Gives an overview of the nervous system, neural and Non - neural cells , it's structure and functions

1. THE CELLS
OF THE
NERVOUS
SYSTEM

2. THE HUMAN NERVOUS SYSTEM

3. DIVISIONS OF THE NERVOUS SYSTEM

4. BASIC FEATURES OF THE NERVOUS SYSTEM
MENINGES:
The brain and spine is encased in bone and covered by protective membrane called the meninges
a) Duramater – The outermost tough membrane.
b) Arachnoid membrane – Present immediately inside the duramater . Subarachnoid space – Beneath the arachnoid
membrane, contains large blood vessels and CSF.
c) Piamater- Adheres to the surface of the CNS.

5. MENINGES

6. THE VENTRICULAR SYSTEM
 The system comprises four ventricles: Interconnected Cavities in the brain
a) Lateral ventricles (C shaped chambers) right and left (one for each hemisphere)
b) Third ventricle
c) Fourth ventricle

7. THE VENTRICLES

8. CEREBROSPINAL FLUID
 Colourless plasma like fluid
 Produced by choroid plexuses – network of small blood vessels. Present in all components of the ventricular
system except cerebral aqueduct (also called the Aqueduct of Sylvius)
 The cerebrospinal fluid percolates through the ventricular system and flows into the subarachnoid space through
perforations of the fourth ventricle; it is eventually absorbed by specialized structures called arachnoid villi into
large blood filled spaces , which run through the duramater and returned to the venous circulation.

9. CEREBROSPINAL PATHWAY

10. FUNCTIONS OF THE CEREBROSPINAL FLUID
Produced by the choroid plexus
 Protection: the CSF protects the brain from damage by "buffering" the brain. In other words, the CSF acts to
cushion
 Buoyancy: Since the brain is immersed in fluid, the net weight of the brain is reduced . Therefore, pressure at the
base of the brain is reduced.
 Excretion of waste products: As the CSF circulates in the brain it takes away debris in the form of potentially
harmful metabolites, drugs and other substances away from the brain.
 Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones
released into the CSF can be carried to remote sites of the brain where they may act.

11. HYDROCEPHALUS
 Overproduction of CSF
 An obstruction at some point within the ventricular system
 Problems with CSF absorption

12. BLOOD BRAIN BARRIER
 In the brain the cells of the blood vessel walls are closely packed . A mechanism that impedes passage of many
toxic substances from the blood into the brain. The barrier is a consequence of special structure of cerebral blood
vessels. Some large molecules critical for normal brain function are actively transported through cerebral blood
vessel walls
Functions:
 Protects the brain from "foreign substances" in the blood that may injure the brain.
 Protects the brain from hormones and neurotransmitters in the rest of the body.
 Maintains a constant environment for the brain.
The BBB can be broken down by blood pressure and also exposure to microwaves, radiation, infections.
Trauma & pressure.

13. DIRECTIONS OF THE HUMAN VERTEBRATE SYSTEM
A simple 3 axis system of neuroanatomical directions.
 Anterior – Towards the nose Vs Posterior – Towards the tails. They are also referred to as rostral Vs caudal
 Ventral (towards the surface of the chest or below the head) Vs Dorsal( towards the surface of the back )
 Medial ( towards the midline of the body) Vs lateral ( Away from the midline of the body)

14. ANATOMICAL PLANES
 An anatomical plane is a hypothetical plane used to transect the body, in order to describe the location
of structures or the direction of movements. The coronal plane is also called the frontal plane. Slices of
the brain taken in the coronal plane are similar to the slices from a loaf of bread.
 Horizontal cuts are made as if you were slicing a hamburger bun or bagel. Horizontal plane is also
called as the transverse plane and divides the body into upper and lower parts
 The sagittal plane divides the right and left side of the brain into parts.

16. HORIZONTAL,CORONAL AND SAGITTAL PLANES.

17. TYPES OF CELLS IN THE NERVOUS SYSTEM
There are fundamentally two different types of cells in the nervous system. They are
a) Neurons
b) Glial cells

18. STRUCTURE OF THE NEURON

19. STRUCTURE AND FUNCTIONS OF THE NEURAL CELL
 Cell membrane: The semipermeable membrane that encloses the neuron. C
 Dendrites : The short processes emanating from the cell body, which receive most of the synaptic contacts from
other neurons.
 Axon hillock: The cone shaped region at the junction between the cell body and axon.
 Cell body: The metabolic center of the neuron, also called the soma. The soma (cell body) contains the nucleus and
much of the machinery that provides for the life processes of the cell. Its shape varies considerably in different
kinds of neurons.
 Axon: The long ,narrow processes that projects from the cell body.
 Myelin – The fatty insulation around many neurons.
 Nodes of Ranvier: The gaps between sections of the myelin.
 Buttons: The button like endings of the axon branches.
 Synapses: The gaps between the adjacent neurons across which chemical chemical signals are translated.

20. INTERNAL STRUCTURE

21. INTERNAL ANATOMY OF NEURONS
 Neuronal cell membrane: Composed of a lipid bilayer. Embedded in this lipid bilayer are numerous
protein molecules that are a basis for cell membranes functional properties.
 Some membrane proteins are called channel proteins , through which certain molecules can pass, others
are signal proteins which transfer a signal to the inside of the neuron
 Nucleus: The nucleus (“nut”) of the cell is round or oval and is enclosed by the nuclear membrane. The
nucleolus and the chromosomes reside here. The nucleolus is responsible for the production of ribosomes, small
structures that are involved in protein synthesis. The chromosomes, which consist of long strands of
deoxyribonucleic acid (DNA), contain the organism’s genetic information.
 When they are active, portions of the chromosomes (genes) cause production of another complex molecule,
messenger ribonucleic acid (mRNA), which receives a copy of the information stored at that location. The mRNA
leaves the nuclear membrane and attaches to ribosomes, where it causes the production of a particular protein.
 Proteins are important in cell functions. As well as providing structure, proteins serve as enzymes. Enzymes are
special protein molecules that act as catalysts and cause a chemical reaction to take place without becoming a part
of the final product themselves.

22. THE CELL MEMBRANE

23.  Cytoplasm: The internal fluid of the cell. The bulk of the cell consists of cytoplasm. Cytoplasm is
complex and varies considerably across types of cells, but it can most easily be characterized as a
jellylike, semi-liquid substance that fills the space outlined by the membrane. It contains small,
specialized structures, just as the body contains specialized organs. The generic term for these
structures is organelle, “little organ.
 Endoplasmic Reticulum: Serves as a storage reservoir and as a channel for transporting chemicals
through the cytoplasm, appears in two forms: rough and smooth.
 Rough endoplasmic reticulum contains ribosomes (site in which proteins are synthesised. It is here that
mRNA is translated to form polypeptides and proteins). The protein produced by the ribosomes that are
attached to the rough endoplasmic reticulum is destined to be transported out of the cell or used in the
membrane. Unattached ribosomes are also distributed around the cytoplasm; the unattached variety
appears to produce protein for use within the neuron.
 Smooth endoplasmic reticulum is involved in metabolic processes. Involved in the synthesis of Lipids
and steroid hormones. Cells that secrete these products such as testes , ovaries, skin oil glands have an
excess of smooth endoplasmic reticulum. Smooth ER stores ions for later use and calcium for
detoxifying substances. T

24. INTERNAL ANATOMY OF THE CELL
 The Golgi apparatus is a special form of smooth endoplasmic reticulum. Some complex molecules,
made up of simpler individual molecules, are assembled here. The Golgi apparatus also serves as a
wrapping or packaging agent. For example, secretory cells (such as those that release hormones) wrap
their product in a membrane produced by the Golgi apparatus. The Golgi apparatus also produces
lysosomes, small sacs that contain enzymes that break down substances no longer needed by the cell.
These products are then recycled or excreted from the cell.
 Mitochondria:. Mitochondria are shaped like oval beads and are formed of a double membrane. Cells
provide mitochondria with nutrients, and mitochondria provide cells with a special molecule—
adenosine triphosphate (ATP)— that cells use as their immediate source of energy. Mitochondria
contain their own DNA and reproduce independently of the cells in which they reside.

25. FUNCTIONS OF A NEURON
All neurons have 3 basic functions:
 Receive signals (or information).
 Integrate incoming signals (to determine whether or not the information should be passed along).
 Communicate signals to target cells (other neurons or muscles or glands).

26. TYPES OF NEURONS
Neurons can be classified based on shape and functions.
DISTINCTION BASED ON SHAPE: Structural classification of neurons is based upon the number of processes
that extend out from the cell body. Three major groups arise from this classification.
a) Multipolar neuron: A neuron with one axon and many dendrites attached to its soma. Examples of multipolar
neurons include spinal motor neurons, pyramidal neurons and, Purkinje cells.
b) Bipolar neuron: A neuron with one axon and one dendrite attached to its soma. Bipolar neurons usually inhabit
sensory organs like the eye and nose. Their dendrites ferry signals from those organs to the cell body and their axons
send signals from the cell body to the brain and spinal cord. Pseudo-unipolar neurons, a variant of bipolar neurons that
sense pressure, touch and pain, have no true dendrites. Instead, a single axon emerges from the cell body and heads in
two opposite directions, one end heading for the skin, joints and muscle and the other end traveling to the spinal cord.
c) Unipolar neuron: A neuron with one axon attached to its soma; the axon divides, with one branch receiving
sensory information and the other sending the information into the central nervous system.

27. DISTINCTION BASED ON SHAPE

28. DISTINCTION BASED ON FUNCTION:
 Information, in the form of light, sound waves, odors, tastes, or contact with objects, is gathered from the
environment by specialized cells called sensory neurons. Movements are accomplished by the contraction of
muscles, which are controlled by motor neurons. (The term motor is used here in its original sense to refer to
movement.) And in between sensory neurons and motor neurons come the interneurons—neurons that lie entirely
within thecentral nervous system. Local interneurons form circuits with nearby neurons and analyze small pieces
of information. Relay interneurons connect circuits of local interneurons in one region of the brain with those in
other regions. Through these connections, circuits of neurons throughout the brain perform functions essential to
tasks such as perceiving, learning, remembering, deciding, and controlling complex behaviours

29. SUPPORTING CELLS
Neurons constitute only about half the volume of the CNS. The rest consists of a variety of supporting cells.
Because neurons have a very high rate of metabolism but have no means of storing nutrients, they must constantly
be supplied with nutrients and oxygen or they will quickly die. Thus, the role played by the cells that support and
protect neurons is very important to our existence.
Glia: The most important supporting cells of the central nervous system are the neuroglia, or “nerve glue.” Glia
(also called glial cells) does indeed glue the CNS together, but they do much more than that.
Glial cells surround neurons and hold them in place, controlling their supply of nutrients and some of the
chemicals they need to exchange messages with other neurons; they insulate neurons from one another so that
neural messages do not get scrambled; and they even act as housekeepers, destroying and removing the carcasses
of neurons that are killed by disease or injury. There are several types of glial cells, each of which plays a special
role in the CNS.

30. THE TYPES OF GLIA
 The three most important types are astrocytes, oligodendrocytes, and microglia. Astrocyte means “star cell,” and this
name accurately describes the shape of these cells. Astrocytes provide physical support to neurons and clean up debris
within the brain.
 Astrocytes are involved in providing nourishment to neurons. Some of the astrocyte’s processes (the arms of the star) are
wrapped around blood vessels; other processes are wrapped around parts of neurons, so the somatic and dendritic
membranes of neurons are largely surrounded by astrocytes.
 Besides transporting chemicals to neurons, astrocytes serve as the matrix that holds neurons in place. These cells also
surround and isolate synapses, limiting the dispersion of neurotransmitters that are released by the terminal buttons.
 When cells in the central nervous system die, certain kinds of astrocytes take up the task of cleaning away the debris.
When these astrocytes contact a piece of debris from a dead neuron, they push themselves against it, finally engulfing and
digesting it. We call this process phagocytosis..

31. TYPES OF GLIA
 The principal function of oligodendrocytes is to provide support to axons and to produce the myelin sheath,
which insulates most axons from one another. (Very small axons are not myelinated and lack this sheath.) Myelin,
80 percent lipid and 20 percent protein, is produced by the oligodendrocytes in the form of a tube surrounding the
axon. This tube does not form a continuous sheath; rather, it consists of a series of segments, each approximately 1
mm long, with a small (1–2 μm) portion of uncoated axon between the segments. (A micrometer, abbreviated μm,
is one-millionth of a meter, or one-thousandth of a millimeter.) The bare portion of axon is called a node of
Ranvier, after the person who discovered it. The myelinated axon, then, resembles a string of elongated beads.
 Microglias are the smallest of the glial cells. Like some types of astrocytes, they act as phagocytes, engulfing
and breaking down dead and dying neurons. But, in addition, they serve as one of the representatives of the
immune system in the brain, protecting the brain from invading microorganisms.

32. SCHWANN CELLS
 In the central nervous system the oligodendrocytes support axons and produce myelin. In the peripheral
nervous system the Schwann cells perform the same functions. Most axons in the PNS are myelinated. The myelin
sheath occurs in segments, as it does in the CNS; each segment consists of a single Schwann cell, wrapped many
times around the axon.