Download What is nerve impulse

• Nervous system controls the functions of
human body
• Nervous system is composed of nerve cells
called neurons
• Each neuron has a body, a long process
called axon and dendrites
• Nervous system correlates sensory stimuli
and coordinates the efferent impulses so that
effector organs work harmoniously.
• What are the effector organs?
• Effector organs are muscles and glands
• Effector is a muscle which contracts in
direct response to nerve impulses
• Effector is a gland which secretes in direct
response to nerve impulses
• Nervous system has the ability to store
sensory information received in past times
and can integrate this information with
other nervous impulses and channel into
common efferent pathways
• Structurally nervous system has two main
parts:
• Central nervous system
• Peripheral nervous system
• What are the component parts of PNS
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Central nervous system consists of brain
and spinal cord
Peripheral nervous system consists of
cranial nerves, spinal nerves and ganglia.
• Functionally nervous system is also divided
into two parts
• Somatic nervous system
• It is that part of nervous system which is
concerned with the innervation of voluntary
structures of the body
• For example skeletal muscles
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Autonomic nervous system
It is the part of nervous system concerned
with the innervation of involuntary
structures of the body
For example heart, smooth muscle, and
glands
• Central nervous system has two main parts:
• Brain
• Spinal cord
• The two parts are continuous with each
others.
• Brain is placed in skull and spinal cord is
present in vertebral column.
• Central nervous system has gray matter and
white matter
• Gray matter consists of neurons embedded
in neuroglia cells
• White matter consists of nerve fibers
embedded in neuroglia cells
• Neuroglia cells are the supporting cells of
nervous tissue
• Autonomic nervous system is distributed
throughout the central and peripheral
nervous systems
• Microscopic picture of cerebral cortex
• Silver stain
• Central nervous system is suspended in
fluid called cerebrospinal fluid
• Both brain and spinal cord are surrounded
by three meninges
• The meninges of brain and spinal cord are
• dura mater, arachnoid mater, pia mater,
• These meninges of brain and spinal cord are
continuous with each other.
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Brain is divided into three main parts
Forebrain or prosencephalon
Midbrain or mesencephalon
Hindbrain or rhombencephalon
• Prosencephalon is further subdivided into
– Telencephalon or cerebrum
– Diencephalon (between brain)
• Mesencephalon is not further subdivided
• Rhombencephalon is further subdivided into
– Metencephalon. It consists of pons, and cerebellum
– Myelencephalon. It is medulla oblongata
• Cerebrum is the largest part of brain
• It consists of two cerebral hemispheres
• The cerebral hemispheres are separated by a
deep cleft called longitudinal fissure, into
which projects falx cerebri
• The two (right and left) cerebral
hemispheres are connected through corpus
callosum
• Cerebrum lies in the cranial cavity. From
before backward it lies superior to anterior
cranial fossa, middle cranial fossa and
tentorium cerebelli
• Each cerebral hemisphere contains a cavity
called lateral ventricle
• Lateral ventricles communicate with third
ventricle through interventricular foramina.
• Diencephalon is the central part of
forebrain.
• It is almost completely hidden.
• What are the component parts of
diencephalon
• Name the cavity of diencephalon
• It consists of a dorsal thalamus and a ventral
hypothalamus
• The cavity of diencephalons is third
ventricle
• Thalamus is a large egg-shaped mass of
gray matter that lies on either side of the
third ventricle.
• The anterior end of thalamus forms the
posterior boundary of interventricular
foramen
• What is interventricular foramen
• Interventricular foramina are the openings
between third ventricle and lateral ventricles
• How many interventricular foramina are in
the brain
• two
• Hypothalamus forms the lower part of the
lateral wall and floor of third ventricle
• Midbrain or mesencephalon is continuous
superiorly to forebrain and inferiorly to
hindbrain.
• What is the cavity of midbrain?
• Cerebral aqueduct
• It connects
• Third and fourth ventricles.
• Pons is continuous superiorly to midbrain
and inferiorly to medulla oblongata.
• It is connected anteriorly to cerebellum
• How. What connects these two?
• Middle cerebellar peduncles
• Medulla oblongata is conical in shape. It is
continuous superiorly to pons and inferiorly
to spinal cord
• It is connected posteriorly to the two
cerebellar hemispheres through inferior
cerebellar peduncles.
• Cerebellum is situated posterior to
brainstem. It lies within the posterior cranial
fossa.
• It consists of two cerebellar hemispheres,
connected by a median portion called
vermis
• Cerebellum is situated posterior to
brainstem.
• Where it lies in the skull
• It lies within the posterior cranial fossa.
• It consists of two cerebellar hemispheres,
• How these are connected with each other
• They are connected by vermis.
• Cerebellum is connected anteriorly to
midbrain through superior cerebellar
peduncles, to pons through middle
cerebellar peduncles, and to medulla
through inferior cerebellar peduncles
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What is the stem of the brain?
Brainstem
What are the parts of brainstem?
Brainstem consists of midbrain, pons and
medulla oblongata.
• Which part of brain is left after the cerebral
and cerebellar hemispheres are removed.
• Brainstem is that part of brain which is left
after the cerebral and cerebellar
hemispheres are removed.
• Hindbrain consists of pons, medulla
oblongata and cerebellum. The cavity of the
hindbrain is fourth ventricle. Fourth
ventricle is connected superiorly to third
ventricle through cerebral aqueduct, and
inferiorly it is continuous with central canal
of spinal cord.
• Spinal cord lies in vertebral column. It
begins at foramen magnum
• Where it terminates
• It terminates inferiorly at the level of the
lower border of the first lumbar vertebra.
• It is continuous superiorly with medulla
oblongata and tapers off inferiorly into the
conus medullaris. Filum terminale descends
from the apex of conus medullaris to the
back of coccyx.
• What is filum terminale
• It is a prolongation of pia mater
• There are two fusiform enlargements in
spinal cord.
• Name these enlargements
• Cervical enlargement. It is in cervical
region. Here spinal cord gives origin to
brachial plexus.
• Lumbar enlargement. It is in lower thoracic
and lumber regions. Here spinal cord gives
origin to lumbo-sacral plexus.
• Spinal cord (SC) has segments.
• One spinal nerve is attached to one segment
of spinal cord.
• How many segments are there in spinal cord
• How many spinal nerves are attached to SC
• Along the entire length of the spinal cord
are attached 31 pairs of spinal nerves.
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Each spinal nerve has two roots.
Name those roots
Anterior or motor root
Posterior or sensory root
• Each root is attached to the spinal cord by a
series of rootlets, which extend the whole
length of the corresponding segment of the
cord.
• Each posterior nerve root has a posterior
root ganglion.
• Spinal cord is cylindrical in cross section. It
has anterior median fissure on ventral
surface and posterior median sulcus on
dorsal surface
• In spinal cord gray mater is inside and white
mater is outside.
• Gray mater is H-shaped and surrounds
central canal.
• White mater surrounds gray mater and is
divided into anterior, lateral, and posterior
white columns.
• What are the components of Peripheral
Nervous System
• Peripheral nervous system consists of
• Cranial nerves and their associated ganglia
• Spinal nerves and their associated ganglia
• Cranial and spinal nerves are grayish-white
cords made up of bundles of nerve fibers
supported by connective tissue.
• Nerve fibers transmit nerve impulses
• What is nerve impulse
• Nerve impulse is a massage either from
central nervous system to the various
structures of the body or from these
structures to central nervous system
• The fibers carrying impulses from central
nervous system to various organs and
structures of the body are called efferent
fibers. The efferent fibers that pass to the
muscles to make them contract are given the
name motor nerve fibers.
• The fibers carrying impulses to central
nervous system are afferent fibers. Because
these fibers are concerned with conveying
information about sensations of touch, pain,
temperature, and vibration, they are called
sensory fibers.
• In addition to the impulses which they carry,
nerve fibers also transmit substances in both
directions in the nerve cell process. Thus
there is a flow of materials to and from the
nerve cells which give rise to these
processes.
• Cranial and spinal nerves are grayish-white
cords made up of bundles of nerve fibers
supported by connective tissue.
• The connective tissue forms three
successive coverings.
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Endoneurium. It is a delicate sheath of
connective tissue around each nerve fiber.
Perineurium. It is a sheath of connective
tissue around each bundle of nerve fiber.
Epineurium. It is in a sheath of dense
connective tissue around the nerve.
• Nerves are classified into two categories
– Cranial nerves
– Spinal nerves
• There are 12 pairs of cranial nerves. They
are attached to brain. They leave brain and
emerge from the skull or cranium through
foramina in the skull.
• There are 31pairs of spinal nerves. They are
attached to spinal cord. They leave spinal
cord and pass through intervertebral
foramina in vertebral column.
• Spinal nerves are named according to the
regions of vertebral column with which they
are associated.
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Name the cranial nerves
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Olfactory nerve or first cranial nerve
Optic nerve or second cranial nerve
Occulomotor nerve or third cranial nerve
Trochlear nerve or fourth cranial nerve
Trigeminal nerve or fifth cranial nerve (V)
Abducent nerve or sixth cranial nerve
Facial nerve or seventh cranial nerve (VII)
• Vestibulocochlear nerve or eighth cranial
nerve (VIII)
• Glossopharyngeal nerve or ninth cranial
nerve (IX)
• Vagus nerve or tenth cranial nerve (X)
• Accessory nerve or eleventh cranial nerve
• Hypoglossal nerve or twelfth cranial nerve
• Cranial ganglia are found along the course
of following cranial nerves
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Trigeminal nerve
Facial nerve
Vestibulocochlear nerve
Glossopharyngeal nerve
Vagus nerve
• Cranial ganglia found along the course of
Trigeminal nerve, Facial nerve,
Vestibulocochlear nerve, Glossopharyngeal
nerve, Vagus nerve are called
• Sensory ganglia of these nerves.
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There are 31pairs of spinal nerves.
8 cervical nerves
12 thoracic nerves
5 lumber nerves
5 sacral nerves
1 coccygeal nerve
• Please note two very important points
• There are 7 cervical vertebrae in vertebral
column and there are 8 cervical nerves
arising from spinal cord.
• There are 4 coccygeal vertebrae and there is
only 1 coccygeal nerve.
• All the spinal nerves emerge caudal to the
corresponding vertebrae except cervical
nerves.
• The first seven cervical nerves emerge
cranial to the corresponding vertebrae while
the eighth emerges between the seventh
cervical and first thoracic vertebrae.
• Each spinal nerve is attached to spinal cord
by two roots. They are
• Anterior or ventral or motor root
• Posterior or dorsal or sensory root
• A typical spinal nerve is formed by the
union of anterior and posterior roots
attached to the sides of the spinal cord
within the vertebral canal.
• Anterior or ventral root consists of bundles
of efferent nerve fibers. It is formed by
axons of spinal neurons occupying anterior
and lateral gray columns. Their cells of
origin lie in the anterior gray horn of the
spinal cord. In thoracic region lateral horn
also share.
• Each root arises as a series of 2-3 regular
rows of rootlets attached to anterolateral
surface of the spinal cord. These nerves
carry motor (efferent) fibers passing on to
skeletal muscles.
• Posterior or dorsal root consists of bundles
of sensory or afferent nerve fibers. The cell
bodies of the nerve fibers in dorsal root are
situated in posterior root ganglion. Each of
these ganglion cells sends one process into
the spinal nerve (peripheral process) and
another into the spinal cord through the
dorsal root (central process).
• Posterior or dorsal nerve root is also
attached to the posterolateral surface of the
spinal cord by a series of rootlets.
• The rootlets of adjacent dorsal are often
connected by oblique filaments.
• A spinal ganglion is present along the
course of each posterior root. They are
called posterior root ganglia. They are
fusiform structures. These spinal ganglia are
also called sensory ganglia of spinal nerves.
• Each ganglion is composed of large groups
of sensory neurons. It is oval and reddish,
and the size corresponds to that of the root
of spinal nerve.
• Immediately lateral to the dorsal root
ganglion, the ventral and dorsal roots unite
to form a mixed spinal nerve which emerges
through the intervertebral foramen.
• Anterior and posterior roots unite to form
the trunk of a spinal nerve at the level of
their respective intervertebral foramina. The
trunk is short. Here the motor and sensory
fibers become mixed together, so that a
spinal nerve is made up of a mixture of
motor and sensory fibers.
• The nerve passes out via intervertebral
foramina. After emerging from the
intervertebral foramen, each spinal nerve
gives of a recumbent meningeal branch and
divides into an anterior or ventral ramus and
a posterior or dorsal ramus. Each ramus
contains both efferent and afferent fibers.
• Posterior or dorsal ramus passes posteriorly
around vertebral column into the muscles
on the back of vertebral column. Here it
divides into lateral and medial branches that
supply the muscles, and one of them sends a
branch to the overlying skin.
• Name the spinal nerves where the dorsal
rami do not divide into lateral and medial
branches
• First cervical and coccygeal dorsal rami do
not divide into medial and lateral branches.
• In cervical region which branch supply skin
• In cervical dorsal rami medial branches give
branches to skin.
• Name the dorsal cervical rami which do not
supply skin
• Lower three dorsal cervical rami
• Posterior or dorsal ramus passes posteriorly
around vertebral column into the muscles
on the back of vertebral column. Here it
divides into lateral and medial branches that
supply the muscles, and one of them sends a
branch to the overlying skin.
• Which branch supply skin in thoracic region
• The medial branches of upper six thoracic
dorsal rami supply skin while lateral
branches of lower six thoracic dorsal rami
supply skin.
• Regarding lumbar dorsal rami
• upper three give of cutaneous nerves
through their lateral branches.
• Sacral dorsal rami
• They supply skin through lateral branches.
• Anterior or ventral ramus is larger. It runs
laterally and anteriorly to supply the
• muscles and skin over the antero-lateral
body wall, and
• all the muscles and skin of the limbs.
• Anterior rami in thoracic region run along
the lower border of corresponding ribs.
• They form eleven intercostal nerves and
• one subcostal nerve (twelfth nerve).
• Each of these ventral rami supplies the strip
of muscle in which it lies.
• Each intercostal nerve gives off a collateral
branch, which follows the inferior border of
the same intermuscular space.
• The collateral branch rejoins the main trunk
before it is distributed as anterior cutaneous
nerve.
• Each intercostal nerve also gives off a
lateral cutaneous branch, which
accompanies the main trunk for a short
distance. Lateral cutaneous branch pierces
the intercostal muscles obliquely and
divides into anterior and posterior branches.
The anterior branch runs forward while
posterior branch runs posteriorly. Both
supply the overlying skin.
• The cutaneous branches of ventral and
dorsal rami supply a strip of skin from
anterior median line to posterior median
line.
• This strip of skin supplied by a single spinal
nerve is called a dermatome.
• It is interesting to note that no area of skin
is supplied solely by a single spinal nerve
because adjacent dermatomes overlap.
• The total mass of muscle supplied by a
single spinal nerve is called a myotome.
• Muscles receive afferent as well as efferent
nerve fibers.
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Central Nervous system (CNS) contains
two types of cells
1. nerve cells proper called neurons
2. neuroglia cells forming the
connective tissue of CNS
Name the different types of neuroglia cells
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Neuroglia consists of three types of cells
1. Astrocytes
2. Oligodendroglia
3. Microglia
• It is believed that astrocytes play an
important part in nerve cell metabolism and
transfer of substances from the blood to the
nerve cells. Their own biochemistry also
alters with that of the nerve cells adjacent to
them.
• What is the reason?
• Astrocytes are star-shaped cells with
processes radiating from them. They form
the surface layer of CNS as well as pervade
CNS and ensheathe the capillaries of CNS.
• Astrocytes have numerous processes. At
least one of the processes passes to form an
end-foot on an adjacent capillary.
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There are two main types of astrocytes
Name them
Where they are located
How will you differentiate them structurally
• Protoplasmic Astrocytes
They are found in grey matter, where nerve
cells predominate.
• Fibrillary Astrocytes
They are found in white matter, where
bundles of nerve fibers predominate.
• Protoplasmic Astrocytes
Their processes branch and rebranch to
form a dense bush.
• Fibrillary Astrocytes
Their processes are long and thin and they
branch infrequently.
• Neuroglia cells develop from which germ
layer
• Astrocytes from ectoderm
• Oligodendroglia from ectoderm
• Microglia from mesoderm
• What is ependyma?
• It is a single layer ciliated columnar or
cuboidal epithelium. It lines the cavities of
brain and covers the vascular pia mater that
invaginates the ventricles of brain to form
the choroid plexuses.
• What are tracts and fasciculi in CNS
• The axons are usually grouped together and
form bundles called tracts and fasciculi.
• What are nuclei in brain?
• The cell bodies and dendrites are grouped to
form clusters called nuclei.