Transcript The Chemistry of the Brain

The Chemistry of the Brain
What is the brain?
What is it composed of?
Why does it have such an important role in living
things?
Why does it sometimes malfunction?
To answer these questions we must
look at the nervous system in humans.
The nervous system in humans is
made up of:
• The CNS - central nervous system
(brain and spinal chord)
• The PNS - Peripheral nervous
system (nerve cells leading to and
from the central system)
These nerve cells are specialised cells
called NEURONS which conduct
messages to and form the brain.
Neurons
• A neuron is a nerve cell and are the basic unit of the
nervous system and are specialised to carry
information from one place to another.
• They are elongated cells that transmit this information
by means of electrical impulses.
Structure of neurons
Neurons consist of the
following:
 Cell body
 Dendrites
 Axon
 Myelin sheath
 Schwann cell
 Neurotransmitter vesicles
 Synapse knobs
There are three types of Neuron :
 Sensory neuron –carries
messages from the sense
organ to the central nervous
system (CNS).
 Interneuron –connects
sensory and motor neurons
and so carries messages
within the CNS.
 Motor neuron –carries
impulses from the CNS to
muscles and glands.
Cell Body
 The cell body contains the nucleus and other organelles
that produces neurotransmitter chemicals, the absence of
which would make impulse transmission impossible!
Axon
 The function of the axon is to conducts nerve
impulses away from the cell body and towards the
CNS or the desired destination.
Schwann Cell
 Schwann cells are located along the length of the
neurons.
 They secrete the myelin sheath, which is a fat-rich
membrane that insulates the electrical impulses.
 In multiple sclerosis (MS), patches of myelin
degenerate in the CNS. As a result, the passage of
nerve impulses is impeded, and the person suffers
symptoms ranging from numbness and tingling to
paralysis and loss of bladder control.
Myelin sheath
 As neurons carry electrical impulses they must be
insulated so that the information is not lost as it
travels to the CNS.
 The myelin sheath acts as an insulator for the
impulse as it travels through the axon.
 The presence of this insulation will also speed up
the transmission of the impulse.
Dendrites
 Dendrites receive information and carry it towards
the cell body
How are impulses initiated?
 When a stimulus is applied to a neuron it causes
movement of positively charged ions i.e. sodium
ions.
 These sodium ions move from the outside to the
inside of the axon.
 This is the action that causes an impulse to travel
to the CNS.
Path of the impulse
 The impulse travels along the axon of the neuron
until it reaches the end.
 It then needs to travel to the next neuron so it may
reach It’s desired destination.
 The impulse now needs to travel across the “gap”
between the two neurons.
How does an impulse cross this “gap”?
 The end of each axon
breaks up into many
small branches
 Neurotransmitters e.g
acetylcholine are stored
in vesicles at the end of
these branches.
 When neurotransmitters
are activated by the ions
they are released into the
cleft for a very short
period of time,
transmitting the impulse
to the next neuron.
 After transmission, the
neurotransmitter is
inactivated by an enzyme
and reabsorbed by the
presynaptic neuron and
used to make new
neurotransmitter
substance.
Central Nervous System
The Brain
 The brain is composed of over 100 billion neurons, each
receiving messages simultaneously from thousands of other
neurons.
 The brain is
protected by the skull
bones, meninges
(three membranes)
and cerebrospinal
fluid.
 The cerebrum is our
conscious brain, with
different parts having
different jobs to do.
hypothalamus
 The hypothalmus is
the centre for the
regulation of the
internal organs.
cerebrum
pituitary
 The pituitary ‘[master] gland secretes hormones that stimulate
other glands to release their hormones.
Conscious actions
A conscious action is one where the brain makes a considered response.
Here’s what happens:
4) The brain
3) Here another sensory neuron
decides to move
carries the signal to the brain
away the hand
5) This impulse is
sent by MOTOR
NEURONS to the
hand muscles (the
effectors) via the
spinal chord…
2) The impulse is carried
by SENSORY NEURONS
to the spinal chord
1) Receptors in
your skin detect
a stimulus
Stimulus
6) Which then
moves the hand
away
Receptor
Motor Neuron
Sensory Neuron
Effector
Coordinator
Response
 The cerebellum co-ordinates processes that we have
learned to do automatically, such as speaking.
Medulla
oblongata
cerebellum
 The medulla oblongata co-ordinates involuntary,
automatic processes — such as breathing, heartbeat.
Nervous System Disorder
Parkinson’s disease is a nervous system disorder, normally
seen in older people, in which muscles become rigid and
movement is slow and difficult, with persistent tremors [shaking].
It is caused by the brain reducing the normal amount of
dopamine that it makes.
There is at present no means of preventing it, but giving L-dopa
(which the body changes into dopamine) can relieve the
symptoms in many patients.