1. Introduction to the NERVOUS SYSTEM
Dr Abubakr H Mossa
Anatomy Instructor
MBBS, 15/9/2011
Introduction to the NERVOUS SYSTEM

2. Divisions of nervous system:
Topic outline:
Divisions of nervous system:
Anatomical (structural):
Cellular components:
Neurons: parts and types
Neuroglia
Central nervous system (CNS)
Brain and spinal cord
White and grey matter
Protection
Peripheral nervous system (PNS)
Nerves and ganglia
Functional:
Somatic nervous system
Motor components
Sensory components
Autonomic nervous system (ANS)
Sympathetic NS
Parasympathetic NS

4. Cellular components of NS
Neuron; is the functional unit of NS and has the ability to generate and transmit impulses.
Consists of:
Cell body (soma or perikaryon): contains the nucleus and other cellular organelles
Processes:
Can be myelinated (if surrounded by myelin sheath) or unmyelinated.
Dendrites (to receive input) and an axon (to convey the impulse
Supporting cells (neuroglia): as the name denotes they support and “serve” the neurons but they do not have the ability to generate or conduct impulses.

5. Myelinated fiber:
The myelinating cell membrane folds on itself many times to create a phospholipid coat
Unmyelinated fibers:
Group of axons invaginate into the cell membrane of Schwan cell or oligodendrocyte

6. Serves and supports the neurons (structurally)
Blood brain barrier
Myelination in the CNS
In the PNS we have Schwan cells
Protection of the NS
Cerebrospinal fluid (CSF) secretion

8. Central nervous system (CNS)
Parts of nervous system protected by the skull and the vertebral column.
Integrate and coordinate body functions and responsible for the higher mental functions.
Comprises the;
Brain: cerebrum, cerebellum and brain stem
Spinal cord

9. Central nervous system (CNS)
White and grey matter
Cell bodies of the neurons tend to aggregate in the CNS to form areas which appear darker than the rest of the brain tissue and so called GREY MATTER.
Grey matter in the CNS is found in the cerebral cortex and cerebellar cortex superficially, while in the spinal cord the grey matter lies internally.
There are other collections of cell bodies (grey matter) deep in the brain called nuclei.

10. Central nervous system (CNS)
White and grey matter
The areas occupied by the myelinted processes of the neurons in the CNS appear yellow-white and thus called WHITE MATTER.
The processes run in bundles called tracts (ascending or descending) within the CNS.
White matter lies internally in the brain and externally in the spinal cord.

11. Grey matter in the cortex of the brain
Spinal cord
Grey matter in the Basal nuclei

12. Protection
As we mentioned before, the CNS is protected in the skull and the vertebral column.
Furthermore, the brain and the spinal cord are surrounded by three protective layers called meninges:
Dura matter: outer most, related to the periosteum of the internal aspect of the skull and vertebral canal. (in spinal cord this layer is separated from the vertebral canal by fat)
Arachnoid matter: fibrous layer, deep to the dura
Pia matter: inner most and applied directly to the brain and spinal cord surface. CSF runs between this layer and the arachnoid.

13. Coverings of the brain (meninges)

14. Peripheral nervous system

15. Peripheral nervous system
Formed by the nervous tissue parts found outside the skull and the vertebral column.
Here also we have collections of cell bodies and bundles of processes.
The collections of neuronal cell bodies in the PNS are called GANGLIA.
The bundles of neuronal processes (fibers) are called NERVES.

16. Ganglia and peripheral nerves
Peripheral nervous system
Ganglia and peripheral nerves
Nerves forming the PNS are:
12 pairs of cranial nerves: arise from the brain and supply structures in the head and neck.
31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 sacral.
Other autonomic nerves and plexuses
Ganglia:
Ganglia related to the cranial nerves
Spinal (dorsal root) ganglia
Autonomic ganglia

17. Peripheral nervous system
peripheral nerves
Structure of a peripheral nerve:
Myelinated nerve axons supported by endoneurium.
A bundle of axons is surrounded by another connective tissue envelope called perineurium to form a fascicle.
Fascicles and the supplying blood vessels are enclosed by the epineurium to form a nerve

18. Peripheral nervous system
peripheral nerves

19. Peripheral nervous system
peripheral nerves
Structure of spinal nerve:
Ventral (motor) and dorsal (sensory) rootlets
Ventral and dorsal root
Dorsal root ganglia
Spinal nerve: mixing of fibers happen here
Sympathetic (paravertebral) ganglion is connected to the spinal nerve by grey and white rami communicans
The spinal nerve, as it leaves the vertebral canal divides into Anterior (ventral) and posterior (dorsal) rami, both are mixed:
Dorsal rami innervate the muscles and the skin over the vertebral column.
Anterior rami supply the lateral and anterior aspects of the trunk as well as the limbs.
The anterior rami also intermingle with each other at certain levels to form plexuses (cervical p. to the neck, brachial p. to the upper limb and lumbosacral p. to the lower limb)

20. Peripheral nervous system
peripheral nerves
Dorsal rami innervate the muscles and the skin over the vertebral column.
Anterior rami supply the lateral and anterior aspects of the trunk as well as the limbs.
The anterior rami also intermingle with each other at certain levels to form plexuses (cervical p. to the neck, brachial p. to the upper limb and lumbosacral p. to the lower limb)

23. Peripheral nervous system
Ganglia
Ganglia:
Ganglia related to the cranial nerves:
They host the cell bodies of the sensory neurons of the cranial nerves and they lie within the skull.
Spinal (dorsal root) ganglia:
Contains the cell bodies of the sensory neurons receiving information from the body to the CNS (spinal cord).
Autonomic ganglia: are either:
Sympathetic : paravertebral or prevertebral
Parasympathetic: close to the target organ

25. Functional division

26. Functional division
Functionally we can not separate the CNS from the PNS. For example if we consider a motor order for a certain muscle, this should involve parts in both; the CNS and PNS.
Generally the NS can be divided according to the functions into:
Somatic nervous system: under our conscious control
Motor
sensory
Autonomic (visceral or involantry) nervous system

27. Somatic nervous system
Functional division
Somatic nervous system

28. Somatic nervous system
Functional division
Somatic nervous system
Motor system:
This includes the parts of the CNS which generate, conduct and coordinate the motor orders (cerebral cortex, basal nuclei, anterior grey horn of spinal cord, descending tracts…) AND the nerve fibers (anterior roots of spinal nerves) which convey these orders to the target muscle via their peripheral nerves.

29. Somatic nervous system
Functional division
Somatic nervous system
Sensory system: Consists of:
The peripheral receptor which are distributed all over the body to receive different stimuli.
Sensory nerves and their cell bodies in the dorsal root ganglia
Ascending tracts in the CNS
Diencephalon and cerebral cortex which understand and process these information

30. Autonomic nervous system
Functional division
Autonomic nervous system

31. Autonomic nervous system
Functional division
Autonomic nervous system
Controls the involuntary function of the internal body organs.
Controlled by higher centers in the brain
Is divided into sympathetic and parasympathetic nervous systems
Each system of the two consists of two sets of neurons and ganglia at which the two neurons synapse.
The cell body of the first neuron is found in the CNS while the cell body of the second is located in peripheral ganglia.
The first neuron is called preganglionic neuron
The second is called postganglionic neuron

32. Sympathetic nervous system
Functional division
Sympathetic nervous system
Structure of the sympathetic nervous system:
Preganglionic neuronal cell body is found in the lateral horn of the spinal cord segments from T1-L2
The ganglia are either:
Paravertebral; on both sides of the vertebral column forming two sympathetic chains
Prevertebral: anterior to the vertebral column related to the major branches of the abdominal aorta
From these ganglia the postganglionic neuronal fiber reaches the target organs through the branches of the spinal nerves or along the blood vessels or by their own nerves (visceral or splanchnic plexuses)

34. Parasympathetic nervous system
Functional division
Parasympathetic nervous system
Structure of the parasympathetic nervous system:
Preganglionic neuronal cell bodies are found in the:
Nuclei of cranial nerves III, VII, IX and X
Grey matter of sacral spinal cord segments 2,3 and 4
Hence they constitute the craniosacral flow
The ganglia are:
Four in the region of head
Plenty of parasymathetic ganglia on the wall of target organ (i.e. the parasympathetic ganglia for the stomach lies in the wall of the stomach and so on)
Thus, the postganglionic neuron is short.
The parasympathetic fibers are distributed to the body via the above-mentioned cranial nerves and through the pelvic plexus.

35. Cranio-sacral flow

39. Thanks