neurons and glial cells 1

true or false: the nervous system is found exclusively in the animal kingdom

true

basic function of the nervous system

sense and respond to the environment

two main subdivisions of the nervous system

• CNS (central nervous system): brain and spinal cord

• PNS (peripheral nervous system): nerves that leave and enter the CNS

neurons function

receiving and sending neuronal signals

what are glial cells

rough-neuronal cells that support neurons

neuron cell structure parts

• cell body

• dendrites

• axon

• axon terminals

3 examples of neuron cells demonstrating “structure determines function”

• purkinje neurons have an extensive network of dendrites

• pyramidal cells have an extensive network of dendrites and long axons

• retinal bipolar neurons have less extensive branching and short axons

three main types of neurons based on directionality

• sensory (afferent): relay sensory information from body to CNS

• motor (efferent): relay motor information from CNS to skeletal muscle

• interneurons: form neural networks

what do interneurons do

• responsible for most brain functions

• form reflex arcs by connecting sensory neurons to motor neurons in the spinal cord

different ways different types of glial cells support neurons

• oligodendrocytes and schwann cells: form myelin sheath

• astrocytes: form the blood brain barrier, provide nutrients to neurons, and fine-tune neuron signaling

• microglia: protect CNS from infection

where do oligodendrocytes form myelin sheath? Where do astrocytes form myelin sheath?

oligodendrocytes → CNS

astrocytes → PNS

what are the connections between neurons called

synapses

between which part of neurons do synapses form

between an axon terminal of one neuron and a dendrite of another

the axon terminals release _____ and the dendrites have ___ that respond to these

neurotransmitters; receptors

three parts of neuronal communication/signaling

• excitation to threshold: neuron 1 released neurotransmitters to receptors on neuron 2 and excite the axon hillock

• action potential: action potential is fired from the axon hillock, causes a chain reaction of action potentials

• synaptic transmission

most neurons are polarized. what does that mean

inside of the neuron is more negatively charged than the outside

the difference in charge or voltage across the membrane is referred to as _____ and is measured in ____

membrane potential; millivolts (mV)

membrane potential is always expressed as the charge ____ the cell relative to the charge ___ the cell

inside; outside

what is resting membrane potential

-60mV

what does the negative value indicate in resting membrane potential

the inside is 60mV more negative than the outside

what do Na+/K+ pumps do

use ATP to establish concentration gradients for Na+ and K+

where is Na+ pumped and where is K+ pumped by Na/K+ pumps

Na+ is pumped out of the cells

K+ is pumped into the cells

resting membrane potential is generated by the coordination of…

Na+/K+ pumps and leaky K+ channels (leaky = always open)

how do leaky K+ channels more K+ ions

down its concentration gradient out of cells

resting membrane potential exists because of high ______ of the membrane to ____ ions

permeability; K+

why does K+ diffuse out the cell at much higher rates than Na+ diffuses in

because there are hundreds of times more leaky K+ channels than leaky Na+ channels

what are gated channels

channels that open and close to allow ions to diffuse down their concentration gradients and create a change in membrane potential

when does depolarization occur

when the inside of the cell becomes less negative

when does hyperpolarization occur

when the inside of the cell becomes more negative

an axon potential is fired only if…

the axon hillock is depolarized to threshold (-55mV)

what depolarizes the axon hillock to threshold

excitatory signals called ESPSs

where are ESPSs generated

at the synapses

what is ESPSs generated in response to

excitatory neurotransmitters released from the axon terminals of pre-synaptic neurons

what happens when the axon hillock is depolarized to threshold

• voltage-gated Na+ channels open up

• Na+ diffuses into the neuron

• the Na+ that diffuses into the neuron completely depolarizes the membrane at the axon hillock

where are voltage-gated Na+ channels found on the neuron

from the axon hillock to the end of axon terminals

when do voltage-gated channels open

when the membrane is depolarized to -55mV

When voltage-gated Na+ channels open, Na+ diffuses into the neuron and completely depolarizes the membrane at that location to _____

+30 mV

after Na+ ions diffuse into the cytosol of the axon, they…

diffuse down the cytosol of the axon and depolarize immediately downstream of the axon hillock to threshold

downsream = ____, upstream = _____

downstream = toward axon terminals

upstream = toward cell body

what does a membrane potential graph show

changes in membrane potential over time at a particular location on an axon

how is a membrane potential graph generated

by placing an electrode at a specific location on the axon to record changes in voltage

membrane potential at the axon hillock broken down into 4 action potential steps

• depolarization from resting potential to threshold (-60mV - -55mV)

• complete depolarization (-55mV - +30mV)

• repolarization (+30mV - <-60mV)

• restoring resting potential (back to -60mV)

Action potentials are “______”: once they are initiated, the membrane is always completely depolarized to +30mV

all-or-none

localized changes in membrane potential of varying intensity

post-synaptic-potentials

what happens if ESPSs depolarize the axon hillock to -55mV

voltage-gated sodium channels open

when do voltage-gated sodium channels inactivate

at +30mV

At the peak of depolarization, V-gated Na+ channels become quickly

______ by a _____ gate

inactivated; ball-and-chain inactivation gate

While inactivated, V-gated Na+ channels become unresponsive to changes in membrane potential, a period known as the…

absolute refractory period

the absolute refractory period ensures that action potentials never go…

back toward the axon hillock

true or false: Na+ diffuses in only one direction (downstream or upstream)

false, it diffuses in both!

By becoming inactivated and unresponsive to threshold, the Na+ ions that diffuse upstream _____ re-open these V-gated Na+ channels and initiate action potentials in the opposite direction (toward the axon hillock)

cannot

saltatory conduction

in myelinated axons, action potentials propagate from node of Ranvier to node of Ranvier

myelin sheath ____ action potentials

speeds up

how does myelin sheath speed up action potentials

insulates the membrane and prevents Na+ from leaking

multiple scerlosis

neurodegenerative disease where nervous system attacks myelin sheath

name of scar tissue from multiple sclerosis

sclerotic plaques

how neurotoxins effect neurons

block voltage-gated channels