The Nervous System: Neural Tissue
Introduction –Nervous system = control center & communications network –Functions Stimulates movements Maintains homeostasis (with endocrine system)
Organization of the Nervous System –Central nervous system (CNS) Brain & spinal cord –Peripheral Nervous System (PNS) Afferent (Sensory) System Efferent (Motor) System –Somatic Nervous System –Autonomic Nervous System Sympathetic Nervous System Parasympathetic Nervous System
The Nervous System
Organization of the Nervous System
Histology of Nervous Tissue –2 types of cells Neurons –Structural & functional part of nervous system –Specialized functions Neuroglia (glial cells) –Support & protection of nervous system
Neuroglia of CNS
Neurons –Function Conduct electrical impulses –Structure Cell body –Nucleus with nucleolus –Cytoplasm Cytoplasmic processes –Dendrites –Axon
Review of Neuron Structure
Anatomy of a Neuron
Nerve Fibers of the PNS –An axon and its sheaths Myelinated axon –Axon is surrounded by a myelin sheath Unmyelinated axon –Axon has no myelin sheath
Myelin –White matter of nerves, brain, spinal cord –Composed primarily of phospholipids –Production Developing Schwann cells wind around axon –Function Increases speed of impulse conduction Insulation and maintenance of axon
Schwann Cells and Peripheral Axons
Myelin –Nodes of Ranvier Unmyelinated gaps between segments of myelin Impulses “jump” from node to node
A Myelinated Axon
Nerve Fibers of the CNS –Umyelinated –Myelinated Production of myelin is from oligodendrocytes Nodes of Ranvier are less numerous
Nerve Fibers of the CNS
Classification of Neurons –Functional – based on the direction of impulse transmission Sensory neurons Motor neurons Interneurons (association)
Functional Classification of Neurons
Nerves –Bundles of cell processes of afferent and efferent neurons –Functional unit = nerve fiber
Nerve Impulse –A change in charge that travels as a wave along the membrane of a neuron –Depends on the movement of K+ and Na+ across the nerve cell membrane.
Resting Neuron –Sodium ions are in large concentration along the outside of the cell membrane –Potassium ions are in large concentration along the inside of the cell membrane
Resting Potential
Action Potential –Requires a stimulus of adequate strength –Membrane is disturbed –Sodium ions flow inward, potassium ions flow outward Action potential –The disturbance at the point of stimulation is enough to disturb adjacent portion of membrane. –The action potential moves along the membrane.
Action Potential
Back to Resting Potential –Potassium and sodium ions are actively transported back across the membrane –Membrane is at rest again
Neurons Exhibit Conductivity –The ability to transmit an impulse to another neuron or tissue. –Action potentials can be transmitted across synapses. Junction between 2 neurons Uses neurotransmitters Transmission is one way only
Synapse
Neural Regeneration after Injury –Axon & myelin sheath distal to the injury deteriorate –Scwann cells form a cord, grow into the cut, and unite the stumps. –The axon forms buds and grows along the cord of Schwann cells –The axon continues to grow into the distal stump and is enfolded by Schwann cells. –(Rate of 1mm/day)
Neural Regeneration