the body and send this information to the        Neuroglia, also known as glial cells, act as the
    CNS.                                             “helper” cells of the nervous system. Each
   Efferent nerves in the PNS carry signals         neuron in the body is surrounded by anywhere
    from the control center to the muscles,          from 6 to 60 neuroglia that protect, feed, and
    glands, and organs to regulate their             insulate the neuron.
    functions.
                                                     Brain
                                                        The brain, a soft, wrinkled organ that
                                                         weighs about 1.36 kg, is located inside the
Nervous Tissue
                                                         cranial cavity, where the bones of the skull
The majority of the nervous system is tissue             surround and protect it.
made up of two classes of cells: neurons and            The approximately 100 billion neurons of
neuroglia.                                               the brain form the main control center of
                                                         the body.
Neurons, also known as nerve cells,                     The brain and spinal cord together form
communicate within the body by transmitting              the central nervous system (CNS), where
electrochemical signals. Neurons look quite              information is processed and responses
different from other cells in the body due to            originate.
the many long cellular processes that extend
                                                        The brain, the seat of higher mental
from their central cell body. There are 3 basic
                                                         functions such as consciousness, memory,
types of neurons,
                                                         planning, and voluntary actions, also
Afferent neurons. Also known as sensory                  controls lower body functions such as the
neurons, afferent neurons transmit sensory               maintenance of respiration, heart rate,
signals to the central nervous system from               blood pressure, and digestion.
receptors in the body.
                                                     Spinal Cord
Efferent neurons. Also known as motor
                                                        It is a long, thin mass of bundled neurons
neurons, efferent neurons transmit signals
                                                         that carries information through the
from the central nervous system to effectors in
                                                         vertebral cavity of the spine beginning at
the body such as muscles and glands.
                                                         the medulla oblongata of the brain on its
Interneurons. Interneurons form complex                  superior end and continuing inferiorly to
networks within the central nervous system to            the lumbar region of the spine.
integrate the information received from                 It is around 45 cm (18 in) in men and
afferent neurons and to direct the function of           around 43 cm (17 in) long in women.
the body through efferent neurons.                      In the lumbar region, the spinal cord
                                                         separates into a bundle of individual
                                                         nerves called the cauda equina (due to its
                                                439