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
Structure of myelinated nerve Fiber (in PNS)
- Axon
- Myelin (layers of schwann cell Plasma membrane)
- Neurilemma (extruded cytoplasm of schwann cell)
Fiber is surrounded by b.m. and endoneurium
Nodes of Ranvier
- gapds between Schwann cells along the myelinated axon
- not covered by Myelin sheath
- Neurilemma is still present
- ion channels present here
Internodal segment
- between two nodes
- one schwann cell myelinates one Segment
- electrical insulation by Lipid Content
- allows for saltatory conductance –> increases speed
Myelination process in the CNS
- by oligodendrocytes
- cytoplasmic processes rotate around axon
- one oligodendrocyte can contribute to myelination to up to 50 axons
Specialties in myelination of CNS
- astrocytes cover nodes
- internodal Segments are Shorter
- chemical differences between PNS and CNS Myelin
- no b.m and no endoneurium!!!!!
- fibers cannot Regenerate!!!!
Regeneration of PNS fibers
- distal part of Fiber degenerates
- Fragmentation
- phagocytosed by macrophages
- Body swells, nucleus moves peripherally, nissl substance disappears
- Schwann cells divide and form the cord - axon follows
- 1-3 mm a day
Functional organization of the nervous system
- somatic
- autonomic
> Sympathetic
> Parasympathetic
Principles of CNS organization
Gray matter:
- neuronal cell bodies
- non-myleinated axons, dendrites, glail cells
- bodies arranged in nuclei or multiple layers
- neuronal processes and glial cells: NEUROPIL
White matter:
- myelinated axons and glial cells
- TRACT / FASCICLE: bundle of axons
Spinal cord
- Deep ventral median fissure and shallow dorsal median Sulcus
- dorsolateral Sulcus on each side –> entry of sorsal nerve roots
- Ventrolateral Sulcus: Exit of ventral nerve roots
Grey matter of spinal cord
- ventral Horns: bodies of large somatic motor Neurons
- dorsal Horns: bodies of intermediate Neurons
- small lateral Horns: bodies of autonomic (sympathetic) efferent Neurons (in T and L)
- central canal: lined by ebendymal cells and contains CSF
White matter of spinal cord
- ascedning tracts of sensory fibers and descending motor tracts
Cerebellum
- for smooth, coordinated movements, posture, Equilibrium
- folds form the arbor vitae which increase size
Cerebellar cortex
three layers
- Outer molecular layer:
- non myelinated fibers
- glial cells: stellate and Basket cells - Purkinje cells
- Inner granular layer: granulae cells and golgi cells
Purkinje cells
- large bodies
- extensively branched dendritic System into molecular layer
- axon extends down though granular layer into White matter
- receive excitatory Inputs from afferent fibers and inhibitory Inputs from molecular layer
Stellate cell (in cerebellum)
- star shaped
- in molecular layer
- dendritic System
- axon synapses with dendrites or bodies of purkinje
Basket cells (in Cerebellum)
- irregular Body
- in molecular layer
- dendritic System
- axon is Long, goes perpendicular to the foldm synapses with Body of purkinje
Cerebellar basket
complex of inhibitory synapses surrounding the Body of purkinje cell
- axons of Basket and stellate cells and axons of purkinje cells
Granular cell (Cerebellum)
- in granular layer
- small Body
- Short, branched dendrites
- axon gies up to molecular layer to Synapse with purkinje, stellate, Basket and Golgi
Golgi cell (Cerebellum)
- in granular layer (superficial part)
- irregular Body
- dendrites in both granular and molecular layers
- axon synapses with dendrites of Granular cells
Afferent fibers in cerebellum
MOSSY AFFERENT
pontine nuclei - granular cells - purkinje dendrites
CLIMBING AFFERENT
olive nuclei - directly with purkinje dendirtes
Cerebellar glomerulus
synapses surrounding the end oof mossy fibers
- mossy afferent Fiber –> Center of Glomerulus
- Dendrites of granular cells
- Axon of golgi –> send inhibitory imp. to granular cells
Efferent Neurons and fibers in cerebellum
- Purkinje cells: only efferent cells
- Purkinje axons: only efferent fibers
purkinje cells send inhibitory projections to deeper cerebellar nuclei
Glia of cerebellar cortex
Lopogliocytes: modified astrocytes
- in Purkinje cell layer
- processes form glial limiting membrane
Cerebral cortex
6 layers: neocortex
less than 6: allocortex
- Molecular layer
- Outer granular layer
- Outer pyramidal layer
- Inner Granular layer
- Inner pyramidal layer
- Multiform cell layer
Molecular layer of cerebral cortex
- few Neurons
- non myeliated fibers
Outer granular layer of cerebral cortex
- small pyramidal cells
- stellate cells
Outer pyramidal layer of cerebral cortex
- Pyramidal cells of medium size
- Martinotti cells
Inner granular layer of cortex
- mainly stellate cells
Inner pyramidal layer of cortex
- large and huge pyramidal cells in motor cortex
- axons in motor Cortex travel tospinal cord : pyramidal tract
Multiform cell layer of cortex
- wide Variety of cells
- contains fusiform cells: Body and processes oriented at righ angle to surface
Types of cerebral cortex
granular type:
- granular layers are predominant in SENSORY ZONE
agranular type
- pyramidal layers are predominant in MOTOR ZONE
Functional types of cerebral Cortex neurons
- medium, large and huge pyramidal cells are efferent
- all others are intermediate
Orientation of cerebral fibers
- tangential (horizontal) fibers: layers 1, 2, 4,5
- radial fibers:
>afferent fibers synapsing with dendrites of efferent and inermediate in superficial layers
>efferent fibersfrom purkinje Neurons in layers 3 and 5
Cortical column
- Morphofunctional unit of cerebral Cortex
- vertical column thriugh cortical layers of brain
- cells of column have same receptive field
Principles of PNS organization
Ganglia: aggregations of Neuron cell bodies
Peripheral nerves: combination of afferent and efferent nerve fibers
Peripheral nerve
- one or more bundles of afferent and efferent fibesr
Organization of a nerve
ENDONEURIUM surrounds nerve Fiber (loose CT)
PERINEURIUM surrounds fascicle (loose CT)
EPINEURIUM surrounds more fascicles (dense irregular)
Ganglia (2 types)
- Sensory: spinal root and cranial ganglia
- Autonomic: sympathetic and parasympathetic
Spinal (dorsal root) ganglion
- contain sensory Neuron cell bodies
- Neurons are pseudo-unipolar
- bodies of Neurons are peripheral, fibers are in the Center
- each nucleus surrounded by satellite cells and capsule of loose CT
Sympathetic glangion
- either paravertebral or prevertebral
- neuronal cells are motor and multipolar
- nucleo of neuronal cells are eccentrally located
Parasympathetic ganglion
- intramural –> lie close to effector organ
- bodies of mulipolar Neurons are clumped together scattered in tissue of organ
- Neurons are surrounded by satellite cells
- large nuclei
Reflex arch
monosynaptic: only two Neurons
polysynaptic: one or more interneurons involved –> allows processing or inhibition
Somatic Reflex arch
- receptor in Skin
- Body of sensory Neuron in spinal Ganglion
- Body of intermediate in dorsal horn
- Body of motor Neuron in ventral horn
- Effector ending in skeletal muscle
Autonomic (parasympathetic) Reflex arch
- Receptor in inner organ, vessel
- Body of sensory Neuron in spinal Ganglion
- Efferent part is made of two Neuron chain, 1st Neuron in laterl horn
- 2nd Neuron in autonomic Ganglion
- Effecotr in smooth muscle, gland
