Biology 241 – Lab
LAB #16
(16th/21 Lab Sessions for Fall Quarter, 2008)
TOPICS TO BE COVERED:
»Demonstration/Dissection/Identification of certain Non-Muscular Structures
»Introduction to the Nervous System components
»Introduction to Cranial Nerves
DESIRED OUTCOMES:
After completing the activities described for this lab session, students should:
»Be able to identify the required non-muscular structures:
Tendinous inscriptions Lymph Node(s) Transverse carpal ligament Sciatic Nerve
Patellar tendon Calcaneal tendon Thyroid gland Transverse Jugular Vein
Parotid salivary gland
Parotid gland duct Submaxillary salivary gland
MATERIALS NEEDED:
»Gloves
»Safety Glasses (or your own glasses)
»Dissection Trays (large, flat pans)
»Preserved cats
»Dissection Tools (large forceps, scissors, blunt probes, dissection needles, scalpels)
»Photographic Atlas, Ch. 8, 9, 13, 15
»Cat Atlas
Activity #1: Demonstration/Dissection/Identification of certain Non-Muscular Structures
Up to this point, you have learned most of the bony landmarks on bones of the skeleton and most of the
superficial muscles of both the human and the cat, along with several of the deep muscles. Along the way, there
have been several structures that have been encountered about which you should be conversant. These are:
Tendinous inscriptions: Regarding the rectus abdominis muscles, these are vertically oriented and lie one to
either side of the midline. Their vertical fibers are interrupted along their course by three transverse fibrous
bands called tendinous inscriptions, believed to be remnants of the myosepta that separated muscle segments,
or myotimes, during embryological development. These result in making the rectus abdominis muscles stronger
by virtue of allowing for four times the potential shortening in length of the muscle compared to if the muscle
did NOT include these “interruptions”. (Also, since the rectus abdominis is 3 times as wide cranially, where
fleshy, as it is caudally, where tendinous, these tendinous inscriptions are longer up near the rib cage.) These
structures are absent on the cat.
Lymph nodes: Lymph nodes (sometimes called “lymph glands”), are small, oval or bean-shaped collections of
lymphatic tissue interposed in the course of lymphatic vessels and macroscopically visible along the routes of all
blood vessels. They are especially aggregated in large collections in the following regions: cervical, axillary,
inguinal, popliteal, intestinal and bronchomediastinal. The tissue of each node is enclosed in a strong fibroelastic
capsule from which septa, or trabeculae, push into the substance of the node to partially subdivide it into a number of compartments. There are both superficial and deep lymph nodes; the superficial ones are palpable as firm
(but not hard), moveable masses. Among the palpable nodes are those in the neck region, in the axilla, and in
the inguinal area. When a lymph node is enlarged, hard, and tender, it is infected (that is, it is actively fighting
a local infectious process), and it is known as a “bubo”. This is how the Bubonic Plague was named: the clinical
symptoms were numerous, large, swollen lymph nodes, or bubos.
Biology 241 – LAB #16 – continued
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Transverse carpal ligament: This structure is also called the flexor retinaculum. It unites the 4 marginal
carpal bones. (The carpus consists of eight bones arranged in two transverse rows of four each. The proximal row from
lateral to medial side is made up of the scaphoid, lunate, triquetrum, and pisiform bones; those of the distal row, in the same
order, are called the trapezium, trapezoid, capitates, and hamate bones. The four marginal bones are the scaphoid and pisiform and the trapezium and hamate.) Remember, the carpal bones are small and irregular in shape. Their names are
more or less suggestive of their appearance. The smallest is the pisiform which rests on the front of the triquetrum, rather than at its side, and can be easily palpated when the wrist is flexed. The bones are closely fitted together and bound by ligaments but they do have synovial cavities and some movement is allowed between them.
The greatest movement, however, is between the proximal an distal rows, at the transverse intercarpal, or midcarpal, joint. The rows of bones are also placed in such a manner as to form a transverse arch with its concavity
anterior. In life, this concavity is bridged by a ligament, the flexor retinaculum (transverse carpal ligament), under
which pass the numerous flexor tendons to the wrist and fingers. See Figure 8.36 of the Photographic Atlas.
(Owing to the irregularity of carpal bones, fractures and other injuries are serious and often may not be restored to 100
percent function.)
Sciatic Nerve: The sacral plexus of nerves is formed by ventral rami of L4, L5, S1, S2, S3 and S4 uniting to form
a large, flattened band, most of which continues into the thigh as the sciatic nerve. The sciatic nerve is the largest nerve in the body, supplying the skin of the foot and most of the leg, the muscles of the posterior side of the
thigh, and all those of the leg and foot. Its terminal branches are the tibial and common peroneal nerves. Together with the lumbar plexus of nerves (L1 – L4), these two great plexuses collectively supply the skin and muscles of the entire lower limb. You will see this large, impressive nervous structure immediately deep to the biceps femoris muscle if you cut its tendinous insertion on the lateral side of the lateral condyle of the tibia and
head of the fibula and reflect the biceps femoris muscle upward.
Patellar tendon: The quadriceps femoris (actually four muscles: rectus femoris, vastus lateralis, vastus medialis,
vastus intermedius) is the great extensor of the leg. Its vasti components cover the anterior, lateral, and medial
surfaces of the shaft of the femur, and reach posteriorly to the linea aspera. The rectus femoris lies in front of
the vastus intermedius and between the vastus medialis and lateralis; but unlike them, it has a double origin –
one head to the anterior inferior spine of the ilium and the other to the posterosupeiror tim of the acetabulum.
These four muscles have a common tendon of insertion into the superior border of the patella, which in turn is
attached to the tuberosity of the tibia by the ligamentum patellae. Actually, since the patella is a sesamoid bone,
which formed in the tendon of the quadriceps femoris muscle, this muscle can be said to have originally inserted
into the tibial tuberosity. In all, the structure we refer to as “the patellar tendon” is really two structures (the
tendon of the quadriceps femoris muscles together with the patellar ligament) AND it includes the patella itself
interposed between the two of these tendinous/ligamentous structures. (See Figures 8.45 – 8.47 and 8.51 – 8.53 of
the Photographic Atlas.) The patella, bearing on the condyles of the femur, serves as a lever to improve the angle
of pull of the quadriceps on the tibial tuberosity. The quadriceps tendon, by sending fibers over the capsule of
the knee joint and by the tension of the muscles helps to strengthen and maintain the integrity of the knee joint.
Since the rectus femoris crosses the hip joint as well as the knee joint, it is a flexor of the thigh as well as an extensor of the knee. The whole group functions in walking, running, climbing, jumping, and kicking.
Calcaneal tendon: With regard to the posterior crural muscles, their primary function is to extend (plantar
flex) the foot at the ankle. The gastrocnemius and soleus together form the “calf of the leg” and they insert by a
common tendon, the tendo calcaneus (aka Tendon of Achilles), into the tuberosity of the calcaneus, or heel bone.
These two muscles are sometimes referred to as the triceps surae. Because the origins of the gastrocnemius are
just above the lateral and medial condyles on the posterior surface of the femur and the muscle crosses the knee
joint, it also flexes the knee. Also know that the plantaris is a small muscle between the proximal ends of the
gastrocnemius and the soleus and inserts into the calcaneus by a long, slender tendon that follows (and often
fuses into) the medial side of the calcaneal tendon (tendo calcaneus.)
Biology 241 – LAB #16 – continued
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Thyroid gland: The thyroid gland is the largest of the endocrine glands, weighing 20 – 30 grams. It lies in the
neck region with one lobe on either side of the lower larynx and upper trachea. The lobes are connected anteriorly across the trachea by the isthmus. (See Figure 10.1 in the Photographic Atlas.) In about a third of all individiauls, a tall, narrow pyramidal lobe extends upward from the isthmus in front of the larynx.
Transverse Jugular Vein: This vein is somewhat variable in size from specimen to specimen (cats or
humans) and is considered a tributary of the external jugular vein fed by venous drainage from the superior,
middle, and inferior thyroid veins. It is a short, but prominent vein that crosses the midline and seems to unite
the R and L external jugular veins.
Parotid salivary gland: There are three pairs of major salivary glands: the parotid, submandibular (aka: submaxillary), and sublingual. (There are also innumerable minor salivary “glands” in the lingual, labial, and buccal mucosa. These are microscopic aggregates of salivary glandular tissue; but they contribute in a very big way to the total
amount of saliva that washes the oral cavity.) The parotid gland lies below and in front of the external ear and
within the cervical fascia. Although the parotids (there are two of these: Right and Left) are the largest of the
three major salivary glands, they produce less saliva (by volume) than do the submandibular salivary glands.
The saliva produced by the parotids is considered to be nearly totally serous (watery) in nature; whereas the
submandibular glands produce a mixed serous/mucous saliva, and the sublingual glands produce a nearly totally
mucous saliva.
Parotid gland duct: Also known as Stensen’s Duct, this large duct crosses the masseter muscle and at its
anterior border, bends inward to penetrate the cheek. The open end of the duct is anchored by a mound of
buccal mucosa called the parotid papilla, and the it opens at the level of the second maxillary molar tooth.
Submaxillary salivary gland: The second largest of the major salivary glands; but the ones (again, these are
bilateral) that produce the most saliva by volume! Each submandibular gland lies below the body of the mandible and the mylohyoid muscle. Its duct (Wharton’s duct) arises from a lobe of the land under the floor of the
mouth from which it pushes upward and forward dto open on the underside of the tongue in the floor of the
mouth.
Activity #2: Introduction to the Nervous System Components
The cranial and spinal nerves constitute in part the peripheral nervous system. As we have seen, the spinal
nerves are paired and form a regular segmental sequence along the spinal cord. They have posterior, or afferent,
roots and anterior, or efferent, roots. There is a sensory ganglion on the posterior root containing the cells of
origin of the afferent neurons; a nucleus made up of the cells of origin of the efferent neurons is in the anterior
gray column of the cord.
Here is a list of the structures of the spinal cord that you should be able to identify on anatomical models
and/or diagrams: (Refer also to Figures 9.4 – 9.6, 9.21, and 9.22 in the Photographic Atlas)
1. Meninges
2. Spinal gray matter
3. Spinal white matter
a. Dura mater
a. Anterior (ventral) horn
a. Anterior column (aka funiculus)
(1) Epidural space
b. Lateral horn
b. Lateral column (aka funiculus)
(2) Subdural space
c. Posterior (dorsal) horn
c. Posterior column (aka funiculus)
b. Arachnoid mater
(1) Subarachnoid space
4. Spinal nerve roots:
c. Pia mater
a. Dorsal root and Dorsal Root Ganglion
(1) Denticulate ligaments
b. Ventral root
Biology 241 – LAB #16 – continued
5. Conus medullaris
6. Filum terminale
7. Cauda equine
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8. Cervical enlargement
9. Lumbar enlargement
10. Central Canal
11. Anterior median fissure
12. Posterior median sulcus
Activity #3: Introduction to Cranial Nerves
The cranial nerves issue from the brain (except, of course I – Olfactory which issue from the superior nasal mucosa and II – Optic which issue from the nervous tunic (retina) of each eye). From our understanding of the development of the brain and cord from a common neural tube, we have reason to expect that as the brain bears some
resemblance to the cord, the cranial nerves should also bear some resemblance to the spinal nerves. This is indeed the case, but as the brain developed its special features, so did the cranial nerves become more specialized.
In studying the cranial nerves, the student should be alert to the similarities and differences between these two
subdivision of the peripheral nervous system.
Twelve pairs of cranial nerves are commonly recognized. Most of these nerves, like the spinal nerves, have
efferent and afferent roots (mixed nerves), but a few have only afferent or only efferent roots (pure nerves). The
afferent, or sensory, components have their cell bodies in ganglia outside of the brain; the efferent, or motor,
components have their cell bodies in gray nuclei within the brain. Except for the first pair of cranial nerves,
which is atypical, they all attach to the “old” brain stem. Cranial nerves have been given both names and
numbers, and Roman numerals should be used. They are as follows:
I
II
III
IV
V
VI
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
VII
VIII
IX
X
XI
XII
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Spinal Accessory
Hypoglossal
Refer to Figure 9.11 in the Photographic Atlas; and to pages 500 – 514 of the Tortora textbook. Also, several
reference sheets follow this exercise.