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A&P Lecture > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

Nervous system

• central nervous system (cns)

A

• brain
• spinal cord

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2
Q

Nervous system

• peripheral nervous system (pns)

A

• all nervous tissues not in the cns

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3
Q

Peripheral nervous system (pns) components

• Nerves

A

•cranial nerves- 12 pairs of nerves emerging from the brain
•spinal nerves- 31 pairs of nerves emerging from the spinal cord

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4
Q

Peripheral nervous system (pns) components

• Sensory receptors

A

•Touch receptors in the skin
•Photoreceptors in the eye
•Olfactory receptors in the nose

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5
Q

Peripheral nervous system (pns) division

• Sensory (afferent) division

A

•Somatic senses
•Special senses

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6
Q

Peripheral nervous system (pns) division

• Motor (efferent) division

A

•Somatic Nervous System
•Autonomic Nervous System
•Sympathetic Nervous System
•Parasympathetic Nervous System
•Enteric Nervous System

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7
Q

Nervous system function

A

• Helps to maintain homeostasis and helps to keep control of conditions that maintain health

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8
Q

Nerve function (pns)

A

• bundle of hundreds- thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord

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9
Q

Sensory receptors function

A

• structures of the nervous system that monitor changes in the external and internal environment
-touch receptors to feel
-photoreceptors to see
-olfactory receptors to smell

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10
Q

Sensory (afferent) division function

A

• conveys input into the CNS from sensory receptors in the body
-Somatic senses- tactile, thermal, pain, proprioceptive sensations
-Special senses- smell, taste, vision, hearing, equilibrium

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11
Q

Motor (efferent) division function

A

• conveys output from the CNS to effectors (muscles and glands)
-Somatic Nervous System- conveys output from the CNS to skeletal muscles (voluntary)
-Autonomic Nervous System- conveys output from the CNS to smooth muscle, cardiac muscle, and glands (involuntary)
•Sympathetic Nervous System- fight or flight
•Parasympathetic Nervous System- rest and digest
•Enteric Nervous System- helps regulate the activity of smooth muscles and glands of the GI tract

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12
Q

Sensory (input) functions

A

•Sense changes in the internal and external environment through sensory receptors
•Sensory Neurons

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13
Q

Integrative (processing) function

A

•Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors
•Integration (inter/association neurons)

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14
Q

Motor (output) function

A

•Respond to stimuli by initiating action by activating effectors through the cranial and spinal nerves.
•Motor Neurons

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15
Q

2 types of cells that make up nervous tissue

A

1.) Neurons- provide most of the unique functions of the nervous system
2.) Neuroglia- support, nourish, and protect neurons

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16
Q

Parts of neuron

• cell body

A

• contains a nucleus, lysosomes, mitochondria, a Golgi complex, cytoplasmic inclusions such as lipofuscin, chromatophilic substances, and neurofibrils

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17
Q

Parts of neuron

• dendrites

A

• receiving/input portions of the neurons (there are many of these)

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18
Q

Parts of neuron

• axon

A

• conducts nerve impulses from the neuron to the dendrites or cell body of another neuron or to an effector organ of the body (usually only one of these)

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19
Q

Parts of neuron

• ganglion

A

• a collection of neuron cell bodies outside the CNS

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20
Q

Structural classification of neurons

• multipolar

A

• several dendrites and one axon
-Most neurons in the brain and spinal cord and all motor neurons

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21
Q

Structural classification of neurons

• bipolar

A

one dendrite and one axon
-Found in the retina of the eye, the inner ear, and olfactory area of the brain

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22
Q

Structural classification of neurons

• unipolar

A

• dendrites and one axon that are fused together to form a contentious process that emerges from the cell body
-The dendrites of most of these function as sensory receptors

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23
Q

Neuroglia characteristics

A

-specialized tissue cells that…
-Support neurons
-Attach neurons to blood vessels
-Produce the myelin sheath around axons
-Carry out phagocytosis
-Not electrically excitable
-Make up about half the volume of the nervous system
-Can multiply and divide
-6 kinds total (4 in CNS, 2 in PNS)

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24
Q

Neuroglia CNS

• Astrocytes

A

•Contain microfilaments that give them considerable strength, which enables them to support neurons.
•Processes of astrocytes wrapped around blood capillaries isolate neurons of the CNS from various potentially harmful substances in blood by secreting chemicals that maintain the unique selective permeability characteristic of the blood-brain barrier.
•help to maintain the appropriate chemical environment for the generation of nerve impulses.
• may also play a role in learning and memory by influencing the formation of neural synapses
Oligodendrocytes
-resemble astrocytes but are smaller and contain fewer processes
•Their processes are responsible for forming and maintaining the myelin sheath
around multiple CNS axons

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25
Q

Neuroglia CNS

• Microglia

A

•function as phagocytes
•remove cellular debris formed during normal development of the nervous system and phagocytize microbes and damaged nerve tissue

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26
Q

Neuroglia CNS

• ependymal cells

A

• cuboidal or columnar cells arranged in a single layer that possess microvilli or cilia
•Line the ventricles of the brain and the central canal of the spinal cord
•Monitor and assist in the circulation of cerebrospinal fluid

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27
Q

Neuroglia PNS

• Schwann cells

A

•Encircle PNS axons and form the myelin sheath around axons
•Each Schwann cell myelinates only a single axon
•1 Schwann cell can also enclose as many as 20 or more UNmyelinated axons

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28
Q

Neuroglia PNS

• satellite cells

A

•Flat cells that surround the cell bodies of the neurons of PNS ganglia
•Provide structural support and regulate the exchange of materials between the neuronal cell bodies and interstitial fluids

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29
Q

Myelin sheath

A

•multilayered lipid and protein covering produced by Schwann cells (PNS) an oligodendrocytes (CNS) that surrounds the axons of most neurons
•Axons without this sheath are called unmyelinated

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30
Q

Myelination in PNS

A

•Schwann cells begin to form myelin sheaths around axons during fetal development:
•Each Schwann cell wraps about 1 mm of a single axon’s length by spiraling many times around the axon.
•Eventually, multiple layers of glial plasma membrane surround the axon, with the Schwann cell’s cytoplasm and nucleus forming the outermost layer.
• The inner portion, consisting of up to 100 layers of Schwann cell membrane, is the
myelin sheath.
•The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is the neurolemma which is found only around axons in the PNS.
•When an axon is injured, the neurolemma aids regeneration by forming a regeneration tube that guides and stimulates regrowth of the axon.
•Gaps in the myelin sheath, called nodes of Ranvier, appear at intervals along the axon. Each Schwann cell wraps one axon segment between two nodes

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31
Q

Myelination in CNS

A
  • oligodendrocyte myelinates parts of several axons:
    •Each oligodendrocyte puts forth about 15 broad, flat processes that spiral around CNS axons, forming a myelin sheath.
    •A neurolemma is not present, because the oligodendrocyte cell body and nucleus do not envelop the axon.
    •Nodes of Ranvier are present, but they are fewer in number.
    •Axons in the CNS display little regrowth after injury.
    •This is thought to be due, in part, to the absence of a neurolemma, and in part to an inhibitory influence exerted by the oligodendrocytes on axon regrowth.
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32
Q

Action potentials (ap)

A

•allow communication over short and long distances whereas
-Production of an AP or a GP depends upon the existence of a resting membrane potential and the existence of certain ion channels

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33
Q

Graded potentials (gp)

A

•allow communication over short distances only
-Production of an AP or a GP depends upon the existence of a resting membrane potential and the existence of certain ion channels

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34
Q

Membrane potential

A

• an electrical potential difference (voltage) across the membrane. In excitable cells this voltage is called resting membrane potential

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35
Q

Ion channels

• leak channels

A

• gated channels that randomly open and close

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36
Q

Ion channels

• Ligand-gated channels

A

• gated channels that open in response to binding of ligand (chemical) stimulus

37
Q

Ion channels

• mechanically-gated channels

A

• gated channels that open in response to mechanical stimulus (such as touch, pressure, vibration, or tissue stretching)

38
Q

Ion channels

• voltage - gated channels

A

• gated channels that open in response to voltage stimulus (change in membrane potential)

39
Q

Cause of resting membrane potential

A

•a small buildup of negative ions in the cytosol along the inside of the membrane, and an equal buildup of positive ions in the extracellular fluid (ECF) along the outside surface of the membrane
•Such a separation of positive and negative electrical charges is a form of potential energy, which is measured in volts or millivolts
•The buildup of charge occurs only very close to the membrane. The cytosol or extracellular fluid elsewhere in the cell contains equal numbers of positive and negative charges and is electrically neutral.

40
Q

Voltage of resting membrane potential

A

• In neurons, the resting membrane potential ranges from −40 to −90 mV. A typical value is −70 mV.
•A cell that exhibits a membrane potential is said to be polarized.
Measured by-
•The tip of a recording microelectrode is inserted inside the cell, and a reference electrode
(device that conducts electrical charges) is placed outside the cell in the extracellular fluid.
•The recording microelectrode and the reference electrode are connected to an instrument known as a voltmeter, which detects the electrical difference (voltage) across the plasma membrane.

41
Q

Factors of resting membrane potentials

• unequal distribution of ions

A

• across the plasma membrane and the selective permeability of the neuron’s membrane to Na+ and K+
- non-conducting neuron is positive outside and negative inside

42
Q

Factors of resting membrane potentials

• most anions cannot leave the cell

A

• Most anions inside the cell cannot leave freely (unlike K+) because they are attached to non diffusible molecules such as ATP and large proteins
- non-conducting neuron is positive outside and negative inside

43
Q

Factors of resting membrane potentials

• Na+/K+ pumps (Na+/K+ ATPase)

A

• Na+/K+ ATPase expels 3 Na+ for every 2 K+ imported. Since this pump removes more positive charges from the cell than it can bring in the pump is electrogenic-contributes to the negative resting membrane potential
- non-conducting neuron is positive outside and negative inside

44
Q

Graded potential

A

• A graded potential is a small deviation from the resting membrane potential that makes the membrane either more polarized (inside more negative) or less polarized (inside less negative)

45
Q

Hyperpolarizing graded potential

A

• When the response makes the membrane more polarized (inside more negative)

46
Q

Depolarizing graded potentials

A

• When the response makes the membrane less polarized (inside less negative)

47
Q

Amplitude

A

electrical signals are graded means that they vary in (size), depending on the strength of the stimulus

48
Q

Postsynaptic potential

A

• When a graded potential occurs in the dendrites or cell body of a neuron in response to a neurotransmitter

49
Q

Receptor potentials

A

• The graded potentials that occur in sensory receptors

50
Q

Stimulus strength

A

•The opening or closing of these ion channels alters the flow of specific ions across the membrane, producing a flow of current that is localized.
•This mode of travel by which graded potentials die out as they spread along the membrane is known as decremental conduction.
•Because they die out within a few millimeters of their point of origin, graded potentials are useful for short-distance communication only
•Summation is the process by which graded potentials add together. If two depolarizing graded potentials summate, the net result is a larger depolarizing graded potential.

51
Q

Action potential

A

•impulse is a sequence of rapidly occurring events that decrease and
reverse the membrane potential and then eventually restore it to the resting state.
•An action potential has two main phases: a depolarizing phase and a repolarizing phase.

52
Q

Depolarizing phase

A

• the negative membrane potential becomes less negative, reaches zero, and then becomes positive

53
Q

Repolarizing phase

A

• the membrane potential is restored to the resting state of −70 mV

54
Q

After-hyper polarizing phase

A

• Following the repolarizing phase there may be an after-hyperpolarizing phase, during which the membrane potential temporarily becomes more negative than the resting level.

55
Q

Causes of action potential phases

A

•Two types of voltage-gated channels open and then close during an action potential.
•These channels are present mainly in the axon plasma membrane and axon terminals.
•The first channels that open, the voltage-gated Na+ channels, allow Na+ to rush into the cell, which causes the depolarizing phase.
•Then voltage-gated K+ channels open, allowing K+ to flow out, which produces the repolarizing phase.
•The after-hyperpolarizing phase occurs when the voltage-gated K+ channels remain open after the repolarizing phase ends

56
Q

Stimulation strength

A

•An action potential occurs in the membrane of the axon of a neuron when depolarization reaches a certain level termed the threshold.
•The generation of an action potential depends on whether a particular stimulus is able to bring the membrane potential to threshold.
•An action potential will not occur in response to a subthreshold stimulus-
a weak depolarization that cannot bring the membrane potential to threshold.
•However, an action potential will occur in response to a threshold stimulus-
a stimulus that is just strong enough to depolarize the membrane to threshold.
•Several action potentials will form in response to a suprathreshold stimulus-
a stimulus that is strong enough to depolarize the membrane above threshold.
•Each of the action potentials caused by a suprathreshold stimulus has the same amplitude (size) as an action potential caused by a threshold stimulus but will have greater frequency

57
Q

Refractory period

A

• The period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus
• During the absolute refractory period, even a very strong stimulus cannot initiate a second action potential.

58
Q

Refractory period

A

• The period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus
- During the absolute refractory period, even a very strong stimulus cannot initiate a second action potential.

59
Q

Relative refractory period

A

• period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus.
•In contrast to action potentials, graded potentials do not exhibit a refractory period

60
Q

Continuous conduction

A

• involves step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane.
•In continuous conduction, ions flow through their voltage-gated channels in each adjacent segment of the membrane.
•Note that the action potential propagates only a relatively short distance in a few milliseconds.
•Continuous conduction occurs in unmyelinated axons and in muscle fibers

61
Q

Saltatory conduction

A

• (= leaping), the special mode of action potential propagation that occurs along myelinated axons, occur because of the uneven distribution of voltage-gated channels.
•When an action potential propagates along a myelinated axon, an electric current (carried by ions) flows through the extracellular fluid surrounding the myelin sheath and through the cytosol from one node to the next.
•The action potential at the first node generates ionic currents in the cytosol and extracellular fluid that depolarize the membrane to threshold, opening voltage-gated Na+ channels at the second node.
•The resulting ionic flow through the opened channels constitutes an action potential at the second node.
•Then, the action potential at the second node generates an ionic current that opens voltage-gated Na+ channels at the third node, and so on.
•Each node repolarizes after it depolarizes

62
Q

Presynaptic neuron

A

• (pre- = before) refers to a nerve cell that carries a nerve impulse toward a synapse. It is the cell that sends a signal

63
Q

Postsynaptic neuron

A

• cell that receives a signal
• (post- = after) that carries a nerve impulse away from a synapse or an effector cell that responds to the impulse at the synapse

64
Q

Axondendritic

A

Axon to dendrite

65
Q

Axosomatic

A

Axon to cell body

66
Q

Axoaxonic

A

Axon to axon

67
Q

Electrical synapse

A

•Gap junctions connect cells and allow the transfer of information to synchronize the activity of a group of cells
•Each gap junction contains a hundred or so tubular connexons, which act like tunnels to connect the cytosol of the two cells directly.
•As ions flow from one cell to the next through the connexons, the action potential spreads from cell to cell

68
Q

Faster communication

A

• Because action potentials conduct directly through gap junctions, electrical synapses are faster than chemical synapses.
-At an electrical synapse, the action potential passes directly from the presynaptic cell to the postsynaptic cell

69
Q

Synchronization

A

• Electrical synapses can synchronize (coordinate) the activity of a group of neurons or muscle fibers.
-A large number of neurons or muscle fibers can produce action potentials in
unison if they are connected by gap junctions

70
Q

Chemical synapse

A

•One-way transfer of information from a presynaptic neuron to a postsynaptic neuron
•Plasma membranes of synapses are close but do not touch, separated by a synaptic cleft
•The presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (released neurotransmitter). The postsynaptic neuron receives the chemical signal and in turn generates an electrical signal (postsynaptic potential).
•The time required for these processes at a chemical synapse, a synaptic delay of about 0.5 msec, is the reason that chemical synapses relay signals more slowly than electrical synapses

71
Q

Axon potential in synapse

A
  1. A nerve impulse arrives at a synaptic end bulb (or at a varicosity) of a presynaptic axon.
  2. The depolarizing phase of the nerve impulse opens voltage-gated Ca2+ channels
    on the synaptic end bulbs. Because calcium ions are more concentrated in the extracellular fluid, Ca2+ flows inward through the opened channels.
  3. An increase in the concentration of Ca2+ inside the presynaptic neuron serves as a signal that triggers exocytosis of the synaptic vesicles. As vesicle membranes merge with the plasma membrane, neurotransmitter molecules within the vesicles are released into the synaptic cleft.
  4. The neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron’s plasma membrane.
  5. Binding of neurotransmitter molecules to their receptors on ligand-gated channels opens the
    channels and allows particular ions to flow across the membrane.
  6. As ions flow through the opened channels, the voltage across the membrane changes. This change in membrane voltage is a postsynaptic potential.
    •Depending on which ions the channels admit, the postsynaptic potential may be a depolarization (excitation) or a hyperpolarization (inhibition).
  7. When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the postsynaptic neuron.
72
Q

Excitatory postsynaptic potentials (EPSP)

A

•A depolarizing postsynaptic potential
•Opening of Na+ channels

73
Q

Inhibitory postsynaptic potentials (IPSP)

A

•A hyperpolarizing postsynaptic potential
•Opening of Cl- or K+ channels

74
Q

Ionotropic receptors

A

receptor that contains a neurotransmitter binding site and an ion channel

75
Q

Metabotropic receptors

A

receptor that contains a neurotransmitter binding site but No ion channel

76
Q

How neurotransmitters are removed from the synapse

A
  1. Diffusion
  2. Enzymatic degradation
  3. Uptake into cells
77
Q

Summation

A

• If several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse

78
Q

Spatial

A

•postsynaptic potentials in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time.
• results from the buildup of neurotransmitter released simultaneously by several presynaptic end bulbs

79
Q

Temporal

A

•postsynaptic potentials in response to stimuli that occur at the same location in the membrane of the postsynaptic cell but at different times.
•results from buildup of neurotransmitter released by a single presynaptic end bulb two or more times in rapid succession

80
Q

Summation of postsynaptic potentials

• EPSP

A

• If the total excitatory effects are greater than the total inhibitory effects but less than the threshold level of stimulation, the result is an EPSP that does not reach threshold.
•Following an EPSP, subsequent stimuli can more easily generate a nerve impulse through summation because the neuron is partially depolarized

81
Q

Summation of postsynaptic potentials

• nerve impulses

A

• If the total excitatory effects are greater than the total inhibitory effects and threshold is reached, one or more nerve impulses (action potentials) will be triggered.
•Impulses continue to be generated as long as the EPSP is at or above the threshold level

82
Q

Summation of postsynaptic potentials

• IPSP

A

• If the total inhibitory effects are greater than the excitatory effects, the membrane hyperpolarizes (IPSP).
•The result is inhibition of the postsynaptic neuron and an inability to generate a nerve impulse

83
Q

Gamma - aminobutyric acid (GABA)

A

• amino acid that acts as the main inhibitory neurotransmitter in the central nervous system
• reduces neuronal excitability by blocking nerve transmission
• binds to post-synaptic GABA receptors which hyperpolarizes the cell and prevents an action potential from being transmitted

84
Q

Diverging circuit

A

• the nerve impulse from a single presynaptic neuron causes the stimulation of increasing numbers of cells along the circuit
•This arrangement amplifies the signal

85
Q

Converging circuit

A

•the postsynaptic neuron receives nerve impulses from several different sources.

86
Q

Reverberating circuit

A

•the incoming impulse stimulates the first neuron, which stimulates the second, which stimulates the third, and so on.
•Branches from later neurons synapse with earlier ones.
•This arrangement sends impulses back through the circuit again and again.
•The output signal may last from a few seconds to many hours, depending on the number of synapses and the arrangement of neurons in the circuit

87
Q

Parallel after-discharge circuit

A

•a single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell.
•A differing number of synapses between the first and last neurons imposes varying synaptic delays, so that the last neuron exhibits multiple EPSPs or IPSPs.
•If the input is excitatory, the postsynaptic neuron then can send out a stream of impulses in quick succession.
•may be involved in precise activities such as mathematical calculations

88
Q

CNS regeneration and repair

A

•In the CNS, there is little or no repair due to:
•Inhibitory influences from neuroglia, particularly oligodendrocytes
•Absence of growth-stimulating cues that were present during fetal development
•Rapid formation of scar tissue

89
Q

PNS regeneration and repair

A

•repair is possible if the cell body is intact, Schwann cells are functional, and scar tissue formation does not occur too rapidly
•Steps involved in the repair process are:
Chromatolysis
•About 24 to 48 hours after injury the Nissl bodies break up into fine granular masses.
Wallerian degeneration
•By the third to fifth day, the part of the axon distal to the damaged region becomes slightly swollen and then breaks up into fragments; the myelin sheath also deteriorates but the neurolemma remains. Degeneration of the distal portion of the axon and myelin sheath

-Macrophages phagocytize the debris. Synthesis of RNA and protein accelerates, which favors rebuilding or regeneration of the axon.

Formation of a regeneration tube
•The Schwann cells on either side of the injured site multiply by mitosis, grow toward each other, and may form this
•The tube guides growth of a new axon from the proximal area across the injured area into the distal area previously occupied by the original axon.

-New axons cannot grow if the gap at the site of injury is too large
or if the gap becomes filled with collagen fibers.

A&P Lecture (3 decks)

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