Lecture 16 notes/ Neuro II

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This is the same principle as water flowing faster in a large hose than in a small tube. If the current flows faster, the effect of depolarization in one region will be felt farther downstream in the next millisecond.

b. More ion channels
Increased diameter is accompanied by greater surface areaof membrane containing more Na+ channels, allowing greater numbers of Na+ ions to pour in and spread.

2. Myelination
a. Schwann cells (PNS) & Oligodendrocytes (CNS)
b. Form myelin sheath
The majority of the cells in the vertebrate nervous system are not neurons, but supporting cells known as glial cells. Two types of glial cells (Schwann cells and oligodendrocytes) wrap around the axons of some neurons forming concentric rings of membrane known as a myelin sheath. In between each pair of glial cells is a gap known as a node of Ranvier.

c. Saltatory conduction48.9
The rings of membrane (made up of lipids) acts like an insulator. The Na+ ions flow down to the gaps (nodes of Ranvier) where the number of Na+ channels is higher and generate an action potential. The action potential "leaps" down the axon; this is known as saltatory conduction.

Large, myelinated Æup to 120 m/sec, 0.02 S from head to toe
Small, nonmyelinated neuronsÆ0.5 m/sec, 4 s from head to toe

Q. Which type of neuron would you like to transmit the information that you just stepped on a hot coal to your brain?

-Sensory axons that carry sharp-pain sensation are myelinated(5-6 m/sec), while most axons carrying sensory information such as temperature are unmyelinated ( 1-2 m/sec.).

Æ35 m/sec, however they are almost 1 mm in diameter

Giant axons

Conduction velocity is directly proportionalto fiber diameter in myelinated neurons, but proportional to the square rootof the diameter in unmyelinated neurons. Above 1 mm in diameter, myelinated neurons are faster and the speed differential increases rapidly.

Your optic nerve would have to be 12 inches in diameter if it were unmyelinated to carry the same information at the same speed.


		This is the same principle as water flowing faster in a large hose than in a small tube. If the current flows faster, the effect of depolarization in one region will be felt farther downstream in the next millisecond. b. More ion channels Increased diameter is accompanied by greater surface areaof membrane containing more Na+ channels, allowing greater numbers of Na+ ions to pour in and spread. 2. Myelination a. Schwann cells (PNS) & Oligodendrocytes (CNS) b. Form myelin sheath The majority of the cells in the vertebrate nervous system are not neurons, but supporting cells known as glial cells. Two types of glial cells (Schwann cells and oligodendrocytes) wrap around the axons of some neurons forming concentric rings of membrane known as a myelin sheath. In between each pair of glial cells is a gap known as a node of Ranvier. c. Saltatory conduction48.9 The rings of membrane (made up of lipids) acts like an insulator. The Na+ ions flow down to the gaps (nodes of Ranvier) where the number of Na+ channels is higher and generate an action potential. The action potential "leaps" down the axon; this is known as saltatory conduction. Large, myelinated Æup to 120 m/sec, 0.02 S from head to toe Small, nonmyelinated neuronsÆ0.5 m/sec, 4 s from head to toe Q. Which type of neuron would you like to transmit the information that you just stepped on a hot coal to your brain? -Sensory axons that carry sharp-pain sensation are myelinated(5-6 m/sec), while most axons carrying sensory information such as temperature are unmyelinated ( 1-2 m/sec.).
				Æ35 m/sec, however they are almost 1 mm in diameter
		Giant axons		Æ35 m/sec, however they are almost 1 mm in diameter
		Conduction velocity is directly proportionalto fiber diameter in myelinated neurons, but proportional to the square rootof the diameter in unmyelinated neurons. Above 1 mm in diameter, myelinated neurons are faster and the speed differential increases rapidly. Your optic nerve would have to be 12 inches in diameter if it were unmyelinated to carry the same information at the same speed.