Organization of Nervous system

1. Nervous System
Mr. Mayur Gaikar
Assistant Professor
Department of Pharmacology
College of Pharmacy (For Women), Chincholi, Nashik.

2. Organization of nervous system

3. The Neuron

5. • Dendrites receive
signals.
• The cell body integrates
signals.
• The axon transmits
action potential. The
myelin sheath makes
the signal travel faster.
• Synaptic terminals
transmit signals.

6. Neuroglia
Four types
1. Astrocytes
2. Oligodendrocytes
3. Ependymal cells
4. Microglia

7. Classification of nerve fiber
A. Direction of signal
transmission
i. Sensory/ Afferent nerves
ii. Motor / Efferent nerves
iii. Mixed nerves
B. Origin & connection to
CNS
i. Spinal nerves
ii. Cranial nerves
C. Diameter & conduction
velocity
i. Type A nerve fibres
(12-20um diameter,
velocity-70-120m/s)
ii. Type B nerve fibres
(3um diameter, velocity-
4-30m/s)
iii. Type C nerve fibres
(0.4-1.2um diameter,
velocity-0.5-4m/s)

8. Properties of nerve fiber
1. Excitability
2. Conductivity
3. Refractory period
4. All or none law
5. Summation
6. Release of chemical
regulators
7. Constant number

9. Resting potential
• Using active
transport, the
neuron moves Na+
ions to the outside
of the cell and K+
ions to the inside of
the cell.
• Large molecules in
the cell maintain a
negative charge.

10. Action potential
• On receiving a
stimulus, sodium
gates and potassium
channels open briefly,
allowing these ions to
diffuse.
• The gates close, and
active transport
restores the resting
potential.

11. 11
Pacemaker and Action Potentials of the Heart
Figure 18.13
Na+
open
influx
Ca+
open
influx (T)
Ca+
open
influx (L)
Ca+
close
influx (L)

12. Receptors
A. On the basis of structure
I. Free nerve ending
II. Encapsulated nerve ending
III. Specialized receptor cell
C. On the basis of Location
I. Exteroreceptor
II. Enteroreceptor- baro,
chemo, noci..
III. Gravitational receptor; in
muscles tendons
B. On the basis of Stimulus detected
I. Mechanoreceptor
II. Thermoreceptor
III. Nociceptors
IV. Photo , chemo , osmo

13. Senses

14. Sensory receptors
• Receptors are
found in the sense
organs. They
receive stimuli from
the environment
and transmit stimuli
to neurons.
• Primary humans
senses:
photoreception,
chemoreception,
mechanoreception,
thermoreception.

15. Thermoreception
• Free nerve endings
in the skin sense
changes in
temperature
(differences rather
than absolutes).
• These are directly
transmitted through
the PNS.

16. Mechanoreception
• Hearing is a form of
mechanoreception.
• Ears gather sound
waves from the
environment.
• The inner ear bones
amplify sounds.
• Sounds are transmitted
to the cochlea.

17. Sound transmission
• Within the cochlea,
hair cells on the
basilar membrane
vibrate to certain
frequencies, and send
signals down the
auditory nerve.
• Loud sounds can
damage these
sensitive hairs
permanently.

18. Photoreception
• Sight is photoreception.
• Light enters the eye
through the cornea and
pupil.
• Light is focused by the
lens.
• Light strikes the retina,
and stimulates
receptors.

19. Photoreceptors
• Light breaks pigments
in the receptor cells,
releasing energy that
stimulates neurons
connecting to the
optic nerve.
• Rod cells detect
amount of light, cone
cells distinguish
colors.

20. Chemoreceptioin
• Taste is one form of
chemoreception.
• Taste buds detect
certain ions
dissolved in saliva.
• Tastes: salty,
sweet, sour, bitter,
“umami.”

21. Chemoreception
• Smell is another
form of
chemoreception.
• Receptors in the
olfactory patch in
the human nose
can distinguish
between about
1000 different
chemicals in the
air.

22. “Flavor”
• What we sense as
the “flavor” of food
is not taste alone.
Smell and taste
together create the
sensation of
“flavor.”
• This is why things
don’t “taste” good
when we have a
cold; we lose the
sense of “flavor.”

23. Chemoreception
• The sense of pain is
another form of
chemoreception.
• Injured tissues release
chemicals as a
response. These
chemicals stimulate
free nerve endings in
the skin and the
stimulation is
perceived as pain.

24. Synesthesia
• Synesthesia can be
described as
“cross-sensory
perceptions.”
• Synesthetes
experience more
than one sensory
perception for a
single sensory
reception, such as
experiencing
flashes of particular
colors or textures
when hearing

25. Synapse
• Neurons usually do
not connect directly
to one another. A
gap called a
synapse controls
the transmission of
signals.
• Neurotransmitters
cross the synapse
and stimulate the
next neuron.

26. Web Address
http://outreach.mcb.harvard.edu/animations/actionpotential.swf
https://www.youtube.com/watch?
v=oa6rvUJlg7o

27. Some Neurotransmitters
Neurotransmitter Location Some Functions
Acetylcholine Neuron-to-muscle synapse Activates muscles
Dopamine Mid-brain Control of movement
Epinephrine Sympathetic system Stress response
Serotonin Midbrain, pons, medulla Mood, sleep
Endorphins Brain, spine Mood, pain reduction
Nitric Oxide Brain Memory storage

28. Central Nervous System
• Consists of brain and spinal cord
• Both are protected from damage & injury, brain
within the skull & spinal cord by vertebra.
• Functions:
• Receives sensory signals and determines
appropriate response
• Stores memory
• Carries out thought their parts.

29. Meninges
• The brain and spinal cord are completely surrounded by
three layers of tissue, the meninges, lying between the skull
and the brain, and between the vertebral foramina and the
spinal cord. Named from outside inwards they are the:
• Dura mater
• Arachnoid mater
• Pia mater

30. .
•The dura and arachnoid maters are separated by a
potential space, the subdural space.
•The arachnoid and pia maters are separated by the
subarachnoid space, containing cerebrospinal fluid.

32. 1. Dura mater
• Consists of two layers of dense fibrous tissue
• The outer layer takes the place of the periosteum
on the inner surface of the skull bones and
• Inner layer provides a protective covering for the
brain.

33. Venous sinuses of the brain viewed from the right

34. Venous sinuses of the brain viewed from above.

35. 2. Arachnoid mater
• This is a layer of fibrous tissue that lies
between the dura and pia maters.
• It is separated from the dura mater by the
subdural space, and from the pia mater by the
subarachnoid space, containing cerebrospinal
fluid.

36. .
• The arachnoid mater passes over the
convolutions (crosses) of the brain and
accompanies the inner layer of dura mater in
the formation of the falx cerebri, tentorium
cerebelli and falx cerebelli.
• It continues downwards to envelop the spinal
cord and ends by merging with the dura mater
at the level of the 2nd sacral vertebra.

38. Pia mater
• Delicate layer of connective tissue containing
many minute blood vessels.
• It adheres to the brain, completely covering the
convolutions (crosses) and dipping into each
fissure.
• It continues downwards surrounding the spinal
cord.

39. .
• Beyond the end of the cord it continues as
the filum terminale, pierces the arachnoid
tube and goes on, with the dura mater, to fuse
with the periosteum of the coccyx.

40. Ventricles of brain
• The brain contains four irregular-shaped cavities, or
ventricles, containing cerebrospinal fluid
1. Right and left lateral ventricles
2. Third ventricle
3. Fourth ventricle.

42. Lateral ventricles
• These cavities lie within the cerebral hemispheres, one
on each side of the median plane just below the corpus
callosum.
• They are separated from each other by a thin
membrane, the septum lucidum, and are lined with
ciliated epithelium.
• They communicate with the third ventricle by
interventricular foramina.

43. Third ventricle
• The third ventricle is a cavity situated below the
lateral ventricles between the two parts of the
thalamus.
• It communicates with the fourth ventricle by a
canal, the cerebral aqueduct.

44. Fourth ventricle
• The fourth ventricle is a diamond-shaped cavity
situated below and behind the third ventricle,
between the cerebellum and pons.
• It is continuous below with the central canal of the
spinal cord and communicates with the
subarachnoid space by foramina in its roof.

45. .
• Cerebrospinal fluid enters the subarachnoid space
through these openings and through the open distal
end of the central canal of the spinal cord.

46. Cerebrospinal fluid
• Cerebrospinal fluid is secreted into each ventricle of the
brain by choroid plexuses.
• CSF passes back into the blood through tiny diverticula of
arachnoid mater, called arachnoid villi (arachnoid
granulations

48. • The movement of CSF from the subarachnoid space to
venous sinuses depends upon the difference in pressure
on each side of the walls of the arachnoid villi, which
act as one-way valves.
• When CSF pressure is higher than venous pressure,
CSF passes into the blood and when the venous
pressure is higher the arachnoid villi collapse,
preventing the passage of blood constituents into the
CSF.

49. • From the roof of the fourth ventricle CSF flows
through foramina into the subarachnoid space and
completely surrounds the brain and spinal cord.
• There is no intrinsic system of CSF circulation but
its movement is aided by pulsating blood vessels,
respiration and changes of posture.
• CSF is secreted continuously at a rate of about 0.5
ml per minute, i.e. 720 ml per day.

50. • The pressure remains fairly constant at about 10 cm H2O
when the individual is lying on his side and about 30 cm
H2O when sitting up.
• If the brain is enlarged by, e.g., haemorrhage or tumour,
some compensation is made by a reduction in the amount of
CSF.
• When the volume of brain tissue is reduced, such as in
degeneration or atrophy, the volume of CSF is increased.

51.  CSF is a clear, slightly alkaline fluid with a specific
gravity of 1.005, consisting of:
 Water
 Mineral salts
 Glucose
 Plasma proteins: small amounts of albumin and
globulin
 A few leukocytes.
 Creatinine
 Urea

52. Functions of CSF
 CSF supports and protects the brain and spinal cord by
maintaining a uniform pressure around these vital structures.
 Acting as a cushion or shock absorber between the brain and the
skull.
 It keeps the brain and spinal cord moist and there may be
exchange of nutrients and waste products between CSF and nerve
cells.
 Involved in regulation of breathing as it bathes the surface of the
medulla where the central respiratory chemoreceptors are located.

53. Structure & Functions of Brain
The brain is a large organ weighing around 1.4kg that
lies within the cranial cavity. Its parts are
• Cerebrum
• Thalamus
• Hypothalamus
• Midbrain
• Pons
• Medulla oblongata
• cerebellum
Diencephalon
Brain stem

56. Blood supply to the brain
 The circulus arteriosus and its contributing arteries
play a vital role in maintaining a constant supply of
oxygen and glucose to the brain

57. Cerebrum
 This is the largest part of the brain and it occupies the
anterior and middle cranial fossae.
 Divided by a deep cleft, the longitudinal cerebral fissure,
into right and left cerebral hemispheres, each containing
one of the lateral ventricles.
 Deep within the brain the hemispheres are connected by a
mass of white matter (nerve fibres) called the corpus
callosum.

58. • The cerebral cortex shows many infoldings or furrows.
• The exposed areas of the folds are the gyri (convolutions)
and these are separated by sulci (fissures).
• Each hemisphere of the cerebrum is divided into lobes
• Frontal
• Parietal
• Temporal
• Occipital.

59. A section of the cerebrum
Important tracts are shown in dark brown

60. Functions of the cerebral cortex
• Mental activities involved in memory,
intelligence, sense of responsibility, thinking,
reasoning, moral sense and learning.
• Sensory perception, including the perception of
pain, temperature, touch, sight, hearing, taste
and smell.
• Initiation and control of skeletal muscle
contraction and therefore voluntary movement.

61. Important tracts are shown in dark brown
 Association (arcuate) tracts: Connect different
parts of a cerebral hemisphere
 Commissural tracts: Connect corresponding
areas of the two cerebral hemispheres; the largest
and most important commissure is the corpus
callosum.
 Projection tracts: Connect the cerebral cortex
with grey matter of lower parts of the brain and
with the Spinal cord, e.g. The internal capsule.

62. The cerebrum showing the main functional
areas

63. Diencephalon
 Connects the cerebrum and the midbrain.
 It consists of several structures situated
around the third ventricle, the main ones
being the thalamus and hypothalamus.
 The pineal gland and the optic chiasma are
situated.

64. Thalamus
• Consists of two masses of grey and white matter situated
within the cerebral hemispheres just below the corpus
callosum, one on each side of the third ventricle.
• Sensory receptors in the skin and viscera send information
about touch, pain and temperature, and input from the
special sense organs travels to the thalamus where there is
recognition, although only in a basic form, as refined
perception also involves other parts of the brain.

65. • Involved in the processing of some emotions and
complex reflexes.
• The thalamus relays and redistributes impulses from
most parts of the brain to the cerebral cortex.

66. Hypothalamus
• Small but imp structure weighs around 7 g and consists of a
number of nuclei.
• It is situated below and in front of the thalamus,
immediately above the pituitary gland.
• Controls the output of hormones from both lobes of the
pituitary gland.
• Other functions control of: the autonomic nervous system ,
appetite and satiety (high fat diet), thirst and water balance,
body temperature, emotional reactions, e.g. pleasure, fear,
rage. sexual behaviour and child rearing, sleeping and
waking cycles.

67. Brain stem
• Brain situated around the cerebral aqueduct
between the cerebrum above and the pons below.
• Consists of nuclei and nerve fibres (tracts), which
connect the cerebrum with lower parts of the brain
and with the spinal cord.
• The nuclei act as relay stations for the ascending
and descending nerve fibres.
1. Midbrain

68. • Situated in front of the cerebellum, below the midbrain
and above the medulla oblongata.
• Consists mainly of nerve fibres (white matter) that form a
bridge between the two hemispheres of the cerebellum,
and of fibres passing between the higher levels of the
brain and the spinal cord.
• Pneumotaxic and apnoustic centres that operate in
conjunction with the respiratory centre in the medulla
oblongata.
2. Pons

69. • Extends from the pons above & is continuous with the
spinal cord below.
• It is about 2.5 cm long, lies just within the cranium above
the foramen magnum.
• The outer aspect is composed of white matter, which
passes between the brain and the spinal cord, and grey
matter, which lies centrally.
3. Medulla oblongata

70. • The vital centres, consisting of groups of cell bodies
(nuclei).
• Cardiovascular centre
• Respiratory centre
• Reflex centres of vomiting, coughing, sneezing and
swallowing.

71. • The medulla oblongata has several special features
• Decussation (crossing) of the pyramids
• Sensory decussation
• The cardiovascular centre (CVC)
• The respiratory centre
• Reflex centres

72. Cerebellum
Behind the pons and
immediately below the
posterior portion of the
cerebrum occupying the
posterior cranial fossa.
It is ovoid in shape and has
two hemispheres, separated by
a narrow median strip called
the vermis.
Grey matter forms the surface of
the cerebellum, and the white
matter lies deeply.

73. Functions of cerebellum
 Coordination of voluntary muscular movement, posture and
balance. Cerebellar activity is not under voluntary control.
 The sensory input for these functions is derived from the
muscles and joints, the eyes and the ears.
 Impulses from the cerebellum influence the contraction of
skeletal muscle so that balance and posture are maintained.

74. • The cerebellum may also have a role in learning and
language processing.
• Damage to the cerebellum results in clumsy uncoordinated
muscular movement, staggering gait & inability to carry
out smooth, steady, precise movements.

75. Spinal cord
• Gross structure,
• Functions of afferent &
• Efferent nerve tracts,
• Reflex activity

77. • Grey matter
• White matter

78. Reflex activity
• An action produced instantaneously & automatically, with no
such intentions in response to mechanical stimulus ( produced
by stimulation of specific receptors) is termed as reflex
activity.
• Actions are involuntary.
• E.g. pricked with needle, hand is spontaneously withdrawn,
strong light flashed eyes close spontaneously, beating of
heart, peristalsis, secretion of glands.

79. Reflexes
• The simplest neural pathway is the reflex arc.
• This involves one or more sensory neurons, association
neurons in the spine, and motor neurons, which carry out the
reflex entirely before the brain is aware of the response.

80. Reflex Arc
5 functional components
1
2
3
4
5