anatomy and physiology

1. Nervous System
A&P-II Unit-IV
Muhammad Iqbal
Lecturer
KMU

2. Objectives
At the end of this unit the learners will be able to:
• Define Nervous system.
• Briefly discuss organization of Nervous system.
• Define nerve & its types.
• Describe the structure and function of Neuron and
neuroglia.
• Identify the principal parts of the brain i.e. Hind brain,
Mid brain & Fore brain.
• Discuss the structure & function of:
--Brain stem (Mid brain, pons & medulla oblongata)
--Cerebellum
• Describe the structure of cerebrum in terms of:
-- Lobes (sulci and gyrus)
--Functional areas

3. Objectives
• Describe the three meninges covering the brain &
spinal cord.
• Identify the ventricles of the brain.
• Briefly explain the formation, circulation,
reabsorption & functions of cerebrospinal fluid
(CSF).

4. Brain

5. Nervous System
• Definition: The network of nerve cells and fibers
that transmits nerve impulses between parts of the
body.
• With a mass of only 2 kg, the nervous system is one
of the smallest and yet the most complex of the 11
body systems. It is an intricate , highly organized
network of billions of neurons and even more
neuroglia.
• The structures that make up the nervous system
include the brain, cranial nerves, and their branches,
the spinal cord, spinal nerves and their branches,
ganglia, enteric plexuses and sensory receptors.

6. • The skull encloses the brain, which contains about 100
billion (1011) neurons.
• Twelve pairs (right and left) of cranial nerves emerging
from the base of the brain.
• The spinal cord connects to the brain through the foramen
magnum of the skull and is protected by the bones of the
vertebral column.
• It contains about 100 million neurons. 31 pairs of spinal
nerves leave the spinal cord for specific region on the right
or left side of the body.
• Ganglia (swelling or knot) are small masses of nervous
tissue, consisting basically of neuron cell bodies that are
located outside the brain and spinal cord.
• Ganglia are closely associated with cranial and spinal
nerves. In the walls of organs of the GIT, extensive
networks of neurons, called enteric plexuses, help
regulate the digestive system.

7. Functions of the Nervous System
• The nervous system carries out different functions like
smell, speech, storing, remembering past events. It
controls body movements and regulates the operation
of internal organs. All these diverse activities are
grouped into three basic functions such as sensory,
integrative, and motor.
• Sensory function: sensory receptors detect internal
stimuli, such as an increase in blood acidity, external
stimuli, such as a housefly sitting on your body part.
Neurons called sensory or afferent neurons (af=toward;
ferrent=carried) carry this sensory information into the
brain and spinal cord through cranial and spinal nerves.

8. • Integrative Function: The nervous system
integrates (processes) sensory information by
analyzing and by making decisions for appropriate
responses. An important integrative function is
perception, the conscious awareness of sensory
stimuli. Perception occurs in the brain.

9. • Motor Function: Once the sensory information is
integrated, the nervous system gives an
appropriate motor response such as muscle
contraction or gland secretion.
• The neurons that serve this function are called
motor or efferent neurons.
• Motor neurons carry information from the brain
to toward the spinal cord or effectors (muscles
and glands). Stimulation of the effectors by
motor neurons causes muscles to contract and
glands to secrete.

10. • The motor part of the ANS consists of two
branches:
• Sympathetic division—“fight-or-flight”
• Parasympathetic division— “rest-and-digest”
These two divisions have opposing actions. For
example, sympathetic neurons increase heart rate
while parasympathetic neurons do opposite.

11. Organization cont…
• The operation of the ENS, the “brain of gut,” is
involuntary.
• The ENS consists of about 100 million neurons in
enteric plexuses that extend most of the length of the
GI tract.
• Many of the neurons of the enteric plexuses function
independently of the ANS and CNS to some extent,
although they also communicate with the CNS via
sympathetic and parasympathetic neurons.
• Sensory neurons of the ENS monitor chemical
changes within the GI tract as well as the stretching of
its walls.
• Enteric motor neurons control the secretions and
contraction of GI tract smooth muscle to propel food
through the GI tract.

12. PNS includes all nervous tissues outside the CNS.
Its components are:
• Cranial nerves and their branches
• Spinal nerves and their branches
• Ganglia, and sensory receptors.

13. 11-13
Properties of Neuron
Special characteristics of neurons
– Longevity – can live and function for a lifetime
– Amitotic— Do not divide
– High metabolic rate – require abundant oxygen and
glucose

14. Properties of Neuron
– Excitability—the ability to respond to the stimulus
and convert it into an action potential.
– Conductivity: The transmission of nerve impulse.
– Secretion: When the electrical signal reaches the end
of a nerve fiber, the neuron secretes a chemical
neurotransmitter that stimulates the next cell.
Action potential (nerve impulse) is an electrical signal
that propagates (travels) along the surface of the
membrane of a neuron.

15. 11-15
Parts of the Neuron
• Most neurons have three parts
1. A Cell Body
2. Dendrites
3. An Axon
• Cell Body or Perikaryon:
– Contains nucleus and organelles

16. 11-16
Neuron Processes
• Dendrites: short, often highly branched.
– Receptive regions of the neuron
• Axons: Long cytoplasmic process capable of propagating a
nerve impulse
– Neuron has only one axon
– Transmits impulse away from soma toward another
neuron, muscle fiber or gland
– Axon hillock: cone shaped elevation of Axon
– Initial segment: the closest part to the axon hillock

17. – Axoplasm: Cytoplasm of axon
– Axolemma: plasma membrane of axon
– Axon terminals or telodendria: Terminal branches of axon
– synaptic end bulbs or synaptic knobs: Bulb shaped
structures on the tip of axon terminals with synaptic
vesicles filled with neurotransmitters
– Synapse: The site of communication between two
neurons or a neuron and an effector.
A nerve fiber is a general term for neuronal process as
Dendrites and an axon.

18. Structural Classification of Neurons
Multipolar – possess more than two processes
• Numerous dendrites and one axon
• Most neurons in the brain and spinal cord are of this type
Bipolar – possess two processes
• One main dendrite and one axon
• Rare neurons – found in some special sensory organs
Unipolar – possess a single short process

19. 11-19
Neurons Classified by Structure
Figure 12.10a–c

20. Neuroglia
• Neuroglia (glia=glue) are cells of the nervous
system that perform various supportive functions.
• They are smaller but 5 to 50 times more than
neurons.
• In contrast to neurons, they divide and multiply.
• Brain tumors arise from neuroglia, called glioma.
• There are six types of neuroglia.
• Four types found in the CNS are astrocytes,
oligodendrocytes, microglia, and ependymal cells.
• Other two types found in the PNS are Schwann,
and satellite cells.

21. Neuroglia of the CNS
Astrocytes (astro=star; cyte=cell)
• These star shaped cells are the largest and most
numerous of the neuroglia.
• The processes of astrocytes make contact with
blood capillaries, neurons, and the pia matter.

22. • Functions of Astrocytes:
• Astrocytes provide a supportive framework.
• Together with the endothelial cells of blood
capillaries they form a blood brain barrier (BBB) to
isolate harmful materials from CNS.
• They help in nourishing neurons.
• Regulate the chemical composition of tissue fluid.
• Take up excess neurotransmitters.

23. Oligodendrocytes: (oligo=few; dendro=tree)
• They resemble astrocytes but have fewer processes.
• Their processes form myelin sheath around axons in
the brain and spinal cord.
Microglia:
• They are small cells with thinner processes.
• They function as phagocytes (macrophages).

24. Ependymal Cells (epen=above; dym=garment):
• They are cuboidal to columnar cells.
• Arranged in a single layer.
• Possess microvilli and cilia.
Functions:
• They line cavities of brain and spinal cord.
• Secrete cerebrospinal fluid (CSF) and circulate it.

25. Neuroglia of PNS
Schwann Cells:
• They surround the axons in the PNS.
• Each cell encircles (myelinates) only one axon.
• They form myelin sheath around the axons.
• They aid in regeneration of damaged axons of PNS.
Satellite cells:
• These flat cells surround the cell bodies of neurons of
PNS and form ganglia.
• They regulate the exchange of materials between
neuronal cell bodies and interstitial fluid.

26. ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM
Nervous
System
CNS PNS ANS
BRAIN
SPINAL
CORD
CRANIAL
NERVES
SPINAL
NERVES
SYMPATHETIC
PARA-
SYMPATHETIC

27. Division of Nervous System
Nervous system Division