cords. Includes sensory and motor
components.
Important structures
• Hyponeural subsystem, a thinner, inner layer of the radial nerve cords
thought to control locomotion.
Comparative physiology
• As in cnidaria, these are very decentralized nervous systems that do
not contain a centralized concentration of neurons.
11. Phylum: Nematoda
Examples
• Roundworms
Centralization
• These animals have highly centralized nervous systems, with most
neurons concentrated in several anterior ganglia. There is a distinct
brain region which forms a ring shape.
Important structures
• Circumoral nerve ring. Anterior ganglia.
Comparative physiology
• The C. elegans connectome, like the brains of vertebrates such as
mammals, features highly connected hubs, which are themselves
interconnected in a central core structure.
• Thus, the macroscopic organization of the C. elegans nervous system
shows scale-invariant conservation with the brains of vertebrates
over many orders of magnitude of anatomical complexity.
12. Phylum: Platyhelminthes
Examples
• Flatworms
Centralization
• They have a centralized nervous system with a distinct brain
located in the head. This brain receives and integrates
information from sensory structures across the whole body.
Important structures
• Centralized brain structure located in the head.
Comparative physiology
• Continuous EEG waveforms have been recorded from the
planarian brain.
• The continuous waveforms suggest the existence of
feedback loop circuits in the neural network.
• This continuous waveform is similar to that recorded from
more developed brains.
13. Phylum: Annelida
Examples
• Earthworms, leeches
Centralization
• Some of these animals have a centralized nervous system with a
distinct brain. Some taxa contain higher brain structures such as
mushroom bodies (also found in arthropods). However, most
annelids lack these brain structures.
• The standard annelid brain is ring-shaped with two cerebral
ganglia.
Important structures
• Two cerebral ganglia forming a bilobed brain (in most annelids).
Mushroom bodies and glomerular neuropil (in some annelids).
Comparative physiology
• Some annelid brains can be divided into fore, mid and hind
sections (this mirrors the gross structure of advanced brains such
as the human brain).
• Some taxa contain mushroom bodies, which are considered
higher brain centers in insects.
14. Phylum: Mollusca, Class: Bivalvia
Examples
• Clams, oysters, mussels
Centralization
• These animals’ nervous systems have some level of
centralization, as they include 3 pairs of ganglia
connected by a nerve cord.
Important structures
• Cerebropleural ganglia, visceral ganglia, pedal ganglia.
Comparative physiology
• Unlike in other molluscs, there is no distinctive brain
structure, although there is centralization in ganglia.
15. Phylum: Mollusca, Class: Gastropoda
Examples
• Snails and slugs
Centralization
• Typically contain 5 pairs of ganglia, including the cerebral
ganglia, which are structurally and functionally
differentiated and receive and send signals across the
body.
Important structures
• Cerebral ganglia (in head). Procerebrum (in cerebral
ganglia), which may contain the learning mechanism.
• 5 paired ganglia throughout body (typically).
Comparative physiology
• These nervous systems are similar to those of bivalves,
although a bit bigger and with ganglia serving as a brain.
16. Phylum: Arthropoda, Class: Insecta
Examples
• Bees, fruit flies, grasshoppers
Centralization
• They have a centralized nervous system with a distinct brain.
The insect brain is segmented into three main regions.
• One of these regions, the protocerebrum, contains the
mushroom bodies which contain a large proportion of the
overall neurons in the central nervous system.
• There is some decentralization – for example the ventral nerve
cord is able to direct complex action even when the central
brain complex has been completely disconnected.
Important structures
• Mushroom bodies, which are important for learning, memory
and integrating information.
17. Phylum: Arthropoda, Subphylum: Crustacea
Examples
• Crabs, lobsters, woodlice
Centralization
• Contains a central nervous system. The largest
ganglion in it is found at the anterior end and
functions as the brain.
Important structures
• Anterior ganglion (the brain).
Comparative physiology
• Crustacean brains are somewhere between insects
and cephalopods in terms of size and complexity.
18. Phylum: Mollusca, Class: Cephalopoda
Examples
• Octopuses, squids
Centralization
• Have a centralized nervous system with a central brain structure. However, only approximately 1/10 of an
octopus’ neurons are found in this central structure.
• It should be noted that of the three main designs of cephalopod nervous system, the nautilus system is
simpler than the decapod and octopod (although still more complex than any non-cephalopod mollusc).
Important structures
• The central brain structure (approx. 40 million neurons in octopuses). Particularly the vertical lobe, which
contains around 25 million of these neurons and is involved in learning and memory.
• Optic lobes (approx. 120-180 million neurons in octopi).
• Tentacles (approx. 300 million neurons in octopi). Appear to retain a significant amount of function without
connection to central brain.
Comparative physiology
• Evidence of greater decentralization than in vertebrates, since individual tentacles appear to contain the
necessary neural circuitry for voluntary movement.
• The brains of octopuses produce similar EEG recordings to vertebrates.
• Analogies have been drawn between lobes in the cephalopod brain and the thalamus in vertebrates, which
likely plays a role in pain and consciousness.
• Analogies have been drawn between the vertical lobe in the octopus and mushroom bodies in insects.
19. Typical vertebrate nerve systems
Examples
Birds, amphibians, reptiles, mammals
Centralization
Contains a central nervous system.
Anterior brain, axial spinal cord and
system of well organised nerves.
Important structures
CNS (the brain and Spinal cord), Nerves
Comparative physiology
Vertebrates have advanced brains and
spinal cord where information is
process quickly
The complexity in terms of size and
processing make them advanced.
20. Nerve physiology
• Ionic Equilibrium and Resting of Membrane Potential
ELECTROCHEMICAL POTENTIAL
Membrane Conductance
Definition
• Membrane conductance refers to the number of channels that are
open in a membrane. For example, Na + conductance is proportional
to the number of open channels that will allow the Na + to pass
through the membrane.
• It does not indicate if there will be a net diffusion of ions through the
channels.
21. General Properties
• If conductance is increasing, channels are opening, and if conductance is
decreasing, channels are closing
• The rate at which ions move across a membrane depends on the number of
open channels and the net force.
• When ions flow through channels, the cell's membrane potential changes.
• However, under physiological conditions, too few ions flow to produce a
significant effect on the ion's extracellular concentration or the concentration
gradient across the membrane.
• Channels are classified into three main groups:
• Ungated channels: Because these channels have no gates, they are always
open. For example, all cells possess ungated potassium channels.
• This means there will be a net flux of potassium ions through these channels
unless potassium is at equilibrium.
22. • Voltage-gated channels: In these channels, the gates open and/or
close in response to a membrane voltage change. For example, many
excitable cells possess voltage-gated sodium channels.
• The channels are dosed under resting conditions, but membrane
depolarization causes them to quickly open and then quickly close.
• Ligand-gated channels: The channel complex includes a receptor to a
specific substance (ligand).
• It is the interaction of the ligand with the receptor that regulates the
opening and dosing of the channel.
• For example, post-junctional membranes of chemical synapses possess
ligand-gated channels, and transmission depends on the interaction of
the transmitter and the ligand-gated channel
23. Net Force
• The net force acting on an ion across a membrane is the sum of two
independent forces.
Concentration Force
• Determined by the concentration difference across the membrane. The
greater the concentration difference, the greater the concentration force.
Electrical Force
• The size of this force is determined by the electrical difference across the
membrane (usually measured in millivolts [mV]).
• The in vivo magnitude is determined by the membrane potential (Em), which
is a value that must be measured or given.
• The direction of the force is based on the fact that like charges repel and
opposite charges attract. For example, if the membrane potential is -70 mV,
this represents a force of 70 mV that attracts all positive ions and repels all
negative ions.
24.
25. Important Points Regarding CI-
• Because the measured membrane potential and the calculated equilibrium
potential are the same in magnitude and charge, the chloride ions are at
equilibrium.
• No matter what the membrane conductance to chloride is, there will not be a
net diffusion of chloride ions, nor will a change in the conductance of chloride
in a steady-state situation alter the cell's membrane potential.
Important Points Regarding K +
• The potassium ion is not at equilibrium. The net force on the potassium ions is
15 mV. Because this is a small force, the potassium ions can be considered dose
to but not quite at equilibrium.
• Because all cells at all times have open potassium channels (ungated), there
must be a net flux of potassium ions across the membrane.
• Also, because the ion will always diffuse to bring the membrane potential closer
to the ion's equilibrium potential, the flux must be an efflux from the cell.
26. • Increasing potassium conductance will accelerate the efflux of potassium ions and
hyperpolarize the cell.
• Increased extracellular potassium ions will reduce the efflux of the potassium ions
or even create an influx of potassium ions, the net result of which will be
depolarization.
• Decreased extracellular potassium ions will accelerate the efflux of the potassium
ions, the net result of which will be hyperpolarization.
• Thus, a cell's resting membrane potential is very sensitive to changes in the
extracellular potassium ion concentration.
Important Points Regarding Na +
• The sodium ion is not at equilibrium. The net force on the sodium ions is 135 mV.
This is considered a large force; therefore, the sodium ions are a long way from
equilibrium.
• In most cells, including excitable cells under resting conditions, there is not a
significant number of open sodium channels (conductance dose to zero). Thus,
even though there is a large net force, flux is minimal.
• An increase in membrane conductance to sodium ions will produce an influx of
sodium ions and depolarization.
27. • Because sodium channels are dosed under resting conditions, changes
in extra cellular sodium will not affect the resting membrane potential.
• Thus, a cell's resting membrane potential is not sensitive to changes in
extra cellular sodium.
