Lecture 25 Neurons Flashcards
(82 cards)
Rundown of nervous system
● The nervous system transmits information between specific locations
● The information conveyed depends on a
signal’s pathway, not the type of signal
● Nerve signal transmission is very fast
Neuron structure
The neuron is a cell that exemplifies the close fit between form and function 7
● Cell body - Most of organelles
● Dendrites, highly branched
extensions that receive signals from other neurons
● The axon is often a much longer
extension that transmits signals to other cells at synapses
● The cone-shaped base of an axon
is called the axon hillock
Structural diversity of neurons
sensory neurons, interneurons, motor neurons
Sensory neurons
transmit information about external stimuli such as light, touch, or smell
Interneurons
integrate (analyze and interpret) the
information
Motor neurons
transmit signals to muscle cells,
causing them to contract
Synapse
is a junction between an axon and another cell
Synapse passes info through neurotransmitters (short distance: chemical)
neurotransmitters
The synaptic terminal of one axon passes
information across the synapse in the form of chemical messengers
Transmitting a signal (long distance)
silde 10
Complex nervous system: Organisation
● Central nervous system (CNS),
where integration takes place;
○ brain or simpler clusters called
ganglia
○ spinal cord
● Peripheral nervous system (PNS),
which carries information into and out
of the CNS
● Neurons of both the CNS and PNS
require supporting cells called glial
cells, or glia
Central nervous system (CNS)
where integration takes place;
○ brain or simpler clusters called ganglia
○ spinal cord
Peripheral nervous system (PNS)
which carries information into and out
of the CNS
● Neurons of both the CNS and PNS
require supporting cells called glial
cells, or glia
Membrane potential
Every cell has a voltage (difference in electrical charge) across its plasma
membrane
Changes in membrane potential can be graded or action potentials
resting potential
is the membrane potential of a
neuron not sending signals
Changes in membrane potential can be graded or action potentials
The plasma membrane is decorated with
proteins
slide 13
3 major ways to transport molecules across membranes
- Facilitated diffusion
- Active transport
- Bulk transport (exocytosis and endocytosis)
Facilitated diffusion: channels
Facilitated diffusion does not require energy
A channel, or a carrier protein, allows passive diffusion to occur through the protein
Active transport
● But cells aren’t simply at equilibrium with their environment!
● E.g. different concentrations of Na+
and K+ ions inside and outside the cell.
● These “electrochemical gradients”are necessary for the transmission of nerve impulses.
Active transport: the Na+/K+ pump
● Transport “up” the concentration gradient for each ion.
● Requires energy (hydrolysis of ATP)
● Phosphorylation / dephosphorylation drive conformational change
how the electrochemical gradient is maintained
What is Active transport
moves substances against their concentration gradients
Active transport requires energy, usually in the form of ATP.
Active transport allows cells to maintain concentration gradients that differ from their surroundings.
Membrane potential
slide 19
Formation of the Resting Potential
● In most neurons, the concentration of K+ is higher inside the cell, while the concentration of Na+ is higher outside the cell.
● Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane.
● These concentration gradients represent chemical potential energy.
Sodium-potassium pump
- Cytoplasmic Na+binds to the sodium- potassium pump. The affinity for Na+
is high when the protein has this
shape.
2.Na+ binding stimulates phosphorylation by ATP.
3.Phosphorylation leads to a change in
protein shape, reducing its affinity for Na+, which is released outside.
4.The new shape has a high affinity for K+
, which binds on the extracellular side and triggers release of the phosphate group.
5.Loss of the phosphate group restores the protein’s original shape, which has
a lower affinity for K+
6.K 6 + is released; affinity for Na+
is high again, and the cycle
repeats
(slide 21 and 22 and 23)
cycle on slide 24
IMPORTANT sodium potassium pump
slide 25
