CHAPTER
21
NEURAL CONTROL
AND COORDINATION
, - Neural (Nervous) system is a system that controls and coordinates the
body activities, conducts and integrates the information and responds to
stimuli.
- It includes brain, spinal
cord and nerves.
- It is made up of specialized
cells known as neurons.
Neuron is the structural and functional unit of neural system. It is com-
posed of Cell body (cyton): Contains cytoplasm, cell organelles and Nissl’s
granules (granular bodies).
Dendron: Short fibres projecting from the cyton. Their sub branches (den-
drites) transmit impulses towards the cyton.
Axon: A long fibre which transmit impulses away from the cell body. The
branching of axon is called axonite. Each axonite ends as a bulb-like
structure called synaptic knob.
Types of Neurons
Unipolar: One axon. No Dendron. Found in embryo.
Bipolar: One axon and one dendron. Found in the retina.
Multipolar: One axon and 2 or more dendrons. Most common type. Found
in the cerebral cortex.
Types of axon
Myelinated axon: It is enveloped with Schwann cells that form a myelin
sheath around the axon. Found in spinal & cranial nerves.The white co-
loured area, formed of myelinated nerve fibres is called white
matter. Gaps b/w 2 adjacent myelin sheaths are called nodes of Ranvier.
anand_mani16 DR. Anand Mani https://www.anandmani.com/ https://discord.io/anandmani t.me/anandmani001
, Non-myelinated axon: Schwann cells present but no myelin sheath. The
gray coloured area without myelin sheath is called gray matter. Found in
autonomous & somatic neural systems.
GENERATION & CONDUCTION
OF NERVE IMPULSES
Impulse transmission is electrochemical. It has 3 steps:
1. Maintenance of resting membrane potential
- Neural membrane contains various selectively permeable ion channels.
- In a resting neuron (neuron not conducting impulse), the axonal mem-
brane is more permeable to K+ ions and nearly impermeable to Na+ ions.
Also, the membrane is impermeable to negatively charged proteins in axo-
plasm.
- Therefore, concentration of K+ and –vely charged proteins in axoplasm is
high and concentration of Na+ is low.
- The fluid outside the axon contains low concentration of K+ and high con-
centration of Na+. This forms an ionic or concentration gradient across rest-
ing membrane.
- The ionic gradients are maintained by the active transport of ions by the
Na-K pump. It transports 3 Na+ outwards for 2 K+ into the cell. As a result,
the outer surface becomes positively charged and inner surface becomes
negatively charged (i.e, polarized).
- The electrical potential difference across the resting plasma membrane is
called as the resting potential.
2. Action Potential
- When a stimulus is applied, the membrane at the site A becomes per-
meable to Na+. This causes rapid influx of Na+ and reversal of the polarity
at that site (outer negative and inner positive). It is called depolarization.
anand_mani16 DR. Anand Mani https://www.anandmani.com/ https://discord.io/anandmani t.me/anandmani001
21
NEURAL CONTROL
AND COORDINATION
, - Neural (Nervous) system is a system that controls and coordinates the
body activities, conducts and integrates the information and responds to
stimuli.
- It includes brain, spinal
cord and nerves.
- It is made up of specialized
cells known as neurons.
Neuron is the structural and functional unit of neural system. It is com-
posed of Cell body (cyton): Contains cytoplasm, cell organelles and Nissl’s
granules (granular bodies).
Dendron: Short fibres projecting from the cyton. Their sub branches (den-
drites) transmit impulses towards the cyton.
Axon: A long fibre which transmit impulses away from the cell body. The
branching of axon is called axonite. Each axonite ends as a bulb-like
structure called synaptic knob.
Types of Neurons
Unipolar: One axon. No Dendron. Found in embryo.
Bipolar: One axon and one dendron. Found in the retina.
Multipolar: One axon and 2 or more dendrons. Most common type. Found
in the cerebral cortex.
Types of axon
Myelinated axon: It is enveloped with Schwann cells that form a myelin
sheath around the axon. Found in spinal & cranial nerves.The white co-
loured area, formed of myelinated nerve fibres is called white
matter. Gaps b/w 2 adjacent myelin sheaths are called nodes of Ranvier.
anand_mani16 DR. Anand Mani https://www.anandmani.com/ https://discord.io/anandmani t.me/anandmani001
, Non-myelinated axon: Schwann cells present but no myelin sheath. The
gray coloured area without myelin sheath is called gray matter. Found in
autonomous & somatic neural systems.
GENERATION & CONDUCTION
OF NERVE IMPULSES
Impulse transmission is electrochemical. It has 3 steps:
1. Maintenance of resting membrane potential
- Neural membrane contains various selectively permeable ion channels.
- In a resting neuron (neuron not conducting impulse), the axonal mem-
brane is more permeable to K+ ions and nearly impermeable to Na+ ions.
Also, the membrane is impermeable to negatively charged proteins in axo-
plasm.
- Therefore, concentration of K+ and –vely charged proteins in axoplasm is
high and concentration of Na+ is low.
- The fluid outside the axon contains low concentration of K+ and high con-
centration of Na+. This forms an ionic or concentration gradient across rest-
ing membrane.
- The ionic gradients are maintained by the active transport of ions by the
Na-K pump. It transports 3 Na+ outwards for 2 K+ into the cell. As a result,
the outer surface becomes positively charged and inner surface becomes
negatively charged (i.e, polarized).
- The electrical potential difference across the resting plasma membrane is
called as the resting potential.
2. Action Potential
- When a stimulus is applied, the membrane at the site A becomes per-
meable to Na+. This causes rapid influx of Na+ and reversal of the polarity
at that site (outer negative and inner positive). It is called depolarization.
anand_mani16 DR. Anand Mani https://www.anandmani.com/ https://discord.io/anandmani t.me/anandmani001
