Chapter 2 Flashcards
neurons
receive messages and transmit it to other cells, there are approx 100 billion neurons in the adult brain. Large neurons have dendrites, soma, and axons, while small neurons lack axons/well defined dendrites
glia
smaller but more numerous than neurons, glia have many functions but do not convey messages/info over great distances
monism
mind (spirit) and the body (brain) are inseparable from each other
dualism
idea mind and the body are separate entities
Charles Sherrington, Santiago Ramon y Cajal
founders of neuroscience
cell membrane
structure that separates the inside of the cell from the outside environment
nucleus
structure at centre of animal cells (except red blood cells) that contains chromosomes
mitochondrion
structure that performs metabolic activities, providing the energy that the cell requires for all other activities
ribosomes
sites at which the cell synthesizes new protein molecules - some are attached to endopasmic reticulum
endoplasmic reticulum
network of thin tubes that transport newly synthesized proteins to other locations
motor neuron
has its soma in the spinal cord - excitation from other neurons through the dendrites of a motor neuron conducts impulses along an axon to a muscle
sensory neuron
specialized at one end to be sensitive to specific stimulation (eg. light receptors). Soma is located on a stalk off of the main trunk of the axon.
dendrites
branching fibres that get narrower at the ends, many dendritic spines/branches - surface lined with synaptic receptors to receive information
nodes of ranvier
interruptions in myelin sheath
axon
thin fibre that sends information to other neurons, often covered in myelin sheath
presynaptic terminal
bulbous end of axon branches where chemicals are released in order to cross the junction between one neuron and the next
afferent axon
brings information in - every sensory neuron is afferent to the rest of the nervous system
efferent axon
brings information out - every motor neuron is efferent from the nervous system
astrocytes
star shaped glial cells that wrap around presynaptic terminals of a group of functionally related axons - by taking up ions released by axons and rereleasing, astrocytes help synchronize messages (also remove waste, control blood flow to the brain and dilate blood vessels during periods of hightened activity)
microglia
remove waste, viruses, and fungi
oligodendrocytes and Schwann cells
specialized types of glia that build the myelin sheaths that surround and insulate certain vertebrate axons
radial glia
guide the migration of neurons and their axons and dendrites during embryonic development - after development is complete, radial glia differentiate into neurons and astrocytes/oligodendrocytes
Blood-brain barrier
densely packed endothelial cells that line the walls of the capillaries in the brain, excluding most chemicals except some small uncharged molecules and those that cross through protein channels
Active transport
A protein mediated process that expends energy to pump chemicals from the blood into the brain
glucose
A sugar made in the liver from carbohydrates and amino acids; most vertebrate neurons depend on glucose - metabolic pathways using glucose require oxygen, as a result the brain uses 20% of oxygen consumed by the body
Thymine (B1)
Thymine is necessary for the use of glucose - prolonged thymine deficiency leads to death of neurons and Korsakoff’s syndrome (severe memory impairment)
Speed of nerve impulse
1m - 100m/sec
Electrical gradient
polarization - different charge inside the cell than out (neuron slightly negative inside)
Resting potential
difference in voltage in a resting neuron - can be measured with a thin micro electrode inside body (commonly a fine glass tube filled with concentrated salt solution and connected to an electrode and voltmeter outside the body) typical level of charge is -70 mV
What is the Sodium-Potassium pump?
protein complex- tranports 3 sodium ions out and draws 2 potassium in, as a result sodium is 10 x more concentrated outside the membrane and potassium is more concentrated inside (if charged ions flowed freely membrane would depolarize). Sodium pumped out stays out, potassium slowly leaks out leaving - charge (BBB lets things out but not in without pump)
How does the sodium potassium pump work?
At rest, sodium is pulled into neuron because of concentration gradient and the slight positive charge is attracted to negative cell interior. Because of pump, more sodium is pushed out than in (contrary to what would naturally happen). Electrical gradient pulls potassium in but concentration gradient pushes it out.
Action potential
messages sent by axons
- stimulus causes neuron to reach threshold
- depolarization (sodium and potassium channels open, sodium rushes in)
- charge flows along axon, opens voltage gated sodium channels
- at peak sodium channels close, now potassium will flow out (due to depolarization) returning neuron to original charge
- potassium channels close
hyperpolarization
further negative charge applied to neuron/ increased polarization
depolarization
reduces charge toward 0
threshold of excitation
stimulation beyond this point produces a massive depolarization of the membrane (subthreshold excitation produces some response, but any stimulation at or above threshold produces big response/action potential, amplitude/velocity of potential are independent of initiating stimulus provided threshold is reached - signals can be more frequent or rhythmically different but not faster/stronger)
absolute refractory period
no stimulation will produce an action potential - 1ms
relative refractory period
stronger than usual stiulation necessary to produce action potential - 2-4 ms
propagation of action potential
movement of message down an axon - new action potential at each point
myelin sheath
insulates axon and increases speed of action potential
myelinated axons
axons covered in fats and proteins (myelin sheath)
saltatory conduction
action potential jumping from node to node (faster, conserves energy as sodium is admitted only at nodes, otherwise sodium has to be pumped out)
graded potential
a membrane potential that varies in magnitude in proportion to intensity of stimulus
