Section 12

The brain is made up of four separate parts that do different jobs

These are:The cerebrumThe cerebellum The medulla oblongataThe hypothalamus

Hypothalamus

Pituitary GlandCerebellum

Cerebrum

Medulla

The cerebrum is the largest part of the brain which split into two cerebral hemispheres

Both halves of the cerebrum are involved in conscious thought and decision making processes, as well as controlling your personality, emotions, sight and speech

http://www.youtube.com/watch?v=kJqCOarebWw&NR=1

Motor Strip Sensory Strip

Front of cerebrum

The sensory strip is an area of the cerebrum that deals with all incoming information from the senses; ears, eyes, nose, tongue and skin

This information is processed here and then you decided what to do

E.g. You taste cabbage, realise that you do not like the taste and then decide to spit it out!

Areas of the body which are more sensitive have a larger area of the sensory strip devoted to it

The motor strip is an area of the cerebrum in front of the sensory strip

The motor strip sends information to muscles of the body that we control by conscious thought

If an area of the body has a greater degree of movement, such as the hands, then a larger area of the motor strip is devoted to the hands

Arm

Fingers

Motor Strip

The area of the motor strip devoted to the fingers is much larger than that of the arm. This is because the fingers have much more movement than the arm.

Sensory Strip

Chest

Lips

The area of the sensory strip devoted to the lips is much larger than that of the chest. This is because the lips have much more sensitive than the chest

The diagram above shows how a human being might look if

their body was in proportion to the number of motor neurones

in the motor strip in the cerebrum

The diagram above shows how a human being might look if

their body was in proportion to the number of sensory neurones

in the sensory strip in the cerebrum

The cerebellum controls subconscious activities associated with the fine motor control of muscles (co-ordination) and balance

Fact! Cats have a larger cerebellum than humans – this makes them great at balancing!

The medulla controls most of the basic bodily functions that we need to stay alive. If your medulla stops working, you are considered clinically dead.

The functions of the medulla include:Heart rateBreathing rateDigestion

The hypothalamus is an organ found just above the pituitary gland, on the underside of the brain

The hypothalamus has many functions, but two important functions are: Monitoring

temperature Monitoring the

osmotic concentration of the blood

Hypothalamus

Use the words cerebrum, cerebellum, medulla and hypothalamus to complete the

following

1. Centre for conscious thought

2. Needed for co-ordinating our muscles for walking

3. Controls sneezing and coughing

4. Monitors our body temperature

5. Contains the motor and sensory strip

6. Regulates out heart rate

1. Cerebrum

2. Cerebellum

3. Medulla

4. Hypothalamus

5. Cerebrum

6. Medulla

The brain and the spinal cord make up the central nervous system (CNS)

The CNS controls all areas of the body by sending information to and from the CNS through special cells called neurones

There are three different types of neurone: Sensory neurones Relay neurones Motor neurones

Sensory neurones pick up information from our senses e.g. information about sound, light, touch, taste or smell

The brain decides what it wants to do with this information and nerve impulses are sent to muscles or glands to bring about the appropriate response

Muscles and glands are known as effectors

A neurone is the term used to describe a nerve cell

A sensory neurone is a type of nerve cell that passes messages back to the CNS from sense organs

Cell Body

Nucleus

Direction of impulseSkinCNS

Relay neurones are found in the CNS. They connect (relay) information from sensory neurones to other neurons in the body.

Motor neurones transmit information to effectors such as muscles

Motor neurones carry nerve impulses from relay neurones in the CNS to effector muscles and glands

Sensory neurone

Motor neurone

Relay neurone

Section of the spinal cord

A reflex arc is an arrangement, usually of three neurones, that allows a reflex response to take place

The response in a reflex arc is extremely fast because only three neurones are involved in the response

Only the spinal cord is involved in this process which means that you do not use your brain to think of what to do in these situations

E.g. sneezing, coughing, blinking, moving your hand from a very hot object

Reflex reactions are very important – they could save you from danger to your life or damage to your body

Sensory neurone

Relay neurone

Motor neurone

Using the diagram on the next slide, describe what is happening using the following words:Motor neuroneSensory neuroneReflex arcRapidRelay neuroneEffector (muscle)Stimulus

AnswerA harmful stimulus is detected by sensory

neurones. This is passed on to the relay neurone in the spinal cord.

The message is then passsed on to the motor neurone which ends in an effector (muscle) to move the hand away from the harmful stimulus. This is an example of a reflex arc because it is a rapid response.

1. What do the letters CNS stand for?

2. Name the two principle types of neurone

3. Which of these two links the CNS with the effectors?

4. Describe three features of reflex actions

5. Give two examples of reflex actions

1. Central Nervous System

2. Sensory and Motor

3. Motor

4. They are quick, automatic and difficult to suppress

5. Coughing and Sneezing

The hypothalamus is the body’s temperature regulatory mechanism

Thermoreceptors are special cells that detect information about heat and cold

There are thermoreceptors in the skin that convey information about the temperature of the skin surface

Hypothalamus

The hypothalamus also contains central thermoreceptors that detect changes in the temperature of the blood and the body core

If the temperature of the body cores gets too high or too low, effectors trigger responses to get the body temperature back to normal

Body Shell

Body Core

Receptors CNS Effectors

The skin plays a leading role in temperature regulation

The skin acts as an effector in order to correct increases or decreases in temperature using the following mechanisms:

i. Increase in rate of sweating

ii. Vasodilation

iii. Decrease in rate of sweating

iv.Vasoconstriction

v. Contraction of erector muscles

http://www3.fhs.usyd.edu.au/bio/homeostasis/Human_BodyTC_Pg03.htm

Temperature Increase

Temperature decrease

Heat energy from the body is used to convert water in sweat to water vapour

When this water vapour evaporates, the core body temperature is lowered and brought back to tolerable limits

Arterioles leading to skin become dilated (larger)

A large volume of blood is allowed to flow through capillaries near the skin surface, where heat radiation can occur

This loss of heat lowers body temperature

Decrease in rate of sweating reduces heat loss as water cannot be converted to water vapour

Vasoconstriction is the opposite of vasodilation – here the arterioles constrict, minimising heat lost by radiation

Contraction of erector muscles – this process is more effective in furry animals than humans

This process works by hairs being raised up from the skin surface, trapping a layer of air which acts as an insulator

Thermoreceptors detect decrease in

temperature

Cerebrum, which controls conscious decision making

becomes aware of cold

Appropriate voluntary action taken to increase body temperature

The ability to make voluntary responses is an important part of control of body temperature

All of the mechanisms that you have learned about are to bring the body’s core temperature back to normal levels

This mechanism is called negative feedback control

When a factor increases beyond a set point i.e. above 37oC, a response is triggered that may cause that factor to decrease to normal levels and vice versa

Normal body temperature

(37oC)

Normal body temperature

(37oC)

Increase in body temperature

decrease in body temperature

Thermoreceptors in hypothalamus

Motor nerve impulses to skin

Motor nerve impulses to

skin

Vasodilation, increased sweating

Vasoconstriction, decreased sweating

Increase in body temperature

decrease in body temperature

Thermoreceptors in hypothalamus

No change in body temperature

(temperature remains at set point)

A

Look carefully at the diagram above.

Decide whether the response is to cold temperature or hot temperature and describe what is happening at points 1, 2 and 3.

Make sure you write in sentences.

B

Look carefully at the diagram above.

Decide whether the response is to cold temperature or hot temperature and describe what is happening at points 1, 2 and 3.

Make sure you write in sentences.

1. What happens to capillaries near the surface of the skin when we are too hot?

2. What must happen to sweat before it has a cooling effect?

3. Which chemicals in our cells are particularly sensitive to temperature change?

4. What term is used to describe the control mechanism that maintains body temperature?

1. More blood is diverted through them to enable the body to lose more heat

2. It must evaporate

3. Enzymes

4. Negative feedback control