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Section 11.1: The Role of the Nervous System
Section 11.1 Questions, page 521
1. (a) Afferent neurons receive signals from sensory receptors; efferent neurons transmit neural
messages to effector tissues; interneurons transmit and integrate neural messages from the
afferent neurons to the efferent neurons; effectors are the tissues where the appropriate
response/stimulus takes place (for example, muscles, glands, and organs).
(b) Afferent neurons, interneurons, efferent neurons, and effectors all work together to complete
a neural circuit. (1) Afferent neurons receive a signal from sensory receptors (for example, on
your skin); (2) the message is transmitted from afferent neurons to interneurons in the spinal
cord; (3) integration of neural messages occurs in interneurons; and (4) there is response
transmission of neural messages by efferent neurons to effectors (muscles or glands) where
action appropriate to the stimulus occurs.
2. The nodes of Ranvier are gaps between sections of the myelin sheath, which expose the
neuron to extracellular fluid. The alternating exposure and insulation from the fluid increases the
rate of nerve impulse transmission.
3. The nervous system cells that provide a supporting role rather than a transmitting role are the
Schwann cells, which produce the myelin sheath, and the glial cells, which provide nutritional
and structural support for neurons. They facilitate the transmission of nerve impulses via neurons
but do not provide nerve transmission themselves.
4. Reflexes have evolved to occur without the need for the brain to process the information
because processing by the brain requires more time, possibly resulting in damage or injury to the
body. The reflex arc is so quick that one experiences pain only after removing the finger from the
hot element or sharp object.
5. A reflex arc is the process by which the body’s nervous system performs an automatic reaction
to a stimulus by routing the neural transmissions through the spinal cord, but not to the brain. It
usually operates very quickly and without the need for processing by the brain. An example is
touching something hot or sharp with your finger, which results in the rapid pulling away of the
finger from the source of the heat or sharp object.
6. Reports will vary. Student reports should include the following information on the causes,
symptoms, and treatments of the disorder: Neurofibromatosis type 1 (NF-1) is a disease that
causes the formation of a multitude of tumours. It occurs because of a malfunction of a gene on
chromosome 17. This gene encodes a protein called neurofibromin, which plays a role in the
control of cell signalling. Symptoms of NF-1 include six or more “cafe-au-lait” spots, which are
areas of darkened skin that are greater than 5 mm in diameter, two or more neurofibromas
(which are tumors of the nervous system), freckling of the armpit or groin, two or more growths
in the eye, a tumor of the optic nerve (glioma), and/or scoliosis of the spine (curvature of the
spine). Treatment of NF-1 can be complicated. There is no cure for the disease itself. Surgery is
often used to remove tumours. In some cases, treatment of tumours with radiation and
chemotherapy is required, if the tumours become cancerous. Other treatments for NF-1 are
directed towards relieving symptoms associated with this disorder such as assistance with
overcoming learning disorders that are often associated with NF-1 or treatment of headaches and
seizures, which can also be experienced as a result of the disease. Neurofibromatosis may be
underdiagnosed because its symptoms are so diverse and non-specific. Many of them can have
other, more common causes.
Copyright © 2012 Nelson Education Ltd.
Chapter 11: The Nervous System 11.1-1
7. Reports or presentations will vary. There are 4 main types of reflex in humans: These are the
spinal reflex (knee jerk), the cranial reflex (reading), somatic reflexes (involving contraction of
skeletal muscles) and the autonomic reflexes (involving responses of muscles in organs and
glands). Students should provide a general description of three of these reflexes. For example,
when the tendon just below the knee cap is tapped with a special hammer, the muscle spindle in
the leg muscle above the knee (the quadriceps femoris muscle) is slightly stretched. The
generates an afferent signal that is sent back to the spinal cord and, via interneurons, conducts an
efferent signal back to the same leg muscle, triggering a contraction of the muscle. This causes
the leg to kick up. The knee jerk reflex was discovered by Sir Michael Foster. In his textbook
published in 1877 he described how "striking the tendon below the patella gives rise to a sudden
extension of the leg, known as the knee-jerk". The knee jerk reflex plays an important role in
maintaining posture and balance without much thought or consciousness. We test for the knee
jerk reaction because its responsiveness can be an indicator of health and disease. In a healthy
person, after the tap of the hammer below the knee cap, the leg normally kicks out once and
returns to relaxed position. If this response is absent or reduced, this is commonly referred to as
Westphal’s sign, which can be an indicator of several disorders including receptor damage,
peripheral nerve disease, brain lesions, and/or interruption of the nerve impulses in the leg. If the
reflex response results in more than one kick of the leg, this may be a sign of a disease in the
cerebellum of the brain.
Copyright © 2012 Nelson Education Ltd.
Chapter 11: The Nervous System 11.1-2