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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

Ependymal cells

Microglia

Oligodendrocytes

Satellite cells

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.

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 !!!!

Fill in all blanks!!!!!

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You will need to research these!!!