Chapter 43 Flashcards
Nervous system parts
Peripheral nervous system
Central nervous system
Peripheral nervous system
Part of nervous system that has a network of wires connects brain and spinal cord to rest of body
In the PNS sensors send sensory input down sensory neurons to the CNS, the CNS then sends motor outputs via motor neurons to effectors
Central nervous system
Consists of brain and is responsible for the processing of all sensory information
Recieves sensory input and sends motor output
Anatomy of neuron
- Dendrite- receives electrical signals from axons
of adjacent cells - Cell body (soma)- includes nucleus, integrates incoming
signals & generates outgoing signal - Axon- sends signal to dendrites of other neurons
Neurotransmitters
Chemical messengers that transmit signal across the synapses
Synapses
Area where axons transmit signals to dendrites
Consists of a pre and postsynpatic terminal
Presynaptic is at the end of the axon and where the action potential (electrical signal) is converted to a chemical signal called neurotransmitter
Resting potential
The voltage of a neuron’s membrane when not in communication with other neurons is called the resting potential
Typically the interior of cell is negatively charged relative to outside it
Action potential
rapid, temporary change in membrane potential
Three parts
1. Depolarization
2. Repolarization
3. Hyperpolarization
Neurons intracellular concentration
High intracellular concentration of K+ and A- (negatively charged proteins)
Low intracellular concentration of Na+ and Ch-
Sodium potassium pump (Na+/K+-ATPase)
Generally imports or takes in K+ ions and releases Na+ ions
- Three Na+ ions enter pump, the ATP provides energy for a shape change that makes it be released outside cell
- Two K+ ions enter pump and is released inside cell
What are resting ions most permeable too?
K+ ions and crosses membrane easily across concentration gradient through K+ leak channels
What happens as K moves out the cell?
Inside becomes more negatively charged compared to the outside
Hyperpolarization
When the membrane potential becomes more negative at a particular spot on the neuron’s membrane
Occurs when ion channels open that let positive ions out, or ion channels that let negative ions in
Threshold potential
negative charge that will not allow
action potential to proceed
Depolarization
When the membrane potential becomes less negative (more positive).
The opening of channels that let positive ions flow into the cell can cause depolarization
What can trigger a membrane voltage change
A stimulus can cause the membrane to open more voltage Na+ ion channels that depolarizes the cell
Movement of Na+ into cells cause even more Na+ channels to open
How is an action potential created
When a large stimulus results in multiple depolarizing inputs that depolarizes the membrane above the potential threshold
Refractory period
Inactivated Na+ channels behind depolarization zones prevents action potential from traveling backwards
What effects speed of action potential
Axon diameter and myelination
Larger axons have a faster action potential because there are less less current leaks and more space for the ions to travel so it won’t bump into other ions
How Myelination effects speed of action potential
membranes of specialized accessory cells (called Schwann cells in PNS & oligodendrocytes in
CNS) are wrapped around axons and form a myelin sheath
The myelin sheath acts as electrical insulation, preventing neurons from leaking, making transmission faster
Glia
Specialized accessory organs that include Schwann cells in PNS and Oligodendrocytes in CNS that wrap around axons and form a myelin sheath
Node of Ranvier
Gaps in the myelin sheath across axon that allow action potential to jump across node to node
Synaptic transmission
- When the action potential that arrives at the end of the axon triggers entry of calcium ions into presynaptic cell through voltage gate calcium ion channels
- Synaptic vesicles fuse with the presynaptic membrane and releases neurotransmitters
- The neurotransmitters bind to receptors on postsynaptic membrane initiating action potential if threshold potential is reached
- Ion channels close and neurotransmitters are broken down or taken back up by presynaptic cell
Threshold potential
critical level to which a membrane potential must be depolarized to initiate an action potential.
Repolarization
Happens after action potential is generated the voltage reaches its highest point
Sodium gates begin to close, and potassium gates open and returns neuron to its resting state
Hyperpolarization
Occurs when potassium channels remain open longer than necessary, making the inside of the neuron more negative than its resting potential
Will net flow of K+ out of the cell occur indefinitely?
No, it will stop once the membrane reaches the equilibrium potential for K+.
What would occur if sodium channels remained open once membrane depolarization was complete?
Repolarization would occur, but much more slowly since potassium moving out would counteract it
Which neurons function to integrate information that reaches the central nervous system
Interneuron
Interneuron
neurons that are found in the CNS and integrate sensory information by connecting sensory input to motor output.
What ion channels are open during the resting potential
Voltage Na+ and K+ channels are closed
What ion channels are open or closed during the rising phase
Na+ channels open
K+ channels closed
What ion channels are open or closed during the falling phase
Na+ channels close
K+ channels open
What happens during refractory period and what determines when it ends
During the refractory period, an action potential cannot be triggered even if the membrane potential reaches threshold because the voltage-gated Na+ channels are inactive.
how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential determines when it ends
A nerve impulse moves toward a neuron’s cell body along
dendrites
Which of these causes the release of neurotransmitter molecules?
an action potential reaching the end of the axon as, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft.
The space between an axon of one neuron and the dendrite of another neuron is called what?
synaptic cleft
Where are neurotransmitter molecules in vesicles located
synaptic terminals
What hyperpolarizes the membrane
Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal.
Where in the neuron do action potentials begin?
Axon hillock which is the region where voltage-gated channels begin in a neuron
Functions of presynaptic membrane
- It propagates action potentials from the synaptic terminal.
- it helps trigger the release of neurotransmitter in response to an action potential.
Voltage gated Ca^2+ channels are found here and reggulates release of neurotransmitter from presynaptic neuron
Synaptic terminal
Membrane that propogate action potential
Ligand-gated ion channels
Open in response to neurotransmitter in the synaptic cliff
