sistem saraf pusat

1. Animal Nervous System
SCBI601201

2. Learning Objectives
• able to infer the evolutionary and development of animal
nervous system.
• able to describe different types of nervous systems in
different animal lineages.
• able to identify and describe basic structures and functions of
the central and peripheral nervous systems.

3. Functions of the Nervous System
1.Sensory input → gathering information
• to monitor changes occurring inside and outside the body (stimuli).
1.Integration
• to process and interpret sensory input and decide if action is needed.
1.Motor output
• a response to integrated stimuli.
• the response activates muscles or glands.

4. Animal Neurulation

5. Diversity of Nervous Systems
• All animals have a true nervous system except sea sponges.
• The nervous systems of invertebrates and vertebrates is that the nerve cords of many invertebrates
are located ventrally whereas the vertebrate spinal cords are located dorsally.
• Compared to invertebrates, vertebrate nervous systems are more complex, centralized, and
specialized. While there is great diversity among different vertebrate nervous systems, they all
share a basic structure: a CNS that contains a brain and spinal cord and a PNS made up of
peripheral sensory and motor nerves.
• Cnidarians, such as jellyfish, lack a true brain but have a system of separate but connected neurons
called a nerve net.
• Echinoderms, such as sea stars, have neurons that are bundled into fibers called nerves.
• Flatworms of the phylum Platyhelminthes have both a CNS made up of a small brain and two nerve
cords, and PNS containing a system of nerves that extend throughout the body.
• The insect nervous system is more complex but also fairly decentralized, with a brain, ventral nerve
cord, and ganglia (clusters of connected neurons). These ganglia can control movements and
behaviors without input from the brain.
• Cephalopods, such as octopi, may have the most complicated of invertebrate nervous systems, with
neurons that are organized in specialized lobes and eyes that are structurally similar to vertebrate
species.

6. Two Alternative Hypotheses of the Origins of
Nervous Systems
• the evolution of animal nervous systems has focused primarily on whether they have a single origin or were
independently derived in ctenophores, the comb jellies, and the common ancestor of all other animals.

7. The Origins of Nervous Systems:
Homologous (Single Origin)
If nervous systems are homologous across
metazoans, and if ctenophores are the earliest-
diverging animals, then nervous systems were lost
in sponges and placozoans.

8. The Origins of Nervous Systems: Non-
homologous (Independent Origins)
If nervous systems are not homologous across
animals then they arose more than once, a
result that is not made more or less likely by
any of the possible placements for
ctenophores.

9. The Orthogon Scenario of Nervous
System
• defined by multiple pairs of longitudinal cords
distributed along the dorsoventral axis of the
animal and connected with transverse
commissures.
• mainly present in Platyhelminthes, but also in
some representatives of other animal lineages
(e.g. annelids).
• the loss of the dorsal longitudinal cords of the
ancestral orthogon would have originated the
ventral cords found in many protostomian
lineages, while the loss of the ventral cords of
the orthogon would explain the dorsal location
of the nerve cord in chordates.

10. The ‘oral nerve ring’ Scenario of Nervous
System
• the oral nerve ring of anthozoan
cnidarians (e.g. sea anemones) directly
corresponds to the longitudinal nerve
cords of bilaterian animals.

11. The ‘nemertean’ Scenario of Nervous System
• nemerteans as the starting point for the
evolution of dorsal and ventral nerve
cords in other bilaterian lineages.
Because nemerteans have lateral nerve
cords.
• the movement of lateral nerve cords to
the dorsal side could lead to the dorsal
nerve cord of chordates, and the opposite
movement would have originated the
ventrally centralized longitudinal cords of
Protostomia .

12. The ‘annelid’ Scenario of Nervous System
• polychaete annelid as the closest relative
of the chordates, explaining the evolution
of the dorsal nerve cord of chordates by
an inversion of the dorsoventral axis of
the ancestral adult polychaete.

13. The Diversity of Neural Anatomies in Metazoa

14. Sponge cells hint at origins of nervous
system
digestive cell
neuroid cell

15. Nerve Nets
• Cnidaria and Ctenophora → the
simplest types of nervous system
(nerve nets) as well as relatively
complex forms, i.e., radially
symmetric nervous systems.
• Epidermal nerve nets
concentrated around the mouth
and the peduncle → nerve rings
• Subumbrellar → inner (large
bipolar neurons), outer (small
multipolar sensory neurons)
(a) The nervous system of the polyp Hydra
(b) radial section through the umbrella of a hydromedusa
ENR=exumbrellar nerve ring, M=mesogloea, RC= ring canal, SNR=subumbrellar nerve ring,
SRM=subumbrellar ring muscle, V=velum, VRM=velar ring muscle

16. Nerve Cords
Three schemes for evolution of the chordate and hemichordate nerve
cords.
(a)The ancestor of chordates and ambulacrarians had a nerve net.
Nerve cords in hemichordates and chordates evolved independently.
(b)The ancestor of the Ambulacraria plus Chordata clade had a ventral
nerve cord. A dorsal/ventral inversion occurred at the base of the
ambulacraria plus Chordata. Thus, the dorsal nerve cord of
hemichordates is homologous to the chordate nerve cord.
(c)The ancestor of the Ambulacraria plus Chordata had a ventral nerve
cord. A dorsal/ventral inversion occurred in the lineage leading to
chordates. Thus, the ventral nerve cord of hemichordates is
homologous to the dorsal nerve cord of chordates.

17. The Nervous System of Annelida
• Paired “ladder-type” central nervous system → the simplest state
consists of a cerebral or supraesophageal nerve ring or ganglion giving
rise to paired ventral cords with a pair of ganglia per body segment
connected by transverse connectives (anastomoses).
• Polychaetes has developed into a three-partite brain → proto-, deuto-,
and tritocerebrum
• Oligochaetes → the first segments of the ventral nerve cord are often
fused into a subesophageal ganglion.

18. The Nervous System of Nematoda
• Simple nervous systems consisting of a nerve ring around the
esophagus and a number of ganglia connected to this ring.
• Local ganglia and nerves are found in the caudal gut and anal region.
Some nerves extend from the esophageal nerve ring to the sense
organs in the “head” region such as sensory papillae and bristles. Other
sense organs are chemoreceptive organs called “amphidia”.

19. The Nervous System of Arthropods
• Ventral, regularly segmented, paired “ladder-type” nerve
cord.
• The first ganglia have fused into a complex brain. In
mandibulates there are three major brain divisions, i.e., a
proto-, deuto-, and tritocerebrum. The protocerebrum is
associated with the paired optic lobes, the
deutocerebrum with the first and the tritocerebrum with
the second pair of antennae.
• Mandibulates display a subesophageal ganglion having
formed by fusion of the three first ventral ganglia. They
supply the mouth region and mandibles, in crustaceans
the first and second maxillae, in insects the maxillae,
mandibles and labium.
• Caudal ganglia of the ventral cords exhibit a strong
tendency to fuse and to form specialized abdominal
structures. (a) Lateral view and (b) ventral view of
the brain and nerves in the scorpion fly
Panorpa (c) Schematic of the brain of a
honey bee

20. Structural Classification of the Nervous
System
1. Central nervous system (CNS) →
Brain & Spinal cord
2. Peripheral nervous system (PNS) →
Cranial nerves & Spinal nerves

21. Peripheral Nervous System (PNS)
1. Sensory (afferent):
• Nerve fibers that carry information to the central nervous system from:
❏ sensory receptors in the skin, skeletal muscles and joints (somatic sensory fibers).
❏ Sensory receptors in the visceral organs (visceral sensory
1. Motor (efferent) division:
• Nerve fibers that carry impulses away from the central nervous system (to Muscles &
glands).
❏ Somatic nervous system = voluntary , it controls skeletal muscles → skeletal
muscle reflexes are involuntary
❏ Autonomic nervous system = involuntary , it controls smooth & cardiac muscles &
glands → Sympathetic & parasympathetic

22. Organization of the Nervous System

23. Histology of Nervous Tissue
• Neurons → excitable nerve cells
that transmit electrical signals.
• Neuroglia ( glial) cells Astrocytes,
Microglia, Ependymal cells,
Oligodendrocytes ) are the
supporting cells.

24. Neuron (Nerve cell)
• Cells specialized to transmit messages:
1. A Cell body with nucleus and the
usual organelles, except centrioles.
2. Extensions processes outside the cell
body → Dendrites conduct impulses
toward the cell body Axons conduct
impulses away from the cell body.

25. Multipolar neurons
many extensions from the cell body; three or more processes.

26. Bipolar neurons
one axon and one dendrite; two processes (axon and dendrite).

27. Unipolar neurons
have a short single process leaving the cell body.

28. Structural Variation of Neurons

29. Neuroglia in CNS: Astrocytes
• Abundant, star shaped cells
• Brace neurons
• Form barrier between capillaries and neurons
• Control the chemical environment of the brain
(CNS)

30. Neuroglia in CNS: Microglia & Ependymal
cells
• Microglia → Spider like phagocytes,
dispose of debris
• Ependymal cells → Line cavities of the
brain and spinal cord, circulate
cerebrospinal fluid
Microglia

31. Neuroglia in CNS: Oligodendrocytes
• Produce myelin sheath around nerve
fibers in the central nervous system.

32. Neuroglia in PNS: Satellite & Schwann
cells
• Satellite cells → surround neuron cell bodies in the periphery, protect neuron cell bodies.
• Schwann cells (neurolemmocytes) → surround axons/dendrites and form the myelin
sheath around larger nerve fibers in the periphery similar to oligodendrocytes in function
insulators.

33. Neuroglia vs. Neurons
• Neuroglia divide.
• Neurons do not.
• Most brain tumors are gliomas
• Most brain tumors involve the neuroglial
cells, not the neurons.

34. Axons and Nerve Impulses
• Axons end in axonal terminals
• Axonal terminals contain vesicles
with neurotransmitters
• Axonal terminals are separated from
the next neuron by a gap:
1. Synaptic cleft gap between
adjacent neurons
2. Synapse junction between nerves

35. Regions of the Brain

36. Specialized Areas of the Cerebrum
• Somatic sensory area → receives
impulses from the body’s sensory
receptors
• Primary motor area → sends impulses to
skeletal muscles
• Broca’s area → involved in our ability to
speak
• Cerebral areas involved in special senses
→ Gustatory area (taste), Visual area,
Auditory area, Olfactory area

37. Sensory and Motor Areas of the Cerebral
Cortex

38. Cerebral cortex-type of neurons:
Pyramidal
• Triangular
• Dendrite arises from three angles
• Axon from the base of cell
• Prominent nucleus and Nissl
substances
• Small sized pyramidal neuron 10-12
micron
• Medium sized neuron 40-50 micron
• Large sized (Betz cells ) >100 micron

39. Cerebral cortex-type of neurons:
Stellate/granular & Fusiform cells
• Stellate/granular cells → Polygonal
/triangular shape, dark condensed
nucleus, dendrites arises all over, axon
terminate next layer and goes deeper.
• Fusiform → Oriented perpendicular to the
surface, One dendrites towards
superficial, one axon towards deeper
layer.
Fusifor
m
Stellate/granula
r

40. Cerebral cortex-type of neurons: Horizontal
cells of Cajal, Cell of Mortinotti, & Golgi type
II
• Horizontal cells of Cajal → spindle
shaped, parallel to the surface,
Internuncial type.
• Cell of Mortinotti → Small triangular cells,
axons goes towards surface
• Golgi type II → process ends close to cell
body, local circuit
Cajal
Golgi
Mortinotti

41. Layers of cerebral cortex
1. Outer Molecular layer → horizontal cells + Golgi type II,
tangential nerve fibers from pyramidal, fusiform and
cells of Mortinotti.
2. Outer granular layer → small pyramidal cells + stellate
cells, dendrites end in first layer, axons forms
association.
3. Outer pyramidal layer → medium and large pyramidal
cells, axons forms association and commissural fibers.
4. Inner granular layer → packed stellate cells, lot of
fibers as band-outer band of Baillarger.
5. Inner pyramidal/ganglion → large Betz cells, axons
continues as projection fibers, horizontal fibers forms
inner band of Baillarger.
6. Multiform layer/fusiform cells → spindle shaped cells,
granular , fusiform and stellate type.

42. Diencephalon
• Sits on top of the brain stem.
• Enclosed by the cerebral hemispheres.
• Thalamus → surrounds the third ventricle, the relay
station for sensory impulses, transfers impulses to
the correct part of the cortex for localization and
interpretation.
• Hypothalamus → under the thalamus, important
autonomic nervous system center (helps regulate
body temperature, controls water balance, regulates
metabolism), important part of the limbic system
(emotions), the pituitary gland is attached to the
hypothalamus.
• Epithalamus → forms the roof of the third ventricle,
houses the pineal body (an endocrine gland),
includes the choroid plexus forms cerebrospinal
fluid.
v
v

43. Brain Stem
• Attaches to the spinal cord.
• Midbrain → Mostly composed of tracts of nerve
fibers (Reflex centers for vision and hearing,
Cerebral aquaduct 3rd- 4th ventricles)
• Pons → the bulging center part of the brain
stem, mostly composed of fiber tracts, includes
nuclei involved in the control of breathing.
• Medulla oblongata → the lowest part of the
brain stem, merges into the spinal cord,
includes important fiber tracts, contains
important control centers (heart rate control,
blood pressure regulation, breathing,
swallowing, vomiting)

44. Cerebellum
• Two hemispheres with
convoluted surfaces.
• Provides involuntary
coordination of body
movements.
Granule
Golgi type II
Purkinje cells Stellate
cells
Basket
cells

45. Layers of Cerebellum
1. Molecular layer → dendrite arborization, densely
packed axons run parallel to surface,
superficially stellate cells, deeper stellate cells
(basket cells).
2. Purkinje layer
3. Granular layer → closely packed granule cells

46. Purkinje Neuron
Stellate
cells
Basket
cells

47. Cerebellum - Golgi stain

48. Cerebellum granular layer (rosette)

49. Protection of the Central Nervous
System
• Scalp and skin
• Skull and vertebral column
• Meninges
• Cerebrospinal fluid
• Blood brain barrier

50. Meninges: Dura mater
❏ Dura mater
● Double layered external covering
→ periosteum attached to surface
of the skull, meningeal layer outer
covering of the brain
● Folds inward in several areas

51. Meninges: Arachnoid layer & Pia mater
Arachnoid layer → middle layer , web like
Pia mater → internal layer, clings to the
surface of the brain

52. Cerebrospinal Fluid
• Similar to blood plasma composition
• Formed by the choroid plexus
• Forms a watery cushion to protect the
brain
• Circulated in arachnoid space, ventricles,
and central canal of the spinal cord.

53. Blood Brain Barrier
• Includes the least permeable capillaries of the body
• Excludes many potentially harmful substances
• Useless against some substances → fats and fat
soluble molecules, respiratory gases, alcohol,
nicotine, anesthesia.

54. Spinal Cord Anatomy
• Exterior white mater → conduction tracts.
• Internal gray matter (mostly cell bodies)
→ dorsal (posterior) horns, anterior
(ventral) horns.
• Central canal filled with cerebrospinal
fluid.