Histology part 2 Flashcards
Neurotransmitters of CNS
-Glutamate
-GABA
Glutamate Neurotransmitter
- The most common neurotransmitter of CNS
- Always excitatory (depolarizes the cell)
- Vast majority of neurons are glutamatergic neurons
GABA neurotransmitter
-Very common neurotransmitter in the CNS
-inhibitory (hyperpolarizes)
Synapses with no effect (neuromodulation)
-some synapses on a neuron do not change the membrane potential (no depolarization or hyperpolarization)
-BUT they change how the cell responds to other neurotransmitters
**So intracellular pathways have the ability to neuromodulate via chemicals and change the future synaptic responses
Neurotransmitters that act as neuromodulators within CNS
-dopamine
-Serotonin
-histamine
-acetylcholine
-norepinepherine
-nitric oxide
-various neuropeptides
Neuromodulator hormone secretion
-neuromodulators are secreted as hormones in a couple ways:
- directly from pre-synaptic neuron
- delivered through the circulatory system or the cerebral spinal fluid, and eventually bind to a receptor on the membrane of a post-synaptic neuron
*Binding is often to G-coupled protein receptors which uses second messengers to pass on information and cause an effect
Potentiation
Refers to the change in a particular synapse that increases or decreases the efficacy of that synapse
-when a synapse is very active, that synapse becomes stronger and there is an increase in the post synaptic response
-using a synapse more often will strengthen the synaptic connection
Long term potentiation
-permanent change in the strength of the synapse
**important because it is associated with learning and memory
Different synapse connections
-synapses on dendritic spines
-axo-dendritic synapse
-axo-somatic synapse
-axo-axonic synapse
Action potential speed
-move down axons
-will be faster if myelinated (by oligodendrocytes)
Neuron shapes
1.bipolar neuron
-cell body in middle and axon on either side
2. unipolar
-sensory neurons; cell body up and away and two axons on either side, usually one connecting to CNS and other linked to PNS
3. multipolar
-most common; cell body with dendrites and single axon
Neuron cellular activity
-has high cellular activity within neuronal cell body
-full of rER (nissl substance)
Anterograde axonal transport
-the synthesis of proteins and the transport of mitochondria, structural proteins, etc. down to the end of the neuron
Retrograde axonal transport
-the process of transporting dead organelles from the synapses back to the cell body to be destroyed
-many pathogens use this as a way to get into the cell body and then the CNS (ex. rabies, herpes)
Tract
-bundle of axons within the CNS
**NOT a nerve
Nucleus
-bundle of cell bodies in CNS
(ganglion in PNS)
Glia
-the support cells of the nervous system. Not involved in signalling or transmitting any information.
-CNS: includes astrocytes, microglia, ependymal cells, oligodendrocytes
-PNS: includes schwann cells and satellite cells
Astrocytes
- most abundant glial cells in CNS (in some parts, up to 90% are astrocytes)
- very diverse cells with many functions
*Most brain tumours are almost all astrocytes
Functions of astrocytes
1.produce extracellular matrix (laminin)
2. induce formation of blood-brain barrier
3. Microcirculation- astrocytes have one process near arterioles and another process within the neuropil and can induce relaxation of arterioles to increase blood flow to certain areas of the CNS
4. Store glycogen and release glucose to neurons when needed
5. take up excess potassium in extracellular space
Astrocyte appearance
1.fibrous astrocytes
2.protoplasmic astrocyte
3. oligodendrocytes
4. microglial cell
Oligodendrocytes
-responsible for myelination within the CNS (schwann cells in the PNS)
-myelination allows for faster signal transmission, as it re-organizes the ion channels (voltage-gated Na and K channels) along the axon to nodes of ranvier
- also involved in insulation
Microglia
-small
-not cells of the neuroepithelium (mesodermal)
-they serve as macrophages in the CNS
Ependymal cells
-line the canal (fluid filled cavities of CNS), and are retained in the adult forming ciliated columnar epithelium
- there are choroid plexus that produces cerebral spinal fluid that is within the ventricles
-neural stem cells will reside along between ependymal cells
White matter
-appears white in fresh tissues (from the lipids)
-formed by myelinated axons
-oligodendrocytes and astrocytes will also be found within the white matter
Gray Matter
-not gray in fresh section (it appears pink)
-makes up most of the matter of the brain
-composed of cell bodies, dendrites, astrocytes, and some myelinated axons
Distribution of white vs. gray matter
Spinal cord: gray matter inside forming the core (butterfly) & white matter forms the outside (around butterfly)
Brain: Reverse. Gray matter outside, white matter inside
**Damage to white matter has different consequences than damage to gray matter
Meninges
-just in CNS, for protection. Derived from mesoderm.
-composed of 3 layers
-dura mater
-arachnoid
-Pia mater
Dura mater
-outermost layer
-dense, fibrous connective tissue
Arachnoid
-middle layer
-there are two parts (one part is adhered to the layer of dura, another part forms trabeculae)
Pia mater
-innermost layer
-thin layer of connective tissue that is adhered to the surface of the brain
