Comparative Anatomy Chapter 7: The Skeletal System

What is an exoskeleton?

A skeleton formed from or within the integument (skin)

Which layer of the integument gives rise to bone in exoskeletal structures?

The dermis

Which layer of the integument produces keratinized structures of the exoskeleton?

The epidermis

How does the endoskeleton differ from the exoskeleton in origin?

Endoskeleton forms deep within the body from mesoderm or other internal sources, not from the integument.

What structures make up the cranial skeleton?

The skull

What is included in the postcranial skeleton?

All skeletal elements except the skull.

What major components make up the skeletal system?

Mineralized connective tissue (calcified tissue), bone, cartilage, enamel, ligaments, tendons, and bursae

What is calcification in the skeletal system?

Mineralization of connective tissue

What does ossification refer to?

Formation of bone

Which cells produce bone, maintain bone, and break down bone?

Osteoblasts produce bone, osteocytes maintain bone, osteoclasts break down bone

Which cells produce dentin?

Odontoblasts

Which cells produce cartilage?

Chondroblasts

Which cells produce enamel?

Ameloblasts

Which cells produce collagen in connective tissues?

Fibroblasts

What is cartilage?

A firm, flexible connective tissue composed of a matrix containing chondroitin sulfate and collagen or elastic proteins

What are lacunae in cartilage?

Spaces within the matrix that house chondrocytes.

What are the three main types of cartilage?

1. Hyaline cartilage

2. fibrocartilage

3. elastic cartilage.

What are the main characteristics of hyaline cartilage?

Mostly collagen with few collagen fibrils; most widespread type; forms articular surfaces of long bones, rib tips, tracheal rings, nose, and parts of the skull; forms many bones in utero before ossification

Where is fibrocartilage found and what characterizes it?

Found in intervertebral discs, pubic symphysis, and menisci; characterized by abundant collagen fibers for resistance to pressure.

Where is elastic cartilage found and what characterizes it?

Found in the external ear and epiglottis; contains elastic fibers and is flexible and springy.

How is bone classified by appearance?

Cancellous (spongy) bone and compact bone

What characterizes cancellous (spongy) bone?

Porous structure

What characterizes compact bone?

Dense bone (often called cortical bone)

How is bone classified by position?

Cortical bone (outer portion) and medullary bone (lining the core)

How is bone classified based on the presence of cells and blood vessels?

Cellular vs. acellular bone; vascular vs. avascular bone

What is nonlamellar (woven) bone?

Immature bone with a disorderly, irregular arrangement of collagen; first bone formed

What is lamellar bone?

Mature bone with an orderly, regular arrangement of collagen fibers and bone cells; replaces woven bone.

How is bone classified by embryonic development?

Endochondral bone and intramembranous bone

What structural feature characterizes spongy (cancellous) bone?

Trabeculae—interconnecting rods or plates of bone.

What fills the spaces between trabeculae in spongy bone?

Bone marrow and blood vessels.

What membrane covers spongy (cancellous) bone?

Endosteum

What is a lamella in bone tissue?

A layer of bone matrix with closely packed collagen fibers aligned in parallel

What is Haversian bone?

A type of lamellar bone that forms osteons.

What is an osteon?

A series of concentric rings of bone cells and matrix surrounding a central (Haversian) canal

What structures travel through the Haversian (central) canal?

Blood vessels, lymphatic vessels, and nerves

What are lines of arrested growth (LAGs)?

Lines in bone indicating periods where growth stopped or slowed.

What is zonal bone?

Bone that contains lines of arrested growth (LAGs)

What does endochondral bone development mean?

Bone development that occurs within or from cartilage

What happens to cartilage during endochondral bone development?

Cartilage forms first and is later replaced by bone

What is the epiphysis?

The end portion of the long bone

What is the diaphysis?

The shaft of the long bone

What is the metaphysis (epiphyseal plate)?

The growth region between the epiphysis and diaphysis where bone lengthening occurs

What is the periosteum?

The outer connective tissue covering the bone

What is the endosteum?

The inner lining of the bone

What is the medullary cavity?

The central cavity within the diaphysis that contains bone marrow

What is the first step in endochondral bone development?

A cartilage model forms

What occurs during the second step of endochondral ossification?

A bone collar forms on the outside while cartilage inside begins to calcify

What happens when the vascular system invades calcified cartilage?

Blood vessels enter the cartilage, bringing cells that begin bone formation

What marks the formation of the primary ossification center?

Osteoblasts appear in the core of the bone and begin forming bone tissue

What occurs after the primary ossification center forms?

Secondary ossification centers develop, usually in the epiphyses

What is the final stage of endochondral bone development?

The bone matures into adult bone

What characterizes intramembranous bone development?

Bone forms directly from mesenchyme without a cartilage precursor

Why is this process called “intramembranous”?

Bone develops within sheets or membranes of mesenchyme.

What happens first in intramembranous ossification?

Mesenchymal cells condense and become supplied with blood vessels

How does bone matrix initially form in intramembranous development?

Dense bars of bone matrix are deposited on the ground substance as osteoblasts form

How does bone growth continue during intramembranous ossification?

Successive layers of bone are deposited

What type of bone develops through intramembranous ossification?

Dermal bone

What is the cranium?

The skull

What are the three main parts that make up the cranium?

Splanchnocranium, chondrocranium, and dermatocranium.

What is the function of the splanchnocranium (visceral cranium)?

Supports the pharyngeal slits; considered the most ancient skull component

What is the chondrocranium and how is it formed?

Structure that supports the brain; formed from cartilage, endochondral bone, or both.

What is the dermatocranium?

Outer skull casing in advanced vertebrates; formed from dermal bone.

What is the braincase?

Structure that supports the brain; formed from cartilage, endochondral bone, or both

What does the term neurocranium refer to?

the chondrocranium alone, or the chondrocranium plus attached sensory capsules

What is the serial theory?

The theory that the first two pairs of branchial arches turned into jaws

What is the composite theory?

The theory that parts of the first four branchial arches turned into jaws.

What structures arise from the pharyngeal (branchial) arches of the splanchnocranium?

First arch makes the mandibular arch (jaw); second arch makes the hyoid arch; remaining arches makes the branchial (gill) arches.

What is the splanchnocranium (visceral cranium)?

A neural-crest-derived structure that supports gills and respiratory muscles and contributes to jaws and the hyoid apparatus; formed by endochondral ossification.

What typically happens to the chondrocranium during vertebrate development?

It is replaced by ossified bone regions

What is the chondrocranium?

Cartilaginous brain support formed from cartilages beside the notochord that fuse and develop sensory capsules; protects the brain (permanent in elasmobranchs, mostly embryonic in other vertebrates

What is the Splanchnocranium (Visceral Cranium)?

The part of the cranium that form the hyoid apparatus, supports tongue and floor of the mouth styloid, and the three middle ear bones

In mammals, do splanchnocranium contribute to adult

jaws or suspension?

No

What are the functions of the skull?

1. Protection and support

2. Food acquisition and manipulation

3. Cooling of the brain

4. Voice box support

Who uses suspension feeding?

Protochordates

Who uses suction feeding?

Most fishes and aquatic amphibians

Who uses lingual feeding?

Most amphibians and many lizards

Who uses prehension?

Most animals

What is suspension feeding?

Food particles trapped in mucus and transported to the gut

What is suction feeding?

Expansion of the buccal cavity that lowers pressures and pulls in the prey

What is lingual feeding?

Capture of prey using a rapid sticky tongue

What is prehension?

Grasping the prey with jaws

What is mastication?

Chewing

Why is mastication important?

It influenced skull evolution, promoting akinetic skulls, precise tooth occlusion, diphyodont teeth, and strong jaw-closing muscles

What is the secondary palate?

The roof of the mouth

What is the Dermatocranium?

Patchwork of dermal bones that forms the sides and roof of the skull

In amniotes, what does the Dermatocranium form?

The brain case and lower jaw.

Which bones belong to the facial series?

Maxilla, premaxilla, nasal, septomaxilla (sometimes absent).

Which bones belong to the orbital series?

Lacrimal, prefrontal, postfrontal, postorbital, jugal

Which bones belong to the temporal series?

Intertemporal, supratemporal, tabular, squamosal, quadratojugal

Which bones form the vault (brain roofing) series?

Frontal, parietal, postparietal.

Which bones belong to the palatal series (roof of the mouth)?

Vomer, palatine, pterygoid, parasphenoid.

Which bones form the lateral mandibular series?

Dentary (teeth), splenial, angular, surangular

Which bones form the medial mandibular series?

Prearticular, coronoid

In Chondrichthyes, how is the brain case made up?

It is made up of cartilage

In bony fish and tetrapods, how is the brain case?

It is ossified

What is the braincase (neurocranium)?

Part of the skull that is made up of several bones that work together as a box to protect the brain

What is the viscerocranium?

The facial skeleton that makes up the face and jaw

What is the braincase made up of?

Sphenoid bones

What are Emarginations?

partial openings/ notches that change the skull outline.

Vertebrates have what kind of skull?

Kinetic skull