Bio 251 Chapter 11: Fundamentals of Nervous System & Nervous Tissues

Central, Peripheral, & Autonomic

3 branches of nervous system

Sensory Input, Integration, & Motor Output/Response

3 overall functions of nervous system

Sensory Input

Various types of receptors in the body respond to particular stimuli; information gained from stimulus is sent to the nerous system

Sensory Receptors

Responsible for input; different types that can send information to brain & spinal cord

Integration

Nervous system processes & interprets what incoming info means; once final interpretation is made, then decides response

Motor Output/Response

Nervous system sends out a response to a certain part of the body; action will take place

Effector Organ

Organs that carry out the response/action dictated by the brain

Central Nervous System & Peripheral Nervous System

2 components of nervous system

Central Nervous System

Brain & spinal cord; integrates info & sends out response

Peripheral Nervous System

Sensory input & motor output; nerves extend to rest of body from CNS; connects CNS to rest of body

Neurons

Functionally important; excitable cells; capable of responding to stimuli & creating & transmitting electrical signals, potentially over long distances

Neuroglia (Glial Cells)

Typically smaller cell types found in nervous system; support neurons to ensure they're capable of performing their function; mostly supportive in function

Astrocytes, Microglial Cells, Ependymal Cells, Satellite Cells, Oligodendrocytes & Schwann Cells

Individualized types of neuroglia/glial cells

Astrocytes (CNS)

Most abundant of neuroglia; central cell body with extensions coming off in star-shaped pattern; individual branches coming from main cell body connect to & wrap around individual structures (some projections wrap around neuron or connect to blood capillaries)

Connect neurons to blood (neurons don't like change), help young neurons migrate (go in right direction/support), & "clean up" (clean leaked K ions & leftover neurotransmitters)

Jobs of astrocytes

Microglial Cells (CNS)

Have several projections (more long, slender, stick-like processes); monitor health of any neuron it directly contacts

Processes extend & touch neurons in diff areas & monitor health; if healthy=cell sits there & does nothing; if damaged, will go to neuron & turn into macrophage

Job of microglial cells

If had autoimmune disorder where attacks nervous system, would be terrible (limit immune system access); w/o microglial cells, would have buildup of dead neurons & would disrupt electrical signals from healthy neurons

Why do microglial cells turn into macrophages (why not bring in real macrophages from immune system)?

Ependymal Cells (CNS)

Found in cavities of CNS; production & circulation of cerebrospinal fluid; has cilia that extends into fluid-filled cavity to circulate cerebrospinal fluid

Cerebrospinal Fluid

Helps cushion & protect CNS; also transports chemicals/ions to other parts of CNS; protective in nature

Satellite Cells (PNS)

Exclusively found in PNS; similar function to astrocytes of CNS; cover & surround PNS neurons; protective; ensure cells in PNS are getting what they need

Oligodendrocytes (CNS) & Schwann Cells (PNS)

Form blanket that wraps around fibers/neurons (produces myelin sheath)

Schwann Cells

Wrap themselves around axon part of neuron, forming a blanket

Oligodendrocytes

1 individual of these cells can wrap around multiple neurons in the CNS, forming a myelin sheath

Myelin Sheath

Insulating covering for individual neurons in CNS & PNS; insulating neurons sends electrical messages quicker

Changing resting membrane potential

Process of creating electrical impulses involves __________

Longevity

Neurons have extreme ________; if healthy, can function for entire lifetime

Amitotic

Neurons are _______; can't reproduce mitotically; can't be replaced

High

Neurons have exceptionally ______(high/low) metabolic rates; brain requires a lot of O2 & glucose, brain gets 1st priority of glucose

Cell Body

Main part of cell that contains nucleus; nucleus containing genetic info; can receive info from surrounding neurons & send out info

Nuclei

Cell bodies in the CNS

Ganglia

Cell bodies in the PNS

Dendrites & Axons

2 types of projections from cell bodies that branch off from neuron

Dendrites

Shorter processes that directly branch off from cell body; main receptive region of neuron; 1st part that receives message & passes it to cell body

Stronger

Dendrites can receive many signals that are conflicting, but the ________ message is received

Hundreds; more likely neuron will pick up on incoming message (increases receiving surface area)

One neuron has _________ dendrites; advantageous because ___________

Axon

Neuron has 1 of these; sends signal to next neuron; generates nerve impulses & transmits it away from cell body

Plasma Membrane

Electrical signal only passed along the ________ of the neuron; not deep within the axon

Bundled; save space

Neighboring neurons frequently ________ together, to _______

Tracts

Bundles of axons in the Central Nervous System

Nerves

Bundles of axons in the Peripheral Nervous System

Terminal Branches

End of axon on opposite side of cell body branches several times & forms these

Axon Terminal

Terminal branches end in ________; portion of neuron that releases neurotransmitter

Neurotransmitter

Ligand; chemical messengers that will act on next neuron in line so impulse spreads; bind to dendrites of neurons in lines

Myelin Sheaths

Fatty covering, white in color; insulators important for large & long neurons; speeds up transmission of axon potential of electrical impulse

Axon portion; because if covered dendrites, it wouldn't be able to receive the message

Myelin sheaths only found on ________ portion of neuron; why

Schwann cells; cells wrap around themselves (more layers=better insulation); longer axon needs more cells

___________ myelinate axons in the peripheral nervous syste

Myelin Sheath Gaps

Schwann cells don't contact neighboring cells directly; tiny gaps in between; don't impair insulating function; speeds up how fast messages are transmitted along axon

Sensory/Afferent Neurons

Carry information from body toward CNS; sensory receptors; neurons responding to stimuli

Motor/Efferent Neurons

Carry info from CNS to body or effector organ; responsible for motor output

Interneurons

Found in between 2 other neurons; 1 neuron afferent & other efferent; pass information thru CNS where integration occurs; allow neurons to talk to each other for more complex responses

More

More complex response=______ (more/less) interneurons have to communicate w 1 another

-70 mV

Resting membrane potential of all cells, on average

Leaky K ion channels (K leaks out & leaves behind - proteins in cell)

How the resting membrane potential is created

Signal Transmission

Communication between neurons

Changing permeability of plasma membrane (easier/harder for ions to paas)

How neurons change the resting membrane potential

Graded & Action Potentials

2 types of signals that can be produced by change in resting membrane potential

Protein-Ion Channels

To change permeability for ions in plasma membrane, accomplished by __________; most are selective & allow for passage of a specific type of ion

Leakage (Non-Gated) Channels)

Leaky proteins, allow slow trickle of ions from 1 side of plasma membrane to another; always "open" with no doors

Gated Proteins

Proteins that need to be opened before ions can move through it to other side of membrane

Chemically, Voltage, & Mechanically Gated

3 ways gated proteins can be opened

Chemically Gated Proteins

Only open when protein binds to specific chemical

Voltage Gated Proteins

Only open & respond to change in voltage/potential of membrane; if -70 mV changes

Mechanically Gated Proteins

Open in response to physical deformation of receptor

Depolarization or Hyperpolarization

2 different responses of the cell by changing voltage

Depolarization

Decrease in membrane potential that makes inside of membrane less negative compared to resting membrane potential (ex: from -70 to -50); generates nerve impulses/electrical signals

Excitation

Depolarized membrane=_______ of neurons; allows to send messages

Hyperpolarization

Increase membrane potential; inside of cell becomes more negative relative to outside/resting

Inhibitory

Hyperpolarization=______ effect on neurons; prevent them from sending messages

Graded Potentials

Allow neuron to receive message from another neuron; strength directly correlated w stimulus strength; brief, travel short distances (stronger=travels farther); charge is lost quickly so current dies off quickly from point of origin

Generating a graded potential

________ is necessary to generate an action potential

Action Potentials

Nerve impulses; message sending signal; fast changes in membrane potential; always from -70 mV to +30 mV

-70 mV to +30 mV

Voltage change for every action potential

Depolarizing

Action potentials can only be _______ (depolarizing/hyperpolarizing) events

Dendrites

Graded potentials only occur at ________

Axon

Action potentials only occur at ________

Trigger Point

Action potential reaches point of axon called _______; action potential origin; if doesn't reach this, nothing happens; voltage-gated channels open from graded potential here

Change in membrane potential

Action potential=________, which is a message

Voltage-Gated Sodium Ion Channel

Gated channel (has 2 doors); involved in generating action potentials

Activation & Inactivation Gates

2 "Doors" of the Voltage-Gated Sodium Ion Channel

Activation Gate

Gate of Voltage-Gated Sodium Ion Channel that's voltage-sensitive; changes to certain voltage, then opens; allows movement of Na across membrane

Inactivation Gate

Gate of Voltage-Gated Sodium Ion Channel that flips closed quickly over channel; closing channel that prevents movement of Na across membrane

Potassium Voltage Gated Ion Channel

Leakage channel for K (always open); slow trickle of K across membrane, but only open to changes in membrane potential (voltage-sensitive); allows K thru when open, but can open/close depending on membrane potential

Resting membrane potential, depolarization, repolarization, hyperpolarization

Process of generating an action potential

Resting Membrane Potential (-70 mV)

Neuron not doing anything/producing message; no movement of Na across membrane (activation gate closed); permeability of Na is low; slow trickle of K across leakage channel but K Channel is closed; permeability of K+ is high

Depolarization (-55 mV specifically, then peaks at +30 mV to end AP)

Neuron gets a message & receives change in membrane potential (reaches threshold voltage at axon); generation of action potential itself; voltage-gated Na channels open; free flow of Na into neuron; decrease in membrane potential

Repolarization

Ending action potential; neurons can't keep firing (CNS would get overstimulated); inactivation gate flips closed (Na can no longer freely enter cell); cutting off Na prevents AP from getting too positive; K channels open at 30 mV; free flow of K out of neuron (makes inside of cell more negative)

Hyperpolarization (-90 mV)

When membrane potential becomes greater than -70 mV; have to fix this; K channels close; Na-K ATPase Pump pumps out remaining Na in cell & brings K back in to reestablish -70 mV; only caused by movement of K out of cell

Frequently

Brain interprets stimulus strength for APs based on how ________ they're fired

Refractory Period

Period of time in which a second action potential can't be generated at an axon; downtime for neuron to reset itself back to original state

Absolute Refractory Period

Neuron can't generate any action potential at this point

Voltage Gated Na Channels open (beginning of depolarization); Na channels have reset to OG state (end of repolarization)

Absolute Refractory Period starts when _________ & continues until __________

Separate

Every action potential is ________; impossible to have 2 at once

1; starts at trigger pt then spreads down length of neuron (axon to axon terminals)

APs are only transmitted in _______ direction; can't go backwards

Relative Refractory Period

Neuron can technically generate another action potential, but stimulus must be much stronger

Before neuron starts to hyperpolarize; neuron is completely reset to OG resting membrane potential

Relative Refractory Period starts ________ & continues until __________

Going from more negative number than -70 to -55 always

Why does it take a stronger stimulus when cell is hyperpolarized

Emergency

Speed of AP depends on how much of an _______ the info is

Axon Diameter & Degree of Myelination

2 factors that determine rate of action potentials (speed)

Larger; can fit more Na Channels (more flow of Na across membrane=faster change in potential)

_______ (larger/smaller) axon diameter sends info fast