BIOL 1051H Chapter Notes - Chapter 12: Central Nervous System, Myelin, Schwann Cell
Neural Physiology
Neurons are highly specialized cells that transmit signals directly to target cells using an
electrical system. Nervous transmission is targeted in that the signal is delivered directly to
target cells, and the signal is fast relative to other signaling systems in the body. However,
nervous signals usually still use chemicals to transmit the signal to recipient cell at the synapse.
Being a highly specialized cell, a neuron has a specialized shape. Most of the cells
cytoplasm and organelles are located inside the cell body or soma. This is where cellular
respiration takes place, enzymes are produced, and nutrients are assembled. The cell body is
the area where all cell maintenance activities take place. The neuron also has dendrites which
are small projections on the cell body. The neuron receives signals from other neurons via the
dendrites, and the cell surface of the cell body. The axon is a distinctive structure. It can be very
long, up to 1 meter in humans, and is the structure responsible for sending signals to other cells.
One very important concept here is the difference between the central and peripheral
nervous system. The central nervous system (CNS) is located inside the confines of the skull
and vertebral column, while the peripheral nervous system (PNS) is located outside the skull
and vertebral column. This division has nothing to do with neurons, however, in that many
neurons physically span both areas. Neurons can be described according to their place or role
in the nervous system but there are some important physical differences between neurons as
well.
From a cellular perspective it is important to remember the significance of such a long
cell in terms of cellular maintenance. It is therefore not surprising that there are a host of cells
dedicated to caring for and protecting various aspects of neurons. These support cells are
called neuroglia.
Myelin is produced in both the CNS and PNS by oligodendrocytes and Schwann cells
respectively. Myelin is primarily composed of layers of plasma membrane and acts like an
insulator. It is found covering the axons of some neurons and protects the neurons as well as
speeds signal transmission along the axon. Multiple sclerosis and Tay–Sachs disease are
degenerative disorders of the myelin sheath.
Schwann cells literally wrap themselves around a section of axon from the inside out.
Most of the cell constituents end up on the outside of the tightly wrapped portion of plasma
membrane.
The result is the same in both the PNS and CNS. Axons are covered segmentally with
myelin leaving short areas uncovered between segments of myelin. These are called Nodes of
Ranvier. The myelin sheath is also important in the process of nerve regeneration after damage.
Document Summary
Neurons are highly specialized cells that transmit signals directly to target cells using an electrical system. Nervous transmission is targeted in that the signal is delivered directly to target cells, and the signal is fast relative to other signaling systems in the body. However, nervous signals usually still use chemicals to transmit the signal to recipient cell at the synapse. Being a highly specialized cell, a neuron has a specialized shape. Most of the cells cytoplasm and organelles are located inside the cell body or soma. This is where cellular respiration takes place, enzymes are produced, and nutrients are assembled. The cell body is the area where all cell maintenance activities take place. The neuron also has dendrites which are small projections on the cell body. The neuron receives signals from other neurons via the dendrites, and the cell surface of the cell body.
