OCR GCSE Biology- B6

What is a stimulus?

A sudden change in an organism's environment, to which the organism must respond in order to maintain suitable conditions for survival.

What is the central nervous system?

The processing centre of the body's nervous system (in vertebrates), which coordinates an animal's response to a stimulus. It is made up of the brain and spinal cord. The CNS is connected to the body by sensory neurons and motor neurons It's a processing centre - it revives information from the receptors & then coordinated a response.

What is the peripheral nervous system?

The part of the body's nervous system that connects the CNS to the body. It is made up of sensory neurons and motor neurons.

What do sensory neurons do?

They carry impulses from receptors to the CNS.

What do motor neurons do?

They carry impulses from the CNS to effectors.

What are receptors?

Groups of specialised cells, which detect stimuli. They tend to be located in an animal's sense organs (ears, eyes, skin etc.). They can form larger complex organs such as the retina of the eye is covered in light receptor cells.

What are effectors?

Any part of the body that produces a response to a stimuli. They respond to nervous impulses. They can also form larger/ complex organs. There are two types: muscle cells (make up muscles)and hormone secreting cells (found in glands).

What is an example of a receptor?

Light receptor cells in the eye's retina- the eye's lens focuses light onto the receptor cells, which are stimulated and send impulses along sensory neurons in the brain.

What is an example of an effector?

Muscle cells in a muscle- impulses travel to the muscle cells, where they stop, causing the muscle cells to contract.

What are neurons?

Specially adapted cells in the body's nervous system, which carry an electrical signal when stimulated. They have elongated bodies and branched endings, so they can make connections between parts of the body and act on numerous other neurons or effectors.

What is an axon?

A long fibre of cytoplasm surrounded by a cell membrane, found in motor neurons. Some are surrounded by a fatty sheath, which insulates the neuron and increases the speed at which the impulse can be transmitted. They also prevent impulses from leaving or entering the axon.

What do electrical impulses and hormones do?

Carry information around the body really quickly so the responses can occur fast; but they're short-lived. Hormones are used to carry information around the body- they're produced in glands and travel in the blood. The responses are slower but they last longer.

What are synapses?

Gaps between adjacent neurons.

How do nervous impulses cross at a synapse?

The impulse reaches the presynaptic neurone. The membrane depolarises thus causing the calcium channels to open, releasing calcium ions. The calcium ions reach the vesticules causing them to open and release neurotransmitters. The neurotransmitters diffuse across the synaptic cleft and reach the postsynaptic membrane at the dendrites. Only specific neurotransmitters bind to specific receptors - stimulating the second neurone to transmit the electrical impulse. Only the sensory neurone can release neurotransmitters, only the post-synaptic neurone has the receptors to take chemicals. The re-uptake of the neurotransmitter by the presynaptic neurone terminates the signal.

What is a reflex action?

Rapid and automatic reponses to certain stimuli. They're quick because you don't think about them - they're involuntary. the route taken by the information in a reflect is called a reflex arc.

What is the basic reflex arc pathway?

The receptor is stimulated, and impulses are sent to the spinal cord along a sensory neuron. The sensory neuron synapses with a relay neuron in the spinal cord, by-passing the brain, which in turn synapses with a motor neuron. The motor neuron sends impulses to the effectors, which dictate a response to the original stimulus.

Why is the reflex response so fast?

Because of the way the fixed pathway of neurons is set out- there is no processing of the information by the brain.

What is the grasping reflex?

A simple reflex of a newborn baby- the baby will tightly grasp a finger placed in its hand.

What is the stepping reflex?

A simple reflex in a newborn baby- the baby will make walking movements when held upright under its arms, with its feet on a firm surface.

What is the rooting reflex?

A simple reflex in a newborn baby- the baby will turn its head an open its mouth, as if it is being fed, when its cheek is stroked.

What is the sucking reflex?

A simple reflex in a newborn baby- the baby will suck on a finger or its mother's nipple, when placed in its mouth.

How do simple reflexes increase the chance of survival?

Simple reflexes cause animals to respond to some stimuli in a way that helps then survive. It protects them from damage and increase the chances of survival.

What is the pupil reflex?

A simple reflex in a human adult- the pupil changes size, depending on the level of light on the eye. In dim light, the radial muscles contract and the circular muscles relax, leading to an increase in pupil size; in bright light, the circular muscles contract and the radial muscles relax, leading to a decrease in pupil size. This is controlled by the iris, and protects the retina from damage.

What is a conditioned reflex action?

A reflex response to a new stimulus, created by building an association between the new, or secondary, stimulus and the stimulus that already triggers the response (primary). It's a form of simple learning that increases the chance of survival. The final response has no direct connection to the secondary stimulus. However, the brain can modify a reflex response via a neuron in the motor neuron of the reflex arc.

What was Pavlov's dog experiment?

Whenever Pavlov brought his dog meat, he rang a bell. The meat caused the dog to salivate. After a while, the dog began to associate the bell ringing with the meat, and the dog would salivate when the bell was rung.

What is the brain and what does it do?

The brain is a complex organ, it contains billions of nerves and trillions of synapses. It allows the modification of behaviour as a result of experience such as learning by experiences and social ones too. as well as coordinate complicated behaviour. .

What are neuron pathways?

Chains of connected neurons, along which a signal can travel.

How are neuron pathways formed?

As the brain grows in the beginning of an animal's life, the neurons mature, sending out multiple branches each due to interactions between other mammals and their environment. This increases the number of synapses and connections between neurons.

How do we learn as a result of experiences?

Different neuron pathways are stimulated by different experiences. When an experience is repeated, the pathway is strengthened, and the pathways which are activated most often are preserved and this is why some skills are learnt through repetition. Pathways that don't get regularly used will eventually get deleted.

How can a babies development be checked?

By looking for certain developmental milestones that a baby should be displaying, such as lifting their head when held to someone's shoulder at 3 months, or holding a cup and drinking from it at 12 months.

What could be the case if the milestones have not been met?

The baby may have neurological problems, or be lacking in stimulation.

What are feral children?

Children that have been isolated from society in some way, so they don't develop in the correct or normal way. Without other human company, they cannot gain the ability to talk, for example, so communicate with a series of grunts.

Why can animals adapt to new situations?

The brain has a very large variety of potential pathways that can be formed.

Why do humans have a high chance of survival?

Humans have large brains with billions of neurons, so they can arrive at complex solutions quickly in many different situations.

What does the cerebral cortex deal with?

The skills enabling human survival- intelligence, memory, language, consciousness etc.

How can psychological techniques be used to map the cerebral cortex?

Different problems, such as memory loss, paralysis or speech loss, are can be caused by damage to different parts of the brain. Studying the effects of the damage can show which parts of the brain control which functions.

How can electronical techniques be used to map the cerebral cortex?

A visual record of the electrical activity generated by neurons in the brain- an electroencephalogram (EEG)- can be used. Electrodes are placed on the scalp, which pick up the neurons' electrical signals. Stimulating a person's receptors will show the parts of the brain that respond, and they can be mapped.

What is MRI scanning?

Magnetic Resonance Imaging- a technique that produces images of different cross-sections of the brain. The image generated uses colour to generate a representation of levels of electrical activity in the brain. The levels change dependent on what the person is doing or thinking.

What is memory?

The ability to store and retrieve information.

What is short-term memory?

Information that is stored for a limited amount of time.

What is long-term memory?

Information that is stored for an unlimited amount of time.

What is the multi-store model?

An idea to explain the brain's storage of information. It states that short-term memory can be rehearsed until it enters long-term storage.

What are the problems with the multi-store model?

It doesn't fully explain memory- some information automatically enters long-term storage (it doesn't need short-term rehearsal). Also, it doesn't explain why we forget.

How can humans more likely to remember information?

-If they see a pattern in it, or create one.
-If information is repeated, especially over prolonged times.
-If there's a strong stimulus associated with it.

What reasons can be given for forgetting?

Decay of neurons (e.g. in Alzheimer's), a lack of retrieval- if a pathway is unused for a long period of time, it is lost.

What is serotonin?

A chemical transmitter with mood-enhancing effects, used in the central nervous system.

How does serotonin work?

It passes across synapses in the brain, and lands on receptor molecules. The remaining serotonin is absorbed back into the transmitting neuron by the transporter molecules.

What is the effect of ecstasy (MDMA) on the central nervous system?

It blocks transporter sites, causing serotonin to build up in the synapses. Serotonin concentrations in the brain therefore increase, and it causes the user to experience feelings of elation, due to the mood-enhancing effects of serotonin. Neurons are harmed by this, and memory loss can be a negative long-term effect.

What are the differences between nervous responses and responses to hormones?

Nervous responses are immediate and short-lived; responses to hormones produced in glands, which travel through the blood, are slower but long-lasting. Both are necessary to control the body's functions.

Describe the parts of the brain.

Frontal lobe - Executes functions, thinking planning, personality, problem solving and behaviour.
Temporal lobe - Memory, understanding and language, small and hearing.
Parietal lobe - Perception, making sense of the world, arithmetic, spelling and speech.
Occipital lobe - Vision (Cerebrum), reading,
Cerebral cortex - Motor and sensory cortex, parietal lobe and frontal lobes.

What are the affects of alcohol, caffeine and anti-depressants on a synapse?

Alcohol: Binds to postsynaptic receptors and prevents neurotransmitters from binding to the receptors which make nervous impulses slow.
Caffeine: Inhibits adenosine neurotransmission which means can increased rate of nervous impulses.
Depression: Fewer neurotransmitters released and their reuptake is prevented by blocking the reuptake channels leader to a higher amount of
neurotransmitters in the synaptic cleft.