Nervous System Introduction

Biology 2121Chapter 11

Nervous System Overview • Sensory input

– Environmental stimulus

– PNS to CNS – Afferent NS

• Integration– Processing of

information

• Motor output– CNS via PNS to the:

– Effector organs

Divisions of the Nervous SystemDivisions of the Nervous System

1. Central Nervous System (CNS)• Brain and Spinal Cord

2. Peripheral Nervous System (PNS)–Cranial and Spinal Nerves

Neurons of the CNS and PNSNeurons of the CNS and PNS

Heart and Soul of the Nervous System – The Neuron

• 1. Cell Body– Organelles

• Nissl Bodies • Golgi • Pigment inclusions

• 2. Processes – Dendrites – Axons

• 3. Axon Terminals – Secretory Region

Neuron

• 4. Axon Hillock

• 5. Axon – Mylenated or

unmylenated – Axon Terminals – NT – Motor neurons (3-4 feet)

Myelination Myelination

Myelination:

• Increases the transmission speeds of neurons

• PNS nerves that serve voluntary organs (example skeletal muscles) have more myelination

• Nerves that serve visceral organs (involuntary or smooth muscle organs) have less myelination.

Characteristics of Nerve CellsCharacteristics of Nerve Cells• 1. Long lifespan

• 2. Amitotic

• 3. High Metabolic Rate

• 4. Large and Complex

• 5. Excitable Neurons– Muscle and nerve cells

Neuroglia Cells Neuroglia Cells

1. Resting or polarized membranes – (-70 mV) membrane potential

2. Changes occur: • Membranes are stimulated • Ion movement into and out of cells

How Nerve Impulses Are Produced How Nerve Impulses Are Produced

Types of Channels Types of Channels

1. Sodium moves in -------- depolarization (0 to +30mV). • Leads to an action potential

(AP)

2. Potassium gates slowly open as sodium gates close quickly. • Leads to Hyper-polarization

3. Potassium gates close. • Repolarization

Depolarization Depolarization

Not All Membranes Produce AP’s Not All Membranes Produce AP’s

Graded Potentials

• The conduction velocity of a neuron depends on the following factors:

1. Axon Diameter• Greater the diameter, faster the conduction speed

2. Degree of Myelination • Greater the mylenation, faster the conduction speed

Conduction Velocities Conduction Velocities

Node of Ranvier Node of Ranvier