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Nervous Systems
PHYSIOLOGY
PHL-226
HUMAN NERVOUS SYSTEM
Your Nervous System is the most
complicated and fragile system. It tells all
your other systems what to do. The
Nervous System carries messages to the
brain.
HUMAN NERVOUS SYSTEM
HUMAN NERVOUS SYSTEM
It is divided into
*central nervous system
(CNS)
Credit Medical Art Service, Munich /, Wellcome Images
cord
*peripheral nervous system
(PNS)
It consists of cranial and spinal
nerves . which connects every organs
to the CNS.
Medical Art Service, Munich /, Wellcome Images
which is the brain and spinal
cranial
nerves-12
pairs
spinal
nerves- 31
pairs
Spinal nerves
 They are a part of the peripheral nervous system
 There are 31 pairs of spinal nerves that originated from spinal
cord.
 They are named according to the spinal cord segment from
which they originate
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
5
C1
C1
Cranial nerves
 They are a part of the peripheral nervous system
 There are 12 pairs of cranial nerves that originated from the
brain it self
 They are numbered I to XII, Their names reflect their general
distribution or function.
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Name and functions of Cranial
Nerves
CN
Name
Function
I
Olfactory
Sense of smell
II
Optic
Sense of vision
III
Oculomotor
Eye movement
Opening of eyelid
IV
Trochlear
Eye movement
V
Trigeminal
Facial sensation
Chewing (Jaw movements)
8
Name and functions of Cranial
Nerves
VI
Abducens
Eye movement
VII
Facial
Facial expression
Taste sensation
Closing of eye lid
VIII
Vestibulocochlear
Equilibrium or balance (vestibular)
Hearing (cochlear)
IX
Glossopharyngeal
Taste sensation
Swallowing
X
Vagus
Control most glands and visera
XI
Accessory
Control neck and shoulder muscles
XII
Hypoglossal
Tongue movements
9
CRANIAL NERVES
Learn them; mneumonic helps, e.g.:
“Oh, oh, oh, to touch and feel very good velvet, ah!”
NERVES (CRANIAL OR SPINAL)
may be
Sensory (Afferent) or Motor (Efferent)
1-sensory (afferent) nerve
e.g., skin
it sends signals or impulses from senses, skin, muscles, and internal organs to the CNS
2- motor (efferent) nerve
e.g., muscle
It transmits
Gray’s Anatomy 38 1999
commands from CNS to muscles, glands and organs
The Withdrawal Reflex
cells of The Nervous System
The nervous system is formed of 2 main
kinds of cells
–1) Neurons (nerve cells)
–2) Neuroglia ( glia cells)
Neuron (nerve cell)
 It is the Basic units of the nervous system
It is the conducting cell as it transmits
electrical impulses from one part of the body
to another part
•
anatomy later
Neurons structure
Dendrites
Cell Body
Myelin
Sheath
Axon of another
neuron
Axon
Dendrites of
another neuron
Specific Parts:
The Neuron
Structure
Structure of neuron
Cell body
•That contains nucleus
Dendrites
Mutiple branching hair like extensions that arise from
the cell body of a neuron . It receives messages from
other neurone and conducts impulses toward the cell
body
Axon
Single long extension of a neuron, ending in branching
terminal fibers ( called axon terminals), through which
messages are sent to other neurons or to muscles or glands
Neural communication
( Synapse)
–It is the site of junction ,
communication and connection
between two neurons (sending and
receiving neurons)
Glial cells (neuroglia)
 They are non conducting cells that cover
some axons forming mylein sheath . The nerve
fibers that are covered by mylein sheath are
called myleinated nerve fibers
Mylein sheath formed of lipid that give a
white colour to the myelinated nerve axon
 They insulate, support and protect
anatomy later
nerve cells
Protection of the Brain
The brain and spinal cord are protected by :1- The bony skull for the brain and vertebrae for the
spinal cord
2- Meninges
3- Cerebrospinal Fluid
4-Blood-Brain Barrier
Meninges
The brain and spinal cord are covered by a tissue known as the
meninges
The meninges is made up of 3 layers:
1. Dura Mater – Which is the outer most layer under the
bony skull. It is strongly adherent to the base of the skull It is a
tough layer, as it is formed of strong connective tissue thus
called tough mother
2. Arachnoid Layer – It is the middle layer .it is a‘spider’ web
like structure filled with cerebrospinal fluid ( CSF ).
3. Pia Mater – It is the innermost layer covering the brain loosely, and
passing over sulci which . It is formed of a delicate membrane thus
called delicate mother.
Meningeal Spaces
Epidural space
Potential space superior to dura.
Subdural space
Potential space between dura and arachnoid mater.
Subarachnoid space
Filled with CSF
Contains the blood vessels supplying brain.
Functions of the Meninges
1- protects the central nervous system and cerebral blood
vessels .
.
2- It contain CSF .
CSF
.1- Cerebrospinal fluid (CSF) is a clear, colorless, bodily fluid
that occupies the subarachnoid space and the ventricular
system of the brain and spinal cord
2- CSF is produced in the choroid plexus. It circulates from
the lateral ventricles to the foramen of Monro , third
ventricle, aqueduct of Sylvius, fourth ventricle, foramen of
Magendie, and the subarachnoid space over the brain and
the spinal cord .
3- in adult the total volume of CSF is a bout 150 mL.
Functions of the CSF
1- Protection of the brain :- CSF protects the brain tissue from different
type of trauma .
2- nourishes the brain :- CSF carries nutrient from the blood to the
brain
3- chemical stability :- it removes waste products from the brain
Blood brain barrier (BBB)
Sensation : is a state of awareness of a stimulus.
Sensation requires:1) A stimulus : Any changes in the environment,
either internal or external , e.g. body temp,
pH, light, sound, pressure ….. etc.
2) Receptor : which receive stimulus
3) Conduction of nerve impulse to the CNS
4) Translation at different regionS of the brain
A
B
C
D
E
A: Free nerve endings (pain,
temperature)
B: Pacinian corpuscle (pressure)
C: Meissner’s corpuscle (touch)
D: Muscle spindle (stretch of
muscle )
E: Merkel discs (light touch)
D: Ruffini’s corpsucles (deep
pressure and stretch)
F
Carries pain, temperature, touch
and pressure signals
 1st neuron enters spinal cord
through dorsal root
 2nd neuron crosses over in
spinal cord; ascends to
thalamus
 3rd neuron projects from
thalamus to somatosensory
cortex
Spinothalamic Pathway
3rd neurone arise from
thalamus to
somatosensory area of
the cortex
Primary somatosensory
cortex
3rd
Thalamus
1st neurone enters
spinal cord through
dorsal root
1st
Medulla
2nd
Spinothalamic
tract
2 nd neurone decussates
the spinal cord and ascend
to the thalamus
Cone and Rod are receptor for Vision
Cones and Rods mediate different kinds of vision
◦ Cones – photopic (day time) vision
High sensitive to color in a good lighting
◦ Rods – scotopic (night time) vision
 High-sensitivite to low-acuity vision in dim light
NB:
Rods and cones present in the retina of the eye
Figure 6.5
Olfactory epithelium in the nose acts as a receptor for smell
sensation
Auditory ( hearing ) receptor : The
special receptor for hearing is the
hair cells in the organ of corti which
is present inside the cochlea in the
inner air
Cochlea
Vestibulococh
lear nerve
sends
impulses to
the auditory
cortex of the
temporal
59
lobe of brain
Equilibrium: is the ability to detect head position and
movement ( or acceleration)
 Utricle and saccule contain sensory or receptor cells for
linear-acceleration
 Crista ampularis contain sensory cells for rotationalacceleration