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Chapter 8 Part B – Comprehensive Skeleton Notes
Let's learn about the human skeleton! Think of your skeleton as the body's natural framework, giving you shape and allowing you to move. It's made up of several parts:
Bones: The main, hard parts.
Cartilages: Flexible, rubbery tissues found in places like your nose, ears, and joints.
Joints: Where two or more bones meet.
Ligaments: Strong bands that connect bones to other bones.
Your skeletal system makes up about 20\% of your total body weight. It's divided into two main sections:
Axial Skeleton: The central part of your body.
Appendicular Skeleton: Your limbs (arms and legs) and the bones that attach them to your body.
Axial Skeleton
This part has 80 bones and forms the central support structure of your body. It includes the skull, the backbone (vertebral column), and the rib cage (thoracic cage). Its main jobs are:
Forming the main line of your body, from head to tail.
Supporting your head, neck, and torso.
Protecting important organs like your brain, spinal cord, and organs in your chest.
The Skull (22 bones)
Your skull is the most complex bony structure. It's made of two groups of bones:
Cranial Bones (the Cranium) – 8 bones
These bones form a protective helmet around your brain, creating the cranial cavity. They also provide places for your head and neck muscles to attach.
Facial Bones – 14 bones
These bones create your face. They contain openings for your senses like sight, taste, and smell. They also provide passages for air and food, hold your teeth, and allow you to make facial expressions. We'll explore these in more detail in BIO 136.
Sutures & Landmarks (selected)
Sutures are like wiggly seams where the skull bones meet. Key ones include the coronal (across the top/front, like a crown), squamous (on the side, near your temple), and lambdoid (at the back, shaped a bit like the Greek letter lambda) sutures.
The Hyoid Bone (1)
This unique bone is found in the front of your neck, just under your jaw. It'sspecial because it's the only bone in your body that doesn't directly touch or connect to another bone. It's held in place by ligaments and acts as a movable base for your tongue and a place for muscles involved in swallowing and speaking to attach.
Vertebral Column (Spine)
Functions & Generalities
Your spine runs from your skull down to your pelvis. It helps transfer your upper body weight to your lower limbs. It also surrounds and protects your spinal cord (a major part of your nervous system) and provides attachment points for your ribs and many muscles. It's a flexible, curved stack of 26 irregularly shaped bones.
Regional Counts (easy to remember with the “meal-time” mnemonic)
Your spine is divided into five regions, each with a specific number of vertebrae (individual bones):
Cervical – 7 vertebrae (like breakfast at 7 a.m.) – These are in your neck.
Thoracic – 12 vertebrae (like lunch at 12 p.m.) – These are in your upper back, connected to your ribs.
Lumbar – 5 vertebrae (like dinner at 5 p.m.) – These are in your lower back.
Sacrum – 1 bone – This is a single bone formed from 5 vertebrae that have fused together in your lower back.
Coccyx – 1 bone – This is your tailbone, formed from 3 to 5 tiny fused vertebrae.
Intervertebral Discs
Between most of your vertebrae are soft, cushioning pads called intervertebral discs. They act like shock absorbers for your spine.
Nucleus pulposus – This is the inner, jelly-like core that gives the disc its springiness and ability to compress.
Anulus fibrosus – This is the outer ring, made of tough collagen and fibrocartilage, which holds the jelly-like core in place and prevents it from bulging out too much.
Generic Vertebra Anatomy
Most vertebrae have a similar basic structure:
Body (centrum): The large, round front part of the vertebra that carries weight.
Vertebral arch: This forms the back part of the vertebra, made of two pedicles and two laminae. It encloses the vertebral foramen, a large hole.
When all the foramina (holes) of stacked vertebrae line up, they form the vertebral canal, which protects your spinal cord.
Intervertebral foramina: These are openings on the sides of the stacked vertebrae, allowing spinal nerves to exit the spinal cord.
Processes (7 per vertebra)
Each vertebra has 7 bony projections (processes) that are attachment points for muscles and ligaments and help with articulation:
1 spinous process (points straight back, you can feel these along your spine).
2 transverse processes (point out to the sides).
2 superior articular processes (top surfaces, connect to the vertebra above).
2 inferior articular processes (bottom surfaces, connect to the vertebra below).
Regional Traits (Summary of differences)
Even though vertebrae have a similar basic structure, they look and function differently depending on their region:
Cervical vertebrae (neck): They have small, oval bodies and short, often split (bifid) spinous processes (except for C7). A unique feature is the transverse foramina, holes in their side processes, which allow blood vessels to pass through. They allow the greatest amount of movement, including bending forward/backward (flexion & extension), sideways (lateral flexion), and twisting (rotation).
Thoracic vertebrae (mid-back): They have heart-shaped bodies and long, downward-pointing spinous processes. They also have special surfaces called costal facets where the ribs attach. While they allow good rotation, bending forward is limited by the rib cage.
Lumbar vertebrae (lower back): These are the largest vertebrae, with massive, kidney-shaped bodies, as they bear the most weight. They have short, blunt spinous processes. They are very strong for bending forward and backward but prevent significant twisting movements.
Special Cervical Vertebrae
Two cervical vertebrae are especially unique:
Atlas (C1): This is the first vertebra, right under your skull. It doesn't have a body or a spinous process. Instead, it has anterior and posterior arches and side masses. It connects with the base of your skull (occipital condyles) and allows you to nod your head “Yes”.
Axis (C2): This is the second vertebra. It has a distinctive upward projection called the dens (or odontoid process), which is essentially the missing body of the atlas. The dens acts as a pivot point, allowing your head to rotate from side to side to say “No”.
Sacrum & Coccyx
Sacrum: This is a large, triangular bone located at the base of your spine, formed by the fusion of five embryonic vertebrae (S1–S5). It connects to the last lumbar vertebra (L5) at the top, the coccyx at the bottom, and your hip bones on the sides (sacroiliac joints).
Coccyx: This is your tailbone, usually made of four small fused bones. It has very little function in adults.
Thoracic Cage
Your thoracic cage, or rib cage, is a bony enclosure around your chest. It's made of:
Thoracic vertebrae (at the back).
Sternum (breastbone) and costal cartilages (at the front).
Ribs (on the sides).
Its main jobs are to:
Protect the vital organs inside your chest, like your heart and lungs.
Support your shoulder girdles and upper limbs.
Provide attachment points for many muscles of your trunk and shoulders.
Sternum (Breastbone)
Your sternum is a flat bone in the middle of your chest, and it has three parts:
Manubrium: The top part, which connects to your collarbones (clavicles) and the first two pairs of ribs.
Body: The long, central part, which connects to ribs 2 through 7 via their costal cartilages.
Xiphoid process: The small, pointed bottom tip. It's mainly an attachment point for muscles and doesn't fully harden into bone until you're about 40 years old.
Ribs (12 pairs)
You have 12 pairs of ribs. All of them connect to the thoracic vertebrae at your back. Ribs are classified by how they connect to the sternum:
True (vertebrosternal) ribs (pairs 1–7): These ribs connect directly to the sternum with their own costal cartilage.
False (vertebrochondral) ribs (pairs 8–10): These ribs connect to the sternum indirectly. Their costal cartilages join the cartilage of the rib above them, rather than connecting directly to the sternum.
Floating (vertebral) ribs (pairs 11–12): These ribs have no connection to the sternum at all; they only attach to the vertebrae at the back.
Key parts of a rib include the shaft (the main curved part), the head (which connects to the vertebral bodies), the neck, and the tubercle (which connects to the transverse process of the vertebra).
Appendicular Skeleton
This division includes all the bones of your limbs (arms and legs) and the
Let's learn about the human skeleton! Think of your skeleton as the body's natural framework, giving you shape and allowing you to move. It's made up of several parts:
Bones: The main, hard parts.
Cartilages: Flexible, rubbery tissues found in places like your nose, ears, and joints.
Joints: Where two or more bones meet.
Ligaments: Strong bands that connect bones to other bones.
Your skeletal system makes up about 20\% of your total body weight. It's divided into two main sections:
Axial Skeleton: The central part of your body.
Appendicular Skeleton: Your limbs (arms and legs) and the bones that attach them to your body.
Axial Skeleton
This part has 80 bones and forms the central support structure of your body. It includes the skull, the backbone (vertebral column), and the rib cage (thoracic cage). Its main jobs are:
Forming the main line of your body, from head to tail.
Supporting your head, neck, and torso.
Protecting important organs like your brain, spinal cord, and organs in your chest.
The Skull (22 bones)
Your skull is the most complex bony structure. It's made of two groups of bones:
Cranial Bones (the Cranium) – 8 bones
These bones form a protective helmet around your brain, creating the cranial cavity. They also provide places for your head and neck muscles to attach.
Facial Bones – 14 bones
These bones create your face. They contain openings for your senses like sight, taste, and smell. They also provide passages for air and food, hold your teeth, and allow you to make facial expressions. We'll explore these in more detail in BIO 136.
Sutures & Landmarks (selected)
Sutures are like wiggly seams where the skull bones meet. Key ones include the coronal (across the top/front, like a crown), squamous (on the side, near your temple), and lambdoid (at the back, shaped a bit like the Greek letter lambda) sutures.
The Hyoid Bone (1)
This unique bone is found in the front of your neck, just under your jaw. It'sspecial because it's the only bone in your body that doesn't directly touch or connect to another bone. It's held in place by ligaments and acts as a movable base for your tongue and a place for muscles involved in swallowing and speaking to attach.
Vertebral Column (Spine)
Functions & Generalities
Your spine runs from your skull down to your pelvis. It helps transfer your upper body weight to your lower limbs. It also surrounds and protects your spinal cord (a major part of your nervous system) and provides attachment points for your ribs and many muscles. It's a flexible, curved stack of 26 irregularly shaped bones.
Regional Counts (easy to remember with the “meal-time” mnemonic)
Your spine is divided into five regions, each with a specific number of vertebrae (individual bones):
Cervical – 7 vertebrae (like breakfast at 7 a.m.) – These are in your neck.
Thoracic – 12 vertebrae (like lunch at 12 p.m.) – These are in your upper back, connected to your ribs.
Lumbar – 5 vertebrae (like dinner at 5 p.m.) – These are in your lower back.
Sacrum – 1 bone – This is a single bone formed from 5 vertebrae that have fused together in your lower back.
Coccyx – 1 bone – This is your tailbone, formed from 3 to 5 tiny fused vertebrae.
Intervertebral Discs
Between most of your vertebrae are soft, cushioning pads called intervertebral discs. They act like shock absorbers for your spine.
Nucleus pulposus – This is the inner, jelly-like core that gives the disc its springiness and ability to compress.
Anulus fibrosus – This is the outer ring, made of tough collagen and fibrocartilage, which holds the jelly-like core in place and prevents it from bulging out too much.
Generic Vertebra Anatomy
Most vertebrae have a similar basic structure:
Body (centrum): The large, round front part of the vertebra that carries weight.
Vertebral arch: This forms the back part of the vertebra, made of two pedicles and two laminae. It encloses the vertebral foramen, a large hole.
When all the foramina (holes) of stacked vertebrae line up, they form the vertebral canal, which protects your spinal cord.
Intervertebral foramina: These are openings on the sides of the stacked vertebrae, allowing spinal nerves to exit the spinal cord.
Processes (7 per vertebra)
Each vertebra has 7 bony projections (processes) that are attachment points for muscles and ligaments and help with articulation:
1 spinous process (points straight back, you can feel these along your spine).
2 transverse processes (point out to the sides).
2 superior articular processes (top surfaces, connect to the vertebra above).
2 inferior articular processes (bottom surfaces, connect to the vertebra below).
Regional Traits (Summary of differences)
Even though vertebrae have a similar basic structure, they look and function differently depending on their region:
Cervical vertebrae (neck): They have small, oval bodies and short, often split (bifid) spinous processes (except for C7). A unique feature is the transverse foramina, holes in their side processes, which allow blood vessels to pass through. They allow the greatest amount of movement, including bending forward/backward (flexion & extension), sideways (lateral flexion), and twisting (rotation).
Thoracic vertebrae (mid-back): They have heart-shaped bodies and long, downward-pointing spinous processes. They also have special surfaces called costal facets where the ribs attach. While they allow good rotation, bending forward is limited by the rib cage.
Lumbar vertebrae (lower back): These are the largest vertebrae, with massive, kidney-shaped bodies, as they bear the most weight. They have short, blunt spinous processes. They are very strong for bending forward and backward but prevent significant twisting movements.
Special Cervical Vertebrae
Two cervical vertebrae are especially unique:
Atlas (C1): This is the first vertebra, right under your skull. It doesn't have a body or a spinous process. Instead, it has anterior and posterior arches and side masses. It connects with the base of your skull (occipital condyles) and allows you to nod your head “Yes”.
Axis (C2): This is the second vertebra. It has a distinctive upward projection called the dens (or odontoid process), which is essentially the missing body of the atlas. The dens acts as a pivot point, allowing your head to rotate from side to side to say “No”.
Sacrum & Coccyx
Sacrum: This is a large, triangular bone located at the base of your spine, formed by the fusion of five embryonic vertebrae (S1–S5). It connects to the last lumbar vertebra (L5) at the top, the coccyx at the bottom, and your hip bones on the sides (sacroiliac joints).
Coccyx: This is your tailbone, usually made of four small fused bones. It has very little function in adults.
Thoracic Cage
Your thoracic cage, or rib cage, is a bony enclosure around your chest. It's made of:
Thoracic vertebrae (at the back).
Sternum (breastbone) and costal cartilages (at the front).
Ribs (on the sides).
Its main jobs are to:
Protect the vital organs inside your chest, like your heart and lungs.
Support your shoulder girdles and upper limbs.
Provide attachment points for many muscles of your trunk and shoulders.
Sternum (Breastbone)
Your sternum is a flat bone in the middle of your chest, and it has three parts:
Manubrium: The top part, which connects to your collarbones (clavicles) and the first two pairs of ribs.
Body: The long, central part, which connects to ribs 2 through 7 via their costal cartilages.
Xiphoid process: The small, pointed bottom tip. It's mainly an attachment point for muscles and doesn't fully harden into bone until you're about 40 years old.
Ribs (12 pairs)
You have 12 pairs of ribs. All of them connect to the thoracic vertebrae at your back. Ribs are classified by how they connect to the sternum:
True (vertebrosternal) ribs (pairs 1–7): These ribs connect directly to the sternum with their own costal cartilage.
False (vertebrochondral) ribs (pairs 8–10): These ribs connect to the sternum indirectly. Their costal cartilages join the cartilage of the rib above them, rather than connecting directly to the sternum.
Floating (vertebral) ribs (pairs 11–12): These ribs have no connection to the sternum at all; they only attach to the vertebrae at the back.
Key parts of a rib include the shaft (the main curved part), the head (which connects to the vertebral bodies), the neck, and the tubercle (which connects to the transverse process of the vertebra).
Appendicular Skeleton
This division includes all the bones of your limbs (arms and legs) and the girdles that attach them to the axial skeleton.
Pectoral Girdle
Scapula (Shoulder Blade)
Medial (Vertebral) Border: The medial border of the scapula runs parallel to the vertebral column.
Lateral (Axillary) Border: The lateral border of the scapula is located closer to the armpit (axilla).
Upper Limbs
Humerus (Upper Arm Bone)
On the distal end of the humerus, the capitulum is a lateral rounded projection that articulates with the head of the radius.
The trochlea is a medial spool-shaped projection that articulates with the trochlear notch of the ulna.
Carpals (Wrist Bones)
You have eight small carpal bones in each wrist, arranged in two rows of four:
Proximal Row (from radial to ulnar side): Scaphoid, Lunate, Triquetrum, Pisiform.
Distal Row (from radial to ulnar side): Trapezium, Trapezoid, Capitate, Hamate.
Mnemonic to remember carpal bones: "She Looks Too Pretty, Try Taking Candy Home."
Scaphoid, Lunate, Triquetrum, Pisiform
Trapezium, Trapezoid, Capitate, Hamate
Pelvic Girdle
Hip Bone (Coxal Bone)
The large, irregular hip bone is formed by the fusion of three separate bones:
Ilium: The large, flaring superior portion.
Ischium: The inferior and posterior portion (often referred to as the "sit bone").
Pubis: The anterior and inferior portion that joins with the other pubic bone at the pubic symphysis.
Male vs. Female Pelvis
The pelvis exhibits significant sexual dimorphism due to its adaptation for childbirth in females.
Female Pelvis:
Generally lighter, wider, and shallower.
Pelvic Inlet (Brim): Wider and more oval/rounded shape.
Pubic Arch (Subpubic Angle): Wider, typically . >90^\circ
Sacrum: Wider and shorter, less curved anteriorly.
Coccyx: More movable and curved posteriorly.
Ischial Spines/Tuberosities: Farther apart.
Male Pelvis:
Generally heavier, narrower, and deeper.
Pelvic Inlet (Brim): Narrower and heart-shaped.
Pubic Arch (Subpubic Angle): Narrower, typically . <90^\circ
Sacrum: Narrower and longer, more curved anteriorly.
Coccyx: Less movable and curved anteriorly.
Ischial Spines/Tuberosities: Closer together.
Lower Limbs
Arches of the Foot
The foot is designed with three arches formed by the arrangement of its bones and supported by ligaments and tendons. These arches are crucial for absorbing shock, distributing body weight, and providing leverage for propulsion during walking and running.
Medial Longitudinal Arch: This is the higher and more prominent arch. It extends from the calcaneus (heel bone) through the talus, navicular, three cuneiforms, and the heads of the first three metatarsals.
Lateral Longitudinal Arch: This arch is flatter and less prominent. It extends from the calcaneus through the cuboid to the heads of the fourth and fifth metatarsals.
Transverse Arch: This arch runs across the midfoot. It is formed by the cuboid, the three cuneiform bones, and the bases of the five metatarsals.