Untitled Quiz

Function of the Nervous System

• The nervous system is responsible for receiving sensory input and coordinating motor output
• Sensory receptors detect changes in the environment
• Effectors carry out responses to stimuli

Neuron Interaction & Integration

• Sensory neurons carry information from sensory receptors to the central nervous system
• Interneurons process and integrate incoming sensory information
• Motor neurons carry information from the CNS to effectors

Neuroglia

• Neuroglia are cells that support and protect neurons
• Neuroglia include Schwann cells, oligodendrocytes, astrocytes, microglia, and ependymal cells

Typical Neuron

• A typical neuron has a cell body, dendrites, and an axon
• Dendrites receive information from other neurons and transmit it towards the cell body
• The cell body contains the nucleus and other cellular organelles
• The axon transmits information away from the cell body towards other cells
• The myelin sheath, a fatty covering, insulates the axon and increases the speed of signal transmission
• The synapse is the junction between an axon and another cell, where communication occurs

Myelin Sheath and Schwann Cells

• The myelin sheath is made up of Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system
• Myelin sheaths wrap around axons, creating an insulator that allows for faster signal transmission
• The gaps between the myelin sheath are called nodes of Ranvier, where the action potential jumps from one node to the next, allowing for faster transmission

Types of Neurons

• Unipolar neurons have a single process extending from the cell body and are found in the dorsal root ganglia
• Bipolar neurons have two processes extending from the cell body and are found in the eye, ear, and olfactory epithelium
• Multipolar neurons have multiple processes extending from the cell body and are the most abundant type of neuron in the central nervous system

Information Transmission

• Information must be transmitted both within each neuron and between neurons
• The membrane surrounding the neuron is composed of lipids and proteins and has an electrical charge across it

Membrane Potential

• The difference in electrical charge across the membrane is called the membrane potential
• The resting potential, when the cell is not firing, is -70mV, with the inside of the cell being more negatively charged than the outside

Maintaining the Resting Potential

• The resting potential is maintained by the concentration of ions on different sides of the membrane
• Sodium (Na+) and chloride (Cl-) ions are more concentrated outside the cell
• Potassium (K+) ions and organic anions are more concentrated inside the cell
• The sodium-potassium pump actively transports 3 Na+ ions out of the cell for every 2 K+ ions pumped into the cell, using energy to maintain the concentration gradient

The Action Potential

• The action potential is a rapid depolarization of the membrane that travels down the axon
• When the membrane becomes partially depolarized and reaches the activation threshold, voltage-gated sodium ion channels open, allowing Na+ ions to rush into the cell rapidly, causing the membrane potential to change from -70mV to +40mV

Repolarization and Hyperpolarization

• The sodium channels close and become refractory, preventing further depolarization for a short time
• Voltage-gated potassium channels open and K+ ions rush out of the cell, repolarizing the membrane and then hyperpolarizing it briefly
• The action potential is “all-or-none”, meaning it is always the same size, and can either be triggered completely or not at all

Conduction of the Action Potential

• The action potential travels down the axon through passive conduction and saltatory conduction
• Passive conduction allows the depolarization to spread to adjacent regions of the membrane
• Saltatory conduction, which is much faster and more efficient, is achieved through myelination

Myelination and Saltatory Conduction

• Myelin sheaths, formed by Schwann cells and oligodendrocytes, insulate the axon, preventing the passage of ions across the membrane
• Action potentials only occur at the nodes of Ranvier, where there is no myelin, allowing the signal to jump from one node to the next, making transmission much faster

Synapse

• Information is transmitted from the presynaptic neuron to the postsynaptic cell via neurotransmitters, which cross the synapse
• The synapse is a very narrow gap between the axon terminal of the presynaptic neuron and the dendrite or soma of the postsynaptic cell

Neurotransmitter Release

• The arrival of an action potential at the axon terminal causes the release of neurotransmitters from the presynaptic membrane through exocytosis
• Vesicles containing neurotransmitters fuse with the presynaptic membrane and release their contents into the synaptic cleft, where they diffuse across the gap

Postsynaptic Effects

• Neurotransmitters bind to receptors on the postsynaptic membrane, altering the membrane potential of the receiving neuron
• This binding triggers either excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) depending on the neurotransmitter and receptor involved

Excitatory and Inhibitory Effects

• Excitatory neurotransmitters depolarize the postsynaptic cell, making it more likely to fire an action potential
• Inhibitory neurotransmitters hyperpolarize the postsynaptic cell, making it less likely to fire an action potential

Ionotropic Receptors

• Ionotropic receptors are fast-acting receptors that directly open ion channels when neurotransmitters bind to them
• An example is acetylcholine (ACh) acting on nicotinic receptors at the neuromuscular junction

Postsynaptic Membrane Potential

• The opening of Na+ and Ca2+ channels in the postsynaptic membrane leads to depolarization, contributing to an EPSP and making an action potential more likely
• The opening of Cl- channels results in hyperpolarization contributing to an IPSP and making the postsynaptic cell less likely to fire an action potential