11B - Nervous System - The Action Potential & Synaptic Transmission Notes

Neurons

Transmit electrical signals rapidly across long distances.

Neuroglial Cells

Support, insulate, and protect neurons; include astrocytes, Schwann cells, oligodendrocytes, microglia.

Myelination

Schwann cells (PNS) and oligodendrocytes (CNS) create myelin sheaths for faster transmission.

CNS (Central Nervous System)

Processing information, decisions.

PNS (Peripheral Nervous System)

Nerves = bundles of neurons. Carries input and outputs between the body and CNS.

Ependymal Cells

Line the ventricles of the brain and the central canal of the spinal cord; produce, monitor, and help circulate cerebrospinal fluid (CSF).

Astrocytes

Maintain the extracellular environment, regulate nutrient transport, assist in repairing the brain after injury, form the blood-brain barrier.

Schwann Cells

Produce the myelin sheath in the Peripheral Nervous System (PNS).

Oligodendrocytes

Produce the myelin sheath in the Central Nervous System (CNS).

Microglia

Act as the brain’s immune defense system; clear pathogens, dead cells, and debris by phagocytosis.

Satellite Cells

Surround neuron cell bodies within ganglia in the PNS; regulate the chemical environment and provide support and nutrients to neurons.

Dendrites

Receive incoming signals from other neurons.

Axon Hillock

Decision point for initiating action potentials based on input summation.

Axon and Terminals

Transmit electrical signals away from the soma to the next neuron or effector.

Cell body

Integrates incoming signals; houses the nucleus.

Neurotransmitters

Chemicals that transmit signals across a synapse.

Myelin sheaths

Insulates axons and speeds up signal conduction.

Ion Gradients

Higher Na^+ outside the cell, higher K^+ inside the cell.

Selective Permeability

Plasma membranes allow differential movement of ions via channels.

Electrical Potential Difference

Results in a voltage (mV) across the membrane, typically -70mV at rest.

Membrane Potential

The difference in electrical potential between the inside and outside of a cell membrane (measured in millivolts, mV).

Resting Membrane Potential (RMP)

The membrane potential of a cell 'at rest,' typically around -70 mV. It is determined by the relative concentrations of negatively and positively charged ions inside and outside the cell.

Voltage-gated ion channels

Open in response to a change in membrane potential (voltage across the membrane).

Threshold potential

The specific membrane voltage (typically around -55 mV) at which an action potential is triggered.

Graded Potentials

Triggered by neurotransmitter binding or sensory stimuli; confined to the region near the stimulus; magnitude varies with strength; can make membrane potential more positive (EPSP) or more negative (IPSP).

Neurotransmitter

A chemical that can open a specific channel.

Chemically-gated channel

A channel that can be opened by neurotransmitter.

Graded potential

A change in membrane potential caused by the opening of an ion channel.

Excitatory (EPSPs)

Excitatory postsynaptic potentials → make an AP more likely.

Inhibitory (IPSPs)

Inhibitory postsynaptic potentials → make an AP less likely.

Chemically-gated channels

Dendrites, cell body. Opened/Activated by neurotransmitters (ligands). Associated with Graded potentials.

Voltage-gated channels

Axon hillock, axon. Opened/Activated by changes in membrane potential (voltage). Associated with action potentials.

Multiple Sclerosis

The immune system attacks and destroys myelin in the CNS. Impaired signal conduction leads to sensory, motor, and cognitive symptoms. Depends on which neurons are affected and extent of demyelination.

Nodes of Ranvier

Gaps between myelin sheaths; only locations with voltage-gated ion channels; enable faster conduction by allowing APs to 'jump' node-to-node