Anatomy Chapter 11

TYPES OF CIRCUITS

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o Actions: Direct versus Indirect what is direct and indirect, what is used in indirect, what iis a neuromodulator

o Actions: Direct versus Indirect § Neurotransmitters that act directly are those that bind to and open ion channels. § These neurotransmitters provoke rapid responses in postsynaptic cells by altering membrane potential. § Neurotransmitters that act indirectly promote broader, longer-lasting effects by acting through intracellular second-messenger molecules, typically via G protein pathways In this way their action is similar to that of many hormones. § Neuromodulator is a term used to describe a chemical messenger released by a neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission. · A neuromodulator may act presynaptically to influence the synthesis, release, degradation, or reuptake of neurotransmitters.

- Action Potentials what is it, what is followed by it, how long does it last, what is another name for it, when does this happen, where does it take place

- Action Potentials o The principal way neurons send signals over long distances is by generating and propagating (transmitting) action potentials. o Only cells with excitable membranes—neurons and muscle cells—can generate action potentials. o An action potential (AP) is a brief reversal of membrane potential with a total amplitude (change in voltage) of about 100 mV (from −70 mV to +30 mV). o Depolarization is followed by repolarization and often a short period of hyperpolarization. § The whole event is over in a few milliseconds. Unlike graded potentials, action potentials do not decay with distance. o In a neuron, an AP is also called a nerve impulse, and is typically generated only in axons. o A neuron generates a nerve impulse only when adequately stimulated. The stimulus changes the permeability of the neuron's membrane by opening specific voltage-gated channels on the axon. § These voltage-gated channels are generally found only on axons, where they are critical for AP formation—no voltage-gated channels means no AP. o Voltage-gated channels open and close in response to changes in the membrane potential. § They are initially activated by local currents (graded potentials) that spread toward the axon along the dendritic and cell body membranes. o In many neurons, the transition from local graded potential to long-distance action potential takes place at the initial segment of the axon.

- Axonal Transport the 2 types of transport and what they do

- Axonal Transport o through the cooperative efforts of motor proteins and cytoskeletal elements (mostly microtubules), substances travel continuously along the axon in both directions: § Anterograde movement · is movement away from the cell body. · Substances moved in this direction include mitochondria, cytoskeletal elements, membrane components (vesicles) used to renew the axon plasma membrane, and enzymes needed to synthesize certain neurotransmitters. § Retrograde movement · is movement toward the cell body. · Substances moved in this direction are mostly organelles returning to the cell body to be degraded or recycled. · Retrograde transport is also an important means of intracellular communication. · It allows the cell body to be advised of conditions at the axon terminals. It also delivers vesicles to the cell body containing signal molecules (such as nerve growth factor, which activates certain nuclear genes promoting growth). o A single basic bidirectional transport mechanism is responsible for axonal transport. It uses different ATP-dependent "motor" proteins (kinesin or dynein), depending on the direction of transport.

- Changing the Resting Membrane Potential what produces a change in membrane potential, what are the 2 type of signals/potentials, what is de- and hyper- polarization

- Changing the Resting Membrane Potential o Neurons use changes in their membrane potential as signals to receive, integrate, and send information. o A change in membrane potential can be produced by (1) anything that alters ion concentrations on the two sides of the membrane, or (2) anything that changes membrane permeability to any ion o Changes in membrane potential can produce two types of signals: § Graded potentials—usually incoming signals operating over short distances that have variable (graded) strength § Action potentials—long-distance signals of axons that always have the same strength o Depolarization is a decrease in membrane potential- the inside of the membrane becomes less negative o Hyperpolarization is an increase in membrane potential- the inside of the membrane becomes more negative

- Chemical Synapses ho common, what is used, the two parts

- Chemical Synapses o the most common type of synapse. o They are specialized to allow the release and reception of chemical messengers known as neurotransmitters. A typical chemical synapse is made up of two parts: § A knoblike axon terminal of the presynaptic neuron, which contains many tiny, membrane-bound sacs called synaptic vesicles, each containing thousands of neurotransmitter molecules § A neurotransmitter receptor region on the postsynaptic neuron's membrane, usually located on a dendrite or the cell body o Although close to each other, presynaptic and postsynaptic membranes are separated by the synaptic cleft, a fluid-filled space approximately 30 to 50 nm (about one-millionth of an inch) wide. o Because the current from the presynaptic membrane dissipates in the fluid-filled cleft, chemical synapses prevent a nerve impulse from being directly transmitted from one neuron to another. § Instead, an impulse is transmitted via a chemical event that depends on the release, diffusion, and receptor binding of neurotransmitter molecules and results in unidirectional communication between neurons. o In short, transmission of nerve impulses along an axon and across electrical synapses is a purely electrical event. o However, chemical synapses convert the electrical signals to chemical signals (neurotransmitters) that travel across the synapse to the postsynaptic cells, where they are converted back into electrical signals.

- Classification of Neurons the three types and what they are associated with

- Classification of Neurons o Multipolar neurons § have three or more processes—one axon and the rest dendrites. § They are the most common neuron type in humans, with more than 99% of neurons in this class. § Multipolar neurons are the major neuron type in the CNS. o Bipolar neurons § have two processes—an axon and a dendrite—that extend from opposite sides of the cell body. § These rare neurons are found in some of the special sense organs such as in the retina of the eye and in the olfactory mucosa. o Unipolar neurons § have a single short process that emerges from the cell body and divides T-like into proximal and distal branches. § The more distal peripheral process is often associated with a sensory receptor. § The central process enters the CNS. Unipolar neurons are more accurately called pseudounipolar neurons because they originate as bipolar neurons. § During early embryonic development, the two processes converge and partially fuse to form the short single process that issues from the cell body. Unipolar neurons are found chiefly in ganglia in the PNS, where they function as sensory neurons.

- Classification of Neurotransmitters by Chemical Structure ACh, biogenic amines, amino acids, peptides, purines, gases/ lipids, endocannabinoids

- Classification of Neurotransmitters by Chemical Structure o Acetylcholine § the best understood because it is released at neuromuscular junctions, which are much easier to study than synapses buried in the CNS. § ACh is released by all neurons that stimulate skeletal muscles and by many neurons of the autonomic nervous system. § ACh-releasing neurons are also found in the CNS. § ACh is synthesized from acetic acid (as acetyl CoA) and choline by the enzyme choline acetyltransferase, then transported into synaptic vesicles for later release. § Once released by the presynaptic terminal, ACh binds briefly to the postsynaptic receptors. § It is then released and degraded to acetic acid and choline by the enzyme acetylcholinesterase (AChE) o Biogenic Amines § Include the catecholamines such as dopamine, norepinephrine, and epinephrine § Also includes the indolamines which include serotonin and histamine § Dopamine and NE are synthesized from the amino acid tyrosine in a common pathway. § The epinephrine-releasing cells of the brain and adrenal medulla use the same pathway. § Serotonin is synthesized from the amino acid tryptophan. § Histamine is synthesized from the amino acid histidine. § Biogenic amine neurotransmitters are broadly distributed in the brain, where they play a role in emotional behavior and help regulate the biological clock. § Additionally, some motor neurons of the autonomic nervous system release catecholamines, particularly NE. § Imbalances of these neurotransmitters are associated with mental illness. · For example, overactive dopamine signaling occurs in schizophrenia. o Amino Acids § The amino acids for which a neurotransmitter role is certain include glutamate, aspartate, glycine, and gamma (γ)-aminobutyric acid (GABA), and there may be others. o Peptides § The neuropeptides, essentially strings of amino acids, include a broad of molecules with diverse effects. § For example, a neuropeptide called substance P is an important mediator of pain signals. § By contrast, endorphins, which include beta endorphin, dynorphin, and enkephalins act as natural opiates, reducing our perception of pain under stressful conditions. · Enkephalin activity increases dramatically in pregnant women in labor. · Endorphin release is at least partially responsible for the "runner's high." § Some neuropeptides, known as gut-brain peptides, are also produced by nonneural body tissues and are widespread in the gastrointestinal tract. · Examples include somatostatin and cholecystokinin (CCK). o Purines § Two purines, ATP and adenosine, also have well-established roles as chemical messengers: · Adenosine triphosphate (ATP), the cell's universal form of energy, is now recognized as a major neurotransmitter (perhaps the most primitive one) in both the CNS and PNS. o Like the receptors for glutamate and acetylcholine, certain receptors produce fast excitatory responses when ATP binds, while other ATP receptors trigger slow, second-messenger responses. o Upon binding to receptors on astrocytes, ATP mediates Ca2+ influx. · Adenosine, a part of ATP, also acts outside of cells on adenosine receptors. o Adenosine is a potent inhibitor in the brain. o Caffeine's well-known stimulatory effects result from blocking these adenosine receptors. o Gases and Lipids § These gases—the so-called "gasotransmitters" nitric oxide, carbon monoxide, and hydrogen sulfide—defy all the classical descriptions of neurotransmitters. § Rather than being stored in vesicles and released by exocytosis, they are synthesized on demand and diffuse out of the cells that make them. § Instead of attaching to surface receptors, they zoom through the plasma membrane of nearby cells to bind with intracellular receptors. § Nitric oxide and carbon monoxide activate guanylate cyclase, the enzyme that makes the second messenger cyclic GMP § NO participates in a variety of processes in the brain, including the formation of new memories by increasing the strength of certain synapses. § Excessive release of NO is thought to contribute to the brain damage seen in stroke patients. In the PNS, NO causes blood vessels and intestinal smooth muscle to relax. o Endocannabinoids § Just as there are natural opiate neurotransmitters in the brain, our brains make endocannabinoids that act at the same receptors as tetrahydrocannabinol (THC), the active ingredient in marijuana. § Their receptors, the cannabinoid receptors, are the most common G protein-coupled receptors in the brain. § Like the gasotransmitters, the endocannabinoids are lipid soluble and are synthesized on demand, rather than stored and released from vesicles. § Like NO, they are thought to be involved in learning and memory.

- Myelination in CNS what cell does this, how does this differ from the Schwann cell

- Myelination in CNS o In the CNS, it is the oligodendrocytes that form myelin sheaths o Unlike a Schwann cell, which forms only one segment of a myelin sheath, an oligodendrocyte has multiple flat processes that can coil around as many as 60 axons at the same time. o As in the PNS, myelin sheath gaps separate adjacent sections of an axon's myelin sheath. o However, CNS myelin sheaths lack an outer collar of perinuclear cytoplasm because cell extensions do the coiling and the squeezed-out cytoplasm is forced back toward the centrally located nucleus instead of peripherally. o As in the PNS, the smallest-diameter axons are nonmyelinated. These nonmyelinated axons are covered by the long extensions of adjacent glial cells.

- Conduction Velocity two factors that relate to it, continous conduction, salatory conduction, group ABC fibers

- Conduction Velocity o They vary widely o Nerve fibers that transmit impulses most rapidly (100 m/s or more) are found in neural pathways where speed is essential, such as those that mediate postural reflexes. o Axons that conduct impulses more slowly typically serve internal organs (the gut, glands, blood vessels), where slower responses are not a handicap. The rate of impulse propagation depends largely on two factors: § Axon diameter · As a rule, the larger the axon's diameter, the faster it conducts impulses. Larger axons conduct more rapidly because they offer less resistance to the flow of local currents, § Degree of myelination · The presence of a myelin sheath dramatically increases the speed of propagation. The conduction velocity increases with the degree of myelination—lightly myelinated fibers conduct more slowly than heavily myelinated fibers. o Action potentials can be propagated in one of two ways, depending on whether myelin is present or absent from the axon: § Continuous conduction · Action potential propagation in nonmyelinated axons occurs by continuous conduction because the voltage-gated channels in the membrane are immediately adjacent to each other. · Continuous conduction is relatively slow. § Saltatory conduction · When an AP is generated in a myelinated fiber, the local depolarizing current does not dissipate through the adjacent membrane regions, which are nonexcitable. · Instead, the current is maintained and moves rapidly to the next myelin sheath gap, a distance of approximately 1 mm, where it triggers another AP. · Consequently, APs are triggered only at the gaps. This type of conduction is called saltatory conduction because the electrical signal appears to jump from gap to gap along the axon. o Saltatory conduction is about 30 times faster than continuous conduction. o Nerve fibers may be classified according to diameter, degree of myelination, and conduction speed. § Group A fibers · are mostly somatic sensory and motor fibers serving the skin, skeletal muscles, and joints. · They have the largest diameter, thick myelin sheaths, and conduct impulses at speeds up to 150 m/s (over 300 miles per hour). § Group B fibers · are lightly myelinated fibers of intermediate diameter. · They transmit impulses at an average rate of 15 m/s (about 30 mi/h). § Group C fibers · have the smallest diameter. · They are nonmyelinated, so they are incapable of saltatory conduction and conduct impulses at a leisurely pace—1 m/s (2 mi/h) or less. § The B and C fiber groups include autonomic nervous system motor fibers serving the visceral organs; visceral sensory fibers; and the smaller somatic sensory fibers that transmit sensory impulses from the skin (such as pain and small touch fibers).

- Dendrites appearance, number, organelles, what are their functions, what helps them do this (think area), what type of potentials are they

- Dendrites o Dendrites of motor neurons are short, tapering, diffusely branching extensions. o Typically, motor neurons have hundreds of twiglike dendrites clustering close to the cell body. o Virtually all organelles present in the cell body also occur in dendrites. o Dendrites, the main receptive or input regions, provide an enormous surface area for receiving signals from other neurons. o In many brain areas, the finer dendrites are highly specialized for collecting information. They bristle with dendritic spines—thorny appendages with bulbous or spiky ends—which represent points of close contact (synapses) with other neurons o Dendrites convey incoming messages toward the cell body. § These electrical signals are usually not action potentials (nerve impulses) but are short-distance signals called graded potentials

- Differences in Ionic Composition concentration of Na and K,

- Differences in Ionic Composition o The cell cytosol contains a lower concentration of Na+ and a higher concentration of K+ than the extracellular fluid. o Negatively charged (anionic) proteins help to balance the positive charges of intracellular cations (primarily K+). o In the extracellular fluid, the positive charges of Na+ and other cations are balanced chiefly by chloride ions (Cl−). o Although there are many other solutes (glucose, urea, and other ions) in both fluids, potassium (K+) plays the most important role in generating the membrane potential.

- Differences in Plasma Membrane Permeability ******kinda explain the flow of K and Na and the pump

- Differences in Plasma Membrane Permeability o Potassium ions diffuse out of the cell along their concentration gradient much more easily than sodium ions can enter the cell along theirs. o K+ flowing out of the cell causes the cell to become more negative inside. o Na+ trickling into the cell makes the cell just slightly more positive than it would be if only K+ flowed. o Therefore, at resting membrane potential, the negative interior of the cell is due to a much greater ability for K+ to diffuse out of the cell than for Na+ to diffuse into the cell. o Because some K+ is always leaking out of the cell and some Na+ is always leaking in, you might think that the concentration gradients would eventually "run down," resulting in equal concentrations of Na+ and K+ inside and outside the cell. § This does not happen because the ATP-driven sodium-potassium pump first ejects three Na+ from the cell and then transports two K+ back into the cell. · In other words, the sodium-potassium pump (Na+-K+ ATPase) stabilizes the resting membrane potential by maintaining the concentration gradients for sodium and potassium

- Electrical Synapses how common, what does it consist of, what do their channel proteins connect to, where can is be found, where is it far more abundant

- Electrical Synapses o Much less common than chemical o They consist of hap junctions o Their channel proteins connect the cytoplasm of adjacent neurons and allow ions and small molecules to flow directly from one neuron to the next o These neurons are electrically coupled, and transmission across these synapses is very rapid o Electrical synapses between neurons provide a simple means of synchronizing the activity of all interconnected neurons. o In adults, electrical synapses are found in regions of the brain responsible for certain stereotyped movements, such as the normal jerky movements of the eyes. Electrical synapses are far more abundant in embryonic nervous tissue, where they permit exchange of guiding cues during early neuronal development so that neurons can connect properly with one another

- Excitatory Synapses and EPSPs what does it do

- Excitatory Synapses and EPSPs o At excitatory synapses, neurotransmitter binding depolarizes the postsynaptic membrane. o In contrast to what happens on axon membranes, chemically gated ion channels open on postsynaptic membranes (those of dendrites and neuronal cell bodies). o Each channel allows Na+ and K+ to diffuse simultaneously through the membrane but in opposite directions o instead of APs, depolarizing graded potentials called excitatory postsynaptic potentials (EPSPs) occur at excitatory postsynaptic membranes. o he only function of EPSPs is to help trigger an AP distally at the initial segment of the postsynaptic neuron's axon

- Myelination in the PNS what forms them, what is in between them, what happened when the coiling process doe snot occur

- Myelination in the PNS o Formed by Schwann Cells o Wrap themselves around o Adjacent Schwann cells do not touch one another, so there are gaps in the sheath. These myelin sheath gaps, or nodes of Ranvier, occur at regular intervals (about 1 mm apart) along a myelinated axon. Axon collaterals can emerge at these gaps. o Sometimes Schwann cells surround peripheral nerve fibers but the coiling process does not occur. In such instances, a single Schwann cell can partially enclose 15 or more axons, each of which occupies a separate recess in the Schwann cell surface. § Nerve fibers associated with Schwann cells in this manner are said to be nonmyelinated and are typically thin fibers.

- Functional Classification the three classifications and what they do

- Functional Classification o This classification groups neurons according to the direction in which the nerve impulses travel relative to the CNS o Sensory, or afferent, neurons § transmit impulses from sensory receptors in the skin or internal organs toward or into the central nervous system. § Except for certain neurons found in some special sense organs, virtually all sensory neurons are unipolar, and their cell bodies are located in sensory ganglia outside the CNS. § Only the most distal parts of these unipolar neurons act as the receptive region, and the peripheral processes are often very long. For example, fibers carrying sensory impulses from the skin of your big toe travel for more than a meter before they reach their cell bodies in a ganglion close to the spinal cord. o Motor, or efferent, neurons § carry impulses away from the CNS to the effector organs (muscles and glands) of the body. § Motor neurons are multipolar. · Except for some neurons of the autonomic nervous system, their cell bodies are located in the CNS. o Interneurons, or association neurons § lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs. § Most interneurons are confined within the CNS. § They make up over 99% of the neurons of the body, including most of those in the CNS. § Almost all interneurons are multipolar, but there is considerable diversity in size and fiber-branching patterns.

- Generating an Action Potential (Basics/ Refer to Focus Figure) 4 basic steps

- Generating an Action Potential (Basics/ Refer to Focus Figure) 1. Resting state- all voltage gated Na and K channels are closed 2. Depolarization- Voltage gated Na channel open 3. Repolarization- Na channels are inactivating and voltage gated K channels open 4. Hyperpolarization- Some K channels remain open, and Na channels reset

- Generating the Resting Membrane Potential what tool is used, whats the common reading, what 2 factors generate the resting membrane potential

- Generating the Resting Membrane Potential o A voltmeter is used to measure the potential difference between two points o In a neuron it reads -70mV o This potential difference in a resting neuron is called the resting membrane potential, and the membrane is said to be polarized. § The value of the resting membrane potential varies (from −40 mV to −90 mV) in different types of neurons. o The resting potential exists only across the membrane; the solutions inside and outside the cell are electrically neutral. § Two factors generate the resting membrane potential: · differences in the ionic composition of the intracellular and extracellular fluids · differences in the plasma membrane's permeability to those ions.

- Graded Potentials length, are they de or hyper, how does their magnitude compare to distance, why are they call graded, what are they triggered by,

- Graded Potentials o Graded potentials are short-lived, localized changes in membrane potential, usually in dendrites or the cell body. o They can be either depolarizations or hyperpolarizations. o These changes cause current flows that decrease in magnitude with distance. o Graded potentials are called "graded" because their magnitude varies directly with stimulus strength. § The stronger the stimulus, the more the voltage changes and the farther the current flows. o Graded potentials are triggered by some change (a stimulus) in the neuron's environment that opens gated ion channels. o Graded potentials are given different names, depending on where they occur and the functions they perform. § A receptor potential or a generator potential is produced when a sensory receptor is excited by its stimulus (e.g., light, pressure, chemicals) § A postsynaptic potential is produced when the stimulus is a neurotransmitter released by another neuron. · Here, the neurotransmitter is released into a fluid-filled gap called a synapse and influences the neuron beyond the synapse. o Because the current dissipates quickly and decays (declines) with increasing distance from the site of initial depolarization, graded potentials can act as signals only over very short distances such as in the dendrites and cell body. o Nonetheless, they are essential in initiating action potentials, the long-distance signals of axons.

- Information Transfer Across Chemical Synapse Steps (Basic/ Refer to Focus Figure) 6 steps and synaptic delay

- Information Transfer Across Chemical Synapse Steps (Basic/ Refer to Focus Figure) 1. Action potential arrives at axon terminal 2. Voltage gated Ca channels open and Ca enters the axon terminal 3. Ca entry causes synaptic vesicles to release neurotransmitter by exocytosis 4. Neurotransmitters diffuse across the synaptic cleft and binds to specific receptors on the post-synaptic membrane 5. Binding of neurotransmitter opens ion channels, creating graded potentials 6. Neurotransmitter effects are terminated o Synaptic Delay § An impose may travel up to 150 m/s but neutral transmission across a chemical synapse is comparatively slow § It reflects the time needed for the neurotransmitter to be released and diffused § This synaptic delay lasts .3-5 ms, making it the slowest part of the process

- Inhibitory Synapses and IPSPs what does it do, what ion is used

- Inhibitory Synapses and IPSPs o binding of neurotransmitters at inhibitory synapses reduces a postsynaptic neuron's ability to generate an AP. o Most inhibitory neurotransmitters hyperpolarize the postsynaptic membrane by making the membrane more permeable to K+ or Cl−. Sodium ion permeability is not affected. o If K+ channels open, K+ moves out of the cell. If Cl− channels open, Cl− moves in. o In either case, the charge on the inner face of the membrane becomes more negative. o As the membrane potential increases and is driven farther from the axon's threshold, the postsynaptic neuron becomes less and less likely to "fire," and larger depolarizing currents are required to induce an AP. o Hyperpolarizing changes in potential are called inhibitory postsynaptic potentials (IPSPs).

- Myelin Sheath composition, what do they do, what are they on

- Myelin Sheath o Many nerve fibers, particularly those that are long or large in diameter, are covered with a whitish, fatty (protein-lipoid), segmented myelin sheath o Myelin protects and electrically insulates fibers, and it increases the transmission speed of nerve impulses. o Myelinated fibers (axons bearing a myelin sheath) conduct nerve impulses rapidly, whereas nonmyelinated fibers conduct impulses more slowly. o myelin sheaths are associated only with axons. Dendrites are always nonmyelinated.

Nervous System is divided into 2 parts- what are the two parts and what do they do, subdivisions of PNS, 2 parts

- Nervous System is divided into 2 parts o The central nervous system (CNS) § consists of the brain and spinal cord, which occupy the dorsal body cavity. § The CNS is the integrating and control center of the nervous system. § It interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience. o The peripheral nervous system (PNS) § is the part of the nervous system outside the CNS. § The PNS consists mainly of nerves (bundles of axons) that extend from the brain and spinal cord, and ganglia (collections of neuron cell bodies). § Spinal nerves carry impulses to and from the spinal cord, and cranial nerves carry impulses to and from the brain. § These peripheral nerves serve as communication lines that link all parts of the body to the CNS. · The PNS has 2 functional subdivisions o Sensory/ Afferent division § Consists of nerve fibers (axons) that convey impulses to the central nervous system from sensory receptors located throughout the body · Somatic sensory fibers convey impulses from the skin, skeletal muscles, and joints · Visceral sensory fibers transmit impulses from the visceral organs (within the ventral body cavity) o The sensory division keeps the CNS constantly informed of what's going on both inside and outside the body o Motor/ Efferent division § Transmits impulses from the CNS to effector organs, which are muscles and glands § These impulses activate muscles to contract and glands to secrete § They effect a motor response § The motor division has 2 main parts · The somatic nervous system o is composed of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles. o It is often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles. · The autonomic nervous system (ANS) o consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscle, and glands. o the ANS is also called the involuntary nervous system. § the ANS has two functional subdivisions: the sympathetic division and the parasympathetic division. § Typically these divisions work in opposition to each other—whatever one stimulates, the other inhibits.

- Neuroglia Support and Maintain Neurons the 2 cells in nervous tissue, what do they each do

- Neuroglia Support and Maintain Neurons o Although it is very complex, nervous tissue is made up of just two principal types of cells: § Supporting cells called neuroglia (or glial cells) · small cells that surround and wrap the more delicate neurons § Neurons · nerve cells that are excitable (respond to stimuli by changing their membrane potential) and transmit electrical signals

- Neuroglia in the CNS comparison to neruons in numbers, 4 different cell types

- Neuroglia in the CNS o They outnumber neurons o Most neuroglia has branching processes and a central cell body o Astrocytes "Star Cells" § are the most abundant and versatile glial cells. § Their numerous radiating processes cling to neurons and their synaptic endings and cover nearby capillaries. § They support and brace the neurons and anchor them to their nutrient supply lines § Astrocytes play a role in making exchanges between capillaries and neurons, helping determine capillary permeability. § They guide the migration of young neurons and formation of synapses (junctions) between neurons. § Astrocytes also control the chemical environment around neurons, where their most important job is "mopping up" leaked potassium ions and recapturing and recycling released neurotransmitters. § Connected by gap junctions, astrocytes signal each other with slow-paced intracellular calcium pulses (calcium waves), and by releasing extracellular chemical messengers. § They also influence neuronal functioning and therefore participate in information processing in the brain. o Microglial Cells § are small and ovoid with relatively long "thorny" processes § Their processes touch nearby neurons, monitoring their health, and when they sense that certain neurons are injured or in other trouble, the microglial cells migrate toward them. § Where invading microorganisms or dead neurons are present, the microglial cells transform into a special type of macrophage that phagocytizes the microorganisms or neuronal debris. § This protective role is important because cells of the immune system have limited access to the CNS. o Ependymal Cells § range in shape from squamous to columnar, and many are ciliated § They line the central cavities of the brain and the spinal cord, where they form a fairly permeable barrier between the cerebrospinal fluid that fills those cavities and the tissue fluid bathing the cells of the CNS. § The beating of their cilia helps to circulate the cerebrospinal fluid that cushions the brain and spinal cord. o Oligodendrocytes § have fewer processes than astrocytes. § Oligodendrocytes line up along the thicker nerve fibers in the CNS and wrap their processes tightly around the fibers, producing an insulating covering called a myelin sheath

- Neuroglia in the PNS 2 cell types

- Neuroglia in the PNS o Satellite Cells § surround neuron cell bodies located in the peripheral nervous system , and are thought to have many of the same functions in the PNS as astrocytes do in the CNS. o Schwann cells § surround all nerve fibers in the PNS and form myelin sheaths around the thicker nerve fibers. § In this way, they are functionally similar to oligodendrocytes. § Schwann cells are vital to regeneration of damaged peripheral nerve fibers.

- Neuron Cell Body what does the plasma membrane act as, what is the cell body considered as, what organelles does it have

- Neuron Cell Body o consists of a spherical nucleus surrounded by cytoplasm (Also called the perikaryon or soma) o In most neurons, the plasma membrane of the cell body acts as part of the receptive region that receives information from other neurons o The cell body is the major biosynthetic center and metabolic center of a neuron. o In addition to abundant mitochondria, it contains many structures: § Protein- and membrane-making machinery · Neuron cell bodies (not axons) have the organelles needed to synthesize proteins—rough endoplasmic reticulum (ER), free ribosomes, and Golgi apparatus. The rough ER, also called the chromatophilic substance or Nissl bodies § Cytoskeletal elements · Microtubules and neurofibrils, which are bundles of intermediate filaments (neurofilaments), maintain cell shape and integrity. · They form a network throughout the cell body and its processes. § Pigment inclusions · Pigments sometimes found inside neuron cell bodies include black melanin, a red iron-containing pigment, and a golden-brown pigment called lipofuscin o Lipofuscin, a harmless by-product of lysosomal activity, is sometimes called the "aging pigment" because it accumulates in neurons of elderly individuals.

- Neuron Processes what are they, how does it differ in the CNS and PNS

- Neuron Processes o Armlike processes extend from the cell body of all neurons. o The brain and spinal cord (CNS) contain both neuron cell bodies and their processes. o The PNS consists chiefly of neuron processes (whose cell bodies are in the CNS). o The two types of neuron processes, dendrites and axons, differ in the structure and function of their plasma membranes.

- Neurons aka Nerve Cells what are they to the nervous system, what do they do, what are their 3 special characteristics

- Neurons aka Nerve Cells o are the structural units of the nervous system. o There are billions of these (typically) large, highly specialized cells that conduct messages in the form of nerve impulses from one part of the body to another. o Besides their excitability, they have three other special characteristics: § Neurons have extreme longevity. · Given good nutrition, they can function optimally for a lifetime. § Neurons are amitotic. · As neurons assume their roles as communicating links of the nervous system, they lose their ability to divide. · We pay a high price for this feature because neurons cannot be replaced if destroyed. · There are exceptions to this rule. For example, olfactory epithelium and some hippocampal regions of the brain contain stem cells that can produce new neurons throughout life. § Neurons have an exceptionally high metabolic rate · They require continuous and abundant supplies of oxygen and glucose. They cannot survive for more than a few minutes without oxygen.

- Organizations of Neurons: Neuronal Pools

- Organizations of Neurons: Neuronal Pools o The billions of neurons in the CNS are organized into neuronal pools. o These functional groups of neurons integrate incoming information from receptors or different neuronal pools and then forward the processed information to other destinations. o In a simple type of neuronal pool, one incoming presynaptic fiber branches profusely as it enters the pool and then synapses with several different neurons in the pool. o When the incoming fiber is excited, it will excite some postsynaptic neurons and facilitate others by bringing them closer to threshold. o Neurons most likely to generate impulses are those closely associated with the incoming fiber, because they receive the bulk of the synaptic contacts. Those neurons are in the discharge zone of the pool. o Neurons farther from the center are not usually excited to threshold, but they are facilitated and can easily be brought to threshold by stimuli from another source. o For this reason, the periphery of the pool is the facilitated zone. Most neuronal pools consist of thousands of neurons and include inhibitory as well as excitatory neurons.

- Parallel Processing

- Parallel Processing o In parallel processing, inputs are segregated into many pathways, and different parts of the neural circuitry deal simultaneously with the information delivered by each pathway. § For example, smelling a pickle (the input) may cause you to remember picking cucumbers on a farm; or it may remind you that you don't like pickles or that you must buy some at the market; or perhaps it will call to mind all these thoughts. For each person, parallel processing triggers unique pathways. o The same stimulus—pickle smell, in our example—promotes many responses beyond simple awareness of the smell. o Parallel processing is not repetitious because the pathways do different things with the information. o Each pathway or "channel" is decoded in relation to all the others to produce a total picture. o Think, for example, about what happens when you step on a sharp object while walking barefoot. The serially processed withdrawal reflex causes you to withdraw your foot immediately. At the same time, pain and pressure impulses are speeding up to your brain along parallel pathways that allow you to decide whether to simply rub the hurt spot or seek first aid. o Parallel processing is extremely important for higher-level mental functioning—for putting the parts together to understand the whole.

- Refractory Periods absolute and relative

- Refractory Periods o When a patch of neuron membrane is generating an AP and its voltage-gated sodium channels are open, the neuron cannot respond to another stimulus, no matter how strong. o Called the absolute refractory period, this period begins with the opening of the Na+ channels and ends when the Na+ channels begin to reset to their original resting state § This ensures that each AP is separate, all or none event § Enforces a one-way transmission of the AP o The relative refractory period follows the absolute refractory period. § During the relative refractory period, most Na+ channels have returned to their resting state, some K+ channels are still open, and repolarization is occurring. § An exceptionally strong stimulus can reopen the Na+ channels that have already returned to their resting state and generate another AP. · Strong stimuli trigger more frequent APs by intruding into the relative refractory period.

- Role of Membrane Ion Channels types of channels, what is the direction of ion movement determined by (2 things)

- Role of Membrane Ion Channels o These channels are selective o Membrane channels are large proteins, often with several subunits o Some channels are leakage or non-gated which means that they are always open o Other channels are gates o There are three main types of gated channels § Chemically/ligand gated § Voltage gated § Mechanically gated o When gated ion channels open, ions diffuse quickly across the membrane. § The direction an ion moves (into or out of the cell) is determined by the electrochemical gradient. § The electrochemical gradient has two components: · The concentration gradient. Ions move along chemical concentration gradients from an area of their higher concentration to an area of lower concentration. · The electrical gradient. Ions move toward an area of opposite electrical charge. o The 2 gradients do not necessarily work together to drive an ion in the same direction o They actually oppose each other § Whichever gradient is stronger wins

- Serial Processing what is it, what is the clear cut example

- Serial Processing o In serial processing, the whole system works in a predictable all-or-nothing manner. o One neuron stimulates the next, which stimulates the next, and so on, eventually causing a specific, anticipated response. The most clear-cut examples of serial processing are spinal reflexes. o Straight-through sensory pathways from receptors to the brain are also examples. o Reflexes are the functional units of the nervous system o Reflexes are rapid, automatic responses to stimuli, in which a particular stimulus always causes the same response. o Reflex activity, which produces the simplest behaviors, is stereotyped and dependable. § For example, if you touch a hot object you jerk your hand away, and an object approaching your eye triggers a blink. o Reflexes occur over neural pathways called reflex arcs that have five essential components—receptor, sensory neuron, CNS integration center, motor neuron, and effector

- Synapses Transmit Signals Between Neurons what is a synapse, the two synapse names

- Synapses Transmit Signals Between Neurons o A synapse is a junction that mediates information transfer from one neuron to the next neuron to an effector cell o The neuron conducting impulses toward the synapse is the presynaptic neuron, and the neuron transmitting the electrical signal away from the synapse is the postsynaptic neuron. o At a given synapse, the presynaptic neuron sends the information, and the postsynaptic neuron receives the information o most neurons function as both presynaptic and postsynaptic neurons. o Neurons have anywhere from 1000 to 10,000 axon terminals making synapses and are stimulated by an equal number of other neurons o Synapses between the axon endings of one neuron and the dendrites of other neurons are axodendritic synapses. o Those between axon endings of one neuron and the cell body (soma) of another neuron are axosomatic synapses o Less common (and far less understood) are synapses between axons (axoaxonal), between dendrites (dendrodendritic), or between cell bodies and dendrites (somatodendritic). o There are two types of synapses: electrical and chemical.

- The Axon Functional characteristics what is the function, what does it generate, where is it generated, what does the-actions potential cause at the axon terminal, what organelles do axons lack, what do they depend on because of this

- The Axon Functional characteristics o The axon is the conducting region of the neuron o It generates nerve impulses and transmits them, typically away from the cell body, along the plasma membrane, or axolemma o In motor neurons, the nerve impulse is generated at the initial segment of the axon (the trigger zone) and conducted along the axon to the axon terminals, which are the secretory region of the neuron. o When the impulse reaches the axon terminals, it causes neurotransmitters—signaling chemicals—to be released into the extracellular space. § The neurotransmitters either excite or inhibit neurons (or muscle or gland cells) with which the axon is in close contact. § Each neuron receives signals from and sends signals to scores of other neurons, carrying on "conversations" with many different neurons at the same time. o An axon contains the same cytoplasmic organelles found in the dendrites and cell body with two important exceptions—it lacks rough endoplasmic reticulum and a Golgi apparatus, the structures involved with protein synthesis and packaging. § Consequently, an axon depends on (1) its cell body to renew the necessary proteins and membrane components, and (2) efficient transport mechanisms to distribute them. Axons quickly decay if cut or severely damaged.

- The Axon Structure how many in a neuron, what do they arise from, and whats under the arising part, what is a long axon called, what are bundles of axons called in the CNS and PNS, what do axons do at the end and what is it called

- The Axon Structure o A neuron never has more than a single axon o The axon arises from a cone-shaped area of the cell body called the axon hillock o The initial segment of the axon narrows to form a slender process that is uniform in diameter for the rest of its length o Any long axon is also called a nerve fiber. Bundles of axons are called tracts in the CNS and nerves in the PNS o Although only one axon arises from the cell body, the axon may have occasional branches along its length. These branches, called axon collaterals, extend from the axon at more or less right angles. An axon usually branches profusely at its end (terminus): 10,000 or more terminal branches (also called terminal arborizations) per neuron is not unusual. The knoblike distal endings of the terminal branches are called axon terminals

- Threshold and the All-or-None Phenomenon

- Threshold and the All-or-None Phenomenon o What determines the threshold point? § One explanation is the threshold is the membrane potential at which the outward current created by K movement is exactly equal to the inward movement created by Na movement § Threshold is typically reached when the membrane has been depolarized by 15-20 mV from the resting value o Action potential is all or nothing

- Voltage, Resistance, Current what does voltage measure, what is current, what does the amount of charge that moves between two points depend on, what is ohms law

- Voltage, Resistance, Current o Voltage, the measure of potential energy generated by separated electrical charges, is measured in either volts (V) § Voltage is always measured between two points and is called the potential difference or simply the potential between the points. § The greater the difference in charge between two points, the higher the voltage. o The flow of electrical charge from one point to another is a current, and it can be used to do work—for example, to power a flashlight. o The amount of charge that moves between the two points depends on two factors: voltage and resistance. § Resistance is the hindrance to charge flow provided by substances through which the current must pass. · Substances with high electrical resistance are insulators, and those with low resistance are conductors. o Ohm's Law outlines the relationship between voltage, current, and resistance § Current (I)= voltage/resistance · Current (I) is directly proportional to voltage: The greater the voltage (potential difference), the greater the current. · There is no net current flow between points that have the same potential. · Current is inversely related to resistance: The greater the resistance, the smaller the current.

Nervous System- 3 overlapping functions and example

o Nervous system has three overlapping functions § 1. Sensory input · The nervous system uses its millions of sensory receptors to monitor changes occurring both inside and outside the body. The gathered information is called sensory input. § 2. Integration · The nervous system processes and interprets sensory input and decides what should be done at each moment—a process called integration § 3. Motor output · The nervous system activates effector organs—the muscles and glands—to cause a response, called motor output. § Example: You are driving and see a red light ahead (sensory input). Your nervous system integrates this information (red light means "stop"), and your foot hits the brake (motor output).