brain and spinal cord

1. NERVOUS SYSTEM

2. A Picture of the Nervous System

3. The need of nervous system
• 1) Keeps us informed about the outside world.
• 2) Helps to think, remember, reason ,etc.
• 3) Controls all voluntary actions.
• 4) Regulates all involuntary actions.

4. Nerve Cell
• The nervous system consists of the brain, spinal cord, sense
receptors and the nerves.
• The basic unit of the nervous system is the Neuron or the
nerve cells.
• It helps to perceive and send messages to the parts of our
body as required.

5. Structure of a neuron
• A neuron consists of the following three parts:
• 1) The Cell body: It is also called the cyton or perikaryon.
• It contains a nucleus with cytoplasm.
• 2) Dendrites: They are branched structures of the cell body.
• They help to conduct the impulses to the cell body.
• 3) Axon: It is an Elongated Dendrite. It is surrounded by the Myelin
Sheath, which is again covered by Nurolemma.
• The Myelin sheath has gaps through out its length called the NODES
OF RANVIER.
• The end portions are swollen like bulbs called Neurotransmitters,
• which store chemicals.

6. A Neuron

7. Synaptic Cleft and Synapse
• The terminals of the bulbs of the Axon are very close to those
of the Dendrites, with gaps between them, called Synaptic
Clefts.
• The point of contact between the bulbs is called the Synapse,
through which messages are passed from one neuron to the
other, with the help of neurotransmitters.
• Example: Acetycholine

8. Diagram showing a synapse

9. Types of Neurons
• There are Three types of neurons:
• 1) Sensory neuron: Convey impulses from sense organ to
brain or spinal cord.
• 2)Motor neuron: Convey
• impulses from brain/spinal
• cord to muscle or gland.
• 3) Association neuron:
• They are present in the
• brain/spinal cord and
• interconnect the sensory
• and motor neurons

10. NERVES
• A nerve is a bundle of axons of different neurons, bundled
together, enclosed in a tubular sheath.
• The myelin sheath prevents the mixing of the nerve impulses.
• There are Three types of Nerves:
• 1) Sensory Nerves: Contain only sensory nerves. They connect
sense organs to brain/spinal cord.
• 2) Motor Nerves: Contain only motor nerves. Connect
muscle/gland to brain/spinal cord.
• 3) Mixed Nerve: Contain both sensory and motor nerves.
• GANGLIA: They are group of nerve cells(afferent neurons)
from where nerve fibers arise.

11. Picture of Nerves
Ganglion

12. The Nervous System
• There are two divisions of the nervous system:
• 1) Central nervous system: consists of brain and spinal cord.
• 2) Peripheral nervous system: It consists of the nerves that
enter and leave the brain/spinal cord.

13. Central Nervous System
• It consists of –
• 1) Brain: It is protected by the cranium.
• It has 80% water and consumes 25% of Oxygen taken in by
our body.
• It is protected by a layer called Meninges, which has-
• a) Duramater: Outermost layer, made of tough fibres.
• b) Arachnoid: A thin middle layer, which is delicate and web
like, acting like a cushion.
• c) Piamater: The innermost layer, richly supplied with blood
vessels.
• The inflammation of the Meninges causes Meningitis.

16. Parts of the Brain-Cerebrum
• The brain is made up of 3 parts:
• 1)Cerebrum: a)It is the largest part of the brain.
• b) It is divided into two halves called cerebral hemispheres,
• c) The outer surface is highly convoluted, containing ridges and
grooves, e) The grey matter is folded to form the ridges and
grooves.
• d) Each hemisphere has an outer cortex and an inner medulla.
• e) Cortex has Cell Bodies (nerve cells) and is grey in colour, so
called Grey Matter.
• f) Medulla has Nerve Fibers ( axons) and is white in colour, so
called White Matter.
• g) Cortex (Grey matter) is highly folded to form Convolutions.

17. • The folds are called Gyri and the grooves are called Sulci.
• The folds help to accommodate more number of nerve cells.
• The two cerebral hemispheres are attached to one another by
a sheet of fibres called Corpus Callosum.
• h) The functions of the cerebrum are:
• 1) To think, reason out, plan and memorise.
• 2) It is the seat of intelligence, conciseness and will power.
• 3) It controls all the VOLUNTARY ACTIONS.

19. Parts of the cerebrum

20. Cerebellum
• Cerebellum is a smaller area than the cerebrum.
• It is located just at the base and under the large cerebrum.
• Functions:
• a) Maintain balance of the body.
• b) Coordinate muscular activity.
• c) Helps in proper coordination and timing of the muscles to
contract and relax.
• d) This is why an alcoholic person walks clumsily.
• The impulse to stand and walk is generated in the CEREBRUM
but act of walking is performed by the CEREBELLUM.

21. The Cerebellum

22. Medulla Oblongata
• a) It is the lowest part of the brain.
• b) It is located at the base of the skull.
• c) It continues behind as the spinal cord.
• Function: It controls all the activities of the internal organs,
that is, all the involuntary actions.
• Hence, injury to the medulla oblongata, generally results in
death,

23. Medulla Oblongata

24. Primary regions of the brain
• Taking all the parts of the brain, that is, cerebrum, cerebellum
and medulla oblongata, the brain can be divided into 3
regions:
• 1) Forebrain: It includes-
(a) Cerebrum-(all the voluntary actions, memory, will power,
etc.)
• (b) Diencephalon-( i)This includes the Thalamus-(relays pain
and pressure to cerebrum)
• (ii) Hypothalamus- (It controls the body temperature and the
pituitary gland)

25. • 2)Midbrain: It is a small tubular part(reflexes involving the
eyes and ears)
• 3) Hindbrain: It includes-
• a) Cerebellum- (coordinates muscular activity and balance of
body)
• b) Pons- It is located in the center of the brain, below the
cerebellum(carries impulses from one hemisphere of the
cerebellum to the other hemisphere)

27. The Spinal cord
• It extends from the medulla oblongata to the whole length of
the backbone ending in the 2nd lumbar vertebra, within the
neural canal.
• Here, the arrangement of the white and grey matter is
reversed from that of the brain, that is, the grey matter with
the cell bodies is on the inner side and the white matter with
nerves is on the outside.
• It is covered by the same three layers of the meninges of the
brain in the same order, in continuation of the brain.

28. Functions of the Spinal Cord
The functions of the spinal cord
are:
1) Reflexes below the neck.
2) Conduct sensory impulse
from skin and muscles to brain.
3) Conduct motor impulse from
brain to muscles of trunk and limbs.

29. Peripheral Nervous System
• The above system(PNS) includes the nerves which carry
impulses to and from the CNS(brain/spinal cord).
• It is divided into-
• 1) Somatic nervous
• system and
• 2) Autonomic
• nervous system

30. Somatic Nervous System
• It consists of two sets of nerves:
• 1) Cranial nerves: They emerge(start) from the brain. There
are 12 pairs of these nerves.
• Example: sensory from olfactory(nose),optic for eyes, auditory
for ears and mixed nerves going to the coming from the face
and tongue.
• 2) Spinal nerves: They emerge from the spinal cord and there
are 31 pairs- (a) 8 pairs in the neck, (b) 12 pairs in the thorax,
(c) 5 pairs in the lumbar region, (d) 5 pairs in the sacral and (e)
1 pair in the coccygeal region.

31. Structure of a Spinal Nerve
• A spinal nerve- (1) It originates from the spinal cord.
• (2) It has 2 roots- a dorsal root and a ventral root.
• (3) Each dorsal root has a dorsal ganglion.
• (4) Each spinal nerve is a mixed nerve, that is, it has both
sensory and motor nerves.
• (5) At the junction of the two roots, the sensory and the
motor nerves separate out.
• 6) The sensory nerves continue as dorsal root. The motor
nerves continue as the ventral root.
• 7) Both the roots enter the grey matter and end in their
corresponding dorsal and ventral projecting horns of the
spinal cord.

33. Autonomic Nervous System
• This system(ANS) consists of a pair of chain of nerves and
ganglia on either side of the spinal cord(backbone). Its function
is to control the involuntary actions.
• It is of Two types: 1)
1) Sympathetic nervous system- It prepares the body during
abnormal conditions. It is stimulated by ‘Adrenaline’
• The nerves of this system arise between the neck and waist
region.
• 2) Para sympathetic nervous system: It brings back the body to
the normal conditions.
• It is located at – (a) anteriorly in the head and neck and
b)posteriorly in the sacral region.

36. Kinds of actions in our body
There are two kinds of actions in our body:
(1) Voluntary actions: These are performed consciously by our
body. Example: You pick an apple to eat.
(2) Involuntary actions: These are performed unconsciously by
our body. These are also called as Reflexes, caused due to some
kind of stimulus. Example: You withdraw your hand when you
touch a hot iron.

37. Stimulus: It is any agent or an environmental change which
initiates a response in the body. It is of different types like
physical, mechanical, thermal or electrical.
Reflex Action: It is an automatic, quick and immediate
involuntary action in the body due to stimulus.
Reflex arc: It is the pathway for any reflex action

38. A reflex action and its path

39. Types of reflexes
There are two types of reflexes:
(1) Natural reflex: This does not have any previous learning
experience. Also called Inborn or Simple reflex.
Example: Blinking, Coughing and Sneezing are protective
reflexes. Salivation, swallowing and peristalsis are functional
reflexes.
(2) Conditioned reflex: This develops with previous experience.
Also called acquired reflex.
Example: Salivation on the sight of a familiar food.
(3) Conditioned reflex is an involuntary, spontaneous automatic
response due to a previously learned experience.

40. Pavlov’s Experiment

41. Natural Reflexes
• Some common natural reflexes are:
• (1) Knee jerk.
• (2) Closing of eye lids..
• (3) Withdrawal of hand on being pricked.
• (4) Peristaltic reflexes.
• (5) Coughing when food swallowed enters food pipe.
• (6) Sneezing when an irritant enters the nose.

42. Acquired Reflex
• Common acquired reflexes are:
• (1) Tying your shoe lace while talking.
• (2) Standing up on seeing your teacher.
• (3) Playing on your musical instrument.
• (4) Giving a hand signal automatically.
• (5) Applying brakes on your vehicle.

43. Difference between Natural and Conditioned
Reflex

46. Terms used in a reflex arc

47. • THANK YOU