Lecture 3 - Intro to Neurophysiology Flashcards
How many molecules (phospholipids) thick is the cell membrane?
2
Where are the hydrophobic tails?
On the inside of the bilayer
Where are the polar head groups
On the outside of the bilayer
How do molecules cross the Cell Membrane?
By simple diffusion - no consumption of ATP
What happens during simple diffusion of small uncharged molecules?
Small uncharged molecules (relatively lipid soluble) can diffuse through the lipid bilayer (steroid hormones)
What happens during simple diffusion of small charged molecules?
Ions can diffuse through water filled pores
What are the two types of Ion Channels?
1.) “Leaky”, ions can flow in or out as needed
2.) Voltage Gated - can only be opened or closed by gates
What is Active Transport?
Needs metabolic energy (usually ATP) to move molecules into and out of cell
What does the Na+/K+ ATPase do?
Move Na+ out of cell and K+ into the cell
What type of transport is ATP synthase?
Primary active transport
What is primary active transport?
Uses ATP directly
What do cell membranes act as?
Barriers to chemical movement
What do Integral Membrane proteins act as?
Transporters
What is Active Transport of Na+/K+ important for?
Establishing the electrochemical gradient
What are Ion channels especially important for?
They help produce electrical impulses that transmit information rapidly
What do all cells in the body have?
A potential difference - or voltage - across the membrane. This is called resting membrane potential
What is the charge of the inside of the cell compared ti the outside?
The inside of the side is negative
What is the charge of a neuron at rest?
-70 mV
What are voltage gated ion channels important for?
Electrical activity in axons because when the channels open, they can change the membrane potential of the cell
Where is Na+ at the start of action potentials?
Outside of the cell (pos)
Where is K+ at the start of action potentials?
Inside of the cell (neg.)
What is an Action Potential?
Signals that o along the nerves, taking the signal from one place to another place
How do Neurons propagate signals?
In the form of action potentials
What causes Action Potentials to be momentary discharges (depolarizations) of the resting membrane potential?
The rapid influx of Na+ caused by the opening of sodium ion channels
What do signals have to continuously be during an Action Potential?
Reamplified along the way using voltage-gated ion channels
What type of channel do Na+ and K+ move through?
Gated channels
What happens during appropriate stimulation?
Positive charges flow into the cell, so the cell becomes more POSITIVE then the resting potential (depolarizationO)
Where does an Action Potential start?
Axon Hillock
What does the explosive increase in Na+ permeability result in?
A rapid reversal of membrane potential in that region, from -70mV to +30mV (depolarization)
What happens once the cell has reached a depolarized state?
The Na+ channels close. There is a rapid decrease in Na+ permeability
How does the cell repolarize?
K+ which is also positively charged will diffuse out of the cell, making the inside of the cell less positive (or more negative) again, restoring the original resting membrane potential
What is constantly working within the plasma membrane?
The Na+ and K+ pumps
Because opening the gated Na+ and K+ channel is stimulated by depolarization, what are the ion channels in the axon said to be?
Voltage-Regulated or Voltage-Gated Channels
What does membrane potential not normally become more positive than and why?
+30mV because the Na+ channels quickly close and the K+ channels open.
What is the amplitude (size) of action potentials?
ALL or NONE principle
What happens if depolarization reaches the threshold?
The maximum potential change is reached
What are Action Potentials sometimes called?
Spike Potentials
What happens in non-myelinated axons?
The action potential passes smoothly along the axon and all parts of the membrane are depolarized
What happens in myelinated axons?
The action potentials jumps between the non-insulated nodes of Ranvier by saltatory conduction
What does myelination allow for?
Allows for more rapid movement of the action potentials, and needs less energy to restore the membrane of the action potential has been transmitted
What does the refractory period help?
Ensure the AP only goes in one direction down the axon to its end
What happens once action potentials reach the end of the axon?
They stimulate the next cell
In the CNS, what is the 2nd cell that an action potential would reach?
A neuron
In the PNS, what is the 2nd cell that an action potential would reach?
A neuron or an effector cell within a muscle or gland via the neuromuscular junction
What direction does a synapse go in?
Pre-synaptic to Post-SYnaptic
What do presynaptic nerve endings release?
Neurotransmitters that stimulate APs in the post synaptic cell
What do pre-synaptic neurons end in?
A terminal bouton and it is separated from the post-synaptic cell by a tiny cleft ~10nm in size.
What are the four steps of a synaptic transmission?
1.) Action Potentials reach axon terminals
2.) Voltage-gated Ca2+ channels open
3.) Ca2+ binds to sensor protein in cytoplasm
4.) Ca2+ protein complex stimulates fusion and exocytosis of neurotransmitters
What happens on the post-synaptic side?
The neurotransmitter binds to its receptor on the dendrite causing ion channels on the post synaptic dendrite to open
What type of regulation is the post synaptic channels?
Chemically regulated which stimulates the cell to produce an A.P
What is the EPSP?
Excitatory postsynaptic potential (depolarization in post0synaptic neuron
What is the “patch clamp” recording technique?
Technique for recording electrical currents in a spinal neuron grown in cell culture
How is the “patch clamp” recorded?
It is recording voltage for a certain area of the cell membrane over time (Electrical changes at one place)
What are neuromuscular disorders characterized by?
Delayed relaxation of skeletal muscle after voluntary contraction or electrical stimulation
What can neuromuscular disorders be caused by?
Mutations in muscle Cl- channel
What does a mutation in the Cl- channel cause?
The channel gates to not open properly and repolarization delayed, several APs fire instead of just one
What is Myotonia in Goats?
When startled or excited it causes a temporary stiffening of the muscles. When the muscles relax after a few seconds, the animal jumps up and continues on its way.
What is the approximate speed of a neuron?
30 - 90 m/sec
What is the present that your brain comprehends?
Around 500 milliseconds behind what is actually happening, as your brain scrambles frantically to keep up and maintain coherence.
What type of matter is the CNS composed of?
Grey Matter and White Matter
What does the grey matter contain?
Neuronal cell bodies and dendrites
Where is the grey matter found?
In the cortex (surface layer) of the brain and deeper within the brain in aggregations known as nuclei
What does white matter consist of?
Axon tracts (myelin sheaths produce white colour) that underlie the cortex and that surround the nuclei.
What is the Dura Mater?
Tough two layers right below skull
What is the Arachnoid Mater?
Webbed like right below dura mater
What is the Pia Mater?
Innermost membrane, clings to surface of brain/spinal cord, follows every fold.
Where is the brain encased in?
The skull and protected by several tough layers of connective tissue (the meninges)
What layers protect the spinal cord?
The same meningeal layers that protect the spinal cord
In addition to the skull and meninges, what is the brain protected by?
Two fluid cushions that give some protection for the brain again head traumas
What is the outer cavity?
The superior sagittal sinus (SSS) - sits under Dura Mater
What is the inner cavity?
The subarachnoid space (sits between arachnoid and Pia mater
What are the cavities of the brain and spinal cord filled with?
Cerebrospinal Fluid
What is cerebrospinal fluid (CSF) similar in?
Composition to blood plasma
What is a CSF tap?
When a sample of CSF can be examined for signs of disease such as bacteria, virus, Multiple sclerosis
How many nerves are there?
31 pairs of spinal nerves
What is each nerve composed of?
Sensory and motor fibers, packed together separated near the attachment of the nerve to the spinal cord
Where does the spinal cord extend from?
The brain stem, to the pelvic region, ending before the end of the vertebral column.
Where do nerves enter or leave the spinal cord?
In between the vertebrae
Where do the interneurons communicate?
Along the length of the spinal cord
Where can an afferent sensory stimulus be translated?
Up or down the spinal cord by interneurons
What is the “simple” withdrawal reflex?
A response to a painful stimulus involving the contraction of several muscles, the relaxation of other muscles and it may also involve responses that are initiated in the brain
What can reflexes be useful for?
Distinguishing between upper and lower motor damage
What will the knee jerk reflex be with lower motor neuron damage?
Diminised
What will the knee jerk reflex be with upper motor neuron damage?
Exaggerated/slightly normal
