Chapter 11 Flashcards
peripheral nervous system (PNS)
it includes sensory receptors, nerves, ganglia, and plexuses. The sensory division of the PNS detects stimuli and transmits information in the form of action potentials to the CNS.
central nervous system (CNS)
consists of the brain and spinal cord.
Sensory receptors
endings of neurons, or separate, specialized cells that detect temperature, pain, touch, pressure, light, sound, odor, and other stimuli.
nerve
bundle of axons and their sheaths; it connects the CNS to sensory receptors, muscles, and glands.
cranial nerves/ spinal nerves
12 pairs originate the brain, and 31 pairs of spinal nerves originate from the spinal cord
ganglion
a collection of neuron cell bodies located outside the CNS.
plexus
an extensive network of axons and, in some cases, neuron cell bodies, located outside the CNS.
The PNS has two functional subdivisions: The sensory division (afferent (toward) division) and the motor division (efferent (away) division)
- sensory - transmits electrical signals, called action potentials, from the sensory receptors to the CNS. The cell bodies of sensory neurons are located in dorsal root ganglia near the spinal cord or in ganglia near the origin of certain cranial nerves.
- motor division - transmits action potentials from the CNS to effector organs, such as muscles and glands.
The motor division is divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS).
-somatic nervous system controls conscious activities -ANS controls subconscious activities.
synapse
junction of a neuron with another cell; axons extend through nerves to form connections with skeletal muscle cells.
The ANS is subdivided into the sympathetic division and the parasympathetic division.
In general, the sympathetic division is most active during physical activity, whereas the parasympathetic division regulates resting functions, such as digesting food or emptying the urinary bladder.
enteric nervous system (ENS)
consists of plexuses within the wall of the digestive tract; enteric neurons monitor and control the digestive tract independently of the CNS through local reflexes.
The two types of cells that make up the nervous system are neurons and nonneural cells.
Neurons receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs. Nonneural cells are called neuroglia cells, and they support and protect neurons and perform other functions.
neuron cell body
cell body
Nissl bodies
The neurofilaments separate abundant ER which are located primarily in the cell body and dendrites; primary site of protein synthesis in neurons.
dendritic spines
Many dendrite surfaces have small extensions called dendritic spines, where axons of other neurons form syn- apses with the dendrites.
axon hillock
In most neurons, a single axon arises from this cone-shaped area of the neuron cell body
initial segment
beginning of the axon
trigger zone
Action potentials are generated at the trigger zone, which consists of the axon hillock and the part of the axon nearest the cell body.
axoplasm/axolemma
The cytoplasm of an axon is sometimes called the axoplasm, and its plasma membrane is called the axolemma.
presynaptic terminals
Axons terminate by branching to form small extensions with enlarged ends
neurotransmitters
Within the presynaptic terminals are these numerous small vesicles that contain chemicals
Sensory neurons (or afferent neurons)
conduct action potentials toward the CNS
motor neurons (or efferent neurons)
conduct action potentials away from the CNS toward muscles or glands.
Interneurons
conduct action potentials from one neuron to another within the CNS
Multipolar neurons
have many dendrites and a single axon.
Bipolar neurons
have two processes: one dendrite and one axon
Pseudo-unipolar neurons
have a single process extending from the cell body; This process divides into two branches a short distance from the cell body. One branch extends to the CNS, and the other extends to the periphery and has dendritelike sensory receptors.
Astrocytes
neuroglia that are star- shaped because cytoplasmic processes extend from the cell body. These extensions widen and spread out to form foot processes, which cover the surfaces of blood vessels, neurons, and the pia mater.
blood-brain barrier
endothelial cells with their tight junctions form the blood-brain barrier, which determines what substances can pass from the blood into the nervous tissue of the brain and spinal cord.
reactive astrocytosis
Almost all injuries to CNS tissue induce reactive astrocytosis, in which astrocytes wall off the injury site and help limit the spread of inflammation to the surrounding healthy tissue.
Ependymal cells
line the ventricles (cavities) of the brain and the central canal of the spinal cord
choroid plexuses
formed by specialized ependymal cells and blood vessels, which are located within certain regions of the ventricles; secrete the cerebrospinal fluid that circulates through the ventricles of the brain
Microglia
neuroglia in the CNS that become mobile and phagocytic in response to inflammation. They phagocytize necrotic tissue, microorganisms, and other foreign substances that invade the CNS.
Oligodendrocytes
have cytoplasmic extensions that can surround axons; form an insulating material called myelin sheath
Schwann cells
neuroglia in the PNS that wrap around axons; form a myelin sheath around a portion of only one axon
Satellite cells
surround neuron cell bodies in sensory ganglia; provide support and nutrition to the neuron cell bodies, protect neurons from heavy-metal poisons by absorbing them and reducing their access to the neuron cell bodies.
myelinated axons
in myelinated axons, the extensions from Schwann cells or oligodendrocytes repeatedly wrap around a segment of an axon to form a series of tightly wrapped membranes rich in phospholipids, with little cytoplasm sandwiched between the membrane layers
nodes of Ranvier
interruptions in the myelin sheath
Unmyelinated axons
rest in invaginations of the Schwann cells or oligodendrocytes
Gray matter
consists of groups of neuron cell bodies and their dendrites, where there is very little myelin.
cortex/nuclei
In the CNS, gray matter on the surface of the brain is called the cortex, and clusters of gray matter located deeper within the brain are called nuclei.
ganglion
a cluster of neuron cell bodies in the PNS
White matter
consists of bundles of parallel axons with their myelin sheaths, which are whitish in color.
White matter of the CNS
forms nerve tracts, or conduction pathways, which propagate action potentials from one area of the CNS to another. In the PNS, bundles of axons and their connective tissue sheaths are called nerves
sodium-potassium pump
The differences in K+ and Na+ concentrations across the plasma membrane are maintained primarily by the action of this
Leak ion channels
nongated ion channels; are always open and are responsible for the permeability of the plasma membrane to ions when the plasma membrane is unstimulated, or at rest
Gated ion channels
closed until opened by specific signals. By opening and closing, these channels can change the permeability of the plasma membrane.
ligand
a molecule, such as a neurotransmitter or a hormone, that binds to a receptor.
receptor
a protein or glycoprotein that has a receptor site to which a ligand can bind; located in plasma membrane
Ligand-gated ion channels
receptors that have an extracellular receptor site and a membrane- spanning part that forms an ion channel.
Voltage-gated ion channels
These channels open and close in response to small voltage changes across the plasma membrane.
other gated ion channels
Gated ion channels that respond to stimuli other than ligands or voltage changes are present in specialized electrically excitable tissues.
polarized
opposite charges, or poles, across the membrane.
potential difference
The electrical charge difference across the plasma membrane
resting membrane potential
In an unstimulated, or resting, cell, this is the potential difference
Depolarization
decrease in the membrane potential caused by a decrease in the charge difference, or polarity, across the plasma membrane
hyperpolarization
an increase in the membrane potential caused by an increase in the charge difference across the plasma membrane; occurs when the inside of the plasma membrane becomes more negative relative to the outside
graded potential
a change in the membrane potential that is localized to one area of the plasma membrane; can result from (1) chemical signals binding to their receptors, (2) changes in the voltage across the plasma membrane, (3) mechanical stimulation, (4) temperature changes, or (5) spontaneous changes in membrane permeability
Summation
Summation of graded potentials can occur when the effects produced by one graded potential are added onto the effects produced by another graded potential, which can lead to an action potential
action potential
an electrical signal conducted from a neuron to its target
threshold
a series of permeability changes results in an action potential
depolarization phase
the membrane potential moves away from the resting state and becomes more positive
repolarization phase
the membrane potential returns toward the resting state and becomes more negative
afterpotential
After the repolarization phase, the plasma membrane may be slightly hyperpolarized for a short period
activation gates and inactivation gates
Each voltage-gated Na+ channel has two voltage-sensitive gates; at rest, NA closed but when reaches threshold NA open and can diffuse; at rest K are closed but when reaches threshold K open but diffuse slower than NA
refractory period
Once an action potential is produced at a given point on the plasma membrane, the sensitivity of that area to further stimulation decreases for a time called the refractory period.
absolute refractory period
The first part of the refractory period, during which complete insensitivity exists to another stimulus
relative refractory period
The second part of the refractory period that follows the absolute refractory period; when the membrane is more permeable to K1 because many voltage-gated K1 channels are open; ends when the voltage-gated K1 channels close
action potential frequency
the number of action potentials produced per unit of time in response to a stimulus.
subthreshold stimulus
any stimulus not strong enough to produce a graded potential that reaches threshold.
threshold stimulus
produces a graded potential that is just strong enough to reach threshold and cause the production of a single action potential.
maximal stimulus
just strong enough to produce a maximum frequency of action potentials.
submaximal stimulus
includes all stimuli between threshold and the maximal stimulus strength.
supramaximal stimulus
any stimulus stronger than a maximal stimulus.
propagate
spread
Hypokalemia
a lower than normal concentration of K in the blood or extracellular fluid. Reduced extracellular K+ concentrations cause hyperpolarization of the resting membrane potential
Hypocalcemia
a lower than normal concentration of Ca2+ in the blood or extracellular fluid.
tetany
uncontrolled contraction of skeletal muscles
local current or an ionic current
The movement of positively charged ions
continuous conduction
action potential conduction in unmyelinated axons
saltatory conduction
In a myelinated axon, an action potential is conducted from one node of Ranvier to another
Nerve fibers (axons)
classified according to their size and myelination.
presynaptic cell
The cell that transmits a signal toward the synapse
postsynaptic cell
the cell that receives the signal
Electrical synapses
gap junctions that allow a local current to flow between adjacent cells
connexons
at these gap junctions, the membranes of adjacent cells are separated by these gap spanned by tubular proteins
The essential components of a chemical synapse are:
the presynaptic terminal, the synaptic cleft, and the postsynaptic membrane
presynaptic terminal
consists of the end of an axon
synaptic cleft
space separating the axon ending and the cell with which it synapses
postsynaptic cell
The membrane of the postsynaptic cell opposed to the presynaptic terminal; typically other neurons, muscle cells, or gland cells.
synaptic vesicles
contain neurotrans- mitters, such as acetylcholine
acetylcholinesterase
in the neuromuscular junction, the neurotransmitter acetylcholine is broken down by the enzyme acetylcholinesterase to acetic acid and choline
monoamine oxidase
This enzyme inactivates some of the norepinephrine.
catechol-O-methyltransferase
Norepinephrine in the circulation is taken up primarily by liver and kidney cells, where the enzymes monoamine oxidase and catechol-O-methyltransferase convert it into inactive metabolites.
Neuromodulators
substances released from neurons that influence the likelihood of an action potential being produced in the postsynaptic cell.
excitatory post- synaptic potential (EPSP)
When depolarization occurs, the response is stimulatory, and the graded potential is called an excitatory post- synaptic potential; important because the depolarization might reach threshold, thereby producing an action potential and a response from the cell.
inhibitory postsynaptic potential (IPSP)
When the combination of a neurotransmitter with its receptor results in hyperpolarization of the postsynaptic membrane, the response is inhibitory, and the local hyperpolarization is called an inhibitory postsynaptic potential; important because they decrease the likelihood of producing action potentials by moving the membrane potential farther from threshold.
inhibitory neurons
Neurons releasing neurotransmitter substances that cause IPSPs
axoaxonic synapses
Many of the synapses of the CNS are axoaxonic synapses, meaning that the axon of one neuron synapses with the presynaptic terminal (axon) of another
presynaptic inhibition
the amount of neurotransmitter released from the presynaptic terminal decreases.
presynaptic facilitation
the amount of neurotransmitter released from the presynaptic terminal increases.
Spatial summation
occurs when multiple action potentials arrive simultaneously at two different presynaptic terminals that synapse with the same postsynaptic neuron.
Temporal summation
results when two or more action potentials arrive in very close succession at a single presynaptic terminal.
convergent pathways
In convergent pathways, many neurons converge and synapse with a smaller number of neurons; Convergence allows different parts of the nervous system to activate or inhibit the activity of neurons.
divergent pathways
in divergent pathways, a smaller number of presynaptic neurons synapse with a larger number of postsynaptic neurons to allow information transmitted in one neuronal pathway to diverge into two or more pathways; allow one part of the nervous system to affect more than one other part of the nervous system.
Oscillating circuits
have neurons arranged in a circular fashion, which allows action potentials entering the circuit to cause a neuron farther along in the circuit to produce an action potential more than once; This response, called afterdischarge, prolongs the response to a stimulus.
