What are the 2 kinds of cells found in neural tissue?
1. Neurons: cells that send and receive signals (the communicators)
2. Neuroglia: cells that support and protect neurons (support, feed, nourish, protect, clean up after)
What makes up the CNS?
- The brain
- The spinal cord
What makes up the PSN?
- Everything that isn't the brain or the spinal cord
- The cranial and spinal nerves
What is the relationship between receptors/effectors and afferent/efferent fibers?
- The receptors are sensory receptors of the PNS that send their information to the brain on afferent fibers
- The effectors are motor neurons that are following the commands of the CNS based on the information from the sensory receptors; the information travels to the muscles and glands on efferent nerve fibers
What are the structures that make up a neuron?
1. Dendrites: short, highly branched projections that receive information from other neurons
2. Soma: the cell body that contains the nucleus
3. Axon: Long projection from the soma that carries an electrical signal; can be myelinated or unmyelinated
What is a synapse?
The area where a neuron communicates with another cell. A presynaptic axon meets a postsynaptic receptor. Neurotransmitters/signals are released from the presynaptic membrane and travel across the synaptic cleft to the postsynaptic receptors
What are the 3 functional classifications of neurons?
1. Sensory neurons: Afferent neurons of the PNS
2. Motor neurons: Efferent neurons of the PNS
3. Interneurons: The in between neurons interpreting sensory information and making decisions in the CNS
What are the 4 neuroglia in the CNS?
1. Oligodendrocytes: support cells that myelinate neurons to allow faster conduction of electrical pulses; one cell can myelinate multiple neurons
2. Astrocytes: create the BBB; controls interstitial environment
3. Ependymal cells: produce CSF, found lining the ventricles and the central canal of the spinal cord
4. Microglia: immune response cells of the brain; clean up debris, waste and pathogens
What are the 2 neuroglia of the PNS?
1. Schwann cells: myelinate the nerves of the PNS; one cell myelinates a group of axons
2. Satellite cells: regulate the environment around the neuron; adjust the gases and neurotransmitters in the interstitial environment
What is myelin?
Myelin is an insulating sheath that surrounds axons in multiple layers of neuroglial membrane; significantly increases the rate of electrical impulses
What are the steps in an action potential?
1. Chemically gated Na channels open allowing Na cause a depolarizing graded potential
2. If threshold of -55mV is reached, voltage gated Na channels open and flood the axon, raising the membrane potential causing a chain reaction of voltage gated Na channels to open down the axon
3. The membrane potential reaches 30mV, VG Na channels slam closed and VG K channels open, allowing a rush of K into the cell to repolarize the membrane
4. VG K channels are open long enough to hyperpolarize to -90mV when they close; Na/K ATPase reestablishes the resting membrane potential
How is the transmembrane potential established?
Na/K ATPase pumps 3 Na out of the cell and 2 K into the cell causing the extracellular fluid to be more positive and the intracellular fluid to less positive
What types of channels cause changes in the membrane potential?
1. Chemically gated channels: open when a ligand/neurotransmitter binds and changes the structure of the protein to open and allow a specific molecule across the membrane
2. Voltage gated channels: open when the membrane reaches a certain electrical charge, when this is reached the gate opens
3. Mechanically gated channels: open when membrane is physically distorted
How do graded potentials differ from action potentials?
1. Graded potentials: local, can be big or small, can depolarize or hyperpolarize the membrane, many can accumulate to allow the membrane to reach threshold, chemically gated channels
2. Action potentials: travel, all or nothing, an action potential WILL occur if the membrane reaches threshold, voltage gated channels
What is the difference between depolarization, repolarization, and hyperpolarization?
1. Depolarization: moves the membrane potential more positive away from -70mV (chemically gated and VG Na channels)
2. Repolarization: moves the membrane potential closer to -70mV (VG Na channels close, VG K channels open)
3. Hyperpolarization: moves the membrane potential more negative (chemically gated channels and VG K channels)
What are the 2 types of refractory periods?
1. Absolute refractory period: Na channels are open or inactivated, no possibility for action potential, lasts 0.4-1.0 msec
2. Relative refractory period: Membrane potential is almost normal, a very large stimulus could initiate an action potential
What are the 2 types of conduction of action potentials?
1.Continuous propagation: unmyelinated axons, requires more energy and is slower
2. Saltatory propagation: myelinated axons, the AP travels from node to node, much faster than continuous propagation, requires less energy
What are the different classifications of nerve fibers?
Type A: Largest, myelinated, 140m/s, carry rapid info to/from the CNS that is the most important information
Type B: Medium, myelinated, 18 m/s, carry intermediate signals
Type C: Smallest, unmyelinated, 1 m/s, carry slower information short distances
What are the 2 types of synapses?
1. Electrical synapses: Direct physical contact between cells, connected by gap junctions
2. Chemical synapses: Signal transmitted across synaptic gap by chemical neurotransmitters
How are neurotransmitters released in a chemical synapse?
1. AP reaches the telodendria and VG Ca channels open
2. Ca triggers exocytosis of ACh
3. ACh binds to receptors and depolarizes the postsynaptic membrane
4. Excess ACh is removed from the synaptic cleft by AChE
What are the 2 types of summation?
1. Temporal summation: rapid, repeated stimuli at one synpase, multiple times
2. Spatial summation: many stimuli arrive at multiple synapses, multiple locations
What are EPSPs and IPSPs?
1. EPSP: Excitatory PostSynaptic Potential, depolarizes the postsynaptic membrane
2. IPSP: Inhibitory PostSynaptic Potential, hyper polarizes the postsynaptic membrane