Flashcards in Week 2 Deck (70):
What does the cell body (soma of a neuron contain?
nucleus, Golgi apparatus, mitochondia, nucleic acids, usual organelle
What is the function of the cell body?
Synthesizes a large quantity and variety of proteins used as neurotransmitters
What do dendrites do?
receive information from other neurons (input sites for the cell)
Where do axons arise and end?
arise from axon hillock
end in presynaptic terminals
What is the length of an axon?
from long (greater than a meter) to short (less the 100um)
What is the function of an axon?
Specialized to send neural signals away to other neurons, muscle cells or glands (= “output unit” of the cell)
What is a pre-synaptic terminal?
Site of communication between neurons, and between a neuron and a muscle or a gland
What are the elements of a pre-synaptic terminal?
presynaptic terminals: fingerlike projections transmitting element of the cell
synaptic cleft: space between neurons
Vetebrate neurons are classified as:
Bipolar cells have:
2 primary processes from cell body
subclass of bipolar cells; sensory neurons having two axons
transits signals from the periphery to cell body
conduct signals to the spinal cord
How do neurons distinguish from most other cells?
by bioelectrical properties and intercellular communications
How do neurons function?
rapid changes in the electrical potential across the cell membrane
What is electrical potential?
difference in electrical charge carried by ions on each side of the cell membrane.
What are the four types of membrane channels?
What does a modality gated channel open in response to?
mechanical forces (stretch or touch), temperature changes or chemicals; specific to sensory neurons
What does a ligand gated channel open in response to?
response to a neurotransmitter binding to the surface of a channel receptor on a postsynaptic cell membrane
What does a voltage gated channel open in response to?
in response to changes in the electrical potential across the cell membrane.
What is a leak channel?
non gated channel
A small number of ions leak at a slow, continuous rate
What causes gated channels to open and close?
‘Gated’ membrane channels open in response to a stimulus and close when the stimulus is removed
What are the three types of electrical potentials?
Resting membrane potential
What is the value of the resting membrane potential?
-40 mV to -80 mV
What occurs when two forces are balanced?
What maintains electrochemical gradient in neurons and membrane resting potential?
- Passive diffusion of ions through leak channels in the cell membrane
- Na+/K+ pump
What is depolarized?
the membrane potential becomes less negative than the resting membrane potential
What is hyperpolarized?
the membrane potential becomes more negative
What does hyperpolarization do?
decreases the neuron's ability to generate an electrical signal, and its inhibitory
What is local potential?
Initial change in membrane potential
How do local potentials spread?
spread passively, confined to a small area of the membrane
-spread only a short distance along the membrane
What can increase the strength of a local potential?
temporal and spatial summation
What is temporal summation?
combined effect of a series of small potential changes that occur within milliseconds of each other
What is spatial summation?
process by which either receptor or synaptic potentials generated in different regions of the neuron are added together
What is an action potential?
a large depolarizing signal actively propagated along an axon by repeated generation of a signal
_____ depolarization is typically sufficient to trigger an AP
What is threshold stimulus intensity?
stimulus intensity sufficient to produce an action potential
What are the 3 events that produce an action potential?
1. Rapid depolarization (voltage-gated Na+ channels open)
2. Decrease in Na+ conduction (channels closed)
3. Rapid repolarization (voltage-gated K+ channels open)
What happens during the refractory period?
Na+ channels become inactivated immediately after opening for an AP and require a specific amount of time before they can be activated again for a subsequent AP
What is the function of the refractory period?
to promote forward propagation of an AP while preventing backward flow
Refractory period is also a period of:
period of hyperpolarization during which the membrane potential is even more negative than during resting (difficult to initiate a subsequent AP)
Why will some axons be specialized for faster action potentials because of 2 structural adaptions:
What does an increased diameter of the axon do?
speed of transmission is faster in larger-diameter axons.
What does myelination do?
increases efficiency of conduction of AP by decreasing the inherent leakiness of the membrane
What is myelination?
a sheath of proteins and fats surrounding an axon; Provides insulation, prevents current flow across the axonal membrane
Thicker myelin leads to what?
faster conduction and greater chances for AP propagation
What are nodes or ranvier?
small patches of myelinated axons which lack myelin
What is saltatory conduction?
quick node-to-node jumping of AP down a myelinated axon
carry sensory information from the outer body toward the CNS
relay commands from the CNS to smooth and striated muscles and to glands
act throughout the nervous system, processing information locally or conveying information short distances; largest class of neurons
What is convergence?
multiple inputs from a variety of cells terminate on a single neuron
What is divergence?
single neuron with many branches that terminate on a multitude of cells
Ratio of glial cells to neurons in the brain:
New literature : 9:1
form a critical support network for neurons
Types of glia cells:
glial stem cells
Types of macroglia:
What are astrocytes?
-star shaped macroglia found throughout the CNS
-primarily in gray matter
-act as scavengers
What stimulates astrocytes?
signals from adjacent neurons or by mechanical changes
spread waves of Ca2+ to neighboring astrocytes
What do oligodendrocytes and schwann cells do?
-form myelin sheath and are found primarily in white matter
What do oligodendrocytes myelinate?
neurons in the CNS
What do Schwann cells myelinate?
neurons in the PNS
What are microglial cells?
- phagocyte that resides in CNS
- act as immune system of CNS
- activated during development of nervous system following injury, infection or disease
What are glial stem cells?
- found throughout developing and adult brain
- immature and undifferentiated cells
- retain capacity to proliferate and generate
What is neuroinflammation?
the response of the CNS to infections, diseases and injuries
What is a beneficial effect of neuroinflammation?
when reactive microglia clean up and remove debris
What is a harmful effect of neuroinflammation?
- Death of neurons and oligodendrocytes, inhibition of neural regeneration
- Correlation between abnormal glial activity and neural damage
What is peripheral neuropathy?
any pathological change involving peripheral nerves
What does peripheral neuropathy result in?
destruction of myelin surrounding the largest, most myelinated sensory and motor fibers
-disrupted proprioception and weakness