nervous tissue Flashcards
what is the nervous system
enables the body to respond to continuous changes in its external and internal environments
what is the central nervous system
spinal cord and brain
what is the peripheral nervous system
cranial, spinal peripheral nerves and ganglia
what is the main component of the nervous system
nervous tissue
what is the function of neurones
conducing cells
- structural and functional unit of nervous system
what is the function of neuroglial cells
supportive and protection cells
- not involved impulse transfer
when does the neural tube develop
3rd week from the ectoderm
what induces neurulation in embryos
- axial structure notochord
what is neurulation
formation of the embryonic neural plate and its transformation into the neural tube
what does the neural crest cells form
- pigment cells
- neurones of the dorsal root ganglia of spinal nerves
- autonomic ganglia
- Schwann cells
- adrenal medulla
- bone and cartilage of lower jaw
what does the neural tube form
- CNS
- neurons and most gilal cells
what does the cranial part of the neural tube form
brain
what does the trunk of the neural tube form
spinal cord
what are the shapes of neurons
- rounded
- oval
- star shaped
- pyramidal shape
how many neurones dose a human have
more than 10 billion
what is the size of neurons
5 micrometers to 130 micrometers
what are the main parts of a neuron
- cell body/ soma/ perikaryon
- processes - axon and dendrites
what is the structure of the neurons cell body
- 4-100 micrometers
- energetic and synthetic centre of neurone
- contains majority of organelles
what is the neurolemma
cytoplasmic membrane of the neurone
what is the structure of the nucleus in the neuron
- single and large
- moves to periphery if cell is injured
- fine chromatin
what is found in the cytoplasm of the cell body of the neuron
- golgi complex, mitochondria and lysosomes
- melanin or lipofuscin
- nissl body
- neurofibrils
what are nissl bodies
highly developed rER organised into aggregates of parallel cisterns and polyribosomes
where are nissl bodies present
cell body and dendrites
what is the function of nissl bodies
high level of protein synthesis for maintenance and repair and production of neurotransmitters and enzymes
what are nissl bodies stained with
basic dyes as they are basophilic
what are nissl substances
- tigroid
- look like cheetah fur
- arranged in basophilic areas
what are neurofibrils
- cytoplasmic fibrils in the cell body where they branch to form a network and extend into all processes
- contain a collection of neurofilaments
what are the centrioles in neurons used for
production and maintenance of microtubules
what are the functions of neurofibrils
- mechanical support and stability
- neurofilament proteins used as marker for neuronal cells
what are dendrites
multiple elongated processes specialised in receiving stimuli from environment or sensory epithelial cells
what is the axon
single process specialised in generating or conducting nerve impulses to other cells
what are neruofibrils stained with
silver impregnation
what is the axolemma
axon membrane
what is the axoplasm
axon cytoplasm
what is the axon hillock
between the body of the neruon and initial segment of the axon
what is the initial segment
first segment of the axon contain a large number of channels and is often where the generation of the action potential occurs
what is the terminal arborization
peripheral branching of axon
what is the terminal bouton
ending of the axon with synapse
what mechanism is axonal transport
bidirectional mechanism
what it anterograde transport
carries material from the nerve cell body to the periphery mediated by kinesin
what is retrograde transport
carries material from the axon terminal and dendrites to the cell body mediated by dynein
what is a slow transport system
conveys substances from cell body to terminal bouton at 0.2 to 4 mm/day
what is a fast transport system
conveys substances in both directions at the rate of 20 - 400mm/day
what viruses use antegrade transport
- neurotropic herpes viruses - HSV and VZV
what viruses use retrograde transport
rabies and polimyelitis
how does infections in the neurones form
- survive in ganglia and is reactivated
- spread along nerve fibres into periphery causing painful blisters
what are the morphological classification of neurones
- unipolar - neuroblast
- pseudounipolar - single process forming a T shape
- bipolar - one axon and one dendrite
- multipolar - more than two processes and one axon
where are pseudounipolar neurons found
sensory ganglia expect vestibular and cochlea
where are bipolar neurons found
cochlear and vestibular gangli, olfactory neuroepithelium and retina
where are multipolar neurons found
motor or interneurons
what are sensory neurons
the reception of sensory stimuli from environment or body
what are interneurons
establish relationship among other neurons
what are motor neurons
control effector organs such as muscle fibres and exocrine and endocrine glands
what are the function of glial cells
- supporting
- delimitative
- trophic
- secretory
- protective
what are the classifications of glial cells
- macroglila - oligodendrocytes, astrocytes and ependymal cells
- microglia
what is the structure of oligodendrocytes
- small round cells
- few cytoplasmic processes
where are oligodendrocytes found
grey and white matter
what are oligodendrocytes functions
- myelination of axons in CNS
what is myelin
- lipid rich sheath that surrounds the axon
what is the myelin sheaths function
facilitates the transmission of electrical signals along the axon
what are the types of oligodendrocytes
- satellite cells
- Schwann cells
what are satellite cells
flattened cells that form a capsule around each ganglion cell
what are the functions of satellite cells
- provide nutrients
- remove metabolites
where are Schwann cells found
around the axon in the Peripheral nervous system
what do the perivascular process of astrocytes do
form a layer around the capillaries of CNS which is part of the blood brain barrier
what are the types of astrocytes
- fibrous astrocytes
- protoplasmic astrocytes
where is fibrous astrocytes found and what are their functions
- located in white matter
- processes are attached to capillaries by perivascular feet
where are protoplasmic astrocytes found and what are their functions
- grey matter
- processes attached to Pia matte and blood vessels
- produce gilial limitations - membrane like barrier on external surface of brain and spinal cord
what are the function of astrocytes in CNS
- physical support to neurons
- maintain metabolic environment for neurones
- store glycogen
- maintain blood brain barrier
- maintain K+ ion concentration in extracellular spaces of brain and spinal cord via potassium spatial buffering
describe the blood brain barrier
- endothelium of CNS capillaries
- tight unction between adjacent endothelium cells prevent non-selective passage
- basal lamina of endothelial cells of CNS
- limiting membrane of perivascular gila formed from projections of astrocytes forming surface of capillaries
what is gliosis
proliferation of astrocytes to heal the damaged zones of nervous tissue
what brain tumour is the most common in adults
fibrous astrocytoma
what is the structure of ependymal cells
- cuboidal to columnar shape
- arrangement resembles epithelium but have no basal lamina
where are ependymal cells found
most cavities
what is the choroid plexuses lined with
choroid epithelial cells that secrete cerebrospinal fluid
what is the floor of 3rd ventricle lined with
tanycytes
what is the function of tanycytes
- monitor levels of metabolites - glucose
- transfer chemical signals from CSF to CNS
- form link from CNF to neuroendocrine events
what are microglia derived from
mesoderm - bone barrow - blood monocytes
what is the structure of microglia
- smaller neuroglia in CNS
- elongated nuclei and few cytoplasmic processes
what are the functions of microglia
- phagocytic cells
- proliferation in response to nervous tissue injuries and disease
what are nerve fibres derived from
glial cells
what are the types of nerve fibres
unmyelinated
myelinated
where are unmyelinated nerve fibres found
autonomic nervous system
what are unmyelinated never fibres characterised by
low speed of carrying out nervous impulses ( 0.5 - 3 m/s)
how are unmyelinated nerve fibres formed
dipping the axial cylinder in the cytoplasm of Schwann cells
where are myelinated nerve fibres found
CNS and PNS
what is characterised by myelinated nerve fibres
high speed of carrying our impulse ( 5-120 m/s)
what produces myelin
oligodendrocytes in CNS and scywann cells in PNS
what is myelin composed of
80% phospholipids
20% proteins
water
what are the functions of myelin
- protect and support axons
- insulate axons
- increase nerve conduction by saltatory conduction
- neurilemmal sheath players major role in nerve regeneration
what are nodes of ranvier
unmyelinated regions between adjacent myelinated segments of the axons in CNS and PNS
what is the function of node of ranvier
contain large amount of Na+ channels allowing saltatory conduction to increase the velocity of action potentials
what is internodium
section of myelin sheath between two ranvier nodes
what is the function of internodium
high concentration of voltage gated sodium channels for saltatory conduction of action potential
what are Schmidt-lantermann openings
residues of cytoplasm in Schwann cells in concentric myelin layers
what is salutatory conduction
action potential jumps from node to node
what is demyelination
process in with myelin sheaths of nerves become damaged which impairs electrical conduction
