Class X - SSLC - Biology Quick Notes : Sensations And Responses-4

  August 16, 2020   ,   Edit
Structure of our spinal cord
The spinal cord is protected inside the vertebral column. Like the brain, the spinal cord is also covered by meninges. The central canal seen in the centre of the spinal cord is also filled with cerebrospinal fluid. In the spinal cord, white matter is seen outside and grey matter is seen inside.

Functions of spinal cord include

  1. Transmitting impulses from different parts of our body to and fro the brain.
  2. Coordinates the rapid and repeated movements during walking, running etc.
  3. Effects certain reflex actions.

Reflex actions are the accidental and involuntary responses of the body, in response to a stimulus. These are two types of Reflex actions

  1. Cerebral reflexes (Example:-Blinking of eyes, sudden fright when hearing a loud noise or seeing a snake, sneezing) 
  2. Spinal reflexes (Example :- On touching hot object, the hand is withdrawn, withdrawal of the leg when a spine pierce in to the feet)


The pathway of impulses in a reflex action is Reflex arc.

Parts that involve in a reflex arc

  1. Stimulus receiving receptor
  2. Sensory neuron
  3. Inter neuron
  4. Motor neuron
  5. Effecting muscles
Inter neuron is the central neuron, which converts sensory impulse in to motor impulse.

Nerves in the peripheral nervous system that function automatically and involuntarily, is known as Autonomous nervous system.

Sympathetic and parasympathetics nervous system activate with or with out the endocrine gland system involuntarily. The contrasting actions of both systems help to maintain the normalcy of the physiological activities.
Action of Sympathetic nervous systems
Action of Parasympathetic nervous systems
Eye
Pupil dilates
Pupil constricts
Heart
Heartbeat increases
Heartbeat becomes normal
Lungs
Trachea expands
Trachea contracts
Liver
Glycogen converts to glucose
Glucose converts to glycogen
Adrenal gland
Hormone secretion increases
Hormone secretion decreases
Urinary bladder
Retain normal state
Constricts
Salivary gland
Production of saliva decreases
Production of saliva increases
Stomach
Working decreases
Increases
Intestine
Peristalsis slows down
Peristalsis increases

Alzheimer's : Caused due to continuous degeneration of neurons due to the accumulation of an insoluble protein. Complete loss of memory.

Parkinsons Degeneration of specific ganglia in the brain due to the deficiency of dopamine. Loss of body balance. Tremor in muscles, flow of saliva

Epilepsy Discharge of irregular electrical impulses from brain. Fits (due to uncontrolled muscular contractions), frothy discharge from mouth, clenching of teeth, unconsciousness

Dopamine is the neurotransmitter, which is secreted in the brain.The deficiency of dopamine may result a disease called parkinsons.
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Class X - SSLC - Biology Quick Notes : Sensations And Responses-3

  August 16, 2020   ,   Edit
The fluid which provides nutrients and oxygen to brain tissues is Cerebrospinal fluid (CSF).

Cerebrospinal fluid is a fluid formed from the blood inside the meninges and eventually reabsorbed to the blood. Functions of CSF are,

  1. CSF provides nutrients and oxygen to brain tissues.
  2. Regulates the pressure inside the brain.
  3. Protects brain from injuries.


Functional parts of human brain
Cerebrum
The largest part of the brain.
Numerous fissures and folds are seen.
The grey coloured outer part of cerebrum is called Cortex and the white coloured inner part is called Medulla.
Centre of thought, intelligence, memory and imagination.
Evokes sensations.
Controls voluntary movements

Thalamus
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.

Cerebellum
The second largest part of the brain.
Seen behind the cerebrum as two flaps.
Fissures and grooves are present.
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.
Controls involuntary actions like heart beat, breathing etc.

Hypothalamus
Situated just below the thalamus.
Plays a major role in the maintenance of homeostasis.

Many fissures and folds in the cerebral cortex  is an adaptation to include more number of neurons and there by increase the efficiency of cerebrum.

Medulla oblongata controls involuntary actions like heart beat and breathing. Any mild injury to medulla oblongata results malfunctioning of breathing and heartbeat and this may lead to death. 

Cerebellum maintains equilibrium of the body through muscular coordination.

The central nerve Spinal cord is seen as the continuation of medulla oblongata.

Spinal cord is protected inside the vertebral column and is covered by the meninges.

The  Central canal of the spinal cord is filled with cerebrospinal fluid.
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Class X - SSLC - Biology Quick Notes : Sensations And Responses-2

  August 15, 2020   ,   Edit
Synapse is the junction between neurons or between neurons and muscles or glands. 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.

The electrical messages conducted through nerves are called impulses.

Impulse is generated as follows : The difference in the distribution of ions maintains positive charge on the outer surface and negative charge inside the plasma membrane of the receptor part of neuron. When stimulated, this ionic equilibrium (polarity) changes there and the outer surface becomes negatively charged and inner become positively charged. As a result, impulse generated. This charge difference stimulates its adjacent parts and similar changes occur there too. Thus a continuous flow of the impulse becomes possible.

Impulses transmission path
Impulse due to stimulus => dendrites => dendrons => cyton => axon => axonites=> synaptic knob => secretion of neurotransmitter to the synaptic cleft => Stimulation in the adjacent dendrites => Impulse forms.
When impulses reach at the synaptic knobs, a chemical substance, known as neurotransmitter is released  in the synaptic cleft. This chemical stimulates the adjacent dendrites to form new electric impulses.

Sensory neurons - Carries impulses from different body parts to the brain and spinal cord.

Motor neurons - Carries impulses from the brain and spinal cord to various parts of body.

A nerve is a group of axons or nerve fibres, covered by connective tissue.

Sensory nerves (consists of sensory neurons) : Carry impulses from sense organs to the brain and
spinal cord.
Motor nerves  (consists of motor neurons) : Carry impulses from brain and spinal cord to different
organs.
Mixed nerves (consists of sensory and motor neurons) : Carry impulses from brain and spinal cord to different organs and vise versa.

Central Nervous System :  Brain , Spinal cord

Peripheral Nervous System : Cranial nerves -12 pairs , Spinal nerves -31 pairs

Brain's protections : 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, also protects the brain. 

The outer covering of brain and spinal cord is Meninges.
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Class X - SSLC - Biology Quick Notes : Sensations And Responses-1

  August 15, 2020   ,   Edit
Stimulus.
The senses that evoke responses in organisms are called stimuli. There are two types,
External stimuli : Sound, touch, heat, chemicals, pressure, cold, radiations.
Internal stimuli : Hunger, touch, infection, pressure variation, thirst, exhaust.

Function of nervous system is to generate and coordinate responses according to external and internal changes.

The following are the parts included in our nervous system

  1. Brain
  2. Spinal cord
  3. Nerves
  4. Receptors

Neurons are the structural and functional units of the nervous system. They consist of a cell body, dendrites, and axon.

Structure of a model neuron.

A neuron has mainly the following parts

  1. Cyton / cell body
  2. Dendrite : Branches of Dendron. Part that receives impulses from adjacent neuron.
  3. Dendron : Short filament from the cell body. Carries impulses from dendrites to the cell body.
  4. Schwann cell : Encircles the axon.
  5. Axon : Longest filament from the cell body. Carries impulses from the cell body to outside.
  6. Axonite : Branches of axon. Carries impulses to the synaptic knob.
  7. Synaptic knob : Tip of axonite. Secretes neurotransmitter.

The protective covering of nerve fibres is Myelin sheath.

Myelin sheath's. main functions are 
  1. Provide nutrients and oxygen to the axon.
  2. Accelerate impulses.
  3. Act as an electric insulator.
  4. Protects the axon from external shocks.
  5. Gives white appearance ('white matter') to the neural parts.
The part of nerve, where myelinated neurons are present in abundance,is called as the white matter.

The part of nerve where the cell bodies and nonmyelinated neurons are present, is called as the grey matter.

These nerve cell and its functions:
  1. Dendrite : Receives impulses
  2. Dendron :Carries impulses from dendrite to the cell body
  3. Cyton / Cellbody :Passes impulses to the axon.
  4. Axon :Carries impulses from the cell body to outside.
  5. Schwann cells : Protects the axon and increases the speed of impulse
  6. Axonite : Carries impulses to the synaptic knob
  7. Synaptic knob : Secretes neurotransmitter
Swollen ends of axon is Synaptic knobs, and this  Secretes neurotransmitter.. When electric impulses from the axon reach the synaptic knob, certain chemical substances are secreted from there to the synaptic cleft. These chemical substances are called neurotransmitters.

Acetylcholine and dopamine are some examples of neurotransmitters.
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Kerala SSLC Examination - 2019 Solved Annual Question and Answer

  August 08, 2020   , ,   Edit
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