Neurons & The Nervous System Flashcards
Why is a nervous system needed?
- Communication between different areas of the organism.
- Controls functions of the organism (e.g. movement).
- Regulates responses to conditions or stimuli (e.g. homeostasis).
- Found in most multicellular organism but varies in complexity.
What are neurons?
Excitable cells capable of producing and transmitting action potentials.
What is an action potential?
The transient change in the potential difference (voltage) across the membrane of a neuron that form the basis of communication.
What are the 3 main components of a neuron?
- Soma - cell body that contains the nucleus and is the site of protein synthesis. Important role in integrating inputs from dendrites of cell.
- Dendrites - Many per neuron. Receive incoming inputs and converge on the soma.
- Axons - A single axon carries the AP to the next neuron. Axon terminals branch into many terminal boutons and are insulated with the myelin sheath.
What is a synapse?
The connection between neurons that transmit signals from one cell to the next. Uni-directional going from an axon terminal of one nerve to the dendrite of next nerve.
How do synapses communicate?
- AP travels down presynaptic cell.
- AP stimulates the release of neurotransmitter across the synapse from the synaptic vesicles.
- Neurotransmitter binds to receptors on postsynaptic cell.
- Receptor binding triggers AP in postsynaptic cell.
- Impulse continues along the postsynaptic cell.
How are neurotransmitters removed from the synapse?
- Neurotransmitters can be returned to axon terminals for reuse or transported into glial cells.
- Enzymes can inactivate them.
- Neurotransmitters can diffuse out of the synaptic cleft.
Why must neurotransmitters be removed from the synapse?
To ensure the nervous system signalling is rapid and dynamic.
What do the terms divergence and convergence mean and what determines which one is used?
Divergence - Synapses expand signals throughout the nervous system.
Convergence - Synapses specifically channel signals down a certain nerve tract.
It is determined by the numbers of presynaptic vs postsynaptic neurons.
What do afferent (incoming) neurons do?
- Carry information from periphery to nervous system.
- Convert sensory information into AP’s using a variety of specialised receptors.
What do efferent (outgoing) neurons do?
Carry commands from the nervous system to effectors (e.g. glands and muscles).
What do interneurons (i.e. circuit or relay neurons) do?
- Form connections and circuits between neurons.
- Often connect afferent neurons to efferent neurons.
- Increases the complexity of the nervous system.
- Involved in storing information.
- Short and simple in structure and almost always found in the CNS only.
Why are reflexes important?
To protect us by removing us from injuries situations quickly.
What is the withdrawal reflex?
The simplest reflex that involves one afferent, one efferent and one interneuron. Doesn’t require the impulses to travel to the brain (only spinal cord) and facilitates a rapid response called the spinal reflex.
Describe the stages of a withdrawal reflex when touching something hot.
- Heat activates skin receptors.
- Produces AP in dendrites of afferent neuron.
- AP travels to SC.
- Activates dendrites of interneuron.
- AP is relayed through interneuron to the efferent neuron.
- Impulse travels down axon of efferent neuron.
- Stimulates muscle contraction to move arm.
- Arm removed from flame.
What is a neural network?
Arrangements containing more than one nerve cell which vary in complexity and degree of interconnection.
What is a nerve net?
The simplest network with small numbers of connected neurons.
What is a nervous system network?
A complex network with huge numbers of cells connected and often contains many sub-divisions and components.
What are ganglia?
Paired or grouped neurons.
What is the brain and the spinal cord?
Brain - main processing consisting of 2 hemispheres and the largest pair of ganglia.
Spinal cord - Thickened cluster of nerve fibres which connects distant parts of organism.
What is the simple nerve network of the sea anemone?
Simple nerve nets innervate the anemone. Lengthy projections with a few connections but not highly branched. Permits simple responses, reflexes and functions such as contraction and relaxation.
What is the more complex nerve network of the earthworm?
Ganglia in each segment of the worm co-ordinate movement through segmental nerves. The anterior ganglia acts like a control centre to co-ordinate more complex behaviour and integration.
What is the more complex nerve network in a squid?
More specialised, organised pattern which gives a greater degree of integration and complex behaviour. Specialised ganglia co-ordinate specific functions through specific nerve projections and sensory systems are more developed.
