2. Nervous System
The nervous system is a complex collection of nerves and specialized
cells known as neurons that transmit signals between different parts of
the body.
The basic unit of the nervous system is a nerve cell, or neuron. The
human brain contains about 100 billion neurons.
Different types of neurons control or perform different activities.
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3. Functions of Nervous System cont..
1. Keep us informed on the external environment through sense
organs
2. Memory, Thought process, Reasoning
3. Controls all voluntary muscular activities E.g. Holding pen
4. Regulation of involuntary activities E.g.: Breathing, Heart beat
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4. Neuron
The basic unit of the nervous system is a nerve cell, or neuron.
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5. Structure of Neuron
Main parts of neuron
1. Cell Body
2. Dendrites
3. Axon
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6. Structure of Neuron cont..
Cell Body
Cell Body is also called as Perikaryon (Peri- outside/surrounding,
karyon – Nucleus) or Cyton
It has well defined nucleus with granular cytoplasm
It has all other cell organelles except centrosomes as nerve cells do not
divide.
Dendrite
Branched cytoplasmic projection of cell body, they conduct the nerve
impulses to the cyton.
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7. Structure of Neuron cont..
Axon
The long threadlike part of a nerve cell along
which impulses are conducted from the
cell body to other cells.
It varies in size between few millimeter
to one meter.
Most neurons are covered by a white
insulating sheath called as Neurolemma.
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8. Structure of Neuron cont..
• The myelin sheath shows gaps called as Nodes of Ranvier
• Axon might have side branches called collaterals
• Swollen structure at the end of axon stores neurotransmitters
• The gap between end of axon of one neuron to end of dendrite of
another neuron called as synaptic gap or synaptic cleft.
• Note: Neurotransmitters are a type of chemical messenger which
transmits signals across a chemical synapse from one neuron (nerve
cell) to another 'target' neuron, muscle cell, or gland cell.
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10. Transmission of Nerve Impulses
The transmission of a nerve impulse along a neuron from one end to
the other occurs as a result of electrical changes across the membrane
of the neuron. The membrane of an unstimulated neuron is polarized—
that is, there is a difference in electrical charge between the outside
and inside of the membrane.
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12. Transmission of Nerve Impulses cont..
• In the normal resting phase, outer side of the nerve fibre carried +
charge called polarized state.
• On stimulation (mechanical, electrical, chemical, heat etc), the axon
membrane at the spot becomes more permeable to Na+ ions which
move inward and causes depolarization. This is called as exited
region.
• The point of depolarization becomes stimuli for the next region which
becomes depolarized leaving the previous area as repolarized.
• This impulse transport is achieved through sodium pump using ATP.
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14. Synapse
Synapse is the point of contact between the terminal branches of axon
of a neuron with the dendrites of another neuron separated by a fine
gap.
In this junction nervous impulse will be passed from one neuron to
another.
As the impulse reaches the terminal end of an axon, acetylcholine (a
chemical) will be released.
This chemical sets new impulse in the dendritic region of next neuron
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15. Types of Neuron
• Sensory Neuron – Passes impulses/messages from sensory organs to
CNS
• Motor Neuron - Passes impulses/messages from CNS to effector
region (muscle or gland)
• Association Neuron – Interconnection between sensory and motor
neuron
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16. Nerves
Bundle of nerve fibres (axons) of separate neurons, enclosed in a
tubular sheath are called Nerves.
Three types of Nerves
Sensory Nerves – Contains sensory fibers bringing information to brain
and spinal cord
Motor Nerves - Contains motor fibers from CNS to effector region
(muscle or gland)
Mixed Nerves – Contains both sensory and motor fibers
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17. Divisions of Nervous System
• Central Nervous System (CNS)
Includes -
➢ Brain
➢ Spinal Cord
• Peripheral Nervous System (PNS)
Includes –
Nerves emerging and entering CNS
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18. Subdivisions of PNS
• Somatic Nervous Systems – Conveys information to
Skeletal/Voluntary muscles
• Autonomic Nervous Systems – Includes ganglia and nerves which
controls involuntary muscles of internal organs
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20. Structure of Brain
➢The brain is one of the largest and most complex organs in the
human body.
➢It is made up of more than 100 billion nerves that communicate in
trillions of connections called synapses.
➢The brain is composed of the cerebrum, cerebellum, and brainstem
➢Adult brain weighs around 1.35 kg
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21. Structure of Brain cont..
• Brain is covered by 3 layers called meninges –
1. Dura meter – the outermost tough fibrous membrane
2. Arachnoid – thin and delicate mid layer giving web-like cushion
3. Pia meter – innermost highly vascular membrane with rich blood
supply
Fluid present between the membranes is called as cerebrospinal fluid.
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22. Structure of Brain cont…
• Cerebrum: is the largest part of the brain and is divided into right and
left hemispheres. It performs functions like vision, hearing,
interpreting touch, as well as speech, learning, reasoning, emotions,
and fine control of movement.
• Cerebellum: is located under the cerebrum. Its function is to
coordinate maintain posture, muscle movements, and balance.
• Brainstem: It acts as a center connecting the cerebrum and
cerebellum to the spinal cord. It performs many automatic functions
such as breathing, heart rate, controlling body temperature,
maintaining sleep cycles, digestion etc
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23. Forebrain
• The Cerebrum: Also known as the cerebral cortex, the cerebrum is
the largest part of the human brain, and it is associated with higher
brain function such as thought and action.
• Nerve cells make up the gray surface, which is a little thicker than our
thumb.
• White nerve fibers beneath the surface carry signals between nerve
cells in other parts of the brain and body. Its wrinkled surface
increases the surface area, and is a six-layered structure found in
mammals, called the neocortex.
• It is divided into four sections, called “lobes”. They are; the frontal
lobe, the parietal lobe, the occipital lobe and the temporal lobe.
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24. Lobes of the brain
• Frontal,
• Temporal,
• Parietal,
• Occipital
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25. Lobes of the brain cont..
Frontal lobe
•Personality, behavior, emotions
•Judgment, planning, problem solving
•Speech: speaking and writing (Broca’s area)
•Body movement (motor strip)
•Intelligence, concentration, self awareness
Parietal lobe
•Interprets language, words
•Sense of touch, pain, temperature (sensory strip)
•Interprets signals from vision, hearing, motor, sensory and memory
•Spatial and visual perception
Occipital lobe
•Interprets vision (color, light, movement)
Temporal lobe
•Understanding language (Wernicke’s area)
•Memory
•Hearing
•Sequencing and organization ArpanAryan Institutions Pvt Ltd
26. Midbrain
The midbrain is located below the cerebral cortex, and above the
hindbrain placing it near the center of the brain.
• Limbic System – the limbic system is often referred to as our
“emotional brain”, or ‘childish brain’. It is found buried within the
cerebrum and contains the thalamus, hypothalamus, amygdala and
hippocampus.
• Thalamus – the primary role of the thalamus is to relay sensory
information from other parts of the brain to the cerebral cortex
• Hypothalamus – the primary role of the hypothalamus is to regulate
various functions of the pituitary gland and endocrine activity, as
well as somatic functions e.g.body temperature, sleep, appetite.
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27. Midbrain cont..
• Amygdala – the primary role of the amygdala is to be a critical
processor for the senses and memory.
• Hippocampus – the primary role of the hippocampus is memory
forming, organizing and storing information. It is particularly
important in forming new memories, and connecting emotions and
senses, such as smell and sound, to memories.
• Pituitary Gland – the primary role of the pituitary gland is an
important link between the nervous system and the endocrine
system. It releases many hormones which affect growth,
metabolism, sexual development and the reproduction system. It is
connected to the hypothalamus and is about the size of a pea. It is
located in the center of the skull, just behind the bridge of the nose.
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28. Hindbrain
• The Cerebellum – The cerebellum, or “little brain”, is similar to the
cerebrum with its two hemispheres and highly folded surface. It is
associated with regulation and coordination of movement, posture,
balance and cardiac, respiratory and vasomotor centers.
• Brain Stem – The brain stem is located beneath the limbic system. It
is responsible for vital life functions such as breathing, heartbeat,
and blood pressure. The brain stem is made of the midbrain, pons,
and medulla.
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29. Hindbrain cont..
• Pons – The primary role of the pons is to serve as a bridge between
various parts of the nervous system, including the cerebellum and
cerebrum. It is responsible for facial expressions, as well as
controlling the muscles that are responsible for biting, chewing, and
swallowing. The pons is also associated with the control of sleep
cycles, and controls respiration and reflexes.
• Medulla – The primary role of the medulla is regulating our
involuntary life sustaining functions such as breathing, swallowing
and heart rate. As part of the brain stem, it also helps transfer neural
messages to and from the brain and spinal cord. It is located at the
junction of the spinal cord and brain.
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30. Thanks for the images and references received by various books and websites.
Thank you…
Arpana P Sharma
arpana@aryaninstitution.com
ArpanAryan Institutions Pvt Ltd
(Aryan Institution)
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