BIO 85 The Skull - Skeletal Summary PDF

BIO 85 THE SKULL Asst. Prof. Leandro Cabrera The Skeletal System Skeleton – gives body shape, supports weight, produces movement, protects soft parts. Endoskeleton – deep within the PROTECTIVE AND SUPPORTIVE SYSTEM body from mesoderm and other sources, and NOT directly from the i...

BIO 85 THE SKULL Asst. Prof. Leandro Cabrera The Skeletal System Skeleton – gives body shape, supports weight, produces movement, protects soft parts. Endoskeleton – deep within the PROTECTIVE AND SUPPORTIVE SYSTEM body from mesoderm and other sources, and NOT directly from the integument. Exoskeleton – within the integument; dermis giving rise to bone and epidermis to keratin. BASIS OF ITS POSITION  THE SKULL The Cranium Chondrocranium – Includes the box that encloses the brain and capsules surrounding the sensory organs; supports and protects the brain. Splanchnocranium (visceral cranium) – first arose; support pharyngeal slits in protochordates. Dermatocranium – composed of dermal bones; outer casing of the skull The Chondrocranium In most vertebrates it is an embryonic structure, a scaffold for the developing brain and support for sensory capsules Neural crest cells – contribute to the nasal capsule, EMBRYOLOGY OF CHONDROCRANIUM trabeculae (only the anterior part), and part of the otic capsule Mesenchyme – from mesoderm; a connective Embryonic cells has two types that tissue; gives rise to most of body’s connective tissues differentiate to form the chondrocranium: (from bones to cartilage of the lymphatic and circulatory systems) The Splanchnocranium The splanchnocranium is an ancient chordate structure. In fact, the forerunner of splanchnocranium is associated with filter feeding surfaces EMBRYOLOGY OF SPLANCHNOCRANIUM Arises from neural crest cells, not from lateral plate mesoderm like the smooth muscle in the walls of the digestive tract. In vertebrates, cells of the neural crest depart from the sides of the neural tube and move into the walls of the pharynx between successive pharyngeal slits to differentiate into the respective pharyngeal arches. Pharyngeal arches of aquatic vertebrates usually are associated with their respiratory gill system. Because of this association, they are referred to as branchial arches, or gill arches.  The Splanchnocranium Jaws appear first in acanthodian and placoderm fishes that used them as ORIGIN OF THE JAWS food traps to grab whole prey or take bites from large prey. Jaws arose from one of the anterior pair of gill arches: The embryology of sharks suggests that jaws and branchial arches develop similarly in series, and both arise from neural crest Two theories explaining the evolution of jaws: ❑ SERIAL THEORY – The first or even the second brachial arch gave rise exclusively to the mandibular arch, to the hyoid bone, and the rest of the arches to the brachial arch of the gnathostomes. ❑ COMPOSITE THEORY - ten branchial arches were present in primitive species, the first and following arches being named terminal, premandibular, mandibular, hyoid, and six branchial arches. Accordingly, the mandibular arch of gnathostomes is formed by fusion of parts of the premandibular arch and parts of the mandibular arch of jawless ancestors. The Splanchnocranium TYPES OF JAWS ATTACHMENTS Because of the mandible’s prominence, evolution of the jaws is often traced through how the mandible is attached to the skull Agnathans represent the earliest paleostylic stage in which none of the arches attaches directly to the skull. In placoderms and acanthodians, the mandibular arch is suspended from the skull by itself without help from the hyoid arch (euautostylic) In early sharks, some osteichthyans, and rhipistians, jaw suspension is amphistylic; the jaws are attached to the braincase through two primary articulations, anteriorly by a ligament connecting the palatoquadrate to the skull and posteriorly by the hyomandibula. In most modern bony fishes, jaw suspension is hyostylic because the mandibular arch is attached to the braincase primarily through the hyomandibula The Splanchnocranium TYPES OF JAWS ATTACHMENTS Because of the mandible’s prominence, evolution of the jaws is often traced through how the mandible is attached to the skull In most amphibians, reptiles, and birds, jaw suspension is metautostylic. Jaws are attached to the braincase directly through the quadrate, a bone formed in the posterior part of the palatoquadrate In mammals, jaw suspension is craniostylic. The entire upper jaw is incorporated into the braincase, but the lower jaw is suspended from the dermal squamosal bone of the braincase. The lower jaw of mammals consists entirely of the dentary bone, which is also of dermal origin. The Dermatocranium Phylogenetically, these bones arise from the bony armor of the integument of early fishes and sink inward to become applied to the chondrocranium and splachnocranium PARTS OF THE DERMATOCRANIUM The Dermatocranium The facial series encircles the external naris and collectively forms the snout. The maxilla and premaxilla define the margins of the snout and usually bear teeth. The nasal lies medial to the naris. The dermal bones in orbital series encircle the eye to define the orbit superficially. The lacrimal takes its name from the nasolacrimal (tear) duct of tetrapods that passes through or near this bone. The prefrontal, postfrontal, and postorbital continue the ring of bones above and behind the orbit. The temporal series lies behind the orbit completing the posterior wall of the braincase. In many primitive tetrapods, this series is indented posteriorly by a temporal notch The vault series, runs across the top of the skull and covers the brain beneath. This includes the frontal anteriorly and the postparietal (interparietal) posteriorly. Between them is the large parietal, occupying the center of the roof and defining the small parietal foramen if it is present. Palatal Series The dermal bones of the primary palate cover much of the roof of the mouth Mandibular Series bones encased in dermal bones. Laterally, the wall of this series includes the tooth- bearing dentary and one or two splenials, the angular at the posterior corner of the mandible and the surangular above. Overview of Skull Morphology: braincase In chondrichthyan fishes, the braincase is an elaborate cartilaginous case around the brain. The dermatocranium is absent, reflecting the elimination of almost all bone from the skeleton In most bony fishes and tetrapods, the braincase is extensively ossified with contributions from several sources. The endoskeletal platform is a platform assembled from a series of sphenoid bones. The occipital bones, which apparently are derived from anterior vertebrae, form the end of this sphenoid platform. In most vertebrates, these endoskeletal elements, along with the brain and sensory organs they support, are enclosed by the exoskeletal elements, derivatives of the dermis, to complete the braincase. Overview of Skull Morphology: jaws The palatoquadrate is fully functional in the jaws of chondrichthyans and primitive fishes, but in bony fishes and tetrapods, the palatoquadrate usually makes limited contributions to the skull through its two derivatives: the epipterygoid, which fuses to the neurocranium, and the quadrate, which suspends the lower jaw except in mammals. In most fishes and tetrapods, Meckel’s cartilage persists but is enclosed in exoskeletal bone of the dermatocranium, which also supports teeth. Meckel’s cartilage, encased in dermal bone, usually remains unossified, except in some tetrapods where its anterior end ossifies as the mental bone. In mammals, the lower jaw consists of a single bone, the dermal dentary. The anterior tooth-bearing part of the dentary is its ramus. Jaw-closing muscles are inserted on the coronoid process, an upward extension of the dentary. Overview of Skull Morphology: hyoid apparatus Elements of the hyoid apparatus are derived from the ventral parts of the hyoid arch and from parts of the first few branchial arches. Typically, the hyoid apparatus includes a main body, the corpus, and extensions, the cornua. In many mammals, including humans, the distal end of the hyoid horn fuses with the otic region of the braincase to form the styloid process. CRANIAL KINESIS MOVEMENT BETWEEN THE UPPER JAW AND THE BRAINCASE AND THE JOINTS BETWEEN THEM. ALLOWS TOOTH-BEARING BONES TO MOVE INTO STRATEGIC POSITIONS DURING RAPID FEEDING. THE WIDESPREAD PRESENCE OF CRANIAL KINESIS AMONG VERTEBRATES , BUT ITS ESSENTIAL ABSENCE AMONG MAMMALS, SEEMS TO CREATE A PROBLEM FOR HUMANS  KINESIS vs AKINESIS Cranial kinesis provides a way to change the size and configuration of the mouth rapidly. Teleost fishes, for instance, swing their anterior tooth-bearing bones forward at the last moment to reach out quickly at the intended prey The venomous viper erects the maxillary bone bearing the fang and swings it from a folded position along its upper lip to the front of the mouth, where it can more easily deliver venom into prey. In many fishes and reptiles with kinetic skulls, teeth on the upper jaw can be reoriented with respect to the prey in order to assume a more favorable position during prey capture or to align crushing surfaces better during swallowing  KINESIS vs AKINESIS Loss of kinesis in mammals leaves us with an akinetic skull. Juvenile and adult can chew firmly with sets of specialized teeth that work accurately from a secure akinetic skull.  The skull is a composite structure derived from the Phylogeny of the Skull splanchnocranium, dermatocranium, and chondrocranium. Each component of the skull comes from a separate phylogenetic source.  The skull is a composite structure derived from the Phylogeny of the Skull splanchnocranium, dermatocranium, and chondrocranium. Each component of the skull comes from a separate phylogenetic source. https://yaybiotic.tumblr.com/post/62120883330/placoderms-are-an-extinct-class-of-fishes-and  The skull is a composite structure derived from the Phylogeny of the Skull splanchnocranium, dermatocranium, and chondrocranium. Each component of the skull comes from a separate phylogenetic source.  The skull is a composite structure derived from the Phylogeny of the Skull splanchnocranium, dermatocranium, and chondrocranium. Each component of the skull comes from a separate phylogenetic source.  The skull is a composite structure derived from the Phylogeny of the Skull splanchnocranium, dermatocranium, and chondrocranium. Each component of the skull comes from a separate phylogenetic source.  The skull is a composite structure derived from the splanchnocranium, dermatocranium, and chondrocranium. Phylogeny of the Skull Each component of the skull comes from a separate phylogenetic source. OVERVIEW OF SKULL FUNCTION AND DESIGN SKULL 1. A multipurpose tool that protects and supports the brain and its sensory receptors. 2. May house cooling equipment to cool the brain. 3. Support the voice box that occasionally serves as a sound resonator. 4. Primarily functions as a part of the feeding system. OVERVIEW OF SKULL FUNCTION AND DESIGN Feeding, proceeds two steps: Food capture and Swallowing 1. What are the different feeding mechanism and how is the skull design important in these mechanisms? 2. Discuss the pros and cons of the different feeding mechanisms in vertebrates as discussed in chapter seven in Kardong. 3. Which skull design is suitable for aquatic habitat and terrestrial habitat? Explain your answer. THE AXIAL SKELETON BASIC COMPONENTS →NOTOCHORD AND VERTBRAL COLUMN →VERTEBRAE →STERNUM →RIBS →GASTRALIA BASIC COMPONENTS Vertebrae → protect spinal cord and aorta → sites for musculature → in tetrapods, roles include suspension of the body to address life on land BASIC COMPONENTS Dorsal and Ventral arches → dorsal arches protect the neural tube → ventral arches enclose the blood vessel *evolution of the basic elements of a vertebra arose from the formation of intercentrum and pleurocentrum. BASIC COMPONENTS Formation of the regions in the vertebral column. → Enlargement of vertebral segments → Vertebral components displace the notochord as the mechanical axis of the body → Vertebral segments composing the axial column tend to become regionally differentiated within the vertebral column  BASIC COMPONENTS Regions of the vertebral column: CENTRA Among vertebrates there is great variation in the structure of the centra, in the extent of ossification, and in the degree to which centra supplement or replace the notochord as mechanical elements of the axial column. FIGURE 8.3 General vertebral types. (a) An aspidospondyl vertebra is characterized by ossified elements that remain separate. The specific type illustrated is a rhachitomous vertebra that has three discrete parts:pleurocentrum,intercentrum, and neural spine. (b) A holospondyl vertebra is characterized by fused construction of all components. Each centrum constitutes the body of the vertebra. In some vertebrates, centra may be absent (aspondyly). Others exhibit one (monospondyly) or two (diplospondyly) centra per segment. CENTRA The centra are linked successively into a chain of vertebrae, the axial column. The shapes of surfaces at the articular ends of the centra affect the properties of the vertebral column and the way in which forces are distributed between vertebrae. FIGURE 8.4 General centra shapes. The shapes of articulating centra ends, as viewed in sagittal section, define specific anatomical types : (a) acoelous , both ends are flat; (b) amphicoelous , both ends are concave; (c) procoelous , anterior end is concave; (d) opisthocoelous , posterior end is concave; (e) heterocoelous , saddlelike articulating ends. Anterior to the right. CENTRA Intervertebral disk - in the adult is a pad of fibrocartilage whose gel-like core, the nucleus pulposus, is derived from the embryonic notochord. By this strict definition, intervertebral disks are found only in mammals , in whom they reside between successive surfaces of adjacent centra. In other groups, the pad between centra is called an intervertebral cartilage or body. Intervertebral ligament - joining the rims of the adjacent centra, which is important in controlling stiffness of the vertebral column when it flexes. RIBS Ribs - provide sites for secure muscle attachment, help suspend the body, form a protective case around viscera (rib cage), and sometimes serve as accessory breathing device. Embryologically, ribs preform in cartilage within myosepta (myocommata), that is, within the dorsoventral sheets of connective tissue that partition successive blocks of segmental body musculature (figure 8.6a–c).  RIBS Dorsal ribs form at the intersection of each myoseptum with the horizontal septum (horizontal skeletogenous FISHES septum), a longitudinal sheet of connective tissue. Ventral ribs form at points where the myosepta meet the walls of the coelomic cavity. TETRAPODS Ventral rib head , or capitulum , articulates with the parapophysis , a ventral process on the intercentrum. Dorsal head, or tuberculum, articulates with the diapophysis, a process on the neural arch. Ribs function in locomotion in tetrapods, they become an increasingly important part of the respiratory system to move air through the lungs. RIBS Intercentrum is lost or incorporated into other elements, so the capitulum must shift its articulation to the pleurocentrum (in most reptiles and birds) or between centra (in mammals). AMNIOTES True ribs - ribs that meet ventrally with the sternum. False ribs - articulate with each other but not with the sternum. Floating ribs - false ribs articulating with nothing ventrally.  Consists of ribs and sternal elements that embrace the viscera. Size and RIB CAGE shape acts to compress or expand the lungs, that happens when we breathe. it offers a site of origin for chest muscles STERNUM it secured the ventral tips of true ribs to complete the protective chondrified rib cage may consist of a single bony plate or several elements in series Tetrapods - it is not a phylogenetic derivative of either its ribs or the pectoral girdle. rather, it has arisen independently several times within the field of midventral of connective tissue Urodeles - sternum is a single midventral sternal plate that continues along to its anterior and next to the procoracoid plate, the shoulder girdle. Anurans - its sternum has a single element, the xiphisternum, tipped with the xiphoid cartilage, which lies posterior or below the pectoral girdle. - In some anurans, there is also a second element, the omosternum with the episternal cartilage, that lies in front of the girdle. Reptiles - absent most of the reptiles, but present in other reptiles - Sternum of reptiles allows stability on weight bearing girdle element during locomotion. STERNUM Birds - their flight muscles arise from a large sternum carries a prominent ventral keel called the carina, which provides additional surface for muscle attachment. Mammals - sternum consists of a chain of chondrified elements, the sternabrae. The first and last are chondrified, the manubrium and xiphisternum. GASTRALIA - Posterior to the sternum in some vertebrates is a separately derived set of skeletal elements. - Gastralia are dermal and restricted to the sides of the ventral body wall between sternum and pelvis and do not articulate with the vertebrae. - They are common in some lizards, crocodiles, and Sphenodon , serving as an accessory skeletal system that provides sites for muscle attachment and support for the abdomen. Ventral dermal scales in the abdominal region of labyrinthodonts preceded the gastralia functionally and perhaps gave rise to them anatomically. These are probably related to the ventral scales of rhipidistian ancestors. In birds and mammals - ventral bones are absent VERTEBRATE PHYLOGENY Tetrapods - In early tetrapods, the vertebrate transition to land brought considerable changes in the selection pressures acting on design. As animals evolved from water to air, their bodies went from a buoyant support design to a design in which bodies were suspended between limbs. - Modern amphibians also have a vertebral column composed of single, solid vertebrae at each segment, suggesting that they might have evolved from these early lepospondyls. - Other changes in the axial skeleton, related to extended exploitation of land, are evident for the first time in labyrinthodonts as well. Connection between the pectoral girdle and back of the skull was lost. This occurred in both Acanthostega and Ichthyostega. VERTEBRATE PHYLOGENY Amniotes phylogenetically receive their vertebrae from the anthracosaur line, so their major centrum is a pleurocentrum, and the small centrum is an intercentrum. In many reptiles and birds and in all mammals, the intercentrum is usually lost to the vertebral column as a bony contribution, being remembered only by the rib’s capitulum that still articulates between vertebrae where the intercentrum would occur. In some amniotes, the intercentrum contributes to parts of the cervical vertebrae. Turtles are unique in that the appendicular skeleton lies within the rib cage rather than on the outside as in all other vertebrates. In amniotes, the head rotates primarily on two anterior cervical vertebrae specialized to the function. The first cervical vertebra is the atlas, the second, the axis. Vertical (nodding) and horizontal (tilting) movements of the head are largely limited to the skull-atlas joint, whereas twisting movements occur largely within the atlantoaxial joint. This divides the labor between two joints yet maintains bony strength in the neck. FORM AND FUNCTION Most phylogenetic changes in the form of the vertebral column address new functions. Transition from water to land was one significant change in vertebrate lifestyle, and it was accompanied by considerable change in the mechanical demands experienced by the axial skeleton. To understand these mechanical forces and their impact on design, we should first compare the general problems faced by aquatic and terrestrial vertebrates. FORM AND FUNCTION The bones resist compression The muscles and ligaments resist tensile forces. muscles and ligaments hold the vertebral column in arches.  Not all vertebrae are morphologically alike even within the same VERTEBRATE DESIGN vertebral column. Differences in design reflect different mechanical demands within parts of the column as well. Direction of the Neural Spine - The angle that the neural spine makes with its centrum often varies from vertebra to vertebra. - Local mechanical forces on the spine arise largely from contraction of the axial musculature. Height of the Neural Spine - Neural spines are levers that transmit the force of muscle contraction to centra - Force is proportional to the physiological cross section of the muscle and to its lever arm, its perpendicular distance to the centrum. - Increasing spine length increases the lever arm from centrum to line of muscle action, and thus effectively increases the mechanical advantage of the muscle. VERTEBRATE DESIGN (a) Skeleton of a pelycosaur , with most of the neural spines of similar height and orientation. (b) Skeleton of a bison , illustrating the tall neural spines in the shoulder. Through ligaments to the skull and cervical vertebrae, these neural spines help support the weight of the heavy head. VERTEBRATE DESIGN Birds are an interesting example, exhibiting a close match of form and function within the vertebral column. Cervical vertebrae are flexibly articulated to give the head great freedom of movement and reach when a bird preens its feathers or probes for food. On the other hand, most of the vertebrae in the middle and posterior part of the column are fused to each other and to the pelvic girdle.This brings rigidity to the vertebral column and establishes a firm and stable axis for control while a bird is in flight. VERTEBRATE DESIGN - OVERVIEW - consist of the notochord and vertebral column. - contributes with musculature, to bending of the body, storing elastic energy, and transmitting useful forces for locomotion generated by appendages (fins or limbs) or by the tail (aquatic) - also holds the position of the body steady against gravity. Vertebral Column Fluid Environment - Whether in cartilaginous or bony fishes, it is made up of - the axial column serves primarily as a chains of articulated vertebrae compression girder, resisting telescoping of the - In a vertebral column, it has an individual vertebra that is body during locomotion and translating axial composed of a centrum, neural muscle forces into lateral swimming arch, spine, even ribs (articulated processes), and undulations. intervertebral disks or bodies, which - These same lateral undulations of fishes are are found in between vertebrae. carried into early tetrapods on land as the early basis of terrestrial locomotion. Intervertebral disks Terrestrial Environment - are composed of fibrous connective tissue and fluid, and - The axial column assumes the additional lie between successive function of suspending the weight of the body, vertebrae. without the aid of aquatic buoyancy, as it is - are made up of various types of collagen that are carried over the surface of the land. arranged in such a way as to resist tension and shear forces.  VERTEBRATE DESIGN - OVERVIEW Design - The design of tetrapod vertebral column is often compared to human engineered structures such as bridges, whereby weight is cantilevered or suspended about or Vertebral Column between supportive columns (limbs). - form and function of the vertebral column are - Torque becomes a feature of quadrupedal locomotion, related directly to the static and dynamic favoring the appearance in demands placed upon it. tetrapods of anti-twist features of the vertebrae, such as - regionalized, reflecting functional demands the zygapophyses. - related to the general environments in which - The height and direction of neural spines reflect their role it serves—aquatic or terrestrial—and the as levers, delivering forces to type of locomotion in which the vertebral the vertebral centra and thereby moving or stabilizing the column is involved. vertebral column APPENDICULAR SKELETON  APPENDICULAR SKELETON Fins dermal fin rays joined together with a membranous or webbed film Pterygiophores (enlarged basals and slender radials) APPENDICULAR SKELETON Limbs (chiridium) muscular appendages with well-defined joints that carry digits (toes and fingers) Three regions: ○ Autopodium - wrists, ankles, digits ○ Zeugopodium - ulna and radius of forearm & tibia and fibula of shank ○ Stylopodium - humerus of upper arm & femur of thigh https Embryonic Development of Tetrapod Limbs Appendicular skeleton of all tetrapod embryos follow the same pattern as it develops Modifications of the Appendicular System from Fishes to Mammals FISHES Had caudal, anal, and dorsal fins but were unpaired medial fins Lacked pelvic fins and even rudimentary pectoral fins Ostracoderms They are known to be bottom feeders due to their heavy bony armor surface, absence or slight development of pectoral fins, small body musculature. Placoderms Some placoderms like have pectoral fins as a specialized spine. Chondrichthyes The early sharks possessed locomotion stabilization through pectoral and pelvic fins. Their girdles were single and of enlarged basal elements. They have three enlarged pterygiophores at the base of the pectoral fin  Modifications of the Appendicular System from Fishes to Mammals Actinopterygians Pectoral girdles that are partly endochondral but mostly dermal. Its dermal shoulder girdle is well-established, forming a u-shaped collar bone. Cleithrum is the largest element present wherein scapulocoracoid usually resides and meets with the clavicle. Sarcopterygians Form a fleshy base of dermal fins. Their pectoral and pelvic appendages supporting dermal finds and possess bones above wrist or ankle homologous with the tetrapod limbs.  Modifications of the Appendicular System from Fishes to Mammals Tiktaalik One of the first tetrapods to quickly display changes in their appendicular skeletons in exploitation of the terrestrial environment. They lost the pectoral girdle attachment to the skull, this resulted to allow an increased cranial mobility and reduce jarring of the head. Their girdles and limbs became more strong, robust, and completely ossified Ichthyostega One of the earliest tetrapods. The pelvic girdle is composed of a single bone with three parts: pubis, ischium, and ilium. Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Modifications of the Appendicular System from Fishes to Mammals Evolution of the Appendicular System Evolution of the Appendicular System Evolution of the Appendicular System FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION FORM AND FUNCTION