ANAT 316 Pt1

Axial Skeleton

Axial Skeleton

• Bones of the skull

• Accessory bones

• Vertebral column

• Thoracic cage (ribs, sternum, thoracic vertebrae)

Appendicular Skeleton

• Upper limbs and pectoral girdle

• Lower limbs and pelvic girdle

Parts of skull

• Neurocranium (braincase) (8 bones)

• Viscerocranium (facial skeleton) (14 bones)

• 22 total bones

Neurocranium - functions

• Surrounds and protects the brain

• Articulates with the vertebral column

Viscerocranium - functions

• Supports and protects entrances to the digestive and respiratory tracts

Accessory bones of the skull - functions

• 7 bones (hearing & muscle attachment)

Unpaired bone, forms part of the:

• Orbital wall, nasal cavity/septum

Ethmoid Features

Crista Galli

Perpendicular projection of the ethmoid bone

• Acts as an anchoring point for membranes surrounding the brain (meninges)

Branches of CN I (olfactory nerve) pass through cribriform plate of ethmoid bone

Sphenoid Bone

Unpaired bone

• Forms part of the eye orbit & the base of the skull

Features of Sphenoid Bone

Pterygoid Process- attachment for muscles of mastication

Features of Sphenoid Bone

Pituitary gland in sella turcica

Skull Foramina: Sphenoid Bone

Skull Foramina: Sphenoid Bone

Skull Foramina: Sphenoid Bone

Skull Foramina: Temporal Bone

Skull Foramina

Skull Foramina

Sutures

• Boundaries between skull bones

• Fibrous, immovable joints

Sutures

• Boundaries between skull bones

• Fibrous, immovable joints

Cranial Fossae

Floor of the cranial cavity divided into 3 fossae (depressions):

• Anterior cranial fossa: frontal lobe of brain

  • Frontal, ethmoid, sphenoid bones

• Middle cranial fossa: temporal lobes of brain

  • Sphenoid, temporal bones

• Posterior cranial fossa: cerebellum

  • Occipital, temporal bones

Features of the Mandible

Accessory Bones of the Skull

Ossicles

• Small bones involved in hearing

• Housed in the temporal bone

• 3 in each middle ear

• CN VIII traveling through the internal acoustic meatus

Hyoid Bone

• "Floating bone" located in the neck

• Important attachment site for the tongue and muscles involved in swallowing

The Nervous System

The nervous system is one of the smallest and most complex body systems:

• Mass of only 2kg (~3% of total body weight)

• Contains approximately 100 billion neurons

• Uses more energy than any other organ (over 20%)

Highly organized network comprised of two cell types:

1. Neurons

2. Neuroglia

Major Components of the Nervous System

• Brain

• Spinal cord

• Cranial nerves

• Spinal nerves

• Ganglia

• Sensory receptors

Anatomical Organization of the Nervous System

Central nervous system (CNS)

• Brain and spinal cord

Peripheral nervous system (PNS)

• Cranial nerves and spinal nerves

• Ganglia and sensory receptors

Cranial nerves

• 12 pairs of nerves (I-XII)

• Emerge from the base of the brain

Spinal nerves

• 31 pairs of nerves

• Emerge from the spinal cord

Ganglia

Relay station for neuron conversations

• Clusters of neuron cell bodies

• Located outside the CNS - in the PNS

• Autonomic ganglia are part of the ANS

  • Function as relay stations between preganglionic and postganglionic neurons of the ANS

Sensory receptors

• Monitor changes in environment

• Detectors of external and internal stimuli

• Skin, eyes, nose, muscles, etc.

Functional Organization of the Nervous System

1. Sensory function (input)

2. Integrative function (control)

3. Motor function (output)

NS Sensory function (input)

• Sensory receptors detect internal and external stimuli

• Sensory (afferent) neurons transmit information to CNS

• Division of the Peripheral nervous system

NS Integrative function (control)

• Interneurons analyze sensory information

• Perception (Conscious awareness) of stimuli to determine whether or not a response is needed and how it will occur

• Division of the Central nervous system

NS Motor function (output)

• Motor (efferent) neurons respond to integration

• Initiate actions in effector organs (e.g., muscles, glands)

Somatic Nervous System

• Division of the Peripheral nervous system

Somatic sensory neurons (Afferent)

• Convey information to the CNS from receptors for somatic senses and receptors for special senses

• Input of information to the CNS for integration

Somatic motor neurons (Efferent)

• Convey information from the CNS to skeletal muscles only

• Output of information from the CNS for muscular contraction

Overall function: Regulates voluntary control of skeletal muscles

Autonomic Nervous System

• Division of the Peripheral nervous system

• Autonomic motor neurons regulate visceral activities by exciting or inhibiting activities in effector tissues

Sympathetic nervous system (SNS)

• Increase in activity and metabolic rate

• "Fight-or-flight" response

• Examples: dilate pupils, increase heart rate, inhibit intestinal activity

Parasympathetic nervous system (PNS)

• Decrease in activity and metabolic rate
  "Rest-or-digest" response

• Examples: constrict pupils, decrease heartrate, stimulate intestinal activity

Overall function: regulates involuntary functions such as cardiac muscle, smooth muscle, glandular tissue

Cell Types of the Nervous System

Nervous tissue is comprised of two cell types:

• Neurons

• Neouroglia

Neurons

• Basic structural and functional units of the nervous system

• Form complex processing networks

• Transfer and processing of information

Neuroglia

• Smaller and more abundant

• Support, nourish, and protect neurons

• Do not participate in transfer of information

Overview of the Cerebrum (telencephalon)

The largest and most anterior part of the brain (telencephalon):

• Located at the front of the skull

• Consists of two hemispheres separated by a fissure

• Initiates and manages conscious thoughts and actions

The cerebrum provides us with the ability to: read, write, and speak; logically make calculations and creatively make art; and remember the past, plan for the future, and imagine things that may not exist.

Label

Label + Explain

Cerebrum Features

Longitudinal fissure

• Separates right and left cerebral hemispheres

• Travels from anterior to posterior

Corpus callosum

• Connects right and left cerebral hemispheres

• Comprised of white matter

• Communication bridge - how left and right hemispheres communicate

Cerebrum Lobes

Frontal lobe

• Largest lobe

• Executive function

  • Planning, mood, decisions

• Integration centre

Temporal lobe

• Responsible for auditory processing and speaking/verbal responses

• Being able to connect thoughts and responses to speaking and hearing

Parietal lobe

• Responding to stimuli from the environment

• Creates mental body map of where you are in space (proprioception)

Occipital lobe

• Responsible for vision

Cerebrum Lobe

Insular lobe (Insula)

• If you pushed up parietal lobe and looked internally

• Automatic processing responses

Which parts of the brain are housed by which parts of the skull?

Which parts of the brain articulate with which parts of the skull?

• Frontal lobe articulates with anterior fossa

• Temporal lobe articulates with middle fossa

• Brainstem and cerebellum articulate with posterior fossa

Cerebrum: Lobe Divisions

Major sulci are usually deeper, more pronounced and travel full length/width of brain until it reaches the next lobe

Cerebellum Features

• Coordinates voluntary movements

• Regulates posture and balance

Cerebellum Structure

Label + Explain

Label + Explain

Label + Explain

Meninges
Label + Explain

• 3 layers of tissue to provide protection and support to the CNS: (Brain and spinal cord)

• From superficial to deep:

  • Dura Mater

  • Arachnoid Mater

  • Pia Mater

Dura Mater

• Thick layer of meninges deep to the calvarium (skull cap)

• Encloses dural venous sinuses, major structures that drain the cranial vault

Dura Mater Invaginations (Folds)

Forms three invaginations (folds) within the cranial vault:

• Falx Cerebri

  • Sits on mid-sagittal plane

• Tentorium Cerebelli

  • Lies along transverse plane

• Falx Cerebelli

  • Helps split the other two

Dura Mater Layers

2 Layers:

• Periosteal Layer

• Meningeal Layer (deeper)

• These layers split to help form the dural venous sinuses (but are often together otherwise)

• At the edge of the skull, at the Foramen Magnum, this meninx splits

• It continues around the edge of the skull (Periosteal Layer) AND around the spinal cord

  (Meningeal Layer)

Dura Mater Spaces

2 Spaces:

• Epidural Space (between skull and dura)

• Subdural Space (between dura and arachnoid)

• These spaces are potential spaces... they are not found unless trauma/disease cause separation of these layers

Arachnoid Mater

• Sits deep to the dura

• Subarachnoid Space, between arachnoid and pia, contains cerebrospinal fluid (CSF)

  • REAL space

• Arachnoid granulations

  • CSF exits the subarachnoid space through arachnoid granulations

  • These pierce through the dura to drain CSF into the dural venous sinuses

• Arachnoid trabeculae support the arachnoid mater

Cerebrospinal fluid (CSF)

• CSF helps to metabolically and physically support the brain

  • Metabolically -Exchange medium (electrolytes and metabolite exchange)

  • Physically - Buoyancy and Cushion

Pia Mater

• Closely covers cortical sulci and gyri

• Subpial Space exists between Pia and Cortex

  • This is another potential space not normally present

Spinal Meninges

Pia Mater

• Thin, transparent connective tissue layer that adheres directly with the surface of the spinal cord and brain

• Many blood vessels that supply cord with oxygen and nutrients.

• Denticulate Ligaments

  • Lateral Extensions/thickenings of pia mater

  • Extend length of spinal cord to increase stability & protect it from sudden displacement (injury)

Arachnoid Mater

• Thin, avascular covering , that's composed of epithelial cells and very thin, loose strands of collagen

• Cover the Spinal Nerve Roots

• Arachnoid - spiderweb arrangement of fibres and collagen

Dura Mater

• Strong, composed of dense irregular connective tissue

• Cover the Spinal Nerve Roots

• Continuous with meningeal layer of cranial dura mater

• Extends to S2 vertebrae

Spinal Meninges Spaces

• Epidural Space

  • Real space

  • Contains fat & venous plexuses & has a cushion effect

  • Between vertebral canal & dura

• Subarachnoid Space

  • Contains CSF

  • Between arachnoid & pia

• Subdural and Subpial Spaces

  • Potential spaces

  • Subdural is between dura & arachnoid

What are the Ventricles?

4 Cavities within the brain responsible for deep CSF flow

Lateral Ventricles

• Explain

Associated with various lobes of the cerebrum (the telencephalon)

Lateral Ventricles

Lateral Ventricles

Third Ventricle

Associated with the thalamus and hypothalamus (the diencephalon)

Third Ventricle

• Label + Explain

Cerebral Aqueduct

The cerebral aqueduct connects the third and fourth ventricles, passing through the midbrain into the pons

Fourth Ventricle

• There are 3 apertures in the fourth ventricle:

  • 2 Lateral and 1 Median

  • Associated with the pons (the myelencephalon)

Central Canal

• The central canal continues all the way down the spinal cord

• Provides metabolic support to the deep spinal cord

Choroid Plexus

• Collection of ependymal cells found on the walls of all 4 ventricles, in specific areas

• Produces cerebrospinal fluid, which flows into the ventricles

Ventricular Flow

1. Lateral Ventricle

2. Interventricular Foramen

3. Third ventricle

4. Cerebral Aqueduct

5. Fourth Ventricle

6. Central Canal/Foramina of Luschka/Foramen of

   Magendie

Exiting the Ventricles - CSF Flow

• CSF exits into small subarachnoid spaces called cisterns (small cavities)

• From these cisterns, CSF flows along the outer cortices of the cerebrum and cerebellum before draining into the dural venous sinuses via arachnoid granulations

Overview of Cranial CSF Flow

1. Choroid Plexus

2. Lateral Ventricle

3. Interventricular Foramen

4. Third Ventricle

5. Cerebral Aqueduct

6. Fourth Ventricle

7. Median/Lateral Apertures

8. Subarachnoid Cisterns

9. Bathes Superficial Brain

10. Arachnoid Granulations

11. Dural Venous Sinuses

Overview of Spinal CSF Flow

1. Choroid Plexus

2. Lateral Ventricle

3. Interventricular Foramen

4. Third Ventricle

5. Cerebral Aqueduct

6. Fourth Ventricle

7. Central Canal

Great Vessels of the Heart

Three major branches off the aorta

• Brachiocephalic Trunk

  • The brachiocephalic trunk bifurcates (ends and splits)

    into the right common carotid artery and the right subclavian artery

• Left Common Carotid Artery

• Left Subclavian Artery

Four Major Arteries to the Brain

Common Carotid Artery → Internal Carotid Artery

• Internal Carotid Artery goes through the Carotid Canal

Subclavian Artery → Vertebral Artery

• The vertebral artery runs through the vertebral foramina of the cervical vertebrae and goes through the anterior portion of Foramen Magnum

Basilar Artery

• Left and Right Vertebral arteries anastomose (join) to form the Basilar artery

• Sits in basilar groove of pons

• Gives off Pontine arteries to supply the pons

Bifurcation of Basilar Artery

• Basilar Artery bifurcates into the 2 Posterior Cerebral arteries

• These arteries supply the posterior cerebral cortex

Circle of Willis

Anastomosis of arteries providing major cerebral blood supply

• Compensatory mechanism: In the case of a clot in a vertebral or internal carotid artery, maintains cerebral blood flow throughout the brain

Circle of Willis

• Label

• Basilar artery bifurcates into Posterior Cerebral Arteries

• Internal Carotid Artery gives off the Anterior and Middle Cerebral arteries

• Internal Carotid Artery also gives off the Posterior Communicating Artery

  • Posterior Communicating Artery connects Internal Carotid Artery with the Posterior Cerebral Artery

  • Communication arteries provide connections

• Anterior cerebral arteries are connected by the anterior communicating artery

Brain Venous Drainage

Consists of dural venous sinuses that drain the inner structures of the cranial vault

1. Superior Sagittal Sinus

   • Lies along mid-sagittal plane, in falx cerebri

2. Confluence of Sinuses

3. Transverse Sinuses

   • The transverse sinuses sit in the tentorium cerebelli