Chapter 7: The Nervous System and Neuronal Excitability

Nervous System Subdivisions

Subcategories of the nervous system

Nervous System Functions

Roles and purposes of the nervous system

Neurons

Nerve cells responsible for transmitting information

Neuroglia

Supporting cells in the nervous system

Myelination

Process of forming a myelin sheath around neurons

Plasticity

Ability to change throughout life

Regeneration

Regrowth after damage

Astrocytes

Neuroglia that help maintain the blood-brain barrier

Oligodendrocytes

Neuroglia that form and maintain myelin sheath in the CNS

Microglia

Phagocytic neuroglia that remove debris and pathogens

Ependymal Cells

Neuroglia that produce and circulate cerebrospinal fluid

Schwann Cell

Neuroglia that form and maintain myelin sheath in the PNS

Nodes of Ranvier

Gaps in the myelin sheath

Leak Channels

Channels with gates randomly alternating between open and closed

Ligand-gated Channels

Channels opening in response to specific chemical stimuli

Mechanically-gated Channels

Channels opening in response to mechanical stimulation

Voltage-gated Channels

Channels opening in response to changes in membrane potential

Membrane Potential

Voltage across the plasma membrane

Ohm's Law

Relates current, voltage, and resistance in electrical circuits

Resting Membrane Potential

Voltage difference across the plasma membrane at rest

Equilibrium Potential

Point where there is no net flow of ions

Nernst Equation

Calculates equilibrium potential based on ion concentrations

Goldman-Hodgkin-Katz Equation

Calculates membrane potential considering ion permeabilities

Graded potentials

Small deviations from resting membrane potential

Depolarizing

Process making the membrane potential less polarized

Hyperpolarizing

Process making the membrane potential more polarized

Stimulus strength

Determines the amplitude of graded potentials

Summation of graded potentials

Combining two or more graded potentials

Generation of action potential

Threshold must be reached, typically -55mV

Subthreshold stimulus

Stimulus not strong enough to depolarize to threshold

Suprathreshold stimulus

Stimulus stronger than necessary for depolarization

All-or-none principle

Action potential firing is consistent in strength

Action potential phases

Depolarizing, repolarizing, after-hyperpolarizing

Depolarizing phase

Rising phase until membrane potential reaches +30mV

Repolarizing phase

Falling phase until membrane potential returns to -70mV

After-hyperpolarizing phase

Undershoot phase after membrane potential restoration

Propagation of action potential

Transmission along the neuron's axon

Conduction velocity

Speed at which action potentials travel

Synapse

Point of communication between neurons or tissues

IPSP

Hyperpolarization of post-synaptic membrane

EPSP

Depolarization of post-synaptic membrane

Summation of IPSP and EPSP

Combined effect determining action potential initiation

Ionotropic receptors

Ligand-gated channels

Metabotropic receptors

Function through G-proteins

Termination of signal

Degradation or removal of neurotransmitters

Presynaptic modulation

Regulates neurotransmitter release

Neurotransmitters

Chemical messengers in neural communication

Neural circuits

Patterns of neuronal connections in the nervous system