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10.1: Introduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites • Cell types in neural tissue: • Neurons • Neuroglial cells (also known as neuroglia, glia, and glial) Cell body Nuclei of neuroglia Axon 1 © Ed Reschke Divisions of the Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brain • Central Nervous System (CNS) • Brain • Spinal cord Cranial nerves Spinal cord • Peripheral Nervous System (PNS) • Cranial nerves • Spinal nerves Spinal nerves 2 (a) Divisions of Peripheral Nervous System • Sensory Division • Picks up sensory information and delivers it to the CNS • Motor Division • Carries information to muscles and glands • Divisions of the Motor Division: • Somatic – carries information to skeletal muscle • Autonomic – carries information to smooth muscle, cardiac muscle, and glands 3 Divisions Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central Nervous System (brain and spinal cord) Brain Peripheral Nervous System (cranial and spinal nerves) Cranial nerves Sensory division Spinal cord Sensory receptors Spinal nerves Motor division Somatic Nervous System Skeletal muscle Autonomic Nervous System Smooth muscle Cardiac muscle Glands 4 (a) (b) Functions of Nervous System • Sensory Function (receiving • Integrative Function (deciding information) what to do about information) • Sensory receptors gather • Sensory information used to information create: • Sensations • Information is carried to the • Memory CNS • Motor Function (acting on information) • Decisions are acted upon • Impulses are carried to effectors • Thoughts • Decisions 5 10.3: Description of Cells of the Nervous System • Neurons vary in size and shape • They may differ in length and size of their axons and dendrites • Neurons share certain features: • Dendrites • A cell body • An axon 6 Neuron Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromatophilic substance (Nissl bodies) Dendrites Cell body Nucleus Nucleolus Neurofibrils Axonal hillock Impulse Axon Synaptic knob of axon terminal Nodes of Ranvier Myelin (cut) Axon Nucleus of Schwann cell Schwann cell Portion of a collateral 7 10.4: Classification of Neurons and Neuroglia • Neurons vary in function • They can be sensory, motor, or integrative neurons • Neurons vary in size and shape, and in the number of axons and dendrites that they may have • Due to structural differences, neurons can be classified into three (3) major groups: • Bipolar neurons • Unipolar neurons • Multipolar neurons 8 Classification of Neurons: Structural Differences • Multipolar neurons • 99% of neurons • Many processes • Most neurons of CNS • Bipolar neurons • Two processes • Eyes, ears, nose • Unipolar neurons • One process • Ganglia of PNS • Sensory Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrites Peripheral process Axon Direction of impulse Central process Axon Axon 9 (a) Multipolar (b) Bipolar (c) Unipolar Classification of Neurons: Functional Differences • Sensory Neurons • Afferent (approach) • Carry impulse to CNS • Most are unipolar • Some are bipolar • Interneurons • Link neurons in CNS • Aka association neurons • Multipolar Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central nervous system Peripheral nervous system Cell body Dendrites Sensory receptor Cell body Axon (central process) Axon (peripheral process) Sensory (afferent) neuron Interneurons • Motor Neurons • Efferent (exit) • Carry impulses away from CNS to effectors • Multipolar Motor (efferent) neuron Axon Effector (muscle or gland) Axon Axon terminal 10 Types of Neuroglial Cells in the PNS 1) Schwann Cells • Produce myelin found on peripheral myelinated neurons • Speed up neurotransmission 2) Satellite Cells • Support clusters of neuron cell bodies (ganglia) 11 Types of Neuroglial Cells in the CNS 1) Microglia • CNS • Phagocytic cell 3) Oligodendrocytes • CNS • Myelinating cell 4) Ependyma or ependymal 2) Astrocytes • CNS • CNS • Ciliated • Scar tissue • Line central canal of spinal • Mop up excess ions, etc. cord • Induce synapse formation • Line ventricles of brain • Connect neurons to blood • Keep CSF moving vessels 12 Types of Neuroglial Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fluid-filled cavity of the brain or spinal cord Neuron Ependymal cell Oligodendrocyte Astrocyte Microglial cell Axon Myelin sheath (cut) Capillary Node of Ranvier 13 10.5: The Synapse Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Nerve impulses pass from neuron to neuron at synapses, moving from a pre-synaptic neuron to a post-synaptic neuron. Synaptic cleft Impulse Dendrites Axon of presynaptic neuron Axon of postsynaptic neuron Axon of presynaptic neuron Impulse Cell body of postsynaptic neuron Impulse 14 Synaptic Transmission Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Direction of nerve impulse • Neurotransmitters are released when impulse reaches synaptic knob Axon Ca+2 Synaptic knob Synaptic vesicles Presynaptic neuron Ca+2 Cell body or dendrite of postsynaptic neuron Mitochondrion Ca+2 Synaptic vesicle Vesicle releasing neurotransmitter Axon membrane Neurotransmitter Synaptic cleft Polarized membrane Depolarized membrane (a) 15