Nervous System Introduction Biology 2121 Chapter 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 System 1. Central Nervous System (CNS) Brain and Spinal Cord 2. Peripheral Nervous System (PNS) – Cranial and Spinal Nerves

Neurons 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: 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 Cells 1. Long lifespan 2. Amitotic 3. High Metabolic Rate 4. Large and Complex 5. Excitable Neurons – Muscle and nerve 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

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

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

Node of Ranvier