2.5.3. ANAT LAB - Gluteal, Anal and Post Thigh

Question 1

What is the largest nerve in the body?

Answer 1

Sciatic nerve (Saphenous nerve is the longest)

Question 2

What are the two triangles in the perineum?

Answer 2

The urogenital triangle (anterior) & the anal triangle (posterior)

Question 3

What forms the pudendal canal?

What passes through the pudendal canal (3)?

Answer 3

The pudendal canal is formed by the obturator fascia

The pudendal artery, internal pudendal veins, and pudendal nerve pass through the pudendal canal.

Question 4

Is the internal anal sphincter voluntary or involuntary?

What part of the anal canal does it surround?

Its contraction is stimulated and maintained by what?

What inhibits contraction?

Answer 4

The internal anal sphincter is involuntary

It surrounds the superior 2/3 of the anal canal

Contraction is stimulated and maintained by sympathetic fibers from the superior rectal and hypogastic plexuses.

Contraction is inhibited by parasympathetic fiber stimulation.

Question 5

Is the external anal sphincter voluntary or involuntary?

It forms a broad band on each side of which part of the anal canal?

It is attached anteriorly to what?

What is its posterior attachment?

Answer 5

The external anal sphincter is a large voluntary sphincter

It forms a broad band on each side of the inferior two thirds of the anal canal

It is attached anteriorly to the perineal body

It is attached posteriorly to the coccyx via the anococcygeal ligament

Question 6

What separates the superior part of the anal canal from the inferior part of the anal canal?

What are the four ways in which the superior and inferior parts of the anal canal differ?

What is the reason for the differences between the two parts of the anal canal?

Answer 6

The pectinate line

The superior and inferior parts of the anal canal differ in arterial supply, innervation, venous drainage, and lymphatic drainage

These differences are due to the different embryological origins of the superior and inferior parts of the anal canal

Question 7

What is the puborectalis?

How does the puborectalis ‘sling’ work?

What is it’s major role?

Answer 7

The puborectalis is the thicker, narrower, medial part of the levator ani, consisting of muscle fibers that are continuous between the posterior aspects of the bodies of the right and left pubic bones.

It forms a U-shaped muscular sling that passes posterior to the anorectal junction bounding the urogenital hiatus.

The puborectalis plays a major role in maintaining fecal continence.

Question 8

Why is the internal anal sphincter contracted most of the time?

Why/when does it relax temporarily?

Answer 8

It is contracted most of the time to prevent leakage of fluid or flatus.

It relaxes temporarily to distension of the rectal ampulla by feces or gas.

Question 9

Gluteus maximus:

Origin (2)

Insertion (2)

Innervation

Action

Answer 9

Origin: Posterior gluteal line, posterior sacrum & coccyx (sacrotuberous ligament)

Insertion: Upper fibers insert on the iliotibial tract

Lower fibers insert on the gluteal tuberosity of the femur

Innervation: Inferior gluteal nerve

Action: Extends thigh and trunk, laterally rotates thigh

Question 10

Gluteus medius:

Origin

Insertion

Innervation

Action

Answer 10

Origin: Ilium between posterior and anterior gluteal lines

Insertion: Greater trochanter of femur

Innervation: Superior gluteal nerve

Action: Abducts and medially rotates thigh

Question 11

Gluteus minimus:

Origin

Insertion

Innervation

Action

Answer 11

Origin: Ilium between anterior and inferior gluteal lines

Insertion: Greater trochanter of femur

Innervation: Superior gluteal nerve

Action: Abducts and medially rotates thigh

Question 12

Tensor fascia lata:

Origin (2)

Insertion

Innervation

Action

Answer 12

Origin: Anterior part of iliac crest, anterior superior iliac spine (ASIS)

Insertion: Iliotibial tract

Innervation: Superior gluteal nerve

Action: Flexes, abducts, and medially rotates thigh

Question 13

Piriformis:

Origin

Insertion

Innervation

Action

Answer 13

Origin: Anterior surface of sacrum

Insertion: Upper border of greater trochanter of femur

Innervation: Ventral rami of S1-S2

Action: Laterally rotates and abducts thigh

Question 14

Obturator internus:

Origin

Insertion

Innervation

Action

Answer 14

Origin: Margin of obturator foramen and internal surface of obturator membrane

Insertion: Greater trochanter, medical surface above the trochanteric fossa

Innervation: Nerve to obturator internus (L5, S1-2)

Action: Laterally rotates and abducts thigh

Question 15

Obturator externus:

Origin

Insertion

Innervation

Action

Answer 15

Origin: External surface of obturator membrane and anterior bony margins of obturator foramen

Insertion: Posteromedial surface of greater trochanter of femur

Innervation: Obturator nerve

Action: Lateral rotation of thigh; also aids in thigh adduction

Question 16

Gemellus superior:

Origin

Insertion

Innervation

Action

Answer 16

Origin: Ischial spine

Insertion: Medial surface of greater trochanter of femur

Innervation: Nerve to obturator internus (L5, S1)

Action: Laterally rotates thigh, abducts flexed thigh; steadies femoral head in acetabulum

Question 17

Gemellus inferior:

Origin

Insertion

Innervation

Action

Answer 17

Origin: Ischial tuberosity

Insertion: Medial surface of greater trochanter of femur

Innervation: Nerve to quadratus femoris (L5, S1)

Action: Lateral rotation of thigh; Abducts flexed thigh; Steadies femoral head in acetabulum

Question 18

Quadratus femoris:

Origin

Insertion

Innervation

Action

Answer 18

Origin: Lateral border of ischial tuberosity

Insertion: Quadrate tubercle on inter-trochanteric crest of femur and area inferior to it

Innervation: Nerve to quadratus femoris (L5, S1)

Action: Laterally rotates thigh; Steadies femoral head in acetabulum

Question 19

Semitendinosus:

Origin

Insertion

Innervation

Action

Answer 19

Origin: Ischial tuberosity

Insertion: Medial surface of superior part of tibia

Innervation: Tibial nerve (L5, S1, S2) (aka Tibial division of sciatic nerve)

Action: Extends thigh; Flex leg; Medially rotate leg when knee is flexed

Question 20

Semimembranosus:

Origin

Insertion

Innervation

Action

Answer 20

Origin: Ischial tuberosity

Insertion: Posteiror part of medial condyle of tibia

Innervation: Tibial nerve (L5, S1, S2) (aka Tibial division of the sciatic nerve)

Action: Extend thigh; Flex leg; Rotate leg medially when knee is flexed

Question 21

Biceps femoris:

Origin (2)

Insertion

Innervation (2)

Action

Answer 21

Origins:

Long head: ischial tuberosity

Short head: linea aspera and lateral supracondylar line of femur

Insertion: Lateral side of head of fibula; tendon is split at this site by fibular collateral ligament of knee

Innervation:

Long head: Tibial nerve (L5, S1, S2)

Short head: Common fibular division of sciatic nerve (L5, S1, S2)

Action: Flexes leg and rotates it laterally when knee is flexed; extends thigh

Question 22

Explain how the muscles in the hip support the pelvis when standing and walking. What is the role of the medial and lateral rotators?

Answer 22

When the weight is on both feet, the pelvis is evenly supported and does not sag. When the weight is borne by one limb the muscles on the supported side fix the pelvis so that it does not sag to the unsupported side. The medial rotators that act unilaterally during the stance phase (planted limb) to keep the pelvis level via abduction can simultaneously produce medial rotation at the hip joint, advancing the opposite unsupported side of the pelvis. The lateral rotators of the advancing (free) limb act during the swing phase to keep the foot parallel to the direction of advancement.

Question 23

Lymphatic vessels from deep parts of the perineum accompany the internal pudendal blood vessels and drain mainly into _____ _____ nodes in the pelvis.

Answer 23

Internal iliac

Question 24

Identify the labeled structure: (This is a picture from the cadaver’s left side)

Answer 24

1. Gluteus Maximus

Question 25

Lymphatic channels from superficial tissues of the penis or the clitoris accompany the superficial external pudendal blood vessels and drain mainly into _______ \_\_\_\_\_\_\_\_ nodes, as do lymphatic channels from the scrotum or labia majora.

Answer 25

Superficial inguinal

Question 26

The glans penis, the glans clitoris, labia minora, and the terminal inferior end of the vagina drain into ________ \_\_\_\_\_\_\_ nodes and _______ \_\_\_\_\_\_\_\_\_ nodes.

Answer 26

Deep inguinal nodes and external iliac nodes

Question 27

Identify the following structure: 

Answer 27

1. Gluteus medius

Question 28

Identify the following structures: 

Answer 28

1. Superior gluteal nerve and artery 2. Inferior gluteal nerve and artery 3. Pyriformis muscle Note: Pay attention to the relationship between the Superior and Inferior Nerves and Arteries and the Pyriformis muscle. This relationship helps you to identify the structures.

Question 29

Identify the following structures (Note: This is a closeup of the area, showing the structures deep to the Gluteus Maximus): 

Answer 29

1. Gluteus medius 2. Obturator internus 3. Superior gemellus 4. Quadratus femoris 5. Pyriformis 6. Inferior gemellus

Question 30

Identify the following structures: 

Answer 30

1. Sacrotuberous ligament 2. Inferior rectal nerve 3. Sciatic nerve 4. Inferior gluteal nerve and artery 5. Inferior rectal artery (cut) 6. Inferior rectal vein

Question 31

What are the boundaries of the Ischioanal Fossa? (4)

Answer 31

Medially: Levator Ani muscle Laterally: Obturator internus fascia Posteriorly: Gluteus maximus muscle lying superficial to the Sacrotuberous ligament Anteriorly: Perineal membrane

Question 32

Identify the following structures: 

Answer 32

1. Sacrotuberous ligament 2. Inferior rectal nerve 3. Fascia of obturator internus muscle

Question 33

Identify the following structures: 

Answer 33

1. Coccyx 2. Sacrum

Question 34

Identify the following structures: 

Answer 34

1. Ischial Spine 2. Ischial tuberosity

Question 35

Identify the following structures: 

Answer 35

1. Greater sciatic notch 2. Lesser sciatic notch Red circle: Greater sciatic Foramen

Question 36

What makes the piriformis muscle a key anatomical/surgical landmark?

Answer 36

The Superior and Inferior gluteal "bundles" (nerves, arteries and veins) exist the pelvis superior and inferior to the piriformis muscle.

Question 37

Where does the sciatic nerve emerge from the pelvis?

Answer 37

Inferior to the piriformis muscle

Question 38

The pudendal nerve and internal pudendal vessels cross between the ______ spine and the ________ ligament on their way to supply the \_\_\_\_\_\_\_\_.

Answer 38

Ischial spine Sacrospinous ligament Supply the perineum (genitourinary areas)