Human Anatomy & Physiology I Supplemental · Exam Block 3
Week 9 · Ch. 7–8 · Full Skeleton
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Week 9 · Chapters 7 & 8
The Axial & Appendicular Skeleton
This week begins Exam Block 3 and covers both remaining skeletal chapters together: the axial skeleton (skull, vertebral column, thoracic cage) that protects the body's core, and the appendicular skeleton (limbs and girdles) that's built for movement. By the end of this week you'll know the full 206-bone skeleton.
By the end of this week, you will be able to:
1Distinguish the axial skeleton from the appendicular skeleton
2Classify the skull's cranial and facial bones
3Identify the five regions of the vertebral column and thoracic cage
4Name the bones of the upper and lower limb, proximal to distal
5Compare the pectoral and pelvic girdles and their mobility/stability trade-off
6Recognize common fracture sites across both skeletal divisions
Part 1 — Big Picture
Two skeletal divisions: axial vs. appendicular
The 206 bones of the adult skeleton split into two functional groups. The axial skeleton (80 bones: skull, vertebral column, thoracic cage) is the body's protective core — that's Part 1 of this week. The appendicular skeleton (126 bones: limbs and girdles), built for movement instead of protection, is Part 2, later in this same lesson.
Part 1 — Vocabulary & Word Parts
Axial skeleton roots
crani/o-skull
Cranial bones form the protective case around the brain.
vertebr/o-vertebra, spine
Vertebral column = the spine, made of individual vertebrae stacked together.
cervic/o-neck
Cervical vertebrae = the 7 neck vertebrae, C1–C7.
thorac/o-chest
Thoracic cage = the ribcage; thoracic vertebrae attach to the ribs.
lumb/o-lower back
Lumbar vertebrae = the 5 lower-back vertebrae, often the site of "lower back pain."
-foramenopening, hole
Vertebral foramen = the hole in each vertebra the spinal cord runs through.
Part 1 — Structure & Function
The skull: two bone groups with different jobs
The 22 bones of the skull split cleanly by function: 8 cranial bones form a protective vault around the brain, while 14 facial bones shape the face and provide anchor points for teeth and facial muscles. Most skull bones are joined by immovable sutures — a detail worth remembering, since sutures are a distinct joint type covered again in Chapter 9.
Part 1 — Structure & Function
Five regions of the vertebral column
A simple memory trick for vertebral counts, largest group to smallest: breakfast (7 cervical), lunch (12 thoracic), dinner (5 lumbar) — "you eat more meals than the number of cervical vertebrae, fewer than thoracic, in between for lumbar." The sacrum and coccyx are each made of individual vertebrae that fuse together during development.
Part 1 — Structure & Function
Anatomy of a typical vertebra
Every vertebra (with some regional variation) shares this basic plan: a weight-bearing body in front, a vertebral foramen in the middle that the spinal cord threads through, and bony processes projecting outward and backward that serve as attachment points for muscles and ligaments.
Part 1 — Structure & Function
The thoracic cage
The thoracic cage is built from the sternum (breastbone, itself divided into manubrium, body, and xiphoid process) plus 12 pairs of ribs. Ribs 1–7 ("true ribs") connect directly to the sternum via their own cartilage; ribs 8–10 ("false ribs") connect indirectly; ribs 11–12 ("floating ribs") don't connect to the sternum at all.
Part 1 — Clinical Correlation
Why cervical spine injuries are treated as emergencies
This is a direct, high-stakes application of the vertebral column's protective structure.
🩺 In practice
Because the cervical vertebrae are the highest point on the spinal cord's path, damage here can affect signals to the ENTIRE body below that point — which is exactly why EMS providers immobilize the neck of anyone with a suspected spinal injury before moving them at all. A fracture lower in the lumbar region, while still serious, generally affects a much smaller portion of the body's nerve supply.
Part 2 — Big Picture
Four regions, one repeating pattern
The appendicular skeleton's 126 bones organize into four groups that repeat a single pattern twice: a girdle anchors a limb to the axial skeleton, then the limb extends outward in a proximal-to-distal sequence. Learn the pattern once, and the upper and lower limb both make sense.
Part 2 — Vocabulary & Word Parts
Appendicular skeleton roots
append/o-attachment, appendage
Appendicular skeleton = the bones "attached to" the axial skeleton — limbs and girdles.
brachi/o-arm
Brachial refers to the arm; the humerus is sometimes called the "brachium" bone.
carp/o-wrist
Carpals = the 8 small wrist bones.
tars/o-ankle
Tarsals = the 7 ankle bones — the lower-limb equivalent of carpals.
phalan/o-finger/toe bone
Phalanges = the bones of the fingers and toes, 14 in each hand and each foot.
pelv/o-basin, pelvis
Pelvic girdle = the hip bones, shaped like a basin that supports the trunk's weight.
Part 2 — Structure & Function
Upper limb: proximal to distal
One bone becomes two, then many, then more: a single humerus in the arm gives way to a paired radius (thumb-side) and ulna (pinky-side) in the forearm, then the 8 carpals, 5 metacarpals, and 14 phalanges of the wrist and hand — built for fine, precise movement.
Part 2 — Structure & Function
Lower limb: proximal to distal
The lower limb mirrors the upper limb's pattern almost bone-for-bone: femur parallels humerus, tibia/fibula parallel radius/ulna, tarsals parallel carpals. The key differences reflect the lower limb's job — weight-bearing and stability instead of fine manipulation. The patella (kneecap) has no upper-limb equivalent.
Part 2 — Structure & Function
Pectoral vs. pelvic girdle: a mobility/stability trade-off
This is the single biggest conceptual takeaway for this half of the week: the pectoral girdle is loosely attached to the axial skeleton, trading stability for an enormous range of arm motion — which is also exactly why shoulder dislocations are so common. The pelvic girdle is firmly fused to the sacrum, trading mobility for the stability needed to support body weight and permit walking.
Part 2 — Clinical Correlation
Why shoulder dislocations are so common
This is a direct, real-world consequence of the pectoral girdle's mobility-over-stability design.
🩺 In practice
The shoulder joint is the most frequently dislocated joint in the body — a direct trade-off for the wide range of motion the loosely-attached pectoral girdle allows. Compare this to the hip joint (part of the firmly-anchored pelvic girdle), which dislocates far less often precisely because it sacrifices some mobility for structural stability. Same basic joint concept, opposite design priorities.
Your Turn — Guided Practice
Apply it before the quiz — one scenario from each chapter
Two quick clinical scenarios, one from each half of this week's material.
Scenario A (Ch. 7) — An X-ray shows a fracture in a vertebra located in the lower back, just above the sacrum. Which vertebral region does this involve?
The lumbar region sits directly above the sacrum in the lower back — exactly matching the fracture's described location. The cervical region is up in the neck, nowhere near the sacrum.
Scenario B (Ch. 8) — A patient falls onto an outstretched hand and reports pain in the forearm on the thumb side, near the wrist. Which bone is most likely fractured?
The radius sits on the thumb side of the forearm — exactly matching the pain location described. This injury pattern (fall onto an outstretched hand, thumb-side pain) is common enough clinically to have its own name: a distal radius fracture.
Mini Knowledge Test
Show what you know — 10 questions across Ch. 7–8
Question 1
The axial skeleton includes all of the following EXCEPT:
The femur (thigh bone) is part of the appendicular skeleton, not the axial skeleton. The skull and vertebral column are both core axial skeleton structures.
Question 2
How many cranial bones are there?
There are 8 cranial bones, which encase the brain. 14 is the number of facial bones instead, and 22 is the combined total of cranial + facial bones together.
Question 3
Which vertebral region has 12 vertebrae and attaches to the ribs?
The thoracic region has 12 vertebrae (T1–T12), each pairing with a set of ribs. Cervical has 7 vertebrae in the neck; lumbar has 5 in the lower back — neither attaches to ribs.
Question 4
Ribs 1–7 are classified as:
Ribs 1–7 are true ribs, connecting directly to the sternum. False ribs (8–10) connect indirectly, and floating ribs (11–12) don't connect to the sternum at all.
Question 5
Which bone is part of the pectoral girdle?
The clavicle (collarbone), along with the scapula, makes up the pectoral girdle. The femur is a lower-limb bone, and the sacrum is part of the axial skeleton.
Question 6
Which forearm bone is on the pinky side?
The ulna runs along the pinky side of the forearm. The radius is on the thumb side instead, and the humerus is the single upper-arm bone above the elbow.
Question 7
The patella (kneecap) has no direct equivalent in the:
The patella is unique to the lower limb — there's no equivalent bone at the elbow in the upper limb.
Question 8
Which girdle is more firmly attached to the axial skeleton?
The pelvic girdle is firmly fused to the sacrum for stability and weight-bearing. The pectoral girdle is loosely attached instead, trading stability for a wide range of arm motion.
Question 9
The spinal cord passes through which part of a vertebra?
The vertebral foramen is the central opening the spinal cord threads through. The vertebral body is the weight-bearing front portion; the spinous process is a posterior projection for muscle attachment.
Question 10
A distal radius fracture from falling on an outstretched hand affects which skeletal division?
The radius is part of the upper limb, which belongs entirely to the appendicular skeleton. The axial skeleton (skull, vertebral column, thoracic cage) is unaffected by this type of injury.
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Debrief
Week 9 Quick-Reference Recap
One page to glance at before Exam 3 — everything from Chapters 7 and 8, condensed.
Next — Week 10: Articulations (Joints) + Exam 3 Synthesis. You'll learn how all these bones connect at joints, then pull Chapters 7–9 together for Exam 3.