Speed of Nerve Impulses and Synaptic Transmission

What factors affect the speed of nerve impulse transmission?

Axon diameter and presence or absence of myelin

How does axon diameter affect conduction speed?

Thicker axons transmit impulses faster

How does myelin affect conduction speed?

It greatly increases transmission speed

What are giant squid axons?

Large non-myelinated axons up to 1 mm in diameter

What is the speed of impulse transmission in giant squid axons?

Up to 25 m s⁻¹

What is the speed in smaller non-myelinated axons?

0.5–2 m s⁻¹

What is the speed in myelinated vertebrate axons?

70–120 m s⁻¹

What is a myelin sheath?

An insulating layer surrounding some axons

What is the function of myelin?

To drastically increase conduction speed

What is saltatory conduction?

Rapid transmission of impulses in myelinated axons

How does conduction speed relate to axon diameter?

Positively correlated

How does conduction speed relate to animal size?

Negatively correlated

What is the coefficient of determination (R²)?

A measure of how much variation in a dependent variable is explained by one or more independent variables

When is R² used in biology?

When more than one independent variable affects a dependent variable

How can R² be used for nerve conduction speed?

To determine the combined effects of axon diameter and animal size

What is a synapse?

The junction between two neurons or between a neuron and an effector

What is a synaptic cleft?

The gap between presynaptic and postsynaptic cells

What is an effector?

A cell that responds to a neural impulse

What are examples of effector cells?

Muscle cells and glandular cells