13.2- neurones Flashcards
What is a stimulus?
Changes in the internal and external environment.
An appropriate response will then be triggered.
What are neurones?
Specialised nerve cells
What is the role of a neurone?
To transmit electrical impulses rapidly so the organism can respond to the stimulus.
What are the 3 key features of a mammalian neurone?
Cell body- Contains the nucleus surrounded by cytoplasm. Within the cytoplasm there are large amounts of ER and mitochondria which are involved in the production of neurotransmitters.
Dendrons- Short extensions that come from the cell body. These extensions divide into smaller and smaller branches known as dendrites.
They are responsible for transmitting electrical impulses towards the cell body.
Axons- Singular, elongated nerve fibres that transmit impulses away from the cell body. These fibres can be very long.
The fibre is cylindrical in shape consisting of a very narrow region of cytoplasm (1 um) surrounded by a plasma membrane.
What is a neurotransmitter?
Chemicals which are used to pass signals from one neurone to the next.
What are the 3 types of neurone?
Sensory neurones- transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or brain. Have one Dendron, which carries the impulses to the cell body, and one axon, which carries impulses away from the cell body.
Relay neurones- transmit impulses between neurones. For example, between sensory neurones and motor neurones. They have many short axons and dendrons.
Motor neurones- they transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a gland. They have one long axon and many short dendrites.
In most nervous responses the electrical impulse follows what pathway?
Receptor –> sensory neurone –> relay neurone –> motor neurone –> effector cell –>
What are myelinated neurones?
Axons of some neurones covered in myelin sheath.
The myelin sheath is made of many layers of plasma membrane . Schwann cells produce these layers of membranes by growing around the axon many times. Each time a double layer of phospholipids is laid down.
The myelin sheath acts as an insulating layer and allows these myelinated neurones to conduct the electrical impulse at a much faster speed than unmeylinated. 100 metres per second, whereas non myelinated is 1 metre per second.
What is the node of ranvier?
The small gap (2-3um) between each adjacent schwann cell. This creates gaps in the myelin sheath.
In myelinated neurones the electrical impulse “jumps” from one node to the next as it travels along the neurone. This allows the impulse to be transmitted faster.
In non-myelinated neurones the impulse is transmitted continuously and is much slower.
What is MS?
Multiple sclerosis. It is a neurological condition that affects the brain and spinal cord.
It causes problems with muscle movement, balance and vision.
MS is an autoimmune disease, this is where the immune system mistakenly attacks healthy body tissue.
The result is in a thinning or complete loss of the myelin sheath and as the disease advances it breaks down the axons of the neurones.
It is thought to be caused by a combination of genetic and environmental factors, such as a viral infection.
