Chapter 39: Neurons Flashcards
What is the main purpose of the nervous system?
You receive lots of stimuli and the nervous system determines what you respond to
What are the 4 components of neural signaling?
reception, transmission, integration, response
What is neural signaling?
the process by which an animal responds appropriately to a stimulus
What is reception? neurons involoved?
(detection of a stimulus) is performed by neurons and by specialized sensory receptors
What is transmission? neurons involved?
is the sending of a message along a neuron to another neuron or to a muscle or gland
What is integration? neurons involved?
sorting and interpretation of neural messages and determination of the appropriate response
What is response? neurons involved?
output or action resulting from the integration of neural messages
What are the 3 functional classes of neurons?
afferent neurons, interneurons, efferent neurons
What are afferent neurons? aka?
transmit stimuli from their sensory receptors to interneurons, aka sensory neurons
What are interneurons?
integrate the information to formulate an PNS appropriate response
What are efferent neurons?
carry signals indicating a response away from the interneuron to the effectors (muscles and glands) – motor neurons are efferent neurons that carry signals to skeletal muscle
What is an axon hillock? location?
site of origin of axon, between cell body and start of axon
How long can an axon be?
1 mm to more than 1 m long
What are glial cells?
include several types of non-neuronal cells that provide nutrition and support to neurons
What are the different types of glial cells?
astrocytes, oligodendrocytes/Schwann cells
What are astrocytes?
(in the vertebrate CNS) closely cover the surfaces of blood vessels, providing physical support and
maintaining concentrations of ions in the ISF, star like
What are oligodendrocytes/Schwann cells?
Oligodendrocytes in the CNS and Schwann cells in the PNS wrap around axons to form insulating myelin sheaths
What are the nodes of Ranvier?
gaps between Schwann cells that speed signal transmission
What is a neural circuit composed of?
an afferent (sensory) neuron, one or more interneurons, and an efferent neuron
What is the peripheral nervous system (PNS)?
In vertebrates, afferent and efferent neurons form the peripheral nervous system (PNS)
What is the central nervous system (CNS)?
Interneurons form the central nervous system (CNS), consisting of the brain and spinal cord
What is a nerve? can it be seen with the naked eye?
bundle of neuronal tails, can be seen
What is ganglia? location, examples?
neurons outside CNA, aka PNA, form the plexuses, examples have ganglia in the name
What is nuclei? location, examples?
concentration of cells in CNA, grey matter of brain, weird names for examples
What is a voltage? Why is it formed? importance?
creates membrane potentail across plasma membrane caused by a difference of charge by ions
What is the resting potential?
from -40 t0 -90 mV
averages about -70 mV
What is the charge distribution across the cell membrane?
ECF is positive while the ICF is negative (inside of the cell is negative)
Do ion leak channels allow more K+ to diffuse out or more Na+ to diffuse in?
more K+ to diffuse out
How does a sodium potassium pump work?
Brings two K+ into cell for every three Na+ it pumps out, needs input of ATP
What is the equilibrium potential for Na+?
+65 mV
What is the equilibrium potential for K+?
-90 mV
What are the 2 factors that go into a resting potential/electro-chemical potential?
- Electrical potential produced by unequal distribution of charges
- Concentration gradient produced by unequal concentrations of molecules
from one side of the membrane to the other
Is the membrane of a neuron that is not conducting an impulse polarized?
yep
a neuron that is not conducting an impulse resting membrane potential?
–50 to –70 mV
What is action potential?
When a neuron transmits an electrical impulse, an abrupt change in membrane potential occurs. This causes positive charges to flow inside or the cell depolarizing it. It depolarizes the cell slowly until it reaches its threshold potential
What is the threshold potential?
10-20 mV, more positive than the resting potential
Where are voltage-gated channels found?
axon and axon hillock
What types of conformations does the sodium channel
open, close, middle (unique to allow membrane potential to return to equilibrium/finish signal)
What is hyperpolarization?
occurs when potential falls to about -80 mV after the action potential fires. This is below the resting potential.
What occurs during the two phases of the refractory period? what does this prevent?
initial phase- cell cannot be restimulated
second phase- threshold required for generation of an
action potential is much higher than normal
prevents an action potential from reversing direction along an axon – only downstream voltage-gated ion channels are able to open, ensuring one-way movement
What is the all-or-nothing principle?
once an action potential reaches its threshold and is triggered, the changes in membrane potential take place
independently of the strength of the stimulus
Are glial cells required?
no, conduction decreases and rate time is limited
How is intensity of a stimulus measured?
frequency of action potentails
What is saltatory conduction? what organisms does this occur in?
In complex vertebrates, saltatory conduction allows action potentials to “hop” rapidly along myelin-coated axons.
Uncoated nodes of Ranvier expose the axon membrane to extracellular fluids at regular intervals
Voltage-gated Na+ and K+ channels at the nodes allow action potentials to develop only at these positions
Na+ ions diffuse rapidly to the next node where they cause depolarization, inducing an action potential at that node
What do larger spaces in between nodes result in?
faster reaction time
What is a synapse?
where a neuron makes a communicating connection with another neuron, or with an effector
What is a presynaptic cell?
neuron that transmits the signal
What is a postsynaptic cell?
dendrite or effector cell that receives the signal
What are electrical synapses?
the plasma membranes of the presynaptic and postsynaptic cells are in direct contact via gap junction. not as common ie heart cells, retina, pulp of tooth
What are chemical synapses?
the presynaptic and postsynaptic cells are separated by a narrow synaptic cleft. The neurotransmitter diffuses across the synaptic cleft and binds to a receptor in the postsynaptic cell membrane
What is the experiment with the 2 hearts?
2 separate heart affected each other when stimulated. led to discover of neurotransmitters.
Where are neurotransmitters store? how are they release?
stored in synaptic vesicles.
Release of synaptic vesicles depends on voltage-gated Ca2+ channels in the plasma membrane
ECa is strongly positive – an action potential opens Ca2+ channel gates, allowing Ca2+ to flow back into the cytoplasm
Rise in Ca2+ concentration in the axon triggers a protein in the membrane of the synaptic vesicle that allows exocytosis
The drop in cytoplasmic Ca2+ stops vesicles from fusing with the presynaptic membrane, and no further neurotransmitter molecules are released
What are the 2 kinds of receptors?
ionotropic and metabotropic
What is a ionotropic receptor? (4)
- binding site and channel combined
- second messenger independent
- rapid responses (10-50 ms)
- postsynaptic in general
What is a metabotropic receptor? (4)
- binding site not associated with channel
- second messenger dependent (g-protein)
- slow responses
- postsynaptic and presynaptic
How many different kinds of neurotransmitters can an axon terminal release?
one or multiple
Can a neurotransmitter inhibit and stimulate action potentials?
yes
tables
gahhh
What is an Excitatory postsynaptic potential (EPSP)?
- A change in membrane potential that pushes the neuron closer to threshold
- Occurs when a ligand-gated Na+ channel opens and Na+ enters the cell, causing depolarization
What is an Inhibitory postsynaptic potential (IPSP)?
- A change in membrane potential that pushes the neuron farther from threshold
- Occurs when a ligand-gated ion channel opens that allows Cl– to flow in and K+ to flow out (hyperpolarization)
What is a graded potential?
membrane potential increases or decreases without necessarily triggering an action potential
What is temporal summation?
single presynaptic neuron over a short period of time
What is spatial summation?
summation of EPSPs produced by the simultaneous firing of two different excitatory presynaptic neuron
What is summation resulting in cancellation?
EPSPs and IPSPs can sum to cancel each other out. leads to no change in membrane potential
How many connection can neurons make? in the brain?
Neurons can make many connections – single interneurons in the human brain may form up to 100,000 synapses
Can synapses change?
yes, through modification, addition, or removal of synaptic connections as animals mature and experience changes in their environment. synapse formation occurs rapidly in human development.
