The Chemistry of the Brain

1
The Chemistry of the Brain
2

• 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?

3

• 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.

4
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.

5
Structure of neurons

• Neurons consist of the following
• Cell body
• Dendrites
• Axon
• Myelin sheath
• Schwann cell
• Neurotransmitter vesicles
• Synapse knobs

6
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.

7
Cell Body

• The cell body contains the nucleus and other
  organelles that produces neurotransmitter
  chemicals, the absence of which would make
  impulse transmission impossible!

8
Axon

• The function of the axon is to conducts nerve
  impulses away from the cell body and towards the
  CNS or the desired destination.

9
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.

10
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.

11
Dendrites

• Dendrites receive information and carry it
  towards the cell body

12
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.

13
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 Its desired destination.
• The impulse now needs to travel across the gap
  between the two neurons.

14
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.

15
Central Nervous System
16
The Brain

• The brain is composed of over 100 billion
  neurons, eachreceiving messages simultaneously
  from thousands of otherneurons.

• The brain is protected by the skull bones,
  meninges (three membranes) and cerebrospinal
  fluid.

17

• The cerebrum is our conscious brain, with
  different parts havingdifferent jobs to do.

cerebrum
hypothalamus
pituitary

• The hypothalmus is the centre for the regulation
  of the internal organs.

• The pituitary master gland secretes hormones
  that stimulateother glands to release their
  hormones.

18
(No Transcript)
19
Conscious actions
A conscious action is one where the brain makes a
considered response. Heres what happens
20

• The cerebellum co-ordinates processes that we
  have learned to do automatically, such as
  speaking.

cerebellum

• The medulla oblongata co-ordinates involuntary,
  automatic processes such as breathing,
  heartbeat.

21
Nervous System Disorder

• Parkinsons 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.