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Chapter 48 Collaboration 2010
Members share responsibility for posting refined answers to the guided readings -
succinct, relevant, clear,
When contributing to the reading guide, follow these steps:
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Chapter 48 Guided Reading Assignment
1. What is a nerve net?
A nerve net is the structure that the neurons controlling the contraction of the gastro-vascular cavity are arranged in
2. Compare and contrast the central and peripheral nervous systems.
The central nervous system (CNS) consists of a brain and longtitudinal nerve cords that extend all the way down to the posterior of the body. All other nerves that send feedback to the CNS via the longitudinal nerve cords or ganglion (nerve clusters) are known collectively as the Peripheral Nervous System (PNS).
CNS- small brain and long logitudinal nerve cords- found in simple organisms such as worms.
PNS-nerves that connect the CNS with the rest of the body.
Below is a video describing the difference in depth:
3. How does the organization of the nervous system of a _ compare with the organization of the nervous system of a ?
a. Hydra and insect
Hydra is made up of a nerve net
Insects have a brain, nerve cord, transverse nerves and eye spots
b. Hydra and flatworm
The hydra lacks a CNS, relying on their nerve net for simple life functions. The flatworm has a simple CNS due to its brain and the collection of lateral nerve cords down its body. Thanks to this it has more complex movement capabilities.
c. Leech and salamander
The leech is an invertebrate, meaning it has no backbone. Instead, it has a CNS made of a small ventral nerve cord lined by ganglia. The salamander, a vertebrate, has a spinal cord (dorsal nerve cord) that attaches to its more complex brain. Along the back bone are clusters of sensory ganglia on both sides of the backbone and tail. The brain is complex enough for eyesight and some primal reasoning while the ganglia around the body and tail control complex quadruped movement and control of its powerful tail.
4. What are the functions of the following:
a. Sensory neurons- receive outside stimuli (heat, touch, light, etc.) and data from within the body (heart rate, hunger, need for O2, etc.) and transmit the data to the interneurons.
b. Interneurons- collect data from sensory neurons (PNS) and process it based on current status and past experience (logic in CNS), then relay an appropriate action to the motor neurons.
c. Motor neurons- receive commands from the interneurons (CNS) and create a response by communicating with surrounding effector cells.
d. Effector cells- cells like muscle cells and endocrine cells that respond to the commands of the motor neurons and perform tasks as a result.
Here's a video about all these parts of the central nervous system:
(skip ahead to around 3:00; the rest is just basic info. about the nervous system) Above is another video, just for fun. -Sam V.
5. Why is it advantageous for the reflex response to circumvent instructions from the brain? Why might it be disadvantageous?
In some cases, a direct reaction from sensory neuron to motor neuron is necessary. When an event harmful to the body requires almost instant action to deal with, there is no time for the sensory nerves in the PNS to send the data all the way to brain's interneurons for processing. Instead, the data is picked up by a motor neuron connecting the spine to a muscle cell to stop the problem. Take this example:
In other cases, this could be a problem. If a nerve transmission from a sensory neuron completely bypasses the brain in a situation where some processing could be beneficial in preventing excess damage to the body, unnecessary pain or trauma can occur. Think about when you trip and fall. In the brief moment between the initial event (you tripping) and the resulting event (you face-planting/falling backward, potentially killing you), your brain takes in data from the PNS, commands motor neurons attached to your arms, and causes you to place your hands between your head and the floor. This comes in handy.
6. Describe the path of a nerve signal below.
The dendrites recieve signals from other neurons, then are passed to the axon. The axon transmits signals to other cells.( neurons or effector cells) The axon hillock that is the place where the conical region joins the cell body is where the signals that travel down the axon are generated. the axons are coverd by the myelin sheath which is an insulating coat that is interrupted by nodes of ranvier. that is where saltatory conduction occurs. then the axon divides into branches called synaptic terminals. they communicate between a synaptic terminal and other cells called synapses. the information is passed from the neron to the recving cell (neurotransmitter). this is what happens in the vertebrate neuron.
- Katie Halbruner
7. Why are glial cells important?
They are important because they are supporting cells. They are essential for the structural integrity of the nervous system and for the normal functioning of neurons. They outnumber neurons in the mammal brain.
8. What are astrocytes?
Astrocytes are located in the Central Nervous System, they have several important roles. The first role is structurally supporting the neuron, next they help to regulate the amount of ions as well as neurotransmitters. Over all Astrocytes help neurons obtain Glucose and Oxygen at a faster rate.
9. What is the blood brain barrier and why is it important?
The blood brain barrier is able to create a barrier between the brain tissue along with the circulating blood. This helps to protect the Central Nervous System. The way it protects the CNS is by controlling the passage way of substances.
10. Explain why myelin is important in nerve conduction?
The myelin sheath is very important in nerve conduction because it provides electrical insulation of the azon anaolgous to plastic insulation that covers many electrical wirse. it helps nerve signal transmisson because without the myelin sheath you could have extreme loss of body funnction, or disruption in the signal transmisson of the nerves.
- Katie Halbruner
11. Define the following terms:
a. Membrane potential
the charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions.
b. Resting potential
It is the membrane potential characteristic of a no conducting, excitable cell, with the inside of the cell more negative than the outside.
12. Discuss the three types of gated ion channels below:
The stretch gated ion channels are in cells that sense stretch. They open when the membrane is deformed.
THE The ligand gated channels are found at the synapses and they open or close when a certain chemical (neurotransmitter binds to the channel )
The voltage ion channels are in axons and sometimes in dendrites and cell bodies of neurons. they open or close when membrane potential changes.
- Katie Halbruner.
13. Define the following terms:
An electrical state in which the inside of the cell is more negative relative to the outside than at the resting membrane potential. A neuron membrane is hyperpolarized if a stimulus increases its voltage from the resting potential of -70 mV, reducing the chance that the neuron will transmit a nerve impulse.
An electrical state in an excitable cell whereby the inside of the cell is made less negative relative to the outside than at the resting membrane potential. A neuron membrane is depolarized if a stimulus decreases its voltage from the resting potential of -70mV in the direction of zero voltage.
A local voltage change in a neuron membrane induced by stimulation of a neuron, with strength proportional to the strength of the stimulus and lasting about a millisecond.
The potential an excitable cell membrane must reach for an action potential to be initiated.
A rapid change in the membrane potential of an excitable cell, causing by stimulus-triggered, selective opening and closing of voltage-sensitive gates in sodium and potassium ion channels.
In this video, it shows how action potential works and goes through the neuron (this is one of the most important concepts to understand in this chapter).
14. Use the diagram to describe the generation of an action potential.
The process of action potential begins when a stimulus opens a gate where Na+ goes through some sodium channels (depolarizes the membrane) as you can see in step 2. Then in step 3 mostly all sodium channels open allowing Na+ to come inside the membrane causing the inside of the membrane to turn positive (step 3). Then most of the sodium channels close and most of the Potassium channels open allowing K+ to efflux, making the inside of the cell negative (step 4). Then (step 5) both gates of the sodium channel are closed, but the activation gates of some potassium channels are still open. As the Potassium gates close, the inactivation gates open on the sodium channels, and the membrane returns to its resting state.
This video is a great example to show how the charges of inside outside the membrane changes as action potential is formed.
15. How do the various factors affect the speed of an action potential?
a. Larger axon:
The larger (wider) the axon’s diameter, the faster the conduction. This is because resistance to the flow of electrical current is inversely proportional to the cross-sectional area of a conductor (such as a wire or an axon).
b. Myelination and salutatory conduction
Myelination: Myelin increases the conduction speed of action potentials by insulating the axon membrane. Insulation has the same effect as increasing the axon’s diameter. The great advantage of myelination is its space efficiency.
Salutatory Conduction: Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.
Salutatory Conduction can transmit action potentials at speeds up to 120 m/s in myelinated axons.
The picture is a good reprisentation of how the myelin acts as a insulation for the axon. Thus allowing the information to pass quicker.
16. Use the diagram below to describe the conduction of the action potential.
1. an action potential is generated as Na+ flows inward across the membrane at 1 location.
2. to the left the membrane is repolarizing as K+ flows outward. depolarization of the action potential spreads to the neighboring region of the membrane reinitiating the action potential there.
3. the depolarization repolarization process is repeated in the next region of the membrane in the way local currents of ions across the plasma membrane cause the action potential to be propagated along the lenght of the axon.
17. What happens at the synaptic cleft?
action potential depolarizes membrane, opens Ca++ channels, neurotransmitter vesicles fuse with membrane, release neurotransmitter to synaptic cleft, neurotransmitter binds with protein receptor, ion-gated channels open, neurotransmitter degraded or reabsorbed
18. Contrast excitatory and inhibitory postsynaptic potentials.
excitatory postsynaptic potential- membrane potential is moved towards the threshold
inhibitory postsynaptic potential- membrane potential is moved away from the threshold
Spatial summation is a orderly firing of multiple action-potentials worth of neurotransmitters onto the postsynaptic neuron that will make reach the threshold and fire a subsequent action potential.
Whereas temporal summation is the single synapse firing a multiple of times, within succession of each other. As the neurotransmitter builds within the synapse, the single becomes stronger, to the post-synaptic neuron.
20. What happens when indirect synaptic transmission takes place?
This happens when a neurotransmitter is sent indirectly and connects and blocks the synaptic receptor.
When this happens it will block and inhibit it for several minutes or seconds.
21. Discuss the neurotransmitters listed below:
most common neurotransmitters in vertebrates and invertebrates. It is excitatory to vertebrate skeletal muscles.
b. Biogenic amines
i. Epinephrine and norepinephrine:
types of biogenic amines derived from amino acids. They are in the group catecholamines produced from tyrosine. They also function as hormones.
biogenic amine closely related to epinephrine and norepinephrine. It is released at many sites in the brain. Effects sleep, mood, attention, and learning.
biogenic amine synthesized from the amino acid tryptophan. Prozac enhances the effect of serotonin by inhibiting its uptake after release.
neurotransmitter at most inhibitory synapses in the brain and produces IPSPs by increasing the permeability of the postsynaptic membrane to Cl-.
neuropeptide that functions as a natural analgesic, decreasing pain perception. Opiates bind to receptors by mimicking endorphins, which are produced in the brain during times of physical or emotional stress, such as childbirth. It also decreases urine output by stimulating ADH secretion, depress respiration, produce euphoria, and have other emotional effects.
e. Nitrous oxide
dissolved gas released by neurons of the vertebrate PNS and CNS. it's released into the erectile tissue penis of a human male during sexual arousal. In response to the NO, smooth muscle cells relax, which causes the blood vessels to dilate and fill the erectile tissue with blood, producing an erection. Unlike typical neurotransmitters, NO is not stored in cytoplasmic vesicles, cells synthesize it on demand.
22. What is the difference between gray matter and white matter?
Composed of Dentrites and Cell Bodies
Composted of Axons and myelin sheath
*Both in CNS
23. Define the following terms:
Central nervous system
(CNS): Involves brain, spinal cord and nerves
Peripheral nervous system
(PNS): Involves sensory and motor neurons that are connected to CNS
Somatic nervous system:
Carries signals to and from skeletal muscles in response to external stimuli. Considered voluntary because it is subject to consious control.
Autonomic nervous system
(Involuntary Movement) Regulates internal environment by controlling smooth and cardiac muscles and organs of the digestive, cardiovascular, excretatory and endocrine systems. 3 Divisons: Sympathetic, Parasympathetic and enteric.
24. Contrast the core functions of the parasympathetic and sympathetic nervous system.
corresponds to arousal and energy generation. Fight of Flight (Before a fight, heart beats faster)
promotes calming and return to self-maintenance functions. Rest and digest
25. What are the three brain region during embryonic development?
Develops into the Thalamus, Hypothalamus and Cerebrum.
Develops into the sensory integrating and relay centers that send sensory information to the cerebrum.
*The cerebrum is composed of the R and L hemispheres, is the integrating center of memory, learning, emotions and other complex functions of the nervous system is.
Later develops into the medulla oblongata, pons and cerebellum.
As they develop they divide structurally and functionally. All are a part of the ancestral and embryonic regions of the vertebrate brain.
26. What are the parts of the brainstem and what are its functions?
Midbrain: sesnort integrating and relay centers that send sensory info to the cerebrum.
Pons: Regulates breathing centers in the Medulla.
Medulla Oblongata: Contains centers that conrtol several visceral functions such as breathing, heart and blood vessel activity, swallowing, vomiting and digestion.
(This is a sheep brain)
27. What is the reticular formation?
A network or neurons containing over 90 seperate clusters of cell bodies. Is present in the brainstem. It filters sensory imput, blocking familiar and repetitive infor that constantly enters the nervous system. It sends the filtered input to the cerebral cortex.
28. What are the core functions of the cerebellum
Some of the core functions of the cerebellum are:
error checking during motor, perceptual, and cognitive functions
including learning, decision making, consciousness, and interpret sensory information in the enviornment.
learning and remembering motor skills
~ Fernanda R. ~
29. What are the parts of the diencephalons and what are its functions?
There are three parts to the diencephalons. The epithalamus includes the pineal gland and clusters of capillaries that help produce CSF (Cerebral Spinal Fluid). However, the diencephalons are mostly made up of the thalamus and the hypothalamus. The thalamus is the area in which sensory information will go to before it hits the cerebrum and its also the main output center for motor information. All senses are sorted in the thalamus and sent to the appropriate place afterwards. The hypothalamus is the center for equilibrium in your body. This part of your brain regulates temperature, the releasing and uptaking of hormones, and other survival methods, just as hunger and thirst.
^^ Simple view of the diencephalon.
- CHRISTOPHER ASIMOS
30. What are circadian rhythms?
Circadian rythms include sleep/wake cycle.
Biological clok that is involved in regulating the circadian rhythms. Regulate: hormone release, hunger, etc.
In mammals, the biological clock is uprachiasmatic nuclei (SCN) is a pair of hypothalamic structures.
31. Describe the cerebral hemispheres.
The cerebrum is divided into 2 parts left and right hemispheres. The corpus callosum connects the left and right hemispheres. The cerebral cortex, gray matter, covers each hemisphere. Each hemisphere also consists of internal white matter and basal nuclei, which is groups of neurons located deep within the white matter.
^^ the left and right hemispheres and what they control
~ Fernanda R. ~
32. What is the corpus callosum?
The corpus callosum is a thick band of axons that enable communication between the right and left cerebral cortices in the brain
This is a short video that shows the functions of the corpus callosum and how communication between the two hemispheres is achieved.
- Alina Dyak
33. What is the limbic system and what is its function?
The limbic system is a ring of structures around the brainstem, including the amygdala, hippocampus and the olfactory bulb. This region of the brain interacts with the higher brain centers, and mediates primary emotions. These structures also interact with the sensory areas of the neocortex, attaching emotional feelings to basic, survival-related tasks controlled within the brainstem, including agression, feeding, and sexuality. These structures form early in development and provide a foundation for cognitive functions.
This video explains the limbic systems functions.
Skim ahead to Ch 49 and try to answer these:
34. Explain how the nervous system produces graded contractions of whole muscles.
Muscle fibers contain one motor neuron each, and together they work as a network to to synape with multiple muscle fibers.
The force of muscle contraction can be graded by changing the frequency of discharge in active motor units and by changing the number of active motor units, resulting in forces graded between the tension of a twitch in the smallest motor unit to the tension of a fused tetanus in all motor units of the muscle.
Normally, the action potential of a muscle fiber produces a quick contraction or twitch, but in most situations, the contraction is graded, meaning we can control its stength. The nervous system does this in two ways: it varies the number of fibers that contract and varies the rate at which the muscle fibers are stimulated. In most cases, each muscle fiber has only one motor neuron, but each branch might synapse with multiple muscle fibers.
35. Labeling the diagram below, explain how a muscle contraction is controlled.
First, ACh is released by synaptic terminal diffusees across the synaptic cleft and binds to receptro proteins on the muscle fibers plansma membran, causing action potential, which is propogated along the plasma membrane and down T tubules. Then the action potential triggers Ca2+ release from sacroplasmic reticulum. The calcium ions then bind to troponin which changes shape and removes the blocking tropomyosin. Myosin cross bridges then alternately attach to actin and detach, pulling actin filaments toward center of sarcomere, all powered by ATP. Following that, calcium in the cytosol is removed by active transport back into the SR and tropomyosin blockage of myosin binding sites is restored, so contraction ends.
This explains how muscle contraction works, showing the importance of ATP.
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