BLOOD-BRAIN BARRIER • Neural tissue protected from general circulation by the blood-brain barrier • Barrier maintained by the glial cells - astrocytes • CNS capillaries impermeable to most ions circulating in the blood • Only lipid compounds can diffuse into interstitial fluid of the brain and spinal cord • Water compounds need special carrier molecules
BLOOD BRAIN BARRIER • 46U
NEUROGLIA OF PNS • Two types of glial cells found in the PNS • Schwann cells - form myelin sheath for the axons of nerves outside the CNS • Satellite cells - similar to Schwann cells
QUESTION The most numerous of all glial cells are: A. microglia. B. astrocytes. C. Schwann cells. D. ependymal cells.
ANSWER Correct answer: B Rationale: • Astrocytes are pervasive throughout the brain and form the blood–brain barrier.
NEUROGLIA • ? v=52NVc9Lku4o
MYELIN SHEATH PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM
WHITE MATTER VERSUS GRAY MATTER • White matter • myelinated nerve fibers - gathered in tracts • Gray matter • Composed of cell bodies, interneurons, and unmyelinated fibers • Ganglia - cluster of cell bodies (gray matter) dispersed throughout white matter in the PNS • Cluster of cell bodies located in the CNS are referred to as nuclei
LEARNING HINT • The gray matter is the cell bodies of the neuron. White matter is composed of the cell axon which is surrounded with myelin. Myelin allows messages to be transmitted faster.
NERVES • Bundles of axons in the PNS • 43 pair nerves attached to the CNS • 12 pairs of cranial nerves • 31 pairs of spinal nerves
NERVE IMPULSE • Caused by an electrical current • Membrane potential: When ions with opposite electrical charges are separated by a membrane • Polarization: When a membrane has an excess of positive ions on one side and an excess of negative ions on the other
NERVE IMPULSE Describe the characteristics of the resting membrane of a neuron • Two functional characteristics of neurons. • Excitability, the ability to respond to a stimulus • Conductivity, the ability to transmit an impulse • The cell membrane of a non-conducting neuron is polarized with an abundance of sodium ions outside the cell and an abundance of potassium and negatively charged proteins inside the cell..
NEURON FUNCTION • Membrane Potential • Cell regulates passage of substances through its semi-permeable membrane • Extracellular fluid contains Na + and Cl - • Intracellular fluid dominated by K + and proteins - • During the resting phase of a cell, there are + • charges outside the cell membrane and an excess of negative charges on the inside of the cell
NEURON FUNCTION • This uneven distribution of charges is called the membrane potential • When the cell is disturbed, the membrane potential can change , changing the distribution of ions across the cell membrane •
NERVE IMPULSES Describe the sequence of events that lead to an
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- Fall '16
- Karen Gleason