Lecture 9: Nervous System 2 Flashcards
True/False: Axon terminates in multiple endings
True
Explain what happens when AP electrical signal travels down the neuron.
When Action Potential (AP; electrical signal) travels down neuron and reaches presynaptic terminal, causes release of neurotransmitters which diffuse across synaptic cleft, bind to receptors on postsynaptic membrane, electrical signal is converted to chemical signal (neurotransmitter release), triggers AP
What are examples of excitatory neurotransmitters?
- Glutamate (major excitatory neurotransmitter)
- Acetylcholine
- Epinephrine
- Histamine (generally excitatory effects)
- Dopamine (both Excitatory and Inhibitory)
What is the major excitatory neurotransmitter?
Glutamate
What kind of effect does histamine have?
excitatory
What kind of effect does dopamine have?
Excitatory and Inhibitory
What are examples of Inhibitory Neurotransmitters?
- GABA (Gamma-aminobutyric acid) (most common
one in nervous system) - Serotonin
What is adenosine and why does it build up in the brain and make your sleepy?
its an inhibitory neurotransmitter that inhibits the activity of the neurons that make you feel awake. When you drink caffeine adenosine builds up and once caffeine unbinds, all the adenosine binds and makes you sleepy.
Is normal resting voltage positive or negative?
Negative
What is action potential?
transient, regenerative*, electrical impulse in which the membrane potential rapidly rises to a more positive peak
What is a synapse?
junction between two neurons
What causes neurons to release chemical neurotransmitter?
AP
Where is AP released by neutrotransmitters?
synapse
True or False: APs can travel long distances along nerve or muscle fibers.
True
What kind of effect does AP cause on neurons?
either excites or hinders
next neuron from firing its own AP
Why are action potentials important
- Allows brain to communicate with periphery via efferent nerves (e=away from brain)
- Allows periphery (e.g. organs, muscles) to communicate with brain via afferent nerves (a= to brain)
AP is an ___ response
all or none (it had rapid depolarization and slow repolarization)
How does AP get triggered?
If Electrical stimulus of nerve or muscle cell causes membrane potential to become more + than threshold voltage
What kind of charge does a stimulus have?
more +
Depolarization stimulus requires certain ___ and ___.
intensity and duration
True/False: Subthreshold depolarizations will lead to AP
False
When a cell fires an AP, how soon can it fire another one?
needs time to recover
What is the absolute refractory period?
- Second response is not possible regardless of strength/duration of stimulus due to Na+ channel inactivation
- Lasts from initiation of AP to when repolarization is almost complete
What is the relative refractory period?
The second response can be elicited but requires a greater stimulus (in strength or duration)
True/False: Variations of AP depend on cell type and its function.
True
Explain the AP in nerves.
Nerves have brief AP to permit rapid signaling
Explain the AP in cardiac and smooth muscle.
Cardiac and certain smooth muscle have prolonged, repetitive AP to allow slow, rhythmic contractions
How does electronic spread of voltage occur?
along cell occurs by flow of electric current carried by ions in intracellular and extracellular medium along pathway of least resistance
What does depolarization and hyperpolarization of small area of membrane produce?
local circuit currents
Describe the charge of the cytosol where membrane is depolarized compared to inactive, adjacent area of membrane.
cytosol is positive and inactive area is negative
What is the importance of the charge difference between the cytosol where membrane is depolarized and the inactive, adjacent area of membrane?
allows flow of ions to adjacent area of cytoplasm
True/False: Nerve and muscle fibers conduct impulses in both directions if inactive fiber is in a central location
True
True/False: If AP is initiated at one end of nerve fiber, it will travel only in one direction and stop
True
What period prevents backward movement of impulse.
refractory
What ion channels mediate cellular communication?
electrical and chemical
How is spontaneous action potential generated?
generated if membrane is depolarized above a certain threshold voltage
What are the two ways animals improve conduction? (just list)
Axon diameters and myelination of smaller diameter axons
What is the adaption of animals involving axon diameter?
-Increased diameter increases conduction velocity
-Decreases internal resistance
Explain how the myelination of smaller diameter axons helps animals improve conduction.
- Improves efficacy of impulse propagation
- Glial cells produce myelin
-Schwann cells in
-periphery
-Oligodendrocytes in
-brain - Leads to increased membrane resistance
- Minimizes current loss across leaky axons
- Forces current to flow longitudinally along inside of fiber
What nerves have an interrupted myeline sheath at regular intervals?
peripheral nerves
What are the nodes of Ranvier?
Short (~1μm) unmyelinated region
High density of voltage-gated Na+ channels
What is Saltatory conduction?
-Current flows from node to node
-Very efficient system
What is affected in the disease multiple sclerosis?
the myeline is demyelinated
What type of disorder is multiple sclerosis?
autoimmune
What is multiple sclerosis?
Immune system attacks the myelin sheath surrounding axons and myelin sheath is progressively lost
