Structure and Function of the Nervous System Flashcards
What are the elementary building blocks of the brain?
Neurons
What are the main cell types in the nervous system?
Neurons and glial cells
Which are the key structural elements of a neuron?
- They consist of a cell soma (body), axon, and dendrites
- Communicate with other neurons and cells at specialized structures called synapses, where chemical and electrical signals can be conveyed between neurons.
How does an action potential occur?
- -70mV
- Threshold @ -55mV
- When neurotransmitters bind on the postsynaptic neuron’s receptors, it can cause depolarisation
- Repeated depolarisation eventually reaches the Threshold @ -55mV - Depolarisation (rising phase)
- When threshold is reached, a large number of sodium channels open and allow Na+ ions into the cell
- Causes massive depolarisation of the neuron (becomes 0 and then positive)
- The influx of positive ions creases the electrical signal known as the ACTION POTENTIAL - Peak, where Na+ channels close and K+ channels open
- K+ ions will flow out of the cell - Repolarisation (falling phase)
- Caused due to the loss of K+ ions - Hyperpolarisation
- Overshoots the resting potential
- Phase known as refractory period where it is very hard for neuron to be fired again - Resting potential
- After refractory period
How does synaptic transmission work?
- As the action potential depolarises the terminal membrane, it causes voltage-gated Ca2+ channels to open WHICH causes Ca2+ to flow into the cell
- Ca2+ causes vesicles (containing neurotransmitters) to bind with cell membrane of presynaptic neuron
- Neurotransmitter is released by exocytosis into the synaptic cleft, and diffuses across the cleft
- Transmitters binds with the receptor molecules in the postsynaptic neuron’s membrane
What are the two main subdivisions of the nervous system?
- Central Nervous System (CNS)
- Brain and spinal cord - Peripheral Nervous System
- Sensory and motor nerves, and associated nerve cell ganglia (groups of neuronal cell bodies)
- Located outside of the CNS
- Made up of the somatic and autonomic systems
- Somatic: neurons bringing messages from the senses to the CNS and vice versa
- Autonomic: neurons that control the heart, intestines and other organs
What is the difference between grey and white matter?
- White matter is composed of myelinated axons
- Gray matter is composed primarily of neurons
Which are the four main lobes of cortex?
- Frontal lobe
- Parietal lobe
- Temporal lobe
- Occipital lobe
What are the main subdivisions of the frontal cortex?
- Motor cortex
- Dorsolateral prefrontal cortex
- Ventrolateral prefrontal cortex
- Orbitofrontal cortex
What is topographical representation?
Illustrates the topographical correspondence between cortical regions and body surfaces with respect to somatosensory and motor processes
What are glial cells’ function?
Provide structural support and insulation for neurons
Oligodendrocytes
- Produce myelin around the axons of neurons
- Central nervous system
- Myelinate axons in the brain and spinal cord
Schwann cells
- Produce myelin around the axons of neurons
- Peripheral nervous system
- Myelinate axons in the periphery of the body
Soma
The soma (cell body) contains the chromosomes
Axons
- Information flows from the dendrites through the cell body to the axon
- Information is summed at the axon hillock
Dendrites
- Branching fibers that form the information-receiving pole of the nerve cell
- Surface is lined with synaptic receptors
- Some have dendritic spines (larger surface area, more info it can receive)
Membrane potential
The voltage across the neuronal membrane at any moment
Resting potential
The difference in voltage between the inside and outside of a neuron
(approx. resting potential is -70mV)
Equilibrium potential
When there is no net flow of ions in or out, the membrane is said to have reached its equilibrium potential
Presynaptic terminal
- The point from which an axon releases chemicals into the synapse
- Releases neurotransmitters when action potentials depolarise its axon terminal
- This release of neurotransmitter is mediated by calcium ions
Postsynaptic terminal
- The point of an axon receiving chemicals
- Neurotransmitters bind to receptors on the membrane of postsynaptic neuron
Purpose of neuronal membrane
To control the exchange of chemicals between the inside and outside of cell
Explain selective permeability
- A cell membrane will allow some ions (incl. water, oxygen and CO2) to pass through more readily than others (uncharged ions can pass through via simple diffusion)
- Ions that cannot flow freely may cross through specialised protein channels
- Without SP, the sodium-potassium pump would be far less effective in creating a conc. gradient (K+ inside; Na+ outside)
Ion channels
- Pore-forming proteins created from an amino acid chain
- Channels differ in selectivity
- Channels move across the lipid bilayer
- Channels can be altered or modulated based on cellular needs
Ligand
A molecule that binds to a protein (ex. of a protein: an ion channel)
Ion pumps
- Works to maintain the concentration gradient
- In the case of the sodium-potassium pump, it repeatedly transports three sodium ions out of the cell while drawing two potassium ions to it
What is the difference between concentration gradients and electrical gradients?
- Conc. gradients: move ions to areas of lowest concentration
- Elec. gradient: move ions to areas having opposite electrical charges
Why is a neuron ‘charged’?
- Neurons are like batteries
- They separate electrical charges, creating potential energy that can be tapped into when needed
- The plasma membrane of a neuron is the barrier that separates ions
- Negative charge inside; Positive charge outside
What is the all-or-none law?
- The all-or-none law states that a neuron will produce either an action potential of maximal strength or none at all
- The decision to send an action potential occurs at the axon hillock
Why is there an overshoot (action potentials)?
- To allow for a refractory period where the neuron cannot be fired for a split second
Why don’t action potentials remain depolarised?
- The inactivation of the Na+ channels means that no sodium will pass through
- No sodium means no depolarisation, which subsequently means no action potential
Depolarisation
- The electrical potential change that results in the propagation of an action
- Due to the depletion of K+ ions
- Neurons will produce an action potential only if the depolarisation exceeds the threshold of excitation (about 15mV from resting potential)
Saltatory conduction
- The process of action potentials moving from node to node along a myelinated axon
- Increases the speed of action potential and decreases the energy expenditure of the neuron
What are the two factors affecting the speed of an action potential?
- Diameter of the axon
- Whether the axon is myelinated
Neurotransmitter
Any substance, such as acetylcholine or dopamine, responsible for sending nerve signals across a synapse between two neurons
How does transmitter release affect the membrane potential?
- The binding of neurotransmitters to the postsynaptic membrane receptors change the membrane potential
- The postsynaptic potentials can either be excitatory (depolarising the membrane) or inhibitory (hyperpolarising the membrane)
- Ex. Transmitter release causes membrane potential to be more positive (depolarise) and it peaks at excitatory postsynaptic potential
