Chapter 2 - Structure and Function of the Nervous System

neurons are…

• a single unit

• vary in forms + functions

what are glial cells used for?

• structural support

• to insulate neurons

what are the four types of glial cells?

• astrocytes

• oligodendrocytes

• schwann cells

• microglial cells

what is the biggest glial cell?

astrocytes

what is the shape of an astrocyte?

astrocytes have a star-like shape

what is the purpose of astrocytes?

they maintain the functional and structural integrity of the blood brain barrier (BBB)

which glial cells make up myelin in the CNS?

oligodendrocytes

which glial cells make up myelin in the PNS?

shwann cells

what do microglial cells do?

clean damaged cells

what is the difference between the somatic nervous system and the autonomic nervous system?

somatic → moving our body parts voluntarily

autonomic → involuntary reactions (blinking, breathing, HR)

what is the purpose of myelin sheath?

it allows electrical signals to travel long distances (myelin = signal travels faster)

what is the purpose of the soma in a nerve cell?

to maintain the neuron’s metabolic activity

what is the purpose of dendrites in a nerve cell?

dendrites receive signals

what is the purpose of axons in a nerve cell?

to deliver signals

where are purkinje cells found?

cerebellum

which neurons send info and which neurons receive info?

presynaptic neurons → send info

postsynaptic neurons → receive info

what type of transmission occurs inside the neuron?

electrical transmission

what type of transmission occurs between neurons?

chemical transmission

what is the electrical potential?

electrical potential is the difference in voltage between the inside and the outside of the neuron

which ions are more prevalent outside the neuron and which are more prevalent inside?

outside: Na+, Cl-

inside: K+

ions travel through the membrane using…

channels or pumps

ion channels can be…

gated or non-gated

give an example of an ion pump

the sodium potassium pump

ion pumps are background mechanisms, this means that…

ion pumps work in the “background” constantly and at a steady rate to keep the cell alive

when a neuron is at rest, the cell membrane is selective to _______ but allows ______ to easily pass through

Na+, K+

dendrites have specialized protrusions called…

spines

what are spines?

• little knobs attached by small necks to the surface of dendrites

• purpose: receive input from other neurons

define dendrites

• receive signals from other neurons at the synapse

• structure: large, tree-like branches

define synapse

where neurons come together → presynaptic neuron sends neuron transmitters to postsynaptic neuron

neurons (like other cells) sit in a bath of salty extracellular fluid composed of…

mixtures of ions (K+, Ca+, Cl-, Na+)

the axon is a structure that extends from…

the soma (cell body)

describe the path of a signal from one neuron to another

• dendrites and spines receive input from another neuron (NTs)

• this produces small, graded potentials

• these potentials are summed at the axon hillock

• if threshold is reached, an action potential fires

• the action potential travels down the axon towards the axon terminal

• if the axon is myelinated, the signal travels faster

• at the axon terminal, NTs are released into the synaptic cleft (depolarization causes Ca2+ channels to open)

• NTs travel through the synaptic cleft and bind to receptors on the postsynaptic neuron

what is saltatory conduction?

when an electrical signal jumps between nodes of ranvier

what are the two forces that affect a neuron’s membrane potential?

1) ionic concentration gradient

2) electrical gradient

what helps create the ionic concentration gradient?

the sodium potassium pump

what helps create the electrical gradient

an ion pump and selective permeability (membrane is selective about what it will allow to pass through it)

the sodium potassium pump moves ions _____ their concentration gradient

against

voltage-gated ion channels react to…

dramatic changes in the electrical gradient

gated ion channels open or close in response to what?

changes in nearby transmembrane voltage or to chemical or physical stimuli

what does get the membrane to threshold?

• excitatory inputs open Na+ channels

• Na+ floods into the membrane

• the neuron becomes depolarized

how does the Na+/K+ pump maintain resting potential?

by keeping a larger concentration of K+ inside the cell and Na+ outside (pump uses ATP as energy)

how do action potentials enable signals to travel for meters with no loss in signal strength?

action potentials continually regenerate the signal at each patch of membrane on the axon

the presence of what allows action potential to regenerate itself?

voltage-gated ion channels

distinguish between the ionic concentration gradient and the electrical gradient

• ion gradient → focus is on the difference in ion amounts

• electrical gradient → focus is on the charge difference (voltage)

while the ionic concentration gradient is driven by a difference in ________________ on each side of the membrane, the electrical gradient is driven by the difference in ________ across a membrane

amounts of ions, charge

in relation to the ionic concentration gradient, ions tend to move…

from areas of high concentration to areas of low concentration

the electrical gradient helps open up…

voltage-gated ion channels (cations pulled towards more negative side, anions pulled towards more positive side)

where is the densest concentration of ion channels found? what is this called?

the axon hillock, the spike-triggering zone

what occurs in the spike triggering zone?

• action potential is initiated

• REMEMBER: depolarization spikes!!!

what would occur if an axon has no myelin?

action potential would move freely around the neuron without the presence of myelin because ions would be moving freely so the signal would dissipate

what is myelin’s main job?

to guide the direction of the signal (preserve the signal)

“all or none” when describing action potential means…

it either happens or it doesn’t (there’s no in between)

a stronger stimulus does not make an action potential bigger, instead it…

increase the frequency (rate) that the action potential fires

what are the 5 phases of action potential?

1. threshold is hit (around -55 mV)

2. depolarization occurs and reaches its peak (peak is around 40 mV)

3. repolarization

4. hyperpolarization (refractory period)

5. resting state (-70 mV)

in myelinated axons what is found along the length of the axon but only at the nodes of Ranvier?

voltage-gated ion channels

what occurs at the synaptic cleft?

chemical transmission

what is the primary excitatory neurotransmitter?

glutamate

what is the primary inhibitory neurotransmitter?

GABA

what are residual neurotransmitters?

NTs that are left in the synaptic cleft after a signal has been delivered

what is one way to get rid of residual NTs?

reuptake

what is reuptake?

when a NT binds to the receptor on the presynaptic neuron

describe SSRIs

• SSRIs stand for selective serotonin reuptake inhibitors

• SSRIs bind to receptors on the presynaptic neuron

• prevents serotonin from reuptake

• more serotonin left in the synaptic cleft to improve mood

for temporal summation, inputs come from __________ while for spatial summation, inputs come from ____________

the same synapse, multiple synapse

which summation has inputs that are repeated and in quick succession and which has simultaneous inputs?

temporal summation → repeated, in quick succession

spatial summation → simultaneous

a gap junction creates…

physical channels between two cells

distinguish between sympathetic and parasympathetic

• sympathetic → prepares the body for action (fight or flight)

• parasympathetic → helps the body maintain its functions

identify dorsal, ventral, rostral and caudal in your mind

…

a region in the brain can be identified by multiple spatial names, for example…

the temporal lobe is ventral and dorsal

identify each line

red → midsagittal section

purple → lateral sagittal section

identify each line

green → axial, transverse, or horizontal

blue → coronal

what does the brain float in and what does this do?

• the brain floats in cerebrospinal fluid

• this reduces the pressure and weight of the brain and protects it from damage

what else is filled with CSF?

ventricles

the brain uses blood from the…

heart (20%)

the brain has no storage for…

glucose or oxygen

since the brain has no storage for glucose or oxygen, disruption of either of these causes…

unconsciousness or death

more neuronal activity =

more blood flow

what parts does the brainstem include?

• medulla

• pons

• cerebellum

• midbrain

identify the medulla, pons, cerebellum, and midbrain

what is the medulla responsible for?

• vital functions like respiration and HR

• sensory/motor relay station between body and brain

• motor commands cross over to contralateral body

describe the pons

• “the bridge”

• main connection between the brain and the cerebellum

• responsible for eye/face movements

what parts does the midbrain include?

inferior/superior colliculus + red nucleus

what is the midbrain responsible for?

sending pain signals down

the diencephalon includes what two parts?

hypothalamus and thalamus

diencephalan means…

between brain

the hypothalamus and thalamus make

interconnections between widespread brain areas