The document summarizes the neural and endocrine systems. It describes how the central nervous system is connected to the peripheral nervous system via afferent and efferent nerves. It also explains the basic structure and function of neurons, including their cell bodies, dendrites, axons, and how nerve impulses are transmitted through myelinated and unmyelinated fibers. Synaptic transmission between neurons is discussed.

2. NEURAL SYSTEM & ENDOCRINE SYSTEM

3.  The neural
system of
all animals
is composed
of highly
specialised
cells called
neurons.

4. Central nervous peripheral
nervous
system (CNS)
system(PNS)


7. The afferent nerve fibres transmit impulses
from tissues/organs to the CNS.
The efferent fibres transmit regulatory
impulses from the CNS to the concerned
peripheral tissues/organs. relays impulses
The somatic neural systemrelays impulses ;-
CNS skeletal muscles.
 The autonomic neural systemtransmits
impulses;- CNS involuntary organs and
smooth muscles of the body.

8. 1) Myelinated Nerve Fibres (with myelin sheth)
2)Nonmyelinated Nerve Fibres(without myelin sheth)

9.  A neuron is a microscopic structure composed of
followings:-
 i) Cell body
 ii) Dendrites
 iii) Axon
 The cell body contains cytoplasm with typical cell
organelles and certain granular bodies called
Nissl’s granules.
 Short fibres which branch repeatedly and project
out of the cell body also contain Nissl’s granules and are
called dendrites.
 These dendrites transmit impulses towards the cell
body.

10.  The axon is a long f iber, t he dist al end of which is
branched. Each branch t erminat es as a bulb-like
st ruct ure called synapt ic knob.
 I t cont ains synapt ic vesicles cont aining chemicals
called neurot ransmit t ers.
 The axons t ransmit nerve impulses away f rom t he cell
body t o a synapse or t o a neuromuscular j unct ion.
 The myelinat ed nerve f ibres are enveloped wit h
Schwann cells, which f orm a myelin sheat h around t he
axon.
 The gaps bet ween t wo adj acent in myeline sheat hs are
called nodes of Ranvier.

14. DIAGRAMMATIC REPRESENTATION OF NERVE
IMPULSE

15.  The elect rical pot ent ial dif f erence across t he plasma
membrane at t he sit e A is called t he action potential,
which is in f act t ermed as a nerve impulse.
 At sit es immediat ely ahead, t he axon (e.g., sit e B)
membrane has a posit ive charge on t he out er surf ace
and a negat ive charge on it s inner surf ace.
 As a result , a current f lows on t he inner surf ace
f rom sit e A t o sit e B. On t he out er surf ace current
f lows f rom sit e B t o sit e A t o complet e t he circuit of
current f low. Hence, t he polarit y at t he sit e is
reversed,
 An act ion pot ent ial is generat ed at sit e B. Thus, t he
impulse (action potential) generat ed at sit e A arrives

16.  The sequence is repeat ed along t he length of the
axon and consequent ly t he impulse is conducted.
 The rise in t he st imulus-induced permeabilit y t o Na+
is ext remely short lived.
 I t is quickly f ollowed by a rise in permeability to
K+. Wit hin a f ract ion of a second, K+ diffuses
out side t he membrane and rest ores t he resting
potential of the membrane at t he sit e of excit at ion
and t he f ibre becomes once more responsive t o
f urt her stimulation.

18.  A nerve impulse is transmitted from one neuron to
another through junctions called synapses.
 A synapse is formed by the membranes of a
 pre-synaptic neuron and a post-synaptic neuron,
which may or may notbe separated by a gap called
synaptic cleft.

19.  At electrical synapses, the membranes of pre- and post-
synaptic neurons are in very close proximity.
 Electrical current can flow directly from one neuron
into the other across these synapses.
 Transmission of an impulse across electrical synapses
is very similar to impulse conduction along a single
axon.
 Impulse transmission across an electrical synapse is
always faster than that across a chemical synapse.