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Nervous System

Nervous System. Chapter 9. Introduction to the NS. Neurons – nerve cells Nerve impulses – electrochemical changes which transmit information Neurons consist of: Cell body – rounded area Dendrites – extensions that receive nerve impulses

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Nervous System

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  1. Nervous System Chapter 9

  2. Introduction to the NS • Neurons – nerve cells • Nerve impulses – electrochemical changes which transmit information • Neurons consist of: • Cell body – rounded area • Dendrites – extensions that receive nerve impulses • Axons – extensions that send nerve impulses (usually has only one) • Nerves – bundles of axons • Neuroglial cells – provide physical support, insulation, and nutrients for neurons

  3. Groups • Central nervous system – consists of brain and spinal cord • Peripheral nervous system – consists of nerves that connect the cns to the other body parts • Functions: • Sensory • Integrative • Motor

  4. Sensory Function • Sensory receptors are found at the ends of peripheral neurons gather info. by detecting changes inside and outside the body. • Monitor such things as light, sound, temperature, oxygen level

  5. Integrative Function • Nerve impulses from sensory receptors are transmitted to the cns • Signals are brought together, creating sensations, adding to memory, or helping produce thoughts that translate sensations into perceptions

  6. Motor Function • Impulses from cns to responsive structures called effectors • Examples: muscles that contract, glands that secrete • Somatic nervous system – motor functions that are consciously controlled • Autonomic nervous system – motor functions that are involuntary

  7. Dimethylmercury Poisoning • Clings to brain neurons, destroying them • Neuroglial cells overgrow

  8. Neuroglial Cells • Microglial – scattered throughout cns; support neurons and phagocytize bacterial cells and cellular debris • Oligodendrocytes – align along nerve fibers; provide insulating layers of myelin around axons within the cns • Astrocytes – found between neurons and blood vessels; provide structural support; help regulate conc. of nutrients and ions within the tissue; form scar tissue • Ependymal cells – form an epithelia-like membrane that covers specialized brain parts; forms inner linings • Schwann cells – form a myelin sheath around axons of the pns

  9. Gliomas • Fast-growing brain tumors • Consist of rapidly dividing neuroglia

  10. Neurons • Cell body • Granular cytoplasm • Cell membrane • Organelles (mitochondria, lysosomes, neurofibrils) • Nissl bodies (similar to rough ER) • Dendrites • Short and highly branched • Main receptive surfaces • Axons • Conducts nerve impulses away from the cell body • Usually a single structure • Surrounded by Schwann cells to form a myelin sheath • Spaces in between are called nodes of Ranvier • Neural stem cells found in the hippocampus

  11. Structural Classification of Neurons • Multipolar – one axon; many dendrites; lie within the brain or spinal cord • Bipolar – one axon; one dendrite; lie within eye, nose, and ears • Unipolar – one axon that branches into two; one assoc. with peripheral body part and the other enters the brain or spinal cord

  12. Functional Classification of Neurons • Sensory neurons – carry nerve impulses from peripheral body parts into the brain or spinal cord • Interneurons – transmit impulses from one part of the brain or spinal cord to another • Motor neurons – carry nerve impulses out of the brain or spinal cord to effectors

  13. Cell Membrane Potential • Surface of a cell membrane is usually electrically charged or polarized with respect to the inside • Polarization due to an unequal distribution of positive and negative ions between sides of the membrane

  14. Distribution of Ions • Greater conc. of Na+ outside cell • Greater conc. of K+ inside cell

  15. Resting Potential of Neuron • Resting membrane more permeable to K+ than to Na+ • K+ leaves faster than Na+ enters • There exists a potential difference of charges in a resting nerve cell between the region inside the membrane and outside the membrane

  16. Potential Changes • Depolarization – resting potential decrease (inside becomes less negative than outside as Na ions leave) • This produces a local current • If additional stimulation arrives before the effect of the previous stimulation subsides, the change in potential is still greater (summation) • Threshold potential is reached as a result of summated potentials

  17. Action Potential • At the threshold potential, permeability suddenly changes at the trigger zone (portion of axon where impulse begins) allowing Na+ in • Cell becomes depolarized and repolarized as K+ enter once more • Action potential – rapid sequence of depolarization and repolarization

  18. Agh! • Local anesthetic drugs decrease membrane permeability to sodium ions • It interrupts impulses from passing through the affected region and reaching the brain • Prevents the sensations of touch and pain

  19. Impulse Conduction • Myelinated sheath prevents almost all ion flow through the membrane it encloses • Nodes of Ranvier between Schwann cells interrupt the sheath • Action potentials occur at these nodes • Speed of nerve impulse conduction is proportional to the diameter of the axon (greater diameter=faster impulse)

  20. All-Or-None Response • If a neuron responds at all, it responds completely • Conduction occurs when a stimulus of threshold intensity or above is applied • All impulses carried on that axon are of the same strength • Greater intensity=more impulses per second

  21. Events leading to the conduction of a nerve impulse • Neuron membrane maintains resting potential • Threshold stimulus is received • Sodium channels in the trigger zone of the neuron open • Sodium ions diffuse inward, depolarizing the membrane • Potassium channels in the membrane open

  22. Potassium ions diffuse outward, repolarizing the membrane • The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane • A wave of action potentials travels the length of the axon as a nerve impulse

  23. Flipbook • Create a flipbook illustrating and describing the events leading to the conduction of a nerve impulse • Must be labeled, colored, and include a short description

  24. The Synapse • Nerve impulses travel along nerve pathways • The junction between any two communicating neurons is called a synapse

  25. Types of Nerves • Afferent fibers bring sensory information into the CNS • Efferent fibers carry impulses from the CNS to effectors (muscles or glands)

  26. Reflex Arc • Type of nerve pathway • Reflexes are automatic subconscious responses to stimuli within or outside the body • Help maintain homeostasis by controlling heart rate, breathing rate, blood pressure, and digestion • Knee-jerk reflex helps maintain upright posture • Withdrawal reflex occurs when a person unexpectedly touches a body part to something painful

  27. Meninges • Membranes that lie between bone and soft tissues of CNS • Dura mater • outermost layer • composed of tough, white, fibrous connective tissue • contains many blood vessels and nerves

  28. Arachnoid mater • thin, weblike membrane • Lacks blood vessels • Lies between the dura and pia maters • Spreads over the brain and spinal cord • Pia mater • Very thin • Contains blood vessels that nourish underlying cells of the brain and spinal cord • Hugs the surfaces of organs

  29. Spinal Cord • Slender nerve column that passes downward from the brain into the vertebral column • Consists of 31 segments, each of which gives rise to a pair of spinal nerves • Conducts nerve impulses • Serves as a center for spinal reflexes

  30. Brain • Composed of about 100 billion multipolar neurons • Weighs about 3.5 lbs. • If all the cells were laid end-to-end, they would cover 600 miles

  31. Cerebrum • Consists of left and right hemispheres • Deep bridge of nerve fibers called the corpus callosum connects the cerebral hemispheres • A layer of dura mater separates them • Gyri – ridges found on surface • Sulcus – shallow groove • Fissure – deep groove

  32. Lobes of Cerebrum • Frontal – forms anterior portion of each hemisphere • Parietal – posterior to the frontal lobe • Temporal – lies below frontal and parietal lobes • Occipital – forms posterior portion of each hemisphere

  33. Cerebrum cont. • Cerebral cortex – outermost portion of the cerebrum composed of a thin layer of gray matter • Just beneath the cerebral cortex is a mass of white matter that makes up the bulk of the cerebrum • Provides higher brain functions • Stores information that comprises memory and utilizes it to reason

  34. Functions of the Cerebrum • Motor area for voluntary muscle control • Motor speech area • Auditory area • Cutaneous sensory area • General interpretative area • Visual area

  35. Hemisphere Dominance • Both hemispheres participate in basic functions • In most persons, however, one side of the cerebrum is the dominant hemisphere, controlling the ability to use and understand language • Left hemisphere is dominant in more than 90% of the population • Non-dominant hemisphere controls emotional and intuitive thinking

  36. Cerebrospinal Fluid • Secreted by choroid plexuses found in the pia mater • Completely surrounds the brain and spinal cord • Organs float • Support and protection is provided by absorption of forces

  37. Diencephalon • Located between the cerebral hemispheres and above the midbrain • Composed largely of gray matter • Thalamus within the diencephalon relays sensory impulses from other parts of the nervous system to the cerebral cortex • Hypothalamus lies below the thalamus and maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems

  38. Brainstem – bundle of nervous tissue that connects the cerebrum to the spinal cord • Midbrain – contains bundles of myelinated axons that join lower parts of the brainstem and spinal cord with higher parts of the brain • Pons – rounded bulge on the underside of the brainstem; relays impulses to and from the medulla oblongata • Medulla oblongata – relays impulses, controls vital visceral activities, and reflexes

  39. Cerebellum • Large mass of tissue located below the occipital lobes of the cerebrum and posterior to the pons and medulla oblongata • Consists of two lateral hemispheres • Reflex center for integrating sensory information concerning the position of body parts and for coordinating complex skeletal muscle movements • Helps maintain posture

  40. Peripheral Nervous System (PNS) • Consists of nerves that branch out from the CNS and connect it to other body parts • Subdivided into the somatic and autonomic nervous systems

  41. Somatic Nervous System • Cranial and spinal nerves • Connect the CNS to the skin and skeletal muscles • Oversees conscious activities

  42. Cranial Nerves

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