CHAPTER 6: NERVOUS SYSTEM Flashcards
neural tissue
communication by neurons = hanges in membrane’s permeability to ions
typical neuron has ____ and _____ regions
dendritic (receive info) & axonal (deliver info)
action potential
an “all-or-none” sequence of changes in membrane potential
(result from a sequence of changes in ion permeability due to operation of voltage-gated Na & K channels.
rapid opening of voltage-gated Na channels allows….
rapid entry of Na moving membrane potential closer to the sodium equilibrium potential
slower opening of voltage-gated K channels allows…
K exit, moving membrane potential closer to the K equilibrium potetial
which neurons conduct action potentials most rapidly?
myelinated neurons
peripheral nervous system contains:
afferent and efferent directions of flow of information projecting out of CNS
class of neuron: afferent flow
“carry towards” –> from the body’s sensory receptors to the central nervous system
class of neuron: efferent flow
“carry away” —> to nerves or signals that transmit information from the central nervous system to the body’s muscles, glands, and other organs
schwann cells
type of glial cells that form myelin sheaths on peripheral nervous system and are vital for nerve development, function, and regeneration
oligodendrocytes
type of glial cells that form myelin sheaths on central nervous system and produce + maintain the myelin sheath, an insulating layer that wraps around nerve fibers (axons)
absolute refractory period
Na channels are either already open or have proceeded to the inactive state
no new action potential
relative refractive period
some of Na channels have returned to resting state and some of the K channels that repolarized the membrane are still open
can have a new action potential
axonal transport of materials depends on…
a scaffolding of microtubules along length of axon + motor proteins that help move material either
towards –> kinesins
or
away –> dyneins
class of neuron: interneurons
function as integrators + signal changers
integrate groups of afferent and efferent neurons into reflex circuits
entirely in CNS, >99% of all neurons
central nervous system contains
brain and spinal cord (all parts of interneurons as well)
nerve
collection with axons encased in connective tissue and is located in PNS
what is a bundle of axons called?
tract
one-way propagation of action potential STEP 1:
action potential initiated in region 1 and local currents depolarizes region 2
one-way propagation of action potential STEP 2:
action potential initiated in region 2 and region 3 is depolarized towards threshold, but region 1 is refractory
one-way propagation of action potential STEP 3:
action potential initiated in region 3, and generates local currents, but region 2 is refractory
saltatory conduction
action potentials jump from one node to the next as they propagate along a myelinated axon
what does the speed of propagation depend on?
internodal spacing (larger spacing = faster speed)
apoptosis
programmed cell death (degeneration)
sequence neural growth and regeneration
1) embryo development begins with series of division of undifferentiated precursor cells (stem cells) that can develop into neurons or glia
2) after the last cell division, cell differentiates and sends out processes that will become its axon and dendrites
3) growth cone at end of each extending axon is involved in finding the correct route and final target for the process
4) after growth/projections of axons, many of the newly formed neurons and synapses degenerate (ex: CNS fine-tunes the neuronal connections this way)
how many primary neurons communicate to one second neuron?
four primary nuerons
how many secondary neurons communicate to one primary neuron?
four secondary neurons
two types of synapses that are the point of communication between 2 neurons that operate sequentially
electrical (needs ions, current flow) & chemical
neurotransmitters
chemical messengers that are released by electric signal to communicate with cells other cells
glial cells
non-neuronal cells that do not participate directly in electrical communication from cell to cell as do neurons
what does a neuron’s cell body contain?
genetic information and machinery necessary for protein synthesis (nucleus and ribosomes)
calcium binds to ______ which stimulates SNARE proteins to induce fusion of the vesicle
synaptotagmin
dendrites
series of highly branched outgrows of the cell that receive incoming information from other neurons
dendritic spines increase surface area
axon
a long process that extends from the cell body and carries outgoing signals to its target cells
axon hillock
region of axon that arises from the cell body
each branch ends in an…
axon terminal (which releases neurotransmitters from the axon)
sheaths of myelin
20 to 200 layers of highly modified plasma membrane wrapped around the axon by a nearby supporting cell
nodes of ranvier
spaces between adjacent sections of myelin where axon’s plasma membrane is exposed to extracellular fluid
axonal transport
organelle/material movement between cell body and axon terminals (1 meter)
purpose is to maintain the structure and function of the axon
excitatory synapse
increases membrane potential
inhibitory synapse
decreases membrane potential
during axonal transport, what do the double-headed motor proteins (kinesins and dyneins) bind to?
their cellular cargo, and the at the other end of the axon, they use the energy derived from ATP hydrolysis to “walk”along microtubules
kinesin transport
occurs from cell body towards axon terminals (anterograde)
dynein movement
occurs from axon terminals towards cell body (retrograde)
at peripheral ends of afferent neurons there are…
sensory receptors
they respond to physical or chemical changes in their environment by generating electrical signals in the neuron
which class of neurons propagates electric signals from their receptors into the brain or spinal cord
affluent neurons
glial cells surround the ______ and _______ and provide them with _______
axon and dendrites, metabolic and physical support
astrocyte
type of glial cell that removes potassium ions and neurotransmitters around synapses to regulate composition of EC fluid & provides glucose and removed secreted metabolic waste of neurons & they have neuron-like characteristics
blood-brain barrier
formed by astrocytes, this is a selective barrier for exchanging substances in the CNS
microglia
type of glial cell that that perform immune functions in CNS
ependymal cells
cells that line the fluid-filled cavities within the brain and spinal cord and regulate production of cerebrospinal fluid
predominant solutes in extracellular fluid:
sodium and chloride ions
predominant solutes in intracellular fluid:
potassium ions and phosphate compounds and proteins
growth cone
forms the tip of each extending axon and is involved in finding the correct route and final target
zika virus related to…
microcephaly
plasticity
brain’s ability to modify its structure and function in response to stimulus and injury
if axons are severed, what can happen?
they can repair themselves and restore significant function provided that the damage occurs outside of CNS
electric potential or potential difference
difference in amount of charge between 2 points
lipid bilayer of the plasma membrane creates _______ to movement of electric charge
resistance (ohm’s law)
an antagonist is a ligand that…
inhibits the activity of receptor proteins
the most common neurotransmitters for neuroeffector communication are…
dopamine and norepinephrine
group neuron cell bodies within the central nervous system is properly referred to as a
nucleus
group neuron cell bodies within the peripheral nervous system is properly referred to as a
ganglia
plasma membrane sodium/potassium pumps maintain _____ intracellular sodium concentration
low (Na+)
plasma membrane sodium/potassium pumps maintain _____ intracellular potassium concentration
high (K+)
electrogenic pump
when a pump moves net charge across the membrane and contributes directly to the membrane potential
leak channels
“ungated” channels that are always open that allow K+ to go through (down its concentration gradient) –> makes the inside of the cell negative relative to the outside
excitability
ability to produce electric signals that can transmit information between different regions of the membrane
membrane is depolarized means:
when the potential becomes less negative than resting level
resting potential =
-70 mV
overshoot means:
reversal of the membrane potential polarity
repolarized means
membrane potential of a cell that has been depolarized returns to resting value
hyperpolarized means
when the potential is more negative than the resting level
graded potentials
changes in membrane potential that are confined to a relatively small region of membrane (magnitude of potential change can vary)
they can only function as signals over very short distances
in which directions can graded potentials occur?
depolarizing or hyperpolarizing
what does it mean when current is decremental?
the flow of charge decreases as the distance from the site of origin of the graded potential decreases
summation
if additional stimuli occur before the graded potential has died away, these can add to graded potential from the first stimulus
action potentials
large and more rapid alterations in the membrane potential, the propagation of APs down the axon is the mechanism the nervous system uses to communicate from cell to cell over long distances
ligand-gated ion channels open in response to…
the binding of signaling molecules
mechanically-gated ion channels open in response to…
physical deformation of plasma membranes
voltage-gated ion channels
give a membrane the ability to undergo action potentials (ex: Na, K, Ca, Cl channels)
when an area of a membrane is suddenly depolarized, which voltage-gated channels open first?
Na channels open first before K channels do because Na channels respond faster to changes in membrane voltage
Na channels have a ______ gate that limits the flux of NA by blocking the channel shortly after depolarizing
inactivation
if extracellular Na is elevated, how would the resting potential and action potential of a neuron change?
value of resting potential would change very little because the permeability of resting membranes to Na is very low.
threshold potential
minimum membrane potential that must be reached to trigger an action potential
afterhyperpolarization
the period after an action potential where K permeability remains above resting levels and the membrane is transiently hyper-polarized toward the K equilibrium potential
what does a positive feedback loop during an action potential look like?
depolarizing stimulus –> opening of Na channels –> increased permeability of Na –> increased flow of Na into cell –> depolarization of membrane potential
what does a negative feedback loop during an action potential look like?
depolarization of membrane by Na influx –> opening of K channels –> increased permeability of K –> increased flow of K out of the cell –> repolarization of membrane potential
threshold stimuli
stimuli that are just strong enough to depolarize the membrane to the level
subthreshold potentials + stimuli
weak depolarizations that cause the membrane to return to resting level as soon as stimulus is removed and no action potential is generated
“all-or-none” concept
action potentials either occur maximally or they do not occur at all
absolute refractory period
the period where, during the action potential, a second stimulus no matter how strong will not produce a second action potential
& occurs when Na channels are either already open or have proceeded to the inactivated state during first action potential
relative refractory period
after absolute RP an interval during which a second action potential can be produced, but only if the stimulus strength is considerably greater than usual
action potential can only travel the length of a neuron if …
each point along the membrane is depolarized to its threshold potential
action potential propagation:
1) action potential is initiated
2) local current depolarizes
3) action potential is in region
4) generates local currents
5) depolarized toward threshold
where do action potentials occur?
the nodes of Ranvier, where myelin coating is uninterrupted and concentration of Na channels is high
receptor potential
in afferent neurons, the initial depolarization to threshold is achieved by a graded potential
generated in the sensory receptors at the peripheral ends of the neurons
synaptic potential
depolarization to threshold due to a graded potential generated by synaptic input to a neuron
pacemaker potential
depolarization to threshold due to spontaneous change in the neuron’s membrane potential
excitatory synapse
where the membrane potential of a postsynaptic neuron is brought closer to threshold (depolarized)
inhibitory synapse
where postsynaptic neuron is stabilized at its resting potential
convergence
hundreds of thousands of synapses from many different presynaptic cells can affect a postsynaptic cell
allows information fro many sources to influence a cell’s activity
divergence
a single presynaptic cell can send branches to affect many other postsynaptic cells
allows one cell to affect multiple pathways
what happens if the membrane of the postsynaptic neuron reaches threshold?
it will generate action potentials that are propagated along its axon to the axon terminals
electrical synapses
the membranes of pre + postsynaptic cells are joined by gap junctions, which allows local current to flow directly across –> depolarizes membrane and continues propagation of AP
chemical synapse
neurotransmitters stored in synaptic vesicles are released by a presynaptic axon terminal into the synaptic cleft, where they transmit signal from presynp to postsynp neuron
active zones
the release regions where many vesicles are docked on the presynaptic membrane prior to activation
when is neurotransmitter release initiated?
when an action potential reaches the presynaptic terminal membrane
SNARE proteins
a group of proteins that cause vesicles to be loosely docked in the active zones
synaptotagmins
the vesicle that calcium ions entering during depolarization bind to a separate family of proteins which triggers a conformational change that leads to a membrane fusion and NT release
after fusion, vesicles can undergo which two possible fates:
1) vesicles completely fuse with the membrane and are later recycled by endocytosis outside of active zone
2) vesicles may fuse only briefly then reseal the pore and withdraw back into the axon terminal
ionotropic receptors
activated receptors on plasma membrane of postsynaptic cell that are ion channels
metabotropic receptors
receptors that influence ion channels through a G protein/second messenger
neurotransmitter binding to receptor is transient and reversible. what does this mean?
it means that it is in equilibrium with the unbound form and if the concentration of it in the synaptic cleft decreases, the number of occupied receptors will decrease. and ion channels return to resting state when neurotransmitters are no longer bound.
unbound neurotransmitters are removed from the synaptic cleft when they:
1) are actively transported back into presynp axon terminal (uptake)
2) transported into nearby gliali cells
3) diffuse away from receptor site
4) are enzymatically transformed into inactive substances, some of which are transported back into the presynp axon terminal for reuse
the electrical gradient opposes the concentration gradient of…
K+
the net movement of positive ions (K and Na) into the postsynaptic cell causes a _____ and this change is called
depolarization, excitatory postsynaptic potential (EPSP)
inhibitory postsynaptic potential (IPSP)
potential change in the postsynaptic neuron that is a hyper-polarizing graded potential
conceptual: with increased K permeability, more K ions leave the cell and K moves closer to the K equilibrium potential, causing a _____
hyperpolarization
temporal summation
when the second synaptic potential adds to the previous one and creates a greater depolarization than from one input alone
input signals arrive from the same presynaptic cell at different times
spatial summation
when more than one EPSP and IPSP arrive together at different synapses on a postsynaptic cell membrane
two inputs occur at different locations on the cell
which of the following has a more negative threshold and why?
1) axon hillock
2) membrane of cell body
3) dendrites
1) axon hillock –> because of a higher density of Na channels in this area of the membrane
this means that a synapse located near the axon hillock will produce a greater voltage change in the axon hillock because it will expose it to a larger local current
axo-axonic synapse
an axon terminal of one neuron ends on an axon terminal of another
presynaptic inhibition vs facilitation
decrease the amount of neurotransmitter released vs increase it
autoreceptors
receptors that are activated by neurotransmitters/messengers released by nearby neurons or glia or even by the axon terminal itself
receptor desensitization
when a receptor responds normally when first exposed to a neurotransmitter but then eventually fails to respond despite the continued presence of its’ NT
agonists
ligands that bind to a receptor and activate it
antagonists
ligands that bind to a receptor and inhibit its activation
neuromodulators
messengers that cause complex responses that cannot be described as EPSP/IPSPs
role of neuromodulators
essentially to alter the effectiveness of the synapse
acetylcholine (ACh)
a major neurotransmitter in the PNS at the neuromuscular junction and in the brain
neurons that release ACh are called:
cholinergic neurons
acetylcholinesterase
the reason that the concentration of ACh at the postsynaptic membrane decreases
nicotinic receptors
an ACh recept that also responds to the compound nicotine (& also a ligand-gated ion channel)
muscarinic receptors
cholingeric receptor that is also stimulated by muscarine (& coupled with g proteins!)
alzheimer’s disease connection
many cholinergic neurons in the brain degenerate in people with alzheimer’s disease (so decreased amount of ACh in certain areas of the brain)
beta-amyloid protein
mutations of genes on chromosomes are associated with abnormally increased concentrations of this protein
neuroeffector junction
the synapse between a neuron and an effector cell
the events at a neuroeffector junction are similar to those at…
synapses between neurons (release, diffusion, binding of NT)
tract/pathway
a group of axons traveling together in the CNS
(long neural & mutlisynaptic pathways)
ganglia
groups of neuron cell bodies in the PNS
nucleus
groups of neuron cell bodies in the CNS
forebrain
cerebrum, diencephalon
midbrain
a single major division
hindbrain
pons, medulla, oblongata, cerebellum (together is brainstem)
cerebral ventricles
four interconnected cavities which are filled with fluid and provide support for the brain
gray matter
cell bodies that give the outer shell of cerebral cortex a gray appearance
white matter
composed of primarily tracts of myelinated axons in the inner layer
corpus callosum
a massive bundle of axons that connect the cortex layers of left and right cerebral hemispheres
the four lobes in the cerebral cortex
frontal, parietal, occipital, temporal lobes
pyramidal cells
cells that form the major output cells of the cerebral cortex, sending their axons to other parts of the cortex and CNS
nonpyramidal cells
cells that are involved in receiving inputs into the cerebral cortex and in local processing of information
basal nuclei
a subcortical nuclei of gray matter that controls movement and posture
limbic system
interconnected group of brain structures consisting of gray and white matter and includes frontal-lobe, temporal lobe, thalamus, hypothalamus
thalamus
collection of several large nuclei that serve as synaptic relay stations and important integrating centers for most inputs to the cortex
attention/arousal
hypothalamus
contains numerous nuclei and their pathways form the master command center for neural and endocrine coordination
how does cerebellum carry out functions
the cerebellum receives information from the muscles and joints, skin, eyes, vestibular apparatus, etc –> movement!!!
reticular formation
consists of loosely arranged nuclei intermingled with bundles of axons running through the core of the brainstem
cranial nerves
peripheral nerves that connect directly with the brain and innervate the muscles, glands, and sensory receptors of the head
spinal cord gray matter consists of…
interneurons, cell bodies & dendrites of efferent neurons, axons of afferent neurons, and glial cells
dorsal horns
regions of gray matter projecting toward the back of the body
ventral horns
regions of gray matter projecting toward the front of the body
dorsal roots
groups of afferent neuron axons that enter the spinal cord from the peripheral nerves enter on the dorsal side of the cord via DORSAL ROOTS (small bumps = dorsal root ganglia)
PNS: 8 pairs of cervical nerves:
neck, shoulders, arms, hands
PNS: 12 pairs of thoracic nerves:
chest, upper abdomen
PNS: 5 pairs of lumbar nerves:
lower abdomen, hips, legs
PNS: 5 pairs of sacral nerves:
genitals and lower digestive tract
types of divisions that peripheral nerves can belong to
efferent and afferent division
role of afferent neurons in spinal nerve
convey information from sensory receptors at their peripheral endings to the CNS
role of efferent neurons in spinal nerve
carry signals out from the CNS to muscles, glands, and other tissues
PNS is subdivided into the _____ and _____ nervous systems
somatic and autonomic
motor neurons
neurons that lead to contraction of innervated skeletal muscle cells
types of meninges (coverings):
dura mater, arachnoid mater, pia mater
(filled with cerebrospinal fluid)
brain tissue depends on a continuous supply of ______ and _______ for metabolism
glucose and oxygen
blood-brain barrier
formed in part by cells lining blood vessels
-tight junctions between blood vessel cells prevent many substances from entering the fluid around neurons
-specific transport systems allow certain molecules to move between the blood and EC fluid around neurons
biogenic amines
small, charged molecules that are synthesized from amino acids and contain an amino group
examples of catecholamines
dopamine, norepinephrine, epinephrine
because they all contain a catechol ring and an amine group
monoamine oxidase
the enzymes that break down catecholamine neurotransmitters in the EC fluid and axon terminal
examples of amino acids
glumate, GABA, glycine
neuropeptides
composed of 2+ amino acids linked together by peptide bonds
