Nervous Flashcards
Nervous tissue is composed of:
Neurons/ nerve cells –> have cytoplasmic processes
Glial cells: support neurons
Neurulation
- 3rd to 4th week
- neuroectoderm develops
- Neural tube –> neuroblasts and spongioblasts –> Neurons and glia of CNS
- Neural crista –> Neurons and glia of PNS
Properties of neurons
- Excitable: Respons to changes in Environment (changes in electrical potential)
- Propagation: Action potentian travels
- Secretory: Neurotransmitter (Synapse) and neurohormones (by neurosecretory Hormones in Hypothalamus)
Morphological types of neurons
UNIPOLAR: embryonic, only one single axon
BIPOLAR: retina and olfactory organ, one single dendrite and one axon
PSEUDO-UNIPOLAR: sensory Neurons of spinal cranial nerve ganglia, dendrite and axon come from common stem
MULTIPOLAR: motor and intermediate, many processes
Functional types of neurons
- Sensory, afferent: accept Stimuli, convey info to CNS
- Motor, efferent: Signals from brain to effector organsvia spinal cord
- Intermediate: in between motor and sensory
- Neurosecretory Neurons: in Hypothalamus, secrete neurohormones
Cell Body of neuron
- large
- central nucleus
- Golgi, mitochondria, ER pigemtn inclusions (Melanin)
- SPECIAL ORGANELLES: nissl substance, neurofilaments
Nissl substance
- also called trigroid
- cytoplasm of cell Body –> rER and ribosomes
- in Body and dendrites and NOT IN THE AXON
- Neurotransmitter are synthesized here
Cytoskeleton of a neuron
- Microtubules
- Intermediate Filaments –> neurofilaments
- Microfilaments
–> supporting anf transporting function
Dendrites
- have dendritic spines: for synaptic contact and increases Surface
- sER, Golgi, cytoskeleton
- short and unmyleinated (except of pseudo-unipolar)
Functions of dendrites
- receive Stimuli and transmit Impulse to cell body
Axon
- arising from axon hillock
- turns into initial Segment
- cytoskeleton, mitochondria, vesicles
- terminal boutons
Axonal transport
–> movement of cellular substances
- along micortubules
- KINESIN and DYNEIN are motor proteins
anterograde Transport: from Body to terminal, by kinesin, towards positive end
retrograde Transport: from terminal to Body, by dynein, towards negative end
slow Transport: anterograde
fast Transport: anterograde and retrograde
Functions of neuroglial cells (7)
- support
- protection
- insulation
- metabolic Exchange
- repair
- clearance of neurotransmitters from cleft
- Regulation of intercellular fluid
Classification of glial cells
PNS
- Schwann cells
- Satellite cells
CNS
- Microglia
- Ependymal cells
- Astrocytes
- Oligodendrocytes
Schwann cells (PNS)
- surround all axons and dendrites in PNS
- form either myleinated OR unmyleinated fibers
- support, protection, regeneration
Satellite cells (PNS)
- small, round or cuboidal
- surround BODIES of Neurons in ganglia
- support and protection
Microglia (CNS) /hortega cells
- small and elongated with processes
- mesenchymal origin
- tissue Damage –> transform into amoeboid cells and belong to MPS
- defense and immune functions
Ependymal cells (CNS)
- epithelial lining of ventricles in brain and spinal canal
- cuboidal or low columnar
- microvilli on apical Surface (Absorption, secretion)
- TANYCYTES: cells that have Long basal processes –> Transfer of chemical Signals from Liquor to CNS
Blood - cerebrospinal fluid - barrier
- Endothelial cells of fenestrated capillary
- b.m.
- Ependymal cells
Astrocytes
- largest
- Long branched processes
- two types
1. Fibrous astrocytes (in White matter), fewer processes
2. Protoplasmic astrocytes (Grey matter), more process. - processes end in “end feet”
- end feet are on Neurons, nodes of ranvier and synapses and on b.m. of capillaries (BBB)
blood- brain- barrier
- endothelial cells of continuous capillaries
- b.m.
- astrocyte perivascular feet
highly selective
>Transports metabolic products
> restricts passage for Bacteria
> protects CNS from fluctuating Levels of electrolytes
Functions of astrocytes
- support
- protection
- metabolic Exchange
- support synaptic activity
- removing excess of neurotransmitters
Oligodendrocytes (CNS)
- small
- numerous cytoplasmic processes
- predominant in White matter
- myelination of axons in CNS
Myelinated nerve fibers
- Schwann cells in PNS
- Oligodendrocytes in CNS
- White
- large Diameter
- abundant in somatic nervous System
- 120m/ sec –> FAST
Non-myelinated nerve fibers
- axons lie loose in schwann cells (PNS)
- Grey
- small Diameter
- in autonomic nervous System
- 1-2 m/sec –> SLOW
Formation of non-myelinated nerve Fiber (in PNS)
- Axons invaginate in clefts of Schwann cells
- MESAXON: Zone of Apposition of schwann cell
- continuous sheath –> no nodes of ranvier
Structure of non-myelinated nerve Fiber (in PNS)
- Axon (one or more)
2. Neurilemma (cytoplasm and organelles of schwann cell)
Formation of myelinated nerve Fiber (in PNS)
- ONE axon invaginates into Schwann cell
- MESAXON rotates around cell, enveloping axon