Exam 4 Study Guide Flashcards
- What is the difference between the CNS and the PNS? What are the subdivisions of the PNS? What are the subdivisions of the ANS?
CNS: integration centers- brain and spinal cord
PNS: all neuron cell bodies outside of the CNS (ganglia) and bundles of axons (nerve fibers). Sensory neurons and motor neurons act as communication lines.
Sensory PNS: somatic and visceral (organs) sensory nerve fibers
Motor PNS: motor nerve fibers. skeletal muscle. Branches into somatic and autonomic:
Somatic: conscious control. cardiac, smooth muscle, glands.
Autonomic: controls automatic processes. Branches into sympathetic and parasympathetic
Sympathetic: mobilizes NRG, fight or flight
Parasympathetic: conserves NRG, rest
What is the difference between a neuron and a glial cells?
neurons: excitable (rapidly change membrane potential)- function for control- 50% of brain volume
neuroglia: support and help neurons to send and receive impulses- 99% of cells in CNS
- Describes the structure of a neuron
neurons are amitotic, cannot divide and cannot proliferate. extreme longevity, high metabolic rate (high need for O2 and glucose to produce a ton of ATP), variable shape.
- What are the functional and structural classifications of neurons.
unipolar: sensory or afferent neuron, exclusively have an axon, they lack dendrites
Bipolar: ex. olfactory cell, the ear, and also in retina. Have one dendrite and one axon, but the process can branch.
Multipolar: ex. major type, motor interneurons. Have an axon and many dendrites.
Functional classification is afferent (unipolar), efferent (multipolar), and interneuron (contained in CNS, relays info between afferent and efferent).
astrocytes
CNS: astrocytes: physical support, control ECF (pick up extra neurotransmitters and ions that have been released from neurons) around neuron, surround capillaries and keep them close to neurons. have arms (cytoplasmic projections) and grab onto neurons and capillaries.
microglia
CNS: microglia: thorny cytoplasmic protrusions that grab onto neurons, monitor health status of neurons, act like macrophages. If not healthy, can engulf dead cells or cellular debris. Also reach out into ECF and pick up foreign material. Phagocytosis
ependymal cells
CNS: ependymal cells: line the ventricles, help produce CSF that fills ventricles. Have cilia to move CSF through ventricles. range in shape from squamous to columnar
oligodendrocytes
CNS: oligodendrocytes: Have a cell body and have arms to wrap around an axon to form myelin sheath. cellular protrusions ARE the myelin sheaths around axons. Are not phagocytic and do not help regenerate.
Satellite cells
satellite cells: same role as astrocytes, PNS
Schwann cells
Schwann cells: similar to oligodendrocytes form the myelin sheath. entire cell wraps around axon. Phagocytic (engulf foreign material and dead cell) and help regenerate damaged neurons. PNS
Myelin sheath
Acts as electrical insulator, meaning it is trying to keep the action potential contained in the myelin so to very efficient, and there is rapid transmission of action potentials. Formed by any layers of plasma/phospholipid membrane, act as insulators.
PNS: Schwann cell- layers of phospholipids and outer collar of perinuclear cytoplasm consists of Schwann cell cytoplasm and nucleus. entire cell wraps around axon
CNS: oligodendrocytes- no outer collar and only the arms/processes wrap around
Non myelinated fibers are also found in both the CNS and PNS- transmit action potentials slower
What are the differences between a Schwann cell and an Oligodendrocyte? How is a myelin sheath produced differently in the CNS compared to the PNS? Why can a regeneration tube be formed in the PNS following an injury to an axon, but not in the CNS?
Schwann cells form the myelin sheath around axons in the PNS and are phagocytic and have the ability to help regenerate and repair neurons in the PNS.
Oligodendrocytes also form the myelin sheaths in the CNS, but are not phagocytic and cannot regenerate neurons.
nodes of ranvier
gaps in the myelin sheath, where action potentials jump from one segment to the next.
regeneration of axons
Schwann cells surround the axon, then they participate in phagocytosis to clean up the debris from severed axon, then they form a regeneration tube and secrete growth factors and cell adhesion molecules to promote regeneration of axon and hook it back together.
multiple sclerosis
unregulated immune response where the body degrades the myelin sheath on the neuron. white matter has myelinated neurons, gray has non myelinated axons and cell bodies, so you can track proportions of both on an MRI. white matter is decreasing while gray matter is increasing.
voltage
the measure of potential energy generated by separated electrical charges
potential (potential difference)
voltage measured between two points. ex. charge difference on either side of plasma membrane because of different ion charges
current
flow of electrical charge
resistance
hindrance to charge flow. anything that prevents ions from moving across the plasma membrane.
relationship between voltage and current
the greater the voltage, the greater the current. The greater the resistance, the smaller the current
how do neurons function in general?
neurons change their membrane (action potential or nerve impulse) potential to receive info.
where neurons are passing action potentials to one another, it is known as a chemical transmission or a synapse.
RMP (resting membrane potentials)
all cells have a membrane potential, or difference in ion concentration and a difference in charge. range from about -50 to -100 mv.
in non excitable cells, membrane potential cannot be changed.
excitable cells can, in order to send and receive nerve impulses. Neurons have an RMP (when not sending and receiving impulses). RMP is -70 mv. Inside of the neuron is slightly negative due to difference in ion concentrations, so the membrane is polarized. Difference in charge only exists at the plasma membrane, overall charge inside and outside of cell are neutral.
Causes: difference in ionic concentrations inside and outside the cell, and difference in membrane permeability. Permeability of membrane can be changed by channels or transporter
Ionic differences in neurons
K+ and protein anions mostly inside cell.
Na+ and Cl- mostly outside cell.
Therefore, there is a gradient for K+ to diffuse out. and a gradient for Na+ to diffuse in.
Membrane ion channels
Leakage channels: non gated, always allows ions to move down their concentration gradients.
Important for generating RMP, allow K+ to move down its concentration gradient, out of the cell- makes RMP to be very negative.
Also allow Na+ to move inside the cell down its concentration gradient. Leakage channels combined equal -70 mv.
Membrane is 25x more permeable to K than Na, so there 25x more K channels than Na channels.
Gated channels: chemically gated/ligand channels, voltage gated channels, mechanically gated
What plays the biggest role in maintaining the ion gradient of -70 mv?
K+ channels, because there are 25x more of these channels than Na+ channels
sodium potassium pump
helps to maintain resting membrane potential
pumps 2 Na+ out, 3 K+ in
- Na+ binds to
How is a change in RMP produced?
- Graded potential: a brief localized change in RMP, occurs on cell body or dendrites. +30 mv
lead to action potentials
Generated on a subsequent neuron after one neuron passes an action potential to it and it spreads the graded potential toward the axon hillock. Then the subsequent neuron generates an action potential at the axon hillock and that action potential spreads toward the terminal.
Graded or vary in strength. Stronger graded potentials produce a greater change in RMP
+30 mv might be considered strong. -50 might not be as strong
Graded potentials are decremental, they decrease in strength as distance increases or they spread toward the axon hillock, so change gets smaller and smaller.
- post synaptic potential- two neurons communicating at a synapse passing action potentials
- receptor potential or generator potential- a receptor would be generating the graded potential
- Action potential: a brief reversal of membrane potential followed by a return to RMP.
exclusively found in excitable cells. In neurons, action potentials can only occur in the axon.
Action potential phases
Depolarization: membrane gets + (+30 mv)
Na+ enters through voltage gated (VG) Na+ channels- positive ions flood the cell and causes positive spike
Repolarization: Diving back down to RMP- go from +30 down to -70 mv, but it overshoots.
K+ leaves through VG K+- loss of positive ions causes negative spike
Hyperpolarization: -70 mv is overshot, membrane gets to -90 mv.
K+ continues to leave through VG K+ channels while VG K+ gates slowly close
sodium potassium pump helps return to normal RMP
action potentials are all or none and cannot summate (can’t be added together)- they are the exact same strength
VG Na+ channels
have two gates, activation and inactivation gates. Allows channels to open and close very quickly.
Activation gate opens first, allowing Na+ to enter, then right after, the inactivation gate slams closed to prevent more Na+ from entering.
closed at rest
open when axon hillock reaches threshold (sufficient stimulus) at -55 mv. -55 because graded potentials are decremental.
Below -55 at axon hillock, an action potential will not be generated (subthreshold)
VG K+ channels
slow to open, slow to close. They are sluggish, which is why the cell is hyper polarized during the last phase of the action potential.
no activation gate
closed at rest
Threshold and action potential sequence for VG channels
-55 mv
VG Na+ and K+ channels are triggered to open and tons of Na+ enters the cell.
K+ open slightly later just as Na+ channels close.
K+ now leaves the cell- repolarization +30mv to -70mv
K+ are sluggish so cells hyperpolarizes -70mv to -90mv
main players in maintaining RMP
K+ leakage channels
Na+ leakage channels
sodium potassium pump- maintaining ionic gradient- 3 Na out, 2 K+ in
Refractory Periods
absolute refractory period: the period of time following stimulation during which no additional action potentials can be evoked. even if graded potentials were spreading toward the hillock, another action potential will not occur because all of the VG + Na channels are already open. reason why each action potential is a separate all or nothing even
relative refractory period: when another action potential could occur, but you would need a greater than normal stimulus for action potential occur. during this period, the VG Na+ channels have closed, so it could be initiated at threshold. You would need a greater stimulus because K+ channels are still open, so to is harder to stay positive and get to threshold because you are losing positive ions.
