Fichas
L8- Neurones and Glia
Fichas del conjunto (20)
- 1Nervous system- Involved in control and communication of all essential functions in the body.
- Provides info on environment and allows body to respond accordingly
- Capable of higher functions eg memory, learning, emotions. - 2Neurones: structureUnspecialised components:
- Rough ER, ribosomes, nucleus and prominent nucleolus, mitochondriation, golgi apparatus
Specialised components:
- Dendritic spine (where most synapses form, increases SA), dendrites, axon, axon hillock (swelling on an axon where APs are generated)
* myelenation increases conduction velocity of AP. - 3Coverings of the peripheral NS- Endoneurium: delicate connective tissue layer surrounding axon and schwann cells. Groups of endonerium covered axons are covered in pereineum and called a fasicle.
- Pereineurium: connective tissue layers surrounding fascicle.
- Epineurium- robust 'tough' layer surrounding induvidual fasicles, containing blood vessels that form the nerve itself. Slightly elastic; implications for nerve regeneration (take longer to regrow). - 4Salutatory conduction- At rest, membrane potential charge is a difference of -70mv
- As sodium comes in, the cell becomes more positive, and if the threshold is reached, an action potential is triggered.
- AP on a myelinated neuron appears to 'jump'. In actual fact, voltage gated sodium channels open at the nodes of Ranvier, inducing a local current flow, and another AP - 5Clinical significance of salutatory conductionDemyelination of salutatory conduction of axons in multiple sclerosis
- 6Nissl staining and chromatolysisNissl staining- stain similar to haematoxylin in that it 'lights up' nucleic acids. Shows neurones in particular as they have lots of ER.
Nissl substance- areas of strong staining as a result of neurons being present.
- Can be used to detect if neurons are healthy or not- if a neuron is damaged, ribosomes fall off the ER, so staining is not taken up. - 7Types of neurons: Functional classificatrion- Sensory/afferent: generates action potential towards the CNS
- Motor/efferent: generate action potentials away from the CNS
- Interneurons: act locally within the CNS and connect neuron to others - 8Types of neurons: Structural classification- Multipolar: include most neurons in the CNS eg motor
- Bipolar: include sensory neurons eg those in the eye. Rarest type.
- Unipolar/pseudounipolar: single process, often divide into 2 branches. Responsible for all somatosisation - 9Diagrams of types of neurons
- 10Axodendritic synapse1. Converts electrical signal to chemical signal
2. Chemical signal is then converted back to an electrical one - 11Synapses- Neurons have many synapses
- Average human neuron has about 10,000 neurons
- Dark area on electromicrograph of synapse: density area where most receptors are located and therefore area that is most electron dense.
-Post-synaptic densities mark the position of active synaptic regions.
- Cells can only make a binary decision; to fire an AP or not. - 12Synapses: convergence and divergence- Convergence- when many presynaptic neurons converge on any single post-synaptic neuron.
- Divergence- when axons of presynaptic neurons divide into many branches that diverge to end on post-synaptic neurons. - 13Neuroglia- Surround and provide support for the neurons
- In the CNS they take the form of:
Astrocytes
Ogliodendrocytes
Ependymal cells
Microglia
- In the PNS they take the form of:
- Schwann cells - 14Types of neuroglia
- 15Roles of neuroglia: Astrocytes- Most numerous glia in the brain
- Structural roles;
Fill spaces between neurons
Support blood-brain barrier
Form glial limitans
- Homeostatic roles;
Regulate water levels
Regulate k+ levels
Regulate neurotransmitter levels
Inhibit axon regeneration - 16Roles of neuroglia: Ogliodendrocyte'many branched cells'
- Myelinate glia in the CNS
- Inhibit axon regeneration - 17Roles of the neuroglia: Ependymal cells- Line brain ventricles and spinal cord central canal
- Specialised ependymal cells form the chloroid plexus. - 18Chloroid plexus- Located in the brain ventricles
- Made up of specialised ependymal cells, which secrete cerebrospinal fluid
- The ependymal cells have cilla which help to move the fluid and processes on their surfaces that have astrocyte-like functions - 19Roles of neuroglia: Microglia- Microglia are specialised macrophages that respond to inflammation, phagocytise necrotic tissue, microorganisms and foreign substances that invade the CNS.
- 20Roles of neuroglia: PNS glia- Schwann cells: wrap the axon to form a myelin sheath
- Allows for rapid propogation of AP by salutatory conduction
- Can be phagocytic and promote axon regeneration