Nervous System Flashcards
Neurons
The signals sent by the nervous system are electrical signals called nerve impulses, and they are transmitted by special nervous system cells called neurons (or nerve cells).
Central Nervous System
It has multiple divisions, beginning with its two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, and the PNS consists mainly of nerves, which are bundles of axons from neurons. The nerves of the PNS connect the CNS to the rest of the body.
Peripheral Nervous System
It has multiple divisions, beginning with its two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and spinal cord, and the PNS consists mainly of nerves, which are bundles of axons from neurons. The nerves of the PNS connect the CNS to the rest of the body.
Nerves
The CNS includes the brain and spinal cord, and the PNS consists mainly of nerves, which are bundles of axons from neurons. The nerves of the PNS connect the CNS to the rest of the body.
Autonomic Nervous System
The PNS can be further subdivided into two divisions, known as the autonomic and somatic nervous systems. The autonomic nervous system controls activities that are not under voluntary control, such as digesting a meal. The autonomic nervous system has three main divisions: the sympathetic division (which controls the fight-or-flight response during emergencies), the parasympathetic division (which controls the routine “housekeeping” functions of the body at other times), and the enteric division (which provides local control of the digestive system).
Somatic Nervous System
The PNS can be further subdivided into two divisions, known as the autonomic and somatic nervous systems. The somatic nervous system controls activities that are under voluntary control, such as turning a steering wheel.
Sympathetic Nervous System
The sympathetic division (which controls the fight-or-flight response during emergencies).
Parasympathetic Nervous System
The parasympathetic division (which controls the routine “housekeeping” functions of the body at other times).
Enteric Nervous System
The enteric division (which provides local control of the digestive system).
Cell Body
The cell body is the part of a neuron that contains the cell nucleus and other cell organelles. It is usually quite compact, and may not be much wider than the nucleus.
Dendrites
Dendrites are thin structures that are extensions of the cell body. Their function is to receive nerve impulses from other cells and to carry them to the cell body. A neuron may have many dendrites, and each dendrite may branch repeatedly to form a dendrite “tree” with more than one thousand “branches.” The end of each branch can receive nerve impulses from another cell, allowing a given neuron to communicate with tens of thousands of other cells.
Axon
The axon is a long, thin extension of the cell body. It transmits nerve impulses away from the cell body and toward other cells. The axon branches at the end, forming multiple axon terminals. These are the points where nerve impulses are transmitted to other cells, often to dendrites of other neurons. An area called a synapse occurs at each axon terminal. Synapses are complex membrane junctions that transmit signals to other cells. An axon may branch hundreds of times, but there is never more than one axon per neuron.
Myelin Sheath
Spread out along axons — especially the long axons of nerves — are many sections of myelin sheath. These are lipid layers that cover sections of the axon. The myelin sheath is a very good electrical insulator, similar to the plastic or rubber that encases an electrical cord.
Nodes of Ranvier
Regularly spaced gaps between sections of myelin sheath occur along the axon. These gaps are called nodes of Ranvier, and they allow transmission of nerve impulses along the axon. Nerve impulses skip from node to node, allowing nerve impulses to travel along the axon very rapidly.
Schwann Cell
A Schwann cell (also on an axon) is a type of glial cell. Its function is to produce the myelin sheath that insulates axons in the peripheral nervous system. In the central nervous system, a different type of glial cell (called an oligodendrocyte) produces the myelin sheath.
