The neuron is the basic functional
unit of the nervous system. It has an enlarge portion, the cell body
(perikaryon), containing the nuclus, from the body extend several process
called dendrites through which impulses enter from their branches into the axon. The axon is surrounded by the
myelin sheath, which forms a whitish, non- cellular, fatty layer around the
axon. Outside the myeline sheath is a cellular layer called the neurilemma or
sheath of schwann cells. The myelin
medullary sheath. The medullary sheath is interrupted at interval by
nodes of Raniver.
unit of the nervous system. It has an enlarge portion, the cell body
(perikaryon), containing the nuclus, from the body extend several process
called dendrites through which impulses enter from their branches into the axon. The axon is surrounded by the
myelin sheath, which forms a whitish, non- cellular, fatty layer around the
axon. Outside the myeline sheath is a cellular layer called the neurilemma or
sheath of schwann cells. The myelin
medullary sheath. The medullary sheath is interrupted at interval by
nodes of Raniver.
Synapse
Nerve impulses pass from neuron to neuron at synapse.
A presynaptic neuron brings the impulse to the synapse while the postsynaptic
stimulated or inhibited. The impulse then travels along the axon to the axon
terminal. Axon usually have several rounded synaptic knobs at their terminal,
which dendrites lack.
A presynaptic neuron brings the impulse to the synapse while the postsynaptic
stimulated or inhibited. The impulse then travels along the axon to the axon
terminal. Axon usually have several rounded synaptic knobs at their terminal,
which dendrites lack.
These knobs have arrays of membranous sacs called
synaptic vesicles, that contain neurotransmitter molecules. When a nerve
impulse reaches a synaptic knob, voltage sensitive calcium channels open and
calcium diffuses inward from the extra cellular fluid. The increased calcium
concentration inside the cell initiates a series of events that fuses the
synaptic vesicle with the cell membrane which release their neurotransmitter by exocytosis.
synaptic vesicles, that contain neurotransmitter molecules. When a nerve
impulse reaches a synaptic knob, voltage sensitive calcium channels open and
calcium diffuses inward from the extra cellular fluid. The increased calcium
concentration inside the cell initiates a series of events that fuses the
synaptic vesicle with the cell membrane which release their neurotransmitter by exocytosis.
Properties of neuron
1.
Irritability
Irritability
2.
Conduction
Conduction
Classification
1. Functionally
(i) Sensory (Afferent) carry
impulses from the sense organ to the CNS
impulses from the sense organ to the CNS
(ii) Motor (Efferent) carry
impulses from the CNS to the effector organs (muscle).
impulses from the CNS to the effector organs (muscle).
(iii) Mixed (associated)
interneuron – both sensory and motor
interneuron – both sensory and motor
2) Structurally
– Unipolar
– Bipolar
– multipolar
1) Multipolar neurons: Multipolar neuron
has many processes arising from their cell bodies. Only one is the axon the
rest is the dendrites. located- in the CNS(Brain and spinal cord).
has many processes arising from their cell bodies. Only one is the axon the
rest is the dendrites. located- in the CNS(Brain and spinal cord).
2) Bipolar neurons: The cell body of a bipolar neuron has only two
processes, one arising from the either end. Locations: – ears, eyes and nose.
processes, one arising from the either end. Locations: – ears, eyes and nose.
3) Unipolar neuron: Each unipolar neuron has a single process extending
from the cell body.
from the cell body.
