resting membrane potential
the electrical charge of a neuron when it is not active
action potential
- a rapid depolarization that occurs in a n excitable cell (neurons and muscle cells)- an electrical event or chemical stimulation that causes increased ion permeability in the cell membrane.
Where at in a neuron is an action potential is generated?
axon hillock
as the action potential is conducted, the area of the membrane directly behind the action potential is still in
absolute refractory state
myelinated
covered in multiple layers of insulating sheath of phospholipid membrane
myelinated sheath is formed by _ in the _
Schwann cells, peripheral nervous system
insulated sheaths are formed from _ in the _
oligodendrocytes , central nervous system
propagation of the action potential breaks are called
nodes of ranvier
the process by which the action potential "jumps" between nodes is known as
saltatory conduction
saltatory conduction allows for
rapid propagation for the action potential
threshold potential
the potential at which an action potential will be initiated by increased conductance of ions
All- or none" response
a given stimulus either triggers an action potential, or none at all.
nondecremental propagation
an action potential at one point on a cell membrane
refractory period
when it is possible to elect a second action
relative refractory period
following the absolute refractory period, when a second potential can be evoked by requires a larger than normal stimulation.
Role of the Sodium-Potassium Pump
Repolarization resets electrical conditions, not ionic conditionsAfter repolarization Na+/K+ pumps (thousands of them in an axon) restore ionic conditions
essential property of neurons
the ability to rapidly propagate an action potential, analogous to an electrical cable.
internal resistance (R1)
impedance to current flow within the cytoplasm (resistance within the axon)
membrane resistance (Rm)
impedance to current flow through the membrane
capacitance (Cm)
the ability of membrane to store charge
structure of neurons
dendrites, cell body, axon, synapse
synaptic cleft
The narrow gap that separates the presynaptic neuron from the postsynaptic cell.
presynaptic cell
neurons that send messages
postsynaptic cells
cell that receives messages
synapse
a site at which an electrical response in one cell is transmitted to another cell
electrical synapse
Electrical current passes directly from one neuron to the next
chemical synapse
release of a neurotransmitter by a neuron results in the electrical stimulation of the postsynaptic cell
depolarization of the neuron reaches the axon terminal
where it causes opening of Ca2+ channels
influx of Ca2+ results in
release of neurotransmitter from presynaptic vesicles into synaptic clefts
transmitter diffuses across the synaptic cleft and binds to
specific membrane receptors on the postsynaptic membrane
binding of the neurotransmitter produces a change in the
membrane receptors on the postsynaptic memrbane
depending on the presynaptic neuron, the chemical transmission may
result in either an excitatory or inhibitory postsynaptic potential
neuromuscular junction
motor neurons are efferent nerves that originate in the CNS and communicates with skeletal muscle fibers at specialized synapse known as motor end plates or NMJ
skeletal muscle contraction
is the basis of voluntary muscle movement
multinucleate cells contain
sarcomeres
sarcomeres are
specialized structures that produce contraction upon stimulation of the muscle
sarcomeres contain
myofibrils
myofibrils are
organized muscle fibers
groups of muscle fibers form
muscle fasciles
contraction is based on sliding of
thin and thick filaments of sacromeres
excitation-contraction coupling
events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract
excitation-contraction coupling step 1
depolarization of the motor neuron terminal resulting in Ca2+ influx
excitation-contraction coupling step 2
vesicles of the axon terminal release acetycholine
excitation-contraction coupling step 3
binding of acetylcholine by nicotinic receptors results in an end plate potential
excitation-contraction coupling step 4
an action potential is initiated and is propagated along the sarcolemma and down the T tubules
excitation-contraction coupling step 5
a conformational change is dihydropyride receptor of the T tubule is transducer to a conformational change in the ryanodine receptor of the sarcoplasmic reticulum
excitation-contraction coupling step 6
Ca2+ is released from the sarcoplasmic reticulum, initiating contraction
smooth muscle
nonstriated muscle found within organs
actin is anchored to the _ membrane and _ bodies within the cell
cell ; dense
actin and myosin
contractile proteins
in depolarization or pharmcomechanical coupling, an increase in _ leads to the activation of phospholase _ , which _ phosphatidulinositol (IP3), which releases Ca2+ from intercellular stores.
Ca2+ ; cleaves
Ca2+ binds to
calmodulin
the complex activates the enzyme myosin kinase
allows myosin and actin interaction
cardiac muscle
- contraction of muscle in involuntary
gap junction sin cardiac muscle are found in
intercalated disk
cardiac contraction is normally under the control of
cardiac pacemaker cells in the sinoatrial node (SA node)