Kerala SSLC Biology Chapter 1 Notes Sensations and Responses English Medium
The senses that evoke responses in organisms are called stimuli. There are many receptors in sense organs and other parts of the body to receive stimuli. Normally, responses occur when the impulses generated by the receptors on receiving the stimuli reach the brain. The nervous system controls and co-ordinates these actions. All responses do not happen consciously. In emergency situations our body responds accidentally and involuntarily. This chapter deals with response and nervous system that co-ordinate life activities in detail.
→ Receptors are specialized cells in the sense organs and other parts of the body to receive stimuli.
→ The nervous system includes the brain, spinal cord, nerves and receptors.
→ Neuron: The structural and functional unit of the . nervous system.
→ Dendron : The part projecting out from the cell body. It carries impulses from dendrites to the cell body.
→ Axon : Longest filament from the cell body. It carries impulses from the cell body to outside.
→ Dendrite : Branches of dendron
→ Axonite : Terminal branches of axon
→ Synaptic knob : Tip of the axonite
→ Myelin sheath : Axon of most of the neurons are covered by the myelin sheath, a membrane having a lipid called myelin.
→ Myelin sheath in the nerves is formed of Schwann cells.
→ Myelin sheath in the brain and the spinal cord is formed of specialized cells called oligodendrocytes.
→ Synapse : The junction between two neurons or a neuron and a muscle cell or a neuron and a glandular cell.
→ Sensory nerve : Carries impulses from various parts of the body to the brain and the spinal cord.
→ Motor nerve : Carries impulses from brain and spinal cord to various parts of the body.
→ Mixed nerve : Carries impulses to and from the brain and spinal cord.
→ Central nervous system : Consists of brain and the spinal cord.
→ Peripheral nervous system : Consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
→ Cerebrum : The largest part of the brain. Centre of thought, intelligence, memory and imagination.
→ Cerebellum : Seen behind the cerebrum as two flaps. Coordinates muscular activities and maintains equilibrium of the body.
→ Reflex action : The accidental and involuntary responses towards stimuli.
→ Reflex arc : Pathway of impulses in the reflex action.
→ Interneuron : The neuron that connects the sensory neuron and the motor neuron.
→ Activities that take place beyond the conscious level are controlled by the autonomous nervous system.
→ The autonomous nervous system: Contains the sympathetic system and the parasympathetic system.
→ Alzheimer’s, Parkinson’s, Epilepsy, etc. are diseases affecting the nervous system.
→ Alzheimer’s : Accumulation of an insoluble protein in the neural tissues of the brain. Neurons get destroyed.
→ Parkinson’s : Destruction of specialised ganglions in the brain. Production of dopamine, a neurotransmitter in the brain gets reduced.
→ Medulla oblongata : Controls involuntary actions like heart beat, breathing etc.
→ Epilepsy : Continuous and irregular flow of electric charges in the brain.