Nervous Tissue Flashcards
Ross & Pawlina - Nervous Tissue
What does the CNS consist of?
the brain and the spinal cord, located in the cranial cavity and spinal canal
what kind of nerves are in the PNS?
cranial, spinal and peripheral nerves, they conduct impulses from and to the CNS, ganglia and specialised nerve endings
what are neural pathways?
neural pathways are formed by interactions between sensory nerves that recieve stimuli, the CNS that interprets them and motor nerves that initiate responses
the nervous system is divided into:
- anatomically
- functionally - one further subdivided into…
- anatomically into the CNS and PNS
- Functionally into the somatic and autonomic nervous system
autonomic nervous system is further subdivided into:
1. sympathetic
2. parasympathetic
3. enteric
what are the two principal cell types of nerve tissue?
neurons
supporting cells
what are synapses?
an axon of the presynaptic neuron terminates into an enlarged tip called the bouton termnal/bulb end. synapses are specialised junctions between neurons that facilitate the transmission of impulses from one (presynaptic) neuron to the other (postsynaptic) neuron. they also occur between axons and effector cells.
they can be stained using siver preparation methods and show up as oval bodies on the surface of receptor neurons.
what are glia/neuroglial cells of the nervous tissue?
4 types in CNS
2 types in PNS
CNS: astrocytes, oligodendrocytes, microglia, ependymal cells
PNS: schwann cells, satellite cells
what are the functions of neuroglial cells? (6)
- physical support for neurons (protection)
- insulation for nerve cell bodies and processes
- repair of neuronal injury
- regulation of the internal fluid enviroment of the CNS
- clearence of neurotransmitter from the synatic clefts
- metabolic exchange between the vascular system and the neurons of the nervous system
what does the autonomic nervous system do?
what do the specific effectors in the internal organs that respond to information of the ANS include?
the ANS regulates the function of internal organs
respond sites include:
smooth muscle
cardiac conduction cells (Purkinje fibres)
Glandular epithelium
what is a neuron and how many are there in the human nervous system?
what are the thre general catagories of neurons?
the neuron is the structural and functional unit of the nervous system. there are more than 10 billion in a human NS
three catagories of neurons:
sensory neuron
motor neuron
interneuron (intercalated neuron)
what are sensory neurons?
in what fibres are the processes of these neurons included?
sensory neurons convey impulses from receptors to the CNS
somatic afferent fibres: convey sensations of pain, touch, temperature and pressure from the body surface, as well as pain and proprioreception from organs within the body
visceral afferent fibres convey pain impulses and other sensations from internal organs, mucous membranes, glands and blood vessels
what are motor neurons?
in what fibres are the processes of these neurons included?
motor neurons convey impulses from the CNS or ganglia to effector cells.
somatic efferent neurons convey voluntary impulses to skeletal muscle
visceral efferent neurons transmit involunary impulses to smooth muscle, cardiac conducting cells and glands
what are interneurons?
what is another name?
what percentage of all neurons are interneurons?
interneurons or intercalated neurons form a communications and integrating network between sensory and motor neurons.
interneurons make up about 99.9% of all neurons
what are the functional components of a neuron?
cell body (perikaryon,) dendrites (short processes that recieve impulses and transmit them toward the cell body) axon (long process that transmit impulses away from cell body) synapse (specialised terminal of axon, contacts other neurons or effector cells)
based on the number of processes, how are neurons anatomically classified and define each class?
multipolar: one axon and one or more dendrites. mostly found to be motor neurons and interneurons
bipolar: one axon and one dendrite. rare. generally receptors for special senses.
psuedounipolar: one process, an axon, that divides close to the cell body. two long axonal processes, one toward the periphery the other toward the CNS. majority are sensory neurons close to the CNS. cell bodies found in dorsal root ganglia and cranial nerve ganglia.
neuron cell body:
describe the nucleus
the neuron contains a large, euchromatic nucleus with prominent nucleolus
neuron cell body:
describe the perinuclear cytoplasm
the perinuclear cytoplasm contains abundant rER and free ribosomes - protein synthetic activity
nissl bodies can be seen, ribosomal content, small bodies that stain intensly with basic dyes. each body corresponding to a stack of rER
perinuclear cytoplasm also contains numerous mitochondria, a large golgi apparatus, lysosomes, microtubules,d neurofilaments, transport vesicles adn inclusions.
what is the axon hillock and how can it be distinguished from dendrites?
the axon hillock is the area of the cell body that is connected to the axon.
the axon hillock is devoid of any cytoplasmic organelles whereas the dentrites may contain Nissl bodies, free ribosomes and golgi .
what are dendrites?
what are the characterists of dendrites?
dendrites are short receptor processes that receive information from other neurons or from external enviroment and carry that information to the cell body.
dendrites:
generally located in hte vicinity of the cell body
have a larger diameter than axons
are unmyelinated
are usually tapered
form dendritic trees (increases receptor surface area of a neuron)
have cytoplasm similar to the perinuclear cyto;plasm of the cell body, with the exception of the presence golgi apparatus
what are axons?
what are the two types of neurons characterised by axon length?
axons are the effector processes of neurons that convey information from the cell body to another neuron or to an effector cell.
golgi type I neurons contain axons that originate in the motor nuclei of the CNS and may travel for more that a meter to their effector targets, skeletal muscles.
golgi type II neurons are interneurons of the CNS and have short axons.
what is the axon hillock and what organelles pass through it to the axon?
the axon hillock is the area between the cell body and the axon and is devoid of large perinuclear cytoplasmic organelles.
microtubules, neurotubules, vesciles and mitochindria may pass through it to the axon.
what is the initial segment of the axon?
the initial segment of the axon is the region between the apex of the axon hillock and the beginning of the myelin sheath.
it is the site where the action potential of the axon is generated.
what is the area between the apex of the axon hillock and the beginning of the myelin sheath? and why is it important?
initial segment
site where the action potential is generated
what are periaxoplasmic plaques?
discrete areas in larger axon terminals capable of local protein synthesis modulated by neuronal activity
may be involved in the processes of neuronal cell memory.
morphologically classify synapses between neurons:
axodentritic: between axons and dendrites
axosomatic: between axons and cell bodies of neurons
axoaxonic: between axons and axons
synapses are classified dependent on two critera, what are they?
what are the two classifications of synapses?
classification of synapses are dependent on:
- the mechanism of conductance of the nerve impulse
- the way the action potential is generated in target cells
synapses are classified are chemical or electrical synapses
what are chemical synapses?
conductance is achieved by the release of chemical substances (neurotransmitters) from the presynatic neuron.
neurotransmitters then diffuse across the narrow intercellular pace that separates the presynaptic neuron and postsynaptic neuron/effector cell
what are electrical synapses?
common in invertebrates. contain gap junctions that permit movements of ions between cells and consequently permit the direct spread of electrical current from one cell to another.
electrical synapse does not require neurotransmitters.
in humans this type of synapse is seen in smooth muscle and cardiac musce cells.
what 3 components does a typical chemical synapse contain?
- presynaptic element
- synaptic cleft
- postsynaptic membrane
what is the presynaptic element?
what is it characterised by?
the presynaptic element is the end of the neuron process from which neurotransmitters are released.
the presynaptic element is characterised by the presence of synaptic vesicles, membrane bound structures that range from 30-100nm in diameter and contain neurotransmitters.
describe the binding and fusion of synaptic vesicles to the presynaptic plasma membrane.
synaptic vesicles bind and fuse to the presynaptic plasma membrane mediated by a family of transmembrane proteins called SNAREs. v-SNAREs and t-SNAREs specifically.
another vesicel-bound protein (synaptotagmin I) then replaces th SNARE complex which is subsequently dimenteled and recycled by NSF/SNAP25 protein complexes.
what are active zones of the presynaptic plasma membrane?
active zones are dense accumulations of proteins present on the cytoplasmic side of the presynaptic plasma membrane. they are specialised areas where synaptic vesicles dock and release neurotransmitters into the synaptic cleft.
active zones are rich in Rab-GTPaase docking complexes, t-SNAREs and synaptotagmin binding proteins.
what is the synaptic cleft?
the synaptic cleft is the 20-30nm space separating the presynaptic element and the postsynaptic membrane or target cell, where neurotransmitters must cross.
where is the vesicle membrane added to the presynaptic membrane and retrieved by endocytosis reprocessed into synaptic vesicles?
synaptic vesicles are formed in the smooth endoplasmic reticulum located in the nerve ending.
