Lecture Exam 2

What is the ionic basis for resting membrane potential?

• typically -65mV to -70mV

• Determined by unequal ion concentrations across the cell membrane

• Selective membrane permeability

• Active transport

What happens in a chemical synapse?

• electrical signal is converted into a chemical message to pass info from on neuron to another across a small gap

What is the function of glial cells?

• support cells in eh central & peripheral NS

• Protect neurons

• Insulate neurons

• Nourish Neurons

• Help regulate brain homeostasis & immune defense

How to know when absolute refractory period will take place?

• ABSOLUTE—> begins at eh onset of the action potential (threshold depolarization)

• Lasts thorough peak of spike until early repolarization

• No second action potential can take place

• Voltage gated Na+ channels =boss

How to know relative refractory period will take place?

• RELATIVE—> begins after absolute until late repolarization through the hyperpolarization phase, until resting potential

• What happens—> second action potential can be generated/ requires stronger stimulus (suprathreshold)

  • Has smaller amplitude & slower conduction velocity

How does membrane permeability change during resting state?

• high K+ permeability

• Low Na+ permeability

How does membrane permeability change during depolarization?

• Na+ increases a lot

• Causes influx of Na+ ions into cell

How does membrane permeability change during repolarization?

• Na+ permeability drops

• K+ permeability Increases

How does membrane permeability change during hyperpolarization?

• K+ permeability Remains high

• Na+ channels reset

How does membrane permeability change during return to rest state?

• K+ channels close

What are voltage gated channels doing during resting state?

• voltage gated Na+ channels are closed

  • No Na+ enters

• Voltage gated K+ channels are closed

  • No K+ exists through these channels

  • Only leak channels are active

What are voltage gated channels doing during depolarization?

• Voltage gated Na+ channels open when memb reached threshold (-55mV)

  • Activation gates open & inactivation gates stay open

  • Na+ rushes into cell bc of concentration & elec gradients Making inside +

• Voltage gated K+ channels closed

  • Barely beginning slow activation process

What are voltage gated channels doing during repolarization?

• voltage gated Na+ channels are inactivated

• Slow inactivation gate closes stoping further Na+ influx

  • Creates absolute refractory period

• Voltage gated K+ channels open

  • Slow activation gates also open at peak

  • K+ rushes out of cell carrying + charge away & dropping mem potential back toward -

What are voltage gated channels doing during hyperpolarization?

• voltage gated Na+ channels go from inactive to closed

• Voltage gated K+ channels are still open but closing slowly

  • K+. Continues to exit

  • Once gone K+ channels close

Define afferent neurons

• towards the brain & spinal cord

  • Incoming/ sensory

• Located in ganglia outside of CNS (dorsal root ganglion)

Define Efferent neurons

• away from the brain & spinal cord

  • (outgoing/motor)

• Located inside CNS

What is myelin?

• fatty lipid rich insulating layer that wraps around the axon of a neuron to speed up electrical signals

What is resting membrane potential?

• The electrical voltage difference across a cells plasma membrane when the cell is at rest& not actively sending signals

• (-70mV)

Describe the function of the Na/K pumps

• transmembrane protein enzyme found in all animal cells

• Actively moves ions against their concentration gradient using energy from ATP

I’d the factors affecting conduction velocity

• axon diameter

• Myelination & saltatory conduction

• Intermodal distance

• Temp

• Ion channel density & distribution

• PH & chem environment

What does depolarization mean?

• there is a shift in cells membrane potential that makes the inside less negative

• Happens whe Na+ rushes into cell through open ion channels

• Increases threshold to happen (-55mV)

What does hyperpolarization mean?

• shift in cells membrane potential that makes the inside more negative

• Happens when K+ ions flow out of cell

• Decreases likelihood of action potential by moving away from threshold

What is a graded potential?

• short lived

• Localized charges in neurons membrane potential

• Vary in size depending on strength of stimulus

• Mostly occur in dendrites & soma

What does IPSP (inhibitory postsynaptic potential) do?

• causes hyperpolarization of postsynaptic memb

• Moves memb potential farther from threshold

• Triggered by influx of K+ exiting cell

• Neurotransmitters— GABA & glycine

What does EPSP (Excitatory Postsynaptic Potential) do?

• causes depolarization

• Triggered by influx of Na+ entering through ligand gated channels

• Moves memb potential closer to threshold

• Neurotransmitters—glutamate & acetylcholine

What is chemical synapse?

• Common

• action potential triggers calcium influx

• Causing synaptic vesicles to release neurotransmitters Into cleft

• They bind to ligand gated channels on receiving cell

• Made of presynaptic axon terminal/ synaptic cleft

What is electrical synapses?

• allows ions & small molecules To pass directly from presynaptic cell to postsynaptic cell

• Formed by specialized protein channels (gap junctions) that bridge the cytoplasm of 2 adjacent neurons

What is the difference between a chem & elec synapse?

• elec syn passes ionic current directly through physical gap junctions

• Chem converts elec signals into chem neurotransmitters to cross a synaptic cleft

What is ionotropic EPSP?

• Neurotransmitters bind directly to ligand gated ion channels

• Na+ rush into cell down electrochem gradient

• Response rapid & short lived

What is metabotropic EPSP?

• neurotransmitters bind to receptors that are structurally separated from ion channels

• Response is Slow but long lasting

How to be able to sum IPSP’s & EPSP’s to determine if a neuron reaches threshold?

• Through axon hillock (trigger zone)

• -55mV- -70mV

What is the role of calcium in a synapse?

• primary trigger for chem communication across a synapse

• Acts as a bridge btwn elec signal & chem message

What does spatial summation mean?

• 2 or more postsynaptic potentials og from diff synapses are generated at approximately the same time

What does temporal summation mean?

• accumulation of graded potentials from single neuron firing repeatedly in rapid succession

What is the effect without Cl- on membrane potential?

• The inside of resting cell is already negative

• Pushes out Cl- out of cell

• No change bc Cl- is balanced electrical charge stays the same

What is the effect of having Cl- pump?

• Cl- is kicked out of cell

• Lots Cl- outside not so much inside

• Becomes hyperpolarized bc inside of cell becomes more negative after all the Cl- goes in

• Prevents electrical signals

Id axoaxonic synapse

• axon to axon

• One cell controls how another cell can be

• Blocks or boosts signal before it can escape

Id axoendritic synapse

• axon to dendrite

• Most common way brain cells chat

• Passes “go” signals

Id axosomstic synapse

• axon to soma

• Very powerful connection

• Used to yell “stop” the cell from firing

Why doe the brain need consistent supply of blood?

• to be able to deliver oxygen & glucose

• Helps remove waste & maintain normal electrical activity

• Brain takes up 2% of weight but consumes 20% of body’s energy & oxygen

What are the features of the BBB?

• Nutrient transport proteins

• Effluent transporters

• Selective permeability

• Endothelial cells

• Tight junctions

• Astrocytes

• Basement membrane

What is the function of white matter tracts in the brain?

• communication & writing network that connect different gray matter regions

• Allows elec signals to travel quick across CNS

Where would you find white & gray matter in the CNS?

• cerebrum (which develops dulcimer & gyri)

What are the meninges?

• dura mater- tough, thick, outer layer closest to skull

• Arachnoid mater- web like, translucent, middle layer, cerebral spinal fluid, cushion

• Pia mater- delicate, think, inner most layer, hugs surface of brain & sp cord

Where are the spinal nerves located?

• peripheral nervous system

• Connects spinal cord to rest of body

What is a labeled line?

• neural pathway connecting specific sensory receptor to region in CNS

Define modality for each sensory receptor

Chemoreceptors- chem stimuli

• detects molecular changes & specific substances

• Ex- smell receptors

Thermoreceptors- temp changes

• ex- free nerve endings in the skin & hypothalamus

Mechanoreceptors- mechanical force & physical distortion

• detects touch, pressure, sound waves, balance

• Ex- pacinian corpuscles (vibrations/pressure), Meissner’s (light touch)

Photoreceptors- electromagnetic radiation (light)

• detects photons w/in visible light spectrum

• Ex- rods (dim light)/ cones (color)

Which receptor is fast adapting?

• phasic receptors

• Meissner’s corpuscles- light touch

• Pacinian- deep pressure

• Hair follicle receptor- detects initial movement

• Olfactory receptors- detects smell

Which receptor is slow adapting?

• tonic receptors

• Merkel’s disks- detects sustained light touch, pressure

• Muscle spindles- detects muscle strength

• Nociceptors- pain receptors