Primary Tissue 3 : Nervous Tissue Flashcards
What is nervous tissue
-a primary tissue with cells called neurons capable of processing stimuli and generating responses and has support support cells called glial
What is the nervous system and its Divisions
-an integrated communication system of the body
- central nervous system
- peripheral nervous system
Function of nervous system
-to respond to stimuli
How do all cells respond to stimuli
-by changing potential gradient across their membranes
Development of nervous system
- develops in outermost embryonic layer called ectoderm
- inductive is influence from underlying axial structure ( notochord ) thickness overlying ectodermal cells as a bending neural plate
- folds of plate extend and fuse forming neural tube
- before tube detaches from overlying ectoderm crest cells detach and form mass of mesenchymal cells
What is neurulation, components of neural plate and what happens to none induced ectoderm cells
- process of forming CNS and PNS cells
- groove, crest and folds
- become epidermis
What does tube and mass of crest mesenchymal cells give rise to
- tube gives rise to entire CNS
- crest cells give rise to PNS
When does nuerulation begin
3rd week of development
General organization of nervous system
1 sensory ( afferent)
/somatic - conscious input
/visceral- unconscious input
2 motor ( efferent ) /somatic - voluntary motor outputs /autonomic - involuntary responses
2 divisions of ANS describe where found and function
1 parasympathetic - maintains normal body homeostasis
/ganglia within or near effector organ
2 sympathetic - controls bodies responses during excitement or emergence
/ganglia near CNS
Autonomic motor nerves have pathways with 2 neurons which are !?
1 pre-ganglionic
/soma in CNS
2 post-ganglionic
/soma in ganglion
Function of soma / perikaryon
- synthesis center or cell for neurotransmitters
- produces cyto for the cell
- in contact with nerve endings of other neurons
Characteristics of neuron soma
-well developed synthesis machinery for secretion and addition into cytoskeleton
What are nissil bodies / chromatophilic substances and where abundant
-basophilic regions in neuron soma with high conc of rER and polysomes
/in large neurons such as motor neurons
What is neuron intermediate filaments made of and what do they make
-neurofilament ( and they make up neurofibrils )
Describe dendrite structure and function
- short branching process extend from soma of neuron
- specialized to receive nerve impulses
Where do synapses on dendrites occur and describe it
- on dendritic spines
- dynamic membrane protrusions
Describe axon structure and function
/1 long fine process specialized to generate and transmit nerve impulses to other cells or neurons
Membrane and cytoplasm name of axon
- axolemma
- axoplasm
Where does the axon originate from
-from a pyramid shaped region of soma called axon hillock
What is beyond hillock and what does it do
-ion Channels to generate nerve impulses
What is arborizations and what does axon branch into !?
- tree like branching of neuron processes
- telondria then synoptic knob
What is terminal bouton
/dilations at the end of axon branches that end at synapses
Function of kinesins and Dynenins in neurons
/carry vesicles with neurotransmitters from soma to axon
/carry endocytized substances such as bacteria from axon to soma
Classification of neurons and types
1 based on number of processes
- multipolar
- unipolar / pseudounipolar
- bipolar
- anaxonic
2 based on direction of propagation
- sensory
- internuerons
- motor
Location of soma and axons In CNS and PNS
CNS
- soma In grey matter
- axons In white matter
PNS
- soma in ganglion
- axons in nerve fibers
How does a nerve impulse travel and where does it originate from and how is it produced
/travels like a wave along axolemma
- originates in axon hillock if impulse received by soma or dendrites exceed a certain threshold
- produced by membrane depolarization of voltage gates Na/K ion channels
Describe membrane potential of unstimulated neurons and how it comes about
- the pumps maintain Na 1/10 that of extra cellular content and K+ greater than outside
- produces potential of -65mV with inside of plasma negative relative to outside
What is a neurons resting potential
-65mV ( lemma or inside of plasma negative relative to outside )
What happens when dendrites receive an impulse meeting a certain threshold and what is the outcome
- Na+ channels at hillock open up allowing influx of Na+
- lemma is now positive relative to outside depolarizing membrane to potential of +30mV
What happens immediately after membrane depolarization
-Na+ channels close and K+ Channel opens returning membrane to resting potential
What does depolarization of hillock cause and outcome
/causes adjacent channels to depolarize as well and return to Resting potential generating nerve impulse through lemma towards nerve endings
What does a nerve impulse do at a nerve ending
What does a neurotransmitter do !?
/promotes discharge of neurotransmitter
- inhibits or stimulates action potential in other cells
- bind to receptors and open or close ion Channels
What are synapses and what do they do
- sites where nerve impulses are transmitted from one neuron to another
- convert electrical signals into chemical signals that affect post synaptic membranes
Parts of synapse their descriptions and components
1 pre-synaptic
-has mito, microtubule and synaptic vesicles which release neurotransmitters
2 synaptic cleft
-20-30 nm gap separating pre and post synaptic terminals
3 post-synaptic
-has receptors for neurotransmitters and mechanisms to initiate nerve impulse
How is a nerve impulse propagated from one cells to another
- nerve impulse In pre-synaptic terminal opens Ca+ channels causing an influx and the ions cause synaptic vesicles to release their neurotransmitters into cleft via exocytosis
- transmitter diffuses through cleft and binds to receptor on post-synaptic membrane
How does neurotransmitter leave pre-synaptic terminal and what 2 types of effects can it have on post-synaptic cell
-exocytosis
1 inhibitory
2 excitory
Describe excitory and inhibitory effect and how they come about
1 neurotransmitter opens Na+ channels initiating membrane depolarization
-nerve impulse continues
2 neurotransmitter opens Cl- channel causing hyperpolarization and cell resistant to depolarization
How is excess neurotransmitter removed from cleft
1 enzymes
2 glial cells
3 endocytosis of pre-synaptic terminal
Types of synapses and function
1 axodendritic - propagate info
2 axosomatic - propagate info
3 axoaxonic - modify impulses of axons
What is neuropil
-fine processes extending from both glial cells and neurons in the intercellular network
Where do glial cells originate from , are they more numerous and what do they substitute
- neural plate
/ yes
-CT made of collagen
Ogliodendrocytes function, characteristics and where found
/wrap repeatedly around numerous axons in CNS
-insulate axon and facilitate rapid transmission of impulses
How is a Myelin sheath formed
-when ogliodendroctyes or Schwann cells warp repeatedly around axons and cyto leaves the processes forming compact layers of membrane
Astrocytes shape, characteristics and types ( where types found )and marker
- star shaped
- in proximal part of processes have intermediate filaments made of GFAP ( glial fibrillary acid protein )
1 fibrous with long processes and found in white matter
2 protoplasmic astrocytes with shorter processes and found in Grey matter
Functions of astrocytes
1 regulates interstitial fluid ionic content
2 provide structural support and physical guide neurons in the CNS during development
3 replicate to fill space left by dead neurons forming astrocytic scar
4 fibrous extend expanded perivascular feet to cover endothelial modulating blood flow and facilitating exchange of metabolites
5 protoplasmic expand and form a layer called glial limiting membrane ( part of blood brain Barrier )
6 extend processes to cover synapses affecting function and formation
Ependymal cells characteristics and function
-cuboid or columnar cells with apical end junctions and basal ends extending into neuropil
1 line fluid filled ventricles of blood.
2 have cilia on apical ends to move cerebrospinal fluid
3 line central canal of spinal cord
Microglial characteristics and function
- small cells with active processes that scan the neuropil for debris or pathogen
- monocytes derived
Schwann cells characteristics and function
-same function similar to ogliodendrocytes
-only cover 1 axon each
/found in PNS
Satellite cells characteristics and function
-small cells found in ganglia surrounding soma of neurons
- facilitate exchange of metabolites
- create conducive micro environment
- insulate soma
List of glial cells where found and their origin
1 astrocytes , ogliodendrocytes and ependymal
- found in CNS and originate from neural tube
2 microglial
- found in CNS
- monocytes origin
3 Schwann , satellite cells
- found in PNS
- originate from neural crest mesenchymal cells
Components of CNS
Cerebrum
Cerebellum
Spinal cord ( brain stem )
What covers the CNS and how strong is it
CT layers called meninges
-soft and easily damaged
Grey and what matter locations In brain and components
-Grey at the peripheral of brain
/neuronal bodies, protoplasmic astrocytes, microglial
-white deep in the brain
/has myelinated axons in bundles called tracts , fibrous astrocytes, ogliodendrocytes
What is white matter tracts , the 3 types and description
-myelinated axons found in the white matter of the brain
1 association - within hemispheres
2 commissural - in between hemispheres
3 projections - entering or leaving hemispheres
What are cerebral nuclei , where found and name them and their locations
-localized deep in brain dark regions with neuronal aggregates
1 putamen- outer layer
2 globus palidus - middle layer
3 caudate nucleus - top layer
Functions of neurons in cerebral and cerebellar cortex
- integration of sensory info and initiation of voluntary motor response
- co ordinates muscles activity in the body
Name and describe the three layers of the cerebellum
1 molecular outer layer - much neuropil and scattered neuronal bodies
2 purkinje cell middle layer - has only large purkinje cells bodies
3 thick granular inner layer - small densely packed neurons
Location and shape of white and gray matter in spinal cord
/white is outer layer
- Grey is inner layer forming H shaped mass with horns
What do the horns of Grey matter spinal cord have !?
- anterior : has cell bodies for large motor neurons
- posterior horns : has inter neurons receiving sensory information from spinal ganglia
Deceive central canal where found and how formed
- found at the middle of the horns
- develops from lumen of neural tube
- continuous with ventricles of brain
Describe dorsal and ventral roots
- has sensory nerves
- has motor nerves
What is meninges and its 3 layers
-CT between bone and nervous tissue in CNS
1 dura mater
2 arachnoid
3 pia mater
List the layers of meninges starting at skin
Skin Periosteum Bone Perosteal layer Meningeal layer Subdura space Arachnoid Arachnoid trabeculae Pia matter Grey matter White matter
Describe dura matter and it’s layers
/thick external layer of irregular CT
/has 2 layers
1 periosteal outer layer continuous with periosteum of bone
2 meningeal layer
Where do the dura mater layers separate and what is formed
/at superiors sagittal sinus
-forms blood filled dural venous
What separates dura mater at spinal cord and what is present there
-epidural space
/has loose CT and vasculature
What separates dura and arachnoid
Subdural space ( potential space )
Describe arachnoid and its layers
1 sheet of CT in contact with dura mater
2 system of loose arranged trabeculae of collagen and fibroblasts continuous with underlying pia mater
What is arachnoid trabeculae surrounded by !?
And it’s function
- large sponge like cavity called subarachnoid spec filled with CSF
- cushioning and protection of CNS
Where are blood vessels In meninges found
Why is arachnoid called a vascular
/in subarachnoid space
-doesn’t have nutrition capillaries
Which 2 layers of meninges are closely associated and what’s the combined name
Pia and arachnoid
Pia-arachnoid
What are arachnoid villus and function
- areas where arachnoid penetrate into dura mater into blood filled venous sinuses
- serve as a site to release excess CSF into blood
Describe pia mater , where found and how is it separated from nerve cells
- flattened mesenchymal derived cells which cover entire CNS
- astrocytes extend processes forming glia limitans
Function of pia mater and glia limitans
-physical barrier to separate CNS from CSF in Arachnoid
How to blood vessels enter CNS and what covers them
/arteries in subarachnoid branch smaller and enter CNS
-initially covered by pia mater at peri vascular space but pia disappears as the vasculature becomes capillaries and now covered by astrocytotic processes
What are the main components of PNS
- cranial and peripheral ganglion
- nerve endings
- nerves
How are axons in PNS myelinated
- Schwann cells become aligned along axon and extend wide cyto process encircling it
- process encircles axon but continuous it’s spiral
- spiral wrappings become compacted layers of myelin as cyto goes to outer layer
What do mature Schwann cells have
-up to 100 lamellae and cyto and cell body in outer layer
White matter tracts are analogue to what
-nerves
What is a nerve fiber
-a myelinated axon
What is neurolemmocyte
-Schwann cells
What is mesoxon
Area where Schwann on axon fuses with itself
Myelin cleft synonym , description ,where found and function
- Schmidt-lanterman cleft
- parts of myelin sheaths with cyto in them between major dense lines
- allow transient movement cyto for membrane maintenance
Function of myelin sheaths
-insulate axons and maintain constant ionic micro environment suitable for action potentials
What is node of ranvier , where found and function
- space between adjacent Schwann cells
- partially covered by interdigitating Schwann cell processes
- expose lemma to ions of interstitial fluid to renew action potential
- has higher conc of Na/K voltage gates
What is saltatory conduction
-propagation of action potentials along myelinated axons from 1 node of ranvier to another
What are internodal segments
-length of axon covered by myelin Schwann cell sheaths
Which fibers are unmyelinated and how
-small diameter nerves
- Schwann cells start by enveloping multiple small diameter axons
- axons spaced apart and covered by Schwann but no wrappings of myelin around
Why are small diameter axons not myelinated
-use action potentials whose formation and maintenance is independent of insulation provided by myelin sheaths
Color of nerve and why
- whitish glistening appearance
- due to lipid rich content of myelin sheaths
The 3 layers of nerves and describe them and their structures and their functions and their locations and what we find in them
1 outer epineueium - around entire fibers. Dense irregular coat. Extends deep to fill space between fascicles
2 middle perineurium - has flat fibrocytes and sealed by tight junctions. 2-6 layers of cells to regulate diffusion into fascicle. Make up blood nerve barrier to maintain fiber micro environment
3 endoneurium - immediately around external lamina of Schwann cells. Thin layer with reticular fibers and fibroblasts
Types of nerves and description
1 sensory- has sensory nerve
2 motor - has motor “
3 mixed - has both sensory and motor
What are ganglia and the 2 types and criteria used to classify them
-ovoid structures with neuronal bodies and their associated satellite glial cells
1 sensory
2 autonomic
-determined based on direction of impulse
What covers ganglia
- outer dense capsule
- inner delicate CT
Function of sensory ganglia , the types and the neuron it has
-has afferent nerves to carry impulses to CNS
1 cranial
2 dorsal
-pseudounipolar neurons
Function of autonomic ganglia , description of structure and type of neuron it has
- controls involuntary actions to maintain homeostasis ( smooth muscle , heart , glands )
- small bulbous dilations in autonomic nerves
- multipolar nerves
Where are is the post ganglion structure for parasympathetic found !?
1 near or within effector organs
-parasympathetic
How many circuits does ANS have and list them as where are they found
2
1 pre ganglion ( in CNS )
2 post ganglion ( in peripheral system )
All pre ganglion ANS synapses use which neurotransmitter
-Acetylcholine
Locations of pre and post ganglion of sympathetic and parasympathetic systems
1 sympathetic
- pre : thoracic and lumbar segments of spinal cord
- post : along vertebrae column
2 parasympathetic
- pre : medulla and midbrain
- post : within or near effector organ
Describe post ganglion of parasympathetic
-may lack capsule and just be soma with satellite forming a loosely organized plexus in CT
Lobes of the brain
How many cranial nerves are there
Frontal
Parietal
Occipital
Temporal
12
What parts constitutes the brain stem
Midbrain
Pons
Medulla oblangata
Brain parts and they synonyms
Cerebrum - telencephalon Hypothalamus- diencephalon Mid brain - mesencephalon Pons - metencephalon Medulla - myelencephalon
