Neural Control And Coordination Notes 2024-2025 PDF - M.E.S Indian School

M.E.S INDIAN SCHOOL, DOHA - QATAR Notes 2024 - 2025 Section : BOYS’ AND GIRLS’ Date : 04/12/24 Class & Div. : XI (ALL DIVISIONS) Subject: BIOLOGY Lesson / Topic:...

M.E.S INDIAN SCHOOL, DOHA - QATAR Notes 2024 - 2025 Section : BOYS’ AND GIRLS’ Date : 04/12/24 Class & Div. : XI (ALL DIVISIONS) Subject: BIOLOGY Lesson / Topic: CH21, NEURAL CONTROL AND COORDINATION xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx NEURAL CONTROL AND COORDINATION The neural system coordinates and integrates functions as well as metabolic and homeostatic activities of all the organs. Human neural system It is divided into two parts. The central nervous system (CNS) It includes brain and spinal cord. The peripheral nervous system (PNS) It includes all the nerves of the body associated with brain and spinal cord. The nerve fibers of the PNS are of two types :- 1. afferent fibers The afferent fibers transmit impulses from tissues or organs to the CNS. 2. efferent fibers The efferent fibers transmit impulses from the CNS to the concerned peripheral tissues or organs. The peripheral nervous system is divided into two divisions 1. somatic neural system Somatic neural system relays impulses from the CNS to the skeletal muscles. 2. Autonomic neural system (ANS) Autonomic nervous system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body. ANS is classified into sympathetic nervous system and parasympathetic system. F 061, Rev 01, dtd 10th March 2020 1|P a g e  NEURONS The neural system of all animals is composed of highly specialized cells called neurons. Neurons are the structural and functional unit of nervous system. Structure of neurons Neurons are formed of mainly 3 parts – cell body, dendrites and axon. The cell body contains cytoplasm with typical cell organelles. Nissl’s granules These are the granular bodies present in the cytoplasm of neurons. Dendrites Short fibers which branch repeatedly and project out of the cell body are known as dendrites. Axon This is the long fiber in the neuron. Schwan cells The special type of cells which cover the axon. Synaptic knob The bulb like structure present at the end of dendrites. These knobs contain synaptic vesicles, which contains neurotransmitters. Based on the number of axon and dendrites, the neurons are classified into 3 types. 1. Multipolar neurons These are neurons with one axon and two or more dendrites. Eg. Neurons in the cerebral cortex. 2. Bipolar neurons Neurons with one axon and one dendrite. Eg. Neurons in the retina of eye. 3. Unipolar neurons Cell body with one axon only. These types of neurons are found only in the embryonic stage. F 061, Rev 01, dtd 10th March 2020 2|P a g e  Myelinated nerve fibre Some neurons have a covering of myelin sheath around the Schwann cells of axon are known as myelinated nerve fibers. Eg. Nerve fibers of the spinal and cranial nerves. Non – myelinated nerve fibre Nerve fibers without myelin sheath around the axon. Eg. Nerve fibers in the somatic and autonomous systems. Nodes of Ranvier The gap between two adjacent myelin sheath is called nodes of Ranvier. GENERATION AND CONDUCTION OF NERVE IMPULSE:- Resting potential In a resting neuron, the axonal membrane bears an electrical charge. Normally, the external surface of the membrane is positively charged and the inner surface is negatively charged. The positive charge of external membrane is due to the high concentration of Na + ions. The inner axoplasm contains K+ ions and negatively charged organic proteins. The organic proteins are greater than K+ ions, hence inside of the axonal membrane has negative charge. F 061, Rev 01, dtd 10th March 2020 3|P a g e  At this resting stage, neurons possess an electrical potential known as resting potential. The normal resting potential is - 70mV. Sodium – potassium pump The outside of the axonal membrane contains more Na+ ions and inside has more K+ ions. The cell membrane is more permeable to K+ ions and nearly permeable to Na+ ions. However, some Na+ ions enter into the axoplasm and these ions are pumped out actively by a mechanism known as sodium – potassium pump. This pump maintains the resting potential by pumping out three Na + ions and pumping in two K+ ions at a time. Depolarization When a stimulus is applied to a neuron at resting potential, the polarity of the cell membrane changes. The sodium – potassium pump upsets for a moment, and the cell membrane becomes highly permeable to Na+ ions. The heavy influx of Na+ ions in to the membrane leads to the reversal of polarity and outside of the membrane become negatively charged and inside positively charged. This change in polarity is called depolarization. Repolarisation The change in polarity due to nerve impulse extremely short lived. The sodium – potassium pump quickly regains its activity and pumps out Na+ ions and K+ ions accumulate inside and resting potential is regained. This recovery is called repolarization. Action potential The momentary depolarization and repolarization of the axonal membrane is called action potential. The action potential can be called as the nerve impulse. The propagation of the nerve impulse is due to the alternate depolarization and repolarization of the membrane or the conduction of the action potential. F 061, Rev 01, dtd 10th March 2020 4|P a g e Impulse conduction through an axon TRANSMISSION OF NERVE IMPULSES AT THE SYNAPSE  Synapse is the junction between two neurons.  A nerve impulse is transmitted from one neuron to another through synapse.  The neuron which bring impulse to synapse is the presynaptic neuron and the neuron which receive impulse is the post synaptic neuron.  The gap in the synapse is the synaptic cleft.  Two types of synapse are present – electrical synapse and chemical synapse. 1. Electrical Synapse Here, the membranes of pre – and post synaptic neurons are very close. Electrical current can flow directly from one neuron into the other across these synapses. Impulse conduction in electrical synapse is always faster than chemical synapse. 2. Chemical Synapse  Here, the membranes of the pre – and post synaptic neurons are separated by fluid filled space called synaptic cleft.  In chemical synapses, impulse conduction occurs through chemical substances in the synapse called neurotransmitters.  The axon terminals contain vesicles filled with neurotransmitters.  When an impulse (action potential) arrives at the axon terminal, it stimulates the synaptic vesicles to break. F 061, Rev 01, dtd 10th March 2020 5|P a g e   The synaptic vesicles break to release the neurotransmitters in the synaptic cleft.  The neurotransmitters bind to the specific receptors of the post – synaptic neurons.  This binding opens ion channels and through these channels action potential reach the post synaptic neuron. Axon terminal and synapse CENTRAL NEURAL SYSTEM Brain is the central information processing organ of our body, and act as the ‘command and control system ‘. Brain controls voluntary movements , balance of the body , functioning of involuntary organs , thermoregulation , hunger , thirst , circadian rhythms of our body , activities of endocrine glands , controls vision ,hearing , speech , memory , intelligence , emotions , thoughts etc. Meninges Inside the skull brain is protected by a covering known as meninges. Meninges has three layers – outer layer is duramater, a very thin middle layer called arachnoid and an inner layer called piamater. F 061, Rev 01, dtd 10th March 2020 6|P a g e  The brain can be divided into three major parts- 1. Forebrain 2. Midbrain 3.hindbrain FOREBRAIN  The forebrain consists of cerebrum, thalamus and hypothalamus. CEREBRUM  Cerebrum is the major part of the brain.  Cerebrum is divided longitudinally into two halves, termed as the left and right cerebral hemispheres.  Corpus callosum: - The group of nerve fibers which connect the two cerebral hemispheres are called corpus callosum. Cerebral cortex  The layer of cells which cover cerebrum externally are called cerebral cortex.  The neuron cell bodies are concentrated in the cortex and it has grey in colour , so called grey matter. Cerebral medulla  The inner layer of cerebrum is medulla.  Medulla contains nerve tracts which are covered with myelin sheath, which give an opaque white appearance to the layer and hence, called white matter. F 061, Rev 01, dtd 10th March 2020 7|P a g e  Areas of cerebrum 1. Sensory area  These are concerned with perception and identification of impulses from sense organs. 2. Motor area  Give out motor information to effects organs. 3. Association area  Responsible for complex functions like intersensory associations, memory and communication. THALAMUS  Thalamus is the major coordinating centre for sensory and motor signaling.  It functions as the relay centre of impulses to and from the cerebrum. HYPOTHALAMUS Hypothalamus lies at the base of thalamus. It controls body temperature, urge for eating and drinking etc. The neurosecretary cells of hypothalamus secrete oxytocin and vasopressin. Limbic system  The inner parts of cerebral hemisphere and a group of associated deep structures like amygdala, hippocampus etc. form a complex structure called the limbic lobe or limbic system.  It is involved in the regulation of sexual behavior, expression of emotional reactions like excitement, pleasure, fear, motivation etc. MIDBRAIN Midbrain is located between the forebrain and hindbrain. Cerebral aqueduct is the canal which passes through the midbrain. Dorsal portion of the midbrain consists four round swelling called corpora quadrigemina. HINDBRAIN  The hindbrain consists of pons, cerebellum and medulla.  Pons consists of nerve tracts that interconnect different regions of the brain.  Medulla is connected to the spinal cord.  Medulla oblongata controls respiration, cardiovascular reflexes and gastric secretions. **** THE END **** F 061, Rev 01, dtd 10th March 2020 8|P a g e