Skeletal System Overview

Skeletal System

• The skeletal system gives vertebrates shape and supports weight.
• It provides a system of levers that, together with muscles, produces movement.
• It protects soft parts, including nerves, blood vessels, and other internal organs.

Exoskeleton

• Formed from or within the integument.
• The dermis gives rise to bone, and the epidermis gives rise to keratin.

Endoskeleton

• Forms deep within the body.
• Derived from mesoderm and other sources.
• Tissues like fibrous connective tissue, bone, and cartilage contribute to the endoskeleton.

Cranial Skeleton

• Includes the skull.
• Composed of splanchnocranium (supports pharyngeal slits), chondrocranium (underlies and supports the brain), and dermatocranium (outer casing of the skull).
• Consists of various components like the oticooccipital unit, the ethmosphenoid unit.

Braincase

• A collective term for the fused components that surround and enclose the brain.
• Consists of dermatocranium, chondrocranium, and splanchnocranium.

Neurocranium

• Equivalent to the chondrocranium.
• Includes sensory capsules (supporting nasal, optic, and otic capsules).

Chondrocranium

• The primitive cartilaginous structure of the fetal skull.
• Encloses the brain and capsules surrounding the sense organs.
• Protects the brain.
• Five main components: sphenoids, mesethmoid, occipitals, optic capsules, and nasal capsules.
• In cartilaginous fishes, it does not ossify.
• In bony fishes, lungfishes, and most ganoids, it retains a prominent cartilaginous structure.
• In most bony vertebrates, the embryonic cartilaginous structure largely converts into replacement bone via endochondral ossification.

Splanchnocranium

• An ancient chordate structure.
• Supports gills and provides attachment sites for respiratory muscles in vertebrates.
• Contributes to jaws and hyoid apparatus in some vertebrates.

Dermatocranium

• Dermal bone derived from the external armor of early fishes.
• Forms the sides and roof of the skull, completing the protection around the brain.
• Provides a bony lining for the roof of the mouth.
• Holds teeth.

Dermal Bone Series

• Facial Series (premaxilla, maxilla, nasals).
• Orbital Series (lacrimal, prefrontal, postfrontal, postorbital, jugal).
• Temporal Series (intertemporal, supratemporal, tabular, squamosal, quadratojugal).
• Vault Series (frontal, parietal, postparietal).
• Palatal Series (vomer, palatine, ectopterygoid, pterygoid, parasphenoid).
• Mandibular Series (dentary, splenials, angular, surangular, prearticular, coronoids).

Jaws

• Formed by a pair of bones.
• Include teeth and allow movement for biting, chewing, and handling food.
• Sharks: Meckel's cartilage.
• Most fish and tetrapods: includes Meckel's cartilage, supported by exoskeletal bone and also supports teeth.
• Mammals: a single dermal bone (dentary).

Cranial Kinesis

• Movement within the skull.
• Allows changes in the size and configuration of the mouth (suction feeding).
• Important for feeding in water.
• Present in many fishes, early tetrapods, and certain reptiles.
• Absence of cranial kinesis in some forms is related to strong jaw mechanics for chewing.

Skull Function and Design

• protects and supports the brain and sensory receptors.
• houses cooling mechanisms, especially in active terrestrial mammals.
• provides sites for muscle attachments.
• Supports sound resonators and deepens calls.

Feeding in Water

• Viscosity presents problems for prey capture.
• Suction feeding uses rapid mouth expansion to create a vacuum, drawing in water and prey.

Suspension Feeding

• A method of capturing and ingesting food particles suspended in water.
• Primarily seen in benthic organisms.

Feeding in Air

• Prehension - process of grasping and securing prey.
• Lingual feeding - use of a specialized tongue for obtaining food.

Swallowing

• The process of moving food from the mouth to the stomach via pharynx and esophagus.

Skeletal System: The Axial Skeleton

• Two structural components: Vertebral column and the notochord.
• The vertebral column is made of repeating units (vertebrae):
• • Vertebrae
• • Ribs
• • Sternum
• • Gastralia.

Vertebrae: Regions of the Vertebral Column

• Specialized regions of the vertebrae:
• cervical region
• thoracic region
• lumbar region
• sacral region
• caudal region
• Structure and function vary among tetrapods.

The Craniovertebral Junction and Neck Vertebrae

• Connections between the skull and the vertebral column at the neck (cervical) region.
• Varies among vertebrate groups.

Ribs

• Support the body, act in breathing, and offer attachment points for muscles.
• Variation exists in their structure and function across different vertebrate groups.

Sternum

• Forms part of the rib cage.
• Serves as an origin for chest muscles and securing ventral tips of true ribs.
• A single bony plate or multiple elements in series (sternal and xiphisternal processes).

Gastralia

• Abdominal ribs.
• Found in certain groups of reptiles.
• Provides support to the abdomen.