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Chapter 14

Anatomy and Physiology HAP101 Chapter Notes - Chapter 14: Supraoptic Nucleus, Medial Longitudinal Fissure, Superior Colliculus


Department
Anatomy and Physiology
Course Code
Anatomy and Physiology HAP101
Professor
Tania Killian
Chapter
14

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HAP101 Week 9/Chapter 14: The Brain and Cranial Nerves
14.1: Brain Organization, Protection and Blood Supply
The brain and the spinal cord develop from the ectodermal neural tube. The anterior part of this tube expands, along
with the associated neural crest tissue. The expanded tube will have constrictions that create three regions
o Primary Brain Vesicles: prosencephalon, mesencephalon, and rhombencephelon
o Secondary Brain Vesicles: formed by the subdivision of the prosencephalon (forebrain; gives rise to the
telencephalon/diencephalon) and the rhombencephelon (hindbrain; develops into the metencephalon and
myelencephalon)
Telencephalon: develops into the cerebrum and lateral ventricles
Diencephalon: forms the thalamus, hypothalamus, epithalamus, and third ventricle
Mesencephalon: forms the midbrain and aqueduct of the midbrain (cerebral aqueduct)
Metencephalon: becomes the pons, cerebellum, and upper part of the fourth ventricle
Myelencephalon: forms the medulla oblongata and lower part of the fourth ventricle
Major Parts of the Brain: adult brain consists of four major parts: brain stem, cerebellum, diencephalon, and
cerebrum
o Brain Stem: continuous with the spinal cord and consists of the medulla oblongata, pons and midbrain
o Cerebellum: posterior to brain stem
o Diencephalon: superior to brain stem and consists of the thalamus, hypothalamus, and epithalamus
o Cerebrum: the largest part of the brain; supported on the diencephalon and brain stem
Protective Coverings of the Brain: the brain is protected by the cranium and cranial meninges, which are continuous
with the spinal meninges
o The Outer Dura Mater: two dural layers called the periosteal (external) layer and the meningeal (internal)
layer. These layers fuse around the brain except where they separate to enclose the venous sinuses. There is no
epidural space. There are three extensions that separate it from parts of the brain: the falx cerebri, the falx
cerebelli, and the tentorium cerebelli
o The Middle Arachnoid Mater:
o The Inner Pia Mater: blood vessels that enter the brain tissue pass along the surface of the brain/ As they
penetrate inwards, they are sheathed by a loose-fitting sleeve of this mater
Brain Blood Flow and the Blood Brain Barrier
o The internal carotid and vertebral arteries supply blood flow to the brain
o The dural venous sinuses drain into the internal jugular veins to return blood from the head to the heart
o The brain uses 20% of the body’s oxygen supply
o When neuron/neuroglial activity increases in a certain region, blood flow to that region increases. Otherwise, a
brief slowing of blood flow can cause disorientation or lack of consciousness.
o The supply of glucose must be continuous. Low levels of glucose cause mental confusion, dizziness, convulsions,
and loss of consciousness.
o The Blood-Brain Barrier (BBB): consists of tight junctions that seal endothelial cells from brain capillaries and
a membrane that surrounds the capillaries. Water-soluble substances cross the BBB by active transport.
Substances such as proteins and anti-biotic drugs do not pass from the brain tissue from the blood. Lipid-soluble
substances (oxygen, carbon dioxide, etc.) are able to cross the brain tissue. Trauma and inflammation can cause a
breakdown of the BBB. It also prevents the passage of harmful substance, since it serves as a selective barrier.
However, sometimes the BBB can prevent the entry of therapeutic drugs.
14.2: Cerebrospinal Fluid
CSF is a clear, colorless, liquid composed of mainly of water that protects the brain and spinal cord from chemical and
physical injuries
It carries small amounts of chemicals from the blood to neurons and neuroglia
It continuously circulates through brain/spinal cord cavities and around the brain/spinal cord in the subarachnoid space.
The four cavities of the brain that are filled with CSF. These areas are called ventricles:
o Two Lateral Ventricle: present in each hemisphere. They are separated by a thin membrane (septum
pellucidium)
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o Third Ventricle: narrow cavity along the midline superior to the hypothalamus. It is located between the right/eft
halves of the thalamus
o Fourth Ventricle: this lies between the brain stem and the cerebellum
o
The CSF has three basic functions
1) Mechanical Protection: the fluid is a shock-absorber that protects delicate tissue of the brain and spinal cord.
The fluid buoys so the brain “floats” in the cranial cavity
2) Homeostatic Function: the CSF pH affects pulmonary ventilation and cerebral blood flow. It serves as a
transport system for polypeptide hormones secreted by hypothalamus.
3) Circulation: it is a medium for minor nutrient and waste product exchange between blood and adjacent nerve
tissue
Formation of CSF in the Ventricles: most of the CSF is produced in the choroid plexuses (network of capillaries in
ventricle walls).
o Blood Cerebrospinal Fluid Barrier: fluid that permits certain substance to enter the CSF, protecting
brain/spinal cord from harmful substances. It is formed by tight junctions of ependymal cells
Circulation of CSF (diagram)
14.3: The Brain Stem and Reticular Formation
The brain stem is between the spinal cord and the diencephalon.
It consists of three structures
o Medulla Oblongata
o Pons
o Midbrain
MEDULLA OBLONGATA
o Forms the inferior part of the brain stem
o Begins at the foramen magnum and extends to the inferior border of the pons
o Its white matter contains all sensory/motor tracts the extend between spinal cord and other brain parts. Some
white matter bulges from the anterior part of medulla (pyramids pg. 482).
o Contains several nuclei that control vital body functions (e.g. cardiovascular centre regulates rate/force of heart
beat & diameter of blood vessels; medullary respiratory centre adjusts basic breathing rhythm
Also control reflexes for vomiting, swallowing, sneezing, coughing, and hiccupping.
o Inferior olivary nucleus: receives input from cerebral cortex, red nucleus of midbrain, and spinal cord. It tells
the cerebellum how to make adjustments to muscle activity as you learn now motor skills
o It also contains nuclei that are part of the sensory pathways for gustation, audition, and equilibrium
o The medulla contains nuclei associated with the following pairs of cranial nerved
1) Vestibulocochlear (VIII) nerves: nuclei receive input and provide motor output to the cochlea of the
internal ear. These nerves convey impulses related to hearing
2) Glossopharyngeal (IX) nerves: nuclei relay sensory and motor impulses related to taste, swallowing
and salivation
3) Vagus (X) nerves: nuclei receive sensory impulses from and provide motor impulses to
pharynx/larynx
4) Accessory (XII) nerves: the nuclei are the origin for nerve impulses that control tongue movements
during speech and swallowing
PONS
o Lie superior to medulla and anterior to cerebellum
o Consists of both nuclei and tracts
o It is a bridge that connects parts of the brain with one another (connections provided by axon bundles). Some
axons connect the right/left sides of the cerebellum; others are part of the ascending sensory and descending
motor tracts
o Two major structural components:
Ventral Region: forms a large synaptic relay station consisting of scattered gray centres (pontine nuclei).
Many white matter tracts enter and exit this region, providing a connection between the cortex of a
hemisphere and the cerebellum of the opposite hemisphere
Dorsal Region: similar to the medulla and midbrain; contains ascending and descending tracts along cranial
nerve nuclei
o Pontine respiratory group: helps control breathing long with the medullary respiratory centre.
o The pons also contains nuclei associated with the following pairs of cranial nerves
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