organisation of central nervous system

2. Organization of the Nervous
System
M JYOTIRMAYEE
SISTER TUTOR

3. Introduction
• We only have one nervous system, but, because of its complexity, it is
difficult to consider all of its parts at the same time;
• so, to simplify its study, we divide it in terms of its
• structures (structural classification) or
• in terms of its activities (functional classification).

4. Structural Classification
• The structural classification, which includes
all of the nervous system organs, has two
subdivisions-
1. the central nervous system and
2. the peripheral nervous system.

5. • Central nervous system (CNS). The CNS consists of the brain and
spinal cord, which occupy the dorsal body cavity and act as the
integrating and command centers of the nervous system
• Peripheral nervous system (PNS). The PNS, the part of the nervous
system outside the CNS, consists mainly of the nerves that extend
from the brain and spinal cord.

6. (Prosencephalon) (Rombencephalon)(Mesencephalon)
(encephalon)

7. PNS
Anatomically
Cranial
Nerves(12P
airs)
Spinal
Nerves (31
Pairs)
Physiologicall
y
Sensory
Neuron
Somatic (Voluntary) Autonomic
(Involuntary)
Motor
Neuron
Sensory
Nerves
(I,II,VIII)
Sympathetic Para Sympathetic
Motor
Nerves
(III, IV,VI,
XI, XII)
Mixed Nerves
(V,VII,IX, X)

9. Functional Classification
• The functional classification scheme is concerned only with PNS structures.
• Sensory division. The sensory, or afferent division, consists of nerves (composed
of nerve fibers) that convey impulses to the central nervous system from sensory
receptors located in various parts of the body.
• Somatic sensory fibers. Sensory fibers delivering impulses from the skin, skeletal
muscles, and joints are called somatic sensory fibers.
• Visceral sensory fibers. Those that transmit impulses from the visceral organs are
called visceral sensory fibers.

10. • Motor division. The motor, or efferent division carries impulses from the CNS to effector
organs, the muscles and glands;
 the motor division has two subdivisions: the somatic nervous system and
the autonomic nervous system.
• Somatic nervous system. The somatic nervous system allows us to consciously,
or voluntarily, control our skeletal muscles.
• Autonomic nervous system. The autonomic nervous system regulates events that are
automatic, or involuntary; this subdivision, commonly called involuntary nervous system,
 has two parts: the sympathetic (fight and flight) and parasympathetic (rest and
digestion), which typically bring about opposite effects.

11. Functions of the Nervous System
• To carry out its normal role, the nervous system has three overlapping functions.
• Monitoring changes. Much like a sentry, it uses its millions of sensory receptors
to monitor changes occurring both inside and outside the body; these changes
are called stimuli, and the gathered information is called sensory input.
• Interpretation of sensory input. It processes and interprets the sensory input and
decides what should be done at each moment, a process called integration.
• Effects responses. It then effects a response by activating muscles or glands
(effectors) via motor output.

12. • Mental activity. The brain is the center of mental activity, including
consciousness, thinking, and memory.
• Homeostasis. This function depends on the ability of the nervous
system to detect, interpret, and respond to changes in the internal
and external conditions. It can help, stimulate or inhibit the activities
of other systems to help maintain a constant internal environment.
• Impulse transmission.

13. Nervous Tissue: Structure and Function
• Even though it is complex, nervous tissue is made up of just two
principal types of cells-
1. supporting cells and
2. neurons.

14. 1. Supporting Cells
• Supporting cells in the CNS are “lumped together” as neuroglia, literally mean
“nerve glue”.
• Neuroglia. Neuroglia include many types of cells that generally support, insulate,
and protect the delicate neurons; in addition, each of the different types of
neuroglia, also simply called either glia or glial cells,has special functions.
• Astrocytes. These are abundant, star-shaped cells that account for nearly half of
the neural tissue; astrocytes form a living barrier between the capillaries and
neurons and play a role in making exchanges between the two so they could help
protect neurons from harmful substances that might be in the blood.

15. • Microglia. These are spiderlike phagocytes that dispose of debris, including dead
brain cells and bacteria.
• Ependymal cells. Ependymal cells are glial cells that line the central cavities of
the brain and the spinal cord; the beating of their cilia helps to circulate
the cerebrospinal fluid that fills those cavities and forms a protective cushion
around the CNS.
• Oligodendrocytes. These are glia that wrap their flat extensions tightly around
the nerve fibers, producing fatty insulating coverings called myelin sheaths.
• Schwann cells. Schwann cells form the myelin sheaths around nerve fibers that
are found in the PNS.
• Satellite cells. Satellite cells act as protective, cushioning cells.

17. Neurons
• also called nerve cells, are highly specialized to transmit messages
(nerve impulses) from one part of the body to another.

19. Parts of NEURON
a
cell body
Axon
Dendrites

20. Functions
• send and receive chemical and electrical signals.

21. • Cell body. The cell body (gray matter) is the metabolic center of the neuron; it has
a transparent nucleus with a conspicuous nucleolus; the rough ER, called Nissl
substance, and neuro-fibrils are particularly abundant in the cell body.
• Processes. The arm like processes, or fibers, vary in length from microscopic to 3
to 4 feet; dendrons convey incoming messages toward the cell body,
while axons generate nerve impulses and typically conduct them away from the
cell body.
• Axon hillock. Neurons may have hundreds of the branching dendrites, depending
on the neuron type, but each neuron has only one axon, which arises from a cone
like region of the cell body called the axon hillock.

22. • function of the axon hillock:
• The axon hillock is located at the end of the soma and controls the firing of the
neuron.
• If the total strength of the signal exceeds the threshold limit of the axon hillock,
the structure will fire a signal (known as an action potential) down the axon.
• Axon: these are the extension of cell body
: form the white matter of Nervous System
: typically has 1 axon in each nerve cell
:length :=100cm (1m) long

23. • Axon terminals. These terminals contain hundreds of tiny vesicles, or membranous sacs that
contain neurotransmitters.
• Myelin sheaths. Most long nerve fibers are covered with a whitish, fatty material called myelin,
which has a waxy appearance; myelin protects and insulates the fibers and increases the
transmission rate of nerve impulses.
• Nodes of Ranvier. Because the myelin sheath is formed by many individual Schwann cells, it
has gaps, or indentations, called nodes of Ranvier.
• Axolema/axoplasm : the cell membrane of an axon.
• : is responsible for maintaining the membrane potential of the axon, and
contains ion channels through which ions can flow rapidly

25. • Neurilemma (also known as neurolemma): is the outermost nucleated
cytoplasmic layer of Schwann cells that surrounds the axon of the neuron.
• It forms the outermost layer of the nerve fiber in the peripheral nervous system
• function of the Neurolemma?
• Neurilemma serves a protective function for peripheral nerve fibers.
• Damaged nerve fibers may regenerate if the cell body is not damaged and the
neurilemma remains intact.
• The neurilemma forms a regeneration tube through which the growing axon re-
establishes its original connection.

26. • Axons often have thousands of terminal
branches, each ending as a bulbous enlargement,
the synaptic knob or synaptic terminal.
• At the synaptic knob, the action potential is
converted into a chemical message which, in
turn, interacts with the recipient neuron or
effector.
• Synaptic cleft. Each axon terminal is separated
from the next neuron by a tiny gap called synaptic
cleft.

28. Do neurons undergo cell division?
• Neurons lack the Centrioles and hence Mitosis is not possible and so
they can't divide.

30. Central Nervous System
• During embryonic development, the
CNS first appears as a simple tube, the
neural tube, which extends down the
dorsal median plan of the developing
embryo’s body.

33. The brain
• Because the brain is the largest and most complex mass of nervous tissue in the body, it
is commonly discussed in terms of its major regions
• Situated in cranial cavity.
• Wt: 1.5kg
 main parts: four
• the cerebrum
• diencephalon
• cerebellum and
• brainstem.

34. Cerebrum
• Largest part of brain
• Consists of 2 hemispheres- right & left
• Gyri. exhibits elevated ridges of tissue called gyri, separated by
shallow grooves called sulci.
• deeper grooves of tissue called fissures

35. Layers of the Cerebrum
Slide 7.33aCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
 Gray matter
Outer layer
Composed mostly of
neuron cell bodies
Figure 7.13a

36. Layers of the Cerebrum
Slide 7.33bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
 White matter
Fiber tracts inside the
gray matter
Example: corpus
callosum connects
hemispheres
Figure 7.13a

37. 4 lobes of brain and their functions

38. basal ganglia/ basal nuclei
• are a group of sub cortical nuclei, situated at the base of
the forebrain and top of the midbrain.
• Basal ganglia are strongly interconnected with the cerebral
cortex, thalamus, and brainstem, as well as several other brain areas.
• Act as a relay center.
• functions, including :
• control of voluntary motor movements
• procedural learning
• habit learning
• eye movement,
• cognition and emotion.

39. • Corpus callosum. One very large fiber tract, the corpus callosum, connect
the cerbral hemispheres; such fiber tracts are called commisures.
• Fiber tracts. Association fiber tracts connect areas within a hemisphere,
and projection fiber tracts connect the cerebrum with lower CNS centers.

41. Hippocampus
• Humans have two hippocampi, one in each hemisphere of the brain.
• They are located in the medial temporal lobe of the brain.
Functions:
• principally involved in storing long-term memories and in making
those memories resistant to forgetting
• spatial processing and navigation. (matter of debate)
• Limbic system

42. Amygdala
• Anatomically, the amygdala,and more particularly its central and
medial nuclei, have sometimes been classified as a part of the basal
ganglia.
• Right amygdala induced negative emotions, especially fear and
sadness.
• left amygdala was able to induce either pleasant (happiness) or
unpleasant (fear, anxiety, sadness) emotions.
• left amygdala plays a role in the brain's reward system.
• Others functions:
• Episodic-autobiographical memory (EAM) networks
• Attentional and emotional processes
• Social processing

44. Diencephalon
• Sits on top of brain stem
• Encloses by cerebral hemisphrere
• encloses a cavity called the third ventricle
• Structure including
a) the thalamus,
b) hypothalamus,
c) posterior portion of the pituitary gland, and
d) the pineal gland.
e) the epithalamus and the subthalamus

45. Thalamus
• located deep within the brain in the cerebral cortex,
• adjacent to the hypothalamus.
• It is a symmetrical structure, situated on top of the brain stem and on either side
of the third cortex
• mostly gray matter structure of the diencephalon
• main function of the thalamus is :
• to relay motor and sensory signals to the cerebral cortex.
• regulation of consciousness and alertness.

46. Hypothalamus
• The hypothalamus makes up the floor of the diencephalon;
• it is an important autonomic nervous system center because
• it plays a role in the regulation of body temperature, water balance, and
metabolism;
• it is also the center for many drives and emotions, and as such, it is an
important part of the so-called limbic system or “emotional-visceral brain”;
the hypothalamus also regulates the pituitary gland and produces
hormones.

47. Epi-thalamus
• The epi-thalamus forms the roof of the third ventricle;
• important parts of the epi-thalamus are :
1. the pineal body (part of the endocrine system) and
2. the choroid plexus of the third ventricle, which forms the
cerebrospinal fluid.

48. The sub-thalamus
• is the most ventral part of the diencephalon.
• It lies in between the thalamus and the midbrain.
• involved with integration of somatic motor function
• function of the Subthalamus:
• responsible for sexuality,
• food and water intake and
• maintenance of hydration, and
• cardiovascular activity.

49. MIDBRAIN
The principal regions are :
• the tectum ( superior (visual) and inferior (auditory) canalculli)
• the cerebral aqueduct (connect 3rd & 4th ventricles)
• tegmentum and
• the cerebral peduncles.
Function:
• associated with vision, hearing, motor control, sleep and wakefulness, arousal
(alertness), and temperature regulation. ...

50. Midbrain Tegmentum
• Located in the ventral region of midbrain.
• Structures included in the midbrain tegmentum are: the red nucleus,
reticular formation, and substantia nigra.
• The red nucleus is responsible for controlling basic body and limb
movements.
• The reticular formation controls arousal and self-consciousness, and
• the [substantia nigra] integrates voluntary movements.

51. Hind brain (The cerebellum)
• (which is Latin for “little brain”)
• is a major structure of the hindbrain
• is located near the brainstem.
Responsible for :
• coordinating voluntary movements.
• including motor skills such as balance, coordination, and posture.

52. Means “Bridge” in Latin

53. Medulla oblongata
• the lowest part of the brain and
• the lowest portion of the brainstem.
• is connected by the pons to the midbrain and
• is continuous posteriorly with the spinal cord, with which it merges
at the opening (foramen magnum) at the base of the skull.

54. functions of The medulla oblongata
• is responsible for regulating several basic functions of the autonomic
nervous system,
• including respiration, cardiac function, vasodilation, and
• reflexes like vomiting, coughing, sneezing, and swallowing

55. Parts of Brain

56. Protection of the
Central Nervous System
(MENINGES)

57. Introduction
• Nervous tissue is very soft and delicate, and the irreplaceable
neurons are injured by even the slightest pressure, so nature has tried
to protect the brain and the spinal cord by enclosing them within
bone (the skull and vertebral column), membranes (the meninges),
and a watery cushion (cerebrospinal fluid).

58. Meninges
• The three connective
tissue membranes
covering and protecting
the CNS structures are
called the meninges.

59. THREE layers
• the dura, (outer)
a) Epidura
b) sub dura
• the arachnoid (middle)and
a) sub arachnoid
• the pia (inner)

61. dura mater ( Anatomy)
• derives from the Latin for tough mother (or hard mother)
• literally 'thick mother of the brain', matrix of the brain
• Cranial dura mater has two layers-
(a) a superficial layer (also called the periosteal layer)
(b) a deep layer called the meningeal layer
• When it covers the spinal cord it is known as the dural sac or thecal sac.
• Unlike cranial dura mater, spinal dura mater only has one layer, known as the meningeal
layer.
• The potential space between these two layers is known as the epidural space.

63. arachnoid mater
• middle element of the meninges
• so named because of its resemblance to a spider web.
• It cushions the central nervous system.
• Separated from the dura matter by the sub dural space that contains
a small amount of serous fluid
• And from the pia matter by the sub arachnoid space , which contains
CSF.

65. Pia mater
• (Latin: tender mother[8]) is a very delicate membrane.
• It is the meningeal envelope that firmly adheres to the surface of
the brain and spinal cord, following all of the brain's contours
(the gyri and sulci).
• It is a very thin membrane composed of fibrous tissue covered on its
outer surface by a sheet of flat cells thought to be impermeable to
fluid.
• The pia mater is pierced by blood vessels to the brain and spinal cord,
and its capillaries nourish the brain.

66. continuation of pia matter
• Continue downwards surrounding the spinal cord
• Beyond the end of the cord it continues as the filum terminale,
pierces the arachnoid tube and goes on, with the dura matter, to fuse
with the periosteum of the coccyx.

67. Leptomeninges
• The arachnoid and pia mater together are sometimes called
the leptomeninges, literally "thin meninges“

68. The subarachnoid space
• is the space that normally exists between the arachnoid and the pia
mater, which is filled with cerebrospinal fluid, and continues down
the spinal cord.

69. function of the meninges
• is to protect the brain and spinal cord from mechanical trauma,
• to support the blood vessels and
• to form a continuous cavity through which the cerebrospinal fluid
(CSF) passes.

70. The ventricles of the brain
• are a communicating network of cavities filled
with cerebrospinal fluid (CSF) and
• located within the brain parenchyma.
• The ventricles:
• 2 lateral ventricles,
• the third ventricle, the cerebral aqueduct, and
• the fourth ventricle

71. Cerebrospinal fluid (CSF)
• is a clear, colorless body fluid found in the brain and spinal cord. It is
produced by specialised ependymal cells in the choroid plexuses of
the ventricles of the brain, and absorbed in the arachnoid
granulations.

74. production
• In normal adults, the CSF volume is 125 to 150 mL (constant)
• approximately 20 mL per hour.
• 0.20-0.35 mL/min
• = 720 ml per day
• Pressure :
• 10 cm of water- in lying
• 30 cm of water – in sitting up
• Specific gravity: 1.005
• Clear and Alkaline in nature

75. Composition