Chapter 12 - Nervous System Flashcards
Neuroglial Cells
- AKA “Nerve Glue Cells”
- Small + numerous
- Capable of mitosis
- 6 Types Total (4 in CNS, 2 in PNS)
- Gliomas = Brain Cancer
Neuropeptides (4 Main Examples)
- Opiate Peptides
- Substance P
- Hypothalamic releasing & release inhibiting hormones
- Cholecystokinin-Pancreozymin (AKA “CCK-PZ” or “CCK”)
Microglia
Microgilal Cells
-Phagocytic cells that are found on CNS injury sites
Distribution of Different Ion Species
Na+ = Main extracellular cation Cl- = Main extracellular anion K+ = Main intracellular cation A= Polyvalent anion "A" (Intracellular fixed anions, e.g., carboxyl groups of proteins)
3 Parts of the Neuron
- Dendrite
2 .Axon - Cell Body
Subcellular Locations of Voltage-gated Channels
Always located in places 2/ action potentials:
- Axons of motor neurons, interneurons, bipolar & unipolar sensory neurons
- Sarcolemmas of skeletal muscle cells
Biogenic Amines (3 Main Examples)
- Noradrenaline
- Dopamine
- Serotonin
* Can be either excitatory or inhibitory
Interneurons
Interneurons = 90% of all neurons
- Only found in CNS
- Conduct nerve impulses between different parts of CNS
- AKA “Association Neurons
Absolute Refractory Period
- Period during which nerve/muscle cell cannot generate another AP, even w/ a strong stimulus
- Caused by open/inactive Na+ channels (Not yet returned to resting state)
- Large diameter fibers: short absolute refractory period
- Small diameter fibers: long absolute refractory period
- Refractoriness = one-way transmission of AP; direction of AP propagation always away from membrane areas which have just fired
3 Steps During Action Potentials
- Receptor Binding
- Depolarization
- Repolarization
Differences in Plasma Membrane Permeability to Ions
Resting Membrane is 50-100x more permeable to K+ than to Na+, so RMP will be near K+ equilibrium potential (-90 mV)
-Defined as membrane potential that just balances K+ outflow
*RMP = -70 mV, so slightly leaky to Na+
Temperature
A low temperature rate will lower AP conduction rate. and sometimes even block conduction
Action Potential (AKA “Nerve Impulse”)
Action Potential = Moving transient electrical polarity reversal; moves from one end of neuronal fiber to the other
Synaptic Cleft
Small gap between 2 chemical synapses
Nitric Oxide
- Is both a neurotransmitter & hormone
- “Endothelium-derived relaxation factor” (EDRF)
- Made by MP Synthetase from arginine
- Very brief activity
- Very dangerous free radical
- NO -> Guanyl cyclase activation -> cyclic-GMP
Agonist
- Agents which enhance synaptic transmission (e.g., metoclopramine; releases ACh)
- Agents which mimic the effects of a hormone/neurotransmitter, showing both affinity for receptor & efficacy (e.g., salbutamol; helps bronchodilation)
3 PNS Subdivisions
- Somatic Nervous System (SNS)
- Autonomic Nervous System (ANS)
- Enteric Nervous System (ENS)
Opiate Peptides
- Endorphins, enkephalins & dynorphins are all examples of Opiate Peptides
- Inhibit pain by blocking substance P
- Aid in learning & memory
- Regulate mood, body temperature & sex drive
- Associated w/ schizophrenia & depression
2 Tract Types
- Myelinated = CNS white matter
- Unmyelinated (+ Neuron cell bodies, dendrites & neuroglia) = CNS gray matter
- “H-shaped” in spinal cord
- Outer covering of cerebral & cerebellar hemispheres in brain
Relative Refractory Period
- Period during which nerve/muscle cell can generate another AP, but only w/ a supra-threshold stimulus
- Caused by Na+ channels being in resting state, but K+ channels still being open
2 Features Affecting Nerve Impulses
- Resting Membrane Potential = Electrical charge separation across lipid bilayer
- Presence of ion channels in membrane = Path for ion movement in electrical current, leading to change of membrane potential (Can be gated or ungated)
3 Factors Affecting Graded Potentials
- # of Opened Channels
- Duration
- Channel type - excitatory or inhibitory
- Mechanically-gated = usually excitatory
- Ligand-gated w/ ACh ligand = usually excitatory
- Ligand-gated w/ glycine ligand = usually inhibitory
Oligodendrocytes
Oligodendrocytes
- Form myelin sheaths around CNS fibers, however do NOT form a neurolemmal sheath
- One oligodendrocyte myelinates many fibers
- CNS fibers cannot regenerate
- Demyelination occurs in some disease conditions (e.g. Tay-Sachs disease)
Suprathreshold Graded Potential
Firing of a series of action potentials, only stopping when electrical potential falls bellow -55mV