How nervous system works
- 1. How the nervous system works? MSC Miroslava Korenova PhD 1
- 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............ 2
- 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 3
- 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 4
- 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 5
- 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........................... 6
- 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 7
- 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 8
- 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 9
- 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 10
- 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 11
- 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 12
- 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 13
- 14. How the nervous system works? Let us explain three main parts responsible for controlling motor function – spinal cord, brain stem and cerebral cortex. 14
- 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 15
- 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 16
- 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 17
- 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 18
- 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) 19
- 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 20
- 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 21
- 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 22
- 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/ 23