Midterm 1 Flashcards
Coronal suture
Stitches the frontal and parietal skull bones
Squamous suture
Stitches the temporal and parietal skull bones
Sagittal suture
Stitches the two parietal bones
Lambdoid suture
Stitches the parietal and occipital skull bones
Dura mater
Outer most layer of meninges
Arachnoid mater
Thin transparent membrane below dura mater
Subarachnoid space
Where CSF resides
Pia mater
Inner most layer of the meninges (wraps the brain and spinal cord)
Functions of CSF
1) Impact absorption
2) Osmotic homeostasis
3) Waste disposal
4) Neutrophic factor secretion
Glymphatic system
Regulates/permits the circulation of CSF through the brain tissue (movement based on blood vessel pressure and rate of flow modified by glial cells)
Factors affecting CSF production
- CSF production increased during anesthetic-induced sleep
- CSF production reduced in Alzheimers
Why is the retina considered part of the CNS?
- The RGCs are CNS neurons; they cannot regenerate
- RGCs myelinated by oligodendrocytes
- Astrocytes and microglia are found in the retina
- Aqueous humor is similar to CSF
- Retina and optic nerve extend from the brain during development
Advantages of chemical synapses
- Amplification of signals
- Modification of the transfer function (neuroplasticity)
- Signal inversion
- Signal termination
Ependymal cells
- Present in CNS ventricles (and more)
- Secrete fluid that becomes CSF (regulate CSF)
- Facilitate peptide hormone transport
Myelin
Electrical insulation that also supplies axons with structure, nutrients, and neurotrophic factors
Schwann cells
Can myelinate only one axon in the PNS (can guide regeneration)
Oligodendrocytes
Can myelinate multiple axons in the CNS
Microglia
- Specialized macrophage descendants that enter the CNS
- Survey the CNS
- Mediate inflammation
- Phagocytose
Microglia dichotomy
M1: causes inflammation and neurodegeneration
M2: suppresses inflammation and promotes neural repair
Astrocytes
- Most populous glial cell in CNS
- Modulate neurotransmission
- Regulate BV diameter and maintain the BBB and BRB
- Neuron growth and connectivity
- CSF flow rate
- Barrier formation around injuries
Astrocytes CNS
Get activated to form a barrier to protect CNS neurons (side effect of preventing regeneration)
Astrocyte dichotomy
A1: causes inflammation and neurodegeneration
A2: suppresses inflammation and promotes neural repair
Pupillary reflex
1) Photoreceptors (rods + cones) = Afferent/sensory neurons that convert light into electrical signals
2) RGCs relay visual information to the midbrain via optic nerve
3) Ciliary ganglion neurons = Effector neurons that synapse with ciliary muscles and adjust pupil size
Patellar reflex
1) Striking patellar ligament stretches spindle and activates sensory neuron
2) Sensory neuron relays information down axon to its axon terminal which inerrvates a motor neuron at the spinal cord
3) Motor neuron stimulates (releases Ach) muscle to contract
Dorsal Root Ganglion (DRG)
- Sensory neuron
- Generally considered PNS
- Located outside the CNS
- Psuedo-unipolar (axon splits into 2 branches)
- Stomata located outside the CNS
- Axon enters spinal cord into dorsal grey matter
Motor neurons
- Multipolar (one axon, many dendrites)
- Stomata and dendrites located in ventral grey matter
- Axon leaves spinal cord via ventral root and innervates skeletal muscle cells
Localization of function: Dorsal horn
Interneurons processing sensory info
Localization of function: Ventral horn
Somatic motor neuron somata
Function-o-topy
Correlation between a region of the nervous system and its function
Somatotopy
Correlation between neuron cell body position and position of the target organ (body part)
Autonomic nervous system
- Component of the PNS that innervates visceral organs
- Preganglionic neurons (visceral motor neurons) located in spinal cord (CNS) innervate postganglionic neurons (PNS) that control visceral organs
- Split into parasympathetic and sympathetic divisions (antagonistic)
Parasympathetic postganglionic neurons neurotransmitter
Acetylcholine
Sympathetic postganglionic neurons neurotransmitter
Norepinephrine/noradrenaline
Enteric nervous system
- Largely independent of the CNS
- Innervated by peripheral nerve fibers but has its own autonomous, involuntary control
- Connected to the brain via the vagus nerve (gut-brain axis)
Gut-brain microbiota axis
- Role in depression
- Based on lifestyle, stress, infection, antibiotics, diet, etc.
Transmembrane potential (Vm)
A voltage difference across the cell membrane
Why do cells have a transmembrane potential?
- Extracellular and intracellular separated by a membrane (ions cannot permeate)
- Specialized transmembrane proteins facilitate ion movement
Biophysical mechanisms that create electrical membrane potential (neuron properties)
1) Unequal distribution of ion species (concentration differences)
2) Selective permeability
Biophysical mechanisms that create electrical membrane potential (ion properties)
1) Concentration (diffusive forces)
2) Charge (attraction and repulsion)
Equilibrium potential (Eion)
The potential at which the diffusive force (concentration) and electromotive force (electrical gradient) are in equilibrium –> no net ion movement
Ek+
-76mV
ENa+
+54mV
Neuronal communication analogy
Ears (dendrites) receive words (neurotransmitters) which can be translated into thoughts (graded potentials –> action potentials)
The vocal cords (axon hillock) allow air to flow through and up the throat (axon) and out the mouth (synaptic terminal) as words (neurotransmitters)
Reversal potential
The membrane potential at which the direction of ionic current reverses (at reversal potential no net flow of ions) (applies to all permeable ions)
Transmembrane current
Due to movement of ions through ion channels
Leak current
Moves charge back to the extracellular fluid
Electrotonic current
Spreads by charge displacement through the cytoplasm
Membrane resistance
The resistance of the membrane and the small amount of current flow that leaks
External resistance
Extracellular fluid provides very small resistance to the flow of electronic current
Internal resistance
Resistance from cytoplasm that impedes the flow of electronic current
Space constant
A constant describing how steeply the potential is falling off from the source of the original transmembrane current
lambda = sqrt(Rm/Ri)
Properties affecting Rm and Ri
1) Membrane permeability - more open conductances (low permeability = high Rm)
2) Diameter - Affects resistivity (high diameter = low Rm and exponentially lower Ri)
Action potentials
- All or none
- Can vary in frequency but not magnitude
- Relatively high amplitude (+40mV) and brief duration
- Crossing threshold triggers an acceleration of depolarization on the membrane potential
- Depolarization -> repolarization -> hyperpolarization
Inward current
Flow of net positive charge into the cell
Tetrodotoxin (TTX)
Eliminates APs by blocking the early current (Na+ current) leaving only the late current (K+ current)
Tetraethylammonium (TEA)
Disrupts APs by blocking the late current (K+ current) leaving only the early current (Na+ current)
Gates at rest
m gate: closed
h gate: open
n gate: closed
Gates during depolarization
m gate: fully open
h gate: fully open
n gate: gradually opening
Gates at peak of depolarization (+40mV)
m gate: fully open
h gate: closes
n gate: fully open
Gates during repolarization
m gate: closing
h gate: closed
n gate: fully open
Gates at end of repolarization/hyperpolarization
m gate: closed
h gate: open
n gate: gradually closing
Factors that affect AP conduction speed
- Temperature
- Diameter
- Myelination
Biophysical properties that determine the speed of traveling graded potentials
- Membrane resistance
- Internal resistance
- Distance
- Diameter
- Myelination
- Temperature
