General Anatomy of Nervous System - Dr Muhammad Ali Rabbani

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General Anatomy of Nervous System
Dr. Muhammad Ali Rabbani
Asst. Professor Anatomy
MBBS (NMC, Multan)
FCPS (Anatomy)
CHPE (Certificate in Health Professional Education)
DHPE (Diploma in Health Professional Education)
MBA (Masters of Business Administration)
MPH (Masters of Public Health)

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Learning Objectives
By the end of this lectures students should be able to
• Describe General Organization of Nervous System (Central &
Peripheral)
• Describe parts and formation of typical spinal nerves
• Enumerate and describe functional components of peripheral nerves
• Give an overview of autonomic nervous system
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The network of nerve cells and fibers which transmits nerve impulses
between parts of the body

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General Organization

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Organization of Nervous System
On basis of Anatomy nervous system is divided into
• Central Nervous System
• Consists of brain and spinal cord
• Peripheral Nervous System
• Consists of cranial nerves and spinal nerves
Functionally nervous system can be divided into
• Somatic Nervous System
• Controls voluntary activities
• Autonomic Nervous System
• Controls involuntary activities

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Cells of Nervous System
• Neurons
• Functional Unit
• Conduct nerve impulses
• Supporting cells
• Non-conducting
• Protect, nourish and maintain neurons

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Neurons
• Highly specialized cells with distinctive property of
• Excitability
• Conductivity
• Each neuron consists of
• Cell body (soma)
• Neurites (processes)
• Dendrites – carry impulse towards the cell body
• Axons – carry impulse away from the cell body

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Neurons - Types
Morphologically neurons can be divided into
• Unipolar neurons – have single process that divides into two
• Bipolar neurons – have two neurites
• Multipolar neurons – have several processes

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Neurons - Types
Functionally the neurons can be divided into
• Afferent – sensory neurons
• Efferent – motor neurons
• Interneurons – connector between sensory and motor
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Supporting Cells
• Peripheral Nervous System
• Schwann Cells
• Form sheath around nerve fibers (neurilemma, myelin sheath)
• Satellite Cells
• Surround cell bodies
• Central Nervous System (neuroglia)
• Oligodendrocytes - myelin sheath around axons in CNS, support
• Astrocytes - blood brain barrier, support
• Microglia - macrophages, defense mechanism
• Ependyma - lines ventricles of brain and central canal of SC, help in CSF circulation

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A Few Terminologies
• Nerve
• bundle of neuronal fibers (cell processes) in PNS
• Tracts
• Bundle of neuronal fibers (cell processes) in CNS
• Ganglia
• cluster of neuronal cell bodies in PNS
• Nucleus
• cluster of neuronal cell bodies in CNS
• Synapse
• neuronal junction
• Grey Matter
• darker tissue of CNS consisting mainly of cell bodies embedded in neuroglia
• White Matter
• paler tissue of CNS consisting mainly of nerve fibers embedded in neuroglia

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Central Nervous System
• Consists of brain and spinal cord
• Composed of neurons embedded in connective tissue (neuroglia)
• Interior of CNS is organized into grey matter and white matter
• In brain, grey matter is outside and white matter is on inside
• In spinal cord, white matter is outside while grey matter is in centre

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Peripheral Nervous System
Consists of distributing nerves and ganglia
Anatomically peripheral nerves are classified into two main groups
• Cranial Nerves (12 pairs)
• Attached to brain
• Peripheral Nerves (31 pairs)
• Attached to spinal cord

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Cranial Nerves
I. Olfactory
II. Optic
III. Occulomotor
IV. Trochlear
V. Trigeminal
VI. Abducent
VII. Facial
VIII. Vestibulococchlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal

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Function Classification
• Somatic Nervous System
• Somatic Afferent Division
• Somatic Efferent Division
• Visceral Nervous System
• Visceral Afferent Division
• Visceral Efferent Division

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Spinal Nerves

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• There are 31 pairs of spinal nerves
• Pass through intervertebral foramen in vertebral column
• They are named according to their origin
• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral,1 coccygeal
• In adults, lower end of spinal cord is at lower border of first lumbar vertebra
• To accommodate length of root increase from above downwards
• Roots of the lumbar and sacral nerves below the level of the termination of
the cord form a vertical bundle of nerves that resembles a horse’s tail and is
called the cauda equina

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Structure of Peripheral Nerve
Nerve is a solid white cord composed of bundles (fascicles) of nerve
fibers which are held together by connective tissue
Connective tissue supporting nerve consists of
• Endoneurium
• surrounds individual nerve fiber
• Perineurium
• surrounds a bundle of nerve fibers (fascicle)
• Epineurium
• surrounds the whole nerve

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Formation of a Spinal Nerve
Each spinal nerve is connected to the spinal cord by two roots
• Anterior root
• consists of efferent / motor fibers
• cell bodies lie in anterior grey horn of spinal cord
• Posterior root
• consists of afferent / sensory fibers
• cell bodies lie in dorsal (posterior) root ganglion
At each intervertebral foramen, the anterior and posterior roots unite
to form a mixed spinal nerve

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Formation of a Spinal Nerve cont.
Immediately after emerging spinal nerve divides into
• Anterior Ramus
• Supply anterolateral body wall and limbs
• Connected to sympathetic ganglia by rami communicantes (discussed later)
• Posterior Ramus
• Supply skin and muscles of back
At the root of the limbs, the anterior rami join one another to form
complicated nerve plexuses
• cervical and brachial plexuses are found at the root of the upper limbs
• lumbar and sacral plexuses are found at the root of the lower limbs

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Dermatomes
area of skin that is
mainly supplied by a
single spinal nerve

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Receptors
Change the environmental stimulus into nerve impulses
• Exteroceptors
• Respond to external stimuli that touch skin directly.
• Teleceptors
• Respond to external stimuli that occur at some distance away from body.
• Interoceptors / Viseroceptors
• Respond to stimuli from within the body
• Proprioceptors
• Respond to internal stimuli relating to sense of position and movement

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Effectors
Carry out functions in response to the nervous system
• Contraction of skeletal muscles
• Contraction of cardiac muscles in heart
• Contraction of smooth muscles in viscera
• Secretion of glands

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Functional Component of Nerve

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Functional Classification
Typical spinal nerve has four functional components
• General somatic efferent
• General visceral efferent
• General somatic afferent
• General visceral afferent
Typical cranial nerve has seven functional components
• Four similar to spinal nerve
• Special somatic afferent
• Special visceral efferent
• Special visceral afferent

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Autonomic Nervous System

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• Visceral part of peripheral nervous system
• Innervates involuntary structures through both CNS and PNS
• Heart, smooth muscle, glands
• Somatic efferent system has one-neuron linkage
• Single neuron from CNS to effectors (no synapse)
• Autonomic Nervous system has two-neuron linkage with its effectors
• Impulse from CNS to effector passes through two neurons
• Preganglionic neuron – from CNS to autonomic ganglion (myelinated)
• Postganglionic neuron – from autonomic ganglion to effector (unmyelinated)

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Types
• Sympathetic Nervous System
• Fight or Flight
• Accelerates heart rate
• Constriction of peripheral vessels
• Increases blood pressure
• Inhibits peristalsis
• Closes sphincters
• Parasympathetic Nervous System
• Rest and Digest
• slow the heart rate
• Relaxation of peripheral vessels
• increase peristalsis of the intestine and glandular activity
• open the sphincter

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Sympathetic Nervous System
• Originate from connector cells in lateral horn of first thoracic to second
lumbar
• Thus also called Thoracolumbar part of Autonomic Nervous System
• Axons of preganglionic / presynaptic neurons leave the spinal cord in the
anterior nerve roots
• Then pass via the white rami communicantes to the paravertebral ganglia
of the sympathetic trunk
• Sympathetic Trunks (chains) are paired series of ganglia connected by
intervening fibers
• 3 cervical, 11 / 12 thoracic, 4 / 5 lumbar, 4 / 5 pelvis, ganglion impar

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Once the preganglionic fibers reach the ganglia in the sympathetic
trunk, they may pass to the following destinations:
1. They may synapse with postganglionic neuron in ganglion at
same level
2. It may pass up or down to different level of sympathetic trunk
before synapse
3. May pass through the ganglia without synapsing as splanchnic
nerve

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• Afferent fibers travel from
viscera through ganglia without
synapsing
• They enter spinal nerve via
white rami communicantes
• Reach their cell bodies in dorsal
root ganglion
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Parasympathetic Nervous System
• Originate from connector cells in
• Brain – CN III, VII, IX, X
• Spinal Cord – S1, S2, S3
• The (presynaptic) myelinated axons leave the spinal cord in the
anterior roots
• They then leave the sacral nerves and form the pelvic splanchnic
nerves

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• Peripheral ganglia are usually situated close to the viscera they
innervate
• Cranial preganglionic relay in – ciliary, pterygopalatine, submandibular, otic
• Sacral preganglionic relay in – hypogastric plexus, walls of viscera
• Postganglionic fibers are non-myelinated and are comparatively short
as compared with sympathetic postganglionic
• Afferent myelinated fibers travel from the viscera to their cell bodies
located either in the sensory ganglia of the cranial nerves or in the
posterior root ganglia of the spinal nerves

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Enteric Nervous System
• Two nerve plexus is found in the wall of tubular part of GIT
• Submucosal plexus
• Myenteric plexus
• This system contains about 100 million neurons (motor, sensory, inter)
• This system is innervated and modulated by both limbs of autonomic
nervous system
• However enteric nervous system can function autonomously even if
the sympathetic and parasympathetic innervations are cut

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Thank You
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