Human Physiology Block 1 Lesson 5: Neurophysiology Action and Graded Potential

what are dendrites?

recieve input

what is the cell body?

nucleus and genetic information

What is the initial segment?

trigger zone

What is the axon?

carries output

What is the axon-terminal?

neurotransmitter release

what is the cell membrane?

the semipermeable membrane that encloses the neuron

What are dendrites?

the short processes emanting from the cell body, which receives most of synaptic contacts from other neurons

What is the axon-hillock?

the cone-shaped region at the junction between the axon and the cell body

what is the myelin?

the fatty insulation around the many axons

What are the nodes of Ranvier?

the gaps between sections of the myelin

What are buttons?

the button like ending of the axon branches, which releases chemicals into synapses

What are synapses?

the gaps between adjacent neurons across which chemicals signals are transmitted

What are afferent neurons?

convey information from tissues and organs into the CNS

What are efferent neurons?

transmit information from the CNS to the effector cells

What are interneurons?

connect neurons within the CNS: can act as a relay station between information going to the brain and information coming from the brain

What is the glial cell?

-outnumber neurons in the brain by 10:1

-are active participants in brain cell communication

-retrograde signaling and cleaning up the synapse

-control of cerebral blood flow via astrocytic end feet

what is an astrocyte?

largest glia, star-shaped, many functions in CNS

What is a microglia?

involved in response to injury or disease in CNS

What is Oligodendrocytes?

extensions rich in mylein create myelin sheaths in CNS

What is Schwann cells?

similar to oligo's but in PNS, can guide axonal regeneration

What impact does Na+ across the membrane have on membrane potential?

depolarizes the membrane(positively charged sodium enters the cell, making the membrane potential less negative)

What impact does K+ have across the membrane?

hyperpolarizes the membrane(making the membrane potential more negative; positively charged ions leave the cell)

Action potentials

all or none events

Post synaptic potentials

summate

What is all-or-none?

when threshold is reached, voltage-activated ion channels are open

What is the mechanism of action of Novacaine? Why does it only affect some nerves in the mouth but not others?

novocaine blocks nerve cells on nerve cell membrane, preventing sodium ions from entering the nerve and inhibiting pain signals to the brain. It only affects some nerves in the mouth because nerves that are not near the injection sites will not be affected

What is post-synaptic potential or graded potential?

neurotransmitters bind post-synaptic ion channels and cause electrical charges

What is post-synaptic depolarization?

excitatory PSP(EPSP)

What ions might cause depolarization?

Na+

What ions might cause hyperpolarization?

K+

EPSPs make it more likely a neuron will fire, whereas IPSPs make it less likely a neuron will fire

T/F

True

What miust the threshold be reached near the axon hillock to generate an AP?

-55 - -60

What is spatial summation?

integration of events happening at different places

What is temporal summation?

integration of events happening at different times

How are graded potentials initiated?

by activation of receptor-operated or mechano-receptor channels

What does variable duration depend on?

how long channels were open

What does variable amplitude depend on?

the number of channels that are open

the kind of channels that are open

What are voltage gated ion channels?

-contains a voltage sensor that monitors equilibrium potential

-At RMP, voltage gated channels are closed

-changes in membrane potential like hyperpolarization and depolarization cause channels to open

What is a ligand-gated channel?

binding of specific chemicals to receptor site causes channels to open

rising phase of action potential

Sodium Channels open, Potassium Channels closed.

repolarization phase

potassium gates open

How do action potentials pronate along the axon?

-neurons communicate via propagation of APs down the axon

-that could communicate via local depolarization down the length of an axon

How could signal propagation be facilitated?

insulated segments that allow passive conduction along a portion of the axon

What is the purpose of the absolute and refractory period?

-prevent the backward movements of AP

-limit the rate of firing

What are characteristics of the absolute refractory period?

-mechanism is inactivation of another AP

-no new stimulus can produce new AP regardless of strength

-recall that APs are not additive but all-or-none

What are characteristics of relative refractory period?

-harder to initiate another AP

-occurs during hyperpolarization phase

-can last 1-15ms

-majority of Na+ channels are at rest

-K+ channels are still open