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TOPICS
•
•
•
•
•
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Nervous system – functions
Components of nervous system
Communication in the nervous system
Resting membrane potential
Action potential
Nervous system disorders
1
NERVOUS SYSTEM
– Regulates all body functions (along with
the
endocrine system)
– Regulate other body systems
– Maintains homeostasis
– Responsible for behaviors, memories,
intelligence
• Neurology – the study of the nervous
system
...
– Spinal cord is located in the vertebral column
...
– Voluntary
• Autonomic (involuntary) nervous systems
– Supply nerves to and stimulate smooth &
cardiac muscle and glands
– Involuntary
– 2 divisions:
• sympathetic nervous system
• parasympathetic nervous system
7
Peripheral Nerves
• Cranial nerves
– emerge from the base of the brain through
foramina of the skull
...
• Ganglia
– Masses of cell bodies of neurons located outside
the brain and spinal cord
...
astrocytes, oligodendrocytes,
microglia, ependymal,
20
schwann and satellite cells
•
•
•
•
NEURONS
Functional unit of nervous system
Histological structures
Cell body
Cell processes
Cell body
– Nissl bodies
• rough ER & free ribosomes for protein
synthesis
Cell processes = dendrites & axons
21
• Dendrites
– Receive impulse from the axon of other
neurons through synaptic connection
...
Functional Classification of Neurons
• Sensory (afferent) neurons
– transport sensory information from skin, muscles,
joints, sense organs & viscera to CNS
• Motor (efferent) neurons
– send motor nerve impulses to muscles &
glands
• Interneurons (association) neurons
– connect sensory to motor neurons
– 90% of neurons in the body
23
SUPPORTING CELLS
• Known as neuroglial or glial cells
– The majority cells of the CNS
– Smaller cells than neurons
– Cells can divide
– 4 cell types in CNS
• astrocytes, oligodendrocytes, microglia &
ependymal
– 2 cell types in PNS
• schwann and satellite cells
24
Astrocytes
• Star-shaped cells
• Form blood-brain barrier by covering blood
capillaries in the brain
Microglia
• Small cells found near blood vessels
• Phagocytic role -- clear away dead cells
Ependymal cells
• Form epithelial membrane lining cerebral
cavities & central canal
• Produce cerebrospinal fluid (CSF)
25
Satellite Cells
• Flat cells surrounding neuronal cell bodies in
peripheral ganglia
Schwann Cell
• Cells encircling PNS axons
• Produces the myelin sheath surrounding
an axon in the PNS
26
• Myelin sheath
– A multilayered lipid and protein covering
produced by Schwann cells and
oligodendrocytes
– surrounds the axons of most neurons
• Myelinated axon vs non-myelinated
axon
– The sheath electrically insulates the axon
and increases the speed of nerve impulse
conduction
...
White matter
– Consists of myelinated processes (the
myelination gives it the white colour)
– Do not contain cell bodies
...
30
Gray matter:
In the spinal cord
• Gray matter forms an H-shaped inner
core surrounded by white matter
In the brain
• Gray matter forms thin outer shell of gray
matter of the cerebral cortex
– and is found in clusters called nuclei
inside the brain
31
• A nucleus
– a mass (group) of nerve cell
bodies and dendrites inside the
CNS
...
32
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Communication in the nervous system
• Refers to the flow of information
between neurons
• Neurons are electrically excitable
...
8
Resting Membrane Potential
• Voltage (V)
– Electromotive force or potential difference,
usually expressed in volts
...
• Resting potential
– refers to the potential difference (- 70 mv)
• between the inside and the outside of
the cell, while at rest
...
36
The outside of the cell is positive
...
8
CHANGES IN MEMBRANE POTENTIAL
• Certain stimuli can cause changes in membrane
potential
...
43
Action Potential (AP)
• A brief reversal of membrane potential
– after the membrane undergoes graded
potential above threshold
...
Depolarization Phase
Membrane permeability to Na increases
Na+ enters the inside of the cell
Membrane potential reverses (towards
positive value)
Threshold – a critical level of depolarization
(-55 to -50 mV)
• Above this level can cause action
potential
47
Repolarization phase
• Membrane permeability to Na+ declines
– Na+ ions stop moving into the inside cell
• K+ moves from inside to outside cell
• Resting membrane potential increases in
negativity towards resting membrane
potential
48
Hyperpolarization
• Excessive movement of K+ (to inside cell)
occurs
• This causes hyperpolarization of the
membrane (undershoot)
– i
...
the potential becomes more negative
than the resting potential
49
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•
•
•
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The Action Potential: SUMMARY
Resting membrane potential is -70mV
Depolarization is the change from -70mV
to +30 mV
Repolarization is the reversal from +30
mV back to -70 mV)
Hyperpolarization – The reversal
continues slightly before attaining the
resting potential
...
– The traveling action potential is called a
nerve impulse
53
54
Propagation of action potential
AP or impulse moves along the axon as:
• Continuous conduction (along unmyelinated
fibers (axons))
– Nerve impulse travels continuosly along
the axon
...
55
Saltatory Conduction
56
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SYNAPTIC TRANSFER OF IMPULSE
–Impulse is transferred from neuron to
neuron via synapse
• THERE IS NO DIRECT CONNECTION
BETWEEN NEURONS
• Synapse
–Is the functional junction between
one neuron and another
–Or between a neuron and an effector
such as a muscle or gland
...
• Excitatory and inhibitory neurotransmitters
• Important neurotransmitters include
acetylcholine,, noradrenalin, adrenalin, and
dopamine, glutamate, aspartate, gamma
aminobutyric acid, glycine, nitric oxide (NO)
66
NEUROTRANSMITTERS
• Many pharmaceutical drugs affect the
synapse or NMJs
• Many Toxins and Diseases NMJ & Synaptic
Transmission
67
Regeneration & repair of nervous tissue
• Limited ability for regeneration (repair)
– PNS - can repair damaged dendrites or
axons
– CNS - no repairs are possible
68
Multiple Sclerosis (MS)
• Nervous disorder causing destruction of
myelin sheaths in CNS
• Muscle weakness
Epilepsy
• Characterized by short, recurrent attacks
initiated by electrical discharges in the
brain
• skeletal muscles may contract involuntarily
69
• loss of consciousness
TOPICS
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•
•
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Parts of brain and their functions
Functional areas of brain
Cerebrospinal fluid
Reticular formation
Brain waves
Consciousness, sleep
Memory
Spinal cord, nerve tracts
70
CENTRAL NERVOUS SYSTEM (CNS)
• Composed of brain and spinal cord
Brain
• Functions in sensations, memory, emotions,
decision making, behavior, etc
• Composed of wrinkled, pinkish gray tissue
• Outer layer - gray matter
• Internal layer- white matter and dispersed
areas of gray matter (known as nuclei)
White matter of the brain is made up of fibre71
tracts - myelinated nerve fibres (axons)
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•
•
•
•
BRAIN STRUCTURES
Cerebrum: Cerebral hemispheres
Cerebral cortex
Cerebral white matter
Basal nuclei
Diencephalon
Thalamus
Hypothalamus
Epithalamus
Midbrain
Brain stem: pons, medulla oblongata
72
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Basic Pattern of the Central Nervous System
75
Figure 12
...
• Contain the higher brain centres
...
8a
Ventricles of the Brain
• Ventricles are cavities filled w/ fluid
• paired lateral ventricles
• third ventricle
• fourth ventricle
85
Ventricles of the Brain
86
Figure 12
...
8b
90
91
Motor Cortex
Figure92
12
...
1
Sensory Areas
93
Figure 12
...
9
...
10a
Fiber Tracts in White Matter
Figure 97
12
...
11a
Basal Nuclei
100
Figure 12
...
12
103
104
Midbrain
• Extends from pons to diencephalon
• Cerebral aqueduct connects 3rd
ventricle above to 4th ventricle below
105
Thalamus
• serve as relay stations
for all sensory impulses, except smell,
to the cerebral cortex
...
13b
110
Epithalamus
• Contains the endocrine pineal gland
– secretes the hormone melatonin which
involves in sleep regulation, sleep-wake
cycles, and mood
Limbic System
• Consists of structures found in the cerebral
hemispheres and diencephalon
• Known as “emotional brain”- because it is
associated w/ emotion (including pleasure, 111
pain) and behavior
...
12
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•
•
Brain Stem
Three regions – midbrain, pons, and
medulla oblongata
Medulla Oblongata
Continuation of spinal cord
Path ascending and descending motor tracts
The vital centres are located here:
Cardiovascular center
Respiratory center
Reflex centres for coughing, sneezing,
113
swallowing etc
...
• Protects brain cells from harmful substances
and pathogens
• Injury to the brain causes a breakdown of the
BBB, permitting the passage of normally
restricted substances into brain tissue
...
117
Protection of the Brain
• The brain is protected by the:
– Cranial bones
– Cranial meninges
(membranes/coverings)
• The cranial meninges are continuous
with the spinal meninges and are
named:
– dura mater, arachnoid, and pia
mater
...
• Functions to transport nutrients and
waste products, etc, througout brain
and spinal cord
...
19
Brain Waves
• Normal brain function involves continuous
electrical activity
• An electroencephalogram (EEG) records
this activity
• Patterns of neuronal electrical activity
recorded are called brain waves
• Each person’s brain waves are unique
• Continuous train of peaks and troughs
• Wave frequency is expressed in Hertz (Hz)
Types of Brain Waves
• Alpha waves – regular and rhythmic, lowamplitude, slow, synchronous waves
indicating an “idling” brain
• Beta waves – rhythmic, more irregular
waves occurring during the awake and
mentally alert state
• Theta waves – more irregular than alpha
waves; common in children but abnormal in
adults
• Delta waves – high-amplitude waves seen in
deep sleep and when reticular activating
Types of Brain Waves
Figure 12
...
21
Summary of Brain Structure
• Medulla oblongata
– Vital centres – vital functions such as
breathing, and CVS functions such as heart
functions and blood pressure
– Centers for reflexes such as vomiting,
coughing, sneezing, hiccupping, swallowing,
and digestion
• Pons
– Respiratory (breathing) centres
– Connects spinal cord, cerebellum and higher
140
brain centers
• Cerebellum (little brain)
–Motor coordination – body
equilibrium
• coordinates body movements
• Midbrain
–Receives visual, auditory, and tactile
information
–This information is sent to the
thalamus and higher brain centers
...
– Contains part of the reticular
formation (which controls arousal)
...
28a
Epidural space
- Epidural injections of drugs and anaesthetics
...
30a
152
153
154
155
Gray Matter and Spinal Roots
• Gray matter consists of soma, unmyelinated
processes, and neuroglia
• Gray commissure – connects masses of gray
matter; encloses central canal
• Posterior (dorsal) horns – interneurons
• Anterior (ventral) horns – interneurons and
somatic motor neurons
• Lateral horns – contain sympathetic nerve
fibers
156
Gray Matter and Spinal Roots
157
Figure 12
...
31
Spinal Cord - White Matter
• Contains nerve fibre tracts or pathways:
Ascending tracts
Descending tracts
• Fibre tracts are composed of axons with
similar functions
• Most consist of two or three neurons
• Pathways are paired (one on each side of
the spinal cord or brain)
161
White Matter: Nerve tracts or pathways
162
Figure 12
...
• Ascending tracts
• Descending tracts
163
Ascending (Sensory) Pathways
• Sensory impulse is carried from the
sensory receptors through the afferent
nerve into the spinal cord (white matter)
• Ascend to the sensory cortex of the
opposite side of the brain
164
Ascending (Sensory) Pathways
• Pathways decussate
– The sensory fibres cross to the
opposite side of the brain at level of
the spinal cord or thalamus (relay
station)
– The right sensory cortex receive
sensory sensation from the left side of
the body and vice versa
165
Ascending (Sensory) Pathway
166
Figure 12
...
33a
Descending (Motor) Pathways
• Descending tracts deliver efferent
impulses from the brain (motor area) to
the spinal cord
• Carry impulses to cause contraction of
the skeletal muscle
• Like the ascending tracts the descending
tracts also decussate – i
...
the right
motor area controls left side of the body
& vice versa
168
Decending
pathway
169
Figure 12
...
34a
171
172
• Paralysis – loss of motor function
• Cross sectioning of the spinal cord
at any level results in total motor and
sensory loss in regions inferior to
the cut
173
174
Reflex Action
• A reflex is an automatic reaction to a
stimulus
• Reflex Arc – consists of neural
pathways
175
Components of a reflex arc
– Receptor – site of stimulus
– Sensory neuron – transmits the afferent
impulse to the CNS
– Integration center –located in the CNS
– Motor neuron – conducts efferent impulses
from the integration center to an effector
– Effector – muscle or gland that responds to
the efferent impulse
176
Components of reflex arc
177
Knee jerk reflex
• A sudden involuntary forward movement
of the lower leg that can be produced by
a firm tap to the patellar tendon located
just below the kneecap
...
This stimulates the
sensory receptor ( muscle spindle) to
produce nerve impulse
178
Knee jerk reflex
• Sensory receptor
afferent (sensory)
neuron
integrating centre in the spinal
cord
efferent (motor) neuron
effector
contraction of quadriceps muscle
the
knee jerks forward involunatrily
179
180
181
182
Types of reflexes
• Somatic reflexes
– PNS – skeletal muscle
– Postural reflexes
• maintaining body equilibrium
• Involving cerebellum
– Spinal reflexes – eg
...
g BP regulation
183
– Pupillary reflexes
Types of reflexes
• Monosynaptic – knee jerk
• Polysynaptic reflexes – cross extensor reflex
• Conditioned reflex
– an acquired response that is under the control of
(conditional on the occurrence of) a stimulus
– Pavlov’s dog
184
185
186
187
188
189
190
Communication in the nervous
system
• Refers to the flow of information
between neurons
• Neurons are electrically excitable
...
• Synapse
– Is the functional junction between one
neuron and another
– Or between a neuron and an effector such
as a muscle (neuromuscular junction) or
gland
...
193
194
Excitatory & Inhibitory Synapses
Excitatory synapse:
– Produces EPSP (Excitatory postsynaptic
potential)
– Leads to the formation of action potential
...
196
Regeneration & repair of nervous tissue
• Limited ability for regeneration (repair)
– PNS - damaged dendrites or axons can be repaired
– CNS – no repairs are possible
•
•
•
•
•
Multiple Sclerosis (MS)
Nervous disorder causing destruction of myelin
sheaths in CNS
Muscle weakness
Epilepsy
Uncontrollable jerking, characteristic of epileptic
seizure
loss of consciousness
Fall stiffly
197
198
199
TOPICS
• Peripheral nervous system
• Receptor physiology
• Reflex action
Peripheral Nervous System (PNS)
• PNS – all neural structures outside the brain
and spinal cord
• Includes sensory receptors, peripheral
nerves, associated ganglia, and motor
endings
• Provides links to and from the external
environment
• Divisions
• Somatic SNS
• Autonomic NS
202
Sensory Receptors
• Structures specialized to respond to
stimuli
• Activation of sensory receptors results
in depolarizations that trigger
impulses to the CNS
• The realization of these stimuli,
sensation and perception, occur in
the brain
Receptor Classification by
Stimulus Type
• Mechanoreceptors – respond to touch,
pressure, vibration, stretch, and itch
• Thermoreceptors – sensitive to changes in
temperature
• Photoreceptors – respond to light energy (e
...
,
retina)
• Chemoreceptors – respond to chemicals (e
...
,
smell, taste, changes in blood chemistry)
• Nociceptors – sensitive to pain-causing stimuli
Receptor Class by Location:
1
...
Interoceptors:
• Respond to stimuli arising within the
body
• Found in internal viscera and blood
vessels
• Sensitive to chemical changes,
stretch, and temperature changes
3
...
1
...
1
...
1
...
1
...
33b
Ascending
(Sensory)
Pathway
Figure 12
...
3b
Classification of Nerves
• Sensory and motor divisions
–Sensory (afferent) – carry impulse
to the CNS
–Motor (efferent) – carry impulses
from CNS
• Mixed – sensory and motor fibers
carry impulses to and from CNS; most
common type of nerve
Reflex Action
• A reflex is an automatic reaction to a
stimulus
• Reflex Arc – consists of neural
pathways
227
Components of a reflex arc
– Receptor – site of stimulus
– Sensory neuron – transmits the afferent
impulse to the CNS
– Integration center –located in the CNS
– Motor neuron – conducts efferent impulses
from the integration center to an effector
– Effector – muscle or gland that responds to
the efferent impulse
228
Components of reflex arc
229
Knee jerk reflex
• A sudden involuntary forward movement
of the lower leg that can be produced by
a firm tap to the patellar tendon located
just below the kneecap
...
This stimulates the
sensory receptor ( muscle spindle) to
produce nerve impulse
230
Knee jerk reflex
• Sensory receptor
afferent (sensory)
neuron
integrating centre in the spinal
cord
efferent (motor) neuron
effector
contraction of quadriceps muscle
the
knee jerks forward involunatrily
231
232
233
234
Types of reflexes
• Somatic reflexes
– PNS – skeletal muscle
– Postural reflexes
• maintaining body equilibrium
• Involving cerebellum
– Spinal reflexes – eg
...
g BP regulation
– Pupillary reflexes
235
Types of reflexes
• Monosynaptic – eg
...
cross extensor reflex
• Conditioned reflex
– an acquired response that is under the control of
(conditional on the occurrence of) a stimulus
– Pavlov’s dog
236
237