02 - Cell Excitability

Brain and Spinal Cord

2 main components of the CNS

Cranial and Peripheral Nerves

2 main components of the PNS

Neurons

The basic unit of the nervous system

Glial Cells

These cells provide physical and metabolic support to the neurons

Dendrites

This type of nerve process receive inputs and conveys it to the soma

Axons

This type of nerve process carries output signals to other cells

Axon Hillock

The part of the axon is where the action potential is generated

Axon Terminals

This is the ending of the axon that releases neurotransmitters

Varicosities

These are bulging areas along the axon that release neurotransmitters

Axonal Transport

This is the movement of materials between the cell body and axon terminal

Kinesin

Carries materials in the anterograde direction

Dynein

Carries materials in the retrograde direction

Oligodendrocytes

This provides myeline sheath to cells in the CNS

Schwann Cells

This provides myeline sheath to cells in the PNS

Nodes of Ranvier

Areas devoid of myelin sheath where electrical signals “jumps”

Myelin Sheath

This speeds up conduction of electrical signal as it acts as an insulator

Saltatory Conduction

This is the “jumping” of electrical signals from node to node

Microglia

This type of glial cells perform immune function in the CNS

Ependymal cell

This type of glial cells regulates the production of CSF and forms the Blood-CSF Barrier

Astrocytes

This type of glial cells stimulate the formation of the BBB

Potassium ions and Neurotransmitters

Astrocytes regulate ECF Composition by removing what two materials?

Ammonia

Astrocytes sustains neurons metabolically by removing what material

Afferent Neurons

This class of neurons convey information from tissues into the CNS

Peripheral Process

This process of afferent neurons originates from the sensory receptor

Central Process

This process of afferent neurons goes into the CNS to connect with other neurons

Efferent Neurons

This functional class of neurons conveys information from the CNS to the effector cells

Interneuron

This functional class of neurons connects neurons within the cell

Synapse

This is the specialized junction between 2 neurons

Presynaptic Neuron

Neuron that conducts a signal towards a synapse

Postsynaptic Neuron

Neuron that conducts a signal away from a synapse

Electrical Signals

Main mode of cell-cell communication

1 < 2

QC: Attraction between molecules of (1) Same Charge (2) Opposite Charge

Potential

Difference in charge between 2 points

Resting Membrane Potential

This is the potential found in all cells across the plasma membrane under normal conditions

1 > 2

QC: Negativity (1) Inside (2) Outside of the cell

Current

This is the movement of an electric charge

Increase in 1 leads to Increase in 2

VR: (1) Potential (2) Current

Nernst Equation

This equation is used to compute equilibrium potential of an ion

Increase in 1 leads to Increase in 2

VR: (1) Concentration Gradient (2) Electrical Potential

1 > 2

QC: Movement of Na+ after channel is opened (1) Inside (2) Outside

1 < 2

QC: Movement of K+ after channel is opened (1) Inside (2) Outside

1 > 2

QC: Movement of Cl- after channel is opened (1) Inside (2) Outside

Increase in 1 leads to Decrease in 2

QC: (1) Na+ Channel Opening (2) Negativity of the cell

Increase in 1 leads to Increase in 2

QC: (1) K+ Channel Opening (2) Negativity of the cell

Increase in 1 leads to Increase in 2

QC: (1) Cl- Channel Opening (2) Negativity of the cell

Goldman equation

Membrane potential can be calculated using what equation?

Potassium

Prime determinant of RMP

1 > 2

QC: Permeability of (1) Na+ (2) Cl-

1 < 2

QC: Permeability of (1) Na+ (2) K+

Excitability

It is the ease of initiating an action potential

Increase in 1 leads to Increase in 2

VR: (1) Stimuli intensity (2) Change of MP in GRADED Potential

Increase in 1 leads to No change in 2

VR: (1) Stimuli intensity (2) Change of MP in ACTION Potential

1 > 2

QC: Change in MP (1) At stimulus site (2) 5 mm from stimulus site from a GRADED Potential

1 = 2

QC: Change in MP (1) At stimulus site (2) 5 mm from stimulus site from an ACTION Potential

1 < 2

QC: Speed of channel gating of (1) K+ (2) Na+ Channels

Na+ Influx

What ion and its direction of flow causes depolarization?

K+ efflux

What ion and its direction of flow causes repolarization?

K+ efflux

What ion and its direction of flow causes hyperpolarization?

Threshold Stimulus

This is the lowest intensity of a stimulus that can trigger an AP

Sub-threshold Stimulus

This is the intensity of a stimulus that cannot trigger an AP

Increase in 1 leads to Increase in 2

VR: (1) TP Negativity (2) Excitability

Increase in 1 leads to Decrease in 2

VR: (1) RMP Negativity (2) Excitability

Absolute Refractory Period

This is the period where any intensity of stimulus cannot trigger an AP

Relative Refractory Period

This is the period where only an above threshold stimulus can trigger an AP

All Na+ Channels are in a non-resting state

Physiologic Explanation of the absolute refractory period

Increase in 1 leads to Decrease in 2

VR: (1) Length of ARP (2) Max frequency of AP

Increase in 1 leads to Increase in 2

VR: (1) Myelination (2) Nerve fiber diameter

Increase in 1 leads to Increase in 2

VR: (1) Nerve fiber diameter (2) Conduction Velocity

False

T/F: Since the AP current flows in both directions, it’s action will also be bidirectional

F, T, F

Multiple T/F: This state of sodium channels are excitable

(1) Activated

(2) Resting

(3) Inactivated

In response to external stimuli

This generation of AP usually occurs in the afferent neuron

In response to a neurotransmitter

This generation of AP usually occurs in the synapse

Na+ Channel

Which channel is inherently responsible for spontaneous generation of AP?

Converging

This type of synaptic connection occurs when 2 or more synapses affect a single post-synaptic neuron

Diverging

This type of synaptic connection occurs when a single presynaptic cell affects many other postsynaptic cells

Gap junction

Electrical synapses are usually joined by what intracellular connection?

Synaptic clefts

Chemical synapses are usually joined by what intracellular connection?

1 > 2

QC: Speed of synaptic transmission (1) Electrical (2) Chemical Synapse

1 < 2

QC: Abundance in brain (1) Electrical (2) Chemical Synapse

F, T

Multiple T/F: The direction of synaptic transmission is unidirectional

(1) Electrical Synapse

(2) Chemical Synapse

Active zones

This is the site of neurotransmitter release in axon terminals

Voltage-gated Ca2+ Channels

What channels are seen in the axon terminal?

Postsynaptic density

This is a special area seen in the postsynaptic membrane that contains an abundance of receptors

Increase in 1 leads to Increase in 2

VR: (1) Ca+ influx in the presynaptic terminal (2) Neurotransmitter Release

ACh moves out of synaptic cleft, reuptaken into the presynaptic neuron, or degraded by enzymes

How is synaptic transmission usually stopped? (3 Mechanisms)

Ionotropic

This type of ligand gated receptor contains the ion channel itself

Metabotropic

This type of ligand gated receptor requires the generation of a second messenger to open the ion channels

1 > 2

QC: Response time of (1) Neurotransmitters (2) Neuromodulators

Increase in 1 leads to No effect in 2

VR: (1) Excitatory Synapse (2) Cl- influx

Increase in 1 leads to Increase in 2

VR: (1) Inhibitory Synapse (2) Cl- influx

Increase in 1 leads to Decrease in 2

VR: (1) Inhibitory Synapse (2) K+ Influx

Increase in 1 leads to Increase in 2

VR: (1) Inhibitory Synapse (2) Distance of TP from MP

Increase in 1 leads to Decrease in 2

VR: (1) Excitatory Synapse (2) Distance of TP from MP

Spatial Summation

This type of synaptic integration occurs when signals from different presynaptic cells arrive at the same location simultaneously

Temporal Summation

This type of synaptic integration occurs when signals from the same presynaptic cell arrive at diff times but at a very short interval

Increase in 1 leads to Increase in 2

VR: (1) Stimuli (2) Frequency of Action potential

1 > 2

QC: Ability to be summed (1) Graded (2) Action Potential

Plasticity

This is the ability of varying the intensity of post synaptic potential generated in response to changing conditions

Glutamate and Aspartate

2 excitatory amino acids

GABA

Major inhibitory amino acid in the brain