Chapter 3A Flashcards
Nervous system is organized into two
main subdivisions:
- Central nervous system (CNS):
brain and spinal cord - Peripheral nervous system
(PNS): all nervous tissue
outside CNS.
Nervous tissue comprises two types of cells:
Neurons
Neuroglia (support neurons, maintain fluid that bathes them)
Neuroglia can be found in the CNS and in the PNS
True/false
True
Neuroglia of the CNS exists of four types:
astrocytes,
oligodendrocytes, microglial cells, and ependymal cells.
Neuroglia of the PNS exists of two types:
Schwann cells
Satellite cells
(see p 12, chapter 3A)
What is electrical excitability?
to respond to stimulus and convert it into an action potential.
stimulus is any change in the environment that is strong enough to initiate
an x
action potential
action potential (nerve impulse) = an x signal that propagates
along the surface of the x of a neuron
x = electrical
x= membrane
an action potential begins and travels due to the movement of x between interstitial fluid and the inside of a neuron through
specific x in its plasma membrane
x = ions
x = ion channels
Dendrites: are the x or x portions of a neuron. The plasma membranes
of dendrites (and cell bodies) contain numerous receptor sites for binding chemical
messengers from other cells. Dendrites usually are short, tapering, and highly
branched.
receiving
input
Axon: propagates x: a muscle fiber, or a gland
cell. An axon is a long, thin, cylindrical projection.
nerve impulses toward another neuron
Trigger zone: this is where..
nerve impulses arise (begin van de steel aan de kant van het lichaam van de cel)
Little neurons contain two or even three types of neurotransmitters
True/false
False (=many)
Direction of information
flows (put in right order)
axon
cell body
axon terminals
dendrites
dendrites → cell body → axon → axon
terminals
Cytoplasm of an axon is called
axoplasm
plasma membrane of axon is called
axolemma
axon collaterals = ?
side branches along the length of an axon
(see p 16, chapter 3A)
Classification of neurons: STRUCTURAL CLASSIFICATION: vs FUNCTIONAL CLASSIFICATION:
structural: number of precesses extending from the body
functional: direction in which the action potential is conveyed relative to the CNS
STRUCTURAL CLASSIFICATION:
Multipolar neurons
Bipolar neurons
Unipolar neurons
multipolar: several dendrites and one axon (brain & spinal)
Bipolar: one main dendrite and one axon (eye, olfactory (smell) area of brain)
Unipolar: dendrites and one axon that are fused together
FUNCTIONAL CLASSIFICATION
Sensory/afferent
Motor neurons/efferent neurons
Interneurons/association neurons
Sensory/afferent: (into the CNS)
Motor neurons/efferent neurons: away from CNS
Interneurons/association neurons: within CNS
Myelin sheath: multilayered lipid and protein covering around some axons that
A them and B of nerve impulse conduction
A insulates
B increases the speed
Two types of neuroglia produce and maintain myelin sheaths
Schwann cells in the PNS (each schwann myelinates a single axon)
Oligodendrocytes in the CNS (single oligodendrocyte myelinates several axons)
Schwann cells begin to form myelin sheaths around axons during fetal development.
* Multiple layers of glial plasma membrane surround the axon
The Schwann cell’s cytoplasm and nucleus forming the X layer.
The x portion (myelin sheath), consisting of up to 100 layers of Schwann cell membrane
x = outermost
x = inner
Neuronal cell bodies are often grouped together in clusters: what are they called in CNS vs PNS?
ganglion in the PNS
and nucleus in the CNS.
The axons of neurons are usually grouped together in x
bundles
white matter vs grey matter: composed of?
White matter: myelinated axons
Gray matter: the rest
neuronal
cell bodies, dendrites,
unmyelinated axons, axon
terminals, and neuroglia
uneven
distribution of ions: ONLY at the cell membrane part? True/false?
True
A cell that exhibits a membrane potential is said to be X
polarized.
Most body cells are polarized.
True/false
true
The minus sign indicates that the outside of the cell is negative relative to the
outside.
True/false
false: inside is negative
the resting membrane potential is maintained by the activity of a protein
called the …
sodium-potassium pump.
The pump moves sodium and potassium ions in opposite directions, each against its
concentration gradient. Thus it requires x
ATP
In a single cycle of the pump, X sodium ions are extruded from and
X ions are imported into the cell.
three sodium
two potassium
Because 3 Na+ are exported for every 2 K+ brought into the cell, the pump makes
the membrane potential slightly more X than it would otherwise be.
negative
In neurons, the resting membrane potential varies from …. mV to …..
-70 mV
-90
The production of potentials depends on two basic features of the plasma membrane
of excitable cells:
- the existence of X across the membrane and
- the presence of specific types of X.
a resting membrane potential
ion channels
A graded potential is a small deviation from the resting membrane
potential that makes the membrane potential:
* more negative: X
* more positive (less negative):
hyperpolarizing
depolarizing (p.36)
1, 2, 3 will tend to ENTER the cell. (type ionen)
4 will tend to LEAVE the cell.
Na+, , Ca+ and Cl-
- K+
The opening of sodium and calcium channels causes ….
The opening of chlorine and
potasium channels causes:
- depolarization: both ions
(positive charges) enter the cell
and make the membrane
potential LESS negative. - hyperpolarization: chlorine
(negative charges) enters the
cell and potasium (positive
charges) leaves the cell. Both
events make the membrane
potential MORE negative).
What is a graded potential?
Graded potentials (small deviation from the resting membrane)
where do graded potentials mostly occur?
mainly in the dendrites and cell body of a neuron. (p40)
The X of a graded potential depends on the stimulus strength. The larger the X, the greater the stimulus strength.
amplitude
X is the process by which graded potentials add together:
Summation
Summation:
If two depolarizing graded potentials summate, the net result is a larger
depolarizing graded potential.
* If two hyperpolarizing graded potentials summate, the net result is a larger
hyperpolarizing graded potential.
* If two equal but opposite graded potentials summate (one depolarizing and
the other hyperpolarizing), then they cancel each other out and the overall
graded potential disappears
bien
A graded potential occurs when a stimulus causes X or X channels to open or close in an excitable
cell’s plasma membrane.
X mechanicallygated,
ligand-gated
An action potential occurs in the A of the axon of a neuron
when depolarization reaches a certain level termed the B
(about − 55 mV in many neurons).
A membrane
B threshold
An action potential will not occur in response to a subthreshold stimulus: a
weak depolarization that cannot bring the membrane potential to threshold.
However, an action potential will occur in response to a threshold stimulus, a
stimulus that is just strong enough to depolarize the membrane to threshold.
True/false
true
Several (read: multiple!!) action potentials will form in response to a X
stimulus, a stimulus that is strong enough to depolarize the membrane above
threshold.
suprathreshold
An action potential has two main phases
After these phases: afterhyperpolarizing phase (more negative than resting)
Depolarizing phase: the negative membrane potential becomes less
negative, reaches zero, and then becomes positive.
2. Repolarizing phase: the membrane potential is restored to the resting
state of − 70 mV.
An action potential is generated in response to a threshold stimulus but
does not form when there is a subthreshold stimulus.
* In other words, an action potential either occurs completely or it does not
occur at all.
* This characteristic of an action potential is known as the X
principle.
all-or-none
ACTION
POTENTIAL
MECHANISM for ion channels:
- Resting state: …. channels are closed
- Depolarizing state: when membrane potential reaches threshold, the …. channels open
- repolarizing state: … channels close and …. channels open
- repolarizing: …. outflow continues.
- Na+ and k+
- Na+
- NA+ close, K+ opens
- K+
Because the voltage-gated K+ channels open more slowly during repolarizing, their opening occurs at
about the same time the voltage-gated Na+ channels are closing.
True/false
true
Refractory period: what cannot happen during this period?
an excitable cell cannot generate another action potential in
response to a normal threshold stimulus. (because the action potential is beginning)
Absolute refractory period: even a very strong stimulus cannot initiate a second action
potential. Is this true? If so, why?
yes
Inactivated Na+ channels cannot reopen; they first must return to the resting state.
At the start of action potential: we say that he Na+ channels are RESTING and the K+ channels are closed.
gracias
In terms of channels open and close, what do the channels do during the absolute refractory period?
NA+ gates open
and, K+ channels open, NA+ inactivating
What two stages can be destinguished of the refractory period?
absolute (no second action potential) and relative (second action potential only with very strong stimulus)
