IN THIS SECTION WE WILL COVER IMPORTANT KERALA SSLC BIOLOGY TOPICS,SENSATION AND RESPONSES
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🔘INTRODUCTION
The senses that evoke responses in organisms are called stimuli.
These are two types of stimuli
External stimuli are stimuli formed outside the body eg; Sound, touch, heat, chemicals, pressure, cold, radiations.
Internal stimuli, are stimuli formed inside the body. Eg; Hunger, thirst,
Receptors; specialized cells in the sense organs and other parts of the body to receive stimuli. These cells are known as receptors.
Function; They receive stimuli and generate suitable impulses
Neuron or nerve cell ; it is the basic structural and functional unit of the nervous system
🔘Parts of neuron;
✅Dendrite
• Branches of Dendron.
FUNCTION;Part that receives impulses from adjacent neuron.
✅Dendron
• Short filament from the cell body.
FUNCTION;Carries impulses from dendrites to the cell body.
✅Axon
• Longest filament from the cell body.
FUNCTION;Carries impulses from the cell body to outside
✅Axonite
• Branches of axon.
FUNCTION; Carries impulses to the synaptic knob
Synaptic knob
• Tip of axonite.
FUNCTION;Secretes neurotransmitter.
🔘Myelin sheath;
Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath.
functions of myelin sheath
• Provide nutrients and oxygen to the axon.
• Accelerate impulses.
• Act as an electric insulator.
• Protects the axon from external shocks.
The part of neuron, where myelinated neurons are present in abundance,is called as the white matter.
The part of neuron where the cell bodies and non myelinated neurons are present, is called as the grey matter.
🔘How generation and transmission of impulses occures
The outer surface of the plasma membrane of the neuron is positively charged and the inner surface is negatively charged. This is due to the difference in the distribution of certain ions.
When stimulated, the distribution of ions in that particular part changes and hence the inner surface becomes positively charged and the outer surface becomes negatively charged .This momentary charge difference stimulates its adjacent parts and similar changes occur there too. As this process proceeds, impulses get transmitted as electric charges. Nerve impulses are messages transmitted through the neurons
🔘Synapse
It is the junction between neurons or between neurons and muscles or glands is known as the synapse. It helps to regulate the speed and direction of impulses. The impulses are transmitted across the synaptic cleft only through a chemical (neurotransmitter), secreted from the synaptic knobs.
❔Neurotransmitters; Acetyl choline and Dopamine
✔️Function; Synapse helps to regulate the speed and direction of impulses
🔘Nerves and functions
✔️Sensory nerves; Carry impulses from sense organs to the brain and spinal cord
✔️Motor nerves; Carry impulses from brain and spinal cord to different organs
✔️Mixed nerves; Carry impulses to and from brain and spinal cord to different organs
The nervous system consists of two parts
Central Nervous System; brain and spinal cord
Peripheral Nervous System; Cranial nerves (12 pairs)
– Spinal cord – Spinal nerves (31 pairs)
The brain is protected inside a hard skull and is covered by a three layered membrane, called the meninges. Cerebrospinal fluid,a fluid formed inside the meninges
🔘CSF
Cerebrospinal fluid is a fluid formed from the blood inside the meninges and reabsorbed in to the blood.
✅Functions of CSF
It provides nutrients and oxygen to brain tissues.
• Regulates the pressure inside the brain.
• Protects brain from injuries
✅Cerebrum
The largest part of the brain with many fissures and folds are seen
Function;
- centre of thought, intelligence, memory and imagination.
• evokes sensations.
• controls voluntary movements
✅Cerebellum
The second largest part. seen behind the cerebrum as two flaps
Function;Coordinates muscular activities and maintains equilibrium of the body.
✅Medulla oblongata
the rod shaped medulla oblongata is seen below the cerebrum, located near the cerebellum.
Function;
Controls involuntary actions like heart beat and breathing
✅Thalamus
It is situated below the cerebrum.
• acts as 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;
Plays a major role in the maintenance of homeostasis
Spinal cord is protected inside the vertebral column and is covered by the meninges.
✅SPINAL CORD
Spinal cord, which is the continuation of medulla oblongata, is situated with in the vertebral column and is covered by a three layered membrane, called meninges. The outer part of spinal cord is white matter and inner is grey matter. The central canal at its centre is filled with CSF. Spinal nerves originate from the spinal cord as dorsal root (sensory) and ventral root(motor).
❔functions of spinal cord.
✔️• Transmitting impulses from different parts of our body to and fro the brain.
✔️• Coordinates the rapid and repeated movements during walking, running etc.
✔️• Effects certain reflex actions
reflex actions;The accidental and involuntary responses towards stimuli are
called reflex actions
Reflex arc is the pathway of impulses in the reflex action. Mainly spinal cord acts as the centre of reflex action and such reflexes are called spinal reflexes
✅PERIPHERAL NERVOUS SYSTEM
Activities that take place beyond the conscious level are controlled by the autonomous nervous system, a part of the peripheral nervous system. The sympathetic system and the parasympathetic system together form the autonomous nervous system
✅Alzheimer’s disease
❔cause;Accumulation of an insoluble protein in the neural tissues of the
brain. Neurons get destroyed.
✔️symptoms;Loss of memory, inability to recognize friends and relatives, inability to do routine works.
✅Parkinsons disease
❔cause;Destruction of specialised ganglions in the brain. Production of dopamine, a neurotransmitter in the brain gets reduced
✔️symptoms;Loss of body balance, irregular movement of muscles, shivering of the body, profuse salivation
✅Epilepsy
❔cause;Continuous and irregular flow of electric charges in the brain.
✔️symptoms;Epilepsy due to continuous muscular contraction, frothy discharge from the mouth,clenching of the teeth following which the patient falls unconscious.
