7. CONTROL AND COORDINATION
In organisms, many movements are responses to changes in the environment or to use changes in environment. E.g.
- Plants grow out into the sunshine.
- Children get pleasure and fun out of swinging.
- Buffaloes chew cud for better digestion.
- Falling light on eyes or touching a hot object cause responses.
Such movements
are carefully controlled and coordinated by specialised tissues. Also, they are connected to recognition of
various events in the environment.
ANIMALS -
NERVOUS SYSTEM
In animals, control and
coordination are provided by nervous and muscular tissues.
Nervous tissue is made up of a
network of nerve cells (neurons). It conducts information (electrical
impulses) from one part of the body to another.
Some nerve cells have specialised
tips called receptors. They are usually located in sense organs. They
detect information from environment. E.g. gustatory
receptors detect taste, olfactory receptors detect smell.
General perception of taste is
jointly created by tongue (taste) and nose (smell). That’s why if nose is
blocked or we have cold, there is a difference in taste of foods.
Transmission of nerve impulse
Information from receptors
→ dendritic tip of nerve cell → sets off a chemical reaction → generation
of electrical impulse → impulse to cell body → axon → axonal
end releases some chemicals → chemicals cross the gap (synapse) → generation
of electrical impulse in dendrite of the next neuron → impulses deliver to muscles
cells or gland.
What happens in Reflex
Actions?
Reflex actions are sudden
unconscious actions of the body in response to a stimulus in the environment.
E.g.
o Withdrawal of
hand when we touch a flame.
o Blinking of eyes
when light falls on them.
Here there is no thinking as
it needs an immediate response.
Thinking needs complicated interaction
of many nerve impulses from many neurons.
In brain, thinking tissue sits
in the forward end of the skull. It receives signals from all over the body and
thinks about before responding to them.
If thinking part is to
instruct muscles to move, nerves must carry this signal back to different parts
of the body. It takes much time and prevents quick response. E.g. when we touch
a hot object, it would take much time to withdraw the hand if thinking tissue
is involved.
The pathway of impulses in a
reflex action is called reflex arc. It includes receptor, sensory
neuron, CNS, motor neuron & effector (muscle or gland).
Nerves from all body parts meet in spinal cord
on their way to the brain.
Reflex arcs evolved as
efficient ways of functioning in the absence of true thought processes in
animals. However, after complex neuron networks have evolved, reflex arcs
continue to be more efficient for quick responses.
Sequence of events (reflex
arc) of focussing bright light on eyes are given below:
Receptor → Sensory neuron →
Brain → Motor neuron → Eye → Eye muscle contracts.
Human Brain
Brain & spinal cord
constitute the central nervous system (CNS). They receive information
from all parts of the body and integrate it.
Brain is protected in a fluid-filled balloon (shock absorber) inside the bony
box (cranium).
Spinal cord is protected in vertebral
column or backbone.
Brain is the main coordinating centre of the body.
It involves more complex mechanisms & neural connections for complex
processes such as thinking.
Spinal cord contains nerves
which supply information to think about.
Brain sends messages to
muscles to control voluntary actions such as writing, talking, moving, clapping
etc.
Communication between CNS and
other parts of the body is facilitated by the peripheral nervous system (PNS).
It consists of cranial nerves (from brain) and spinal nerves (from
spinal cord).
Brain has 3 regions: forebrain,
midbrain & hindbrain.
Forebrain is the main
thinking part of the brain. It has the following regions:
o Sensory regions: which receive
sensory impulses of hearing, smell, sight etc.
o Association areas: They interpret sensory
information by associating with information from other receptors and previously
stored information. Thus, a decision is made to respond. This information is passed
to the motor areas which control the movement of voluntary muscles.
o Centre of hunger: It gives sensations such as
feeling full when food is eaten.
In our
body, there are involuntary actions between simple reflex actions and
thought-out actions. We do not have thinking control on them. E.g. salivation,
heartbeat etc. They are controlled by mid-brain and hind-brain.
Medulla in hindbrain
controls involuntary actions such as blood pressure, salivation, vomiting etc.
Cerebellum in hindbrain controls
voluntary actions like walking, riding a bicycle, picking up a pencil etc. It also
maintains the posture and balance of the body.
How does Nervous Tissue cause Action?
When a nerve impulse reaches
the muscle, the muscle fibres (muscle cells) move by changing their shape so
that they shorten.
Muscle cells have special proteins
that change their shape and arrangement in response to nervous electrical
impulses. This gives the muscle cells a shorter form.
Voluntary muscles: The muscles attached to
skeleton. They can be moved as we decide.
Involuntary muscles: The muscles found in visceral organs. They are not under our control.
Select Your Next Topic 👇
👉 Part 1: Animals- Nervous System
👉 Part 2: Coordination in Plants
👉 Part 3: Hormones in Animals
