Module 7: The Nervous System and Nervous Tissue

Lesson 3: The Function of Nervous Tissue

Chức Năng Của Mô Thần Kinh

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module The Nervous System and Nervous Tissue.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Nervous System and Nervous Tissue

absolute refractory period
time during an action period when another action potential cannot be generated because the voltage-gated Na+ channel is inactivated
action potential
change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
activation gate
part of the voltage-gated Na+ channel that opens when the membrane voltage reaches threshold
astrocyte
glial cell type of the CNS that provides support for neurons and maintains the blood-brain barrier
autonomic nervous system (ANS)
functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue
axon
single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell
axon hillock
tapering of the neuron cell body that gives rise to the axon
axon segment
single stretch of the axon insulated by myelin and bounded by nodes of Ranvier at either end (except for the first, which is after the initial segment, and the last, which is followed by the axon terminal)
axon terminal
end of the axon, where there are usually several branches extending toward the target cell
axoplasm
cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body
biogenic amine
class of neurotransmitters that are enzymatically derived from amino acids but no longer contain a carboxyl group
bipolar
shape of a neuron with two processes extending from the neuron cell body—the axon and one dendrite
blood-brain barrier (BBB)
physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS
brain
the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord
central nervous system (CNS)
anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord
cerebral cortex
outermost layer of gray matter in the brain, where conscious perception takes place
cerebrospinal fluid (CSF)
circulatory medium within the CNS that is produced by ependymal cells in the choroid plexus filtering the blood
chemical synapse
connection between two neurons, or between a neuron and its target, where a neurotransmitter diffuses across a very short distance
cholinergic system
neurotransmitter system of acetylcholine, which includes its receptors and the enzyme acetylcholinesterase
choroid plexus
specialized structure containing ependymal cells that line blood capillaries and filter blood to produce CSF in the four ventricles of the brain
continuous conduction
slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na+ channels located along the entire length of the cell membrane
dendrite
one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells
depolarization
change in a cell membrane potential from rest toward zero
effector protein
enzyme that catalyzes the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor
electrical synapse
connection between two neurons, or any two electrically active cells, where ions flow directly through channels spanning their adjacent cell membranes
electrochemical exclusion
principle of selectively allowing ions through a channel on the basis of their charge
enteric nervous system (ENS)
neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections
ependymal cell
glial cell type in the CNS responsible for producing cerebrospinal fluid
excitable membrane
cell membrane that regulates the movement of ions so that an electrical signal can be generated
excitatory postsynaptic potential (EPSP)
graded potential in the postsynaptic membrane that is the result of depolarization and makes an action potential more likely to occur
G protein
guanosine triphosphate (GTP) hydrolase that physically moves from the receptor protein to the effector protein to activate the latter
ganglion
localized collection of neuron cell bodies in the peripheral nervous system
gated
property of a channel that determines how it opens under specific conditions, such as voltage change or physical deformation
generator potential
graded potential from dendrites of a unipolar cell which generates the action potential in the initial segment of that cell’s axon
glial cell
one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons
graded potential
change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it
gray matter
regions of the nervous system containing cell bodies of neurons with few or no myelinated axons; actually may be more pink or tan in color, but called gray in contrast to white matter
inactivation gate
part of a voltage-gated Na+ channel that closes when the membrane potential reaches +30 mV
inhibitory postsynaptic potential (IPSP)
graded potential in the postsynaptic membrane that is the result of hyperpolarization and makes an action potential less likely to occur
initial segment
first part of the axon as it emerges from the axon hillock, where the electrical signals known as action potentials are generated
integration
nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response
ionotropic receptor
neurotransmitter receptor that acts as an ion channel gate, and opens by the binding of the neurotransmitter
leakage channel
ion channel that opens randomly and is not gated to a specific event, also known as a non-gated channel
ligand-gated channels
another name for an ionotropic receptor for which a neurotransmitter is the ligand
lower motor neuron
second neuron in the motor command pathway that is directly connected to the skeletal muscle
mechanically gated channel
ion channel that opens when a physical event directly affects the structure of the protein
membrane potential
distribution of charge across the cell membrane, based on the charges of ions
metabotropic receptor
neurotransmitter receptor that involves a complex of proteins that cause metabolic changes in a cell
microglia
glial cell type in the CNS that serves as the resident component of the immune system
multipolar
shape of a neuron that has multiple processes—the axon and two or more dendrites
muscarinic receptor
type of acetylcholine receptor protein that is characterized by also binding to muscarine and is a metabotropic receptor
myelin
lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals
myelin sheath
lipid-rich layer of insulation that surrounds an axon, formed by oligodendrocytes in the CNS and Schwann cells in the PNS; facilitates the transmission of electrical signals
nerve
cord-like bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system
neuron
neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system
neuropeptide
neurotransmitter type that includes protein molecules and shorter chains of amino acids
neurotransmitter
chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
nicotinic receptor
type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor
node of Ranvier
gap between two myelinated regions of an axon, allowing for strengthening of the electrical signal as it propagates down the axon
nonspecific channel
channel that is not specific to one ion over another, such as a nonspecific cation channel that allows any positively charged ion across the membrane
nucleus
in the nervous system, a localized collection of neuron cell bodies that are functionally related; a “center” of neural function
oligodendrocyte
glial cell type in the CNS that provides the myelin insulation for axons in tracts
peripheral nervous system (PNS)
anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord
postsynaptic potential (PSP)
graded potential in the postsynaptic membrane caused by the binding of neurotransmitter to protein receptors
precentral gyrus of the frontal cortex
region of the cerebral cortex responsible for generating motor commands, where the upper motor neuron cell body is located
process
in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites
propagation
movement of an action potential along the length of an axon
receptor potential
graded potential in a specialized sensory cell that directly causes the release of neurotransmitter without an intervening action potential
refractory period
time after the initiation of an action potential when another action potential cannot be generated
relative refractory period
time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K+ channels are not closed
repolarization
return of the membrane potential to its normally negative voltage at the end of the action potential
resistance
property of an axon that relates to the ability of particles to diffuse through the cytoplasm; this is inversely proportional to the fiber diameter
response
nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli
resting membrane potential
the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV
saltatory conduction
quick propagation of the action potential along a myelinated axon owing to voltage-gated Na+ channels being present only at the nodes of Ranvier
satellite cell
glial cell type in the PNS that provides support for neurons in the ganglia
Schwann cell
glial cell type in the PNS that provides the myelin insulation for axons in nerves
sensation
nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue
size exclusion
principle of selectively allowing ions through a channel on the basis of their relative size
soma
in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites)
somatic nervous system (SNS)
functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes
spatial summation
combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential
spinal cord
organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors
stimulus
an event in the external or internal environment that registers as activity in a sensory neuron
summate
to add together, as in the cumulative change in postsynaptic potentials toward reaching threshold in the membrane, either across a span of the membrane or over a certain amount of time
synapse
narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell
synaptic cleft
small gap between cells in a chemical synapse where neurotransmitter diffuses from the presynaptic element to the postsynaptic element
synaptic end bulb
swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse
temporal summation
combination of graded potentials at the same location on a neuron resulting in a strong signal from one input
thalamus
region of the central nervous system that acts as a relay for sensory pathways
thermoreceptor
type of sensory receptor capable of transducing temperature stimuli into neural action potentials
threshold
membrane voltage at which an action potential is initiated
tract
bundle of axons in the central nervous system having the same function and point of origin
unipolar
shape of a neuron which has only one process that includes both the axon and dendrite
upper motor neuron
first neuron in the motor command pathway with its cell body in the cerebral cortex that synapses on the lower motor neuron in the spinal cord
ventricle
central cavity within the brain where CSF is produced and circulates
voltage-gated channel
ion channel that opens because of a change in the charge distributed across the membrane where it is located
white matter
regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin
Nội dung này đang được cập nhật.
Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
Having looked at the components of nervous tissue, and the basic anatomy of the nervous system, next comes an understanding of how nervous tissue is capable of communicating within the nervous system. Before getting to the nuts and bolts of how this works, an illustration of how the components come together will be helpful. An example is summarized in Figure 1.

Imagine you are about to take a shower in the morning before going to school. You have turned on the faucet to start the water as you prepare to get in the shower. After a few minutes, you expect the water to be a temperature that will be comfortable to enter. So you put your hand out into the spray of water. What happens next depends on how your nervous system interacts with the stimulus of the water temperature and what you do in response to that stimulus.

Found in the skin of your fingers or toes is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor. When you place your hand under the shower (Figure 2), the cell membrane of the thermoreceptors changes its electrical state (voltage). The amount of change is dependent on the strength of the stimulus (how hot the water is). This is called a graded potential. If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. You have learned about this type of signaling before, with respect to the interaction of nerves and muscles at the neuromuscular junction. The voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential. In this example, the action potential travels—a process known as propagation—along the axon from the axon hillock to the axon terminals and into the synaptic end bulbs. When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter.

The neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron. When the molecular signal binds to the receptor, the cell membrane of the target neuron changes its electrical state and a new graded potential begins. If that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its axon hillock. The target of this neuron is another neuron in the thalamus of the brain, the part of the CNS that acts as a relay for sensory information. At another synapse, neurotransmitter is released and binds to its receptor. The thalamus then sends the sensory information to the cerebral cortex, the outermost layer of gray matter in the brain, where conscious perception of that water temperature begins.

Within the cerebral cortex, information is processed among many neurons, integrating the stimulus of the water temperature with other sensory stimuli, with your emotional state (you just aren’t ready to wake up; the bed is calling to you), memories (perhaps of the lab notes you have to study before a quiz). Finally, a plan is developed about what to do, whether that is to turn the temperature up, turn the whole shower off and go back to bed, or step into the shower. To do any of these things, the cerebral cortex has to send a command out to your body to move muscles (Figure 3).

A region of the cortex is specialized for sending signals down to the spinal cord for movement. The upper motor neuron is in this region, called the precentral gyrus of the frontal cortex, which has an axon that extends all the way down the spinal cord. At the level of the spinal cord at which this axon makes a synapse, a graded potential occurs in the cell membrane of a lower motor neuron. This second motor neuron is responsible for causing muscle fibers to contract. In the manner described in the chapter on muscle tissue, an action potential travels along the motor neuron axon into the periphery. The axon terminates on muscle fibers at the neuromuscular junction. Acetylcholine is released at this specialized synapse, which causes the muscle action potential to begin, following a large potential known as an end plate potential. When the lower motor neuron excites the muscle fiber, it contracts. All of this occurs in a fraction of a second, but this story is the basis of how the nervous system functions.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

(1) The sensory neuron has endings in the skin that sense a stimulus such as water temperature. The strength of the signal that starts here is dependent on the strength of the stimulus. (2) The graded potential from the sensory endings, if strong enough, will initiate an action potential at the initial segment of the axon (which is immediately adjacent to the sensory endings in the skin). (3) The axon of the peripheral sensory neuron enters the spinal cord and contacts another neuron in the gray matter. The contact is a synapse where another graded potential is caused by the release of a chemical signal from the axon terminals. (4) An action potential is initiated at the initial segment of this neuron and travels up the sensory pathway to a region of the brain called the thalamus. Another synapse passes the information along to the next neuron. (5) The sensory pathway ends when the signal reaches the cerebral cortex. (6) After integration with neurons in other parts of the cerebral cortex, a motor command is sent from the precentral gyrus of the frontal cortex. (7) The upper motor neuron sends an action potential down to the spinal cord. The target of the upper motor neuron is the dendrites of the lower motor neuron in the gray matter of the spinal cord. (8) The axon of the lower motor neuron emerges from the spinal cord in a nerve and connects to a muscle through a neuromuscular junction to cause contraction of the target muscle.

Receptors in the skin sense the temperature of the water.

On the basis of the sensory input and the integration in the CNS, a motor response is formulated and executed.

Nội dung này đang được cập nhật.
Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. Sensation starts with the activation of a sensory ending, such as the thermoreceptor in the skin sensing the temperature of the water.
  2. The sensory endings in the skin initiate an electrical signal that travels along the sensory axon within a nerve into the spinal cord, where it synapses with a neuron in the gray matter of the spinal cord.
  3. The temperature information represented in that electrical signal is passed to the next neuron by a chemical signal that diffuses across the small gap of the synapse and initiates a new electrical signal in the target cell.
  4. That signal travels through the sensory pathway to the brain, passing through the thalamus, where conscious perception of the water temperature is made possible by the cerebral cortex.
  5. Following integration of that information with other cognitive processes and sensory information, the brain sends a command back down to the spinal cord to initiate a motor response by controlling a skeletal muscle.
  6. The motor pathway is composed of two cells, the upper motor neuron and the lower motor neuron.
  7. The upper motor neuron has its cell body in the cerebral cortex and synapses on a cell in the gray matter of the spinal cord.
  8. The lower motor neuron is that cell in the gray matter of the spinal cord and its axon extends into the periphery where it synapses with a skeletal muscle in a neuromuscular junction.
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