14 Coordination and

Homeostasis : is the maintenance of a constant internal environment in an organisms body

Organs That Take Part In Homeostatic Processes

1. Lungs: maintain the concentration of CO2 and O2 constant
2. Skin: regulates body temperature
3. Kidneys: regulate the concentration of water and urea/salt
4. Liver: regulates the blood sugar level and removes poisons

Optimum : best values for cells to function

How homeostasis is brought about / Regulation of body temperature :

(SHORT ANS) Receptors detect change in temperature and carry impulses to hypothalmus (brain)
(EXP) Temperature receptors in the brain sends messages along nerves when the temperature of blood rises
above the normal in order to decrease or return the temperature back to normal
The opposite also occurs if blood temp drops below normal

Structure of skin : (memorize)

-Ways of losing heat :

1. Evaporation of sweat
2. Excretion of warm faeces
3. Excretion of warm urine
4. Expiration of warm air

Skin in regulating body temperatue :

HOT COLD
Production of sweat / sweating No sweating , Shivering occurs

Blood vessels dilate/ Blood vessels constrict / Vaso-

Vasodilation (to release heat) constriction (to reduce heat loss)
Muscles relax / lowering of hair - Muslces contract / hair erects -
hair is flat (so no air is trapped to (hair traps air to provide insulation
provide insulation) , reduce rate of heat loss)

More detailed :
( In over-heating )
- Production of sweat : Evaporation requires heat energy , an amout of this energy is gained from the body , thus
decreasing its temperature (Evaporation)
- Vasodilation : It means to keep blood vessels in the skin wide , this helps in getting rid of excessive heat from
warm blood to the surroundings (Radiation)
- Lowering of hair : this helps in getting rid of excessive heat by reducing the amount of trapped air that acts as
an insulator (Convection)

( In over-cooling )
- Shivering : shivering reflex causes muscles around the vital organs to shake in small movements to attempt and
create warmth by expending energy
- Vasoconstriction : It means that blood vessels of the skin constrict , this reduces the excretion of sweat and heat
loss from warm blood when it comes near the body surface
- Erection of hair : hair erector muscles contract to erect hair and hair traps air ,which is a bad conductor of heat ,
therefore it reduces the rate of heat loss
- Storage of fats under skin : Fats are bad conductors of heat therefore they reduce the rate of heat loss
Negative feedback : body counteracts the action experienced by your body to bring it back to normal conditions /
process by which different internal conditions of the body is controlled to maintain homeostasis , a change sets
off a response that cancels out the change , sequence of steps :

1. A sense organ detects a change or deviation ( acts as a signal to control centre )

2. A control center sends a message to the responding organ to decrease or increase its production
3. The information from the responding organ is detected by the sense organ

Example :-
(When blood glucose levels increase) : the pancreas secretes the hormone insulin to stimulate body cells to use
up glucose and liver cells to store it as glycogen- When the blood glucose level drops down to its normal level, it
causes a negative feedback mechanism on the pancreas, causing the secretion of insulin to be switched off.
(When blood glucose level decrease) :
Pancreas secretes the hormone glucagon which stimulates the conversion of glycogen into glucose to be added in
the blood stream- When the blood glucose levels drops back to the normal level, it causes a negative feedback
mechanism on pancreas, causing the secretion of glucagon to be switched off.
SO...

Insulin - released when BS is too high , stimulates release of GC

1. Blood glucose level gets too high
2. Stimulates enzyme production in pancreas
3. Insulin stimulates liver to change glucose to glycogen
4. Blood glucose concentration decreases
5. Glycogen stored for energy

Glucagon - released when BS is too low , stimulates release of GC

1. Blood glucose level gets too low
2. Stimulates enzyme production in pancreas
3. Glucagon stimulates liver to change glycogen back to glucose
4. Blood glucose concentration increases

High blood glucose (Insulin)--> Glycogen stored

Low blood glucose (Glucagon)<-- Changes back to glucose

Hormones : chemical secretions , produced by a gland and carried by blood , which alters activity of one or more
target organs

Effects of adrenaline (‫ )شعراوي‬:

- Muscle contraction
- Dialted pupils
- Increased breathing rate
- Increased heart rate
- Increased blood pressure

- Coordination and Response

Sense organs : group of receptor cells that respond to specific stimuli

-> Eye - light receptors
-> Skin - temperature and pressure receptors
-> Nose and tongue - chemical receptors

Effector : a part of the body that goes into action when it receives impulses
-> Muscles
-> Glands

+ Stimulus : a change in enviroment detected by receptors

+ Receptor : cells that detect a stimulus and convert it into an electric impulse
+ Effector : muscle or gland that responds to a stimulus

Coordination or communication is the way in which receptors pick up stimuli and then pass the information to
effectors / is how the body will be controlled

Systems needed for coordination

-> Nervous system (NS) - Short and rapid effect
-> Endocrine system (ES) - Longlasting and slow effect

- Nervous system
Consists of :
1. Central nervous system (CNS) : composed of brain and spinal cord
2. Peripheral nervous system (PNS) : composed of cranial nerves (nerves branched from the brain) and spinal
nerves (branched from the spinal cord)

Nerve impulses : series of electro-chemical (imp) signals that travel down nerve fibers

- Functions of CNS
-> Receive impulses from different receptors
-> Integrates the received messaged or impulses
-> Produces nerve impulses to the proper effector

- The spinal cord

Protected by : vertebral column
Its regions : White matter on the outside , grey on the inside
Its functions :
-> Controls reflex actions in parts below the neck
-> Conducts impulses from the sense organs below the neck to the brain
-> Conducts impulses from the brain to the effectors below the neck

- Building units of NS
+ Made up of nerve cells called neuros
Types of neurons :
-> Sensory neuron - its function is to carry impulses from a sensory organ or receptor to CNS ( Carry info TO
CNS ) , it has a long dendron and a short axon
-> Motor/Effector neuron - its function is to carry impulses from CNS to an effector ( Carry info FROM CNS )
-> Connecter/relay neuron : connects neurons in the CNS

Myelin sheath : made of cells rich in fats and proteins and contains narrow gaps called the node of ranvier
-> Functions :
- Protection
- Insulation
- Increases speed of nerve impulse transmission

Sensory neuron Relay neuron Motor neuron

Long Short Long
Cell body branching Small cell body Large cell body
off middle of axon at one end at one end
Dendrite ? Many dendrites Long dendrites
 # Speed in myelinated sheath nerve cell is 100 m/s while in non-mylinated nerve cell is only 5 m/s

Ganglion : swelling in sensory nerve cells that contain the cell bodies of sensory neurons

- Adaptations of nerve cells to their function :

-> Long axon or dendron , transmit nerve impulses
-> Nerve endings; transmit impulses to another nerve cell or effector
-> Dendrites; receive nerve impulses from other cells
-> May have myelin sheath for protection, insulation and an increased nerve impulse transmission speed

- Synapse
A junction between nerve cells consisting of a minute gap across which impulses pass, by diffusion of a
neurotransmitter substance

Structure of synapse :
-> The gap is known as synaptic cleft
-> The end of a nerve cell is called a synaptic knob
-> In a synaptic knob, vesicles containing neurotransmitter substances are made
Transmission of impulses along a synapse
1. Impulses arrive at the end of a synaptic knob
2. Transmitter substance/chemical is secreted/diffurses across into the synaptic gap/cleft to reach the adjacent
neuron , where it binds to special receptors ( act as lock and key )
3. A new impulse is generated in the adjacent neuron
Importance of synapse :
+ Ensures the one way transmission of nerve impulses as neurotransmitters are only produced in synaptic bib
(knob) while receptors for the neurotransmitter substances are found in the post synaptic membrane.
+ Slower transmission as time is needed for the release of neurotransmitter substances and their diffusion across
the synaptic cleft. Time is also needed for the neurotransmitter substances to bind with their receptors.

Compare :

- Reflex action and Reflex arc

Reflex action : rapid and automatic involuntary response to stimulus , its important for
-> Survival value , it is rapid and does not need thinking as it does not involve the higher centers in the brain
-> Reflex actions have a role in learnt skills such as walking or driving

Reflex arc : the pathway of impulses in a reflex action

Stages of RAC
1. Receptor cells send sensory impulses along a sensory neuron to the CNS , through the dorsal root
2. Sensory neuron forms a synapse with the connector neuron
3. Impulses are transmitted through the connector to the motor neuron , again through a synapse
4. Motor neuron carries impulses through the ventral root to the muscle to contract and pull the arm (example)
away from the source of harm
SO..
receptor -> sensory neurone -> relay neurone -> motor neurone -> effector

# The cell body of a sensory neuron is found in the ganglion of the dorsal root
# Cell bodies of motor and relay neuron are found in the gray matter of the brain or spinal cord

Benefits of reflexes :
● Fast response because the brain is not involved
● Keeps us safe e.g. finger in flame reflex action to move it away
● Minimises damage to the body from harmful conditions
● Doctors can use reflex reactions to check if a patient's nervous system is functioning properly
The CNS processes information from receptors and passes instructions to effectors to tell the organism how to
respond , this complex series of operations referred to as integration

- Antagonistic muscles :
Two sets of muscles work against each other to move the body parts in opposite directions

Sets Of Antagonistic Muscles

+ One is called flexor; bends the joint due to its contraction
+ One is called extensor; straightens out a joint due to its contraction

Example :-
Biceps is a flexor , contracts to pull the forearm towards the shoulder
Triceps is an extensor , contracts to pull the end of the ulna
(bone in the forearm) causing the arm to be straightened

# Each bone and muscles are joined by a bundle of strong non-stretchy fibers called tendons
# Triceps: joined to the shoulder by means of three tendons
# Biceps: joined to the shoulder by two tendons

Muscle cells : these are modified cells responsible to carry out contraction for movement

Adaptations of muscles to their function :

1. Lots of mitochondria; for sufficient energy production
2. Have the ability to respire anaerobically in addition to aerobic respiration; again for the production of energy
needed for their actions to be carried out.
3. Store carbohydrates in the form of glycogen to be used as a source of energy.
4. Part of its cytoplasm is modified into contractile filaments.\