The Human Nervous System
1- The Autonomic Nervous System (ANS)
Physiology -I
PHL 215
Prof. Dr/ Gamal Soliman
Pharmacy College
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The human nervous system - Introduction

The human nervous system is the most important system in the body.
 Major divisions of the nervous system :
 The nervous system is divided into 2 main sections:
I- The Central Nervous System or CNS.
 The CNS consists of the brain and the spinal cord
 The CNS is protected by bone and the meninges.
 The brain is protected within the cranium, while the spinal cord is
protected within the vertebrae.
II- The Peripheral Nervous System or PNS.
 The PNS forms a network of nerves between the CNS and other body
organs.
 It consists of cranial and spinal nerves (OR sensory and motor nerves)
which connect the organs to the CNS.
 Unlike the CNS, the PNS is not protected by bone or the meninges.
NOTE:
 The bony covering around the brain is called the cranium, which
combines with the facial bones to form the skull.
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Nervous Tissue

Nervous tissue is composed of 2 main types of cells:
1] The neurons (nerve cells).
 They are responsible for transmitting nerve impulses.
2] The neuroglia (glial cells).
 They are responsible for supporting and nourishing the neurons.
1] The neurons (nerve cells):
 The neuron represents the basic unit of the nervous system.
 The nervous system is consists of more than 1011 neurons (100
billion neurons).
 The neuron is amitotic (i.e, can not divides). This means that
neurons cannot reproduce after damage.
 Each neuron is composed of 3 parts:
a- The cell body (soma).
b- The dendrites.
c- The axon (nerve fiber).
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a- The cell body (soma):
 It is the main part of the neuron that contains all of the
necessary components of the cell.
 It contains the nucleus (which contains DNA), ribosomes
(which synthesize proteins) and mitochondria (which
produce energy).
b- The dendrites :
 The dendrites are fine branches surrounding the cell body.
 They conduct the nerve impulses (action potential) toward
the cell body.
c- The axon (nerve fiber):
 The axon is the long extension of the nerve cell.
 It carry the nerve impulse away from the cell body.
 There is usually only one axon per neuron.
 Some axons are covered with myelin sheath which is
formed by the glial cells SO, there are 2 types of axons;
mylinated and unmylinated.
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NOTES:
 Axons that covered with myelin sheath are called myelinated axons.
 Axons without myelin sheath are called unmyelinated axons.
Functions of the neurons:
o The neurons are responsible for receiving, sending and interpreting information from/ to
all parts of the body.
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2] The neuroglia (glial cells):
 The neuroglia are the supporting cells of the nervous system.
 These cells are non-conductive (don't carry nerve impulses) and undergo
mitotic division.
Classification:
 The neuroglia are classified into CNS glia and PNS glia.
 The neuroglia of the CNS:
 The number of neuroglial cells in the CNS is about ten times more than
that of nerve cells.
 The neuroglia of the CNS are of 2 types: the microglial cells and the
macroglial cells.
A- The microglial cells:
 The microglial cells are small cells with few tortuous ‫ متعرج‬processes.
 The microglial cells are phagocytic cells SO, they act as the first line of
immune defense in the CNS.
 They are responsible for phagocytosis of different types of pathogenic
microbes and digestion of dead neurons.
Functions of microglial cells:
1. Phagocytosis of different types of pathogenic microbes.
2. Digestion of dead neurons.
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B- The macroglial cells are of 3 types :
1- Astrocytes (astroglia):
 Astrocytes are the main type of macroglial cells in the CNS.
 They have numerous projections that attach neurons to the blood
capillaries.
Functions of astrocytes:
o Some of the processes of astrocytes are attached to the outer surface of the
capillaries of brain to acts as Blood-Brain Barrier.
o Astrocytes supply neurons with nutrients and oxygen (by transporting
certain molecules from the blood to the neuron).
o Astrocytes are primary glycogen store in the CNS.
2- Oligodendrocytes:
 Oligodendrocytes are smaller than astrocytes and contains less branched
processes.
 They manufacture the myelin which form myelin sheath around some
axons of CNS.
Functions:
o Oligodendrocytes manufacture the myelin sheath which insulate each
neuron from another SO they are responsible for normal transmission of
nerve impulses.
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3- Ependymal cells:
 They line the ventricles of the brain and central canal of spinal cord.
Functions:
o Ependymal cells create and secrete the cerebrospinal fluid (CSF).
 The neuroglia of the PNS
1- Schwann cells:
 Schwann cells are the main type of the neuroglia of the PNS.
 These cells are equivalent to the oligodendrocytes of the CNS.
 Schwann cells manufacture the myelin which form myelin sheath
around some axons of the PNS.
 The sheath is not continuous and the gaps between adjacent Schwann
cells are called nodes of Ranvier.
Functions:
o Schwann cells manufacture the myelin sheath which insulate each
neuron from another SO they are responsible for normal transmission
of nerve impulses.
2- Satellite glial cells:
 Satellite glial cells surround the cell bodies of neurons in the PNS.
Functions:
o They protect and support the cell bodies of neurons of the PNS.
o They supply neurons with nutrients and oxygen (by transporting
molecules from the blood to the neuron).
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NOTES:
 Myelin is a fatty substance that surrounds and
insulates the nerve axons to facilitates the conduction
of the nerve impulses SO myelinated nerves can
conduct impulses quicker than unmyelinated nerves.
 Myelin is composed of 70-80% lipids (give white
colour to the myelinated axons) and 20-30% protein.
 Myelin is produced in the CNS by Oligodendrocytes
and in the PNS by Schwann cells.
 Clinically, glial cells are important because they are
a common source of tumors of the nervous system.
 Nodes of Ranvier are the unmyelinated gaps between
sections of myelin.
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Types of neurons of the PNS
 Neurons of the PNS are classified in 2
ways:
1- According to the origin of the neuron OR
anatomically into:
A- Cranial neurons:
 The cranial neurons are 12 pairs of neurons
originating from the brain.
 Only the olfactory nerve (I) and the optic
nerve (II) originate from the cerebrum,
while the rest emerge from the brain stem.
 Ten of the cranial nerves control the sense
organs and muscles of the head.
 Only the vagus nerve (X) and the accessory
nerve (XI) extends beyond head and neck.
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Cranial neurons
No.
Name
Function
I
Olfactory nerve
This is the nerve of smell (olfaction). It transmits the sense of smell to the brain.
II
Optic nerve
This is the nerve of vision. It transmits visual information to the brain.
III
Oculomotor
nerve
It innervates muscles which are responsible for movement of the eyes (for looking
around) and the size of eye pupil (responsible for pupillary constriction).
IV
Trochlear nerve
This nerve also innervates muscles which are responsible for movement of the
eyes (for looking up and down).
V
 It is the largest cranial nerve.
Trigeminal nerve  It is responsible for the ability to feel the face and inside the mouth.
 It innervates muscles which are responsible for mastication (chewing).
VI
Abducent nerve
VII Facial nerve
It innervates muscles which are responsible for movement of the eyes (for looking
laterally).
 It innervates muscles which are responsible for facial expression (smile, wink).
 It is responsible for the sense of taste. It transmits the taste (gustatory)
information from the anterior 2/3 of the tongue to the brain.
 It innervates the salivary glands (except parotid) and the lacrimal gland (SO, it
is responsible for secretion of saliva and tears).
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Cranial neurons
No.
VIII
IX
Name
Function
Vestibulocochlear
nerve
It transmits the sense of sound and rotation to the brain SO it is responsible
for hearing and balance.
Glossopharyngeal
nerve
 It is responsible for the sense of taste. It transmits the taste (gustatory)
information from the posterior 1/3 of the tongue to the brain.
 It innervates the parotid glands (secretion of saliva)
 It innervates pharyngeal muscles (swallowing action).
X
Vagus nerve
XI
Spinal Accessory
nerve
XII Hypoglossal nerve
 It is responsible for the ability to swallow and the gag reflex.
 It transmits the taste (gustatory) information from the tongue to the brain.
 It innervates most organs with the parasympathetic nerves, SO it control
cardiac muscle, smooth muscles and exocrine glands.
It innervates muscles which are responsible for movement of the shoulders
and neck.
It moves the tongue for speech and swallowing.
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 Gag reflex (pharyngeal reflex):
 It is a reflex contraction of the back of the throat
evoked by touching the roof of the mouth, the back
of the tongue, the area around the tonsils and the
back of the throat.
 It prevents the passage of anything to the throat,
except during normal swallowing.
B- Spinal neurons:
o The spinal nerves are 31 pairs of nerves originating
from the spinal cord.
 Cervical nerves
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 Thoracic nerves 12
 Lumbar nerves
5
 Sacral nerves
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 Coccygeal nerve 1
NOTE:
 Adult spinal cord often terminates at the vertebral
level of L 1-2.
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2- According to the direction of the nerve impulses OR functionally into:
A- Sensory neurons (afferent neurons) :
 They transmit impulses from the sense organs (as skin) to the CNS (i.e. toward the CNS).
B- Motor neurons (efferent neurons) :
 They transmit impulses from the CNS to effectors (muscles or glands) to cause an action
(i.e. away from the CNS).
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Motor neurons are classified into:
a- Autonomic neurons:
 They are motor neurons that transmit impulses to cardiac muscle, smooth muscles and
exocrine glands.
 They controls the involuntary functions, so called the autonomic nervous system or the
involuntary nervous system.
b- Somatic neurons:
 They are motor neurons that transmits impulses to the skeletal muscles.
 They controls the voluntary functions, so called the somatic nervous system or the
voluntary nervous system.
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NOTES:
 Cardiac muscle, smooth muscles and exocrine glands are effector organs for the
autonomic nervous system.
 Skeletal muscles are the effector organs for the somatic nervous system.
 Interneuron is a type of neurons that is found completely within the CNS and transmit
signals between motor and sensory neurons.
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Some Terms






Neuron is the nerve cell in either CNS or PNS. It is composed of 3
parts: cell body, dendrites and a single axon.
Nucleus is the collection of cell bodies within the CNS.
Ganglion is the collection of cell bodies within the PNS.
Tract is the bundles of axons within the CNS
Nerve is the bundles of axons within the PNS, SO there are no cell
bodies in the tracts and nerves.
Synapse is the gap between two neurons or between a neuron and an
effector organ (gland or muscle cell). The synapse between a neuron
and skeletal muscle is called a neuromuscular junction.
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Nervous System
CNS
(Brain + Spinal cord)
PNS
(Cranial Ns + Spinal Ns)
OR
Sensory Ns + Motor Ns
(Afferent Ns) (Efferent Ns)
To Skeletal Ms
To Cardiac M, Smooth Ms and Exocrine
glands
Somatic Nerves
Autonomic Nerves
OR
OR
Somatic Nervous System
(Voluntary Nervous System)
Autonomic Nervous System
(Involuntary Nervous System)
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