Video Transcript
Which specialized cells are
described as cells that carry electrical impulses to allow rapid responses in the
body? (A) Sperm cells, (B) endocrine
cells, (C) epithelial cells, or (D) nerve cells.
To answer this question, let’s take
each of the specialized cells in turn and briefly review their structure and
function.
First of all, let’s look at the
sperm cells, which are male gametes. In other words, they are haploid
sex cells. Haploid means they carry half the
normal number of chromosomes in their nucleus. During fertilization, the nucleus
of the egg cell and sperm cell fuse and the normal number of chromosomes is
restored. As well as the haploid nucleus,
sperm cells have other special structures, which help them carry out their role. They are streamlined in shape and
have a long flagellum or tail, so they can swim to the egg.
Many mitochondria in the midpiece,
at the base of the flagellum, provide the energy required for swimming. Then, there is an acrosome at the
front of the head, which contains digestive enzymes to enable the sperm to penetrate
the egg so it can be fertilized. We can therefore rule out option
(A) as the sperm is for reproduction, not for carrying electrical impulses.
Endocrine cells are part of the
endocrine system. The endocrine system works with the
nervous system to coordinate the body. The endocrine system releases
hormones, special chemical messengers, which are carried around the body, usually in
the bloodstream, to their target cells, where they bring about a response, for
example, insulin, which is released from the pancreas when blood glucose levels rise
and targets liver and muscle cells to take up and store excess glucose as
glycogen. The endocrine system brings about a
relatively slow but long-lived response to a stimulus. It is not a fast response, so
option (B) can also be eliminated.
Option (C), the epithelial cells
are cells that line the surfaces all over the body, such as blood vessels, the skin,
and the bladder. Their roles include protection,
filtration, and secretion but not carrying of electrical impulses, so we can also
rule out this option.
This leaves us with the nerve
cells, which are part of the nervous system. As already mentioned, this system
works with the endocrine system to coordinate the body. It communicates through electrical
impulses and carries out rapid responses to internal and external stimuli. It contains a specialized type of
tissue known as nervous tissue.
As you may recall, tissues are made
up of cells and nervous tissue contains many nerve cells, which are known as
neurons. These are highly specialized for
their role. Dendrites receive signals from
other cells, and the cell body contains the nucleus, mitochondria, and other
organelles. They typically have an axon that
carries the signal from the cell body towards the target cells. The axon may have a myelin sheath
around it to insulate it and speed up the transmission of the electrical
impulse. The axon terminals release
neurotransmitters, special chemical signals that pass the signal on to the target
cell, which may be another nerve cell or the effector, a muscle or gland, which
carries out the response.
This means that the correct answer
to this question is (D). The specialized cells that are
described as cells that carry electrical impulses to allow rapid responses in the
body are the nerve cells.
