Biology Short Notes and Video Lectures : Control and Co-Ordination (Nervous System)

Living organisms respond and react to various stimuli like heat, light, cold, touch, pressure etc. Plants and animals both respond to stimuli but in different manner. These different Reactions are helpful for control and Co-ordination between the body and the environment .

Example : Withdrawl of hand on touching a hot object.

Click Here to revise Endocrine System

It is brought about in all animals with the help of two main systems

1. Nervous System
2. Endocrine System

Functions

i) To receive the information from environment

ii) To receive the information from various body parts. (Stimuli Response)

iii) To act accordingly through muscles and glands

Stimulus : Any change in environment or within that brings about the reaction ex: touching a hot plate.

Response : The reaction of our body to these changes. ex. withdrawal of our hand

Neuron : Structural and functional unit of nervous system.

Parts of Neuron

• Cyton or cell body: It  is somewhat star-shaped; with many hair-like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.
• Axon: This is the tail of the neuron. It ends in several hair-like structures; called axon terminals. The axon terminals relay nerve impulses.
• Myelin Sheath: There is an insulator cover around the axon called myelin sheath. The myelin sheath insulates the axon against nerve impulses from the surroundings.

Types of Neuron

• Sensory neuron: These neurons receive signals from a sense organ.
• Motor neuron: These neurons send signals to a muscle or a gland.
• Association neuron: These neurons relay the signals between sensory neuron and motor neuron.

Reflex Action:

Reflex action is a special case of involuntary movement in voluntary organs. When a voluntary organ is in the vicinity of a sudden danger, it is immediately pulled away from the danger to save itself. For example; when your hand touches a very hot electric iron, you move away your hand in a jerk. All of this happens in flash and your hand is saved from the imminent injury. This is an example of reflex action.

• Human brain is a highly complex organ; which is mainly composed of the nervous tissue.
• The tissues are highly folded to accommodate a larger surface area in less space.
• The brain is covered by a three layered system of membranes; called meninges. Cerebrospinal fluid is filled between the meninges. The CSF provides cushion to the brain against mechanical shocks.
•  The brain is  inside the skull for optimum protection. The human brain can be divided into three regions, viz. forebrain, midbrain and hindbrain.

Cerebrum: The cerebrum is the largest part in the human brain. It is divided into two hemispheres; called cerebral hemispheres.

Functions of cerebrum:

• The cerebrum controls the voluntary motor actions.
• It is the site of sensory perceptions; like tactile and auditory perceptions.
• It is the seat of learning and memory.

Hypothalamus: The hypothalamus lies at the base of the cerebrum. It controls sleep and wake cycle (circadian rhythm) of the body. It also controls the urges for eating and drinking.

Cerebellum: Cerebellum lies below the cerebrum and at the back of the whole structure. It coordinates the motor functions. When you are riding your bicycle; the perfect coordination between your pedaling and steering control is achieved by the cerebellum.

Medulla: Medulla forms the brain stem; along with the pons. It lies at the base of the brain and continues into the spinal cord. Medulla controls various involuntary functions; like hear beat, respiration, etc.

Coordination in Plants:

Unlike animals, plants do not have a nervous system. Plants use chemical means for control and coordination. Many plant hormones are responsible for various kinds of movements in plants.

Types of movements


The movement of a plant during its growth can be directional or non-directional.

Directional movements: These are also called as tropic movements. Tropic movements are the movements which occur in the direction of the stimulus.

• Positive phototropism is seen in shoots which respond by bending towards light.  Negative geotropism is seen in shoots by growing away from the ground.


• Roots bend away from light exhibiting negative phototropism. They grow towards the ground exhibiting positive geotropism

Non- directional movements:  These are also called as nastic responses.  These are exactly the movement of plant parts.


• These movements are independent of growth.


• Plant cells must change their shape for this movement to happen.


• The movement in plants occurs in the direction opposite to the stimulus.

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