Download 11.3: The Central Nervous System The nervous system consists of

11.3: The Central Nervous System
The nervous system consists of two parts. The Central Nervous System
(CNS), made up of the Brain and the Spinal Cord, and the Peripheral
Nervous System (PNS), made up of the Afferent and Efferent Neurons,
which extend to and from the Spinal Cord and Brain from the extremities of
the body.
Humans have the most complex nervous system of all animals, which allows
us to have complex behaviours, ability to reason, develop intellect, complex
memories, various languages, and distinct personalities.
In chordates, (any of a phylum (Chordata) of animals having at some stage
of development a notochord, gill slits, and a dorsal tubular nerve cord), the
nervous system develops dorsally as a hollow neural tube. At the anterior
end the Brain develops, and posteriorly from there the spinal cord develops.
Figure 1: The Central and peripheral nervous systems and their subsystems.
Figure 2: During the midway development of vertebrates, the brain is elongate. In later
development in birds and mammals, the brain becomes folded so that the very prominent
forebrain lies above the other regions and the size of the ventricle is reduced.
Spinal Cord
The Spinal cord runs from the base of the Brain, along the vertebrae canal of
the back bone, and contains the interneuron circuit that controls motor
reflexes. The Spinal Cord has both grey matter and white matter. Grey
matter has a butterfly shape and consists of the dendrites and cell bodies of
nerve cells. The white matter surrounds the grey matter and is made up of
the axons, covered by their myelin sheaths.
The afferent axons enter the Spinal Cord via the dorsal root, and synapse
with the interneurons of the grey matter. The interneurons send the message
to the Brain along axons, white matter.
Efferent axons of the interneurons of the Brain send their message down
through the white matter and synapse with the grey matter (dendrites and
cell bodies). Efferent axons leave the Spinal Cord along the ventral root, and
deliver message to the muscles, glands, and organs.
Figure 3: The spinal cord is protected by the vertebral column. Afferent
(sensory) nerves enter the spinal cord through the dorsal root, and efferent
nerves leave through the ventral root
The Brain
The Brain is the major centre that receives, integrates, stores, and retrieves
information. The Brain and its network of interneurons provide the basis for
our voluntary movements, consciousness, behaviour, emotions, learning,
reasoning, language and memory. The brain contains grey and white matter,
surrounded by cerebrospinal fluid which provides neural connections to the
Endocrine system.
Medulla Oblongata – is the hindbrain region that contacts the spinal cord to
the cerebellum; important in autonomic nerve control.
Cerebellum – is the hindbrain region that is involved in muscle movement
and balance.
Pons – is the brain region that transfers nerve signals between the
cerebellum and the medulla.
The hindbrain is made up of there parts, the medulla oblongata, cerebellum,
and the pons.
The medulla deals with the involuntary motions, such as breathing, digestion,
heart rate, and blood pressure.
The cerebellum deals with the motor responses, balance and fine motor
control.
The pons connect the cerebellum to the higher centres of the brain. The
combination of the pons, medulla, and midbrain form the brain stem, which
also connects to the forebrain.
The forebrain, forms the cerebrum, and makes up most of the mass of the
brain and is highly developed. The cerebrum controls the sensory and motor
activities.
Figure 4: The adult brain loses the elongated structure of the embryonic brain. The
cerebrum, which develops from the forebrain, fold to cover the regions of the brain that
develops from the mid brain and hindbrain.
Figure 5: The cerebral cortex of the lobes of the cerebrum is divided into
major regions and association areas.
Figure 6: The primary somatosensory and motor areas of the cerebrum form
a band across the top of the brain. The distorted images of the human body
show the relative areas of the sensory and motor cortex devoted to different
body regions