A+ BIOLOGY - SSLC - Chapter 1 Sensations and Responses PDF Notes

[A+ BIOLOGY] Chapter – 1 Sensations and Responses Stimulus and responses Stimuli  The senses that evoke responses in an organism are called stimuli. Externa...

[A+ BIOLOGY] Chapter – 1 Sensations and Responses Stimulus and responses Stimuli  The senses that evoke responses in an organism are called stimuli. External stimuli  Stimuli are formed from external surrounding E.g: Heat, cold, touch, sound etc. Internal stimuli  Stimuli are formed internal E.g: Hunger, Thirst Receptors  Receptors are specialized cells in the sense organs and other parts of the body to receive stimuli.  Receptors receive stimuli and generate suitable impulses. E.g.: Photo receptors in the eye, Taste receptors in the tongue. Response  Responses occur when the impulses generated by the receptors on receiving the stimuli reach the brain. Nervous system  The nervous system controls and co-ordinates the body activity  The nervous system includes the brain, spinal cord, nerves and receptors.  Neuron is the structural and functional unit of the nervous system. TOPIC 1 Neuron (Nerve cell)  Like all other cells, the neuron also has a cell membrane, cytoplasm and nucleus. Sructure of neuron Part Peculiarity Function Dendron Short filament projecting out from the cell Carries impulses from dendrites to the cell body. body. Dendrite Branches of dendron Receives impulses from the adjacent neuron. Axon Longest filament arising from the cell body Carries impulses from the cell body to outside Axonite Branches of axon Carries impulses to the synaptic knob Synaptic knob Tip of the axonite Secretes neuro transmitter. Schwann cell Cell which encircle the axone Provide protection to neurons Myelin sheath  Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 1  [A+ BIOLOGY] Formation of myelin sheath in nerves  Myelin sheath in the nerves is formed of Schwann cells. Formation of myelin sheath in the brain and spinal cord  Myelin sheath in the brain and the spinal cord is formed of specialized cells called oligodendrocytes Functions of myelin sheath  It provides necessary nutrients and oxygen to the axon  It accelerate impulses along the axon  It acts as an electric insulator  It protects the axon from external shocks. White matter  In the brain and the spinal cord, where myelinated nerve cells are present in abundance is called white matter  The part looks like shiny white in colour. Grey matter.  The part where non-myelinated nerve cells are present is called grey matter The part looks like greyish in colour. TOPIC 2 Generation and Transmission of impulses Impulses  Nerve impulses are messages transmitted through the neurons. Ø: What is reason for the formation of impulses?  Impulses are generated when stimuli evoke changes in polarity in the plasma membrane of receptors. Ø:How are impulses transmitted through neurons? Q: Charges on either side of the plasma membrane A: This is the condition of the neuron before it receives stimulus  The plasma membrane of a resting neuron is electrically polarized. It is in a state of ionic equilibrium.  There is positive charge on the outer surface and negative charge inside the plasma membrane of the neuron. Reason: The difference in the distribution of ions (K+& Na+) helps to maintain positive charge on the outer surface and negative charge inside the plasma membrane of the neuron. Q: Change in the charges of ions when stimulated B: This is the condition when stimulus is received. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 2  [A+ BIOLOGY]  When a neuron stimulated, the ionic equilibrium in the particular part changes. As a result polarity changes and the outer surface becomes negatively charged while the inner surface becomes positively charged  This change does not persist for long. It regains its original state. C: Transmission of nerve impulse  The momentary charge difference in the axon membrane stimulates its adjacent parts and similar changes occur there too. As this process continues, impulses get transmitted through axon. Transmission of impulses  Impulses generated in the receptor cells have to reach the brain or spinal cord. When impulses reach the brain, the brain analyses them and sends appropriate direction to the muscles or glands. Then responses occur. Synapse  Synapse is the junction between two neurons or a neuron and a muscle cell or a neuron and a glandular cell. Structure of synapse Different type of synapses  Between two neuron, a neuron and a muscle cell, a neuron and a glandular cell Importance of synapse  Helps to regulate the speed and direction of impulses. Synaptic cleft  The gap between synaptic knob and dendrite is called synaptic cleft. Impulse transmission through synapse  When electric impulses from axon reach the synaptic knob a neuro transmitter (eg. Acetyl coline, dopamine) is secreated into the synaptic cleft. The neurotransmitter stimulate adjacent the adjacent dendrite or cell and new electric impulses are generated Neurotransmitter.  The chemical substance secreted from the synaptic knob.  Help to transmit the impulses to the adjacent cells through the synaptic cleft  Acetylcholine and dopamine are examples of neurotransmitters. Function of neurotransmitter  Stimulates the adjacent dendrite and create new electric impulse Flow chart: Impulse transmission from one neuron to next Neuro Dendrite  Dendron Cell body Axon Axonite Synaptic knob transmitter (Acetyl choline) Synapse Dendrite of the next neuron A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 3  [A+ BIOLOGY] Different types of Neuron  Based on the direction of impulses, neurons can be classified into sensory neurons and motor neurons. Sensory neurons  Sensory neurons carry impulses to the brain and spinal cord Motor neurons  Motor neurons carry impulses from the brain and spinal cord to various parts of the body TOPIC 3 Nerves  A groups of axons or nerve fibres covered by connective tissue constitutes a nerve Cross section of nerve  On the basis of their functions, nerves are further classified in to three. They are sensory nerve, motor nerve, mixed nerve Nerves Peculiarities Functions Sensory nerve Formed of sensory nerve fibres Carries impulses from various parts of the body to the brain and the spinal cord. Motor nerve Formed of motor nerve fibres Carries impulses from brain and spinal cord to various parts of the body Mixed nerve Formed of sensory nerve fibres and Carries impulses to and from the brain and spinal cord. motor nerve fibres TOPIC 4 Kinds of Nervous system  The nervous system consists of two parts, namely the central nervous system(CNS) and the peripheral nervous system (PNS) Nervous system Central Nervous system Peripheral Nervous system Brain Spinal cord Cranial nerves (12 pair) Spinal nerves (31 pair) Autonomous nervous system Sympathetic system Para sympathetic system TOPIC 5 Brain  Brain is the central part of nervous system. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 4  [A+ BIOLOGY] Protection of the brain  The brain is protected inside the skull made of bone.(cranium)  It is covered by a three - layered membrane called meninges.  A nutritive fluid called cerebrospinal fluid (CSF) is filled within the inner membranes of meninges and the ventricles of the brain. Cerebrospinal fluid  The cerebrospinal fluid formed from blood is reabsorbed into the blood.  It fills between the layers of meninges (brain and spinal cord), cerebral ventricles (cavities in the brain) and central canal (central part of spinal cord). Functions of the cerebrospinal fluid (CSF)  Provide nutrients and oxygen to the tissues of the brain  Regulate the pressure inside the brain  Protect the brain from injuries. Parts of the brain  Cerebrum, Cerebellum, Medulla oblongata, Thalamus and Hypothalamus Parts Location and peculiarities Function Cerebrum  The largest part of the brain.  Centre of thought, intelligence,  Numerous fissures and folds are seen memory and imagination.  Grey matter is seen in the external cortex  Evoke sensation like sight, hearing and white matter is seen in the internal and taste etc are made possible by medulla cerebrum.  Controls voluntary movements Cerebellum  The second largest part of the brain.  Coordinates muscular activities and  Seen behind the cerebrum as two flaps maintains equilibrium of the body.  Fissures and grooves are present ( body balance) Medulla oblongata  The rod shaped medulla oblongata is seen  Controls involuntary actions like below the cerebrum, located near the heartbeat, breathing etc. cerebellum.  The outer part is made up of white matter and the inner part is made up of grey matter. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 5  [A+ BIOLOGY] Thalamus  Situated below the cerebrum.  It acts as a relay station of impulses to and from the cerebrum.  Analyses impulses from various parts of the body and sends the important ones to the cerebrum. Hypothalamus  Situated just below the thalamus.  Plays a major role in the maintenance of homeostasis. TOPIC 6 Spinal Cord  Spinal cord is a tubular structure protected inside the vertebral column and it is the continuation of the medulla oblongata. Protection of spinal cord  Spinal cord protected inside the vertebral column  It is covered by a three layered membrane called meninges.  The space between the meninges and the central canal are filled with the nutritive fluid called cerebrospinal fluid. Structure of spinal cord  The outer part of the spinal cord is made up of white matter and the inner part is made up of grey matter.  There is a canal at the center of the grey matter called the central canal.  The spinal cord is connected to different parts of the body through 31 pairs of spinal nerves. Formation of spinal nerves  Spinal nerves formed from the combination of nerve fibres from its dorsal and ventral roots Ø: How does the dorsal root differ from ventral root?  Sensory impulses reach the spinal cord through the dorsal root.  Motor impulses go out of the spinal cord through the ventral root. Functions of the spinal cord  Impulses from different parts of the body are transmitted to and from brain through the spinal cord.  The spinal cord coordinates the repeated movements during walking, running etc.  The spinal cord initiates reflex action (Spinal reflex) TOPIC 7 Reflex actions  The accidental and involuntary responses towards stimuli are called reflex actions. Examples  The sudden withdrawal of legs while stepping on fire accidently.  Withdrawal of hand when it touches a thorn unknowingly.  When a house fly flies towards the eye, the eye blinks. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 6  [A+ BIOLOGY] On the basic of control center reflex actions are of two types  Spinal reflex Reflexes formed from the spinal cord are called Spinal reflex. E.g. the sudden withdrawal of legs while stepping on fire accidently  Cerebral reflex/ cranial reflex Reflexes formed from the brain are called cerebral reflexes. Eg. Winking of eyes when light suddenly falls on our eye or when objects move towards them. Reflex arc  Reflex arc is the pathway of impulses in the reflex action. Parts of reflex arc  Receptor- Part that receives the stimulus.  Sensory neuron – Carries the impulses from the receptor to the spinal cord/ Cerebrum.  Inter neuron- Connects the sensory neuron and the motor neuron.  Motor neuron - Carries the messages from the spinal cord/ Cerebrum to the effector muscles.  Effector – The action takes place in response to stimulus. Spinal reflex arc Cerebral reflex arc  Light fall on the eyes → Receptors, receive the stimuli → Impulses are formed →Sensory neuron carries impulses, to the brain →Interneuron →Motor neuron carries response to the eyes → blink our eyes. TOPIC 8 Autonomous nervous system (ANS)  The autonomous nervous system is a part of the peripheral nervous system that controls the activities beyond our conscious area.  The autonomous nervous system consists of sympathetic and parasympathetic systems. A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 7  [A+ BIOLOGY] Peripheral nervous system Autonomous nervous system Sympathetic system Para sympathetic system Physical changes during emergency situation Organ Sympathetic system parasympathetic system Pupil The pupil in the eye dilates The pupil in the eye constricts Salivary gland Production of saliva decreases. Production of saliva increases Trachea Trachea expands Trachea contracts Heart Heart beat increases Heart becomes normal Stomach Gastric activities slow down. Gastric activities becomes normal Liver Glycogen is converted to glucose. Glucose is converted to glycogen. Intestine Peristalsis in the intestine slows down. Peristalsis in the intestine becomes normal. Urinary bladder Urinary bladder regains normal state Urinary bladder contracts. Adrenal Gland Production of hormone increases Production of hormone decreases. Health of a Nervous system  A healthy nervous system is the basis of rhythmic body activities. Even minor changes in the nervous system may affect physiological activities. TOPIC 9 Diseases or defects affecting the nervous system Disease Causes Symptoms Alzheimer's  Accumulation of an insoluble protein in the  Loss of memory neural tissues of the brain. Neurons get  Inability to recognize friends and destroyed. relatives  Inability to do routine works. Parkinson’s  Destruction of specialised ganglions in the  Loss of body balance Disease brain.  Irregular movement of muscles  Production of dopamine, a neurotransmitter  shivering of the body in the brain gets reduced  Profuse salivation. Epilepsy  Continuous and irregular flow of electric  Epilepsy due to continuous muscular charges in the brain. contraction.  Frothy discharge from the mouth  Clenching of the teeth following which the patient falls unconscious.  Humanity, fraternity, fellowship (values): A complete cure through treatment is not possible for several diseases affecting the nervous system. Diseased person needs care and love. Caring with great love and consider- ation help the patient to overcome the disease easily. Prepared by: Riyas More Resources, Visit https://apluseducare.blogspot.com/ PPMHSS Kottukkara Telegram Group: https://t.me/joinchat/ELv60hbE_g9Hvimlp0s1BA Kondotty-Malappuram www.apluseducare.blogspot.com 09747944422 A+ BLOG-www.apluseducare.blogspot.com or Whatsapp 9746544422 8