Nervous system ppt

Detail anatomy of nervous system. component of nervous system, detail of nervous tissue , ascending and descending tract, supporting cells, myelinated cells, reflex. types of reflex,

1. Nervous System Hari Sharan Makaju M.Sc. Clinical Biochemistry PG Student

2. Content Introduction of nervous system Organization of nervous system Nervous tissue Neurons and its types Supporting cells Ascending tract and descending tract Reflex

3. Introduction Nervous system is: A physically connected network of cells, tissues and organs that allow us to communicate with and react to the environment and perform life activities . Master controlling and communicating system Has two main division Central nervous system Peripheral nervous system

4. FOUR PRIMARY FUNCTIONS OF NERVOUS SYSTEM Sensing the world Vision, Hearing, Smell, Taste, Touch Transmitting information Processing information Producing a response

5. Organization A. Central Nervous System (CNS ) ▫ Brain & spinal cord ▫ Integrative and control centers -Receives , interprets and sends signals to PNS B. Peripheral Nervous System (PNS) ▫ Nerves ( 31 pairs of spinal nerves, 12 pairs of cranial nerves) ▫ Communication lines between CNS and rest of body ▫ Two Divisions: Sensory (afferent) Division : Sensory receptors -- CNS Motor (efferent) Division : CNS -- effectors (muscles & glands )

6. Motor Division Somatic nervous system ( voluntary ) control skeletal muscles Autonomic nervous system (ANS) ( involuntary ) – regulate smooth muscles, cardiac, glands ▫ Subdivisions : Sympathetic : “Fight or Flight” Activated during emergencies, exercise or vigorous physical activity Revs up body to respond to situations that upset homeostasis Parasympathetic: “Rest & Digest” Reduces energy use Promotes: Storage of energy E limination of wastes Homeostasis

7. The mammalian brain is highly complex, containing many specialized regions that carry out specific functions. Generally, the brain is divided into: Hindbrain Midbrain Forebrain THE COMPLEX BRAIN

8. Hindbrain Medulla : Controls autonomic functions. Pons: Controls sleep stages. Cerebellum: Coordinates movement, stores some motor memory. Helps maintain posture, muscle control, and balance

9. Midbrain Located between the hindbrain and forebrain. All sensory and motor information that travels between the forebrain and the spinal cord passes through the midbrain making it a relay station for the central nervous system . the “traffic cops” of the brain. Filters sensory input, which allows us to concentrate. Filtering can be affected by higher thoughts .

10. Forebrain Thalamus: relay station channeling sensory information. Limbic system: basic emotions, drives, and behaviors. Cortex: higher thought

11. Limbic system Hypothalamus: Master controller of the endocrine system. Amygdala: sensations of pleasure or fear, recognition of fear in others. Hippocampus: formation of memories . Damage to these areas can lead to amnesia or emotional disturbances “ controls: emotions and memories ”

12. Cortex Various areas : control sensory processing motor control, thought , memory. Top layer of the brain Stores: experiences and/or learning behavior & emotion Sensory info concerning touch vision memory & emotion, speech and hearing

13. Spinal cord Grey matter mostly made up of cell bodies of neuron White matter composed of nerve fibers ( ascending and descending tracts ) embedded in neuroglial cells

14. Nervous Tissue Neurons (nerve cells ) F unctional unit of the nervous system T ransmit message Anatomy : Cell body – contains nucleus; metabolic center Dendrite – fiber that conveys messages toward cell body Axon – conduct nerve impulses away from the cell body Axon terminals – end of axon; contain neurotransmitters & release them Synaptic cleft/synapse – gap between neurons

15. Nervous Tissue 2. Supporting cells ( Neuroglia ) CNS: astrocytes, microglia, ependymal cells, oligodendrocytes barrier between capillaries and neurons protect neurons immune/defense line brain and spinal cord cavities wrap nerve fibers produces myelin sheaths (covering ) PNS: Schwann cells, satellite cells surround large neurons protect & cushion

16. Myelin W hitish , fatty material that covers nerve fibers to speed up nerve impulses Schwann cells S urround axons and form myelin sheath Myelin sheath T ight coil of wrapped membranes Nodes of Ranvier G aps between Schwann cells

17. Ganglia : collections of cell bodies Bundles of nerve fibers = tracts (CNS) or nerves (PNS) White matter D ense collections of myelinated fibers Gray matter U nmyelinated fibers & cell bodies ( nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color )

18. Dendrites receive signals. The cell body integrates signals. The axon transmits action potential. The myelin sheath makes the signal travel faster. Synaptic terminals transmit signals. The Neuron

19. Neurons Neuron Function Irritability : ability to respond to stimulus & convert to nerve impulse Conductivity : transmit impulse to other neurons , muscles, or glands Classification of Neuron Functional Classification Structural Classification

20. 1. Functional Classification : D irection nerve impulse is traveling Sensory n e u r ons Motor n e u r o n s Interneurons carry impulses from sensory receptors to CNS carry impulses from CNS to muscles & glands connect sensory & motor neurons Vision, hearing, equilibrium, taste, smell, pain, pressure, heat

21. 2. Structural Classification : P rocesses extending from cell body Multipolar Bipolar Unipolar 1 axon, several dendrites 1 axon, 1 dendrite 1 process Most common (99%) Rare Short with 2 branches (sensory, CNS) Eg. Motor neurons, i n te r n e ur o n s Eg. retina, nose, ear Eg. PNS ganglia

22. Nerve Impulses Cell membrane at rest = polarized Na + outside cell, K + inside cell Inside is (-) compared to outside Stimulus --- excited neuron (Na + rushes in) -- becomes depolarized Depolarization activates neuron to transmit an action potential (nerve impulse) All-or-none response Impulse conducts down entire axon K+ diffuses out --- repolarization of membrane Na+/K+ ion concentrations restored by sodium- potassium pump (uses ATP) Exciting a Neuron

23. Synapse Neurons usually do not connect directly to one another. A gap called a synapse controls the transmission of signals. Depending on the site of the synapse, they are often referred to as axodendritic , axosomatic , or axoaxonic Types of synapse Chemical Neurotransmitter E lectrical presynaptic neuron Post synaptic neuron

24. Information Transfer Across Chemical Synapse Action potential reaches axon terminal ---- vesicles release neurotransmitters (NT) into synaptic cleft NT diffuse across synapse  bind to receptors of next neuron Transmission of a nerve impulse = electrochemical event

25. Segmental division of Spinal cord

26. Spinal cord Grey matter mostly made up of cell bodies of neuron White matter composed of nerve fibers ( ascending and descending tracts ) embedded in neuroglial cells

27. CENTRAL NERVOUS SYSTEM integration / processing / modulating stimulus receptor neurone motor / descending tracts effector organ / response P NS transmission lower motor neurone sensory / ascending tracts

28. Ascending tract 1 st The ascending tracts transmit sensory information from the sensory receptors to higher levels of the CNS . sensory information exteroceptive sensation origin:- outside the body e.g . temp, touch, light, sound, chemicals, mechanical receptors:- surface layer of skin, mucosa proprioceptive sensation origin :- within the body e.g . muscles, joints, tendons receptors :- deeper layer of skin, tendons, joints , muscle spindles, ligaments I n f o rmat i o n conscious sensation reach the cerebral cortex unconscious sensation reach to the areas other than cortex

29. Ascending tract V P L 1 st 2 nd cross the mid line in front of central canal The pathways consist of thousands of sets of three neurons: first-order neuron, second-order neuron, and a third-order neuron .

30. Ascending tract First order neuron : cell body in posterior root ganglion peripheral process connects with sensory receptor ending central process enter the spinal cord through the posterior root synapse with second order neuron in spinal gray matter Second order neuron: cell body in posterior gray column of spinal cord axon crosses the midline ( decussate ) ascend & synapse with third order neuron in nucleus of thalamus Third order neuron : cell body in the thalamus give rise to projection fibres to the cerebral cortex, postcentral gyrus ( sensory area )

31. Ascending Tracts of the Spinal Cord Lateral Spinothalamic Tract pain, temperature Anterior Spinothalamic Tract touch, pressure Posterior White Column: Fasciculus Gracilis and Fasciculus Cuneatus conscious proprioceptive sense, discriminative touch, vibratory sense Posterior Spinocerebellar Tract&Anterior Spinocerebellar Tract unconscious information from muscle, joints, skin, subcutaneous tissues Spinotectal Tract Spinoreticular Tract Spino-olivary Tract

32. Descending tracts The descending tracts originate from different cortical areas and from brain stem nuclei. The descending pathway carry information associated with maintenance of motor activities such as posture, balance, muscle tone, and visceral and somatic reflex activity

33. The Descending Tracts of the Spinal Cord Corticospinal Tracts for fine skilled movements Reticulospinal Tracts Inhibit or facilitate voluntary movement; hypothalamus controls sympathetic, para-sympathetic outflows Rubrospinal Tract Vestibulospinal Tract Olivospinal Tract Tectospinal tract Reflex postural movements concerning sight Descending Autonomic Fibers

34. Corticospinal Tracts

35. Neuron Function Irritability: ability to respond to stimulus & convert to nerve impulse Conductivity: transmit impulse to other neurons, muscles, or glands

36. Reflex Reflex is an action that is performed without conscious thought as a response to a stimulus. Rapid, predictable, involuntary responses to stimuli Somatic Reflexes: stimulate skeletal muscles Eg . jerking away hand from hot object Autonomic Reflexes: regulate smooth muscles, heart, glands Eg . salivation, digestion, blood pressure, sweating Reflex arc It is the nerve pathway involved in a reflex action, including at its simplest a sensory nerve and a motor nerve with a synapse between them.

37. Reflex Arc 1) Receptor - reacts to stimulus 2) Sensory Neurons - afferent impulses to CNS 3) Integration centers - synapses in CNS 4) Motor Neurons - efferent impulses from Integration centers to effector 5) Effector - muscle or glands

38. Reflex Activities Patellar (Knee-jerk) Reflex Pupillary Reflex Gently tap your quadriceps tendon, which is located immediately below  your knee cap, with a  reflex hammer Optic nerve -- brain stem -- muscles constrict pupil Useful for checking brain stem function and drug use

39. Other Reflexes Stimulus ( receptors) Response ( effector) The aroma of your favorite food Salivation A nasty odor Nausea A bright light shining in your eye Pupils get smaller An insect flying towards your eye Blinking

40. Voluntary Reactions More neurons and synapses are involved -- longer response times Reflex = Involuntary Reaction Voluntary Reaction

41. References Elaine N. Marieb , Human Anatomy and Physiology 9 th Edition . Dr. Henry Gray and Dr. Henry Vandyke Carter , Grays Anatomy for Students 40 th Edition. Various internet sources.