Electrical Properties of Neurons - Lecture Slide 7

Upper Motor Neuron Location & Function

Resides in the pre-central gyrus and extends an axon to a spinal cord motor neuron.

Resting Membrane Potential (RMP) Value

Approximately -70mV, representing a negative electric charge across the neuronal membrane.

Body and Brain Water Content

Approximately 60-70% of the human body and 95% of the brain consist of water.

Ion Definition

An atom or molecule with a net positive or negative electrical charge.

Major Ions in the Body

Chloride (Cl-), Sodium (Na+), Potassium (K+), Magnesium (Mg++), and Calcium (Ca++).

Electrochemical Diffusion Gradient

Ions move from high to low concentration and toward opposite electrical charges until equilibrium.

Cell Membrane Lipid Bilayer

A hydrophobic phospholipid barrier separating the cytoplasm from the extracellular environment.

Phospholipid Structure

A hydrophilic phosphate head paired with two hydrophobic fatty acid tails.

Ion Channels and Transporters

Membrane proteins forming pores for selective, passive, or gated ion movement.

Primary Factors Maintaining RMP

Passive K+ and Na+ channels, Cl- channels, Na+/K+ pumps, and negatively charged intracellular proteins.

Na+/K+ Pump Mechanism

Uses ATP to pump 3 sodium ions out and 2 potassium ions into the neuron.

EPSP vs. IPSP

EPSP depolarizes the neuron (more positive); IPSP hyperpolarizes it (more negative).

Axon Initial Segment Role

Monitors the sum of all inputs and triggers an action potential when threshold is reached.

Action Potential Generation

Voltage-gated Na+ channels open at threshold, allowing Na+ influx to depolarize the axon.

Membrane Repolarization

Voltage-gated K+ channels open later than Na+ channels, causing repolarization and brief hyperpolarization.

Refractory Period Functions

Blocks Na+ channels briefly to limit frequency, prevent strength increase, and ensure one-way propagation.

All-or-None Action Potential

Once initiated at the initial segment, action potential strength remains constant to the axon terminal.

Lidocaine Mechanism of Action

Acts as a local anesthetic by blocking voltage-gated sodium channels and action potentials.

Channelopathies Definition

Diseases caused by abnormal ion channel function, often due to gene mutations.

Axon Diameter and Conduction Velocity

Larger axon diameters reduce internal resistance, leading to faster conduction velocity.

Myelin-Forming Glial Cells

Formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

Nodes of Ranvier Function

Gaps with high Na+ channel density where action potentials jump rapidly during saltatory conduction.

Babinski Sign Significance

Present in newborns; indicates upper motor neuron disease when found in adults.

Multiple Sclerosis (MS)

A CNS disease where antibodies attack myelin, causing swelling, detachment, and nerve degeneration.

Neurotransmitter Release Trigger

An arriving action potential at the synapse initiates neurotransmitter release into the synaptic cleft.