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The Nervous System and Tissue

The Nervous System and Tissue. Organization. The nervous system has 3 overlapping functions: Sensory input Integration Motor output. Figure 11.1 The nervous system’s functions. Sensory input. Integration. Motor output. Organization.

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The Nervous System and Tissue

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  1. The Nervous System and Tissue

  2. Organization The nervous system has 3 overlapping functions: • Sensory input • Integration • Motor output

  3. Figure 11.1 The nervous system’s functions. Sensory input Integration Motor output

  4. Organization The nervous system is divided into 2 major divisions: • Central Nervous System (CNS) which is made up of the brain and spinal cord

  5. Organization The nervous system is divided into 2 major divisions: • Central Nervous System (CNS) which is made up of the brain and spinal cord • Peripheral Nervous System (PNS) which is made up of all nerves out side the CNS

  6. Organization The PNS is further divided into the: • Afferent division which brings in sensory input • Efferent (Motor) division which carries motor signals to muscles and glands

  7. Organization The Efferent division is further divided into: • Somatic Nervous System which carries out voluntary actions • Autonomic Nervous System which carries out involuntary actions

  8. Figure 11.2 Schematic of levels of organization in the nervous system. Peripheral nervous system (PNS) Central nervous system (CNS) Cranial nerves and spinal nerves Brain and spinal cord Communication lines between the CNS and the rest of the body Integrative and control centers Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory nerve fibers Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Conducts impulses from receptors to the CNS Somatic sensory fiber Autonomic nervous system (ANS) Somatic nervous system Skin Visceral motor (involuntary) Somatic motor (voluntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Conducts impulses from the CNS to skeletal muscles Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Parasympathetic division Mobilizes body systems during activity Conserves energy Promotes house- keeping functions during rest Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) division of PNS Bladder Parasympathetic motor fiber of ANS Motor (efferent) division of PNS

  9. Histology of Nervous Tissue Two cell types make up the nervous system. Those called supporting cells or neuroglia cells and those involved in transmission of nerve impulses, the neurons.

  10. Neuroglia There are 6 types of neuroglia cells (glial cells). • 4 are associated with the CNS • 2 with the PNS.

  11. Neuroglia Each has a unique function either producing chemicals to aid in neuron growth, insulating or offering support.

  12. Neuroglia of the CNS The four types are: • Astrocytes • Microglia • Ependymal Cells & • Oligodendrocytes

  13. Astrocytes These are the most abundant and versatile of the glial cells. They have radiating process, hence their name “star cells” that connect to neurons and near by capillaries.

  14. Astrocytes They provide support and bracing for the neurons and keep them close to the capillaries, their source of nutrition.

  15. Figure 11.3a Neuroglia. Capillary Neuron Astrocyte (a) Astrocytes are the most abundantCNS neuroglia.

  16. Microglia They monitors the health of the neurons. When injured or invading organisms are present they convert into a special type of macrophage.

  17. Figure 11.3b Neuroglia. Neuron Microglial cell (b) Microglial cells are defensive cells inthe CNS.

  18. Ependymal Cells They are found lining the central cavities of the brain and spinal cord. The beating of the cilia helps to circulate the cerebral spinal fluid in the CNS.

  19. Figure 11.3c Neuroglia. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinalfluid-filled cavities.

  20. Oligodendrocytes They are responsible for forming the insulating myelin sheaths which aid in nerve conduction.

  21. Figure 11.3d Neuroglia. Myelin sheath Process of oligodendrocyte Nerve fibers (d) Oligodendrocytes have processes that formmyelin sheaths around CNS nerve fibers.

  22. Neuroglia cells of the PNS These include • Satellite Cells • Schwann Cells

  23. Satellite & Schwann cells • Satellite cells surround the neuron cell bodies and have the same functions as the astrocytes do in the CNS. • Schwann cells (neurolemmocytes) surround and form the myelin sheaths

  24. Figure 11.3e Neuroglia. Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells (whichform myelin) surround neurons in the PNS.

  25. Diseases Demyelinating diseases involving the Schwann cells & Oligodendrocytes include: • Multiple Sclerosis of the CNS • Guillian Barre’ of the PNS

  26. Neurons • Neurons are more commonly called nerve cells. • They are responsible for conducting nerve impulses

  27. Neurons They have the following characteristics: • Extreme longevity, they can function for a lifetime if maintained. • Amitotic, they have lost the ability to divide. • High metabolic rate, they require constant supply of oxygen and glucose.

  28. Cell Body It is also called the perikaryon or soma. It contains the usual cytoplasmic organelles and is the center for biosynthetic processes.

  29. Nissl bodies The rough endoplasmic reticulum is usually well developed and stains darkly with basic dyes. They are also termed Nissl bodies.

  30. lipofuscin granules Some neurons contain lipofuscin granules, by products of lysosomal activity. They are sometimes referred to as aging pigment

  31. Processes • The CNS contains both neuron cell bodies and their processes. • The PNS consist primarily of processes. • In the CNS bundles of neurons are called tracts. • In the PNS they are referred to as nerves.

  32. Processes Two types of processes are: • Dendrites • Axons

  33. Dendrites These are short, diffuse branching extensions that are typically found near the cell body. They are designed to provide a huge surface area for receiving signals from other neurons.

  34. Figure 11.4a Structure of a motor neuron. Neuron cell body (a) Dendritic spine

  35. Axons In contrast to the dendrites, each neuron has only one axon. The axon arises from the cell body in an area termed the axon hillock.

  36. Axons The axon terminates in a profusion of branches of 10,000 or more axon terminals or synaptic knobs. Think of the neuromuscular junction in muscle.

  37. Figure 11.4b Structure of a motor neuron. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Impulse direction Nucleus Node of Ranvier Nissl bodies Axon terminals (secretory region) Axon hillock Schwann cell (one inter- node) Neurilemma (b) Terminal branches

  38. Classification of Neurons Neurons are classified based on structure and function

  39. Structural Classification Neurons are grouped depending on the number of processes that extend from the cell body.

  40. Structural Classification Multipolar neurons have three or more processes. These consist of one axon and 2 dendrites. They represent the most common type making up 99% of all the neurons.

  41. Structural Classification Bipolar neurons have two processes one axon and a dendrite. These are located in the retina of the eye and the olfactory mucosa.

  42. Structural Classification Unipolar neurons have a single short process that emerges from the cell body and divides into a T with one called the distal process and the other the proximal process. These are found with sensory neurons.

  43. Functional Classification This groups the neurons according to the direction the nerve impulse travels relative to the central nervous system. With this there are three types, motor neurons, sensory neurons and interneurons.

  44. Sensory or afferent neurons • These transmit impulses from the sensory receptors toward or into the CNS. • These are almost always unipolar. • The cell bodies are located in the sensory ganglion outside the CNS.

  45. Motor or efferent neurons • These carry impulses away from the CNS to effector organs such as muscles or glands. • Motor neurons are multipolar. Their cell bodies are located in the CNS.

  46. Interneurons or association neurons These lie between sensory and motor neurons in the CNS. They make up 99% of the neurons in the body.

  47. Membrane Potentials Neurons are excitable cells. When they respond to a stimulus, an electrical impulse is generated. This impulse is always the same regardless of the type of stimulus

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