Skeletal System - The Skull Flashcards
Skeletal framework of the head
Skull = cranium = head skeleton
the skulll of vertebrates are composed of these
Main braincase, the cranium (neurocranium) which surrounds and protect the brain
Sense capsules associated in development with the olfactory, auditory and visual sense organs
Numerous components of the visceral skeleton
the skull is composed of three originally independent units:
Neurocranium or primary braincase
Dermatocranium
Splanchnocranium or visceral skeleton
part of the skeleton that is loosely associated in early vertebrates and closely associated in amniotes
skull
Components of the Cranium
Cartilage or endochondral bone
Floor and wall of braincase and sense capsules
Neurocranium
Components of the Cranium
Membrane or dermal bone but never cartilage nor endochondral bone
Superficial covering of the skull (roof and sides of skull and parts of the mandible)
Dermatocranium
Components of the Cranium
Cartilage or endochondral bone
Part of the visceral skeleton (gill arches) associated with the skull
Mostly visceral arches I and II
Splanchnocranium
Components of Splanchnocranium
composed of the embryonic upper jaw cartilage and its replacement bones
Embryonic lower cartilage and its replacement and investing bones
Components of the Cranium
Protects the brain and certain special sense organs
Arises as cartilage
Subsequently partly or wholly replaced by bone except in cartilaginous fishes
Neurocranium
how is the Neurocranium formed
Starts as several independent cartilages that later expand and unite to form a cartilaginous braincase
Embryology process
After the formation of the embryonic brain, the mesenchyme differentiate to form a membranous layer called the membranous cranium
The notochord extends forward beneath the brain, terminating near the infundibulum
The membranous cranium surrounds the anterior portion of the notochord
The parachordal plates are located lateral to the notochord and otic capsules
Prechordal cartilages formed in front of the parachordals
The ventral region of the membranous cranium will become the ______
neurocranium
Neurocranium begins as pair of ______________ cartilages below the brain
parachordal and prechordal cartilages
plates that are located lateral to the notochord and otic capsules
parachordal plates
expand and join along with the notochord to form the basal plate enclosing the tip of the notochord and later becomes the floor beneath the midbrain and the hindbrain
Parachordal cartilages
______________ formed in front of the parachordals
Prechordal cartilages
cartilages expand and join to form an ethmoid plate that later will become the rostrum
Prechordal
contributes to the formation of the internasal septum between the nasal capsules
rostrum
Simultaneou with the formation of cartilages, three pair of capsules are formed from the developing sense organs:
Nasal capsules from the olfactory sense organ
Otic capsules from the auditory sense organ
Optic capsules from the optic sense organ
fuses with olfactory capsules and the basal plate fuses with otic capsules to complete the roof, sides and floor of the brain
ethmoid plate
unite posteriorly leaving a prominent opening in the center, the hypophyseal fenestra, where the pituitary gland lies
prechordals and parachordals
Endochondral ossification occurs more or less simultaneously at 4 regional ossification centers:
Occipital
Sphenoid
Ethmoid
Otic
Cartilage surrounding the foramen magnum can be replaced by as many as 4 bones:
Supraoccipital bone dorsally
Exoccipital bones laterally
Basioccipital bone ventrallly
One or more of the 4 may remain cartilaginous in what modern class of vertebratesn
modern amphibians
Cartilage surrounding the foramen magnum can be replaced by as many as 4 bones and All four bones fuse in mammals to form a single bone called the
occipital bone
Articulation of the neurocranium with the 1st vertebra is via the ________
occipital condyles
what class have a single condyle borne out of the basioccipital bone
Stem amphibians
two classes that have a single condyle
Living reptiles and birds
two classes that have shifted the condyle to the two exoccipitals
Modern amphibians and mammals
what centers Osssifies independently in the synapsid and reptilian lineages
Sphenoid Centers
sphenoid that forms from the cartilage underlying the midbrain and pituitary gland
Basisphenoid
sphenoid that ossifies anterior to the basisphenoid in mammals
Also contributes to the sidewall above the basisphenoid
Presphenoid
sphenoid bone (crocodiles and dinosaurs) forms the lateral ossification of the sphenoid redion
Laterosphenoid
sphenoid bone (archosaurs) forms a separate interorbital septum
Orbitosphenoid
sphenoid bone helps to form the lateral wall in some mammals though it is derived from the palatoquadrate cartilage
Alisphenoid