The document describes the central nervous system (CNS) and peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, while the PNS is all nervous structures outside the CNS. The brain contains the cerebral hemispheres, cerebellum, and brainstem. The brainstem consists of the medulla, pons, and midbrain. The medulla contains nuclei that regulate vital functions like breathing, heart rate, and swallowing. The document also discusses the meninges, blood supply, and metabolism of the brain.

1. CNS and PNS
M Tuapati JNR

2. Can be separated into parts based on
structure & function
Structurally: CNS & PNS
Functionally: Somatic & Visceral
CNS is composed of the brain & spinal
cord
PNS composed of all nervous structures
outside the CNS.

3.  BRAIN:
 Parts of the brain are the cerebral
hemispheres, cerebellum & brainstem
 Cerebral hemispheres consists of:
 Outer Portion-grey matter containing cell
bodies
 Inner Portion-white matter made up of axons
forming tracts
 Ventricles-space filled with Cerebrospinal
Fluid
 Components of Brainstem are
Diencephalon, Midbrain, Pons & Medulla.

4. SPINAL CORD:
The part of CNS in superior 2/3rd of
vertebral canal. Roughly cylindrical in
shape, & circular to oval in cross section
with a central canal.

5.  MENINGES:
 Are 3 connective tissue coverings that
surround, protect & suspend the brain &
spinal cord within the cranial cavity &
vertebral canal respectively
 Dura Mater-thickest & most exterior part of
the covering
 Arachnoid Mater-is against the internal
surface of Dura Mater
 Pia Mater-is adherent to brain & spinal cord.
 Subarachnoid space-between arachnoid &
pia mater which contains CSF

6.  Nervous system can be divided into somatic
& visceral parts
 SOMATIC PART: innervates structures (skin
& skeletal muscle) derived from somites in
the embryo & mainly involved with receiving &
responding to information from external
environment.
 VISCERAL PART: innervates organ systems
in body & other visceral elements such as
smooth muscle & glands. Mainly concerned
with detecting & responding to information
from internal environment.

7.  Consist of 4 major parts:
 Brainstem, Cerebellum, Diencephalon, &
Cerebrum
 The brain stem is continuous with spinal cord
& consists of the medulla oblongata, pons &
midbrain.
 Cerebellum-posterior to brainstem
 Superior to brainstem is the diencephalon
which consists of Thalamus, Hypothalamus &
Epithalamus.
 Supported on the Diencephalon & Brainstem
is the Cerebrum-the largest part of the brain.

8. Blood flows to the brain mainly via the
Internal Carotid arteries & Vertebral
arteries.
The dural venous sinuses drain into the
Internal Jugular Veins to return blood from
the head to the heart.
In an adult, brain represents only 2% of
total body weight, but consumes 20% of
the O2 & glucose used by the body, even
when resting

9.  Neurons synthesize ATP almost exclusively
from glucose via rxns that use O2.
 When activity of neurons & neuroglia
increases in a particular region of the brain,
blood flow to the area also increases.
 Typically, an interruption in blood flow for 1-2
min impair neuronal function & total
deprivation of O2 for about 4 min causes
permanent injury.
 Because, virtually NO GLUCOSE is stored in
the brain hence supply must be continuous.

10.  The blood-brain-barrier (BBB) consists mainly
of tight junctions that seal together the
endothelial cells of brain blood capillaries.
 Astrocytes are 1 type of neuroglia; the
processes of many astrocytes press up
against the capillaries & secrete chemicals
that maintain the permeability characteristic of
the tight junctions.
 A few water-soluble substances such as
glucose cross BBB by active transport.

11.  Substances such as Creatinine, Urea & most
ions cross BBB slowly.
 Still other substances-proteins & most
antibiotic drugs-do not pass at all from the
blood into the brain tissue.
 However, lipid soluble substances-such as
O2, CO2, alcohol, & most anesthetic agents,
are able to access brain tissue freely.
 Trauma, certain toxins & inflammation can
cause a breakdown of blood-brain-barrier.

12. Brainstem is part of the brain btw the
spinal cord & diencephalon.
Consists of three structures; medulla
oblongata, pons, & midbrain.
Extending through the brain stem is the
Reticular Formation, a net-like region of
interspersed gray & white matter.

13.  Medulla Oblongata:
 Continuous with the superior part of the spinal
cord; it forms the inferior part of the
brainstem.
 Begins at the Foramen Magnum & extends to
the inferior border of the pons-a distance of
abt 3cm.
 The Medullas’ white matter contains all
sensory(ascending) tracts &
motor(descending) tracts that extend btw the
spinal cord & other parts of the brain.

14.  Large corticospinal tracts pass from the cerebrum
to the spinal cord through the medulla.
 These tract control voluntary movements of the
limbs & trunks.
 Just superior to the junction of medulla with the
spinal cord; 90% of the axons in the left crosses to
the right side, & 90% of the axons in the right
crosses to the left side.
 This crossing is called DECUSSATION and
explains why each side of the brain controls
voluntary movements on the opposite side of the
body.

15.  The medulla also contains several nuclei.
 Some control vital body functions:
 The Cardiovascular Center that regulates rate & force
of the heart beat & the diameter of blood vessels.
 The medullary Respiratory Center adjusts the basic
rhythm of breathing
 The Vomiting Center causes vomiting.
 The Deglution Center of the medulla promotes
swallowing of a mass of food that has moved from the
oral cavity of the mouth to pharynx.
 Sneezing involves spasmodic contraction of breathing
muscles that forcefully expel air through nose & mouth;
Coughing, Hicupping-spamodic contraction of
diaphragm.