Nervous Flashcards
Central nervous system
Brain
Spinal cord
Peripheral nervous system
Cranial nerves (12 pairs; I-XII)
Spinal nerves (31 pairs)
Peripheral nerves (numerous)
The nervous system comprises the brain, spinal cord, spinal nerves, ganglia, enteric ___, and sensory receptors
plexuses
Receptors: detect changes in the internal or external environment
____ nerve cells (neurons) carry the sensory information from the receptors to the brain and spinal cord
____ neurons are afferent neurons
Sensory neuron
Analyze and store information
Make decisions
Many (maybe most) ____ neurons are interneurons, relatively short neurons in the brain, spinal cord, and ganglia that connect nearby neurons
Integrative neuron
Respond to decisions
____ neurons carry information from the brain and spinal cord to effectors (muscles or glands)
___ neurons are efferent neurons
motor neuron
Sensation from body wall, limbs, head, special senses (sight, hearing, taste, balance, smell)
Motor control of skeletal muscle (voluntary control)
somatic
Sensation from internal organs like heart, lungs, bladder, etc.
Motor control of smooth and cardiac muscle (i.e. involuntary muscle), glands (involuntary control)
autonomic
Sensation from gastrointestinal tract
Motor control of smooth muscle and glands of the gastrointestinal tract (involuntary control)
enteric
Each subdivision of the PNS has both sensory and motor neurons. The motor part of the autonomic nervous system consists of two branches: _____ division
sympathetic division and parasympathetic
Peripheral nervous system (PNS) consists of all nervous tissue outside the central nervous system:
somatic
autonomic
enteric
an association (a bundle) of neuronal axons in the peripheral nervous system
nerve
a group of neuronal cell bodies in the peripheral nervous system (plus associated tissue)
Ganglion
an association (a bundle) of neuronal axons in the central nervous system
Tract
an association (a bundle) of (unmyelinated) nerve cell bodies in the central nervous system
Nucleus
an extensive network of nerves found within the peripheral nervous system(PNS)
plexus
cells that have the property of electrical excitability, and are specially adapted to produce and transmit action potentials
neuron
cells of the nervous system that support, nourish, and protect the neurons
neuroglia
There are more neuroglia than neurons
Axoplasm (the ___ of an axon)
cytoplasm
Axolemma ( the ____ of axon)
plasmalemma
Also specialized forms of typical organelles, primarily ___, which are prominent clusters of rough ER
Nissl bodies
Like most cells, neurons have nucleus, cytoplasm, typical organelles (lysosomes, Golgi, mitochondria, etc.)
The receiving portion of a neuron
Typically short, tapering, highly branched
dendrites
Propagates impulses to another neuron, muscle, or nerve
Can approximate three feet long in humans
axon
Virtually always only a ___ axon per neuron
single
Typically arises from an elevation in the cell body called the axon ___
(axon)
hillock
First part is called the ___ segment
axon
initial
Impulses (action potentials) generally arise in the trigger zone, the junction of the ___ and initial segment
(axon)
hillock
Axon ___may branch off main axon
collaterals
Axon and collaterals end by dividing into axon terminals (telodendria), which end in either:
synaptic end bulbs, bulb-shaped structures
varicosities, string of swollen bumps
Axon contains:
But does not contain:
Mitochondria
Microtubules
Neurofibrils
endoplasmic reticulum, so protein synthesis does not occur in the axon
Axon cytoskeleton has ____ and ____
Neurofibrils
(Intermediate filaments
Provide cell shape and support)
Microtubules
(Tubulin that participate in moving material between the cell body and axon)
Synthesis of new proteins, vesicles, etc. takes place in the ___, not axon
cell body
Things made in the cell body must be transported along the interior of the axon to reach the axon ___
terminal
1-5 mm per day
One-way only, from cell body to axon terminals
Transports axoplasm to growing or regenerating axons
Slow axonal transport
200-400 mm per day
TWO WAY transport, both toward and away from cell body
Uses microtubules as “tracks” and “motors”
Transports organelles and materials that are used to form axolemma membranes, synaptic end bulbs, and synaptic vesicles
Fast axonal transport
Structural classification of neurons is based on the number of processes (axons or dendrites) extending from the cell body. For example:
multipolar
bipolar
pseudounipolar
Most neurons are classified as
multipolar
Bipolar neurons are typically found ___
special senses (olfactory)
Pseudounipolar are our ____ neurons
sensory
have several dendrites and only one axon and are located throughout the brain and spinal cord
Multipolar neurons
have one main dendrite and one axon
Bipolar neurons
They are used to convey the special senses of sight, smell, hearing and balance.
As such, they are found in the retina of the eye, the inner ear, and the olfactory (olfact = to smell) area of
the brain
Bipolar neurons
contain one process which extends from the body and divides into a central branch that functions as an axon
pseudounipolar
is often
employed for sensory neurons that convey touch
and stretching information from the extremities
pseudounipolar
Not excitable cells
Smaller, more numerous than neurons
Play a supporting role
Make up about half the volume of the CNS
In cases of injury or disease, neuroglia multiply to fill in the spaces formerly occupied by neurons
Neuroglia
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Neuroglia of the CNS
Schwann cells (neurolemmocytes)
Satellite cells
Neuroglia of the PNS
Regulate the composition of the
extracellular fluid in the CNS; help
form the blood-brain barrier; take up excess neurotransmitters; may influence formation of neural synapses
Astrocytes (CNS)
Myelinate axons in the CNS
Oligodendrocytes
Phagocytes of the CNS
Microglia (CNS)
Line the ventricles of the brain; produce, monitor, and aid in circulation of CSF; help form the blood-CSF barrier
ependymal cells (CNS)
Myelinate axons in the PNS
Schwann cells
the second type of PNS neuroglia. They provide structural support and regulate the exchange of materials between neuronal cell bodies and interstitial fluid
Satellite Cells
Neuroglia of the ____ completely surround axons and cell bodies of neurons
PNS
___ do not typically undergo mitosis, meaning if a neuron dies there is no reservoir of cells to replace it
Neurons
___ cells do undergo mitosis
Neuroglial
_____, brain tumors derived from glia, can be highly malignant and grow rapidly, and include astrocytomas, oligodendrogliomas, and schwannomas
Gliomas
____ is a multi-layered complex of lipids and proteins, i.e., layers of plasma membranes
Myelin
____ prevents loss of electrical signal; speeds up conduction of nerve impulses
myelin
insulates the axons
A _____ or an _____ can be associated with a neuron, yet the neuron may be unmyelinated.
Schwann cell (PNS)
oligodendrocyte (CNS)
___ requires the glial cell to have wrapped its plasma membrane around the axon many times
Myelination
A Schwann is called a ____ when it wraps its plasma membrane many times around the neuron’s axon.
neurolemmocyte
A Schwann cell migrates around the axon multiple times and multiple layers of the Schwann cell ____ surround the axon
plasma membrane
The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is the ____
neurolemma
Unmyelinated axons can be associated with Schwann cells, but the axons simply lay in ___ on the surface of the Schwann cell, in which case there is no myelin sheath (multiple layers) and no neurolemma
grooves
The nucleus of the neurolemmocyte comes to reside in the ____, which is the outer nucleated cytoplasmic layer of the Schwann cell
neurolemma
Outer layer of a myelinating Schwann cell
Contains the nucleus and virtually all the cytoplasm
Not to be confused with the axolemma
Found only around axons in the PNS
Neurolemma
Only on nerve fibers supplied by potentially myelin-producing cells
Gaps between myelinating cells (where there is no myelin)
Found in PNS and CNS
Nodes of Ranvier
A nerve fiber consists of axon plus ___(when present)
myelin sheath
The ____ surrounds the nerve fiber
endoneurium
Therefore, the ___ overlies the Schwann cells
endoneurium
slide 38 for reference
A nerve is a bunch of neurons
Slide 38 man
Oligodendrocytes have ___ processes
multiple
Each process of an oligodendrocytes can form a ____
myelinated sheath
Can myelinate several segments of one axon
or
Can participate in myelination of several axons
A neurolemma is not present in the ___ because the oligodendrocyte cell body and nucleus do not envelop the axon
CNS
Myelination in the CNS three key notes:
One oligodendrocyte can myelinate multiple times
There is no neurolemma
There are nodes of Ranvier
(slide 40)
_____ is a region predominantly filled with myelinated tract fibers. The appearance is due to the whitish color of myelin
(CNS)
White matter
___ is a region predominantly filled with neuronal CELL BODIES. There is little or no myelin in these areas, and the Nissl bodies impart a ___ color
(CNS)
Gray matter
Virtually all cells in the body exhibit a membrane potential, which is an electrical voltage difference across the ____
membrane
Neurons communicate with one another by using two types of electrical signals
Action potentials (nerve impulses)
Graded potentials
_____ (nerve impulses), for both short and long distance communication within the body. This is “all-or-none”
Action potentials
___,for short-distance (localized) communication only. The physiological role of ____ is to affect (and effect) the generation of action potentials. This is NOT “all-or-none”
Graded potentials
Both types of signal (AP and GP) depend on two features of the plasma membrane of excitable cells
Existence of a resting membrane potential
Presence of specific ion channels
In the body, ___ means flow of ions: sodium (Na+), potassium (K+), calcium (Ca2+), etc
“current”
When a current flows through a membrane, charges are redistributed across the membrane and the ___ changes
potential
When ion channels are open, specific ions are allowed to move across the plasmalemma, down their electrochemical gradient
there still has to be a gradient
Ion channels open and close due to the presence of ____, the part of a channel protein that opens or closes to allow or prevent the passage of ions
gates
Not all membrane channels have gates
There are more specific leakage channels for K+ than for Na+
The resting membrane is more permeable to K+ than to Na+
Leakage channels
not gated; randomly open and close
A ligand is a chemical (e.g., a neurotransmitter) that binds to a receptor molecule
Channels open or close in response to ligand binding
Ligand-gated channels
____ open in response to mechanical stimuli (e.g., tension in the plasma membrane due to pressure)
Mechanically gated channels
____ open and close in response to changes in the membrane potential
Voltage-gated channels
Resting membrane potential is ___ mV
-70
The -50 mV (depolarized) does not result from K+ movement out, but rather previous ___ movement in
Na+
from the picture
____ is the voltage difference measured across the plasma membrane when the neuron isn’t signaling
Resting membrane potential
Membrane is polarized
All membrane potentials are reported as the potential of the _____________
inside of the membrane relative to the outside of the membrane
Na+ and Cl- are in higher concentration in the ___ fluid
extracellular
K+, organic phosphates (-), amino acids (-), and proteins (-) are in higher concentration in the ____ fluid
intracellular
The resting membrane is 50 to 100 times more permeable to K+ than to Na+
Relative permeability of the resting membrane
(Cl- permeability is in between that of Na+ and K+)
(The membrane is impermeable to nearly all of the negatively charged intracellular molecules)
K+ diffuses down its concentration gradient __ of the cell
The intracellular ___ ions are left behind because they can’t get through the membrane
The interior of the membrane becomes ___ charged; the exterior becomes positively charged; net diffusion of K+ stops (electrochemical equilibrium)
__ diffuses into the cell but at a much lower rate than K+ diffuses out because the membrane is less permeable to Na+
A little Cl- diffuses into the cell, also making the interior more negative
Net result: the resting membrane potential
out
negatively charged
negatively
Na+
Ligand-gated or mechanically gated ion channels produce ___ potentials in response to stimuli
graded
means the size of the change in the membrane potential varies in proportion to the strength of the stimulus (not all-or-none)
membrane becomes more polarized (more negative)
Hyperpolarization
membrane becomes less polarized (less negative or more positive)
Depolarization
Whereas graded potentials are a localized phenomenon, and do not travel far before being attenuated, once an ___ is generated it travels the length of the neuron and can initiate an action potential in subsequent neurons, muscles, or glands
action potential
____ accompanies opening of voltage-gated Na+ channels. Stimulus causes depolarization to ____ (-55 mV)
Depolarization
threshold
____ accompanies opening of voltage-gated K+ channels and closure of Na+ channels
Repolarization
Resting state has both Na+ and K+ voltage-gated channels closed
Depolarization has Na+ gates open
Repolarization accompanied by K+ gates open and Na+ gates closed or closing
Resting state restored finds K+ gates closed
Slide 62
___ ions appear to bind to the exterior surfaces of the sodium channel protein molecule
Calcium
The positive charges of the calcium ions alter the electrical state of the channel protein, ____ the voltage level required to open the gate
increasing
____ the bound calcium ions, smaller than normal voltages are required for gate activation
Absent
Calcium ion concentration in the extracellular fluid therefore has an effect on the ___ level at which sodium channels become activated
voltage
When there is a deficit of calcium ions, the sodium channels become activated (open) by ___ change of the membrane potential from its normal resting level
very little
The nerve fiber then becomes highly excitable, sometimes discharging repetitively without provocation, rather than remaining in the resting state.
Nerve impulses must travel from where they arise at a trigger zone (typically the ___) down the neuron to the axon terminals
axon hillock
That movement is called propagation, or conduction
Propagation depends on ___ feedback
positive
The inflow of sodium ions causes depolarization that ___ voltage-gated Na+ channels in adjacent segments of the membrane
opens
Those in turn allow in sodium ions, causing that segment to depolarize, and so on down the axon
positive feedback
Receive stimuli through activation of ligand-gated or mechanically-gated channels
dendrites
produces excitatory and inhibitory potentials
Receives stimuli and excitatory and inhibitory potentials
cell body
slide 72
Inflow of __ caused by depolarized phase of nerve impulse which triggers exocytosis
Ca++
Step-by-step depolarization and repolarization of adjacent segments is termed
continuous conduction
Special mode of impulse propagation that occurs along myelinated axons
Saltatory conduction
Only in myelinated axons
Voltage-gated channels are concentrated at nodes of Ranvier, with few in regions where the myelin sheath covers the axolemma
Electric current is carried by extracellular and intracellular ions from one node to the next, and the nodes depolarize and repolarize as previously discussed
Saltatory conduction
Saltatory conduction is also more energy efficient, requiring less __ to repolarize
ATP
Neurons produce virtually all their ATP via ___ metabolism of glucose
This process requires large amounts of oxygen, so the nervous system requires a high blood flow, and is consequently highly vascularized
aerobic
___ of the brain’s energy consumption goes into sustaining the electric charge of neurons
Most
The greater the ___ of the axon, the faster the conduction will be (less resistance to the flow of ions through the axoplasm)
diameter
Large diameter
Myelinated
Conduct at about 100 meters/second
A fiber
Medium diameter
Myelinated
Conduct at about 15 meters/second (around 32
B fiber
Small diameter
Unmyelinated
Conduct at about 1 meter/second (around 3 miles per hour)
C fibers
Two mechanisms enable stimuli of differing intensities to be registered as such
Frequency of impulses
Number of sensory neurons activated (recruited)
A light touch generates a ___ frequency of widely spaced nerve impulses
low
A firm pressure causes nerve impulses to go down the axon ____
closer together (i.e. at a higher frequency)
A light touch stimulates only ___ pressure sensitive neurons
a few
A firm pressure stimulates ___ pressure sensitive neurons
more
No action potential is generated by a ___ stimulus
subthreshold
slide 82
Several action potentials result from a ____ stimulus, yet each has the same amplitude. This is perceived as a stronger stimulus
suprathreshold
slide 82
