Neuroanatomy And Neurocytology Flashcards
What are Neurons?
Anatomical and functional units for signal transmission
What are Glia?
(Non-neuronal cells)
- supportive structural matrix, maintains homeostasis, nourishment, regulation of neuronal functions
What are the anatomical components of a neuron?
Dendrites, Soma (cell body), Axon, Presynaptic axon terminal
Bipolar Neuron
1 dendrite root and 1 axon
Pseudounipolar neuron
Subclass of bipolar
Multipolar neuron
Multiple dendrites and 1 axon
(Most common)
3 functional classifications of neurons?
Motor neurons, sensory neurons, interneurons (between sensory and motor neurons)
Types of macroglia and their functions
Astrocytes (CNS): star shaped cells that include neuronal signaling (liaison, communications, pathways for neuronal migration), housekeeping, nutritive functions for neurons
Oligodendrocytes ( Schwann cells
What are Microglia?
- Work as immune system of CNS
- function as phagocytes
- activate during nervous system development
- activate after injury or infection
Which cells contribute to myelination of neurons in CNS and PNS?
Oligodendrocytes and schwann cells
What is Myelin?
An effective insulator, shielding neurons from extracellular environment (think of the rubber around an electrical wire)
Which cells are the only supporting cells of the PNS?
Schwann cells
Sequence of events for neural transmission?
Receptor is stimulated -> Local potential -> Action potential -> Synapses
What is a local potential?
Small graded potential in amplitude and duration
- receptor or synaptic potential
- spreads passively and confined to small area of neuron membrane
What is an Action Potential?
- Large “all or none”, depolarizing signal
- Actively propagates along neuron axon, traveling 1-way to presynaptic terminal
What happens at the Synapses?
Transports signal to other neurons by release of neurotransmitters
What kind of membranes do neurons have?
Selectively permeable
What is the membrane potential and what ions are associated?
- Separation of different charges across the membrane creating electrical potential of -70mV
- Caused by uneven distribution of Na+, K+, and Anions
- Cell membrane is more permeable to K+ than to Na+
What happens when the protein ion channels are open at the membrane?
Influx of Na+ into the cell since Na+ is normally in a higher concentration out of the cell
When at resting membrane potential, which side is more + and which side is more -?
Extracellular fluid is more positively charged than (+) and intracellular fluid is more negatively (-) charged at resting membrane potential
What is a Leak channel?
(Non-gated): small amount of ions that diffuse through the membrane at a slow continuous rate
What is a Modality-gated channel?
(Sensory neurons only) and they open in reaction to mechanical stimulation, temperature, or chemicals
What is a Ligand-gated channel?
Opens when neurotransmitter binds to post-synaptic receptors, generating local potentials
What is a Voltage-gated channel?
opens in reaction to change in electrical potential, generating action potentials
At resting membrane potential what are the relative charges of each side and where are the ions concentrated?
At rest, inside of the neuron is more - than outside
- inside has more K+ and Anions
- Outside with more Na+ and Cl-
How is Dynamic equilibrium during the resting potential maintained?
- Charged anions trapped inside the neuron
- Passive diffusion of K+ and Na+ through leak channels
- Na+/k+ pump requires ATP
What is the ratio of molecules for the sodium-potassium pump?
- 2 K+ into the cell for every 3 Na+ out
What stimulus threshold intensity is required to produce an action potential?
-55mV, though google says -50mV to -55mV
(INCREASING THE STIMULUS INTENSITY WILL NOT CHANGE THE AMPLITUDE OFR DURATION OF THE ACTION POTENTIAL)
what are the 3 stages of an Action potential?
- Rising depolarizing phase: more+ from -70 to +30mV
- Falling repolarizng phase: more - from +30 to -70mV
- Re-setting/hyperpolarizing phase:
What is depolarization?
- small change in membrane voltage depolarizes it enough to open Na+ channels (voltage gated Na+ channels)
- AS more Na+ moves into the neuron, more and more Na+ channels open
- Polarity rapidly changes from - to + to produce action potential
What causes repolarization?
Na+ channels start to close, and K+ voltage-gated channels start to open (K+ channels are slower to respond to the AP’s depolarization)
- K+ ions exit and membrane potential falls toward RP from + to - toward -70mvs
What causes hyperpolarization?
K+ channels remain open during repolarization leading to hyperpolarized membrane potential (below -70mv)
How does the neuron get back to RP/Resting potential?
Gradually active Na+/K+ pumps the ions to restore RP of -70mv
What is the ratio in/out of sodium potassium pump?
2 potassiums in for 3 sodiums out (against their concentration gradients)
an easy way to remember is bananas with potassium are better for you than fries which have sodium
What is the refractory period?
Absolute: completely unresponsive to stimuli
- Na+ channels open and not yet reset
Relative: may respond to stronger stimuli
- Most of Na+ channels are reset
Refractory periods advantageous for promotion of fwd propagation of AP and preventing backward flow
What factors influence an action potential?
- Diameter of axon (larger means faster)
- Myelin (prevents current flow across membrane, preserves amplitude of impulse)
- Temperature (warm proteins react faster)
Nodes of ranvier
