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Bio Chap 35: Animal Nervous System
Terms in this set (90)
What multicellular animals possess a nervous system?
Except for sponges, all multicellular animals possess a nervous system
What is a nervous system?
network of interconnected neurons (nerve cells).
What is the Neuron?
The neuron is the basic functional unit of the nervous system.
(TRUE OR FALSE) Nervous systems evolved to be more complex as other body systems became more complex
How many types of nerve cells do animals have? What are they?
Animal nervous systems have three types of nerve cells: the sensory neurons, interneurons, and motor neurons.
What do sensory neurons do?
Sensory neurons receive and transmit info about an animal's environment or its internal physiological state. They respond to features like temperature, light, touch, odor, taste, etc.
What do interneurons do?
Interneurons process the info received by the sensory neurons and transmit it to different body regions
What do motor neurons do?
Motor neurons receive the info from interneurons and act to make a reaction happen such as flexing a muscle, constricting or dilating blood vessels, or causing wavelike contractions of the gut to aid digestion.
Why is the nervous system so important?
The nervous system's actions and functions are extremely important for maintaining homeostasis, which is the ability of animals, organs, etc to regulate and maintain a stable internal state.
Where did the ability to process info first evolve in neurons?
The ability to process information first evolved with the formation of ganglia (singular, ganglion) which are groups of nerve cell bodies that process sensory information received from a local, nearby region (there are these in our stomachs). Eventually the brain evolved (look up its definition if you don't know what a brain is)
In general, what does the organization and complexity of an animals nervous system usually reflect?
The organization and complexity of an animal's nervous system reflects its lifestyle. So simple and immobile organisms have relatively simple nervous systems and complex organisms that move around a lot have more complex nervous systems. Again, the sponge is the only multicellular organism that lacks a nervous system for some reason.
Where are the simplest nervous systems found?Describe.
The simplest nervous systems are found in cnidarians, which are radially symmetric animals such as jellyfish and sea anemones. There are few neurons and no ganglia or central brains in these animals. Neurons are arranged in a net, often organized around a central body cavity.
More complex nerve connections develop in the head end of flatworms, segmented annelid worms, insects, and cephalopod mollusks, such as squid and octopus.
What is the overall group that contains these animals: flatworms, segmented annelid worms, insects, and cephalopod mollusks, such as squid and octopus.
These animals are all bilaterians, animals with symmetrical right and left sides and a distinct front and back end.
Why are bilaterian nervous systems important?
These nervous systems are important in determining and sensing information from in front of the body while moving forward. Paired ganglia do this in flatworms.
In animals with an organized nervous system, how is info transmitted?
In animals with an organized nervous system, info is transmitted to different regions along the length of the animal's body by distinct nerve cords and nerves (bundles of fiber-like extensions from multiple nerve cells)
Where are centralized collections of neurons forming a brain located?
They are present in annelid worms, insects, and mollusks.
How many neurons do a fruit fly, cockroach, mouse and human have in comparison to each other?
Be aware that in terms of animal brains, fruit flies have 250,000 neurons in them, cockroaches have about a million, mice have about 75 million, and humans have about 100 billion
What is Cephalization?
The concentration of nervous system components at one end of the body (makes it the front). This is inherent in most multicellular organisms.
(TRUE OR FALSE) Cephalization evolved independently several times.
TRUE - Cephalization most likely offers several advantages, which likely include the ability to sense stimuli ahead of the organism and to process it.
Neurons share a common organization, what are they?
A large cell body from which emerge two kinds of fiber-like extensions: dendrites and axons.
What are dendrites?
Dendrites receive signals from other nerve cells, or, in the case of sensory nerves, from specialized sensory endings. These signals travel along the dendrites to the neuron's cell body.
Where and what is the axon hillock?
The Axon hillock is located at the junction between the cell body and the axon and is where the signals are summed. If the sum is high enough, the neuron then fires an action potential, or nerve impulse that travels down the axon.
What do Axons do?
Axons transmit information away from the cell body to the axon terminal (the end of each axon swells a bit and is called the axon terminal). The terminal communicates with a neighboring cell through a junction called a synapse.
What is a synapse?
A space, the synaptic cleft, separates the end of the axon of the presynaptic cell and the neighboring postsynaptic cell. Is about 10 to 20 nm wide.
What do neurotransmitters do?
Describe the process all the way until the target cell. Neurotransmitters convey the signal from the end of the axon to the target cell. This is accomplished when a signal reaches the terminal. This causes vesicles to form, trapping neurotransmitters and pushing them out into the synapse, where they then diffuse across the synapse and bind to receptors on the plasma membrane of the target cell. This causes a change in the electrical charge across the membrane of the target cell which produces a signal in it which then propagates down the target cell.
Some neurons do not synapse with other neurons, but instead with other types of cell that produce some response in the animal. Give two example of this
Muscle cells and secretory cells in response to motor neurons.
(TRUE OR FALSE) Axons usually have fewer branches than dendrites.
What is the integration of information?
The process of bringing together information gathered from different sources
Neurons are supported by other types of cells. What are these supporting cells?
Glial cells and Astrocytes
What are Glial cells?
Glial cells are a major class of supporting cell. Glial cells surround neurons and provide them with nutrition as well as physical support. During development they orient neurons while they develop their connections.
What's an example of glial cells being the major class of supporting cells?
The human brain has more glial cells than neurons.
What are Astrocytes?
Astrocytes (star-shaped glial cells) contribute to the blood-brain barrier, a set of structural adaptations of the blood vessels supplying the brain that prevent pathogens and toxic compounds in the blood from entering the brain (although small things like alcohol still affect the brain since they can get in)
Glial cells also provide electrical insulation to vertebrate neurons. What do they form in order to do this?
They form multiple lipid-rich layers or sheaths called myelin sheaths which wrap around the axons of neurons and help them more speedily relay information.
What kind of cell is a Schwann cell?
A Glial cell
What type of cells produce the mylelin sheath?
What are Schwaan cells?
Schwann cells are Glial cells that insulate sensory and motor neurons (peripheral nervous system). They also produce the myelin used by myelin sheath cells.
What are oligodendrocytes?
Oligodendrocytes insulate brain cells and those in the spinal cord (central nervous system) whereas schwann cells insulate sensory and motor neurons (the peripheral nervous system).
Is the resting membrane potential positive or negative? Why is this?
The resting membrane potential is negative and results in part from the movement of potassium ions
What causes an action potential to move?
The propagation of an electrical charge down a neuron causes an action potential to move.
What is the difference in electrical charge called?
The difference in electrical charge is the voltage and is measured in volts.
What is the cells membrane potential caused by?
The charge difference between the inside and outside of a neuron is the cell's membrane potential.
What are the only type of cells that response to changes in their membrane potential?
Only nerve cells and muscle cells respond to changes in their membrane potential.
At rest, when no signal is being received or sent, the cell's membrane voltage is negative on its inside relative to its outside- What does this mean?
This means the cell is polarized.
What is the resting membrane potential of a cell? (Give approximations)
The resting membrane potential is about -40 to -85 millivolts (most commonly -65 to -70 mV).
At rest, where are the sodium ions and potassium ions in relation to the cell membrane?
At rest sodium ions are outside the cell more and potassium ions are inside the cell more (be aware of the sodium-potassium pump)
What largely determines the resting membrane potential?
It is the movement of K ions relative to other ions that largely determines the resting membrane potential.
What happens in the depolarization step of an action potential?
The increase in membrane potential is depolarization of the membrane. It causes voltage-gated sodium channels to open, allowing sodium ions to enter the cell. Voltage-gated channels (VGC) open in response to changes in membrane potential.
What happens if a nerve impulse is strong enough to depolarize the membrane of the nerve cell body? How much must the voltage be above resting membrane potential in order to do this?
The voltage must be around 15 mV above the resting membrane potential (for most, to about -50 mV) for the nerve to fire an action potential at the axon hillock. When this happens, the threshold potential is reached, and the nerve goes all-or-nothing, and spikes the voltage up to +40 mV within 1-2 msecs. This is an example of positive feedback where an response is enhanced by itself leading to a greater response to a stimuli.
What is hyperpolarization/undershoot? What does this help do?
Sodium VGCs close automatically after a certain time, and potassium VGCs open automatically after a time. This leads to the membrane potential peaking and then falling again. It briefly falls below the resting potential (hyperpolarization/undershoot) which helps reestablish the resting potential accurately.
During what stage can the cell not response to another impulse?
During the hyperpolarization stage, the cell cannot respond to another impulse, and is in a refractory period.
Does the sodium and potassium ever run out?
There are always available ions for this process (action potential).
Does the amount of sodium/potassion released affect the strength of the action potential?
Yes, generally, a higher firing frequency codes for a more intense stimulus (such as a brighter light) or a stronger signal transmitted by the nerve cell to other cells it contacts.
How to neurons propogate action potentials?
Neurons propagate action potentials along their axons by sequentially opening and closing adjacent Sodium and potassium ion channels.
What are the nodes of Ranvier?
In regards to myelin, which help impulses self-propagate faster; at regular intervals, the axon membrane is exposed at sites called nodes of Ranvier that lie between adjacent segments wrapped with myelin.
Where are the voltage gated channels primarily located?
The VGCs are concentrated at the Nodes of Ranvier-which makes signals seem to "jump" from node to node rather than be continuously propagated at the same rate. This speeds up propagation.
Where do Neurons communicate with each other?
They communicate at synapses
What are the two types of synapses?
There are two types of synapses: electrical, and chemical.
What are electrical synapses?
Electrical synapses provide direct electrical communication through gap juntions that form between neighboring cells. They likely help to speed up information processing (not absolutely confirmed
What are chemical synapses?
Chemical synapses are much more common than electrical synapses, and use neurotransmitters. When an action potential reaches the end of an axon the resulting depolarization induces voltage-gated calcium ion channels to open (found only in axon terminal membranes). These ions diffuse through these channels into the axon terminal. In response to this rise in concentration, the vesicles fuse with the presynaptic membrane and release neurotransmitter molecules into the synaptic cleft by exocytosis.
What are the two types of signals made by neurons?
Signals between neurons can be excitatory or inhibitory
(TRUE OR FALSE) Neurotransmitters can either stimulate or inhibit the firing of action potentials. It depends on the importance of the signal being processed. In a situation where someone is about to shoot you, sensory impulses coming in about the itch on your stomach are inhibited because at that moment you don't particularly care about that. But the sensory impulses that show you information about the dangerous situation at hand are enhanced since you care about that.
TRUE (lol literally didn't know how else to make this a question)
What is EPSP?
Excitatory postsynaptic potential (EPSP) which is the enhancing.
What is IPSP?
Inhibitory postsynaptic potential (IPSP) which is the inhibiting.
What stage of an action potential makes a neuron more likely to response to an action potential and what stage inhibits the neuron from sending an action potential?
Membrane depolarization makes a neuron more likely to respond to an action potential while hyperpolarization inhibits the neuron from sending an action potential. The relationship between these kinds of postsynaptic potentials is also important for coordinated movement as well as gut movements and the like.
(TRUE OR FALSE) EPSPs and IPSPs can be summed over time and space.
What is temporal summation?
Temporal summation deals with frequency of synaptic stimuli deciding whether or not a neuron fires an action potential.
What is spatial summation?
Spatial summation deals with the number of synaptic stimuli being received from different regions determining whether or not a neuron fires.
What are the following examples of? Note if they are exitatory or inhibitory. Glutamate, Glycine, GABA, dopamine, norepinephrine, and serotonin
The amino acids glutamate (excitatory), glycine (inhibitory), and GABA (inhibitory) as well as dopamine, norepinephrine, and serotonin act as neurotransmitters in the brain.
(TRUE OR FALSE) Simple peptides are neurotransmitters for sensory neurons? What two compounds have recently been discovered as neurotransmitters?
TRUE. Recently it's been discovered that nitrous oxide and carbon monoxide are also neurotransmitters for various part of the nervous system.
What is acetylcholine?
Acetylcholine is the excitatory neurotransmitter released by motor neurons to stimulate muscle fibers at a type of synapse called the motor endplate. All vertebrate motor synapses rely on acetylcholine and are therefore excitatory only.
What make up the peripiheral nervous system?
Sensory and motor nerves as well as interneurons and ganglia make up the peripheral nervous system (PNS)
What makes up the Central Nervous System?
The brain and spinal cord make up the central nervous system (CNS)
What neurons send signals toward the CNS?
Afferent neurons send signals toward the CNS (info from the periphery)
What neurons send signals toward the PNS?
Efferent neurons send signals away from the CNS (info towards the periphery)
(TRUE OR FALSE)
The spinal cord is divided into segments, each controlling body movement in a particular region along the animal's length. Each segment contains axons from peripheral sensory neurons, a set of interneurons, and a set of motor neuron cell bodies (all distinct from but associated with ganglia that lie outside the spinal cord)
How is the PNS organized?
The PNS is organized into left and right sets of cranial nerves located within the head and spinal nerves running from the spinal cord to the periphery. Most of the cranial nerves and all of the spinal nerves contain axons of both sensory and motor neurons. Cranial nerves link specialized sensory organs (eyes ears tongue) to the brain-as well as control eye movement, facial expression, speech, feeding, etc.
The Nervous systems has both voluntary and involuntary components, what are they?
Somatic and Automatic
What does it mean to be somatic?
What does it mean to be autonomic?
involuntary or visceral
Do you walk on purpose?
Do you make your heart beat on purpose?
What is the sympathetic nervous system used for?
Sympathetic nervous system is used for exciting or arousing the organism
What is the parasympathetic nervous system used for?
The parasympathetic nervous system is largely complimentary and calms the organism.
(TRUE OR FALSE)
The nervous system helps to maintain homeostasis
What happens when negative feedback is used?
A stimulus acts on a sensor that communicates with an effector, which produces a response that opposes the initial stimulus until it is resolved (different from positive in that it doesn't lead to signal enhancement, but rather the signal appropriately decreases until the issue is resolved)
What part of the brain acts as the body's thermostat?
The nerve cells in the hypothalamus act as the body's thermostat-thermoregulation is the most common association with the term homeostasis.
How are we able to react quickly to stimuli?
Simple reflex circuits provide rapid responses to stimuli. Fast responses are possible due to simple reflex circuits that bypass the brain by directly connecting sensory neurons with motor neurons.
When is an example of a simple reflex circuit reaction?
When you accidentally touch a hot stove-top, you withdraw your hand before you really think about how hot the stove is. If you had to wait for your brain to think about it, you'd have taken more burn damage (lowering your Pokemon's attack stat). Also know that the knee-jerk reflex is an example of this.
What is reciprocal inhibition?
The relationship between muscles with opposite movements. You can't flex your biceps and triceps in the same functional movement or else you'd tear both muscles since they are used for opposite movements. If that wasn't clear, you can also think like this: using the same neck at the same time, you can't turn your head left and right at the same time because doing so would tear up your neck muscles.
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