NERVOUS SYSTEM
DR MANESHA PERERA
OBJECTIVES
Describe the different parts of the nervous system – central and peripheral
Describe the organization of the central nervous system – brain and spinal
cord
Briefly explain the macroscopic structure of the brain and identify important
areas/structures of the brain
Identify the localization of the hypothalamus and pituitary
Describe the organization of the peripheral nervous system – spinal and
cranial nerves
Describe the organization of the autonomic nervous system – sympathetic
and parasympathetic
CLASSIFICATION
THE NEURON
•
•
Neurons are the fundamental units of the brain and
nervous system, responsible for receiving sensory input
from the external world, for sending motor commands
to our muscles, and for transforming and relaying the
electrical signals at every step in between.
While neurons have a lot in common with other types of
cells, they're structurally and functionally unique.
Specialized projections called axons allow neurons to
transmit electrical and chemical signals to other cells vis
synapses.
Synapse
CENTRAL NERVOUS
SYSTEM
•
The central nervous system (CNS) is comprised of the
brain and spinal cord.
•
Both of these are protected by three layers of
membranes known as meninges.
•
For further protection, the brain is encased within the
hard bones of the skull, while the spinal cord is
protected by the vertebral column.
•
A third form of protection is cerebrospinal fluid,
which provides a buffer that limits impact between
the brain and skull or between spinal cord and
vertebrae.
•
The three broad functions of the CNS are to take in
sensory information, process information, and send
out response signals.
GREY AND WHITE MATTER
In terms of tissue, the CNS is divided into grey matter and white
matter.
•
Grey matter- neuron cell bodies and their dendrites, glial cells,
and capillaries.
• In the brain, grey matter is mainly found in the outer layers, while in
the spinal cord it forms the core ‘butterfly’ shape.
•
Brain (Transverse section)
White matter - areas of the CNS which host the majority of
axons. Most axons are coated in myelin - a white, fatty
insulating cover that helps nerve signals travel quickly and
reliably.
• In the brain, white matter is buried under the grey surface, carrying
signals across different parts of the brain. In the spinal cord, white
matter is the external layer surrounding the grey core.
Spinal cord(Transverse section)
BRAIN
•
The brain’s cerebral cortex is the
outermost layer that gives the brain
its characteristic wrinkly appearance.
•
The cerebral cortex is divided
lengthways into two cerebral
hemispheres connected by the corpus
callosum.
•
Traditionally, each of the hemispheres
has been divided into four lobes:
frontal, parietal, temporal and
occipital.
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BUMPS AND GROOVES OF THE BRAIN
• The lobes of the brain are divided by a number of
bumps and grooves.
• These are known as gyri (bumps) and sulci
(groves or fissures).
• The folding of the brain, and the resulting gyri
and sulci, increases its surface area and enables
more cerebral cortex matter to fit inside the
skull.
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Although we now know that most
brain functions rely on many
different regions across the entire
brain working in conjunction, it is
still true that each lobe carries out
the bulk of certain functions.
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FRONTAL LOBE
• The frontal lobe is generally where higher
executive functions including emotional
regulation, planning, reasoning and problem
solving occur.
Frontal lobe damage/degeneration causes
personality changes
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PARIETAL LOBE
•
The parietal lobe is behind the frontal lobe, separated
by the central sulcus.
•
Areas in the parietal lobe are responsible for
integrating sensory information, including touch,
temperature, pressure and pain.
Because of the processing that occurs in the parietal
lobe, we can, for example, discern from touch alone that
two objects touching the skin at nearby points are
distinct, rather than one object. This process is called
two-point discrimination.
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TEMPORAL LOBE
•
The temporal lobe contains regions dedicated to processing sensory
information, particularly important for hearing, recognising
language, and forming memories.
•
The temporal lobe contains the primary auditory cortex, which
receives auditory information from the ears and secondary areas and
processes the information, so we understand what we’re hearing.
•
Certain areas in the temporal lobe make sense of complex visual
information including faces and scenes.
•
The medial temporal lobe contains the hippocampus, a region of the
brain important for memory, learning and emotions.
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OCCIPITAL LOBE
• The occipital lobe is the major visual processing
centre in the brain.
• The primary visual cortex receives visual
information from the eyes.
• This information is relayed to several secondary
visual processing areas, which interpret depth,
distance, location and the identity of seen
objects.
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• Apart from the cerebrum, the brain also
contains several small, but highly important
structures located towards the centre of the
brain and are included in the limbic system.
• They are involved in regulating things like the
body’s sensory perception, motor functions, and
hormones.
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THALAMUS
• The thalamus consists of two lobes of grey matter tucked
away right under the cerebral cortex.
• It is a prime processing centre for sensory information, as it
links up the relevant parts of the cerebral cortex with the
spinal cord and other areas of the brain important for our
senses.
• The thalamus also controls sleep.
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HYPOTHALAMUS
• The hypothalamus is quite small, only about the size of an
almond.
• It is found right underneath the thalamus and is the major
control centre of the autonomic motor system.
• It is involved in some hormonal activity and connects the
hormonal and nervous systems.
• The hypothalamus also works to regulate things like our
blood pressure, body temperature, and overall
homeostasis.
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PINEAL GLAND
• The pineal gland is even smaller than the hypothalamus only about the length of a grain of rice - and is tucked
between the two lobes of the thalamus.
• It is shaped like a tiny pinecone, and its main job is to
produce the hormone melatonin, which regulates our
sleep-wake cycles.
• Just like the hypothalamus, it is also involved in regulating
hormonal functions.
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PITUITARY
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BRAIN STEM
•
The Midbrain is the topmost part of the brainstem, the
connection central between the brain and the spinal cord.
•
The Pons sits right underneath the midbrain and serves as a
coordination centre for signals and communications that flow
between the two brain hemispheres and the spinal cord.
•
The Medulla oblongata contains the control centres for our
autonomic vital functions - heart rate, blood pressure,
breathing - and many involuntary reflexes such as swallowing
and sneezing.
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CEREBELLUM
• The cerebellum coordinates our sensations with
responses from our muscles, enabling most of
our voluntary movements.
• It also processes nerve impulses from the inner
ear and coordinates them with muscle
movement, thus helping us maintain balance and
posture.
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SPINAL CORD
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Grey matter
•
The anterior horns have motor neurons, which carry information
from the brain and spinal cord to the body’s muscles, stimulating
their movement.
•
The posterior horns have sensory neurons which carry sensory
information – about, for example, touch, pressure or pain – from
the body back to the spinal cord and the brain.
White matter
•
This contains axons that allow different parts of the spinal cord to
communicate smoothly.
•
These axons travel in both directions - some carry signals from the
body to the brain, while others deliver signals from the brain to
neurons located elsewhere in the body.
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PERIPHERAL NERVOUS
SYSTEM
THE NERVE
•
A nerve is a cordlike structure composed of
fibers that conduct sensory and motor
impulses between the brain and spinal
cord and other areas of the body.
•
Nerve fibers can convey sensory signals to
the brain from the skin or organs (afferent
nerves) or conduct stimulatory signals from
the brain to the muscles (efferent nerves).
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AUTONOMIC NS
• It controls the involuntary functions and influences the activity of internal organs.
• The autonomic nervous system is regulated by the hypothalamus and is required for
cardiac function, respiration, and other reflexes, including vomiting, coughing, and
sneezing.
• Divided into sympathetic and parasympathetic components
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SYMPATHETIC NS
• Sympathetic fibres, located in spinal
nerves are responsible for the "fight
or flight" response, which is an
acute response that takes place in
case of an imminent harmful event
or intense mental distress.
• To activate this response, the
sympathetic fibres use the
neurotransmitter noradrenaline to
activate the blood flow in skeletal
muscles and lungs, dilating lungs
and blood vessels and raise the
heart rate.
PARASYMPATHETIC NS
• This regulates resting responses such as heart
rate, salivation, lacrimation (secreting tears),
digestion.
• Parasympathetic motor fibres are found in four
of the 12 pairs of cranial nerves.
• So, synapses established by the parasympathetic
fibres are typically inhibitory, with acetylcholine
as the main neurotransmitter.
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SOMATIC NS
• The somatic nervous system (SNS) is also known as the voluntary nervous system.
• It contains both afferent nerves made of sensory neurons that inform the central
nervous system about our five senses; and efferent nerves which contain motor
neurons responsible for voluntary movements.
• The nerves in the somatic nervous system are classified based on their location,
either in the head (Cranial n.) or in the spine (spinal n.)
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CRANIAL NERVES
• There are 12 pairs of cranial nerves, which send
information to the brain stem (base of the brain where the
spinal cord connects) or from the brain stem to the
periphery.
• These nerves are required for the five senses and for the
movement of head, neck and tongue.
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SPINAL NERVES
• The spinal nerves are 31 pairs of nerves that send sensory
information from the periphery to the spinal cord and
muscle commands from the spinal cord to the skeletal
muscles.
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REFLEX ARC
• In addition to regulating the voluntary movements of the
body, the somatic nervous system is also responsible for
reflexes, controlled by a neural pathway known as the
reflex arc.
• A reflex arc includes a sensory neuron that sends a signal
straight to the spinal cord (bypassing the brain) which in
turn generates a response such as a quick muscle
contraction so fast that it’s subconscious.
QUIZ!
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1. The human nervous system is capable of a wide range of functions. What is the basic unit of the nervous system?
A. Glial cell
B. Meninges
C. Neuron
D. Cerebrospinal fluid
2. The neuron cell is made up of which of the following parts?
A. Axon
B. Dendrite
C. Nucleus
D. All of the Above
3. Neurons come in which different type(s)?
A. Sensory
B. Motor
C. Skeletal
D. A and B
4. How do neurons communicate with one another?
A. Electrically
B. Chemically
C. Through weak, radio-wave-like impulses
D. A and B
5. What is a common neurotransmitter?
A. Acetylcholine
B. GABA
C. Serotonin
D. All of the above
6. Centre for heat, touch, pressure is in the,
A. Frontal lobe
B. Parietal lobe
C. Occipital lobe
D. Temporal lobe
7. Primary visual centre is situated in the…
A. Occipital lobe
B. Parietal lobe
C. Hypothalamus
D. Frontal lobe
8. ______ helps maintain balance and posture
A. Cerebrum
B. Pons
C. Cerebellum
D. Medulla oblongata
9. In reflex action, the reflex arc is formed by,
A. Brain  Muscle  Spinal cord
B. Muscle  Spinal cord  Brain
C. Receptor  Spinal cord  Muscle
D. Spinal cord  Receptor  Muscle
10. How many pairs of Cranial nerves are there?
A. 12
B. 30
C. 10
D. 22