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Lecture 14

ANAT 1010 Lecture Notes - Lecture 14: Dura Mater, Arachnoid Mater, Pia MaterPremium

20 pages77 viewsFall 2018

Department
Anatomy
Course Code
ANAT 1010
Professor
A. Jaffar
Lecture
14

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Lecture: Chapter 18 Brain and the Cranial Nerves
October 15, 2018
[BRAIN] = portion of the CNS that is contained within the cranium.
100 billion neurons + 10-15 trillion neuroglia make up the brain (each neuron forms 1000
synapses with other neurons).
The brain is the center for registering sensations, correlating them with one another and with
store information, making decisions, and taking actions. it is also the center for intellect,
emotions, behaviour, and memory.
Major Parts of the Brain:
The adult brain consists of 4 major parts: brainstem, cerebellum, diencephalon, and cerebrum.
[Brainstem] = medulla oblongata, pons + midbrain. it Is continuous with the spinal cord
[Cerebellum] = posterior to the brainstem, “little brain”.
[Diencephalon] = thalamus, hypothalamus, and epithalamus.
[Cerebrum] = supported on the diencephalon and the brainstem; the largest part of the brain.
Protective Coverings of the Brain:
Overview: bone, meninges, and fluid.
The cranium and the cranial meninges surround and protects the brain.
[Cranial Meninges] are the same as around the spinal cord; they consist of:
a. Outer dura mater
b. Middle arachnoid mater
c. Inner pia mater
The cranial dura mater has 2 layers, compared to the single layer of the spinal dura mater
external layer is the “periosteal layer”, and the internal layer is the “meningeal layer”. These
two dural layers around the brain are fused together except where they separate to enclose the
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dural venous sinuses (endothelial-lined venous channels). sinuses drain venous blood from
the brain + deliver it into the internal jugular veins.
[Epidural space] = potential space between the periosteal layer of the dura mater and skull
bones.
Blood vessels that enter the brain tissue will pass along the surface of the brain; as they
penetrate inward, the vessels become sheathed by a loose-fitting sleeve of pia mater.
Three extensions of the dura mater separate parts of the brain:
1) Falx cerebri separates 2 hemispheres (sides) of the cerebrum
2) Falx cerebelli separates the 2 hemispheres of the cerebellum
3) Tentorium cerebelli separates the cerebrum from the cerebellum.
Medulla Oblongata:
The medulla oblongata is a continuation of the superior part of the spinal cord forms the
interior part of the brainstem.
It begins at the foramen magnum and extends to the inferior border of the pons (3 cm).
resembles the spinal cord in many ways.
Like the spinal cord, the medulla oblongata gives rise to many nerve roots; however, these are
the roots of cranial nerves rather than spinal nerves. 6/12 pairs of cranial nerves arise from
this region.
Within the medulla’s white matter are all of the sensory (ascending) and motor (descending
tracts that extend between the spinal cord and other parts of the brain. some of the white
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matter forms bulges on the anterior aspect of the medulla [pyramids], formed by the largest
motor tracts that pass from the cerebrum to the spinal cord.
The medulla contains several nuclei, masses of gray matter where neurons will form synapses
with one another, and some of these nuclei control vital body functions.
[Cardiovascular Center] regulates the rate and the force of heartbeat + diameter of blood
vessels.
[Medullary Respiratory Center] adjusts/sets the basic rhythm of breathing.
Other nuclei in the medulla control reflexes for vomiting, coughing, and sneezing.
Ventral Surface of the Medulla Oblongata:
Superior to the medulla junction with the spinal cord, 90% of axons in the left pyramid cross to
the right side, and 90% of the axons in the right pyramid cross to the left side, [decussation of
pyramids] explains how each brain side controls movements on opposite body sides. left
cortex controls right muscles, and vice versa.
And just lateral to each pyramid is an oval-shaped swelling [olive], and within each olive is the
inferior olivary nucleus. Neurons within the structure relay impulses from proprioceptors
(receptors that monitor joint and muscle positions) to the cerebellum.
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