Nervous System Flashcards
What is the CNS?
Central Nervous System
What is the PNS?
Peripheral Nervous System
What does the CNS consist of?
The brain and spinal cord
What does the PNS consist of?
Nerves leading to and from the CNS
What does a typical nerve cell contain?
Sensory and motor neurons and ganglia
What is a neuron?
Neurons are nerve cells which are specialised to carry impulses.
How are neurons classified?
According to their function.
What do sensory neurons do?
Transmit impulses from sense organs towards the central nervous system.
What do motor neurons do?
Transmit impulses away from the central nervous system towards effectors.
What do interneurons do?
Transmit impulses within the central nervous system.
What are receptors?
Sensory cells that detect a stimulus and generate impulses.
What are effectors?
Muscles or glands that are capable of producing a response e.g muscles cause movement
Write a note on interneurons.
They are all located within the CNS.
They are the most abundant neurons.
They lack a myelin sheath.
They transfer impulses from the sensory neurons to the motor neurons within the CNS.
Describe the cell body.
Contains the nucleus surrounded by cytoplasm and organelles such as mitochondria.
What is the function of the cell body?
Produces neurotransmitter chemicals such as dopamine.
Describe an axon.
Elongated nerve fibre.
What is the function of the axon?
Transmits impulses away from the cell body.
Describe a dendrite.
Branched nerve fibre, generally.
What is the function of the dendrite?
Transmits impulses towards the cell body.
Describe the myelin sheath.
A fat-enriched membrane around nerve fibres.
What is the function of the myelin sheath?
Insulates and speeds up impulse transmission.
Describe the Schwann cell.
Wrapped thinly around the axon or dendrite.
What is the function of the Schwann cell?
Produces the myelin sheath.
What are axon terminals?
Small branches of the main axon, makes contact with the dendrites of other neurons.
Ends in swelling called neurotransmitter swellings.
What are the functions of axon terminals?
Neurotransmitter swellings release neurotransmitter chemicals like dopamine.
Dopamine is stored in vesicles within neurotransmitter swellings.
What is an impulse?
An electrical message and a positive flow of ions carried by a neuron.
What does the transmission of a nerve impulse require?
The movement of Na and K ions in and out of dendrites and axons.
Energy in the form of ATP
Name the type of particle whose movement in and out of neurons is an essential feature of nerve impulse transmission.
Ion
Describe the characteristics of nerve impulses.
The Threshold Stimulation:
A threshold is the minimum level of stimulus needed for impulse transmission. Once the threshold is reached an impulse is generated and transmitted. Below the threshold, no impulse is generated.
Example: lukewarm water is below the threshold so no impulse is generated.
The all or nothing effect:
The impulse will travel the entire length of the neuron or not at all.
The refractory period:
The timespan after impulse transmission, when the stimulus fails to cause a response.
Speed of impulse:
Impulses are faster when a myelin sheath is present and when the diameter of the nerve fibre is greater.
What is a synapse?
A region where two neurons come in close contact, allowing impulses to pass from one neuron to another.
What is the synaptic cleft?
A tiny gap between two neurons, ie. between the presynaptic and postsynaptic neurons at the synapse.
Describe the sequence of events that allows an impulse to be transmitted across a synapse from one neuron to the next.
OR
Give an account of how neurotransmitters work.
The impulse arrives at the neurotransmitter swelling.
Ions stimulate the vesicles to fuse with the cell membrane and release neurotransmitters into the synaptic cleft for a very short time.
The neurotransmitter diffuses across the synaptic cleft chemically transmitting the impulse into the next neuron.
Neurotransmitter reacts with receptors in the postsynaptic neuron.
An impulse is therefore transmitted to the postsynaptic neuron
Following impulse transmission, the neurotransmitter is broken down by enzymes and reabsorbed by the presynaptic neuron where it is used to make new neurotransmitters.
