The Nervous System Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 10 The Nervous System Notes, Summary, Definition, Diagram. The Nervous System Notes.
INTRODUCTION-
Nervous system provides an organised network of point-to-point connections for quick coordination.
Function of Nervous System-
→ Controls all voluntary muscular activity (running, writing)
→ Regulates involuntary activities (breathing, heartbeat)
NEURON-
– Highly specialised cells
Structure of Neuron –
i.) Cell body (perikaryon/cyton)-
- Well defined nucleus present with granular cytoplasm known as Nissl’s Granules.
- Centrosome absent
ii.) Dendrites (Dendron) –
- Branched cytoplasmic projection of cell body
- Fibres transmit impulse towards cell body
iii.) Axon –
- Long fibres, branched at distil end
- Size-few millimetres to more than 1 metre in length
- Surrounded by insulating sheath known as Myelin sheath which is covered by Neurolemma.
- The gap between 2 myelin sheath is called “Nodes of Ranvier”.
- Axons with side branches known as collaterals.
- Each axon terminates with a bulb like structure which contain chemicals called Neurotransmitters.
- Gap between 2 synaptic cells are called “synaptic cleft/synaptic gap”.
Transmission of Nerve impulse-
i.) Polarised / Resting state –
- Positive charge
- More Na+ ions outside the axon membrane
ii.) Depolarisation / Exciting state –
- Occurs on stimulaton
- More permeable to Na+, which move inward and cause loss of polarisation
iii.) Repolarisation / Recovery state-
- Active transport of Na+ ions outside
This transport is achieved by “sodium pump” using ATP as energy.
Synapse – point of contact between 2 different neuron, i.e one terminal end with dendrite of another neuron.
Acetylcholine – releases new impulse in dendrites
Types of Neurons-
a.) Sensory neurons- carry impulse from sense organ (receptors) to main nervous (brain or spinal cord)
b.) Motor neuron- carry impulse from main nervous to effector (muscle or gland)
c.) Associated neuron (connecting)- connect sensory and motor neurons present in brain and spinal cord.
Nerve – thread like white structure emerging from brain and spinal cord and branch to all parts of body.
a.) Sensory nerve
b.) Motor nerve
c.) Mixed nerve (both sensory and motor fibres)
NERVOUS SYSTEM
I.) CNS (central nervous system) – Brain and Spinal cord
a.) Brain- adult brain -1.35kg weight and 80% water and 25% oxygen.
- Meninges (covering) –
– Duramater- outermost tough fibres membrane
– Arachnoid- thin delicate middle layer, web-like cushion
– Piamater – innermost highly vascular membrane
- Cerebrospinal fluid- watery fluid present in the space between the covering membrane which act like a cushion to protect brain.
3 region
i.) Forebrain –
a) Cerebrum –
- Largest portion of brain
- 2 hemisphere (cortex and medulla)
- Cortex – grey matter- (outer side )contains cell bodies
- Medulla – white matter- (inner side) contains axons and nerve fibres
- Copus Callosum- “hard body” – transfer information from one hemisphere to another.
- Function – intelligence, consciousness and will power, control all voluntary actions
b.) Diencephalon-
- Thalamus (relays pain and pressure impulses to cerebrum)
- Hypothalamus (control body temperature and pituitary )
II.) Mid-brain- small tubular part
III.) Hindbrain-
a) Cerebellum-
- Smaller area of the brain
- Maintain balance of body and co-ordinate muscular activity
- Proper co-ordination and timing of their contraction and relaxation.
b) Pons- located in centre of brain, carries impulse from 1 hemisphere to another.
c) Medulla oblongata-
- Lowest portion of brain
- Controls the activities of internal organs (involuntary action)
b) Spinal cord-
– grey matter (inside)
– white matter (outside)
– Functions- reflexes below neck, carries both sensory and motor impulse.
II.) PNS- (Peripheral nervous system)- nerves which carries impulse to and from CNS.
a) Somatic nervous system-
i.) Cranial nerves-
– from brain
– 12 pais of cranial nerve
– Olfactory, optic,auditory
ii.) Spinal nerves-
– Emerges from spinal cord
– 31 pairs total ( 8 pairs neck region, 12 pairs throax region, 5 pair lumbar region, 5 pair sacral region, 1 pair coccygeal region)
– 2 roots = dorsal and ventral root from which spinal nerves originates.
b) Autonomic nervous system-
– Consist of pair of chains of nerves and ganglia
– Controls involuntary actions of internal organs
– Influenced by emotions
i.) Sympathetic
– arises from spinal cord between neck and waist region
– stimulated by adrenalne
– prepare for action
ii.) Parasympathetic
– Present at anteriorly in head and neck and posteriorly in sacral region
– Prepares for relaxation
TYPES OF ACTIONS-
i.) Volunatary action- conscious
ii.) Involuntary action – performed unconsciously
Reflexes – (involuntary action)
– Shivering, sudden withdrawal of hand, etc
I.) Types of reflexes-
a) Natural (inborn) reflex- blinking, coughing, sneezing
b) Condition (acquired ) reflex- developed by experience, playing instrument, tie shoe laces
Pavlov’s experiment on a dog
→ He gave food and the dog salivated
→ He rang a bell but no effect and dog didn’t salivate
→ He rang the bell and showed the food, dog salivated
→ Now even without food, by just ringing the bell , dog salivate because of the condition reflex.
Reflex arc-
Shortest route that can be taken by an impulse from receptor to effector.
PATH OF REFLEX
All reflex are involuntary but not all involuntary actions are reflexes.
GLOSSARY-
1.) Stimulus- agent or sudden external/internal environmental changes
2.) Response- change in organism due to stimulus
3.) Impulse – electrical disturbance, wave irritability
4.) Ganglia- aggregates of cell body
Meningitis- inflammation of meninges.
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