Interested in neural circuit functionning? Find an answer right here

1. How the nervous system
works?
MSC Miroslava Korenova PhD
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2. How the nervous system works?
 What do you think – how our nervous system works?
 What enables the nervous system to work properly?
 How the nervous signal is transducted? – where it emanates?
 What is the simplest functional unit of the nervous system?
 Think and discuss............
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3. How the nervous system works?
 The nervous system provides the most of the
control functions over the body (maintaining
homeostasis, proccessing information to and fro,
reacting to external and internal stimuli...)
 It receives billions of bits of information from
different sensory organs (can you name all sensory
organs we have?)
 More than 99% of all sensory informations is
discarded by the brain as irrelevant and unimportant
 After the sensory impuls has been selected as
important – impuls is channeled to proper motor
region to evoke desired response.......or is stored for
use in the future cognitive processes or motor
activities
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4. Organization of the nervous system
Central nervous system
(consisting of brain and spinal cord)
Peripheral nervous system
(consisting of cranial and spinal nerves
Communication between CNS and rest of body)
Sensory (afferent division) –
conducts signals from
receptors to the CNS
Motor (efferent division)
Conducts signals from CNS
to effectors
Autonomic nervous system
Visceral (involuntary) motor movements
From CNS to glands and smooth muscles
Somatic nervous system
Somatic (voluntary) motor movements
Signals from CNS to skeletal muscles
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5. How the nervous system works?
 According to the direction the signal is transducted in central nervous system –
two main divisions can be named
Sensory division
Motor division
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6. How the nervous system works?
 1. Sensory division:
 Most activities of the nervous system are
initiated by sensory experience
(emanating from sensory receptors)
 Sensory experience usually causes
immediate response – or its memory can
be stored and used when necessary
Example:
When I return home, I can smell the fantastic
apple pie made by my grandma – what do
you think – what am I going to do first?
Make your own examples...........................
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7. A short about sensory organs
Humans have multitude of senses, here are the most
traditionally recognized senses:
 Sight - vision
 Hearing – audition
 Taste – gustation
 Smell – olfaction
 Touch – somatosensation
However the ability to detect a much wider range of
sensory modalities detected by these five senses
include- temperature (termoreception), kinesthetic
sense (proprioreception), balance (equilibrium),
vibration (mechanoreception) and various internal
stimuli..
Sensory organs transduct signals to goal area
(muscles) through the sequences of nerve synapses
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8. How the nervous system works?
 Sensory information is integrated at all levels of the
nervous system and causes appropriate motor response
begining with
 A) spinal cord – responsible for basic simmple reflexes
 B) extending to the brain stem – for more complicated
reflex responses
 C) reaching cerebrum (cerebral cortex) – where the
most complicated reflex responses are controlled
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9. How the nervous system works?
 2. Motor division (muscles):
The most important ultimate role of
nervous system
Provides control of bodily activities
(contraction of skeletal muscle,
contraction of smooth muscle,
secretion from glands)
Muscles and glands are called the
effectors – perform functions
mediated by the nerve signals
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10. How the nervous system works?
Major function of the central nervous system (CNS) is to process
incoming (sensory) information in such way that appropriate
motor response (effector) may occur
 This channeling response is called
The INTEGRATIVE FUNCTION OF THE CNS
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11. How the nervous system works?
Reflexes
 Reflexes do not require conscious thought
 They produce a consistent and predictable result
 Are very quick, protecting body from painful stimuli, but also
maintaining homeostasis
 Are integrated within the brain stem and spinal cord – higher
cortical centers may supress or exaggerate reflexes
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12. How the nervous system works?
Reflex arc
Example of integrative function of the
CNS:
Reflex ARC
placing a finger over a candle flame (sensory
division)– will elicit immediate lift of the
hand (motor division) to escape from
nociceptive stimulus and minimize injury.
1. Receptor - detects a harmful stimulus
2. afferent nerve fibres conduct signal
from receptors to spinal cord
3. spinal cord – integrating center
4. efferent nerve fibres conduct signal to
muscles – effector (to make a desired
movement)
Reflex responses are automatic involuntary
movements – they ususally does not involve
brain in signal transduction – therefore they are
very quick, cause signal is without the delay routing
to the brain
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13. Role of synapses in information processing
Synapse
 is a junction point of one neuron to the next
 Is site for controlling signal transmission
 Contains vesicles of neurotransmitter – that
is released when signal is transducted
 Determines the direction that the nerve
signal spreads from one neuron to the next
 Some signals open/close synapse for
transmission
 Blocking weak signals, allowing only strong
signals to pass – all or nothing rule
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14. How the nervous system works?
 Let us explain three main parts responsible for controlling motor function –
spinal cord, brain stem and cerebral cortex.
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15. A) Motor function of the spinal cord
 The spinal cord is not merely a conduit for sensory signals to the brain
(or from signals from brain back--)
 Without a special neuronal system of the cord – even the simplest
movement cannot be performed properly (Motor control system in the
brain alone cannot evoke any purposeful muscle movement )
 Brain has a role to control, „ cord activities“
Example:
 there is no specific structure in the brain that causes a specific to-fro
movement of the legs (e.g. walking pattern).
 Instead – circuits for these movements are in the cord and the brain
simply send a commant signals to set in motion walking process
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16. Motor function of the spinal cord
reflex responses regulated by spinal cord
 The flexor reflex – called also a withdrawal reflex – is spinal reflex in which a painful
stimulus applied to e.g. – a toe, results in a flexion, or withdrawal of the leg.
 Positive supporting reaction – pressure on the footpad causes the limb to extend
against the pressure – limbs are able to support the weight of the body
 Scratch reflex – is initiated by the itch and tickle sensation. Involves two functions –
position sense - exact localization of the itching spot , and to and fro scratching
movement
 Cord righting reflex – when an animal is laid on its back, it will immediately turn into
standing position
 But also evacuation of bladder and colon
 Autonomic reflexes of the gut
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17. B) Brain stem control of the motor function
 Brain stem area predominantly controls
body posture and its visuospatial
orientation in space - by integrating
visual, sensory, vestibular and
somatosensory information
 Brain stem is also responsible of
controlling goal – directed movement of
distal limb muscles – thus is important
for goal directed movement of arm and
hand
 Also important for eye and head
movements
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18. Reflex responses regulated by
brain stem
Corneal reflex – causes an eye blink in response to tactile stimulus
Pupillary light reflex – relfex that controls the diameter of pupilla in
response to incoming light
Cough – induced by mechanical or chemical irritating stimulus
Gag reflex – is a reflex contraction of the back of the throat evoked by
touching the roof of the mouth
Vestibulo-ocular reflex – (Doll;s eyes test) – is elicited by turning the
head of the experimental subject – eyes will move the opposite
direction of the movements – are fixed in still position
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19. C) Cortical control of the motor function
 Primary motor cortex and several premotor
areas project directly to the spinal cord -
through corticospinal tract – and also
regulates motor tracts that originate in the
brain stem
 Premotor areas are responsible for planning
and coordinating complex sequences of
movement
 Example:
 Motions followed by visual or acoustic
instruction (dancing, doing exercise - zumba)
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20. Cerebellum and Basal ganglia
In addition to previous are three hierarchical levels
two other parts also regulate planning and
execution of movement –
 Cerebellum
 Basal ganglia
They do not send significant signals to the spinal
cord, but they directly act on neurons in brain stem
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21. Functions of the autonomous nervous
system – in shortcut
 Autonomous nervous system is divided into sympathetic and
parasympathetic nervous system
 Generally these two subsystems have the opposite effect on the same set
of organs
SYMPATHICS – active during awake state, stress , emergency
PARASYMPATHICS – associated with relax state and digestion
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22. Conclusions
 Nervous system provides the most of the control functions over the body
 Most activities of the nervous system are initiated by sensory experience
 CNS can be divided into two main divisions – sensory and motor division
 Sensory division (receptors) send information to the CNS via afferent nerve fibres
 Motor division (effectors) receive information from the CNS via efferent nerve
fibres
 Reflex arc is the main functional unit of the CNS
 Reflexes are unconscious responses of nervous system to sensory stimulation –
they are very quick, predictable and frequently are protecting body from painful
stimuli
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23. references
Kandel, E. R., Schwartz, J. H. 1., & Jessell, T. M. (2000). Principles of neural science(4th
ed.). New York: McGraw-Hill, Health Professions Division.
Hall, John E.Guyton, Arthur C. (2011) Guyton and Hall textbook of medical
physiology /Philadelphia, PA : Saunders/Elsevier,.
https://www.wikipedia.org/
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