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PHYSIOLOGY OF THE NERVOUS SYSTEM

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  1. PHYSIOLOGY OF THE NERVOUS SYSTEM Sept 20, 2011 Group 4

  2. Physiology of the Nervous System • Functions and Divisions • Nervous Tissue • Neurons and neuroglia • Types • Nerve signal and transmission • Central Nervous System • Brain and spinal cord • Peripheral Nervous System • Types of nerves • Somatic Motor Nervous System • Autonomic Motor Nervous System • Diseases

  3. Functions • Sensory Input - sensory receptors in the skin and organs generate nerve signals 2. Integration - brain and spinal cord interpret the data and signal nerve responses • Motor Output - nerve impulses from the brain and spinal cord go to the effectors

  4. Divisions • Central Nervous System (CNS) - lie midline of the body - brain and spinal cord • Peripheral Nervous System (PNS) - project out from the CNS - cranial and spinal nerves 1. afferent/ sensory 2. efferent/ motor

  5. CNS Brain Spinal cord PNS Sensory Nerves (afferent) Motor Nerves (efferent) Somatic Sensory Nerves Visceral Sensory Nerves Somatic Motor Nerves Autonomic Motor Nerves Sympathetic Parasympathetic

  6. Nervous Tissue • Neurons • Dendrite- receives signals from receptors • Cell Body- contain nucleus and most of the cytoplasm • Axon- conducts nerve impulses • Fibers- long axons • Nerves- fibers outside the brain and spinal cord • Tracts- fibers in the brain and spinal cord

  7. Nervous Tissue Types of Neurons • Motor Neurons- (multipolar) take nerve impulses from the CNS to muscles, organs or glands • Sensory Neurons- (unipolar) take nerve impulses from sensory receptors to the CNS • Interneurons/ Association neurons- (multipolar) convey nerve impulses between various parts of the CNS

  8. A Typical Nerve Cell/ Neuron

  9. Types of Neurons

  10. Nervous Tissue B. Neuroglia-nourish the neurons • In the brain: 1. microglia- engulf bacterial and cellular debris 2. astrocytes- provide nutrients and produce a hormone 3. oligodendrocytes- form myelin 4. ependymal cells- form cerebrospinal fluid

  11. Nervous Tissue • Outside the brain: Schwann Cells/ neurolemmocytes- provide myelin sheath to nerve fibers • Nodes of Ranvier/ neurofibril nodes- gaps between Schwann cells • Myelin sheath- speeds up conduction

  12. A Neuroglia

  13. Nerve Signal Conduction • Neurons- transmit nerve signals • Nerve Signal- action potential, conducted by the axon

  14. Nerve Signal Conduction • Resting Potential • nerve cell has -70 mV of stored energy • exists because cell membrane is polarized • necessary for efficient work • Maintained through the sodium-potassium pump

  15. Resting Potential

  16. Nerve Signal Conduction • Action Potential • Process of conduction that occurs in the axons • Begins with a stimulus • Depolarization - protein channels for Na+ open • Repolarization- protein channels for Na+ close and channels for K+ open

  17. Action Potential

  18. Action Potential

  19. Conduction of Action Potentials • Unmyelinated Axons • Action potential at one local stimulates an adjacent part of the axon membrane to produce an action potential • Slow, 1m/sec in thin axons because each section of the axon must be stimulated • Myelinated Axons • Action potential at one node of Ranvier causes an action potential at the next node(saltatory conduction) • Faster, 100m/sec in thick axons

  20. Conduction of Action Potentials

  21. Refractory Period • occurs soon as the action potential has passed by each successive portion of the axon • Axon is unable to conduct an action potential • Ensures one-way direction of an impulse

  22. Transmission Across a Synapse • Axon terminal- swelling at the tip of the axon • Synapse – region of close proximity between the axon terminal of a neuron and a dendrite or cell body of another neuron • Presynaptic membrane- membrane of the first neuron • Postsynaptic membrane- membrane of the next neuron • Synaptic cleft- small gap between the two membranes

  23. Transmission Across a Synapse • Neurotransmitters • Carry out transmission across a synapse • stored in synaptic vesicles in the axon terminals • e.g. Ach and NE • Excitatory neurotransmitter • Inhibitory neurotransmitter • graded potential • small signals from a synapse

  24. Transmission Across a Synapse

  25. Transmission Across a Synapse

  26. Central Nervous System • Consists of the brain and spinal cord • Composed of: • Gray mater- contains cell bodies and short, nonmyelinated axons • White mater- contains myelinated axons that run together in tracts

  27. Central Nervous System • Meninges (sing. Meninx)- protective membranes of the spinal cord and brain • Dura mater- outer meninx; tough, white, fibrous connective tissue that lies next to the skull and vertebrae • Arachnoid mater- “spider-like”; consists of spider web like connective tissue • Pia mater- deepest meninx; very thin and closely follows the contours of the brain and spinal cord

  28. Central Nervous System • Subarachnoid space • space in between arachnoid and pia mater • Contains cerebrospinal fluid • similar to the plasma that forms a protective cushion around and within the CNS • Fills ventricles and hollow ventral canal of the spinal cord

  29. Spinal Cord • Long, thin tubular bundle of Nervous System. • Found inside the vertebra. • Supports cells that extends the brain. • Begins at the occipital bone. • Main pathway for information connecting the brain and peripheral nervous system.

  30. Layers of Spinal Cord (Meninges) • Dura Mate • Archnoid Mater • Pia Mater

  31. The subarachnoid space is the space which normally exists between the arachnoid and the pia mater, which is filled with cerebrospinal fluid. Normally, the dura mater attached to the skull, or to the bones of the vertebral canal in the spinal cord. The arachnoid is attached to the dura mater, while the pia mater is attached to the central nervous system tissue. When the dura mater and the arachnoid separate through injury or illness, the space between them is the subdural space.

  32. Spinal Cord Level Numbering System • The spinal nerves carry information to and from different levels (segments) in the spinal cord. Both the nerves and the segments in the spinal cord are numbered in a similar way to the vertebrae. The point at which the spinal cord ends is called the conusmedullaris, and is the terminal end of the spinal cord. It occurs near lumbar nerves L1 and L2. After the spinal cord terminates, the spinal nerves continue as a bundle of nerves called the caudaequina. The upper end of the conusmedullaris is usually not well defined.

  33. There are 31 pairs of spinal nerves which branch off from the spinal cord. In the cervical region of the spinal cord, the spinal nerves exit above the vertebrae. A change occurs with the C7 vertebra however, where the C8 spinal nerve exits the vertebra below the C7 vertebra. Therefore, there is an 8th cervical spinal nerve even though there is no 8th cervical vertebra. From the 1st thoracic vertebra downwards, all spinal nerves exit below their equivalent numbered vertebrae. • The spinal nerves which leave the spinal cord are numbered according to the vertebra at which they exit the spinal column. So, the spinal nerve T4, exits the spinal column through the foramen in the 4th thoracic vertebra. The spinal nerve L5 leaves the spinal cord from the conusmedullaris, and travels along the caudaequina until it exits the 5th lumbar vertebra.

  34. BrainOverview on the parts of the brain • Forebrain • Telencephalon • Cerebrum • Cerebral Cortex Frontal lobe Parietal lobe Temporal lobe Occipital lobe insula Brocas area • Corpus callosum • Basal Ganglia • The Limbic System • Diencephalon • Thalamus • Hypothalamus • Midbrain • Tectum • Tegmentum • Hind brain • Cerebellum • Pons • Medulla oblongata

  35. ForebrainCerebrum • Largest portion of the brain • Last center to receive sensory input • Carry out integration before commanding voluntary motor responses • Carries out higher thought of processes required for learning and memory and for language and speech • Compose of 2 hemispheres • Left and right cerebral hemisphere • Frontal lobe- reasoning and movement • Parietal lobe- somatic sensing includes taste • Temporal- hearing • Occipital- vision Brocas area- found only in left cerebral hemisphere; motor speech area

  36. Cerebral cortex -thin but convulated outer layer of gray matter which covers the cerebral hemisphere -accounts for sensation, Voluntary movement, and all thought processes we associate with consciousness • Limbic system • hippocampus (sea horse)and the amygdala (almond), along with portions of the hypothalamus, thalamus, caudate nuclei, and septum function together function: • Causes the subject to experience pain, rage, pleasure or sorrow Corpus callosum white matter connects the cerebral hemisphere

  37. Diencephalon Hypothalamus- forms the floor of the 3rd ventricle • Maintains homeostasis by regulating hunger, sleep, thirst, body temperature and water balance. • Also controls the endocrine system and autonomic nervous system Thalamus- consists of 2 masses of gray matter located in the sides and roof of the 3rd ventricle - - integrates visual, auditory and somatosensory information and sends it to appropriate portions of the cerebrum

  38. Mesencephalon Tectum- include the superior colliculi and theinferiorcolliculi - visual reflexes and reaction to moving stimuli Tegmentum- reticular formation, periaqueductal gray matter, and the red nucleus and substantianigra receives sensory information and is involved with attention, sleep and arousal, muscle tonus, movement, and various vital reflexes

  39. Hind brain Cerebellum- separated from the brain stem by 4th ventricle • Receives sensory input from eyes, ears, joints and muscles • Receives motor output from cerebral cortex where this part should be located • Maintains posture and balance • Ensures that the muscles work together for smooth and coordinated movements

  40. Pons - large bulge in the brain stem between the mesencephalon and the medulla oblongata •  believed important in the role of sleep and arousal • Medulla oblongata- origin of the reticular formation and consists of nuclei  • control center for cardiac, vasoconstrictor, and respiratory functions.  • Reflex activities, including vomiting, are controlled by this structure of the hindbrain

  41. Peripheral Nervous System • Composed of: • Nerves- bundles of axons • Ganglia- swellings associated with nerves that contain collections of cells bodies

  42. Peripheral Nervous System • Subdivisions: • Afferent/ sensory system • Somatic sensory system- serves the skin, skeletal muscles, joints and tendons; special senses • Visceral sensory system- supplies internal organs • Efferent/ motor system • Somatic motor system- carries commands away from the CNS to the skeletal muscles • Autonomic motor system- regulates activity of cardiac and smooth muscles and glands

  43. Types of Nerves • Cranial Nerves • 12 pairs, concerned with the head, neck and facial regions of the body • Motor nerves- with only motor fibers • Sensory nerves- with only sensory fibers • Mixed nerves- with both motor and sensory nerves

  44. Table, fig 8.11