Chr. 12 - Nervous Tissue Flashcards
(138 cards)
1
Q
[12.1] What is the central nervous system, and what is it responsible for?
A
Consists of the brain and the spinal cord and is responsible for processing information. Also generates thoughts, emotions, memories, and stimulates muscles for contraction and glands for secretions.
2
Q
[12.1] What is the peripheral nervous system?
A
Consists of all nervous tissue outside CNS, primarily nerves and sensory receptors.
3
Q
[12.1] What is a nerve?
A
A bundle of many neurons and associated connective tissue that lie outside the brain and spinal cord.
4
Q
[12.1] What is a sensory receptor?
A
A structure of the nervous system that monitors or detects changes in the external or internal environment.
5
Q
[12.1] What are the two divisions of the peripheral nervous system?
A
Sensory and motor.
6
Q
[12.1] Describe the sensory division of the PNS.
A
Sends information about stimuli to the CNS from sensory receptors.
7
Q
[12.1] Describe the motor division of the PNS.
A
Sends impulses from the CNS to effectors throughout the body.
8
Q
[12.1] What are the divisions of the motor division?
A
Somatic nervous system and autonomic nervous system.
9
Q
[12.1] Describe the somatic nervous system.
A
Subdivision of the motor division, conveys impulses to skeletal muscles only.
10
Q
[12.1] Describe the autonomic nervous system.
A
Subdivision of the motor division, conveys impulses to smooth muscle, cardiac muscle, and glands.
11
Q
[12.1] What are the branches of the autonomic nervous system?
A
The sympathetic, parasympathetic, and enteric nervous system.
12
Q
[12.1] List and describe the functions of the nervous system.
A
Sensory function, to detect internal/external stimuli and relate it to the CNS.
Integrative function, process and analyze sensory information and make decisions accordingly.
Motor function, send impulses to effectors to generate a response to stimuli.
13
Q
[12.2] Which types of cells compose nervous tissue?
A
Neurons and neuroglia.
14
Q
[12.2] What is electrical excitability?
A
The ability to respond to a stimulus and convert it into an action potential.
15
Q
[12.2] Define stimuli.
A
Any change in the environment that initiates an action potential.
16
Q
[12.2] Define an action potential.
A
An electrical signal that propagates along the surface of a membrane.
17
Q
[12.2] List the parts of a neuron.
A
Cell body, axon, dendrites.
18
Q
[12.2] Describe the cell body of a neuron.
A
A nucleus surrounded by cytoplasm and containing typical organelles except for having free floating ribosomes and clusters of rough ERs termed Nissl bodies.
19
Q
[12.2] What are neurofibrils?
A
Bundles of intermediate filaments.
20
Q
[12.2] What is lipofuscin?
A
A pigment occurring in the cytoplasm as a neuron ages, yellow-brown in colour.
21
Q
[12.2] What is a ganglion?
A
A collection of neuron cell bodies outside the CNS.
22
Q
[12.2] What is a nerve fiber?
A
Any neuronal process emerging from the cell body of a neuron, termed either an axon or a dendrite.
23
Q
[12.2] What is a dendrite?
A
Processes of neurons that exist on a receiving end of a synapse. Usually short, tapering, and highly branches to allow for a large amount of synapses.
24
Q
[12.2] What is an axon?
A
A neuronal process that propagates nerve impulses toward n effector or another neuron.
25
[12.2] Describe the anatomy of an axon.
A long, thin, cylindrical projection that joins to the body at the axon hillock. The initial segment is the portion of the axon that articulates with the axon hillock, and together the are known as the "trigger zone" as this is where action potentials are generated. Axons contain cytoplasm known as axoplasm, and the plasma membrane is known as the axolemma. Side processes of an axon are axon collaterals and the axon processes that form synapses are axon terminals.
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[12.2] What is a synapse?
The site of communication between two neurons, or a neuron and an effector cell.
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[12.2] What are synaptic end bulbs?
Bulb-shaped structures on axon terminals that contain synaptic vesicles that store a neurotransmitter.
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[12.2] What are variscosities?
A string of swollen bumps present on the tips of axon terminal containing synaptic vesicles.
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[12.2] What are synaptic vesicles?
Vesicles found in synaptic bulb ends and varicosities containing neurotransmitters.
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[12.2] What is a neurotransmitter?
A molecule released from a synaptic vesicle that excites or inhibits another neuron.
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[12.2] What is slow axonal transport?
A transport system moving axoplasm from cell body to axon terminals.
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[12.2] What is fast axonal transport?
A transport system using proteins the move materials along microtubules of the cytoskeleton, in anterograde or retrograde.
33
[12.2] List and describe the structural classifications of neurons.
Multipolar neurons, contain several dendrites and one axon. Found primarily in CNS.
Bipolar neurons, contain one main dendrite and one axon. Found in special sensory areas.
Unipolar neurons, contain a dendrite and axon that form a single process, also known as pseudounipolar neurons.
34
[12.2] What are Purkinje and pyramidal cells?
Purkinje cells are undescribed in the textbook thusfar and are found in the cerebellum.
Pyramidal cells are cells with a pyramid shape and are found in the cerebral cortex.
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[12.2] List and describe functional classifications of neurons.
Sensory neurons, unipolar neurons that contain sensory receptors on dendritic ends or are located immediately after sensory receptor cells. Forms action potential that is conveyed towards CNS.
Motor neurons, multipolar neurons that convey action potential away from CNS and to effectors.
Interneurons, multipolar neurons that lie between sensory and motor neurons. Integrate sensory information and elicit a motor response with appropriate motor neurons.
36
[12.2] What are neuroglia?
Cells making up a large portion of nervous tissue that do not propagate action potentials, are able to multiply, and fills absent spaces.
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[12.2] What is a glioma?
A tumour derived from neuroglia.
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[12.2] List the neuroglia of the CNS.
Astrocytes, oligodendrocytes, microglial, ependymal.
39
[12.2] Describe astrocytes.
Star-shaped cells that support neurons with structure and isolate neurons of the CNS blood supply, forming a part of the blood-brain barrier. Two varieties exist: protoplasmic astrocytes, with many short, branching processes found in grey matter; and fibrous astrocytes with many long, unbranched processes found in white matter.
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[12.2] Describe oligodendrocytes.
Cells similar to astrocytes but with fewer processes. Form and maintain the myelin sheath of multiple axons by extending processes and forming sheath from these processes.
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[12.2] What is the myelin sheath?
A multilayered lipid-protein covering around axons that provides electrical insulation increasing speed of nerve impulse conduction.
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[12.2] Describe microglial cells.
Small cells that act as phagocytes, removing cellular debris and harmful microbes.
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[12.2] Describe ependymal cells.
Cuboidal/columnar cells arranged in a single layer. Produce, monitor, and assist in circulation of cerebrospinal fluid.
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[12.2] List the neuroglia of the PNS.
1. Schwann cells
2. Satellite cells
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[12.2] What are Schwann cells?
Cells encircling segments of the axon of PNS creating a myelin sheath. Each cell is the myelin sheath, typically myelinates one cell but multiple axons can pass through same cell.
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[12.2] What are satellite cells?
Flat cells that provide structure and nutrition for PNS ganglia.
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[12.2] What is the neurolemma as it relates to Schwann cells?
The outer cytoplasmic layer of the Schwann cell that contains the nucleus and encloses the myelin sheath. Only found on PNS cells.
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[12.2] What are nodes of Ranvier?
Gaps in the myelin sheath appearing at intervals.
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[12.2] What is the difference between a ganglion and a nucleus in the nervous tissue?
A ganglion is a collection of neuronal cell bodies in the PNS.
A nucleus is a collection of neuronal cell bodies in the CNS.
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[12.2] What is the difference between a nerve and a tract.
A nerve is a bundle of axons located in the PNS.
A tract is a bundle of axons located in the CNS.
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[12.2] Describe white matter.
Groups of nervous tissue composed primarily of myelinated axons.
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[12.2] Describe grey matter.
Groups of nervous tissue composed of neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia.
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[12.3] What are the types of electrical signals used by nervous tissue?
Graded potential and action potential.
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[12.3] What is a membrane potential?
An electrical potential difference across the membrane.
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[12.3] What is voltage?
A difference in electrical charge.
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[12.3] What is current?
A flow of charged particles.
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[12.3] What is an ion channel?
Proteins that can open or close to allow specific ions to move down the electrochemical gradients across a membrane.
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[12.3] List the four types of ion channels.
Leak channels, ligand-gated channels, mechanically-gated channels, and voltage-gated channels.
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[12.3] Describe leak channels.
Transmembrane proteins that randomly alternate between open and close allowing ions to flow across their concentration gradient. Typically contain more potassium channels than sodium channels.
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[12.3] Describe a ligand-gated channel.
Transporter proteins that open and close in response to binding of a ligand. Located primarily in dendrites of sensory neurons, and dendrites and cell bodies of interneurons and motor neurons.
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[12.3] Describe a mechanically-gated channel.
Transporter proteins that open and close in response to mechanical stimulation (touch, vibration, pressure, stretching, etc).
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[12.3] Describe a voltage-gated channel.
Transporter proteins that open and close in response to membrane potential.
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[12.4] Describe the resting membrane potential.
An electrical charge difference built up across the plasma membrane with negative ions on the cytosol side and positive ions in the extracellular fluid. Typically rests at a voltage of -70mV.
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[12.4] What does it mean for a cell to be polarized?
A polarized cell is a cell that has a membrane potential.
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[12.4] What factors contribute to the resting membrane potential?
1. Unequal distribution of ions in the ECF and cytosol
2. Inability of most anions to leave the cell
3. Electrogenic nature of sodium-potassium ATPases.
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[12.5] Describe a graded potential.
A small deviation from resting membrane potential that shifts polarization in either direction (more positive or more negative). They vary in amplitude and strength depending on the specific stimuli, and are a localized current.
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[12.5] What is a hyperpolarizing graded potential?
When a graded potential makes the resting membrane potential more negative.
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[12.5] What is a depolarizing graded potential?
When a graded potential makes the resting membrane potential more positive.
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[12.5] What is decremental conduction?
The mode of travel of graded potentials, where a potential loses charge across a distance through leak channels.
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[12.5] What is summation?
The process by which graded potentials add together.
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[12.6] Describe an action potential.
A sequence of rapidly occurring events that decrease, reverse, then restore the membrane potential.
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[12.6] What are the phases of an action potential?
Depolarizing phase, repolarizing phase, and after-hyperpolarizing phase which does not always occur.
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[12.6] What is a threshold?
A level of voltage that when reached, triggers an action potential.
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[12.6] List the types of a stimulus.
1. Subthreshold stimulus
2. Threshold stimulus
3. Suprathreshold stimulus
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[12.6] What is a subthreshold stimulus?
A weak depolarization that does not reach threshold and therefore does not trigger an action potential.
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[12.6] What is a threshold stimulus?
A stimulus strong enough to depolarize the membrane and trigger an action potential.
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[12.6] What is a suprathreshold stimulus?
A stimulus stronger than necessary to trigger an action potential and results in an increase of frequency of action potential until the maximum rate.
78
[12.6] What is the all-or-none principle?
The rule that an action potential either triggers completely or doesn't.
79
[12.6] Describe the depolarizing phase.
The first phase of an action potential that occurs when a threshold stimulus is introduced. Voltage-gated sodium channels open and allow sodium to move across the electrochemical gradient freely. The inflow changes membrane potential from -55/-70mV to +30mV.
80
[12.6] What are activation gates and inactivation gates?
Gates that allow sodium to flow into the cytosol from the extracellular fluid only when both are open. Inactivation gates are only open during resting, and activation gates only open during an action potential; however, both gates are open for a brief moment as a membrane depolarizes, allowing the influx of sodium.
81
[12.6] Describe the repolarizing phase.
Voltage-gated sodium channels close and potassium-gated channels open allowing potassium to exit the cell, re-establishing the -70mV charge.
82
[12.6] What is the after-hyperpolarizing phase?
Occurs when there is a large outflow of potassium, creating a voltage of -90 mV which then resets to -70mV.
83
[12.6] What is the refractory period?
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.
84
[12.6] What is the absolute refractory period?
The section of a refractory period in which no stimulus can elicit an action potential, no matter how strong.
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[12.6] What is the relative refractory period?
The period of time which a second action potential can be trigger due to a suprathreshold stimulus. Occurs when potassium channels are open and sodium channels have returned to resting state.
86
[12.6] What is propagation?
A method of conduction where an action potential keeps its strength as it travels, relying on positive feedback.
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[12.6] What are the types of propagation?
Continuous conduction and saltatory conduction.
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[12.6] Describe continuous conduction.
A slow type of conduction that propagates through step-by-step depolarization and repolarization of each adjacent section of the neuronal plasma membrane. Occurs in unmyelinated and muscle fibers.
89
[12.6] Describe saltatory conduction.
A fast type of conduction that propagates through myelinated axons. Occurs due to uneven distribution of voltage-gated channels between myelinated portions and nodes of Ranvier. Depolarization at nodes triggers depolarization at other nodes faster as the electric current travels through the extracellular fluid and cytosol rather than along the plasma membrane.
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[12.6] List and describe the factors that affect propagation.
Amount of myelination, a larger amount of myelination increases speed.
Axon diameter, larger diameter increases surface area which increases speed.
Temperature, a higher temperature increases speed of propagation.
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[12.6] List the classifications of nerve fibers.
A fibers, B fibers, C fibers.
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[12.6] Describe A fibers.
Largest diameter of nerve fibers, myelinated with a brief absolute refractory period and conduct nerve impulses the quickest. Associated with touch, pressure, proprioception, and some thermal/pain. Innervate muscles.
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[12.6] Describe B fibers.
Myelinated nerve fibers with longer absolute refractory periods. Innervate viscera and ANS.
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[12.6] Describe C fibers.
Smallest diameter axons, unmyelinated. Longest absolute refractory period. Conduct impulses for pain, touch, proprioception, heat, and cold from skin, pain from viscera.
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[12.6] Describe the qualities of graded potentials.
Arise from dendrites, feature ligand- and mechanically-gated channels that do not have refractory period,and allow for summation. Decremental conductions propagating over short distances with varying voltage that can prevail for a long duration and are able to hyperpolarize.
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[12.6] Describe the characteristics of action potentials.
Arise at trigger zones of axons, feature voltage-gated channels with refractory periods disallowing for summation. All-or-nothing conductions propagating over long distances with shorter duration and only depolarizing.
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[12.7] What is a presynaptic neuron?
A nerve cell that carries an impulse towards a synapse.
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[12.7] What is a postsynaptic neuron?
A nerve cell that receives an impulse.
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[12.7] List and describe the structural types of synapses?
Axodendritic, from axon to dendrite
Axosomatic, from axon to cell body
Axoaxonic, from axon to axon.
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[12.7] What are the functional types of synapses?
Electrical and chemical.
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[12.7] Describe electrical synapses.
Electrical synapses conducting action potentials through cell membrane using gap junctions. This is achieved through tubular connexons that connect the cytosol of both cells.
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[12.7] What are the advantages of electrical synapses?
Faster communications and synchronization.
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[12.7] Describe chemical synapses.
Synapses separated by a cleft filled with interstitial fluid. Release neurotransmitters to transform electrical signals into chemical signals that then stimulate the postsynaptic cell with graded potentials until an action potential is triggered again.
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[12.7] What is synaptic delay?
The time required for transmission at chemical synapse, about 0.5 msec.
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[12.7] Describe the process of a chemical signal transmission.
A nerve impulse arrives at the synaptic bulb end of an axon, depolarizing the membrane and opening voltage-gated calcium channels. The influx of calcium triggers exocytosis of synaptic vesicles that are released into the synaptic cleft. Neurotransmitters diffuse across the synaptic cleft and bind to receptors in the postsynaptic cell. Binding triggers ligand-gated channels to open, generating a graded potential that is either depolarizing or hyperpolarizing.
106
[12.7] What is excitatory postsynaptic potential (EPSP)?
An EPSP is a depolarizing postsynaptic potential.
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[12.7] What is an inhibitory postsynaptic potential (IPSP)?
An IPSP is a hyperpolarizing postsynaptic potential.
108
[12.7] Describe ionotropic receptors.
A type of neurotransmitter receptor that contains a binding site and an ion channel in the same protein. Excitatory receptors typically contain cation channels, and inhibitory receptors contain anion channels.
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[12.7] Describe metabotropic receptors.
Receptors that contain a binding site but no channel - instead they are coupled to a channel linked by a G protein, which opens the channel when the receptor binds a ligand.
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[12.7] List the ways neurotransmitters are removed.
Diffusion, enzymatic degradation, and uptake by cells.
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[12.7] List and describe the types of summation.
Spatial summation, when a postsynaptic potential is generated in response to stimuli occurring at different locations of a membrane.
Temporal summation, when a postsynaptic potential is summated in response to stimuli occurring at the same location repeatedly over time.
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[12.8] What is a neurosecretory cell?
A neuron that also secretes hormones.
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[12.8] List the categories of neurotransmitters.
1. Acetylcholine
2. Amino Acids
3. Biogenic amines
4. Purines
5. Nitric Oxides
6. Carbon Monoxide
7. Neuropeptides
114
[12.8] Describe acetylcholine.
A neurotransmitter that acts as both excitatory and inhibitory based on receptor. Released mainly by PNS, with some CNS activity.
115
[12.8] Describe amino acids as neurotransmitters.
Amino acids that function as neurotransmitters within the CNS.
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[12.8] What are the excitatory amino acid neurotransmitters?
Glutamate and aspartate.
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[12.8] What are the inhibitory amino acid neurotransmitters?
GABA (gamma-aminobutyric acid) and glycine
118
[12.8] Describe biogenic amides.
Amino acids are modified in structure in addition to having their carboxyl group removed, resulting in biogenic amides.
Typically bind to metabotropic receptors and can cause excitatory or inhibitory effects depending on the receptor.
119
[12.8] What are catecholamines?
Biogenic amines with an amino group and a catechol ring involving two hydroxyl groups. Derived from tyrosine.
120
[12.8] List the important catecholamines.
Norepinephrine, epinephrine, and dopamine.
121
[12.8] What is monoamine oxidase?
An enzyme that breaks down catecholamines.
122
[12.8] What is seratonin?
A biogenic amine not categorized as a catecholamine but plays a distinct and important role.
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[12.8] What are purines?
A classification of neurotransmitter featuring purine rings that exhibit excitatory properties.
124
[12.8] Describe the role nitric oxide plays as a neurotransmitter.
Nitric oxide is important in excitatory potentials in the brain, spinal cord, adrenal glands, and nerves to the penis. Formed from arginine by nitric oxide synthase.
125
[12.8] Describe the role carbon monoxide plays as a neurotransmitter.
An excitatory neurotransmitter in the brain and in response to neuromuscular and neuroglandular functions.
126
[12.8] What are neuropeptides?
Neurotransmitters formed by a chain of 3 - 40 amino acids linked by peptide bonds. Excitatory or inhibitory depending on receptor.
127
[12.8] List the types of neuropeptides.
Enkephalins, endorphins, dynorphins, and substance P.
128
[12.9] What are neural circuits?
Complicated networks of neurons organized into functional groups that process specific types of information.
129
[12.9] What is a simple series circuit?
A neural circuit where a presynaptic neuron stimulates a single postsynaptic neuron.
130
[12.9] Describe a diverging circuit.
An neural circuit in which a single presynaptic neuron synapses with several postsynaptic neurons permitting a single presynaptic potential to proliferate and stimulate multiple postsynaptic potentials.
131
[12.9] Describe a converging circuit.
A neural circuit in which a single postsynaptic neuron receives impulses from multiple presynaptic neurons permitting enhanced stimulation or inhibition to the postsynaptic neuron.
132
[12.9] Describe a reverberating circuit.
A neural circuit with a chain of neurons simple circuits, but each neuron can branch to previous ones directly or through other neurons causing an action potential to loop back to previous neurons and commence the action potential cascade again.
133
[12.9] Describe a parallel after-discharge circuit.
A neural circuit where a single presynaptic neuron begins a diverging circuit that continues into a converging circuit, ending with a single postsynaptic neuron. Differing numbers of synapses in each branch leading to the post synaptic neuron leads to a delay in some action potentials, causing a rapid succession of EPSPs or IPSPs as they move throughout the circuit.
134
[12.9] Describe plasticity.
The capability to change based on experience.
135
[12.9] Describe regeneration.
The capability to replicate or repair.
136
[12.9] Describe neurogenesis.
The birth of new neurons from undifferentiated stem cells.
137
[12.9] What is epidermal growth factor?
A hormone-like protein that stimulates cells to proliferate into neurons and astrocytes.
138
[12.9] What factors contribute to the repair of neurons in the PNS?
Cell body remaining intact, Schwann cells remaining functional, and scar tissue not forming rapidly.
