27/12/14

B6 Brain and MindB6 Brain and Mind

W Richards

The Weald School

OCR 21st Century Additional Science

27/12/14B6.1 How do animals respond to B6.1 How do animals respond to changes in their environment?changes in their environment?

27/12/14The Nervous SystemThe Nervous SystemThe CENTRAL NERVOUS SYSTEM (CNS) enables us to react to changes in our surroundings (“stimuli”). It consists mainly of the brain, the spinal chord, nerve cells (“neurones”) and receptors.Types of receptor:

1) Light receptors in the eyes

2) Sound receptors in the ears

3) Taste receptors on the tongue

4) Smell receptors in the nose

5) Touch, pressure and temperature receptors in the skin

6) Changes of position receptors in the ears (balance)

27/12/14Nervous ReactionsNervous ReactionsWhen we react to a stimulus our bodies use the following pattern and these signals are sent using electrical impulses:

Stimulus Receptor Coordinator Effector Response

For example, consider a man and a camel: Oh

No!

What are the stimulus, receptor, coordinator, effector and response in this situation?

27/12/14Examples of reactionsExamples of reactionsStimulus Receptor

(i.e. the thing that detects the

stimulus)

Effector (i.e. the thing that will do the

reaction)

Response (i.e. action

taken)

Bright light

Sour taste

Losing balance

Sit on a drawing pin

27/12/14Simple reflexes in humansSimple reflexes in humansBabies can demonstrate simple reflexes:

1) Stepping reflex

2) Startle (or moro) reflex

3) Grasping reflex

4) Rooting reflex

5) Sucking reflex

27/12/14The Iris ReflexThe Iris Reflex

When the light is bright the radial muscles relax, the circular muscles contract and the pupil increases in size.

When the light is bright the radial muscles _____, the circular muscles _______ and the pupil ________ in size.

27/12/14Reflex Actions in AnimalsReflex Actions in Animals

Simple animals rely on reflex actions for most of their behaviour:

Stimulus in a simple animal What is their response?

Feeling hungry

Feeling cold

Feeling threatened

27/12/14Slower responses - hormonesSlower responses - hormonesNervous impulses are electrical signals and are transmitted quickly through the body. The body can also produce a slower response using chemical messengers called hormones.

Examples of bodily processes that use hormones:

Controlling of water content by the

kidneys and the brain:

The menstrual cycle, using hormones from the brain and ovaries:

The development of nervous and hormonal communication systems depended on the evolution of multicellular organisms.

27/12/14B6.2 How is information passed B6.2 How is information passed through the nervous system?through the nervous system?

27/12/14Conscious actionsConscious actionsA conscious action is one where the brain makes a considered response. Here’s what happens:

Stimulus Receptor Sensory Neurone Coordinator

Motor Neurone Effector Response

1) Receptors in your skin detect a stimulus

3) Here another sensory neurone carries the signal to the brain

4) The brain decides to move away the hand

5) This impulse is sent by MOTOR NEURONES to the hand muscles (the effectors) via the spinal chord…

2) The impulse is carried by SENSORY NEURONES to the spinal chord

6) Which then moves the hand away

27/12/14Reflex actionsReflex actionsSometimes conscious action is too slow to prevent harm, e.g…

In situations like this the body bypasses the brain to produce a quicker response. Here’s how it works…

27/12/14Reflex actionsReflex actions

1. Receptor

2. Sensory neurone

3. Relay neurone in the spinal chord

4. Motor neurone

5. Effector

27/12/14Types of nerve cell (“neuron”)Types of nerve cell (“neuron”)

NucleusMuscle strands

(effector)

Axon – a long extension of cytoplasm surrounded

by a membrane

Nerve cells (neurons) are elongated with branched endings to connect to many muscles fibres and aid the transmission of electrical impulses:

Fatty sheath to increase the speed of transmission and to insulate the neuron from surrounding cells

27/12/14The CNS and the PNSThe CNS and the PNS

There are two types of neurone we need to consider:

The Central Nervous System (CNS) is the spinal cord and brain:

The Peripheral Nervous System (PNS) is the collection of neurones connected to the CNS:

2) Motor neurone

Impulse

These carry impulses from the CNS to effectors

1) Sensory neurone

Impulse

These carry impulses from the receptors to the CNS

27/12/14SynapsesSynapses

Neurones never ____ each other – there is a small gap between them called a _____. A signal is sent from one _______ to the next by a _______ transmitter across the synapse (called a “neurotransmitter”). These transmitters are then ________ back into the sensory neurone to be used again. This process only reacts with specific chemicals that bind to the receptor molecules.

Words – chemical, synapse, neurone, touch, reabsorbed

27/12/14Drugs and the Nervous System Drugs and the Nervous System Drugs are classed as “a substance that affects the central nervous system, causing changes in psychological behaviour and possibly addiction”. They do this by affecting the transmission of impulses. Consider Ecstasy for example:

Ecstasy (MDMA) blocks the sites in the brain’s synapses

where the transmitter substance serotonin is removed.

Beta blockers and Prozac can also affect the transmission of impulses.

27/12/14The Cerebral CortexThe Cerebral Cortex

The cerebral cortex is the part of our brain most concerned with intelligence, memory and consciousness. By studying the effects (e.g. memory/sight loss) when different parts of the brain are damaged scientists have been able to identify which parts of the brain control which functions.

27/12/14Other techniques of studying the brainOther techniques of studying the brain1) An electroencephalogram (EEG) is a visual record of the electrical activity generated by neurons in the brain. It works by amplifying and detecting the electrical signals from the brain.

2) Magnetic resonance imaging (MRI) scanning is a new technique that produces images of different cross sections of the brain and uses colours to represent activity.

27/12/14Conditioned reflexes - Pavlov’s DogConditioned reflexes - Pavlov’s Dog

Ivan Pavlov, 1849-1936

I won the Nobel Prize in 1904 and am most famous for investigating

“conditioned responses”:

1) Steak + dog = saliva

2) Steak + bell + dog = saliva

3) Bell + dog = saliva

Notice that the final response (saliva) has no direct relation to the stimulus (the bell). Conditioned reflexes can increase an animal’s chance of survival!

27/12/14Reflex actionsReflex actions

Sometimes the brain can modify a reflex response via a neuron to the motor neuron of the reflex arc, meaning that you could keep hold of a hot object:

27/12/14B6.4 How do humans develop more B6.4 How do humans develop more complex behaviour?complex behaviour?

27/12/14Human BrainsHuman BrainsUg. My chances of survival were made a

lot better when my brain got bigger. Notice I can now use simple tools!

Mammals have complex brains with billions of neurons. The interaction between our ancestors and their environment caused neuron pathways to form in the brain.

27/12/14Learning Complex BehaviourLearning Complex Behaviour

When the brain is asked to do certain tasks different areas are “activated”. New experiences cause new neuron pathways to develop, while pathways that are not used are eventually destroyed. This is why we become better at certain tasks when we practice them more often.

PET scan showing areas “activated” by doing algebra.

27/12/14Feral childrenFeral children

Task: to find out what “feral children” are, what has caused their condition and what the consequences are.

27/12/14MemoryMemoryOur memory is divided into two types: short term and long term.

Short term memory is capable of storing a limited amount of information for a limited amount of time. Long term memory is when more information is stored over a much longer time.

Ways of improving short term memory, e.g. a phone number

Ways of improving long term memorye.g. exam revision

27/12/14Using Models to Explain MemoryUsing Models to Explain MemoryWe can understand memory better by using models to explain it, for example:

What could cause a model to be limited in explaining how memory works?