DAT bio Chapter 11.4 Nervous system Flashcards
Structure of neuron
has three parts: the soma (cell body),
dendrites (extensions that receive signals), and
the axon (sends signals out).
What is the axon hill lock?
Place where the axon connects to the cell body.
Responsible for the
summation of graded potentials.
What is myelin sheath?
fatty insulation of the axon
that speeds up action potential propagation by
stopping ion exchange.
In the CNS myelin sheath is formed by
oligodendrocytes
In the PNC myelin sheath is formed by
schwann cells
What are the nodes of ranvier?
- gaps between myelin
sheaths where ion exchange occurs.
Propagation of the action potential occurs
here, jumping from gap to gap (node to node)
in a process called saltatory conduction.
Steps of an action potential
1)
At resting potential, the membrane potential of the neuron is around -70mV and is maintained by Na+/K+ ATPases, which pump three Na+ ions out and two K+ ions in, powered by hydrolysis of one ATP. K+ leak channels are also present and help maintain resting potential through passive K \+ leakage.
Steps of an action potential
2)
When a stimulus causes threshold potential
to be reached (around -55mV in neurons),
voltage-gated Na+ channels open up, letting
Na+
in, resulting in depolarization of the
neuron (reaches a peak of around +30mV to
+40mV).
Steps of an action potential
3)
Next is repolarization of the neuron due to
the opening of voltage-gated K+ channels,
letting K+ out. This causes the membrane
potential to become less positive since positive
ions are leaving.
Steps of an action potential
4)
When the membrane potential becomes even
more negative than the normal resting
potential, this is known as hyperpolarization.
This results in a refractory period being
established, during which another action
potential cannot be fired because the
membrane potential is very negative.
Steps of an action potential
5)
The membrane potential returns to normal
resting potential through the pumping of
Na+/K+ ATPases and K+
leak channels.
What is the absolute refractory period?
refers to the
period after the initiation of the action potential
during which another action potential cannot be
fired no matter how powerful the stimulus is. It is
due to the inactivation of voltage-gated Na
+
channels after they open.
What is The relative refractory period?
period after the action potential fires during which
a stronger than normal stimulus could cause
another action potential to be fired.
What is the synapese?
space between two neurons
who sends the signal the presynaptic or postynaptic
presynaptic
Steps of synaptic transmission step 1
Action potential reaches the end of the
presynaptic axon, causing voltage gated
calcium channels to open and letting Ca2+
ions into the neuron.
Steps of synaptic transmission step 2
The Ca2+ ions cause synaptic vesicles to fuse
and undergo exocytosis, releasing
neurotransmitters into the synapse.
Steps of synaptic transmission step 3`
The neurotransmitters (described in the table
on the next page) bind to ligand-gated ion
channels on the postsynaptic neuron,
producing graded potentials (depolarizations
or hyperpolarizations of the membrane).
Steps of synaptic transmission step 4
These graded potentials summate at the axon
hillock and an action will fire if the summation
of graded potentials is higher than the
threshold potential of neurons.
What is excitatory postsynaptic potential (EPSP)
graded potential that depolarizes the membrane.
What does excited neurotransmitter cause in EPSP
cause Na+
ion gates to open and let Na+
ions flow into the cell.
What is inhibitory postsynaptic potential (IPSP)
graded potential that hyperpolarizes the
membrane.
What does excited neurotransmitter cause in IPSP
Inhibitory neurotransmitters cause K+ ion gates to open and let K+ ions flow out of the cell. Another IPSP type allows influx of Cl-, allowing negative Cl- ions in.
What are non neuronal cells in the nervous system that help support and surround neurons?
glial cells
Glial cells are divided into
microglial cells and macroglial cells
Microglial cells are _______that protect the ______
macrophages
CNS
Microglial cells have many subtypes
astrocytes schwann cells oligondendrocytes satellite cells ependymal cells
Astrocytes
the most abundant glial cell
and form the blood-brain barrier. They also
help recycle neurotransmitters and provide
blood supply to the CNS neurons.
Schwann cells
form the myelin sheath in the
peripheral nervous system (PNS).
Oligodendrocytes
form the myelin sheath in
the central nervous system (CNS).
Satellilte cells
same functions as
astrocytes but instead help PNS neurons.
Ependymal cells
produce cerebrospinal fluid
(CSF), which cushions the CNS.
CNS is composed of
brain and spinal cord