Nervous System And Brain 2024-2025 (Birla Public School)

**[Birla Public School, Doha- Qatar]** **[Academic year 2024- 2025]** **[Chapter- 7]** **[CONTROL AND COORDINATION]** Coordination is working together of various organs in a systematic way so as to produce a proper reaction to a stimulus. **[Structure of neuron]** (Unit of nervous system) Neuro...

**[Birla Public School, Doha- Qatar]** **[Academic year 2024- 2025]** **[Chapter- 7]** **[CONTROL AND COORDINATION]** Coordination is working together of various organs in a systematic way so as to produce a proper reaction to a stimulus. **[Structure of neuron]** (Unit of nervous system) Neurons are the structural and functional unit of nervous system. It is the largest cell in the body. It carries messages in the form of electrical signals called nerve impulses. It has three main components. Cell body, Dendrites and Axon. (a)Cell Body or Cyton:-It contains a central nucleus surrounding cytoplasm. Stimulus is changed into impulse in the cyton. (b)Dendrites: -They are short and branched processes connected to cell body. They receive the stimulus. (c)Axon:-It is the longest part of the neuron. It is a single, elongated fibre arising from one side of cyton. The plasma membrane of an axon is covered by a protective sheath called myelin sheath. The branched axon endings are called a nerve ending which ends in synaptic knob. At the end of the neuron electrical impulses sets off the release of the neurotransmitters from the synaptic knob, which cross the synapse and start a similar electrical impulse in the dendrite of the next neuron. **[Functions of Myelin sheath]** :-(a) It acts as an insulator (b) It increases the rate of transmission of signals (c) It protects the axon. **[Synapse]**:-It is the functional junction between two adjacent neurons or nerve cells i.e. between the axon endings of one and dendrites of the next. **[Nerve impulse]**:-It is the information in the form of chemical and electrical signals passing through neurons. **[Neuro muscular junction]**:-It is the point where a muscle fibres comes in contact with a motor neuron which carries nerve impulse from the central nervous system. Impulse transmission takes place by means of neurotransmitter. **[Receptor]**: -Cell specialized to detect a particular stimulus and initiate impulse transmission. taste (gustatory receptor), smell (Olfactory Receptor) **[Types of Neurons]**: - ([a) Sensory Neurons]: -carry impulses from the receptors to the central nervous system **[(b)Relay neurons or interneurons]**: -present in the central nervous system which act as the link between sensory neurons and motor neurons. **[(c)Motor Neurons]**: - carry impulses from the central nervous system to the effector organs i.e. muscles or glands **[Nerve Impulse transmission: -]**Receptors receive the stimulus and reaches the dendrite tip of a neuron sets off a chemical reaction which creates an electrical impulse. This impulse travels from the dendrite to the cell body, axon and finally reaches the synaptic knob. Electrical impulse sets off the release of neurotransmitters (e.g.: acetyle choline) which cross the synapse and start a similar electrical impulse in the dendrite of the next neuron. **[Reflex Action: -]** It is defined as the unconscious, involuntary, spontaneous or automatic response of effectors, to a stimulus. It is monitored through a spinal cord. [Advantages of reflex action: -] It enables the body to give quick responses to harmful stimuli and protects our body. It minimizes the overloading of the brain. **[Reflex Arc]**: - It is the pathway taken by the nerve impulses and responses in a reflex action. Stimulus\-\--🡪Receptors\--🡪Sensory neurons\-\-\--🡪Spinal cord\--🡪Motor Neurons\-\-\-\--🡪Effectors\-\-\-\-\--🡪Response [Mechanism of reflex action(a)]Receptors receive the stimulus and activate a sensory neuron (b)Sensory neuron carries the message in the form of sensory impulse to the spinal cord. (c)Spinal cord acts as a modulator. Relay neurons transmit the impulse to the motor neuron (d)Motor neuron conducts the impulses to the effectors. **[HUMAN NERVOUS SYSTEM]** - It is divided into Central nervous system and Peripheral nervous System - [Central nervous system] consists of brain and spinal cord - [BRAIN: -] It is highest coordinating Centre in the body. It is protected inside the bony box called [cranium.] It is surrounded by three membranes called meninges. The space between the membranes is filled with a [cerebro spinal fluid] which protects the brain from mechanical shocks.12 pairs of cranial nerves arising from the brain. Brain is divided into three main regions: forebrain[, midbrain and hind brain]. Forebrain consists of cerebrum and hypothalamus. Midbrain does not have any further divisions. Hind brain is divided into cerebellum, Pons and medulla oblongata. **[FORE BRAIN-Cerebrum:-]**It is the largest part of the brain. [Cerebrum] is the main thinking part of the brain. It has two sensory areas and motor areas. Sensory areas receive information from the sense organs. Motor areas send information to the various muscles of the body. Hypothalamus controls body temperature, regulates hunger, thirst etc. **[MID BRAIN:-]**It controls reflex movements of the head, neck, and trunk in response to visual and auditory stimuli. **[HIND BRAIN:]** - - [Pons] takes part in regulating respiration. - [Cerebellum] helps in maintaining posture and balance of the body. It is responsible for precision of voluntary actions such as walking in a straight line, riding a bicycle, picking up a pencil etc. - [Medulla oblongata] is the regulating Centre for blood pressure, breathing, swallowing, coughing, sneezing and vomiting **[FUNCTIONS OF BRAIN]** (a)It correlates the various stimuli. (b)It stores information so that behavior can be modified according to the past experience. (c)It coordinates body activities. (d)It responds to the impulses brought by sensory organs **SPINAL CORD:[-]**It is a cylindrical structure and part of the central nervous system. It begins in continuation with medulla oblongata and extends downwards. It is enclosed in a bony cage called a vertebral column. It is also surrounded by meninges.31 pairs of spinal nerves arising from the spinal cord. [ ] **Functions: -** (a) Main Centre of reflex action (b) It is concerned with the conduction of nerve impulse to and fro from the brain. **Peripheral Nervous System[:]** - It consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. 1. **What is the role of brain in the reflex action?** **Reflex action takes place in the spinal cord**. Reflex actions are sudden involuntary responses which does not involve thinking. For example, when we touch a hot object, we withdraw our hand immediately without thinking. The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves and responding to it quickly is known as reflex arc. **Reflex arcs are formed in the spinal cord and the information also reaches the brain and the brain responds to it.**