Coordination and control

Co-ordination is the way all the organs and systems of the body are made to work efficiently
together.
Types of coordination
• Nervous coordination
• Hormonal coordination
Nervous system/coordination
The nervous system (brain, spinal cord and nerves) coordinates and regulates body functions
The nervous system includes the central (brain & spinal cord) and peripheral nervous systems
(sense organs, including the eye, contain receptors that are sensitive to stimuli and respond with
reflex actions). In otherwards

• the central nervous system (CNS) – the brain and spinal cord
• the peripheral nervous system – nerve cells that carry information to or from the CNS
Functions of cerebrum, cerebellum, pituitary gland and hypothalamus, medulla, spinal cord and
nerves
Cerebrum: The cerebrum (the outer layer is called the cerebral cortex), which is split into two
hemispheres and is highly folded. It controls intelligence, personality, conscious thought and high-
level functions, such as language and verbal memory.
Cerebellum: which controls balance, co-ordination of movement and muscular activity.
Pituitary gland: This gland is attached to the base of the brain. Also known as a 'master gland'
(because it controls other glands). It secretes several/many hormones into the blood in response
to the body's condition, such as blood water levels. For example, follicle stimulating hormone
(FSH) which, when it reaches the ovaries, makes one of the follicles start to mature and to
produce oestrogen. Luteinising hormone (LH), also known as lutropin, is also produced from the
pituitary and, together with FSH, induces ovulation.
Hypothalamus: It plays homeostatic roles by regulating temperature, water content, blood
glucose e.t.c
Medulla; controls unconscious activities such as heart rate and breathing rate.

The spinal cord and brain make up the central nervous system. The spinal cord in particular
coordinates unconscious activities such as reflex actions.
Nerve cells : Nerve cells are called neurones. They are adapted to carry electrical impulses from
one place to another. A bundle of neurones is called a nerve. There are three types of neurons

• Sensory neurones: carry electrical impulses from the receptors to the Central nervous
system (CNS).
• Motor neurone: transmits electrical impulses from the Central nervous system to the
effectors.
• Relay neurone: (also called multi-polar or connector neurones). Relay neurones are
located in the CNS. Their job is to pass electrical impulses from the sensory neurone onto
the motor neurone.
Each neurone has a cell body consisting of a nucleus surrounded by a little cytoplasm. Branching
fibres, called dendrites, from the cell body make contact with other neurones. A long filament of
cytoplasm, surrounded by an insulating sheath, runs from the cell body of the neurone. This
filament is called a nerve fibre.

Reflex action
• A reflex action is an automatic response to a stimulus. (A stimulus is a change in the
external or internal environment of an organism. They involve
three neurones: a sensory neurone, a relay neurone and a motor neurone.
• The gap between neurones is called a synapse.

When a particle of dust touches the cornea of the eye, you will blink; you cannot prevent
yourself from blinking. A particle of food touching the lining of the windpipe will set off a
coughing reflex that cannot be suppressed. When a bright light shines in the eye, the pupil
contracts. You cannot stop this reflex and you are not even aware that it is happening.
Reflex arc
The nervous pathway followed by a reflex action is called a reflex arc. A reflex follows a
general sequence and does not involve the brain:

stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector →

response
For example, a simple reflex arc happens if we accidentally touch something hot.

1. Receptor in the skin detects a stimulus (the change in temperature).

2. Sensory neurone sends impulses to relay neurone.
 3. Motor neurone sends impulses to effector.

4. Effector produces a response (muscle contracts to move hand away).

Other examples of reflex actions
knee jerk, pupil reflex, blinking, removing your hand from a sharp object e.t.c

In Figure below the nervous pathway for a well-known reflex called the ‘knee-jerk’ reflex
is shown.
One leg is crossed over the other and the muscles are totally relaxed. If the tendon just below the
kneecap of the upper leg is tapped sharply, a reflex arc makes the thigh muscle contract and the
lower part of the leg swings forward.

On the picture below, the stimulus is a drawing-pin sticking in the finger. The response is the
withdrawal of the arm due to contraction of the biceps.
The sequence of events is:
Stimulus (sharp pain in the finger)
↓
Receptors (pain receptor in skin)
↓
Coordinator (spinal cord)
↓
Effector (biceps muscle)
Reflexes
The reflex just described is a spinal reflex. The brain, theoretically, is not needed for it to
happen. Responses that take place in the head, such as blinking, coughing
and iris contraction, have their reflex arcs in the brain, but may still not be consciously
controlled.

Synapses
In order for an impulse to be conducted from one neurone to another, it must travel across
the synapse.

Synapse: a junction between two neurones, consisting of a gap across which impulses pass by
diffusion of a neurotransmitter
• The synapses ensure that impulses travel in one direction only.
• Synaptic cleft: the small gap between each pair of neurones
• Inside the neurone’s axon, there are 100s of tiny vacuoles (vesicles, each containing a
chemical called neurotransmitter)
• When an impulse arrives, the vesicles move to the cell membrane and empty their content
into the synaptic cleft.
• The neurotransmitter quickly diffuses across the tiny gap and attaches to receptor
molecules in the cell membrane of the relay neurone.
• This can happen because the neurotransmitter molecules' shape complements the receptor
molecule's shape.
14.2 Mammalian sense organs
 The eye
The eye is a sense organ.

Sense organs are groups of sensory cells responding to specific stimuli, such as light, sound,
touch, temperature and chemicals.

Sense organ Stimulus

ear sound, body movement (balance)
eye light
nose chemicals (smells)
tongue chemicals (taste)
skin temperature, pressure, touch, pain
 Principal functions of component parts of the eye

Structure Function

Cornea Clear area of the sclera, refracts the light entering and helps to focus it.

Iris Muscles which alter the size of the pupil, controlling the amount of light entering
the eye.

Lens Focuses light onto the retina.

Retina a light-sensitive layer made up of rods, which detect light of low intensity, and
cones, which detect different colours
Optic Carries impulses between the retina and the brain.
nerve

Sclera White, tough outer layer.

Choroid Pigmented middle layer with many blood vessels. It absorbs light to avoid reflection
and nourishes the retina.

Blind spot Where the optic nerve leaves the retina so lacks receptor cells.

Pupil Small hole at the centre of the iris through which light enters the eye.

The Blind Spot

• At the point where the optic nerve joins the retina, there are no light-sensitive rod and
cone cells on that part of the retina
• Light falling onto that part of the retina will not result in an image being detected
o the brain 'fills in' from surrounding light so we don't see a black hole where no
light has fallen
• This causes a blind spot, where we cannot detect an object in our peripheral vision even
if it is there.

The Pupil

The pupil isn’t really a structure at all as it is simply a circular hole in the iris. The iris is a
coloured muscular disc at the front of the eye.

The iris has two sets of antagonistic muscles in it that can contract or relax to change the
diameter of the pupil. There are radial muscles arranged like the spokes of a bicycle tyre and
also circular muscles in the iris as shown in the diagram below.
The Pupil Reflex

• This is a reflex action carried out to protect the retina from damage in bright light and
protect us from not seeing objects in dim light
• In dim light the pupil dilates (widens) in order to allow as much light into the eye as
possible
• In bright light the pupil constricts (narrows) in order to prevent too much light entering
the eye and damaging the retina
• In dim light, the pupil dilates (becomes larger) to allow more light to enter the eye to
improve vision.
• In bright light, the pupil constricts (gets smaller) to allow less light to enter the eye to
protect the retina from damage.

Accommodation (focusing)
• The eye can produce a focused image of either a near object or a distant object. To do this
the lens changes its shape, becoming thinner for distant objects and fatter for near objects.
This change in shape is caused by contracting or relaxing the ciliary muscle, which forms
a circular band of muscle in the ciliary body

• The way the lens brings about fine focusing is called accommodation
• The lens is elastic and its shape can be changed when the suspensory ligaments attached
to it become tight or loose
• The changes are brought about by the contraction or relaxation of the ciliary muscles.

• When an object is far away:

o The ciliary muscles relax (the ring of muscle increases in diameter)
o This causes the suspensory ligaments to tighten
o The suspensory ligaments pull on the lens, causing it to become thinner
o Light is refracted less.
• When an object is close up (near)
o The ciliary muscles contract (the ring of muscle decreases in diameter)
o This causes the suspensory ligaments to loosen
o This stops the suspensory ligaments from pulling on the lens, which allows the
lens to become fatter
o Light is refracted more
 Rod & Cone Cells
Rods and cones are light-sensitive cells in the retina. When stimulated they generate electrical
impulses, which pass to the brain along the optic nerve.

• There are two types of receptor cells in the retina:

o Rods, which are sensitive to dim light
o Cones, which distinguish between different colours in bright light
 • There are 3 types of cone cells which are sensitive to different colours of light (red,
blue and green)
• The fovea is an area on the retina where almost all of the cone cells are found
• Rod cells are found all over the retina, other than the area where the optic nerve attaches
to the retina - there are no light-sensitive cells at all in this area, and so it is known as
the blind spot.

14.3 Mammalian hormones

Hormones & Their Associated Glands

What is a Hormone?
A hormone is a chemical substance produced by a gland and carried by the blood
The hormone alters the activity of one or more specific target organs i.e. they are chemicals
which transmit information from one part of the organism to another and bring about a change
The glands that produce hormones in animals are known collectively as the endocrine system.
Transport around the body

• Endocrine glands have a good blood supply as when they make hormones they need to
get them into the bloodstream (specifically the blood plasma) as soon as possible so they
can travel around the body to the target organs to bring about the response
• Hormones only affect cells with target receptors that the hormone can bind to. These are
either found on the cell membrane, or inside cells. Receptors have to be complementary
to hormones for there to be an effect.
• The liver regulates levels of hormones in the blood; transforming or breaking down any
that are in excess.
How hormones work
Important hormones in the human body:
Comparison of Nervous & Hormonal Control

Glucagon: Extended

• Blood glucose levels are controlled by a negative feedback mechanism involving the
production of two hormones - insulin and glucagon
• Both hormones which control blood glucose concentration are made in the pancreas
• Insulin is produced when blood glucose rises and stimulates liver and muscle cells to
convert excess glucose into glycogen to be stored
• Glucagon is produced when blood glucose falls and stimulates liver and muscle cells
to convert stored glycogen into glucose to be released into the blood
Negative feedback regulation of blood glucose levels

Exam Tip
The terms glucagon and glycogen are very often mixed up by students as they sound similar.
Remember:

• Glucagon is the hormone

• Glycogen is the polysaccharide glucose is stored as

Learn the differences between the spellings and what each one does so you do not get confused
in the exam!
 The Hormone Adrenaline

• Adrenaline is known as the 'fight or flight' hormone as it is produced in situations

where the body may be in danger
o Flight = remove oneself rapidly from a dangerous situation eg. run away
o Fight = if flight is not possible, resort to physical combat to overcome danger
• It causes a range of different things to happen in the body, all designed to prepare it for
movement (ie fight or flight).
• These include:
• Increasing blood glucose concentration for increased respiration in muscle cells
• Increasing pulse rate and breathing rate so glucose and oxygen can be delivered to
muscle cells, and carbon dioxide taken away, from muscles cells more quickly
• Diverting blood flow towards muscles and away from non-essential parts of the body
such as the alimentary canal; again to ensure the reactants of respiration are as available
as possible
• Dilating pupils to allow as much light as possible to reach the retina so more
information can be sent to the brain

Exam Tip
It is worth learning this list of effects of adrenaline as it is a fairly common exam question and
can be worth several easy marks.

More on Adrenaline: Extended

More on Adrenaline: Extended

• Additional effects of adrenaline include;

o Increasing the concentration of glucose in the blood
▪ This help deliver more important glucose to muscles for respiration
o Increasing heart rate
▪ This has the same effect, to ensure that all muscles are well prepared for
high levels of activity in a flight or fight situation