Name: __________________________ Period: _____
Laboratory Exercise and Activity: Nervous Tissue, Somatic and Autonomic Reflexes
A. Nervous Tissue
The nervous system has two subdivisions: central nervous system (CNS) and peripheral nervous
system (PNS). CNS integrates information received from sensory receptors and initiates and transmits
impulses to neurons, muscles, or glands. The PNS contains an afferent division composed of sensory
receptors and nerves, and an efferent division composed of motor nerves. Sensory receptors detect
changes in the environment and transmit information along sensory or afferent nerves to the CNS.
Motor nerves transmit impulses from the CNS to target organs (neurons, muscles, or glands).
Nervous Tissue is found in the organs of the nervous system—the nerves, brain, and spinal cord, and
contains cells that enable the nervous system to generate and transmit electrical signals called nerve
impulses or action potentials. The cells of nervous tissue are neuroglia and neurons. Neuroglia are cells
that support, protect, furnish nutrients to, and augment the speed of neuron transmission. Neurons
conduct action potentials and are structural and functional units.
1. Neuroglia Cells
Neuroglia cells are usually smaller and more abundant than neurons. Although they do
not create action potential, neuroglia cells have important roles in the nervous system. Of the
six types of neuroglia cells, four are in the CNS and two in the PNS. The four neuroglia cells in the
CNS are: astrocytes, ependymal cells, microglia, and oligodendrocytes. Astrocytes have many
processes that make them look star-shaped. Their perivascular feet wrap around and cover
neurons and blood vessels to keep neurons in place. Astrocytes also guide neurons during
development and control the composition of the chemical environment of the neurons by
forming a blood-brain barrier. This barrier only allows certain substances to enter the nerve
tissue at the blood vessel sites. Ependymal cells line all four ventricles of the brain, as well as the
central canal of the spinal cord. These cells form cerebrospinal fluid (CSF), and their cilia move
the CSF through the ventricles. Microglia are the phagocytes of the CNS that engulf debris,
necrotic tissue, and invading bacteria or viruses. Oligodendrocytes support the CNS neurons and
have processes that form myelin sheaths around axons that increase the speed of nerve
impulses. The two neuroglia cells in the PNS are Schwann cells and satellite cells. Schwann cells
are flattened cells that wrap around the axons in the PNS. Many Schwann cells form the myelin
sheath around one axon that increases nerve impulse speed and aids in the regeneration of PNS
axons. Satellite cells have processes that flattened and surround the neuron cell bodies located
in ganglia in the PNS. They give support to these neurons and regulate their chemical
environment.
ACTIVITY 1~ Neuroglia Cells
1. Complete Table 13.1 on page 2.
2. Label the neuroglia cells in Figure 13.1 on page 2.
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Complete Table 13.1 using the cells listed below. Under location, circle CNS or PNS.
 Astrocytes
 Oligodendrocytes
 Ependymal cells
 Satellite cells
 Microglia
 Schwann cells
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2. Structure of a Neuron
Neurons are the longest cells in the body they can be over 3 feet long. All neurons have
three basic parts: dendrites, a cell body, and an axon. The dendrites and the single axon are
extensions of the cell body called processes. Dendrites receive information from receptors or
other neurons and send it as a change in membrane potential to the nerve cell body or soma
(soma means body). Neuron cell bodies have their own organelles like most other cells. The
triangular or cone-shaped area of the cell body are called the axon hillock. The axon is a longer
process then the dendrites than extends from the axon hillock. When changes in membrane
potential travel to the axon hillock region they are integrated to determine if an action potential
will be initiated in the axon. The first part of the axon is known as the trigger area (initial
segment), where the nerve impulse begins. The axon may be a single process, or it may have
side branches called axon collaterals. Axons and axon collaterals conduct action potentials along
their full lengths to end at fine processes called axon terminals. Neurotransmitter molecules are
released from axon terminals and transmit signals across a synapse to other neurons or to
effectors such as muscles or glands.
ACTIVITY 2~ Structure of a Neuron
1. Examine a prepared slide of motor neurons.
Use low power objective, find a large motor neuron and center it in the field of view.
Now switch to high power and draw the motor neuron and a few surrounding neuroglia in
detail in the circle provided below, label the cell body, nucleus, dendrites, axon hillock, and
axon.
Notice the small dark-stained neuroglia cells near the neuron, include them in your drawing
and label them.
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3. Functional Classification of Neurons
There are three classifications of neurons based on their functions: sensory, interneuron
(associated neuron), and motor neuron. Changes in the environment produce a stimulus that is
detected by the receptors associated with the dendrites of a sensory (afferent) neuron. This
neuron changes the stimulation into an action potential or nervous impulse which travels along
the axon to the spinal cord.
In the spinal cord, the axon of the sensory neuron synapses with either a motor neuron
or an interneuron. The interneuron (associated neuron) is structurally an unmyelinated neuron
and comprises about 90% of the neurons in the CNS. In the spinal cord, the interneuron can
synapse with a chain of interneurons sending the signal to the brain, and/or it can synapse with
a motor (efferent) neuron that takes the impulse out of the spinal cord via a spinal nerve to an
effector.
ACTIVITY 3~ Functional Classifications of Neurons
1. Identify and label the neurons in Figure 13.4b as either interneuron (associated neuron),
motor neuron (efferent), or sensory neuron (afferent).
4. _____________________________
5. _____________________________
6. _____________________________
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4. Myelination of Axons
Two neuroglia cells, the oligodendrocytes (CNS) and the Schwann cells (PNS), form insulated
wrappings called myelin sheaths around axons. As Schwann cells wrap around axons, their
cytoplasm is pushed to the periphery and is called neurolemma. The multiple layers of myelin
that surround the axons are composed of lipoprotein (about 80% lipids and 20% protein), similar
to the make-up of plasma membranes. The high amount of lipid in myelin sheath give the axons
a whitish appearance. Because babies and children do not have the complete myelin coverings
encircling the axons, their need for dietary fat is different than that of an adult and is necessary
for proper nervous system development. There is not a continuous myelin sheath around the
axon, and gaps do exist between the cells. Gaps in myelin sheaths are called nodes of Ranvier
and are more numerous in the PNS than in the CNS. The myelin sheath provides protection and
insulation for the axon, and also increases the speed of conductivity of the nerve impulse (action
potential). Myelinated axons are also called myelinated fibers. The axons that are not
myelinated are called unmyelinated fibers. They still have neuroglia cells, but only have a thin
coating of the Schwann cell of oligodendrocyte plasma membrane covering the axons.
Unmyelinated fibers conduct impulses slower than myelinated fibers.
ACTIVITY 4~ Myelination of Axons
1. Label the structures on Figure 13.6a and Figure 13.6b.
2. Label the structures on Figure 13.7 on page 6.
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B. Somatic Reflexes
Reflexes are rapid, involuntary motor responses to an environmental stimulus detected by
sensory receptors. A nerve impulse travels from the receptor through a neural reflex arc pathway to
an effector. If the motor response is contraction of skeletal muscle, the reflex is a somatic reflex. If
the motor response involves cardiac muscle, smooth muscle, or glands, the reflex is an autonomic
(visceral) reflex. Most reflexes help our bodies maintain homeostasis and therefore have a
protective function.
ACTIVITY 1~ Reflexes
1. Identify whether the reflexes in Table 17B.1 are somatic reflexes or autonomic reflexes. This
may require some research…
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1. Reflex Testing
A series of reflex tests are used clinically to evaluate the nervous system and to diagnose an
abnormality or dysfunction.
(1) Patellar Reflex (Knee Jerk): the patellar reflex is the extension of the knee that occurs when
the patellar tendon is stretched. Fill in all blanks!!!
Patellar Tendon
area
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Achilles tendon
AKA: calcaneal tendon
No help with this one figure out what
is the plantar surface of the foot and
go from there…
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Table 9.1 in your textbook is a good resource for answers
Two answers apply here
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You need to research these; textbook glossary is a good resource
2 answers
here
2 answers
here
You need to research these; common disorders in textbook and Table 9.1 might help
You need to research these
WORD BANK:
Spinal cervical nerve (musculocutaneous nerve)
Femoral nerve
Sciatic nerve
Radial nerve
Tibial nerve
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C. Autonomic Reflexes
Autonomic reflexes control many body functions such as blood pressure, respiration, and
digestion. The autonomic reflex arc contains the same components as the somatic reflex arc:
receptor, sensory neuron, integrating center, motor neurons, and effector. Although most
autonomic sensory receptors are located in visceral organs, some autonomic reflexes are responses
to change in the external environment. Autonomic integrating centers are polysynaptic and most
are located in the hypothalamus and brain stem. However, the autonomic reflex arcs that control
urination and defecation have integrating centers in the spinal cord, ANS reflex arcs have two motor
neurons, preganglionic and postganglionic neurons, which synapse in the autonomic ganglia, ANS
effectors are cardiac muscle, smooth muscle, and glands.
Most ANS effectors receive motor neurons from both the sympathetic and parasympathetic
branches of the ANS. Since sympathetic and parasympathetic responses usually oppose each other,
the hypothalamic integrating center determines which response is appropriate.
1. Pupillary Light Reflex
When photoreceptors in the retina of the eye are stimulated by light, nerve impulses are sent
via the optic nerve to integrating centers in the brain. Interneurons from the integrating centers
send impulses to motor neurons in the midbrain. Axons from these motor neurons travel along
cranial nerve III (oculomotor nerve) to smooth muscles in the iris of the eye. When these
muscles contract, the pupil constricts.
All answers except #5 in paragraph above; fill in blanks on item #1 then answer the discussion questions
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1. The Effect of Higher Brain Centers on ANS Function
The cerebral cortex, limbic system (emotional brain), and thalamus can also alter the
ANS responses. For example, when some people tell a lie, the limbic system causes the following
ANS responses: dilation of the blood vessels in the face and neck area resulting in redness,
constriction of the pupils, and an increase in breathing rate, heart rate, and/or blood pressure.
However, detection of autonomic changes by observation is a subjective exercise. Also, some
people can lie without feeling emotion, avoiding ANS responses.
Fill in all blanks!!!!!
NOTE: You will need to find out have to take the subject’s pulse and unfortunately I do not have
temperature strips.
Table 18.1 and the discussion questions are on page 13. YOU MUST FILL IN TABLE 18.1
COMPLETELY !!!!
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You will need to research these!!!
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