12. Histology of the Nervous System Flashcards
What are the 3 meninges?
Meninges (three layers)
Membrane surrounding brain
-
1 - Dura mater
- Outermost, fibrous
- Epidural space periosteal side (attached to the cranium, has a rich blood supply)
-
2 - Arachnoid mater
- Subarachnoid space, with vessels, filled with CSF
-
3 - Pia mater (capsule of brain & spinal cord)
- Delicate membrane outside of a simple squamous epithelium
Arachnoid & pia mater = Lepto*meninges
*Lepto meaning small, fine or narrow from the Greek to peel
In the brain/cerebrum, where is the grey matter and what is it composed of?
In the brain/cerebrum, where is the white matter and what is it composed of?
Brain/Cerebrum
-
Grey matter/ Cortex
- Nerve cells
- Glia (4 types of support cells)
-
White matter/ Medulla
- Neuronal cell processes and glia
What is CSF?
- Where is it found in the brain?
- Which cells make it?
Cerebrospinal fluid (CSF)
- Bathes brain
- Outside = Subarachnoid space
- Inside = Ventricles
- Space extends into central canal of the spinal cord
- Made by ependymal cells of choroid
Where are ependymal cells found?
- Epithelial cell type?
- What do they it form in the brain?
Ependymal cells
- Lines ventricle of the brain, central canal of the spinal cord and surface of choroid plexus
- Composed of a single layer of ciliated, specialized epithelium, with microvilli
- Epithelium with NO basement membrane
- Further specialized cells in ventricle known as the choroid plexus make the CSF
- Provide the Blood/CSF barrier (tight junctions)
What is the cell body of a neuron called?
- What does the nucleus of a nerve cell look like?
- What are the nucleoli described as?
- Which substance/granule is distinctive of the neuron cell body?
- Perikaryon (soma) = cell body of a neuron which remains in the CNS (grey matter)
- Nucleus is large & spherical
- Large prominent nucleolus (owl eye)
- Fine chromatin
-
Nissl substance = Clumps of RER & polysomes
- Nissl’s granules are present only in the cytoplasm of the cell body of neurons.
- Even distribution
- Neurofilaments (cytoskeleton)
- Throughout neuron and cell processes
What is the shape and size of neuronal cells?
Neuronal Cell Shape
- Large size (up to 135μm)
- Shape:
- Pyramidal (triangular)
- Globular
- Stellate (star)
- Uni-, bi- & multi-polar (number of cell processes)
What are the 2 types of neuronal cell processes?
- How many axons do each neuron have?
- Length of axon?
- Which cells of the CNS/PNS are responsible for axon myelination?
- Which of the 2 processes contain nissl substance?
- How many dendrites do each neuron have? Length?
Neuronal Processes
• Cell processes(inCNS&PNS)
– Axon (one only from mm to m in length), transmit
NO Nissl substance (axon hillock)
Neurofilaments & mitochondria present
Most myelinated (oligodendroglia CNS & Schwann cell PNS)
– Dendrites (one or more) receive • Short, often branched
• Contain Nissl substance
What is the cerebellum also known as?
- Structure?
- What forms the Granular layer of neurons?
Cerebellum (little brain)
- Numerous folds
- Grey matter thin layer in cortex
- Granular layer of neurons (Purkinje cells) & glia
What are neuroglia?
- General function?
- 4 types? 3 macroglia? 1 microglia?
- Specific functions of each neuroglia?
Neuroglia (Glia [glue])
- Support cells
- Metabolic exchange
- Nuclei only visible under LM
Four types:
-
Astrocytes
- Ground substance
- Attachment to neurons, vessels (blood brain barrier), other glia & pia mater
- Regulate K+ ions
- Oligodendroglia/oligodendrocytes → Myelin
-
Ependymal cells - ciliated
- Tanycyte – blood brain barrier
- Apical surfaces are covered with cilia that circulate CSF around the CNS.
- Apical microvilli absorb CSF.
- Microglia (bone marrow derived) – Phagocytosis
What is the Brain Blood Barrier?
- Which junctions are present?
- Which cells are involved?
Blood Brain Barrier
- Capillaries have reduced permeability to some macromolecules
- Junctions (zonulae occludentes [occluding junctions]) between endothelial cells prevent transport between them
- Astrocytes provide further covering
Where is Nissl substance found?
Nissl substance - clumps of rER & polysomes.
Even distribution throughout cell body & dendrites
NOT found in axonal hillock or axon!
What are the differences between Axons and Dendrites?
What are Astrocytes/Astroglia?
- Shape?
- 5 Functions?
Astrocytes/Astroglia
- Shape: “Star”-shaped (astro-) with processes.
- Attach to neurons, BVs (blood brain barrier), other glia & pia
- Functions:
- Regulating the ionic balance of the ECF – regulate K+ ions
- Neurotransmitter metabolism
- Injury clean up – removal of dead tissue
- Radial glia – pathway for newly produced neurons to travel along
- Induce BBB
What are the 2 myelin-forming cells of the nervous system?
- How many oligodendrocytes to axons?
- How many Schwann cells to axons?
Myelin-Forming cells
-
Oligodendrocytes - CNS
- One oligodendrocyte myelinates many axons.
-
Schwann** **cells - PNS
- 1 to 1 relationship between Schwann cell and axon
What is the resident macrophage of the brain?
Microglia (CNS) = Resident macrophage in the brain – phagocytosis.
What are ependymal cells?
- Where?
- Function?
- Structure? Basement membrane?
- Which barrier to they form?
Ependymal Cells - CNS
- Line the ventricles of the brain, central canal of the spinal cord & surface of choroid plexus.
- Involved in production of CSF.
- Composed of single layer of ciliated specialised epithelium with microvili.
- No basement membrane?
- Provide the blood/CSF barrier (tight junctions).
What is the structure of the spinal cord?
- What is it surrounded by?
- Where is the white/grey matter? Contents?
- Structure/horns of grey matter?
Spinal Cord
- Surrounded by pia mater
- White matter of cortex*
- Myelinated and unmyelinated axons (fibres)
- Grey matter central medulla*
- H-shaped horns
- anterior (ventral) = motor neurons
- posterior (dorsal) = receives sensory info
- H-shaped horns
What are Ganglia?
Peripheral Nervous System (PNS)
• Ganglia (plural of Ganglion)
–Group of nerve cell bodies outside the CNS
–Variable in size and number of neurons
Which cells of the PNS are the CNS equivalent of Astrocytes?
What are nerve bundles of the PNS composed of?
What are they encapsulated by - 3 layers?
Nerve bundles in the PNS
- Axonal & dendritic processes
- Encapsulated by collagen & with reticulin support
- Epineurium – surrounds & binds nerve fascicles into a common bundle = outermost tissue of peripheral nerves.
- Perineurium – surrounds each nerve fascicle (contains many nerve fibers).
- Endoneurium – surrounds each individual nerve fibre.
What are the nerve bundle PNS support cells called?
What 2 things do they contain?
Nerve bundles PNS Support Cells
Schwann cell = Support cell forms myelin (neurilemma)
- Nodes of Ranvier
- Glycolipid (galactocerebroside)
What are Schmidt- Lanterman (SL) clefts? What are their function?
Myelin incisures or Schmidt- Lanterman (SL) clefts, which subdivide the myelinated axon into irregular portions.
They provide communication channels through every layer of the Schwann cell cytoplasm.
What are the 3 types of synapses in the nervous system?
- Which synapses are present in cardiac muscle?
- What are chemical synapses separated by?
- Which ion causes release of NT from a presynaptic neuron?
- What does the terminal bouton release in a NMJ?
- Where is the postsynaptic membrane of a NMJ?
- What is ACh destroyed by?
Synapses
1 - Gap junctions/electrical synapses – connexon formed by six connexins act like tunnels to connect the cytoplasms of the two cells = electrically coupled.
- Flow of ions from cytoplasm to cytoplasm – i.e. directly from cell to cell.
- Example: cardiac muscle.
2 - Chemical synapses
- Pre- & post-synaptic neurons are close but do not touch - separated by a synaptic cleft.
- Presynaptic neuron releases a NT ((+) by Ca2+) → traverses synaptic cleft → binds to the plasma membrane of the post-synaptic neuron → turns the chemical signal into a post-synaptic potential.
3 - Neuro-muscular junction (NMJ) - synapse b/w a neuron & a muscle.
- Terminal bouton releases ACh → crosses synaptic cleft → attaches to Rs → opens chemical gates (ACh channels) in the sarcolemma (postsynaptic membrane) → Na+ influx → generation of action potential in the sarcolemma.
- ACh destroyed by acetylcholinesterase.
- The muscle membrane has invaginations to ↑SA.
