Exam 2 - Nervous Flashcards
two systems responsible for maintaining homestasis
nervous and endocrine
regulates body activities by responding rapidly using nerve impulses
nervous system
system responds more slowly by use of hormones
endocrine system
the branch of medical science that deals with the normal functioning and disorders of the nervous system
neurology
brain and spinal cord
CNS
12 cranial nerves, spinal nerves (31 pairs), peripheral nerves
PNS
The nervous system comprises:
brain, spinal cord, spinal nerves, ganglia, enteric plexuses, and sensory receptors
functions of the nervous system
sensory, integrative, motor
detect changes in internal / external environment
carry info to brain and spinal cord
afferent neurons
sensory
afferent neurons
sensory receptors
analyze and store info
make decisions
many are interneurons, relatively short in brain, spinal cord, and ganglia that connect nearby neurons
Integrative
responds to decisions
motor neurons carry info from brain to spinal cord to effectors (muscles or glands)
efferent neurons
Motor
efferent neurons
motor neurons
general organization of the nervous system
somatic
autonomic
enteric
sensation from body wall, limbs, head, special senses (sight, hearing, taste, balance, smell)
somatic
motor control of skeletal muscle
somatic (voluntary control)
sensation from internal organs like heart, lungs, bladder
autonomic
motor control of smooth and cardiac muscle (i.e. involuntary muscle), glands (involuntary control)
autonomic
sensation from gastrointestinal tract
enteric
motor control of smooth muscle and glands of the GI (involuntary control)
enteric
consists of all nervous tissue outside the CNS
PNS
made up of Somatic, Autonomic, and Enteric Nervous Systems
PNS
has both sensory and motor neurons
PNS
The motor part of the ANS has which two branches?
sympathetic and parasympathetic
an association (a bundle) of neuronal axons in the PNS
nerve
a group of neuronal cell bodies in the PNS
ganglion
an association (a bundle) of neuronal axons in the CNS
tract
an association (a bundle) of (unmyelinated) nerve cell bodies in the CNS
Nucleus
an extensive network of nerves found within the PNS
Plexus
cells that have the property of electrical excitability, and are specially adapted to produce and transmit AP’s
Neurons
cells of the NS that support, flourish, and protect the neurons
Neuroglia
are there more neuroglia or neurons? Why?
neuroglia stupid!
neurons do not replace themselves via mitosis like neuroglia
what are the basic parts of the neuron
cell body and nerve fibers comprising of an axon and dendrites
name adaptions for neurons
axoplasm (the cytoplasm of an axon)
axolemma (the plasmalemma of axon)
axoplasm
(the cytoplasm of an axon)
axolemma
(the plasmalemma of axon)
like most cell neurons have nucleus, cytoplasm, typical organelles
what are the specialized forms of organelles?
Nissl bodies (prominent clusters of rough ER)
prominent clusters of rough ER in a neuron
Nissl bodies
little trees
dendrites
typically short, tapering, highly branched
dendrites
propagates impulses to another neuron, muscle, or nerve
axon
can approximate three feet in humans
axon
almost always a single axon per nueron, T or F
True
typically arises from an elevation in the cell body called the axon hillock
axon
small hill of the neuron
axon hillock
first part of the axon
intial segment
impulses i.e. AP’s generally arise in the
trigger zone
the junction of the hillock an initial segment
trigger zone
if an axon is cut what happens
distal fragment dies
does axon contain RER?
No… protein synthesis does not occur in axon
axon contains?
Mitochondira
Microtubules
Neurofibrils
may branch of main axon
axon collaterals
end of axons and collaterals
axon terminal (telodendria)
telodendria
end of axons and collaterals
telodendria end in either
synaptic bulbs
varicosities
synaptic bulbs are
bulb-shaped structures at end of telodendria
varicosities are
string of swollen bulbs at end of telodendria
cytoskeleton of typical neuron comprised of
neurofibrils
microtubules
neurofibrils of typical neuron
intermediate filaments which provide structure and support
microtubules of typical neuron are made of and do what?
tubulin
moving material between the cell body and axon
what does synthesis of new proteins, vessicles, etc take place in the neuron?
cell body not axon
how far apart can cell body and axon terminals be?
over a meter
one way only, cell body to axon terminals
transports axoplasm to growing or generating axons
slow axonal transport
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 vessicles
fast axonal transport
Look at slide 21 of ppt… before you do imagine the three structural classifications of neurons
multipolar
bipolar
pseudounipolar
special senses think
bipolar neuron
sensory neurons think
pseudounipolar neuron
structural classification of neurons is based on…
processes (axons or dendrites) extending from the cell body
key takeaway from structural classification?
trigger zone of each neuron location
the vast majority of the neurons in the human body are
multipolar neurons
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
are used to convey the special senses of sight, smell, hearing, and balance and are found where?
bipolar neurons
found in retina of eye, inner ear, and olfactory area of the brain
contain one process which extends from the body and divides into a central branch that functions as an axon and as a dendritic root
unipolar neurons (psuedounipolar)
often employed for sensory neurons that convey touch and stretching info from extremities
unipolar neurons (psuedounipolar)
not excitable cells
small, more numerous than neurons
neuroglia
play a supporting role (nourishment)
make up half the volume of the CNS
neuroglia
in cases of injury or disease, multiply to fill in spaces formerly occupied by neurons
neuroglia
not excitable cells
small, more numerous than neurons
play a supporting role (nourishment)
make up half the volume of the CNS
in cases of injury or disease, multiply to fill in spaces formerly occupied by neurons
neuroglia
astrocytes
microglia
oligodendrocytes
ependymal cells
AMOE
Neuroglia of the CNS
Neuroglia of the CNS
astrocytes
microglia
oligodendrocytes
ependymal cells
Neuroglia of the PNS
Schwann cells (neurolemmoytes) Satellite cells
Schwann cells (neurolemmoytes) Satellite cells
Neuroglia of the PNS
regulate the composition of the extracellular fluid in the CNS
help form the BBB
take up excess neurotransmitters
may influence formation of neuronal synapses
Astrocytes (star shaped)
phagocytes of the CNS
Microglia
line the ventricles of the brain; produce, monitor, and aid in circulation of CSF; help form the blood CSF barrier
Ependymal cells (of CNS)
myelinate axons in the PNS
Schwann cells
neuroglia of the CNS completely surround ___ and ___ of neurons
axons and cell bodies of neurons
do not typically undergo mitosis, meaning if a neuron dies there is no reservoir of cells to replace it
neurons
do undergo mitosis (can be highly malignant and grow rapidly i.e. brain tumors – can be highly malignant and grow rapidly, and include astrocytomas, oligodendrogliomas, and schwannomas
neuroglial cells
No mitosis
nuerons
yes mitosis
neuroglial cells
myelination is produced by ___ of the CNS and ____ of the PNS
Oligodendrocytes (CNS)
Schwann cells (PNS)
a multi-layered complex of lipids and proteins, i.e. player of plasma membranes
insulates axons (prevents loss of electrical signal speeding up conduction of nerve impulses)
myelin
a ___ or ___ can be associated with a neuron, yet the neuron may be unmeylinated. Myelination requires
Schwann cell (neurolemmocyte) or oligodendrocyte
requires the glial cell to have wrapped its plasma membrane around the axon many times
schwann cell in the
PNS
oligodendrocytes in the
CNS
the outer nucleated cytoplasmic layer of the schwann cell, which encloses the myelin sheath is the ____
neurolemma
unmyelinated cells w/ Schwann cells means axons lay in grooves on the surface of schwann cells but there is no
myelin sheath and no neurolemma
neurolemmocyte
schwann cell
schwann cell inner portion encircles the axon, forming many layers that comprise the
myelin sheath
resides in the neurolemma (outer nucleated cytoplasmic layer of the schwann cell)
nucleus of the neurolemmocyte
outer lay of a myelinating Schwann cell
neurolemma
contains the nucleus and virtually all the cytoplasm of Schwann cells, not to be confused with Axolemma
which NS?
Neurolemma
in the PNS
only on nerve fibers supplied by potentially nerve-producing cells
gaps between myelinating cells (where there is no myelin)
nodes of ranvier (found in CNS and PNS)
a nerve fiber consists of
axon plus myelin sheath
the ___ surrounds the nerve fiber
endoneurium
the endoneurium overlies the
Schwann cells
have multiple processes
each process can form a myelinated segment where they can myelinate several segments of ONE axon OR several axons
oligodendrocytes
are neurolemmas present in the CNS?
why?
NO; oligodendrocyte cell body and nucleus do not envelope the axon
one oligodendrocyte can myelinate multiple times
there is no?
there are?
no neurolemma
are nodes of Ranvier
color of myelin and type of matter
white; white matter of the CNS
matter or region with neuronal cell bodies and no myelin
what makes it gray?
gray matter; Nissl bodies make it gray
Virtually all cells in the body exhibit a
membrane potential, which is an electrical
voltage difference across the membrane
T or F
True
Nerve cells are highly adapted for using
membrane potentials, and changes in
membrane potentials, to initiate and
transmit nerve impulses
T or F
T
Neurons communicate with one another by using which two types of electrical signals?
Action potentials (nerve impulses), for both short and long distance communication within the body. This is “all-or-none”
Graded potentials, for short-distance (localized) communication only. The physiological role of graded potentials is to affect (and effect) the generation of action potentials. This is NOT “all-or-none”
Neuronal signals: Both types of signal depend on which two features of the plasma membrane of excitable cells?
– Existence of a resting membrane potential
– Presence of specific ion channels
Are there more specific leakage channels for K+ or for Na+
K+
Is the resting membrane is
more permeable to K+ or to
Na+
K+
The resting membrane potential is due to a small buildup of anions in the cytosol just inside the membrane, and an equal buildup of cations in the extracellular fluid just outside the membrane
Equal numbers, but on opposite the membrane, sides!
higher sodium and Cl where
ECF
Higher K, organic phosphates, amino acids, proteins where?
ICF
The resting membrane is 50 to 100 times more
permeable to ___ than to ____
K+ than to Na+
Cl- permeability is in between that of Na+ and K+
True dat
The membrane is impermeable to nearly all of the negatively charged intracellular molecules
True dat times two
▪ K+ diffuses down its concentration gradient out of the cell
▪The intracellular negatively charged ions are left behind
because they can’t get through the membrane
▪The interior of the membrane becomes negatively
charged; the exterior becomes positively charged; net
diffusion of K+ stops (electrochemical equilibrium)
▪Na+ 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
ESTABLISHING THE RESTING MEMBRANE POTENTIAL
▪___ or ____ gated ion channels produce graded potentials in response to stimuli
▪_____ means the size of the change in the membrane potential varies in proportion to the strength of the stimulus (not all-or-none)
▪Local effects only: channels open, current flows through the membrane and along the membrane, and travels only a short distance before diminishing to zero
GRADED POTENTIALS
▪Ligand-gated or mechanically gated ion channels produce graded 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)
▪Local effects only: channels open, current flows through the membrane and along the membrane, and travels only a short distance before diminishing to zero
A graded potential can either ____ the membrane or ____the membrane
depolarize
hyperpolarize
membrane becomes more polarized (more negative)
hyperpolarization
membrane becomes less polarized (less negative or more positive)
–Depolarization:
difference between graded potentials and action potentials?
▪graded potentials are a localized phenomenon, and do not travel far before being attenuated, once an action potential is generated it travels the length of the neuron and can initiate an action potential in subsequent neurons, muscles, or glands
▪Action potentials are all-or-none
▪_____ accompanies opening of voltage-gated Na+ channels. Stimulus causes depolarization to threshold (-55 mV)
▪_____ accompanies opening of voltage-gated K+ channels and closure of Na+ channels
Depolarization
Repolarization
– ___ has both Na+ and K+ voltage- gated channels closed
– ____ has Na+ gates open
– ______ accompanied by K+ gates open and Na+
gates closed or closing
– Resting state restored finds K+ gates closed
Resting state
Depolarization
Repolarization
▪The _____ progresses sequentially down the
length of the axon
▪The _____ measured at a fixed point on the axon varies with time as the action potential transits the point
action potential
voltage
CALCIUM ION DEFICIT
▪______ appear to bind to the exterior surfaces of the sodium channel protein molecule.
▪The _____ charges of the calcium ions alter the electrical state of the channel protein, increasing the voltage level required to open the gate.
▪Absent the bound calcium ions, ____ than normal voltages are required for gate activation.
Calcium ions
positive
smaller
CALCIUM ION DEFICIT
▪Calcium ion concentration in the _____ therefore has an effect on the voltage level at which sodium channels become activated.
▪When there is a deficit of calcium ions, the sodium channels become ______ by very little change of the membrane potential from its normal resting level.
▪The nerve fiber then becomes ___ ____, sometimes discharging repetitively without provocation, rather than remaining in the resting state.
extracellular fluid
activated (open)
highly excitable
_____ is associated with muscle contraction, cramps, and even tetany, which can be lethal because of tetanic contraction of the respiratory muscles
low blood calcium
Propagation of nerve impulses
▪Nerve impulses must travel from where they arise at a trigger zone (typically the axon hillock) down the neuron to the axon terminals.
▪That movement is called _________
▪Propagation depends on ______ feedback
propagation, or conduction
positive
Positive feedback of propagation
▪The inflow of _____ ions causes depolarization that opens voltage-gated Na+ channels in adjacent segments of the membrane
▪Those in turn allow in sodium ions, causing that segment to _____, and so on down the axon
sodium
depolarize
Explain the function of dendrites:
Receive stimuli through activation of ligand-gated or mechanically-gated ion channels. In sensory neurons produces generator or receptor potential. In motor neurons and interneurons produces excitatory and inhibitory postsynaptic potentials
Explain the function of the cell body:
Receives stimuli and produces EPSPs and IPSPs through activation of ligand-gated or mechanically gated ion channels
Explain the function of the Junction of the axon hillock and initial segment of axon:
Trigger zone in many neurons
integrates ESPSs and IPSPs— if sum is depolarization that reaches threshold, initiates action potential (nerve impulse)
Explain the function of the axon:
Propagates (conducts) nerve impulses to axon terminals in a self- reinforcing manner. Impulse amplitude does not change as it propagates along the axon
Explain the function of the axon terminals and synaptic end bulbs (varicosities):
Inflow of Ca2+ caused by depolarizing phase of nerve impulse triggers exocytosis of neurotransmitters from synaptic vesicles
Types of conduction
▪Step-by-step depolarization and repolarization of adjacent segments is termed ______.
▪______ is a special mode of impulse propagation that occurs along myelinated axons
continuous conduction.
Saltatory conduction
Saltatory conduction
▪Only in ______
▪Voltage-gated channels are concentrated at _______, with few in regions where the myelin sheath covers the ______
▪______ is carried by extracellular and intracellular ions from one node to the next, and the nodes depolarize and repolarize as previously discussed
myelinated axons
nodes of Ranvier; axolemma
Electric current
▪ Saltatory conduction is much ____ than continuous conduction
▪ It is also more energy efficient, requiring less ____ to repolarize
faster
ATP
Metabolism
▪Neurons produce virtually all their ATP via _____ of glucose
▪This process requires large amounts of ____, so the nervous system requires a high blood flow, and is consequently highly vascularized
▪Alternative—and very minor—sources of energy for neurons are ______, ____, and ____.
aerobic metabolism
oxygen
ketones, medium chain fatty acids, and possibly amino acids
Metabolism
▪Most of the brain’s energy consumption goes into
sustaining the __________
▪The majority of vertebrate species devote between 2% and 8% of basal metabolism to the brain. It is higher in primates, and in humans it rises to 20% to 25%
electric charge of neurons
The greater the diameter of the axon, the faster the conduction will be (less resistance to the flow of ions through the axoplasm)
▪ __ fibers
– Large diameter
– Myelinated
– Conduct at about 100 meters/second (around 200 miles per hour)
▪__ fibers
– Medium diameter
– Myelinated
– Conduct at about 15 meters/second (around 32 miles per hour)
▪__ fibers
– Small diameter
– Unmyelinated
– Conduct at about 1 meter/second (around 3 miles per hour)
▪ A fibers
– Large diameter
– Myelinated
– Conduct at about 100 meters/second (around 200 miles per hour)
▪B fibers
– Medium diameter
– Myelinated
– Conduct at about 15 meters/second (around 32 miles per hour)
▪C fibers
– Small diameter
– Unmyelinated
– Conduct at about 1 meter/second (around 3 miles per hour)
Perceiving stimulus intensity
▪Since all nerve impulses are the same size, there would not seem to be a way to distinguish between stimuli of different magnitudes
▪Two mechanisms enable stimuli of differing intensities to be registered as such ________
– Frequency of impulses
– Number of sensory neurons activated (recruited)
Example of intensity perception (using touch)
▪Frequency of impulses
– A light touch generates a _____ of widely spaced nerve impulses
– A firm pressure causes nerve impulses to go down the axon closer together (i.e. at a higher frequency)
▪Number of sensory neurons recruited
– A light touch stimulates only a few pressure sensitive neurons
– A firm pressure stimulates more pressure sensitive neurons
low frequency
Stimulus strength and generation of action potential
▪No action potential is generated by a ___ stimulus.
▪Several action potentials result from a ____
stimulus, yet each has the same amplitude. This is perceived as a stronger stimulus.
subthreshold
suprathreshold
