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Title: NERVOUS SYSTEM
Description: Here are are precise nervous system notes for medical and nursing students. the notes are comprehensive and clear to understand. This is a suitable tool for success for students preparing for anatomy and physiology exam.
Description: Here are are precise nervous system notes for medical and nursing students. the notes are comprehensive and clear to understand. This is a suitable tool for success for students preparing for anatomy and physiology exam.
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THE NERVOUS SYSTEM
1
The nervous system
Neurons
Central nervous system
Brain
Spinal cord
Peripheral nervous system
Autonomic nervous system
2
• The nervous system detects and responds
to changes inside and outside the body
...
• Nervous system stimulation provides an
immediate response while endocrine is
slower and more prolonged
...
• Organization of nervous tissue
with in the body enables rapid
communication between different
parts of the body
...
The peripheral nervous system (PNS)
consisting of all the nerves which extend
between the brain or spinal cord and the
body muscles, glands, and sense organs
5
6
• The PNS comprises of 2 functional parts:
The sensory division
The motor division
• In turn the motor division is involved in
activities that are;
Voluntary- the somatic nervous system
Involuntary- the autonomic nervous
system (functioning of smooth and cardiac
muscle and glands)
...
• Neurons occur in a variety of sizes and shapes,
nevertheless, most of them contain four parts:
– 1 cell body, dendrites, an axon and axon
terminals
• Neurons are commonly referred to as nerve
cells
...
• The strength of the impulse is maintained
throughout the length of the neuron
...
9
Cell body
• The neuron’s cell body contains the nucleus
and ribosomes and thus has the genetic
information and machinery necessary for protein
synthesis
...
• Groups of cell bodies are called nuclei in the
CNS and ganglia in the PNS
...
• The dendrites form a series of highly branched
outgrowths from the cell body
...
• The branching dendrites increase the cell’s
receptive surface area and thereby increase its
capacity to receive signals from other neurons
...
• Axons are found deep in the brain and in groups
called, tracts, at the periphery of the spinal cord
...
• The initial segment is where in most neurons,
the electric signals are generated that then
propagate away from the cell body along the
axon
12
• The axon ends as axon terminal, which is
responsible for releasing neurotransmitters
from the axon
...
13
Structure of an axon
• The membrane of an axon is called axolemma
and it encloses the cytoplasmic extension of the
cell body
...
• In the central nervous system these myelin
forming cells are the oligodendria (glial cells)
and in the peripheral nervous system, they are
the schwann cells
...
• Between the layers of plasma membrane there
is a small amount of fatty substance called
myelin
...
15
• The spaces between adjacent myelin
forming cells where the axon’s plasma
membrane is exposed to extracellular fluid
are the nodes of ranvier
...
16
• Post ganglionic fibers and some small
fibers in the central nervous system are
non-myelinated
...
• The speed of transmission of nerve
impulses is significantly slower in nonmyelinated fibers
...
• The cell body
integrates signals
...
The
myelin sheath makes
the signal travel
faster
...
18
Properties of neurones
• Neurones have the characteristics of irritability
and conductivity
...
g
...
g
...
• Conductivity means the ability to transmit an
impulse
...
Sensory or afferent nerves
• When action potentials are generated by
sensory receptors on the dendrites of
these neurones, they are transmitted to
the spinal cord by the sensory nerve
fibers
...
20
Sensory receptors
• Specialized endings of sensory neurones
respond to different stimuli inside and
outside the body
...
• These originate in the skin
...
• Sensory nerve endings in the skin are fine
branching filaments without myelin sheath
...
Proprioceptor senses
• These originate in muscles and joints and
contribute to maintenance of balance and
posture
...
Autonomic afferent nerves
• These originate in internal organs, glands
and tissues, e
...
baroreceptors,
chemoreceptors, and are associated with
reflex regulation of involuntary activity and
visceral pain
...
Motor or efferent nerves
• Motor nerves originate in the
brain, spinal cord and autonomic
ganglia
...
24
There are 2 types:
• Somatic nerves- involved in voluntary
and reflex skeletal muscle
contraction
...
25
3
...
• Outside the spinal cord, when
sensory and motor nerves are
enclosed with in the same sheath of
connective tissue, they are called
mixed nerves
...
• There is no physical contact between
these neurons
...
27
• At its free end the axon of the presynaptic
neuron breaks up into minute branches
which terminate in small swellings called
synaptic knobs, or terminal boutons
...
• The space between them is the synaptic
cleft
...
• Neurotransmitters are synthesized by
nerve cells, actively transported along the
axons and stored in the synaptic vesicles
...
• They act on specific receptor sites
on the post synaptic membranes
...
31
• A knowledge of the action of different
neurotransmitters is important
because some drugs neutralize or
prolong their effect
...
32
Synapse
33
Some Neurotransmitters
Neurotransmitter
Location
Some Functions
Acetylcholine
Neuron-to-muscle
synapse
Activates muscles
Dopamine
Mid-brain
Control of movement
Epinephrine
Sympathetic system
Stress response
Serotonin
Midbrain, pons,
medulla
Mood, sleep
Endorphins
Brain, spine
Mood, pain reduction
Nitric Oxide
Brain
Memory storage
34
The neuromuscular junction
• The axons of motor neurons, conveying
impulses to skeletal muscle to produce
contraction, divide into fine filaments
terminating in minute pads called motor
end plates
...
35
• Each muscle fiber is stimulated through a
single motor end- plate, and one motor
nerve has many motor end plates
...
36
• The nerve impulse is passed across a
gap between the motor end plate and
the muscle fiber by the
neurotransmitter acetylcholine
...
37
• Nerve impulses cause serial
contraction of motor units in a muscle
and each unit contracts to its full
capacity
...
38
• The endings of autonomic nerves
supplying smooth muscle and
glands branch near their effector
structure and release a
neurotransmitter which stimulates
or depresses the activity of the
structure
...
40
Membranes covering the brain
and spinal cord (the meninges)
...
• Named from outside inwards they are:
Dura mater
Arachnoid mater
Pia mater
41
Meningeal Layers
42
Figure 9-4b
• The dura and arachnoid maters
are separated by a potential
space, the subdural space
...
43
Dura mater
• The cerebral dura mater consists of dense
fibrous tissue
...
• Venous blood from the brain drains into
venous sinuses between the layers of the
dura mater
...
• There after it encloses the filum
terminale and fuses with the
periosteum of the coccyx
...
• Nerves entering and leaving the
spinal cord pass through the epidural
space
...
47
Arachnoid mater
• This delicate serous membrane
lies between the dura and pia
maters
...
48
• The arachnoid mater passes over
the convolutions of the brain
...
49
Pia mater
• This is a fine connective tissue
containing many minute blood
vessels
...
• It continues downwards surrounding
the spinal cord
...
51
Ventricles of the brain and
cerebrospinal fluid
• With in the brain there are 4 irregular
shaped cavities, or ventricles,
containing cerebrospinal fluid (CSF)
...
52
Cerebrospinal fluid (CSF)
• CSF is secreted into each ventricle of
the brain by choroid plexuses
...
53
• The movement of CSF from the
subarachnoid space to venous
sinuses depends upon the
difference in pressure on each
side of the walls of the arachnoid
villi, which acts as one way
valves
...
• There may also be some re-absorption of
CSF by cells in the walls of the ventricles
...
56
• CSF is secreted continuously at a
rate of about 0
...
e
...
• The amount around the brain and
spinal cord remains fairly constant at
about 120mls, which means that
absorption keeps pace with secretion
...
• When the volume of the brain
tissue is reduced, such as in
degeneration or atrophy, the
volume of CSF is increased
...
• If the brain is enlarged by, e
...
hemorrhage or tumor, some
compensation is made by a reduction
in the amount of CSF
...
005,
consisting of :
Water, mineral salts, glucose, plasma
proteins (small amounts of albumin
and globulin), creatinine and urea
(small amounts), a few leukocytes
...
It maintains a uniform
pressure around these delicate
structures
...
It keeps the brain and the spinal cord
moist and there may be interchange
of substances between CSF and
nerve cells, such as nutrients and
waste products
...
• The parts are:
Cerebrum
Midbrain
Pons
Medulla oblongata
Cerebellum
• The midbrain, pons, and medulla oblongata
make up the brainstem
...
Sensory perception
2
...
Language
4
...
Sophisticated mental events, such as thinking memory,
decision making, creativity, and self-consciousness
1
...
Coordination of slow, sustained movements
3
...
Relay station for all synaptic input
2
...
Some degree of consciousness
4
...
Regulation of many homeostatic functions, such as temperature
control, thirst, urine output, and food intake
2
...
Extensive involvement with emotion and basic behavioral patterns
1
...
Enhancement of muscle tone
3
...
Origin of majority of peripheral cranial nerves
2
...
Regulation of muscle reflexes involved with equilibrium and posture
4
...
Role in sleep-wake cycle
65
Blood supply to the brain
• The circulus arteriosus and its contributing
arteries play a vital role in maintaining a
constant supply of oxygen and glucose to
the brain even when a contributing artery
is narrowed or the head is moved
...
66
Cerebrum
• This is the largest part of the brain
...
• Deep with in the brain the hemispheres
are connected by a mass of white matter
(nerve fibers) called corpus callosum
...
68
• The cerebral cortex shows many
infoldings or furrows of varying depth
...
• These convolutions greatly increase
the surface area of cerebrum
...
70
71
• The boundaries of the lobes are
marked by deep sulci (fissures)
...
72
Functions of the cerebrum
• There are 3 main varieties of activities
associated with the cerebral cortex;
Mental activities involved in memory,
intelligence, sense of responsibility,
thinking, reasoning, moral sense and
learning are attributed to the higher
centres
...
Sensory perception, including the
perception of pain, temperature,
touch, sight, hearing, taste and
smell
...
This lies in
the frontal lobe immediately anterior
to the central sulcus
...
75
• A nerve fiber from a Beltz’s cell passes
downwards through the internal capsule to
the medulla oblongata where it crosses to
the opposite side then descends in the
spinal cord
...
• This means that the motor area of
the right hemisphere of the
cerebrum controls voluntary
muscle movement on the left side
of the body and vice versa
...
• Damage to either of these
neurons may result in paralysis
...
This lies in
the frontal lobe immediately
anterior to the motor area
...
79
• For example in tying a shoe lace
or writing, many muscles contract
but the movements must be
coordinated and carried out in a
particular sequence
...
• It is dominant in the left hemisphere in
right handed people and vice versa
...
This extends
Anteriorly from the premotor area
to include the remainder of the
frontal lobe
...
82
• It is thought that communications
between this and the other
regions in the cerebrum are
responsible for the behavior,
character and emotional state of
an individual
...
This is the
area behind the central sulcus
...
• The sensory area of the right hemisphere
receives impulses from the left side of the
body and vice versa
...
This lies behind
the somatosensory area and includes
the greater part of the parietal lobe of
the cerebrum
...
85
• It has been suggested that
objects can be recognized by
touch alone because of the
knowledge from past experience
(memory) retained in this area
...
This is situated in the lower part of the
parietal lobe and extends into the temporal
lobe
...
• There is a dominant area in the left
hemisphere in right handed people and
vice versa
...
This
lies immediately below the lateral
sulcus with in the temporal lobe
...
88
The olfactory (smell) area
...
89
The taste area
...
• This is the area where impulses from
special nerve endings in taste buds in
the tongue and in the lining of the
cheeks, palate and pharynx are
perceived as taste
...
• This lies behind the parieto-occipital
sulcus and includes the greater part of the
occipital lobe
...
91
Cerebral Cortex
92
Other areas of the cerebrum
• Deep with in the cerebral hemispheres
there are groups of cell bodies called
nuclei (previously called ganglia) which act
as relay stations where impulses are
passed from one neuron to the next in a
chain
...
93
Basal nuclei
• These are areas of the grey matter, lying deep
with in the cerebral hemispheres, with
connections to the cerebral cortex and thalamus
...
• If control is inadequate or absent, movements
are jerky, clumsy and uncoordinated
...
• Sensory input from the skin, viscera and
special sense organs is transmitted to the
thalamus before redistribution to the
cerebrum
...
• It is situated below and in front of the
thalamus, immediately above the pituitary
gland
...
96
• Through these connections, the
hypothalamus controls the output of
hormones from both lobes of the gland
...
97
Body temperature
Emotional reactions, e
...
pleasure, fear,
rage
...
Biological clocks or circadian rhythms, e
...
sleeping and waking cycles, body
temperature and secretion of some
hormones
...
• It consists of groups of cell bodies and
nerve fibers (tracts) which connect the
cerebrum with lower parts of the brain and
with the spinal cord
...
Pons
• The pons is situated in front of the cerebellum,
below the midbrain and above the medulla
oblongata
...
100
Medulla oblongata
• The medulla oblongata extends from the pons
above and is continuous with the spinal cord
below
...
• Some cells constitute relay stations for sensory
nerves passing from the spinal cord to the
cerebrum
...
• These are the:
Cardiac centre
Respiratory centre
Vasomotor centre
Reflex centres of vomiting, coughing,
sneezing and swallowing
...
• Sympathetic and parasympathetic nerve
fibers originating in the medulla pass to
the heart
...
103
• The respiratory centre controls the
rate and depth of respiration
...
104
• The vasomotor centre controls the
diameter of blood vessels, especially the
small arteries and arterioles which have a
large proportion of smooth muscle fibers in
their walls
...
105
• Stimulation may cause either constriction
or dilatation of the blood vessels
depending on the site
...
106
Reflex centres
• When irritating substances are
present in the stomach or respiratory
tract, nerve impulses pass to the
medulla oblongata, stimulating the
reflex centres which initiate the reflex
actions of vomiting, coughing and
sneezing to expel the irritant
...
• It is ovoid in shape and has 2
hemispheres separated by a narrow
median strip called the vermis
...
110
Functions of the cerebellum
• The cerebellum is concerned with the
coordination of voluntary muscular
movement, posture and balance
...
• The cerebellum controls and coordinates
the movements of various groups of
muscles ensuring smooth, even, precise
actions
...
• The sensory input for these functions
is derived from the muscles and
joints, the eyes and the ears
...
113
• Impulses from the cerebellum influence
the contraction of the skeletal muscle so
that balance and posture are maintained
...
114
SPINAL CORD
• The spinal cord is the elongated, almost
cylindrical part of CNS, which is
suspended in the vertebral canal
surrounded by meninges and
cerebrospinal fluid
...
115
• It is approximately 45cm long in an adult,
and is about the thickness of the little
finger
...
e
...
This procedure is called lumbar
puncture
...
• Nerves conveying impulses from the
brain to various organs and tissues
descend through the spinal cord
...
• Similarly, sensory nerves from
organs and tissues enter and
pass upwards in the spinal cord to
the brain
...
e
...
• To facilitate these there are extensive
neurone connections between
sensory and motor neurones at the
same or different levels in the cord
...
120
121
Sensory nerve tracts (afferent or
ascending) in the spinal cord
...
• 1
...
Sensory receptors
(nerve endings) in the skin called
cutaneous receptors, are stimulated
by pain, heat, cold and touch,
including pressure
...
• Crossing to the other side, occurs either at
the level of entry into the cord or in the
medulla oblongata
...
The tendons, muscles and joints
...
• Together with impulses from the eyes and
the ears they are associated with the
maintenance of balance and posture and
with perception of the position of the body
in space
...
By 2 neurone system the nerve impulses
reach the cerebellar hemisphere on the
same side
...
• Neurones which transmit nerve impulses away
from the brain are motor (efferent or descending)
neurones
...
126
Voluntary muscle movement
• The contraction of the muscles which
move the joints is, under conscious
(voluntary) control, which means that the
stimulus to contract originate at the level of
consciousness in the cerebrum
...
127
• This involuntary activity is associated with
coordination of muscle activity, e
...
when
very fine movement is required in the
maintenance of posture and balance
...
128
Spinal reflexes
...
Sensory neurones
Connector neurones in the spinal
cord
Lower motor neurones
129
130
Figure 9-8
• A reflex action is an immediate motor
response to a sensory stimulus
...
g
...
131
• These stimulate many connector and
lower motor neurones in the cord which
results in contraction of many skeletal
muscles of the hand, arm and shoulder,
and the removal of the finger
...
132
• Reflexes of this type are invariably
protective but they can on occasion be
inhibited
...
133
Stretch reflexes
• Only 2 neurones are involved
...
• There is no connector neurone involved
...
134
• By tapping the tendon just below the knee
when it is bent, the sensory nerve endings
in the tendon and in the thigh muscles are
stretched
...
135
• As a result the thigh muscles suddenly
contract and the foot kicks forward
...
• This type of reflex has a protective
function- it prevents excessive joint
movement that may damage tendons,
ligaments and muscles
Title: NERVOUS SYSTEM
Description: Here are are precise nervous system notes for medical and nursing students. the notes are comprehensive and clear to understand. This is a suitable tool for success for students preparing for anatomy and physiology exam.
Description: Here are are precise nervous system notes for medical and nursing students. the notes are comprehensive and clear to understand. This is a suitable tool for success for students preparing for anatomy and physiology exam.