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1. Nervous System
Hari Sharan Makaju
M.Sc. Clinical Biochemistry
PG Student

2. Content
o Introduction of nervous system
o Organization of nervous system
o Nervous tissue
o Neurons and its types
o Supporting cells
o Ascending tract and descending tract
o Reflex

3. Introduction
 Nervous system is:
 A physically connected network of cells, tissues and organs
that allow us to communicate with and react to the
environment and perform life activities.
 Master controlling and communicating system
 Has two main division
 Central nervous system
 Peripheral nervous system

4. FOUR PRIMARY FUNCTIONS OF
NERVOUS SYSTEM
 Sensing the world
 Vision, Hearing, Smell,
Taste, Touch
 Transmitting information
 Processing information
 Producing a response

5. Organization
A. Central Nervous System (CNS)
▫ Brain & spinal cord
▫ Integrative and control centers
-Receives, interprets and sends signals to PNS
B. Peripheral Nervous System (PNS)
▫ Nerves (31 pairs of spinal nerves,12 pairs of cranial nerves)
▫ Communication lines between CNS and rest of body
▫ Two Divisions:
1. Sensory (afferent) Division: Sensory receptors --
CNS
2. Motor (efferent) Division: CNS -- effectors (muscles &
glands)

6. Motor Division
 Somatic nervous system (voluntary)
- control skeletal muscles
 Autonomic nervous system (ANS) (involuntary)
– regulate smooth muscles, cardiac, glands
▫ Subdivisions:
o Sympathetic :
o “Fight or Flight”
o Activated during emergencies, exercise or vigorous physical activity
o Revs up body to respond to situations that upset homeostasis
o Parasympathetic:
o “Rest & Digest”
o Reduces energy use
o Promotes:
o Storage of energy
o Elimination of wastes
o Homeostasis

10.  The mammalian brain is
highly complex, containing
many specialized regions that
carry out specific functions.
 Generally, the brain is divided
into:
 Hindbrain
 Midbrain
 Forebrain
THE COMPLEX BRAIN

11. Hindbrain
 Medulla:
 Controls autonomic functions.
 Pons:
 Controls sleep stages.
 Cerebellum:
 Coordinates movement,
stores some motor memory.
 Helps maintain posture,
muscle control, and balance

12. Midbrain
 Located between the hindbrain and forebrain.
 All sensory and motor information that travels
between the forebrain and the spinal cord
passes through the midbrain
 making it a relay station for the central nervous
system.
 the “traffic cops” of the brain.
 Filters sensory input, which allows us to
concentrate.
 Filtering can be affected by higher thoughts.

13. Forebrain
 Thalamus:
 relay station channeling
sensory information.
 Limbic system:
 basic emotions, drives, and
behaviors.
 Cortex:
 higher thought

14. Limbic system
 Hypothalamus:
 Master controller of the
endocrine system.
 Amygdala:
 sensations of pleasure or
fear, recognition of fear
in others.
 Hippocampus:
 formation of memories.
Damage to these areas can lead to
amnesia or emotional disturbances
“controls: emotions and memories”

15. Cortex
 Various areas :
 control
sensory
processing
 motor control,
 thought,
 memory.
Top layer of the brain
Stores: experiences and/or learning
behavior & emotion
Sensory info
concerning touch
vision
memory &
emotion, speech
and hearing

16. Spinal cord
 Grey matter
 mostly made up of cell bodies of neuron
 White matter
 composed of nerve fibers ( ascending and descending tracts )
embedded in neuroglial cells

18. Nervous Tissue
1. Neurons (nerve cells)
• Functional unit of the nervous system
• Transmit message
Anatomy:
 Cell body – contains nucleus; metabolic center
 Dendrite – fiber that conveys messages toward cell body
 Axon – conduct nerve impulses away from the cell body
 Axon terminals – end of axon; contain neurotransmitters&
release them
 Synaptic cleft/synapse – gap between neurons

20. Nervous Tissue
2. Supporting cells (Neuroglia)
 CNS: astrocytes, microglia, ependymal cells,
oligodendrocytes
 barrier between capillaries and neurons protect
neurons
 immune/defense
 line brain and spinal cord cavities wrap nerve
fibers
 produces myelin sheaths (covering)
 PNS: Schwann cells, satellite cells
 surround large neurons protect & cushion

22. Myelin
 Whitish, fatty material that covers nerve fibers to
speed up nerve impulses
Schwann cells
 Surround axons and form myelin sheath
Myelin sheath
• Tight coil of wrapped membranes
Nodes of Ranvier
 Gaps between Schwann cells

23. • Ganglia: collections of cell bodies
• Bundles of nerve fibers = tracts (CNS) or nerves (PNS)
• White matter
• Dense collections of myelinated fibers
• Gray matter
• Unmyelinated fibers & cell bodies
• (nerve cell bodies, dendrites, axon terminals, bundles of
unmyelinated axons and neuroglia (gray color)

24.  Dendrites receive signals.
 The cell body integrates
signals.
 The axon transmits action
potential. The myelin
sheath makes the signal
travel faster.
 Synaptic terminals
transmit signals.
The Neuron

25. Neurons
 Neuron Function
 Irritability:
 ability to respond to stimulus & convert
to nerve impulse
 Conductivity:
 transmit impulse to other neurons,
muscles, or glands
 Classification of Neuron
 Functional Classification
 Structural Classification

26. 1. Functional Classification:
Direction nerve impulse is traveling
Sensory
neurons
Motor
neurons
Interneurons
carry impulses from
sensory receptors to
CNS
carry impulses from
CNS to muscles &
glands
connect sensory &
motor neurons
Vision, hearing,
equilibrium, taste,
smell, pain,
pressure, heat

27. 2. Structural Classification:
Processes extending from cell body
Multipolar Bipolar Unipolar
1 axon, several
dendrites
1 axon, 1 dendrite 1 process
Most common
(99%)
Rare
Short with 2
branches (sensory,
CNS)
Eg. Motor
neurons,
interneurons
Eg. retina, nose,
ear
Eg. PNS ganglia

29. Nerve Impulses
 Cell membrane at rest = polarized
 Na+outside cell, K+inside cell
 Inside is (-) compared to outside
 Stimulus ---excited neuron (Na+rushes in)--
becomes depolarized
 Depolarization activates neuron to transmit an
action potential (nerve impulse)
 All-or-none response
 Impulse conducts down entire axon
 K+ diffuses out ---repolarization of membrane
 Na+/K+ ion concentrations restored by sodium-
potassium pump (uses ATP)
Exciting a Neuron

30. Synapse
 Neurons usually do not connect
directly to one another. A gap
called a synapse controls the
transmission of signals.
 Depending on the site of the
synapse, they are often referred to
as axodendritic, axosomatic, or
axoaxonic
 Types of synapse
 Chemical
 Neurotransmitter
 Electrical
presynaptic
neuron
Post synaptic
neuron

32. Information Transfer Across Chemical
Synapse
 Action potential reaches
axon terminal ----
vesicles release
neurotransmitters (NT)
into synaptic cleft
 NT diffuse across
synapse
bind to receptors
of next neuron
 Transmission of a nerve
impulse =
electrochemical event

33. Segmental division of Spinal cord

34. Spinal cord
 Grey matter
 mostly made up of cell bodies of neuron
 White matter
 composed of nerve fibers ( ascending and descending tracts )
embedded in neuroglial cells

35. CENTRAL NERVOUS SYSTEM
integration / processing / modulating
stimulus
receptor neurone
motor / descending tracts
effector organ / response
PNS
transmission
lower motor neurone
sensory / ascending tracts

36. Ascending tract
1st
 The ascending tracts transmit sensory information from the sensory
receptors to higher levels of the CNS.
sensory information
 exteroceptive sensation
 origin:-outside the body e.g. temp, touch, light, sound, chemicals,
mechanical
 receptors:- surface layer of skin, mucosa
 proprioceptive sensation
 origin:-within the body e.g. muscles, joints, tendons
 receptors:- deeper layer of skin, tendons, joints, muscle spindles,
ligaments
Information
• conscious sensation
– reach the cerebral cortex
• unconscious sensation
– reach to the areas other than cortex

37. Ascending tract
VPL
1st
2nd
• cross the mid line
• in front of central canal
The pathways consist of thousands of sets of three
neurons: first-order neuron, second-order neuron, and a
third-order neuron.

38. Ascending tract
 First order neuron :
 cell body in posterior root ganglion
 peripheral process connects with sensory receptor ending
 central process enter the spinal cord through the posterior root
 synapse with second order neuron in spinal gray matter
 Second order neuron:
 cell body in posterior gray column of spinal cord
 axon crosses the midline ( decussate )
 ascend & synapse with third order neuron in nucleus of thalamus
 Third order neuron:
 cell body in the thalamus
 give rise to projection fibres to the cerebral cortex, postcentral gyrus (
sensory area )

40. Ascending Tracts of the Spinal
Cord
 Lateral Spinothalamic Tract
 pain, temperature
 Anterior Spinothalamic Tract
 touch, pressure
 Posterior White Column: Fasciculus
Gracilis and Fasciculus Cuneatus
 conscious proprioceptive sense,
discriminative touch, vibratory sense
 Posterior Spinocerebellar Tract&Anterior
Spinocerebellar Tract
 unconscious information from muscle,
joints, skin, subcutaneous tissues
 Spinotectal Tract
 Spinoreticular Tract
 Spino-olivary Tract

41. Descending tracts
 The descending tracts originate from different cortical areas and
from brain stem nuclei.
 The descending pathway carry information associated with
maintenance of motor activities such as posture, balance, muscle
tone, and visceral and somatic reflex activity

42. The Descending Tracts
of the Spinal Cord
 Corticospinal Tracts
 for fine skilled movements
 Reticulospinal Tracts
 Inhibit or facilitate voluntary
movement; hypothalamus
controls sympathetic, para-
sympathetic outflows
 Rubrospinal Tract
 Vestibulospinal Tract
 Olivospinal Tract
 Tectospinal tract
 Reflex postural movements concerning sight
 Descending Autonomic Fibers

44. Corticospinal Tracts

45. Neuron Function
1. Irritability: ability to respond to stimulus &
convert to nerve impulse
2. Conductivity: transmit impulse to other
neurons, muscles, or glands

47. Reflex
 Reflex is an action that is performed without conscious thought
as a response to a stimulus.
 Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
 Eg. jerking away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles, heart, glands
 Eg. salivation, digestion, blood pressure, sweating
 Reflex arc
 It is the nerve pathway involved in a reflex action, including at
its simplest a sensory nerve and a motor nerve with a synapse
between them.

48. Reflex Arc
1) Receptor - reacts to stimulus
2) Sensory Neurons - afferent impulses to CNS
3) Integration centers - synapses in CNS
4) Motor Neurons - efferent impulses from Integration centers to
effector
5) Effector - muscle or glands

51. Reflex Activities
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
Gently tap your quadriceps tendon, which is located immediately
below your knee cap, with a reflex hammer
Optic nerve --brainstem--muscles
constrictpupil
• Useful for checking brain stem
function and drug use

52. Other Reflexes
Stimulus (receptors) Response (effector)
The aroma of your favorite
food
Salivation
A nasty odor Nausea
A bright light shining in your
eye
Pupils get smaller
An insect flying towards your
eye
Blinking

53. Voluntary Reactions
• More neurons and synapses are involved --
longer response times
Reflex = Involuntary Reaction Voluntary Reaction

55. References
 Elaine N. Marieb, Human Anatomy and Physiology 9th Edition .
 Dr. Henry Gray and Dr. Henry Vandyke Carter , Grays Anatomy for
Students 40th Edition.
 Various internet sources.