Nervous System Overview.I Histology.II Electrical Signals.III Signal Transmission at Synapses Neurotransmitters.V Neural Circuits.VI Repairs.VII Pathology.VIII.IV 1
Controls and integrates all body activities within limits that maintain life Three basic functions 1. sensing changes with sensory receptors 2. interpreting and remembering those changes 3. reacting to those changes with effectors Nervous Tissue 2
Major Structures of the Nervous Brain spinal cord System cranial nerves spinal nerves ganglia enteric plexuses sensory receptors 3
Subdivisions of the PNS 1. Central nervous system (CNS) 2. Peripheral nervous system (PNS) a) Somatic (voluntary) nervous system (SNS) b) Autonomic (involuntary) nervous systems (ANS) c) Enteric nervous system (ENS) 5
Organization Sensory Integration Motor SNS (Sensory) SNS (Motor) ANS (Sensory) Brain Spinal cord ANS (Motor) ENS (Sensory) 6
Functional unit of nervous system 1. Cell body a) Nissl bodies (rer) b) Neurofilaments c) Microtubules d) Lipofuscin pigment clumps 2. Cell processes a) Dendrites b) Axons Neurons 7
Electron Microscopy Light-Stained Purkinje Neurons
Gray and White Matter White matter = myelinated processes (white in color) Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) 11
Dendrites Conducts Impulses Towards The Cell Body Typically short, highly branched & unmyelinated Surfaces specialized for contact with other neurons Contains neurofibrils & Nissl bodies (rer) impulse 12
Conduct impulses Away From Cell Body Long, thin cylindrical process of cell Arises at Axon Hillock Impulses arise from initial segment (Trigger Zone) Side branches (collaterals) end in fine processes called Axon Terminals Swollen tips called synaptic end bulbs contain vesicles filled with Neurotransmitters Axons 13
Structural Classification of Neurons Based on number of processes found on cell body 1. Multipolar = several dendrites & one axon most common cell type 2. Bipolar Neurons = one main dendrite & one axon found in retina, inner ear & olfactory 3. Unipolar Neurons = one process only(develops from a bipolar) are always sensory neurons 15
Structural Classification of Neurons Based on number of processes found on cell body 1. multipolar = several dendrites & one axon most common cell type 2. bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory 3. unipolar neurons = one process only(develops from a bipolar) are always sensory neurons 16
Structural Classification of Neurons Based on number of processes found on cell body 1. Multipolar Neurons= several dendrites & one axon most common cell type; Motor Neuron 2. Bipolar Neurons = one main dendrite & one axon found in retina, inner ear & olfactory (Special Senses) 3. Unipolar Neurons = one process only(develops from a bipolar) are always Sensory Neurons 17
Half of the volume of the CNS Smaller cells than neurons Cells Can Divide rapid mitosis in tumor formation (Gliomas) 4 cell types in CNS astrocytes, oligodendrocytes, microglia & ependymal 2 cell types in PNS schwann and satellite cells Neuroglial Cells 18
Neuroglial Cells (CNS): Astrocytes Star-shaped cells Form Blood-brain Barrier Forms Perivascular Feet by covering blood capillaries Metabolize neurotransmitters Regulate K+ balance Provide structural support 19
Neuroglial Cells (CNS): Most common glial cell type Each forms Myelin Sheath around more than one axons in CNS Analogous to Schwann cells of PNS Oligodendrocytes 20
Neuroglial Cells (CNS): Microglia Small cells found near blood vessels Phagocytic Cell Derived macrophages & monocytes 21
Neuroglial Cells (CNS): Ependymal Form epithelial membrane lining cerebral cavities & central canal Produce Cerebrospinal Fluid (CSF) cells 22
Neuroglial Cells (PNS): Satellite Cells Flat cells surrounding neuronal cell bodies in peripheral ganglia Support Neurons In The PNS Ganglia 23
Neuroglial Cells (PNS): Schwann Cell Cells encircling PNS axons Each cell produces part of the myelin sheath surrounding an axon in the PNS 24
Myelination Insulation of axon Increase speed of nerve impulse
All axons surrounded by a lipid & protein covering (Myelin Sheath) produced by Schwann cells Neurilemma is fused layers of membranes of Schwann cell gaps called nodes of Ranvier Myelination: PNS Node of Ranvier Myelinated fibers Unmyelinated fibers
Oligodendrocytes myelinate axons in the CNS Broad, flat cell processes wrap about CNS axons. One Oligo Can Myelinate Upto 50 Nerves. Schwan Cell: PNS Many Schwan Cells Myelinate One Peripheral Nerve End of one Schwan Segment Node of Ranvier Myelination: CNS 27
Myelination Process
Electrical Signals in Neurons Neurons are electrically excitable due to the voltage difference across their membrane Communicate with 2 types of electric signals 1. action potentials that can travel long distances 2. graded potentials that are local membrane changes only In living cells, a flow of ions occurs Through Ion Channels In The Cell Membrane 29
Continuous versus Saltatory 1. Continuous conduction (unmyelinated fibers) 2. Saltatory conduction (myelinated fibers) Conduction Na Na Na Na Na Na Na Na Na Na A.P. 31
Nerve impulse conduction in which the impulse Jumps (Salta) from node to node Saltatory Conduction Na A.P. Na Na Na Na 32
Signal Transmission at Synapses 2 Types of synapses 1. Electrical ionic current spreads to next cell through gap junctions faster, two-way transmission & capable of synchronizing groups of neurons 2. Chemical one-way information transfer from a presynaptic neuron to a postsynaptic neuron axodendritic -- from axon to dendrite axosomatic -- from axon to cell body axoaxonic -- from axon to axon 33
Synapses
Spinal Ganglia Cell bodies Lie on posterior Nerve Root of Spinal Cord. Have Sensory Neurons (Unipolar). Widely Apart Sympathetic Ganglia Multipolar Type: Hence Many Dendrites Hence Widely Apart.