Lecture notes, lecture 10 - Dr. krista howarth PDF

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Dr. Krista Howarth...

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FUNCTIONAL ORGANIZATION OF NERVOUS TISSUE

Cells of Nervous System 1. Neurons 2. Neuroglia cannot generate action potentials Nervous tissue is electrically excitable (diff than epithelial and connective!)

Neuron Structure Dendrites: decision making process > signal goes on or no?? Axon hillock & initial segment make up trigger zone > we get signals from other axons but the actual action potential isn’t generated until it gets to trigger zone Schwann cell > helps with conduction of signal. Wraps around axon, forming myelin sheath Sometimes branching happens to send signal to other neurons

Axonal transport Neurotransmitter is a chemical/molecule that gets released from end of neuron in presynaptic terminal > transmits across synapse to create signal in next tissue. Found inside vesicles. Need vesicles to hold transmitter in end then they can expel them.

Types of Neurons 1. Functional Classification - Sensory: Gathering info and bringing it back to spinal cord/brain - Motor: away from CNS - Interneurons/association neurons: DIRECTION. Signal reaches brain, then where? 2. Structural Classification Based on number of processes that we have from the nerve cell body - Multipolar: most neurons, and all motor neurons - Bipolar: in sensory organs. E.g. retina of eye - Pseudo-unipolar: one branch as sensory receptors and one branch extends to CNS. Cell body located in dorsal root ganglion

Other cells: SUPPORTING CELLS 4 PART of CNS and 2 part of PNS -

Nervous system GLUE—non-neuronal (don’t generate action potential), they support/protect nerve cells They are smaller than nerve cells but there is a larger number of them than nerve cells Retain ability to multiply and divide!!!

CNS: 1. Astrocyte: - largest and most numerous - Provide STRUCTURE - Form “foot process” - Protection and release of chemicals - Highly regulating what can move thru/between endothelial cells > blood brain barrier - Help maintain chemical environment for nerve impulses – need proper amount of ions - Synthesis, absorption, recycle of neurotransmitters - Formation of synapses > bring dendrites and presynaptic terminals together to create junction between diff nervous cells 2. Ependymal cells: - Change shape between cuboidal and columnar - May be ciliated in some cases - Spaces within brain tissue - Specialized cells in brain form choroid plexus which produces cerebral spinal fluid (CSF) which helps move nutrients in brain and spinal cord 3. Microglial cells: - Smaller, thinner, and fewer process than astrocytes - Act as macrophage > phagocytic action (protection) - Inflammatory response 4. Oligodendrocytes: - Wraps form myelin sheaths - Very dense layer of lipid > insulation and helps conduct action potential PNS: 5. Schwann cells: - Can only wrap around ONE axon, unlike oligodendrocytes 6. Satellite cell: - Cell bodies protected by satellite cells - Support, nutrients, protection of cell bodies OUTSIDE of CNS

Myelinated: wrapping around multiple times around an axon. Oligodendrocytes in CNS and Schwann cells in PNS Node of Ranvier: single layer from Schwann cell so still protected but not by layers Unmyelinated: doesn’t wrap multiple times, axons just chill in a membrane of Schwann cell so Schwann can have multiple axons! Signals way slower

Multiple Sclerosis: Degradation of Myelin sheath > action potential slower > neural issues in muscle activation and senses

Organization of Nervous Tissue White matter: bundles of myelinated axons. In CNS: nerve tracts. In PNS: Nerves. Grey matter: not a lot of lipid (which makes the white colour) so the tissue looks grey -

In CNS when we have a cluster of nerve cell bodies and grey matter > nuclei Outer cortex and cerebellum and patches in brain connected together by white matter

In spinal cord: white outer and gray deeper like a butterfly transversely -

White matter (axons) carrying info up and down the spinal cord on the OUTSIDE, and the grey matter (cell bodies) is found deeper into spinal cord

*Cell bodies outside of CNS > ganglia. Inside > nuclei...