1. Introduction to the
Nervous System
Prof. Vajira Weerasinghe
Professor of Physiology
Faculty of Medicine
University of Peradeniya
(This lecture is available at www.slideshare.net/vajira54)

3. Why study nervous system?
Neurological diseases are disabling
and debilitating and very little treatment
is available

4. Stroke or paralysis Parkinsonism
Alzheimer’s disease (Memory loss)
Migraine
(severe headache) Muscle wasting

5. Why study nervous system?
Activities such as walking and running and
various forms of exercise and sports require
proper functioning of the nervous system

7. Controlling system
Nervous system is the main
controlling system of the body
Quick
Electrical
Endocrine system also
controls body functions
Slow
Chemical

8. Nerve impulses
• It controls other organs by sending electrical
messages called nerve impulses
It is also the main communication system (like

9. What does it do ?
Functions of the nervous system
1. Receives sensory messages from the external environment
2. Organizes information and integrates it with already stored
information
3. Uses integrated information to send out messages to muscles
and glands, producing organized movement and secretions
4. Provides the basis for conscious experience

10. Functional Subdivisions
• Sensory functions
 feeling, eg. pain
• Motor functions
 movement, eg. walking
• Integrative functions
 eg. reflexes
• Autonomic functions
 control of blood pressure
• Higher functions
 memory, learning

11. Anatomical Subdivisions
• Central Nervous system
Brain and spinal cord
• Peripheral Nervous system
Cranial Nerves & Peripheral Nerves
• Autonomic system
sympathetic & parasympathetic

13. Brain
• Brain contains the main
controlling centres
• It is divided into several
lobes by several grooves

14. Brain - Lobes
• Frontal lobe
Located in the front
Performs motor functions
• Parietal lobe
Located laterally
Performs main sensory
functions

15. Brain - Lobes
• Occipital lobe
Located in the back
Performs visual functions
• Temporal lobe
Located laterally
Performs hearing functions

16. White matter and grey matter
• In the nervous system
 Cell bodies are collected as
grey matter
 Nerve fibres are collected as
white matter
• In the brain
 grey matter is located in the
peripheral cell layer
 White matter consists of
central nerve fibre tracts

17. White matter and grey matter
• With nerve fibre tracts each lobe
is connected to different
structures of the body
• Frontal lobe is connected to the
muscles
• Parietal lobe is connected to the
sensory organs of the skin
• Occipital lobe is connected to the
eye

18. Spinal cord
• Nerve fibre tracts starting from
the brain then continue as spinal
cord
• Divided into following areas
 Cervical
 Thoracic
 Lumbar
 Sacral

19. Spinal cord
• Functions
To transmit impulses to and from the
brain to the periphery
To cause reflex action
To process information

20. Peripheral nervous system
• Cranial nerves
There are 12 cranial nerves which
connects brain & brainstem with
different organs of the head and neck
region
• Spinal nerves
There are several pairs connecting
different segments of the spinal cord
with peripheral organs

21. Cranial nerves
I-Olfactory nerve - smell
II-Optic nerve - vision
III-Occulomotor nerve - eye movements
IV-Trochlear nerve - eye movements
V-Trigeminal nerve - mastication
VI-Abducens nerve - eye movements
VII-Facial nerve - facial expressions
VIII-Vestibulocochlear nerve - hearing, balance
IX-Glossopharyngeal nerve - taste
X-Vagus nerve - parasympathetic
XI- Spinal accessory nerve - neck muscles
XII-Hypoglossal nerve - tongue

22. • Spinal nerves
Cervical
Thoracic
Lumbar
Sacral

23. Brain stem
• This is important part of the
nervous system that connects
brain with the spinal cord
• Many cranial nerves arise from
brain stem
• It also contain vital centres
Cardiac, respiratory functions,
consciousness

24. Brain stem
• It has three areas
Midbrain
Pons
(or pons Varoli)
Medulla
(or medulla oblongata)

25. Cerebellum
• This is hind brain
• This is connected to the
brainstem
• Main function is motor
coordination
• Abnormalities result in difficulty

26. Sensory functions
• Functions that make us feel the
environment
• Nerve signals come from the
sensory organ towards the CNS
Afferent signals
• There are different types of
sensory modalities human nervous
system could feel

27. General and special sensations
• There are two main types of sensations
General sensations
Special sensations

28. General sensations
• Mechanical sensations
 Touch
 Pressure
 Vibrations
 Stretch
• Thermal sensations
 Hot, cold
• Chemical sensation

29. Somatic and visceral sensations
• Somatic sensations
External stimuli sensed by the skin
eg. Feeling of hot environment
• Visceral sensations
Internal sensations sensed by the
visceral afferent nerves
eg. acidity in stomach

30. Special sensations
• These are specialised sensations
•
Vision
Hearing
Taste
Smell

31. Proprioception
• Joint and position sensation
• Muscles and tendons contain
receptors which could feel
Muscle length
Joint angle
Position of bones and joint
• This is very important feedback
information for movements of
muscles

32. General plan of the sensory system
• Stimulus
• Receptor
• Nerve pathway
• Central connections

33. Sensory area
in the brain
NT
Ascending
RE
Sensory pathway
E
AFF Central Connections
Sensory nerve
Touch stimulus
Receptor
Sensory
modality

34. se
n
so
3rd
ry
c
order
or
te
neuron
x
internal capsule
thalamus
2nd
order
Brain stem neuron
Skin receptor 1st
order
Spinal Cord neuron

35. Motor functions
• Movements are of two
types
Voluntary movements
Consciously controlled
movements
Well thought and planned
Involuntary movements
Reflex action
Control of posture
Balance

36. Voluntary movements
• Planning starts from the brain (frontal
lobe)
• Modified by various intermediate
structures
 Brainstem
 Cerebellum
• Executed by the brainstem and spinal
cord (lower motor neuron)

37. mo
to
r
Upper
co
motor
rte
x
neuron
internal capsule
Brain stem
Spinal Cord
Muscle contraction
Lower
Motor Nerve
motor
neuron

38. Motor map in the brain
• In the frontal lobe different
areas controlling different
muscles of the body are
distinctly organised
• eg. there is a hand area,
thumb area, face area

39. concept of homunculus
Map
Representation
•upside down
•distorted

41. Cerebellum
• This is very important for
motor coordination
eg. In walking many muscles
should contract and relax in
smooth coordination
• Cerebellum receives
proprioception
• Cerebellum is used as an
error correction centre

42. What is a reflex?
• Response to a stimulus
• Stimulus -> Response
• Task:
Write down 3 reflexes.

43. Reflexes
• Response to a stimulus
• This is an involuntary action
eg. Hot object touching the hand
will cause it to withdraw
• This is called withdrawal reflex

44. What is a reflex?
Central control
Receptor Afferent nerve
Stimulus
Central
connections
Response
Effector organ Efferent nerve

46. Reflexes
• Reflexes involve many systems of the body
• eg.
Withdrawal reflex (pain and motor pathways)
Pupillary reflex (eye)
Salivatory reflex (salivary glands)
Swallowing reflex (GIT)
Micturition reflex (urinary system)
Baroreceptor reflex (blood pressure control)
Stretch reflex (main reflex in the motor system)

47. Autonomic functions
• Controls involuntary functions of
the body
• Two main divisions
Sympathetic
Parasympathetic

48. Sympathetic system
• This is involved in fight or flight
reaction
• What happens when somebody is
excited
Blood pressure increases
Heart rate increases
Respiratory rate increases
Increased sweating
Pupillary dilatation
GIT function suppressed

49. Parasympathetic system
• This is involved when somebody s
resting
• Blood pressure decreases
• Heart rate decreases
• Respiratory rate decreases
• Decreased sweating
• Pupillary constriction
• GIT function increased

51. Higher functions
• Brain is involved in controlling
higher functions
• Learning
• Memory
• Intelligence
• They are called cognitive functions

52. Each side controls opposite of the
body
• Right side of the brain controls
left side of the body
• There is a cross over of nerve
pathways at the brain stem

53. Basic cell in the nervous system is
is a neuron
Nerve signals are electrochemical impulses
called “action potentials”