21. Nervous Tissue Structure And Function Flashcards
What are the 2 parts of the nervous system?
CNS - brain and spinal cord
PNS - cranial nerves and spinal nerves
What neurons are present in the CNS and PNS?
CNS - relay
PNS - sensory, motor
What is grey matter?
Peripheral in brain and in areas called nuclei
Central in spinal cord (butterfly shaped)
Has nerve cell bodies, dendrites, axon terminals, non-myelinated axons, neuroglia
What is white matter?
Central in brain
Peripheral in spinal cord
Has myelinated material
Has nerve fibres that form ascending and descending tracts
What are the anterior and posterior prongs in the great matter referred to?
Ventral and dorsal horns, connected by grey commissure
What is the outer connective tissue layer surrounding the spinal cord called?
Pia mater
What are the properties of a neuron?
Many dendrites
Single axon
Often myelinated
Which parts of a neuron are in the CNS?
Main cell body
Dendrites
Proximal part of axon
Which parts of a neuron are in the PNS?
Distal axon
Arborisations
What is the myelin for the axon produced by and is part of in the CNS and PNS?
CNS - oligodendrocyte
PNS - Schwann cell
Describe a motor neurone
Located in CNS to periphery
Function is to end signals to effector tissues
Describe a sensory neurone
Located in periphery towards CNS
Function is to send environmental signals to integrative centre
Have ganglions along axon, both pseudounipolar and bipolar
Describe integrative neurons
Located in the CNS
Function is to collate all information
Can be pyramidal, interneurons or purkinje cells
Describe anaxonic neurons
Location is in retina
Function is to act as relays and thought to hold memory
No axons but many dendrites
Which cell bodies are located outside the CNS?
Pseudounipolar (unipolar)
Bipolar
Postsynaptic autonomic neuron cell bodies
Which is the most predominant cell type in the CNS?
Interneurons
What is a multipolar neuron?
One axon and multiple dendrites
Most common
Most neurons in CNS
What is a bipolar neuron?
One axon and one dendrite Olfactory cells (smell), retina, inner ear
What is a unipolar neuron?
Single process leading away from soma
Sensory from skin and organs to spinal cord
What are the characteristics of the neuron cell body?
Lots of RER
Lots of Golgi apparatus
Many free ribosomes
What are Nissl bodies?
In cytoplasm of neuron
Made of RER and Golgi
What is the anterograde movement?
Microtubules in axon attract kinesin
Kinesin binds to empty vesicles and mitochondria
Moves these organelles from soma to synapse
What is the retrograde movement?
Microtubules attract dynactin
Dynactin binds to retrograde vesicles
Moves vesicles back from synapse to soma
Describe what happens to the vesicle as it moves down the axon
Immature vesicles contain only enzyme in its membrane
As it travels, starts to synthesise neurotransmitter
What are the 2 things that could happen to vesicles at the synapse?
Recycled through clathrin-coated endocytosis
Lost to neurolemma
What nerve fibres can be present in peripheral nerves?
All types - sensory, integrative, motor
Each separated by connective tissue layers
What is the endoneurium?
Loose connective tissue
Surrounds single nerve cells
What is the perineurium?
Specialised connective tissue
Maintains ionic composition
Surrounds clusters of axons (fascicles)
What is the epineurium?
Dense irregular connective tissue
Separates different types of nerves and fills spaces between facsicles
Surrounds groups of fascicles
What is the paraneurium?
Fascia that separates nerves from surrounding structures
What creates faster saltatory conduction?
Myelinated axons
What creates faster conduction?
Large diameter axons
How does myelination occur?
- Axon sitting in grove is surrounded by Schwann cell
- Mesaxon membrane initiates myelination by surrounding embedded axon
- Sheet-like extension of mesaxon membrane wraps successively round axon, forming multiple membrane layers
- Cytoplasm extruded from between 2 apposing plasma membranes of Schwann cell, the becomes compacted to from myelin
What is an oligodendrocyte?
Does same thing as Schwann cell but in CNS
Cytoplasmic processes from oligodendrocyte cell body form flattened cytoplasmic sheaths that wrap around each axon
How is oligodendrocyte different to Schwann cell?
Oligodendrocytes in CNS
Oligodendrocyte wraps around more than one axon simultaneously
Oligodendrocytes are incredibly small
What are astrocytes?
Control flow of nutrients in CNS
Regulate nerve impulses by releasing glutamate near to node of ranvier
Impact on numerous nerve cells
‘Feet’ contribute to blood-brain barrier (attach to capillaries causing it to be almost completely covered)
Name the 4 support cells in the CNS
Oligodendrocytes
Astrocytes
Microglial cells
Ependymal cells
What are microglial cells?
Large cells with elongated nucleus and relatively few processes emanating from cell body
Found in CNS
Resident macrophage
What are ependymal cells?
Line spinal canal
Apical surface has cilia and microvilli
Synthesise and secrete CSF in ventricles
Cilia move cerebrospinal fluid (CSF) through ventricles to spinal cord
Microvilli absorb CSF
Modified tight junctions between epithelial cells control fluid release into brain
How can the molecular and cellular contents of the brain be monitored?
Spinal tap
