Neurological Microstructures PDF

Presentation by Neurological Anna Gould Micro-structures Senior Lecturer Brainfacts.org Intended Learning Outcomes Describe the function of neuroglia Identify the key histological features of the neuron and how that relates to it...

Presentation by Neurological Anna Gould Micro-structures Senior Lecturer Brainfacts.org Intended Learning Outcomes Describe the function of neuroglia Identify the key histological features of the neuron and how that relates to its function Describe the clarification of neurons  Nervous Tissue Two Types of Cells: 1. Neurons – have the property of electrical excitability i.e. the ability to produce action potentials 2. Neuroglia – support, nourish and protect Neurogli a Supporting cells Do not generate or propagate action potentials Neuroglia of the Peripheral Nervous System 1. Schwann cells 2. Satellite Cells Neuroglia of the PNS Tortora, p.513 Schwann Cells Form the myelin sheath around the axons of peripheral nerves Satellite Cells (c) Provide structural support Regulate the exchange of materials between the neuronal cell bodies and the interstitial fluid  Neuroglia of the CNS Astrocytes Contain microfilaments which give them strength – helps to provide structural support to neurons Maintain chemical environment for the generation of nerve impulses Oligodendroc Forming and ytes maintaining the myelin sheath Microglial Phagocytic Tortora, p.511 cells properties – digesting foreign particles Ependymal Produce and Cells assist the  Two types of processes emerge from the cell body Dendrites of which typically there are many Axon - one only Dendrites (little trees) The receiving part of the neuron Receiving information from other neurones Ligand-gated channels (open and close in response to a chemical stimulus e.g. neurotransmitter) often located in dendrites and cell bodies Cell Body Cell body contains a nucleus surrounded by cytoplasm Usual cellular organelles such as lysosomes, mitochondria, a Golgi complex. Neuronal cell bodies also include: Nissl bodies for protein synthesis neurofibrils for support microtubules to move materials from cell body to axon.  Axon Sending part of the neuron – sends impulses to other neurons, muscle fibres or gland cells.  The Axon The axon joins the cell body at the axon hillock. The first part of the axon is called the initial segment. Generally speaking, impulses arise at the junction of the axon hillock and the initial segment. The point where an impulse arises is called the trigger zone.  Transmission Impulses arising at the trigger zone are conducted along the length of the axon. The axon ends by dividing into many fine processes called axon terminals. Some axon terminals expand into bulb-like structures called synaptic end bulbs , sometimes called terminal boutons or pre-synaptic terminals. The impulse is conveyed in action the form of an potential.  Communication The impulse is passed on to; Another neuron An effector i.e. a muscle fibre or a gland cell The point of communication is called a synapse Myelination Most neurons are surrounded by a lipid and protein covering called the myelin sheath. This acts as insulation and increases the speed of impulse conduction. Gaps in the myelin sheath are called Nodes of Ranvier which allow for faster propagation of the action potential down the axon (via a process called saltatory conduction) Which cells of the CNS produce myelin? Which cells of the PNS produce myelin?  Factors affecting the speed of propagation 1. Amount of myelination - myelination increases the speed of conduction. 2. Axon diameter – large diameter axons propagate action potential faster than smaller ones due to larger surface areas 3. Temperature – Axons propagate action potentials at lower speeds when cooled. Rule of Thumb: The wider the diameter, the quicker the speed of conduction and vice versa.  Hypothesis You touch the hotplate on your kitchen stove. Form a hypothesis about the diameter size and myelination of a fibre carrying this information. Structural Classification of neurons According to the number of processes extending from the cell body 3 types Intended Learning Outcomes Describe the function of neuroglia Identify the key histological features of the neuron and how that relates to its function Describe the classification of neurons Further reading Tortora’s principles of anatomy and physiology Chapter 12 Nervous Tissue 12.2 Histology of Nervous Tissue (pp.506-515)