21 - Nervous Tissue Flashcards
Where is neural grey matter found?
- Peripheral in the brain
- Central in the spinal cord (butterfly shape)
Where is neural white matter found?
- Centrally in the brain
- Peripheral in the spinal cord
What forms grey matter?
Nerve cell bodies, dendrites, axon terminals, non-myelinated axons and neuroglia
What forms white matter?
Myelinated material
What is the ventral fissure of the spinal cord?
A groove in the anterior medial side of the spinal cord that runs down its length. Divides activity into left and right.
What is the basic structure of a neurone?
- Normal cell organelles
- Cytoplasmic projections - many dendrites and a single axon (does differ)
- Main cell body and dendrites are in the CNS
- Distal axon is in the PNS
- Often coated with myelin
How does the source of the myelin sheath differ in the CNS and PNS?
CNS - part of an oligodendrocyte
PNS - part of a Schwann cell
What are the 4 different types of neurone?
- Motor - CNS to effector
- Sensory - signal to CNS
- Integrative - collate information
- Anaxonic - relays
The majority of the nerves in the CNS are …………… (a type of integrative neurone).
Interneurones
What is a multipolar neurone?
- Most common neurone type
- One axon and multiple dendrites
- E.g. brain and spinal cord
What is a bipolar neurone?
- One axon and one dendrite
- E.g. olfactory cells, retina, inner ear
What is a unipolar neurone?
- Single process leaves the soma and splits into two axons
- E.g. sensory neurones from the skin
What is an anaxonic neurone?
- Many dendrites but no axon
- E.g. visual processing
What are nissl bodies?
- Large granular body in neurones containing rough endoplasmic reticulum and free ribosomes
- Sites of protein synthesis
Describe the microtubule shuttle system used to transport vesicles within a neurone.
- Filled vesicles and mitochondria are transported in the anterograde direction away from the soma
- Empty vesicles are transported retrograde back to the cell body (mitochondria cannot return)
What are the two possible fates of neurotransmitter vesicles?
- Recycled through clathrin-mediated endocytosis
2. Lost to the neurolemma
Define the following terms:
- Endoneurium
- Perineurium
- Epineurium
- Paraneurium
- Endoneurium - loose connective tissue surrounding individual neurones
- Perineurium - specialised connective tissue surrounding clusters of axons (fascicles) - maintains ionic composition
- Epineurium - dense irregular connective tissue - coats the nerve and fills spaces between fascicles
- Paraneurium - fascia that separates nerves from surrounding structures
What types of neurone do peripheral nerves contain?
- Sensory
- Motor
Sometimes can contain both.
What is the structure of an unmyelinated nerve?
- Several axons bound by a central Schwann cell
- Held together by Schwann cell but not wrapped (clefts allow fluid to reach the axon), not electrically isolated
Myelinated nerves transmit impulses by ………………… conduction.
Saltatory
In larger diameter axons, conduction is faster or slower?
Faster - less resistance
Nerves can be grouped into types A, B and C. Which of these:
- are the thickest?
- are the fastest?
- have the largest internodal distance?
Thickest - A (C is thinnest)
Fastest - A (C is slowest)
Largest internodal distance - A (C has none as they are unmyelinated)
Where are type A, B and C nerve fibres each found?
A - CNS
B - Viscera
C - Periphery
Which of type A, B and C nerve fibres are myelinated?
A - myelinated
B - myelinated
C - unmyelinated
Which of type A, B and C nerve fibres are:
- motor?
- sensory?
A - motor
B - sensory
C - sensory
How does myelination occur from a Schwann cell?
- axon is surrounded by a Schwann cell
- sheet-like extension of the membrane wraps successively around the axon forming multiple membrane layers
- Cytoplasm is extruded from the two apposing plasma membranes of the Schwann cell, which become compacted to form myelin
How does myelination by an oligodendrocyte in the CNS differ from Schwann cells in the PNS?
Oligodendrocytes wrap around more than one axon simultaneously
What is a mesaxon?
A pair of parallel plasma membranes of a Schwann cell, marking the point of edge-to-edge contact by the Schwann cell encircling the axon
What is the structure of an astrocyte? What does it do?
- Star-like structure with projecting ‘feet’ that contain gap junctions
- Regulate nerve impulses by releasing glutamate
- Contribute to formation of blood-brain barrier
- Control flow of nutrients (e.g. lactate) from blood to CNS
What is a microglial cell? What does it do?
- Large cells with an elongated nucleus and relatively few processes, found throughout the CNS
- CNS macrophages (immune function, remove damaged neurones, sense increased K+)
- Also thought to digest protein aggregates associated with dementia and Alzheimer’s
What is an ependymal cell? What does it do?
- Are neural tissue (derived from neural crest)
- Look like columnar epithelium lining the spinal canal and ventricles of the brain (contain CSF)
- Synthesise and secreted CSF in the ventricles (choroid plexus)
- Cilia on surface move CSF to the spinal cord
- Microvilli absorb CSF for the removal of pathogens (present to microglia and astocytes)
- Tight junctions control fluid release into the brain
What is multiple sclerosis?
- A degenerative disease caused by autoimmune degradation of myelin (likely due to Epstein-Barr Virus)
- Relapsing-remitting disease
What are the symptoms of multiple sclerosis?
- Fatigue
- Vision problems (diplopia)
- Slurred speech (dysarthria)
- Numbness and tingling (paraesthesia)
- Mobility issues (muscle spasms)
- Urinary retention
- Constipation
