18.1. Brain and Nervous System Fundamentals Flashcards
We need a nervous system for…
Communication between different areas of an organism.
Control of internal functions (digestion, movement etc.).
Homeostasis.
Types of neurons…
Around 100 billion neurons in the brain. They are excitable cells that transmit action potentials.
A transient change in potential difference across the membrane.
Afferent: transmit information from the periphery (PNS) to the nervous system. They detect sensory information and convert it into action potential.
Interneurons: connect afferent and efferent neurons increasing the complexity of the nervous system. They also store information.
Efferent: transmit information from the nervous system to effectors (such as muscles and glands).
A neuron consists of…
Dendrites: dendrites receive information from other neurons and converge on the soma.
Soma: the neuronal cell body where the nucleus is stored. This is the site of protein synthesis.
Axon: a single, myelinated axon carries action potential away from the soma and towards the next neuron. It branches off into terminal boutons towards the end of the axon.
Synapses
Help bridge the gap between two neurons.
Allow transmission of action potential from the axon boutons to the dendrites of the next neuron.
Ensure unidirectional transmission of the action potential.
Can be convergent: shush signals, where many axon boutons lead to less dendrites.
Can be divergent: expand signals, where few axon boutons lead to more dendrites.
Neurotransmission…
Neurotransmitters are contained within a vesicle in the presynaptic membrane.
As action potential arrives at the synapse, it triggers an influx of calcium ions into the presynaptic cell, which releases the neurotransmitter.
The neurotransmitter diffuses across the synaptic cleft and binds to specialised receptors on the postsynaptic membrane.
The binding of neurotransmitters to the receptors triggers an action potential in the post synaptic neuron.
Excess neurotransmitters are removed…
They can be broken down by enzymes.
They can diffuse out of the synaptic cleft into the bloodstream.
They can return to the axon terminals or be transported into glial cells.
Reflexes…
Automatic and rapid responses to situations that bypass the brain.
Such as the withdrawal reflex, that involves one afferent neuron, one interneuron and one efferent neuron.
Neuronal networks…
Nerve set: the simplest network with the smallest number of neurons.
Nervous system: a complex network with huge numbers of cells connected. They often contain many subdivisions and components.
Neurons that are grouped are termed ganglia:
- The brain: main processing centre, containing two hemispheres.
- The spinal cord: a thickened cluster of nerve fibres that connect distant parts of organisms.
