Animal Nerve Cell Biography
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Nerve Nets
Cnidarians are radially symmetrical and have the simplest nervous system
Nerve network conducts signals from sensory cells to muscle cells.
There is no centralization of the nervous system.
Cephalization and Bilateral Symmetry
The anterior end of bilaterally symmetrical animals contains most of the sense organs because this end of the animal moves through the environment first. As evolution proceeded, the anterior end of the central nervous system became larger to accommodate these sense organs. The larger, anterior end of the central nervous system is called the brain. The development of the brain is called cephalization; highly cephalized animals have a large brain.
Flatworms
Bilateral symmetry has led to paired structures (nerves, muscles, sense organs, brain).
Some flatworms have a nerve net like Cnidarians but others show more organization including a brain and nerve cords.
Planarians
The nervous system of planarians resembles a ladder. It has two nerve cords with ganglia ("a brain") at the anterior end.
Sensory receptors are located in the auricles.
The eyespots contain photoreceptors.
Transverse nerves that connect the two cords keep movements of the two sides coordinated.
Mollusks
Mollusks show a great diversity of nervous systems. Some mollusks such as bivalves have no cephalization. Slow-moving animals have some cephalization, enabling sensory reception as the animal moves through the environment. The active predatory lifestyle of cephalopods require complex sense organs; they are highly cephalized.
Annelids, Arthropods
Annelids and arthropods have repeating segments and an anterior brain.
Each segment contains a ganglion; the nerve cord extends through all of the segments.
The ganglion in each segment controls the muscles of that segment. The brain exerts overall control to coordinate the animal.
Echinoderms
Sea stars have a central nerve ring and a nerve that extends from the ring into each arm. Each arm also contains a nerve net.
Vertebrates
Vertebrates have complex sense organs and exhibit complex behaviors. These require a complex nervous system. The vertebrate nervous system is extremely cephalized.
Divisions of the Vertebrate Nervous System
The central nervous system (CNS) is the brain and spinal cord.
The peripheral nervous system (PNS) is composed of the nerves and ganglia. Ganglia are clusters of nerve cell bodies outside the CNS.
Peripheral Nervous System
Nerves
Nerves are bundles of neurons; either long dendrites and/or long axons.
There are no cell bodies in nerves. The cell bodies are in the ganglia (PNS) or nuclei (in gray matter of the CNS).
Most nerves contain both kinds of neurons (sensory and motor). The sensory neurons conduct information to the CNS, the motor neurons conduct away from the CNS.
All of the neurons in some nerves conduct in the same direction. These nerves contain either sensory or motor neurons.
Cranial Nerves and Spinal Nerves
Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Cranial nerves are sensory, motor, or mixed, and all but the vagus are involved with the head and neck region; the vagus nerve manages the internal organs.
Spinal nerves are all mixed nerves. Their regular arrangement reflects the segmentation of the human body.
Spinal nerves are connected to the spinal cord by two branches called roots.
The dorsal root contains sensory neurons. The dorsal root ganglion contains the cell bodies of sensory neurons. Sensory neurons therefore have long dendrites.
The ventral root contains motor neurons. Motor neurons have short dendrites and long axons.
Somatic Nervous System
The somatic nervous system provides conscious, voluntary control.
It includes all of the nerves that serve the skeletal muscles and the exterior sense organs.
It also includes reflexes.
Reflex arcs
Reflexes are simple, stereotyped and repeatable motor actions (example: movements) brought about by a specific sensory stimulus. The reflex is involuntary but may involve the use of voluntary (skeletal) muscle and nerves.
Reflexes are quick and produce behaviors that are typically beneficial. For example, when you fall, reflex arcs immediately act to extend your arm so that your arm prevents your head and body from hitting the ground.
Some reflexes involve the brain, others do not.
A whole series of responses may occur since some sensory neurons stimulate several interneurons which, in turn send impulses to other parts of the CNS. If you were to fall forward, interneurons would use information from the ears to determine the direction of the fall and extend the arms in a forward direction. If you were to fall toward the left side, interneurons would select neurons that activate muscles to extend your arm to the left side.
Example: The stretch reflex
The stretch reflex is involved in helping the body maintain its position without having to consciously think about it.
Stretch-sensitive receptors in the muscles contain stretch-gated channels. When the muscle is stretched, the channels open, causing the neuron to depolarize. Action potentials are conducted to the spinal cord. The axon terminals synapse with motor neurons leading right back to the muscles. This causes the muscle to contract to its original position.
Autonomic Nervous System
This part of the nervous system sends signals to the heart, smooth muscle, glands, and all internal organs.
It is generally without conscious control.
The autonomic nervous system uses two or more motor neurons:
The cell body of one of the motor neurons is in the CNS. The cell body of the other one is in a ganglion.
Sympathetic Division
The sympathetic nervous system stimulates the body. For example, it helps prepare the body to deal with emergency situations. This is often called the "fight or flight" response.
Stimulation from sympathetic nerves dilates the pupils, accelerates the heartbeat, increases the breathing rate, and inhibits the digestive tract.
The neurotransmitter is norepinephrine.
Sympathetic nerves arise from the middle (thoracic-lumbar) portion of the spinal cord.
Parasympathetic Division
When there is little stress, the parasympathetic system tends to slow down the overall activity of the body.
It causes the pupils to contract, it promotes digestion, and it slows the rate of heartbeat.
The neurotransmitter is acetylcholine.
The actual rate of stimulus to each organ is determined by the sum of opposing signals from the sympathetic and parasympathetic systems.
Parasympathetic nerves arise from the brain and sacral (near the legs) portion of the cord.
Enteric Division
The enteric division contains neurons that control the digestive tract, pancreas, and gallbladder.
Activity of the enteric division is usually regulated by the sympathetic and parasympathetic divisions.
Evolution of Vertebrate Central Nervous Systems
The central nervous system evolved in vertebrates by adding on to what was there. The oldest parts of the human nervous system deal with reflexes. Newer additions and modifications are associated with memory, learning, and thinking.
Central Nervous System
The central nervous system is the brain and spinal cord.
It is wrapped in 3 layers of membranes called meninges. Meningitis is an infection of these coverings.
The brain contains fluid-filled ventricles that are continuous with the central canal of the cord. Fluid within the ventricles and central canal originates from the blood. It slowly circulates, carrying nutrients and wastes from cells. The fluid eventually returns to the circulatory system and is replaced by fresh fluid
Cnidarians are radially symmetrical and have the simplest nervous system
Nerve network conducts signals from sensory cells to muscle cells.
There is no centralization of the nervous system.
Cephalization and Bilateral Symmetry
The anterior end of bilaterally symmetrical animals contains most of the sense organs because this end of the animal moves through the environment first. As evolution proceeded, the anterior end of the central nervous system became larger to accommodate these sense organs. The larger, anterior end of the central nervous system is called the brain. The development of the brain is called cephalization; highly cephalized animals have a large brain.
Flatworms
Bilateral symmetry has led to paired structures (nerves, muscles, sense organs, brain).
Some flatworms have a nerve net like Cnidarians but others show more organization including a brain and nerve cords.
Planarians
The nervous system of planarians resembles a ladder. It has two nerve cords with ganglia ("a brain") at the anterior end.
Sensory receptors are located in the auricles.
The eyespots contain photoreceptors.
Transverse nerves that connect the two cords keep movements of the two sides coordinated.
Mollusks
Mollusks show a great diversity of nervous systems. Some mollusks such as bivalves have no cephalization. Slow-moving animals have some cephalization, enabling sensory reception as the animal moves through the environment. The active predatory lifestyle of cephalopods require complex sense organs; they are highly cephalized.
Annelids, Arthropods
Annelids and arthropods have repeating segments and an anterior brain.
Each segment contains a ganglion; the nerve cord extends through all of the segments.
The ganglion in each segment controls the muscles of that segment. The brain exerts overall control to coordinate the animal.
Echinoderms
Sea stars have a central nerve ring and a nerve that extends from the ring into each arm. Each arm also contains a nerve net.
Vertebrates
Vertebrates have complex sense organs and exhibit complex behaviors. These require a complex nervous system. The vertebrate nervous system is extremely cephalized.
Divisions of the Vertebrate Nervous System
The central nervous system (CNS) is the brain and spinal cord.
The peripheral nervous system (PNS) is composed of the nerves and ganglia. Ganglia are clusters of nerve cell bodies outside the CNS.
Peripheral Nervous System
Nerves
Nerves are bundles of neurons; either long dendrites and/or long axons.
There are no cell bodies in nerves. The cell bodies are in the ganglia (PNS) or nuclei (in gray matter of the CNS).
Most nerves contain both kinds of neurons (sensory and motor). The sensory neurons conduct information to the CNS, the motor neurons conduct away from the CNS.
All of the neurons in some nerves conduct in the same direction. These nerves contain either sensory or motor neurons.
Cranial Nerves and Spinal Nerves
Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Cranial nerves are sensory, motor, or mixed, and all but the vagus are involved with the head and neck region; the vagus nerve manages the internal organs.
Spinal nerves are all mixed nerves. Their regular arrangement reflects the segmentation of the human body.
Spinal nerves are connected to the spinal cord by two branches called roots.
The dorsal root contains sensory neurons. The dorsal root ganglion contains the cell bodies of sensory neurons. Sensory neurons therefore have long dendrites.
The ventral root contains motor neurons. Motor neurons have short dendrites and long axons.
Somatic Nervous System
The somatic nervous system provides conscious, voluntary control.
It includes all of the nerves that serve the skeletal muscles and the exterior sense organs.
It also includes reflexes.
Reflex arcs
Reflexes are simple, stereotyped and repeatable motor actions (example: movements) brought about by a specific sensory stimulus. The reflex is involuntary but may involve the use of voluntary (skeletal) muscle and nerves.
Reflexes are quick and produce behaviors that are typically beneficial. For example, when you fall, reflex arcs immediately act to extend your arm so that your arm prevents your head and body from hitting the ground.
Some reflexes involve the brain, others do not.
A whole series of responses may occur since some sensory neurons stimulate several interneurons which, in turn send impulses to other parts of the CNS. If you were to fall forward, interneurons would use information from the ears to determine the direction of the fall and extend the arms in a forward direction. If you were to fall toward the left side, interneurons would select neurons that activate muscles to extend your arm to the left side.
Example: The stretch reflex
The stretch reflex is involved in helping the body maintain its position without having to consciously think about it.
Stretch-sensitive receptors in the muscles contain stretch-gated channels. When the muscle is stretched, the channels open, causing the neuron to depolarize. Action potentials are conducted to the spinal cord. The axon terminals synapse with motor neurons leading right back to the muscles. This causes the muscle to contract to its original position.
Autonomic Nervous System
This part of the nervous system sends signals to the heart, smooth muscle, glands, and all internal organs.
It is generally without conscious control.
The autonomic nervous system uses two or more motor neurons:
The cell body of one of the motor neurons is in the CNS. The cell body of the other one is in a ganglion.
Sympathetic Division
The sympathetic nervous system stimulates the body. For example, it helps prepare the body to deal with emergency situations. This is often called the "fight or flight" response.
Stimulation from sympathetic nerves dilates the pupils, accelerates the heartbeat, increases the breathing rate, and inhibits the digestive tract.
The neurotransmitter is norepinephrine.
Sympathetic nerves arise from the middle (thoracic-lumbar) portion of the spinal cord.
Parasympathetic Division
When there is little stress, the parasympathetic system tends to slow down the overall activity of the body.
It causes the pupils to contract, it promotes digestion, and it slows the rate of heartbeat.
The neurotransmitter is acetylcholine.
The actual rate of stimulus to each organ is determined by the sum of opposing signals from the sympathetic and parasympathetic systems.
Parasympathetic nerves arise from the brain and sacral (near the legs) portion of the cord.
Enteric Division
The enteric division contains neurons that control the digestive tract, pancreas, and gallbladder.
Activity of the enteric division is usually regulated by the sympathetic and parasympathetic divisions.
Evolution of Vertebrate Central Nervous Systems
The central nervous system evolved in vertebrates by adding on to what was there. The oldest parts of the human nervous system deal with reflexes. Newer additions and modifications are associated with memory, learning, and thinking.
Central Nervous System
The central nervous system is the brain and spinal cord.
It is wrapped in 3 layers of membranes called meninges. Meningitis is an infection of these coverings.
The brain contains fluid-filled ventricles that are continuous with the central canal of the cord. Fluid within the ventricles and central canal originates from the blood. It slowly circulates, carrying nutrients and wastes from cells. The fluid eventually returns to the circulatory system and is replaced by fresh fluid
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
Animal Nerve Cell Animal Cell Model Diagram Project Parts Structure Labeled Coloring and Plant Cell Organelles Cake
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