5.1 Homeostasis and 5.2 the human nervous system

Define homeostasis

It is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal + external changes.

why does the core body temperature need to be controlled by homeostasis?

To maintain the optimum temperature for enzymes

(they can denature when temp is too high and can work too slowly when temp is low)

why do PH levels need to be controlled by homeostasis?

Enzymes denature if PH increases or decreases too far away from the optimum PH

why does the blood glucose concentration need to be controlled by homeostasis?

Glucose needed as it is the main substrate for respiration to provide energy for metabolic processes

why do the water levels of blood need to be controlled by homeostasis?

Needed to prevent water movement into or out of the cells by osmosis

(too high- water moves into the cell causing them to lyse (burst). Too low- water moves out of cells causing them to plasmolyse (shrivel))

why does the ion concentration of blood need to be controlled by homeostasis?

water will move into or out the cells by osmosis if this is incorrect

(Too high- plasmolyse. Too low- lyse)

why does the concentration of waste material need to be controlled by homeostasis?

These are usually poisonous + need to be removed from the body before they build up to toxic levels + cause damage to cells

What do receptors do?

They detect changes in the internal/external environment (called stimuli)

What do coordination centres do?

They receive and process the information from the receptors + then coordinate the response (where it needs to go)

What are the effectors?

Muscles or glands, which bring about a response when it receives a message from the brain

State 3 ways in which your external environment may vary:

• Temperature

• PH levels

• Lack of food

What is a stimulus and a response?

• A change that can be detected

• What happens as a result of the stimulus

What is a sensory neurone?

It sends electrical impulses from the receptors in the sense organs, to the brain

What is a motor neurone?

Sends electrical impulses from the brain to the muscles and glands (effectors)

What is a coordinator?

The brain and the spinal column, also known as the CNS. This processes the information from the sensory neurones.

What is the path of a nerve impulse?

1. Stimulus detected by receptor

2. Nerve impulse passed along sensory neurone

3. Synapse between neurones

4. Central nervous system (CNS) processes the information

5. Nerve impulse passes along the motor neurone

6. Message reaches the effector (a muscle or gland) causing a response

What is a neurone?

Nerve cells which send + receive signals from the brain

What is a nerve impulse?

Electrical charge that travels along the membrane of a neurone

What is the synapse?

A junction between 2 nerve cells consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

1. The electrical nerve impulses can’t cross the synapse

2. Chemicals called neurotransmitters are released which diffuses across the synapse

3. The neurotransmitter binds to receptors on the membrane of the next neurone causing a new nerve impulse

Suggest how drugs could affect the transmission of information at synapses:

• Blocking the neurotransmitter from binding to the receptor and stopping the impulse in the next nerve

• Binding to the receptor + causing a new impulse, even when there’s no neurotransmitter

Define a reflex action:

Automatic responses that don’t involve the conscious part of your brain

Examples of reflex actions:

• Breathing

• Sneezing

• When you touch something hot or sharp you pull your hand back

• If something comes near your face you blink

• Moving food through your digestive system

Why are reflexes important?

They are faster than conscious actions therefore….

• Protect the body from damage/ injury

• Increase chances of survival (for animals)

Why are reflexes faster than conscious actions? (IMPORTANT)

• There is only one relay neurone (either in the spinal column or the brain) in a reflex, where conscious actions will have many relay neurones

• Therefore reflex actions involve fewer synapses

• Diffusion of neurotransmitters across

Factors affecting reaction time:

• Drugs (e.g. cocaine)

• Alcohol

• Lack of sleep

• Stress

• Adrenaline

• Energy (how much you have eaten)

REQUIRED PRACTICAL 9

STRUCTURES IN THE BRAIN ON PHYSICAL REVISION CARDS

Main function of the meninges:

To protect and support the central nervous system

Main function of the cerebral cortex:

It is responsible for higher level processes of the human brain (e.g. language, memory and learning)

Main function of the medulla:

It controls breathing, heart rate + peristalsis

Main function of cerebellum:

It controls movement, balance and co-ordination

Main function of hypothalamus:

Detects changes in blood temperature + water concentration

Main function of the pituitary gland:

Secretes several hormones into the blood in response to the bodies conditions

Name different ways in which scientists can study the brain:

• MRI scans

• Scanning the living brain

• Post mortem examinations

• FMRI (functional magnetic resonance imaging)

Explain some of the difficulties of investigating brain functions and treating brain damage and disease: