Human Anatomy From Unit 4 Of Correspondence Course

Front 1

Define Myology

Back 1

Myology is the study of muscles.

Front 2

Name and describe the three principle functions of muscles

Back 2

1.Movement – voluntary and involuntary

2.Heat production – metabolism within the cells releases heat as an end product; muscles are the primary source of body heat

3.Posture and body support – skeletal system provides the framework of the body, but skeletal muscles maintain posture, stabilize the flexible joints, and support the viscera.

Front 3

Name and describe the 4 basic properties that characterize all muscle tissue (smooth, cardiac, and skeletal)

Back 3

1.Irritability – Muscle tissue is sensitive to stimuli from nerve impulses.

2.Contractility – Muscle tissue responds to stimuli by contracting lengthwise, or shortening.

3.Extensibility – Once a stimulus has subsided and the fibers within muscle tissue are relaxed, they may be stretched even beyond their resting length by the contraction of an opposing muscle. The fibers are then prepared for another contraction.

4.Elasticity – Muscle fibers, after being stretched, have a tendency to recoil to their original length.

Front 4

Describe the attachment of skeletal muscles

Back 4

·Muscles are attached to the periosteum of bone by tendons on both sides. Shortening of the muscle causes tension of the tendons and attached bones, and results in movement at a Synovial joint where one attached bone moves more that the other.
·Insertion: the more moveable bony attachment of the muscle; distal attachment in girdles and limbs.
·Origin: the less moveable attachment; proximal attachment in girdles and limbs.

Front 5

Define facial and describe its 3 types

Back 5

Fascia is a fibrous connective tissue of varying thickness that covers muscle and attaches to the skin.
1.Superficial fascia – secures the skin to the underlying structures; can be thick or thin and is laced with adipose tissue.
2.Deep fascia – an inward extension of the superficial fascia; lacks adipose tissue; blends with the epimysium of muscle; surrounds adjacent muscles, compartmentalizing and biding them into functional groups.
3.Subserous fascia – extends between the deep fascia and serous membranes; nerves and vessels traverse subserous fascia to serve serous membranes.

Front 6

How do muscle cells differ from most other cells in the body?

Back 6

1. Elongated shape
2. Multinucleated
3. Striated

Front 7

Differ thin muscle filaments from thick muscle filaments

Back 7

Thin filaments are about 6 nm in diameter and are composed of the protein actin.

Thick filaments are about 16 nm in diameter and are composed of the protein myosin.

Front 8

Explain, in detail, the characteristic light and dark striations of skeletal muscle myofibrils

Back 8

These striations are caused by the patterned arrangement of thick and thin muscle filaments

1.A bands - the dark bands or striations on skeletal muscle myofibrils; the edges are a mixture of thin and thick filaments, and therefore, appear darker; the center portion of the A band is lighter, and is composed solely of thick filaments.

2.H zones – the central lighter regions of the A bands which are composed of thick filaments only

3.I bands - the light bands or striations on skeletal muscle myofibrils; they extend from one stack of thick filaments to the edge of the next stack of thick filaments; contain only thin filaments, but these thin filaments extend into the thick filaments of the A band

4.Z lines – thin dark lines located in the center of the I bands

5.Sarcomeres – subunits of myofibrils; the arrangement of thick and thin filaments between pairs of Z lines that forms a repeating structural pattern

Front 9

Define a Neuromuscular Junction. Describe its surrounding structures and the functions that occur there.

Back 9

·A Neuromuscular Junction is the area consisting of the motor end plate and the sarcolemma (cell membrane) of a muscle fiber.

·Surrounding structures:
1.A nerve serving a muscle is composed of both motor and sensory neurons.
2.Each motor neuron has an axon that extends form the CNS to a group of skeletal muscle fibers.
3.Close to the skeletal muscle fibers, the axon divides into axon terminals.
4.The axon terminals contact the sarcolemma of the muscle fiber by means of motor end plates. (Neuromuscular junction)

·Function: site of interaction between the CNS and muscular system
1.A nerve impulse reaching the axon terminal causes a release of the neurotransmitter, acetylcholine, into the neuromuscular cleft of the neuromuscular junction.
2.Acetylcholine contacts the receptor sites of the sarcolemma, it initiates physiological activity within the muscle fiber, resulting in contraction.

Front 10

Define and describe the location and function of acetylcholine

Back 10

·Acetylcholine is a neurotransmitter chemical that is stored in the synaptic vesicles at the axon terminal.
·Function - Initiates muscle contraction:
1.A nerve impulse reaching the axon terminal causes the release of acetylcholine into the neuromuscular cleft of the neuromuscular junction
2.As this chemical mediator contacts the receptor sites of the sarcolemma, it initiates physiological activity within the muscle fiber, resulting in contraction

Front 11

Describe the structure and function of a motor unit.

Back 11

· Structure: a motor unit consists of a single motor neuron and the aggregation of muscle fibers innervated by the motor neuron. The size of the motor neurons vary:

1. Small motor neurons - neurons with small innervation ratios have smaller cell bodies and axon diameters; smaller neurons are also stimulated by lower levels of excitatory input & are therefore used most often

2. Larger motor neurons - neurons with larger innervation ratios have larger cell bodies and axon diameters; larger motor units are active only when very forceful contractions are required.

· Function: when a nerve impulse travels through a motor unit, all of the fibers served by it contract simultaneously to their maximum.

Front 12

Explain what is meant by an innervation ratio in muscle fibers. What are some typical ratio sizes?

Back 12

· An innervation ratio is the ratio between the number of motor neurons, and the number of muscle fibers that are innervated by the neurons within a motor unit.
· Most muscles have an innervation ratio of 1 motor neuron for each 100 to 150 muscle fibers. Muscles capable of precise, dexterous movements (e.g. eye muscles) may have an innervation ratio of 1:10. Massive muscles that are responsible for gross body movements (e.g. quadriceps) may have innervation ratios exceeding 1:500 (they vary from 1:100 to 1:2,000, depending on the size of the motor neuron.

Front 13

Name the muscles that move the vertebral column and the exact movements that they are involved in.

Back 13

1. Anterior vertebral muscles – a group of muscles that extends along the antero-lateral surfaces of the three upper thoracic and the cervical vertebrae to the skull; Functions – flexion and rotation of the neck, and they maintain the balance of the head and the cervical spine
i. Rectus abdominus – flexes the v. column; a long straplike muscle of the anterior abdominal wall
2. Lateral vertebral muscles
i. Scalene muscles (Scalenus anterior, Scalenus medius, and Scalenus posterior) - extend downwards from the cervical vertebrae to the first and second ribs; Functions:
a. When the head is fixed in position – contraction elevates the first and second ribs, helping with respiration
b. If the thorax is fixed and the head is free to move – contraction bends the cervical portion of the vertebral column to one side
c. When the muscles of both sides contract together, they flex the vertebral column
d. In the erect position, they help to maintain the balance of the neck both anteriorly and laterally
ii. Sternocleidomastoid muscles – produces lateral flexion of the head and neck and rotation of the neck to the opposite side; simultaneous contraction of the right and left Sternocleidomastoids flexes the cervical spine and bends the head forward.
3. Posterior vertebral muscles – responsible for extension; stronger than the flexors; responsible for maintaining the stability of the vertebral column, and all posterior muscles acting together, extend the vertebral column & control flexion of the trunk
i. Superficial layer
a. Erector spinae muscles – muscle group that extends from the sacrum to the skull; consists of three groups of muscles:
i. Iliocostalis muscles – most lateral group
ii. Longissimus muscles – intermediate group
iii. Spinalis muscles – medial group; comes in contact with the spinous processes of the vertebrae
b. Superficial Trapezius and Latissimus dorsi muscles
ii. Intermediate layer (Levator scapulae and the Romboids)
iii. Deep layer (the Serratus Posterior Superior & Inferior muscles)
a. Quadratus Lumborum muscle – originates on the iliac crest and the lower three lumbar vertebrae; incerts on the transverse processes or the first 4 lumbar vertebrae and the inferior margin of the 12th rib; when the right and left quadratus lumborum contract together, the vertebral column in the lumbar region extends; separate contraction causes lateral flexion of the spine

Front 14

In general, describe the muscles of facial expression (location, general origin & insertion, innervation, and general functions)

Back 14

· Located in a superficial position o the scalp, face, and neck.
· Origin - the bones of the skull or in the facia
· Insertion - the skin
· Innervation – facial nerves
· Functions – contraction causes movements around the eyes, nostrils, or mouth; allow complex facial expressions as a means of communication.

Front 15

Name the muscles of Mastication and the functions of each

Back 15

1. Temporalis muscle – large muscle; works with the Masseter and the medial pterygoid muscles to elevate the mandible

2. Masseter muscle – large muscle; works with the Temporalis and the medial pterygoid muscles to elevate the mandible

3. Medial pterygoid muscle – primary function is to provide grinding movements of the teeth; works with the Temporalis and the Masseter muscles to help elevate the mandible

4. Lateral pterygoid muscle – primary function is to provide grinding movements of the teeth; protracts the mandible

Front 16

Name the basic divisions of the muscles of the trunk, and the muscles involved in each group.

Back 16

The muscles of the trunk include the muscles of the thorax and the abdomen.

1.Muscles of the thoracic wall – mainly the respiratory muscles which are called intercostals muscles; they are thin planes of muscles that occupy each of the intercostals spaces. There are two layers:
a. External intercostals muscles
b. Internal intercostals muscles

2.Muscles of the abdominal wall – muscles are unsupported by bone; support & protect the contents of the abdominal cavity & aid in breathing. There are three layers of the lateral abdominal wall, and one medial muscle pair:
a.External oblique muscle
b.Internal oblique muscles
c.Transversus abdominis
d.Rectus abdominis

Front 17

Describe in detail the muscles of the Thoracic Wall

Back 17

Muscles of the thoracic wall – mainly the respiratory muscles which are called intercostals muscles; they are thin planes of muscles that occupy each of the intercostals spaces.

There are two layers:
1.External intercostals muscles – the superficial layer; fibers are directed obliquely downwards and medially.

2.Internal intercostals muscles – the deeper layer; the fibers are directed downward and laterally.

Front 18

Describe in detail the muscle of the Abdominal Wall

Back 18

Muscles of the Abdominal wall – span the interval between the ribcage and the bony pelvis; muscles are unsupported by bone; support the contents of the abdominal cavity. Composed of 4 pairs of sheet-like muscles; there are three layers on the lateral abdominal wall:

1. External oblique muscle – strongest & outermost layer; fibers are directed downwards and medially
2. Internal oblique muscles – middle layer; fibers are oriented downward and laterally
3. Transversus abdominis – innermost layer; fibers run almost horizontally

Rectus abdominis – located on each side of the midline; runs vertically from pubis to ribcage & xiphisternum; enclosed by the Rectus sheath (a strong fibrous sheath formed by the aponeuroses of the three layers of the abdominal cavity); the linea alba (a band of connective tissue on the midline of the abdomen) separates the two rectus abdominis muscles; tendinous inscriptions transect the muscles at several points seen which causes a segmented look (a “six pack”) in muscular individuals.

Front 19

Name the 5 major functions of the muscles of the abdominal wall

Back 19

Five functions:
1. Allow the abdomen to stretch to accommodate a meal, a distended bladder, or a pregnant uterus
2. Allow the abdomen to contract to expel the contents of the abdomen or the pelvis (defecation, micturition, childbirth or vomiting)
3. Normal tone of the abdomen helps to keep the abdominal organs in proper position. (Keeps them from protruding)
4. Produces movements of the trunk
5. Helps to maintain posture due to their ability to produce a normal pelvic tilt

Front 20

What movement occurs with the contraction of the
1. Rectus abdominis
2. Simultaneous contraction of both external obliques
3. Simultaneous contraction of both internal obliques
4. Oblique muscles on one side of the body

Back 20

1. Forward flexion of the spine
2. Forward flexion of the spine
3. Forward flexion of the spine
4. Lateral flexion and rotation of the trunk

Front 21

Describe the special features of the aponeurosis of the external oblique muscle.

Back 21

The aponeurosis is a strong tendinous sheath that surrounds the muscles of the abdominal cavity. This aponeurosis of the external oblique muscles forms some special features:
1. Inguinal ligament – formed as the lower border of the aponeurosis folds inwards; on each side of the abdomen, this ligament extends from the anterior superior iliac spine to the pubic tubercle, and gives attachment to the deep fascia of the thigh.
2. Superficial inguinal ring – an opening in the aponeurosis located just superior to the pubic tubercle; allows for the passage of the spermatic cord in the male or of the round ligament of the uterus in the female.
3. Deep inguinal ring – an arched opening in the aponeuroses of the internal oblique and the transverse abdominis between their attachments to the medial and lateral aspects of the inguinal ligament; also allows for the passage of the spermatic cord in the male or of the round ligament of the uterus in the female.
4. Inguinal canal – an oblique pathway on the lower part of the anterior abdominal wall parallel to the inguinal ligament; extends from the superficial inguinal ring to the deep inguinal ring; houses the spermatic cord in the male or of the round ligament of the uterus in the female; it is larger in the male

Front 22

Describe a hernia and two factors that can lead to one in the abdominal cavity. Also, name and describe the most common type of hernia in the abdomen.

Back 22

A hernia is a protrusion of any structure (abdominal contents) through an opening that it does not normally traverse.

Two main factors that can lead to one are:
1. An increase in intra-abdominal pressure
2. Weakness in the anterior abdominal wall itself

The most common hernia in the abdomen is the inguinal hernia, which is most common in males and are usually repaired surgically. An inguinal hernia may be indirect or direct:
1. Indirect inguinal hernia – follows the normal pathway of the testicular descent (inguinal canal). Any protrusion of the intestines or other abdominal contents along this pathway is an indirect inguinal hernia.
2. Direct inguinal hernia – protrudes through the medial portion of the abdominal wall and the superficial inguinal ring to enter the scrotum. Weakness of the abdominal wall may encourage the development of such a hernia.

Front 23

Describe the descent of the testes during embryonic development

Back 23

· Descent of the testes from the site of development begins between the 6th and 10th week of embryonic development
· Descent into the scrotal sac does not occur until about week 28
· Process seems to be associated with the shortening and differential growth of the gubernaculum, which is attached to the testes and extends through the inguinal canal to the wall of the scrotum.
· As the testes descends, the it passes to the side of the urinary bladder and anterior to the symphys pubis
· It caries with it the ductus deferens, the testicular vessels and nerve, a portion of the internal abdominal oblique muscle, and lymph vessels. All of these structures form the spermatic cord.

Front 24

Describe the Iliacus and the Psoas major.

Back 24

Iliopsoas - The Iliacus and the Psoas major (together called the Iliopsoas) are the chief flexors of the hip joint; they are the anterior muscle that move the thigh at the hip joint; they work synergistically in flexing and rotating the hip joint and flexing the vertebral column.
1. Iliacus – the triangular muscle that arises from the iliac fossa and inserts on the lesser trochanter of the femur
2. Psoas major – a long, thick muscle that originates on the bodies and transverse processes of the lumbar vertebrae, and inserts (along with the iliacus) on the lesser trochanter. This muscle flexes the lower spine & helps hold the spine erect during heavy lifting. It is also responsible for lateral flexion of the spine.

Front 25

Name the posterior muscles that move the thigh at the hip joint.

Back 25

1. Gluteus maximus – powerful extensor muscle of the hip joint
2. Gluteus medius - deep to the maximus; abducts and medially rotates the hip joint
3. Gluteus minimus – smallest and deepest; acts with the gluteus medius and the tesor fasciae latae to abduct the hip
4. Tensor fasciae latae – positioned superficially on the lateral surface of the hip; works synergistically with the gluteus medius in abduction.

Front 26

Name the medial muscles that move the hip joint.

Back 26

1. Gracilis pectineus – a long, thin muscle; the most superficial of the medial thigh muscles; can adduct the hip joint or flex the knee.
2. Adductor longus – the uppermost of the medial muscles that move the hip joint; flexes and adducts the hip.
3. Adductor longus – located immediately laterally to the gracilis on the upper 3rd of the thigh; most anterior of the adductor muscles; synergistic with other two adductor in adducting, flexing and rotating the hip joint.
4. Adductor brevis – located deep to the adductor longus and pectineus muscles
5. Adductor magnus – a large, thick muscle thatis located deep to the other two adductor muscles (longus and brevis)