Principles of Human Anatomy ANAT 3651 Lecture Notes (PDF) 2024

Principles of Human Anatomy ANAT 3651 Lecture notes: Axial Skeleton Objectives: 1. Name and describe the bones of the skull 2. Identify specific features of skull bones 3. Describe the location of paranasal sinuses and the relationship to the nasal cavity 4. Understand the anatomy of the temporomand...

Principles of Human Anatomy ANAT 3651 Lecture notes: Axial Skeleton Objectives: 1. Name and describe the bones of the skull 2. Identify specific features of skull bones 3. Describe the location of paranasal sinuses and the relationship to the nasal cavity 4. Understand the anatomy of the temporomandibular joint 5. Understand the general structure and regions of the vertebral column 6. Describe a typical vertebra and the unique features for each vertebral region 7. Identify features of the ribs and sternum 8. Understand how ribs articulate with vertebrae 9. Identify muscles attaching to the axial skeleton with their origins, insertions, and movements ______________________________________________________________________ The Skull The skull is made up of 8 neurocranial bones that house the brain and 14 facial bones. Some of these bones are paired meaning there is a left and right version of the bone, whereas others are unpaired meaning there is only one. 8 cranial bones: Unpaired- frontal, occipital, sphenoid, ethmoid Paired- parietal and temporal 14 facial bones: Unpaired- mandible and vomer Paired- maxilla, zygomatic, nasal, lacrimal, palatine, inferior nasal concha The following is a list of the bones and their features that you should be familiar with. Use the unlabeled images on the Canvas site to practice identifying these bones and features. Cranial bones & features Frontal bone o Supraorbital foramen- passageway for nerves and vessels above the orbit Parietal bone Temporal bone Axial Skeleton 1 o Squamous portion- flat part of the temporal bone along the side of the cranium o Petrous portion- portion of the temporal bone that forms part of the cranial base and holds the inner and middle ear structures o Mastoid process- bony projection for attachment of muscles o Styloid process- thin bony projection for attachment of muscles o External acoustic (auditory) meatus- canal through temporal bone for vibrations in air to travel to contact tympanic membrane (ear drum) o Mandibular fossa- depression in bone, articulation site for mandibular condyle to form the temporomandibular joint Occipital bone o Foramen magnum- large opening in the base of the skull for the passage of the spinal cord o Occipital condyles- smooth surfaces for articulation with first cervical vertebrae (atlas) Sphenoid bone o Greater wing- larger lateral projections of the sphenoid bone o Lesser wing- flat, superior portions of the sphenoid bone o Sella turcica- means “Turkish saddle”. Saddle-shaped depression where the pituitary gland sits o Pterygoid process- inferior projection of 2 plates from the bottom of the sphenoid bone Ethmoid bone o Crista galli- superior projection into cranial cavity o Perpendicular plate- inferior projection that forms the superior part of the nasal septum Sutures o Coronal suture- between parietal and frontal bones o Sagittal suture- between left and right parietal bones o Lambdoid suture- between parietal and occipital bones o Squamosal suture- between parietal and temporal bones Fontanelles- soft spots of an infants skull where bones have not yet fused together. They allow for more skull growth during infancy and flexibility during birth Facial bones & features Vomer- vertical plate that forms the inferior part of the nasal septum Nasal septum- the nasal septum divides the left and right spaces of the nasal cavity. It is formed by the perpendicular plate of the ethmoid bone and vomer. Maxilla o Infraorbital foramen- opening below the orbit for nerves and blood vessels to pass Axial Skeleton 2 Palatine bones- these bones with the maxilla form the hard palate. Failure of the left and right palatine or maxillae to fuse together results in a cleft lip and/or palate Zygomatic bone o Zygomatic arch- projections from the zygomatic and temporal bones articulate to form the zygomatic arch Nasal bones- form the bridge of the nose Lacrimal bones o Nasolacrimal duct- passageway from the lacrimal bone (orbit) to the nasal cavity for the drainage of tears Mandible o Ramus- vertical portion of the mandible o Corpus (body)- horizontal part of the mandible that holds the teeth o Mandibular condyle- posterior projection from the ramus that articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint o Coronoid process- anterior projection from the ramus o Mental foramen- opening below the teeth near the chin for nerves and blood vessels to pass Paranasal sinuses- spaces within bones that surround the nasal cavity, produce mucus that drains into the nasal cavity o o o o Frontal sinus- within frontal bone Maxillary sinus- within maxillae Sphenoid sinus- within sphenoid bone Ethmoid sinus- within ethmoid bone (sometimes called ethmoid air cells) Temporomandibular joint The temporomandibular joint (or TMJ) is formed by the mandibular fossa of the temporal bone and mandibular condyle of the mandible. An articular disc of fibrocartilage sits between the two bones. To open the mouth, rotation of the mandible occurs first followed by anterior gliding of the mandible. Opening the mouth too wide can result in a dislocation where the condyle is stuck outside of the mandibular fossa. Axial Skeleton 3 Accessory Bones of the Skull Auditory ossicles- series of 3 tiny bones within the temporal bone that attach to the tympanic membrane (ear drum) to transmit sound vibrations to the inner ear (cochlea) o Malleus o Incus o Stapes Hyoid- bone that sits high in the neck, below the mandible. Does not articulate with any other bone but is an important bone for neck muscles to attach Vertebral Column The vertebral column is an S-shaped structure comprised of many individual vertebrae stacked on top of each other that can be grouped into regions. From superior to inferior, the regions are: Cervical- 7 small vertebrae found in the neck Thoracic- 12 vertebrae in the thorax that articulate with ribs Lumbar- 5 large vertebrae of the lower back Sacrum- 5 vertebrae that have fused together to form one bone, forms part of the pelvis Coccyx- 4 very small vertebrae that have fused to form one bone, the vestigial tail The vertebral column is S-shaped in humans in order to support our body weight as bipedal creatures. This is also why the vertebrae near the bottom (lumbar & sacrum) are larger and the ones at the top (cervical) are smaller. Other animals (monkeys, apes, dogs, cats, etc.) have C-shaped vertebral columns because they carry their bodies horizontally. Axial Skeleton 4 A typical vertebrae has the following features: Body- main weight bearing portion Vertebral (neural) arch- arch of bone from the body, formed by the pedicles and laminae Pedicle- section between the body and transverse process Lamina- section between the transverse process and spinous process Transverse processes- lateral projections from the vertebral arch Spinous process- posterior projection from the vertebral arch Vertebral foramen- hole in the vertebrae for the passage of the spinal cord Articular processes- projections to articulate with adjacent vertebrae Vertebral bodies are stacked on top of each other. Discs of fibrocartilage (intervertebral discs) are located between vertebral bodies. Intervertebral discs have a gel-like internal substance that can protrude outside of the disc. This is called a slipped disc which can pinch nerves in the surrounding area. When vertebrae are stacked, openings called intervertebral foramina are formed that allow for spinal nerves to leave the spinal cord. Cervical Vertebrae Cervical vertebrae have some unique features not found in other vertebrae: Bifid spinous process- the spinous process splits into 2 projections Transverse foramina- holes within the transverse processes The 2 superior-most vertebrae are special. C1 (atlas)- Articulates with the occipital condyles of the skull. Does not have a body. Has a posterior tubercle rather than a spinous process. C2 (axis)- has a superior projection called the dens (or odontoid process) that articulates with C1 Atlantoaxial joint- pivot joint between the atlas and axis that allows for rotation of the head (shaking your head “no”) Axial Skeleton 5 Thoracic Vertebrae The 12 thoracic vertebrae have a unique feature called demifacets. Demifacets are small articular surfaces on the vertebral bodies for the articulation with ribs. Lumbar Vertebrae The 5 lumbar vertebrae have large vertebral bodies to support the most body weight and have short, blunt spinous processes. Spinal Curvatures Scoliosis- abnormal lateral curvature of the spine Kyphosis- excessive thoracic curvature (“hunchback”) Lordosis- excessive lumbar curvature Axial Skeleton 6 Ribs There are 24 ribs, 12 on each side. The first 7 ribs are considered true ribs with direct attachments to the sternum. Ribs 8-12 are false ribs. Ribs 8-10 attach to the sternum by first articulating with the cartilage of the ribs above it. Ribs 11 and 12 are also called “floating ribs” because they do not form an attachment to the ribs. Ribs have a few different features: Head- posterior end of the bone that articulates with vertebral bodies Tubercle- posterior bump that articulates with transverse processes Costal groove- groove along inferior surface, where nerves and blood vessels travel under the bone The head of a rib articulates with the demifacets of adjacent vertebral bodies rather than just the body of one vertebra. Sternum The sternum is the central breast bone. It has 3 parts: the manubrium (superior), body (middle), and xiphoid process (inferior). The junction of the manubrium and the body is the sternal angle that can often be palpated. Axial Skeleton 7 Muscles of the Head Muscles of Facial Expression There are many muscles of facial expression and insert onto the skin in order to move the face and create various expressions. These muscles reside in they hypodermis layer of skin. We will cover 4 muscles of facial expression: orbicularis oculi, orbicularis oris, buccinator, and platysma. Muscles of Mastication There are 4 muscles of mastication: temporalis, masseter, medial pterygoid, and lateral pterygoid. We will only be learning the temporalis and masseter muscles. The muscles of mastication move the mandible to masticate or chew food. The buccinator muscle of facial expression is often confused as a muscle of mastication because it helps to manipulate food in the oral cavity; however, it is NOT a muscle of mastication. Muscles of facial expression Muscle Origin Orbicularis oculi Orbital bone Orbicularis oris Maxilla and mandible Buccinator Maxilla and mandible Platysma Action Close eyelid Purse/close lips Compresses cheeks/Hold food between molars Skin of shoulder and chest Skin over mandible and cheek Tense skin of the neck Muscles of mastication Muscle Origin Masseter Zygomatic arch Temporalis Lateral side of cranium Insertion Skin of eyelid Skin surrounding mouth Fibers of orbicularis oris Insertion Action Mandibular ramus and angle Elevates/protracts mandible Coronoid process of mandible Elevates/retracts mandible Muscles of the Neck and Deep Back The sternocleidomastoid (SCM) muscle is a superficial muscle that can often be viewed in the anterior neck near its origin at the sternum and clavicle. As with some other muscles, the action cause by this muscle changes whether it contracts on one side (unilaterally) or on both sides at the same time (bilaterally). When it contracts bilaterally, it causes flexion of the neck. When it contracts unilaterally, it causes ipsilateral (same side) side bending and contralateral (opposite side) head rotation. Some infants are born with a condition called torticollis which is a spasm or fibrosis of the SCM which positions the head in a way that demonstrates the unilateral action of this muscle. We will divide the other muscles in the anterior neck into those below the hyoid bone (infrahyoid muscles) and those above the hyoid (suprahyoid muscles). Axial Skeleton 8 There are many layers of muscles in the back. We will cover some of the more superficial muscles with the upper extremity since they move the pectoral girdle and upper extremity. The erector spinae are a muscle group in the deep back that has 3 parts: spinalis, longissimus, and iliocostalis. Spinalis is most medial along the spine. Longissimus is in the middle. Iliocostalis is most lateral and inserts onto the ribs. Muscle Sternocleidomastoid Origin Sternum and clavicle Infrahyoid muscles Sternum, scapula Suprahyoid muscles Erector spinae Mastoid and styloid processes, hyoid Spinous processes, sacrum, & ilium Insertion Mastoid process of temporal Hyoid bone Action Flexes neck/ipsilaterally side bends and contralaterally rotates head Depress or stabilize the hyoid Mandible Depress the mandible (when hyoid is stable), or elevate the hyoid Extends the spine to maintain posture Vertebrae & ribs Muscles of Abdominal Wall There are 4 muscles of the anterior abdominal wall that, together, flex and rotate the trunk and also compress the abdomen. Along the central portion of the abdomen is the rectus abdominis muscle. It is a segmented muscle covered by a sheet-like muscle tendon called the rectus sheath. The rectus sheath from either side meet at the midline of the abdomen as the linea alba (or white line). Lateral to the rectus abdominis muscles are three layers of sheet-like muscles. The external layer is external oblique with muscle fibers that travel down and in. The middle layer is internal oblique which muscle fibers that travel up and in. The deepest layer is transversus abdominis with muscle fibers that travel from side-to-side. The muscle tendons for all of these layers coalesce to form the rectus sheath. Muscle External oblique Origin Inferior ribs Insertion Linea alba Internal oblique Iliac crest Linea alba Transversus abdominis Inferior ribs & iliac crest Rectus abdominis Pubic bone Linea alba Action Flex and rotate trunk, compresses abdomen Flex and rotate trunk, compresses abdomen Rotate trunk, compresses abdomen Xiphoid process and ribs Flexes trunk, compress abdomen Muscle of Breathing Breathing occurs when the volume of the thorax increases or decreases. The lungs sit in a vacuum and expand or shrink to fit the thoracic cavity. Thus, muscle increasing or decreasing the volume of the thorax cause breathing rather than intrinsic forces caused by the lungs. Axial Skeleton 9 Different muscles are active during breathing at rest versus forced breathing (taking a deep breath in and out). The respiratory diaphragm is the main muscle of breathing. It contracts during both breathing at rest and forced breathing. The diaphragm sits as a dome between the thorax and abdomen. It originates all along the margins of the thoracic cage and inserts on the central tendon which is a tendon sitting at the middle of the muscle. When the diaphragm contracts, it flattens which causes the thoracic cavity to increase in volume and inhalation occurs. When it relaxes, it domes back up into the thoracic cavity, reducing the space and causing exhalation. Additional muscles are active during forced breathing which pull up or down on the rib cage to increase or decrease its volume. Intercostal muscles sit in the space between each pair of ribs and pull up on the ribs for forced inhalation and pull down on the ribs for forced exhalation. There is an external and internal layer of intercostal muscles, and the muscle fibers run perpendicular to each other and similar to the abdominal oblique muscles. Muscle Intercostal muscles Origin Ribs Insertion Adjacent rib Respiratory diaphragm Ribs, xiphoid process, Central tendon and lumbar vertebrae Action Forced inhalation and exhalation Breathing at rest and forced breathing Axial Skeleton 10