NERVES NERVES a nerve is a bundle of

NERVES

NERVES • a nerve is a bundle of neurons

sensory neuron interneuron motor neuron sensory receptors effector

Nerves 2 main types of nerve cells • Glial cells –non-conducting and used for structural and nutritional support • Neurons – carry nerve impulses

dendrite cell body Myelin sheath axon Synapse

Neuron Structure • Functional cells of NS • Transmit electrochemical messages called nerve impulses to • Other neurons • Effectors (muscles or glands) 25 -7

Neuron Structure (cont. ) • Neurons lose their ability to divide • If destroyed, not replaced • Neuralgia • • 25 -8 Support cells for neurons that can divide Astrocytes – anchor blood vessels to nerves Microglia – act as phagocytes Oligodendrocytes – assist with production of myelin sheath

Neuron Structure (cont. ) Neurons have a cell body and processes called nerve fibers that extend from the cell body. o Dendrites – short n o Axons – long n 25 -9 Receive nerve impulses for the neuron Send nerve impulses away from the cell body

Neuron Structure (cont. ) • White matter – axons with myelin sheath Dendrites Schwann cells • Schwann cells • Wrap around some axons • Cell membranes contain myelin • Myelin insulates axons and enables axons to send nerve impulses more quickly • Gray matter – axons without myelin sheath Axon 25 -10

Nodes of Ranvier

• myelinated nerve fibers are covered by neurilemma which, along with the Schwann cell, promotes the regeneration of the nerve fiber after trauma

Components of a Neuron • Dendrites are short branches that surround the cell body of the neuron. • Axons carry impulses away from the cell body Myelin sheath Axons may be enclosed in a fatty sheath produced by a Schwann cell or glial cell. Acts as insulation for neurons by preventing the loss of charged ions. Very white in appearance.

Neurilemma covers myelinated nerve fibers and it promotes the regeneration of the nerve fiber after trauma Nodes of Ranvier. small gaps between each Schwann cell on an axon Saltatory Action myelin sheath increases the speed of nerve transmission. , from 1 m/s to 100 m/s or 360 Km/h

• myelinated neurons form white matter in the unmyelinated grey matter • myelinated nerve fibers are covered by neurilemma which promotes the regeneration of the nerve fiber after trauma • Unmyelinated nerves lack a myelin sheath. These will not be regenerated after injury.

Multiple Sclerosis Not hereditary. The cause of MS is not known. T cells (immune cells) attack cells and tissues in the CNS. This results in damage to myelin, nerve fibers and the cells that make myelin.

The main functions of the nervous system: • Receive information • Make decisions about the response • Sorts impulses and sets priorities for action i. e. walking across the street – eat a bar or drive a car • Transmit impulses to the motor units (muscles) which carry out appropriate action