a breif note on cns

1. NERVOUS TISSUE
DR Mubashar iqbal

2. Nervous System

3. • The master controlling and communicating system of the
body
• Functions
• Sensory input –the stimuli goes to CNS
• Integration – interpretation of sensory input
• Motor output – response to stimuli coming from CNS
Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center
Peripheral nervous system (PNS)
• Paired spinal and cranial nerves
• Carries messages to and from the spinal cord and brain

4. PROTECTIVE LAYERS OF THE CNS( OR)
MENINGES
• Nervous tissue is very delicate, bones, connective tissue
layers, and a watery cerebrospinal fluid (CSF) surround
and protect the brain and the spinal cord.
The CN-tissue are three membrane called meninges.
1.Dura Mater (dura mean hard):
The outermost meningeal layer is the dura mater, a tough,
strong, and thick layer of dense connective tissue fibers.
dura mater also lodges a number of sensory nerves and
blood vessels.
• 2.Arachnoid Mater:
Deep to the dura mater is a more delicate thin layer
connective tissue, the arachnoid mater. The dura mater
and arachnoid mater surround the brain and spinal cord
on their external surfaces.

6. 3.Pia Mater:
• The innermost meningeal layer is the delicate
connective tissue pia mater. This layer contains
numerous blood vessels and adheres directly to the
surfaces of the brain and spinal cord.
• Between the arachnoid mater and the pia mater is the
subarachnoid space. Delicate,weblike strands of
collagen and elastic fibers attach the arachnoid mater
to the pia mater.
• Circulating in the subarachnoid space is the
cerebrospinal fluid (CSF) that bathes and protects
both the brain and spinal cord.

7. CEREBROSPINAL FLUID
• Clear, colorless fluid cushions and protects brain and
spinal cord
• Continually produced by choroid plexuses in brain
ventricles
• Important for homeostasis and brain metabolism
• Reabsorbed into venous blood via arachnoid villi.
• CSF circulates through the ventricles and around the
outer surfaces of the brain and spinal cord in the
subarachnoid space. CSF also fills the central canal of
the spinal cord.

8. MORPHOLOGY OF NEURON
• The structural and functional cells of the nervous tissue
are the neurons. Although neurons vary in size and shape,
a general structure of these cells can be described. Each
neuron consists of soma or cell body, numerous dendrites,
and a single axon.
• The cell body or soma contains the nucleus, nucleolus,
numerous different organelles, and the surrounding
cytoplasm or perikaryon.
• Projecting from the cell body are numerous cytoplasmic
extensions called dendrites that form a dendritic tree.
• Surrounding the neurons are the smaller and more
numerous supportive cells collectively called neuroglia.
These cells form the non neural components of the CNS.

9. TYPES OF NEURONS IN THE CNS
• This anatomic classification is based on the number of
dendrites and axons that originate from the cell body.
1.Multipolar neurons:
These are the most common type in the CNS and include
all motor neurons and inter neurons of the brain,
cerebellum, and spinal cord. Projecting from the cell body
of a multipolar neuron are numerous branched dendrites
and a single axon.
2. Bipolar neurons: These are not as common and
are purely sensory neurons. Single dendrite and a single
axon are associated with the cell body.
Bipolar neurons are found in the retina of the eye, in the
organs of hearing and equilibrium in the inner ear, and in
the olfactory epithelium in the upper region of the nose

10. • Unipolar neurons:
Most neurons in the adult organism that exhibit only
one process leaving the cell body were initially
bipolar during embryonic development. The two
neuronal processes fuse during later development and
form one process. The unipolar neurons (formerly
called pseudounipolar neurons) are also
sensory.Unipolar neurons are found in numerous
sensory ganglia of cranial and spinal nerves.

11. Myelin Sheath and Myelination of Axons
• Highly specialized cells present in both the CNS and
the PNS wrap around the axon numerous times to
build up successive layers of modified cell membrane
and form a lipid-rich, insulating sheath around the
axon called the myelin sheath.
• Interspersed along the length of a myelinated axon
are small gaps or spaces in the myelin sheath between
individual cells that myelinated the axons. These gaps
are called nodes of Ranvier. Axons in both the CNS
and the PNS can be either myelinated or remain
unmyelinated.

12. • In the PNS, all axons are surrounded by specialized
Schwann cells that either myelinate the axons or
envelope the unmyelinated axons. Schwann cells
myelinate individual peripheral axons and extend
along their length, from their origin to their
termination in the muscle or gland
• There are no Schwann cells in the CNS. Instead,
neuroglial cells called oligodendrocytes myelinate
the axons in the CNS. Oligodendrocytes differ from
Schwann cells in that the cytoplasmic extensions of
one oligodendrocyte envelopes and myelinates
numerous axons.

13. White and Gray Matter
• The brain and the spinal cord contain gray matter and
white matter.
• The gray matter of the CNS consists of neurons, their
dendrites, and the supportive cells called neuroglia. This
region represents the site of connections or synapses
between a multitude of neurons and dendrites. Gray
matter covers the surface of the brain (cerebrum) and
cerebellum.
• White matter in the CNS is devoid of neuronal cell bodies
and consists primarily of myelinated axons, some
unmyelinated axons, and the supportive neuroglial
oligodendrocytes. The myelin sheaths around the axons
impart a white color to this region of the CNS.

14. NEUROGLIA(Supporting Cells in the CNS)
• Highly branched, supportive, non neuronal cells in
the CNS that surround the neurons, their axons, and
dendrites. These cells do not become stimulated or
conduct impulses, but are morphologically and
functionally different from the neurons.
• The CNS contains approximately tenfold more
neuroglial cells than neurons. The four types of
neuroglia cells are astrocytes, oligodendrocytes,
microglia, and ependymal cells.
1. Astrocytes
• Are the largest and most numerous in gray matter
Consist of two types, fibrous astrocytes and
protoplasmic astrocytes

15. • Both types abut on capillaries and neurons, and form
blood brain barrier. Form glial limiting membrane
that surrounds the brain and spinal cord
• Support metabolic exchange and contribute to energy
metabolism of CNS. Control chemical environment
around neurons by clearing neurotransmitters.
2. Oligodendrocytes
• Surround and myelinate numerous axons at one time,
in contrast to Schwann cells.
3. Microglia
• Part of the mononuclear phagocyte system and found
throughout CNS. Phagocytic cells in the CNS, similar
to connective tissue macrophages

16. 3.Ependymal Cells
• Line the ventricles in the brain and central canal of
the spinal cord
• Ciliated cells move the CSF through the central canal
of spinal cord.

17. SPINAL CORD
• Thoracic region of spinal cord contains anterior,
posterior, and lateral gray horns. Lateral horns contain
motor neurons of sympathetic division of autonomic
nervous system
• Anterior horns of gray matter contain motor neurons.
Axons from anterior horns form anterior roots of spinal
nerves
• White matter contains closely packed ascending and
descending axons
• Posterior columns of white matter contain fasciculus
gracilis and fasciculus cuneatus
• Gray matter inside the spinal cord is H-shaped and
contains neurons and interneurons
• Gray commissure connects two sides of the gray matter
and contains the central canal

19. CEREBRAL CORTEX
• Molecular layer (I): most superficial and covered
by pia mater; contains neuroglial cells and
horizontal cells of Cajal
• External granular layer (II): contains neuroglial
cells and small pyramidal cells
• External pyramidal layer (III): medium-sized
pyramidal cells predominant type
• Internal granular layer (IV): thin layer with small
granule, pyramidal cells, and neuroglia
• Internal pyramidal layer (V): contains neuroglial
cells and largest pyramidal cells
• Multiform layer (VI): deepest layer, adjacent to
white matter with various cell types