Y2 s1 introduction to the nervous system


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Y2 s1 introduction to the nervous system

  1. 1. Introduction to the Nervous System Prof. Vajira Weerasinghe Professor of Physiology Faculty of Medicine University of Peradeniya(This lecture is available at www.slideshare.net/vajira54)
  2. 2. Why study nervous system? Neurological diseases are disablingand debilitating and very little treatment is available
  3. 3. Stroke or paralysis Parkinsonism Alzheimer’s disease (Memory loss) Migraine(severe headache) Muscle wasting
  4. 4. Why study nervous system? Activities such as walking and running andvarious forms of exercise and sports require proper functioning of the nervous system
  5. 5. Controlling systemNervous system is the main controlling system of the body Quick ElectricalEndocrine system also controls body functions Slow Chemical
  6. 6. Nerve impulses• It controls other organs by sending electrical messages called nerve impulses It is also the main communication system (like
  7. 7. What does it do ? Functions of the nervous system1. Receives sensory messages from the external environment2. Organizes information and integrates it with already storedinformation3. Uses integrated information to send out messages to musclesand glands, producing organized movement and secretions4. Provides the basis for conscious experience
  8. 8. Functional Subdivisions • Sensory functions  feeling, eg. pain • Motor functions  movement, eg. walking • Integrative functions  eg. reflexes • Autonomic functions  control of blood pressure • Higher functions  memory, learning
  9. 9. Anatomical Subdivisions• Central Nervous system Brain and spinal cord• Peripheral Nervous system Cranial Nerves & Peripheral Nerves• Autonomic system sympathetic & parasympathetic
  10. 10. Brain• Brain contains the main controlling centres• It is divided into several lobes by several grooves
  11. 11. Brain - Lobes• Frontal lobe Located in the front Performs motor functions• Parietal lobe Located laterally Performs main sensory functions
  12. 12. Brain - Lobes• Occipital lobe Located in the back Performs visual functions• Temporal lobe Located laterally Performs hearing functions
  13. 13. White matter and grey matter• In the nervous system  Cell bodies are collected as grey matter  Nerve fibres are collected as white matter• In the brain  grey matter is located in the peripheral cell layer  White matter consists of central nerve fibre tracts
  14. 14. White matter and grey matter• With nerve fibre tracts each lobe is connected to different structures of the body• Frontal lobe is connected to the muscles• Parietal lobe is connected to the sensory organs of the skin• Occipital lobe is connected to the eye
  15. 15. Spinal cord• Nerve fibre tracts starting from the brain then continue as spinal cord• Divided into following areas  Cervical  Thoracic  Lumbar  Sacral
  16. 16. Spinal cord• Functions To transmit impulses to and from the brain to the periphery To cause reflex action To process information
  17. 17. Peripheral nervous system• Cranial nerves There are 12 cranial nerves which connects brain & brainstem with different organs of the head and neck region• Spinal nerves There are several pairs connecting different segments of the spinal cord with peripheral organs
  18. 18. Cranial nervesI-Olfactory nerve - smellII-Optic nerve - visionIII-Occulomotor nerve - eye movementsIV-Trochlear nerve - eye movementsV-Trigeminal nerve - masticationVI-Abducens nerve - eye movementsVII-Facial nerve - facial expressionsVIII-Vestibulocochlear nerve - hearing, balanceIX-Glossopharyngeal nerve - tasteX-Vagus nerve - parasympatheticXI- Spinal accessory nerve - neck musclesXII-Hypoglossal nerve - tongue
  19. 19. • Spinal nerves Cervical Thoracic Lumbar Sacral
  20. 20. Brain stem• This is important part of the nervous system that connects brain with the spinal cord• Many cranial nerves arise from brain stem• It also contain vital centres Cardiac, respiratory functions, consciousness
  21. 21. Brain stem• It has three areas Midbrain Pons (or pons Varoli) Medulla (or medulla oblongata)
  22. 22. Cerebellum• This is hind brain• This is connected to the brainstem• Main function is motor coordination• Abnormalities result in difficulty
  23. 23. Sensory functions• Functions that make us feel the environment• Nerve signals come from the sensory organ towards the CNS Afferent signals• There are different types of sensory modalities human nervous system could feel
  24. 24. General and special sensations• There are two main types of sensations General sensations Special sensations
  25. 25. General sensations• Mechanical sensations  Touch  Pressure  Vibrations  Stretch• Thermal sensations  Hot, cold• Chemical sensation
  26. 26. Somatic and visceral sensations• Somatic sensations External stimuli sensed by the skin eg. Feeling of hot environment• Visceral sensations Internal sensations sensed by the visceral afferent nerves eg. acidity in stomach
  27. 27. Special sensations• These are specialised sensations• Vision Hearing Taste Smell
  28. 28. Proprioception• Joint and position sensation• Muscles and tendons contain receptors which could feel Muscle length Joint angle Position of bones and joint• This is very important feedback information for movements of muscles
  29. 29. General plan of the sensory system• Stimulus• Receptor• Nerve pathway• Central connections
  30. 30. Sensory area in the brain NT Ascending RE Sensory pathway E AFF Central Connections Sensory nerveTouch stimulus Receptor Sensory modality
  31. 31. se n so 3rd ry c order or te neuron x internal capsule thalamus 2nd order Brain stem neuronSkin receptor 1st order Spinal Cord neuron
  32. 32. Motor functions• Movements are of two types Voluntary movements Consciously controlled movements Well thought and planned Involuntary movements Reflex action Control of posture Balance
  33. 33. Voluntary movements• Planning starts from the brain (frontal lobe)• Modified by various intermediate structures  Brainstem  Cerebellum• Executed by the brainstem and spinal cord (lower motor neuron)
  34. 34. mo to r Upper co motor rte x neuron internal capsule Brain stem Spinal CordMuscle contraction Lower Motor Nerve motor neuron
  35. 35. Motor map in the brain• In the frontal lobe different areas controlling different muscles of the body are distinctly organised• eg. there is a hand area, thumb area, face area
  36. 36. concept of homunculus Map Representation •upside down •distorted
  37. 37. Cerebellum• This is very important for motor coordination eg. In walking many muscles should contract and relax in smooth coordination• Cerebellum receives proprioception• Cerebellum is used as an error correction centre
  38. 38. What is a reflex?• Response to a stimulus• Stimulus -> Response• Task: Write down 3 reflexes.
  39. 39. Reflexes• Response to a stimulus• This is an involuntary action eg. Hot object touching the hand will cause it to withdraw• This is called withdrawal reflex
  40. 40. What is a reflex? Central control Receptor Afferent nerveStimulus Central connectionsResponse Effector organ Efferent nerve
  41. 41. Reflexes• Reflexes involve many systems of the body• eg. Withdrawal reflex (pain and motor pathways) Pupillary reflex (eye) Salivatory reflex (salivary glands) Swallowing reflex (GIT) Micturition reflex (urinary system) Baroreceptor reflex (blood pressure control) Stretch reflex (main reflex in the motor system)
  42. 42. Autonomic functions• Controls involuntary functions of the body• Two main divisions Sympathetic Parasympathetic
  43. 43. Sympathetic system• This is involved in fight or flight reaction• What happens when somebody is excited Blood pressure increases Heart rate increases Respiratory rate increases Increased sweating Pupillary dilatation GIT function suppressed
  44. 44. Parasympathetic system• This is involved when somebody s resting• Blood pressure decreases• Heart rate decreases• Respiratory rate decreases• Decreased sweating• Pupillary constriction• GIT function increased
  45. 45. Higher functions• Brain is involved in controlling higher functions• Learning• Memory• Intelligence• They are called cognitive functions
  46. 46. Each side controls opposite of the body• Right side of the brain controls left side of the body• There is a cross over of nerve pathways at the brain stem
  47. 47. Basic cell in the nervous system is is a neuron Nerve signals are electrochemical impulses called “action potentials”