Download - Lecture Cns 1
-
8/12/2019 Lecture Cns 1
1/45
Overview of
Nervous system Functions
Dr Che Badariah Ab Aziz
-
8/12/2019 Lecture Cns 1
2/45
-
8/12/2019 Lecture Cns 1
3/45
Contents
Central nervous system
Peripheral nervous system
Somatic
Autonomic
Conduction of action potentials
-
8/12/2019 Lecture Cns 1
4/45
Organization of the Nervous
System
Sensory Division(afferent)
Peripheral Nervous SystemCranial Nerves
Spinal Nerves
Somatic Nervous System
(voluntary)
Autonomic Nervous System
(involuntary)
Motor Division(efferent)
Central Nervous System
Brain
Spinal Cord
-
8/12/2019 Lecture Cns 1
5/45
-
8/12/2019 Lecture Cns 1
6/45
Design
Receives million of information from
different sensory organs
Information is processed
Necessary actions are taken
-
8/12/2019 Lecture Cns 1
7/45
Brain
Cerebrum
Cerebellum
Diencephalon
Brain stem
-
8/12/2019 Lecture Cns 1
8/45
The Brain
Cerebrum: site of mind and intellect,motor control, sensory input and
interpretation. Frontal Lobe: general intellect and motor control
Temporal Lobe: auditory input and its interpretation
Parietal Lobe: general sensory input and its
interpretation Occipital Lobe: visual input and its interpretation
-
8/12/2019 Lecture Cns 1
9/45
BRAIN
-
8/12/2019 Lecture Cns 1
10/45
The Diencephalon
Thalamus: interprets sensory input and relays
it to the appropriate area of the brain.
Hypothalamus: maintains homeostasis.
Thalamus
Hypothalamus
-
8/12/2019 Lecture Cns 1
11/45
The Brain and Spinal
Cord Cerebellum: movement control.
Brain Stem: relays information betweenthe brain and the spinal cord.
Spinal Cord: tracts of nerve fibers thatallow two-way conduction of nerve impulses.
afferent -vs- efferent
-
8/12/2019 Lecture Cns 1
12/45
-
8/12/2019 Lecture Cns 1
13/45
Brain stem
The brain stemis the lower part of the brain, adjoining andstructurally continuous with the spinal cord.
Midbrain is involved in functions such as vision, hearing, eyemovement, and body movement.
Pons contains nerve fibres that connect the two halves of thecerebellum.
Vital in coordinating movements involving right and left sides of thebody.
Medulla oblongata transmits ascending and descending nerve fibersbetween the spinal cord and the brain.
The medulla also directly controls many involuntary muscular and
glandular activities, including breathing, heart contraction, arterydilation, salivation, vomiting.
The nuclei of some of the nerves that originate in the brain are alsolocated in the brain stem. (Medulla- IX, X, XI and XII; Pons- V, VI,VII and VIII; midbrain III and IV)
Nerve fibers in the brain stem do not readily regenerate, hence injury
may result in permanent loss of function.
-
8/12/2019 Lecture Cns 1
14/45
The Peripheral Nervous
System
The PNS contains 12 pairs of cranialnerves and 31 pairs of spinal nerves.
Sensory neuronsenter the spinal cord
through the dorsal root. mechanoreceptors (touch)
thermoreceptors (temperature)
nociceptors (pain)
chemoreceptors (oxygen,
glucose, electrolytes, etc.)
kinesthetic receptors (movement in joints, balance,etc.) ie. golgi tendon organs
-
8/12/2019 Lecture Cns 1
15/45
NOCICEPTORS
NEURAL PATHWAY
(A)
(B)
-
8/12/2019 Lecture Cns 1
16/45
Sensory division
Activities are initiated from sensory
receptors
The receptors transform the energy intoaction potentials (electrical energy)
Information is carried to various regions
on the CNS to be processed(interpreted)
-
8/12/2019 Lecture Cns 1
17/45
Motor division
To control various activities of the body
Contraction of appropriate mucles
(skeletal or smooth) Secretion of exocrine and endocrine
glands
Muscles and glandseffectors They perform functions dictated by
nerve signals
-
8/12/2019 Lecture Cns 1
18/45
Motor division
Skeletal muscles can be controlled by
various structures inc.
Spinal cord
Brain stem
Basal ganglia
Cerebellum
Motor cortex
-
8/12/2019 Lecture Cns 1
19/45
-
8/12/2019 Lecture Cns 1
20/45
Role of the nervous system
To monitor the internal and external environment of
the body
To process this information
To direct behaviour and body processes
-
8/12/2019 Lecture Cns 1
21/45
Autonomic nervous system
Control smooth muscles, glands and
other internal system e.g. heart rate,
motility of the gastrointestinal tract Involuntary
-
8/12/2019 Lecture Cns 1
22/45
Sympathetic nervous
system
-fight and flight reaction
Parasympathetic nervous
system
-non-emergency
-
8/12/2019 Lecture Cns 1
23/45
Neurons The functional and structural unit ofthe nervous system
Specialized to conduct information from one part of the body to
another
There are many, many different types of neurons but most have
certain structural and functional characteristics in common:
Cell body
Dendrites
Axon
Nerve cell terminal
-
8/12/2019 Lecture Cns 1
24/45
Components Functions
Cell body Synthesis proteinsCoordinates cellular
activities
Dendrites Receive information fromthe surrounding
environment
AxonConduct nerve
impulses
Terminals Transmit informationto neighbouring
neurons via synapses
-
8/12/2019 Lecture Cns 1
25/45
Information
Information is carried in a form of actionpotentials
Nerve cells have plasma membrane that arecapable of producing action potentials
Their ability to generate action potentials isknown as excitability
-
8/12/2019 Lecture Cns 1
26/45
Resting membrane potential
-70mV (when they are not transmittingsignals)
-
8/12/2019 Lecture Cns 1
27/45
Resting membrane potential
(RMP)Factors that contribute to RMP
Large protein molecules (-ve charged) cannot
cross the membrane K+can cross the membrane easily (the
membrane is more permeable to K+) leak
channels.
The membrane is less permeable to Na+
The contribution of Na+-K+pump
-
8/12/2019 Lecture Cns 1
28/45
Na+-K+pump
Continuous pumping of 3 Na+ions to
the outside for each 2 K+ions pumped
to the inside Loss of positives charges from the cell
More negative in the inside
-
8/12/2019 Lecture Cns 1
29/45
Nerve action potentials
Rapid changes in the membrane
potential that spread rapidly along the
nerve fiber membrane
-
8/12/2019 Lecture Cns 1
30/45
Changes in the
voltages at different
parts of the axon and at
different time.
*AP is not weaken as it
travel
-
8/12/2019 Lecture Cns 1
31/45
Action Potentials
-
8/12/2019 Lecture Cns 1
32/45
-
8/12/2019 Lecture Cns 1
33/45
-
8/12/2019 Lecture Cns 1
34/45
Depolarization
Membrane becomes more permeable to Na+ions (Opening of voltage gated Na+channels)
More Na+enter the cells
Membrane potential is now more positive
Depolarization must exceed threshold value (1530mV more positive -65 mV) before it can
trigger an action potential More voltage gated Na+channels open
At the peak- voltage gated Na+channels close
- voltage gated K+channels open
-
8/12/2019 Lecture Cns 1
35/45
Repolarization
Voltage gated Na+channels close
Simultaneous increase in K+permeability
Afterhyperpolarization (membrane potentialbecomes more negative than RMP)
Closing of voltage gated K+channels-RMPwill be achieved
** Cl-permeability does not change during theaction potential
-
8/12/2019 Lecture Cns 1
36/45
Voltage gated Na+channels
Activation gate and inactivation gate
Fast opening
Fast closing
Inactivate spontaneously
The inactivation gate will not reopen
until the membrane potential returns to
or near RMP level
-
8/12/2019 Lecture Cns 1
37/45
-
8/12/2019 Lecture Cns 1
38/45
Roles of other ions
Ca2+bind with the sodium channel proteinmolecule
The positive charges alter the electrical stateof the channel protein (alter voltage level foropening sodium channels)
Hypocalcaemia (low Ca 2+in blood) -thenerve becomes more excitable
The threshold to elicit an AP is reduced
Ca Ca
-
8/12/2019 Lecture Cns 1
39/45
Characteristics of AP
Propagation of action potential
The direction is away from the region
that has recently been active (refractoryperiod)
The velocity depends on the fiberdiameter and whether it is myelinated
Larger fiber and myelinated fibers-propagation of AP is faster
-
8/12/2019 Lecture Cns 1
40/45
In a myelinated fiber, ionic conduction only occurs at thenodes of Ranvier
Jumping of the AP- saltatory conduction is faster
-
8/12/2019 Lecture Cns 1
41/45
Characteristics of AP
Follows All or None Law
Once membrane is depolarized to the
threshold, amplitude is independent ofthe initiating event
Cannot be summed
-
8/12/2019 Lecture Cns 1
42/45
Characteristics of AP
Refractory period
Absoluterefractory period- a second stimulus
no matter how strong will not produce an AP Voltage gated Na+channels are opened and
inactivation gate blocks the channels
Relativerefractory period- the stimulus strength
should be stronger than the first one to producean AP
Some of the Na+channels have returned to itsresting stage
K+ channels are opened
-
8/12/2019 Lecture Cns 1
43/45
Relative Refractory Period
Could an AP be generated during the undershoot?
Yes! But it would take an initial stimulus that is much, much
stronger than usual.
WHY?
This situation is known as the relative refractory period.
Imagine, if you will, a toilet.
When you pull the handle,water floods the bowl. This event takes acouple of seconds and you cannot stop it in the middle. Once the bowl
empties, the flush is complete. Now the upper tank is empty. If you trypulling the handle at this point, nothing happens (absolute refractory).Wait for the upper tank to begin refilling. You can now flush again, but theintensity of the flushes increases as the upper tank refills (relativerefractory)
-
8/12/2019 Lecture Cns 1
44/45
Factors influencing impulse
conduction Size of the neuron
Myelinated/unmyelinated
Ions
1. Hypocalcaemia (low Ca2+)-excitable (tetany)2. Hyperkalaemia (high K+)-RMP less negativemore
excitable, easier to reach the threshold to generatethe AP
3. Hypokalaemia (low K+) -RMP more negative-
paralysis Drugs-anaesthetics e.g. procaine reduces Na+
permeability and prevents impulse transmission
K+ ECF
-
8/12/2019 Lecture Cns 1
45/45
Factors influencing impulse
conduction Temperature- If increase, rate of
conduction increases
Hypoxia (reduce in oxygen in blood)reduces excitability of neurons
Ouabain, dinitrofenol, cyanide inhibit Na+-K+pump
Toxin e.g. tetrodotoxin blocks Na +ionchannel