Unit 2.2 Control and Communication Flashcards
Function of the nervous system
Allows an organism to detect changes in its external and internal environment, analyse and store information and respond to changes.
What are the 2 main parts of the nervous system?
Central nervous system (CNS) and peripheral nervous system (made up of nerves linking the CNS to other areas).
Central nervous system (CNS)
The brain and spinal cord.
Receptors
Specialised cells that detect changes in the internal and external environment.
Receptors detect a stimulus and change it into an electrical signal (impulse) which is sent to the CNS.
Where are receptors found?
They are found in sense organs (eg. photoreceptors in the eye), the skin (pressure, pain and thermoreceptors) and inside the body (eg. stretch receptors in blood vessels and the gut wall).
Brain
A complex organ made of billions of nerve cells.
It interprets electrical signals from other parts of the nervous system and sends out more signals in response.
What are the 3 main areas of the brain?
Cerebrum, cerebellum and medulla.
Cerebrum
Responsible for high level processing - thought, memory, reasoning and intelligence
Medulla
Controls breathing and heart rate.
Cerebellum
Used for muscular co-ordination and balance.
Spinal cord
A bundle of nerve fibres that runs the length of the body from the brain through a hole in each vertebra (back bone).
Electrical signals travel up and down the spinal cord to/from the brain or enter and leave through peripheral (side) nerves during a reflex action.
Nerve
A bundle of nerve fibres wrapped in a protective cover (sheath)
Nerve fibres are bundles of axons (the long fibres of neurons - nerve cells)
Neurons
Specialised nerve cells that carry electrical impulses around the body.
They have long fibres called axons which carry the impulses, and smaller fibres that connect with other neurons.
What are the 3 types of neuron?
Sensory, inter (relay) and motor neurons.
Sensory neuron
Transmits impulses from a receptor to the CNS.
The cell body (containing the nucleus and most of the cytoplasm) is found in the middle of the sensory neuron - off to one side.
Inter (relay) neurone
Found within the CNS (brain and spinal cord).
Link sensory to motor neurons.
The cell body is in the centre of the inter neuron.
Motor neuron
Transmit impulses from the CNS to an effector (muscle or gland)
The cell body is found at one end, inside the CNS
Synapse
A tiny space between neurons, which connects them together.
A nerve impulse is transmitted across the space by release of a chemical transmitter from the axon of one neuron.
The chemicals travel across the gap by diffusion and bind to receptors in the membrane of the next neuron.
Reflex arc
The simplest possible arrangement of the 3 types of neuron.
Shows the path taken by electrical impulses during a reflex action.
Reflex action
A response to a stimulus which does not involve the brain.
It is fast, automatic and protects the body from harm. eg. knee jerk, eye blink reflex or sneezing.
No conscious thought is involved.
Reflex arc pathway
stimulus –> receptor —> sensory neuron —> inter neuron in CNS —> motor neuron —> effector (muscle or gland) —> response
Hormones
Chemical messengers released by endocrine glands into the blood.
They are carried throughout the body, but only target cells (with complementary receptors) respond.
Hormones act slowly but have a long-lasting effect.
Endocrine glands
Release hormones into the blood.
Endocrine glands include the pancreas (insulin and glucagon), adrenal glands (adrenaline), ovary and testis (sex hormones).
Homeostasis
Maintaining a constant internal environment eg. blood glucose level, temperature.
Control of blood glucose
Allows body cells to work efficiently, as they require a constant energy supply.
Low/high blood glucose results in cell damage, as water moves in/out by osmosis.
Pancreas
Monitors blood sugar levels.
Releases 2 hormones - insulin and glucagon to correct it.
Glycogen
A storage carbohydrate made by linking many glucose molecules together into long chains.
Glucose is removed from the blood and stored as glycogen, under the control of insulin.
If more glucose is required in the blood, glycogen is broken down to release glucose, under the control of glucagon.
Insulin
A hormone released by the pancreas, when blood glucose is too high.
Target cells for insulin are in the liver - they absorb glucose from the blood and store it as glycogen, reducing blood glucose levels.
Glucagon
A hormone released by the pancreas when blood glucose is too low.
Target cells for glucagon are found in the liver - they break down stored glycogen and release glucose into the blood to increase blood glucose levels.
Diabetes
A disease caused by a failure in the blood glucose control mechanism.
Detected by glucose appearing in urine.
Blood vessels are damaged by high blood glucose levels, resulting in kidney, heart, brain and nerve damage, loss of limbs and blindness.
Type 1 diabetes
The pancreas stops producing insulin due to an inherited or autoimmune disorder (the body’s own cells are destroyed by its immune system).
Occurs in childhood/adolescence
Treated by insulin injections, controlled diet and exercise.
Type 2 diabetes
The pancreas makes less insulin, or the body stops responding to it.
Linked to obesity, high sugar intake and unhealthy lifestyles, so usually occurs later in life.
Treated by medication, controlled diet and exercise.
Most diabetes cases are type 2.
