NERVOUS TISSUE
It consists of
1,Excitable and conducting cells called neurons.
2,Supporting and non excitable neuroglia.
NEURONS
NEURONS The functional unit in both the CNS and PNS is the neuron.
PARTS OF NEURON
Most neurons have three parts:
■ The cell body or perikaryon or soma
■ Neurites i.e. Cell processes.
Neurons in cerebellar granular layer, are among the body’s smallest cells.
1.CELL BODY OR PERIKARYON OR SOMA
It acts as a trophic center, producing most cytoplasm for the processes.
It consists of:
1.Vesicular nucleus with prominent nucleolus,It is centrally placed and
removed to periphery in case of injury.
2.Cell organelles,they are same as in other cells with few exceptions as
follow:
A.Nissl substance or chromatophilic substance which are granules of
RER.Synthesizes proteins and are absent from axon hillock and axon,fatigue and
injury result in concentration NS at periphery.In damage if NS is disappeared, it is
known as chromatolysis.
B.Intermediate filaments in the form of neurofilaments fibres.
C.Melanin granules are found in the cytoplasm of cells in certain parts of the
brain e.g.,the substantia nigra of the midbrain, where there role is to produce
dopamine.
3.The plasma membrane is called neurolemma.
2.NEURITES
DENDRITES
Dendrites are short, small processes emerging and branching off the soma .
Usually covered with many synapses, dendrites are the principal signal reception
and processing sites on neurons.Dendrites cytoplasm contain all organelles
except golgi. In the CNS, most synapses on dendrites occur on dendritic
, spines, which are dynamic membrane protrusions along the small dendritic
branches.. Changes in dendritic spines are of key importance in the constant
changes of the neural plasticity.( the ability of neural networks in the brain to
change through growth and reorganization).
AXON
Most neurons have only one axon, typically longer than its dendrites.. The
plasma membrane of the axon is often called the axolemma and its contents are
known as axoplasm containing few ribosomes and abundant mitochondria.
Axons originate from a pyramid-shaped region of the perikaryon called the axon
hillock. Axons generally branch less profusely than dendrites, but do undergo
terminal arborization . Axons of interneurons and some motor neurons also have
major side branches called collaterals.Axon end by dividing into telodendria.Both
telodendria and collaterals ends with a dilation called a terminal bouton that
contacts another neuron or non-nerve cell at a synapse to initiate an impulse in
that cell.
AXONAL TRANSPORT
It is of 2 types
Rapid transport which can be either of the two types:
1.retrogade (towards the cell body)which is done by Dynein, motor
protein.Examples are activated growth factor receptors can be carried along the
axon to their site of action in the nucleus. Pinocytotic vesicles arising at the axon
terminals can be quickly returned to the cell body. Worn-out organelles can be
returned to the cell body for breakdown by the lysosomes.
2.anterograde transport(away from cell body)which is done by kinesin, another
motor protein.It refers to the transport of proteins and transmitter substances or
their precursors.
Slow transport refers to the transport of axoplasm and it is anterograde usually.
TYPES OF NEURON
ACCORDING TO NUMBER OF NEURITES
i.UNIPOLAR NEURON OR PSEUDOUNIPOLAR
Unipolar neurons are those in which the cell body has a single neurite that divides
a short distance from the cell body into two branches,one proceeding to some
It consists of
1,Excitable and conducting cells called neurons.
2,Supporting and non excitable neuroglia.
NEURONS
NEURONS The functional unit in both the CNS and PNS is the neuron.
PARTS OF NEURON
Most neurons have three parts:
■ The cell body or perikaryon or soma
■ Neurites i.e. Cell processes.
Neurons in cerebellar granular layer, are among the body’s smallest cells.
1.CELL BODY OR PERIKARYON OR SOMA
It acts as a trophic center, producing most cytoplasm for the processes.
It consists of:
1.Vesicular nucleus with prominent nucleolus,It is centrally placed and
removed to periphery in case of injury.
2.Cell organelles,they are same as in other cells with few exceptions as
follow:
A.Nissl substance or chromatophilic substance which are granules of
RER.Synthesizes proteins and are absent from axon hillock and axon,fatigue and
injury result in concentration NS at periphery.In damage if NS is disappeared, it is
known as chromatolysis.
B.Intermediate filaments in the form of neurofilaments fibres.
C.Melanin granules are found in the cytoplasm of cells in certain parts of the
brain e.g.,the substantia nigra of the midbrain, where there role is to produce
dopamine.
3.The plasma membrane is called neurolemma.
2.NEURITES
DENDRITES
Dendrites are short, small processes emerging and branching off the soma .
Usually covered with many synapses, dendrites are the principal signal reception
and processing sites on neurons.Dendrites cytoplasm contain all organelles
except golgi. In the CNS, most synapses on dendrites occur on dendritic
, spines, which are dynamic membrane protrusions along the small dendritic
branches.. Changes in dendritic spines are of key importance in the constant
changes of the neural plasticity.( the ability of neural networks in the brain to
change through growth and reorganization).
AXON
Most neurons have only one axon, typically longer than its dendrites.. The
plasma membrane of the axon is often called the axolemma and its contents are
known as axoplasm containing few ribosomes and abundant mitochondria.
Axons originate from a pyramid-shaped region of the perikaryon called the axon
hillock. Axons generally branch less profusely than dendrites, but do undergo
terminal arborization . Axons of interneurons and some motor neurons also have
major side branches called collaterals.Axon end by dividing into telodendria.Both
telodendria and collaterals ends with a dilation called a terminal bouton that
contacts another neuron or non-nerve cell at a synapse to initiate an impulse in
that cell.
AXONAL TRANSPORT
It is of 2 types
Rapid transport which can be either of the two types:
1.retrogade (towards the cell body)which is done by Dynein, motor
protein.Examples are activated growth factor receptors can be carried along the
axon to their site of action in the nucleus. Pinocytotic vesicles arising at the axon
terminals can be quickly returned to the cell body. Worn-out organelles can be
returned to the cell body for breakdown by the lysosomes.
2.anterograde transport(away from cell body)which is done by kinesin, another
motor protein.It refers to the transport of proteins and transmitter substances or
their precursors.
Slow transport refers to the transport of axoplasm and it is anterograde usually.
TYPES OF NEURON
ACCORDING TO NUMBER OF NEURITES
i.UNIPOLAR NEURON OR PSEUDOUNIPOLAR
Unipolar neurons are those in which the cell body has a single neurite that divides
a short distance from the cell body into two branches,one proceeding to some
