Nervous Tissue

Neural tube (via notochord)

except microglia!!!

Neural Crest

Neural Crest

• - Neuronal cell bodies / processes
• - Astrocytes
• - Microglia
• - Some oligodendroglia

(Neurons organized by function into nuclei)

• Myelinated axons
• (myelin formed by oligodendroglia)

• white matter (black)
• gray matter (gray)

stains myelin

a.k.a. Nissl stains

Stains nissl substance (RER / polysomes)

• Motorneuron
• • euchromatic nucleus (highly active)
• • prominent nucleolus
• • abundant Nissl substance (RER / polysomes)

• cytoplasm = basophilic

• Microglia
• (bone marrow origin)

• - Neurons
• - Glia (support cells)
• 1. Ependymal cells
• 2. Choroid plexus cells
• 3. Astrocytes
• 4. Oligodendrocytes
• 5. Microglia

• Lines ventricles of brain / central canal
• - Cuboidal cells linked by desmosomes
• - Apical microvilli & cilia
• - Abundant mitochondria

looks like epithelium (neural tube = ectoderm derived)

• Specialized ependymal cells (third ventricle)
• - Linked to each other and to ependymal cells by tight junctions
• - Basal processes form end-feet on blood vessels

• Secrete CSF
• - Cuboidal epith. linked by tight junctions
• - Apical microvilli
• - Infolding of basal plasma membrane
• - Abundant mitochondria

• White Matter
• - long slender processes packed w/ intermediate filaments
• - filaments composed of glial fibrillary acidic protein (GFAP)
• - use antibodies to GFAP to determine if neural tumor is of astrocytic origin
• - structural support for white matter tracts

• Gray Matter
• - short, thick. bushy processes
• - fewer intermediate filaments
• - stains less intensely w/ GFAP antibodies
• - supportive cells for neurons (growth factors)

• End-feet
• - Cover neurons (soma / dendrites)
• - Create barrier along the pia mater (glia limitans)
• - Create barrier around CNS blood vessels (blood-brain barrier)

Myelination of CNS axons (up to 50 each)

Some act as satellite cells (not myelinating cells)

• Phagocytic cells (Bone marrow origin)
• - Resting macrophages in CNS derived from monocytes
• - Migrate to CNS during development of CNS vasculature
• - Respond to CNS injury

• Divide and phagocytize injured neurons and glia
• - microglial nuclei enlarge / elongate (rod cells)
• - increased damage = cells become phagocytic (gitter cells)

Outer layer -> inner layer

• - Molecular layer
• - Purkinje cell layer
• - Granule cell layer

Small neuroglia

Pyramidal cells (apical dendrites)

• Receptor region
• Soma / Nissl bodies / Axon hilock

• Conductive region
• Axon / Node of Ranvier

• Effector region
• Telodendron

Neuronal cell body

Synapses closer to the cell body have more influence than those more distal

FALSE

• Inputs (excitatory / inhibitory) summate to cause a graded potential
• (i.e. membrane potential becomes more +/ - depending on input)

• Dendrites
• proximal parts have nissl substance
• diameter tapers distally
• irregular contours
• branches bifurcate @ acute angles
• use graded membrane potential

• Axons
• No nissl substance
• uniform diameter
• smooth contours
• branches @ obtuse angles
• use action potential

• Neurofilaments (maintain axon diameter)
• Microtubules (fast anterograde / retrograde transport)
• Neurofilaments are more abundant

• 0.2 - 4 mm/day
• Anterograde only
• Conveys structural elements
• (tubulin / neurofilament proteins / actin)

1. Neurofilaments / microtubules are transported as polymers

2. Disassembled @ axon terminal (due to high Ca⁺ environment)

w/o this process, axons will swell (protein accumulation)

• 20 - 400 mm/day
• Microtubule dependant (motor protein)

• Anterograde - Kinesin (ATPase)
• conveys organelles
• (mitochondria / synaptic vesicles / SER)
• Retrograde - Dynein
• conveys worn organelle / endocytosed materials
• (growth factors / toxins / viruses)

Uses fast retrograde axonal transport

• Neuron targets make growth factors
• (carried back to soma by dynein)

Material in retrogradely transported endosomes

Cannot be digested (lysosomes in soma)

Accumulates w/ age & in some diseases

• 1. Chemical
• - most common
• - excitatory / inhibitory

• 2. Electrical (present in some parts of CNS)
• - allows neurons to act in unison
• - gap junctions

• 1. Presynaptic membrane depolarizes
• 2. Induces opening of Ca⁺ channels (brief)
• 3. Ca⁺ influx promotes exocytosis of synaptic vesicles
• 4. Release of neurotransmitters (synaptic cleft)
• 5. Neurotransmitters react with receptors
• 6. Postsynaptic membrane depolarizes
• 7. Presynaptic membrane retrieval (coated vesicles)

• Contains sensory neurons that signal:
• - pain
• - temperature
• - touch
• - pressure
• - vibration
• - porprioception

Perineurium

• Due to loss of target-derived neurotrophic factors
• 1. cell body swells
• 2. dissolution of Nissl substance (chromatolysis)
• 3. nucleus moves eccentrically
• 4. actin / tubulin genes up-regulated (growth cone)
• 5. neurofilaments / neurotansmitters down-regulated

• Proximal part = retrograde degeneration
• Distal part = anterograde (wallerian) degeneration

Distal part separated from cell synthetic machinery

• Motile structure w/ receptors for neurotrophic factors / laminin
• (basal lamina surrounds schwann cells)