Class 10 Sensations and Responses Notes
Stimuli and Receptors: The senses that evoke responses in organisms are called stimuli. Receptors are specialized cells in sense organs and other parts of the body that receive stimuli and generate impulses.
Neurons and Myelin Sheath: Neurons or nerve cells are the basic structural units of the nervous system. They have a cell membrane, cytoplasm, and nucleus. Most neurons have a myelin sheath, which is formed of Schwann cells in nerves and oligodendrocytes in the brain and spinal cord. Myelin sheath accelerates impulses, acts as an electric insulator, and protects the axon.
Transmission of Impulses: Nerve impulses are messages transmitted through neurons. Impulses are generated when the distribution of ions inside and outside the neuron’s membrane changes, resulting in electric charges that propagate as impulses.
Synapse: Synapse is the junction between two neurons or between a neuron and a muscle/glandular cell. Neurotransmitters are chemical substances that facilitate the transmission of impulses across the synapse.
Types of Neurons: Neurons can be classified into sensory neurons, which carry impulses to the brain and spinal cord, and motor neurons, which carry impulses from the brain and spinal cord to various body parts.
Nervous System: The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The brain is the central part of the nervous system and is protected by the meninges and filled with cerebrospinal fluid.
Functions of Cerebrospinal Fluid: Cerebrospinal fluid provides nutrients and oxygen to brain tissues, regulates pressure inside the brain, and protects the brain from injuries.
Parts of the Brain: The brain has different parts with specific functions:
Cerebrum: Controls thought, intelligence, memory, imagination, sensations, and voluntary movements.
Thalamus: Acts as a relay station for impulses to and from the cerebrum.
Cerebellum: Coordinates muscular activities and maintains equilibrium.
Medulla Oblongata: Controls involuntary actions like heart rate and breathing.
Hypothalamus: Plays a major role in maintaining homeostasis.
Spinal Cord: The spinal cord is the continuation of the medulla oblongata, protected by the vertebral column and meninges. It contains both white and grey matter and coordinates various movements.
Reflex Actions: Reflex actions are accidental and involuntary responses towards stimuli. The reflex arc is the pathway of impulses in a reflex action, and some reflexes are controlled by the spinal cord (spinal reflexes), while others are controlled by the cerebrum (cerebral reflexes).
Autonomic Nervous System: The autonomous nervous system controls activities beyond the conscious level. It consists of the sympathetic system and the parasympathetic system.
Maintaining Nervous System Health: A healthy nervous system is crucial for normal body activities. Care should be taken to maintain its health.
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