PSIO 201 - Unit IV

overall function of the nervous system

communication and regulation

name other more complex functions of the nervous system

rapid information transmission

regulation of body

homeostasis maintained

seat of intelligence and thought

perception

movement

behavior, learning, memory, and more!

what is the nervous system made up of?

neural tissue (neurons and neuroglia)

two basic divisions of the nervous system?

central nervous system and peripheral nervous system

what makes up the CNS?

the brain and spinal cord

what makes up the PNS?

cranial and spinal nerves

what two subdivisions make up the PNS?

somatic and autonomic

what does the somatic PNS do?

effects the skeletal muscles, voluntary movement.

what does the autonomic PNS do?

effects smooth muscle, cardiac muscle, and glands. works with involuntary movement. also includes sympathetic and parasympathetic divisions.

explain how the sympathetic and parasympathetic divisions work within the autonomic PMS

body receives dual innervation, where both of these work together to produce up and down regulations, and it is all dependent on the bodily system which is assigned a different job.

give a simple neural pathway

Sensory Receptor: sensory input —> Brain and Spinal Cord: integration

—> PNS: motor output —> Effector

flow of information in nervous system goes like…

PNS —> CNS —→ PNS

what neurons are used during sensory input?

afferent (sensory) neurons

what neurons are used during integration and processing?

interneurons

what neurons are used during motor output?

efferent (motor) neurons

sensory (afferent) nerves come from and go to?

PNS to CNS

motor (efferent) nerves come from and go to?

CNS to PNS

whats the enteric nervous system?

division of the autonomic nervous system that controls the function of the gastrointestinal tract

what kind of cells are neurons?

excitable cells

what are neuroglia’s functions?

support, protection, and nourishment of neurons.

neuron dendrite

collects signals

neuron cell body (soma)

integrates incoming signals and generates outgoing signal to axon

axon

passes electrical signals to dendrites of another cell or to an effector cell

synapse

connection point between 2 neurons

myelin

insulating material wrapped around the axon of many neurons which enhances propagation of an electrical signal

name functional neurons

• afferent neurons (headed to CNS)

• interneurons (integrates sensory info by analysis and storage)

• efferent neurons (headed to effector through PNS)

structural types of neurons

• multipolar neurons

• bipolar neurons

• unipolar neurons

what neuron is this?

multipolar neuron

what neuron is this?

bipolar neuron

what neuron is this?

unipolar neuron

what category do bipolar neurons land in for function?

sensory

what category do unipolar neurons land in for function?

sensory

what category do multipolar neurons land in for function?

integrative and motor

astrocytes

nourish the neuron

structural support

K+ regulation

talks to neurons via glutamate

neurotransmitter uptake

ependymal cells

line ventricles and central canal

neural stem cells

makes CSF

oligodendrocytes

insulation to speed electrical conduction in CNS

growth and repair

schwann cells

insulation to speed electrical conduction in PNS

growth and repair

microglia

immune defense cells

mobile

can prune synapses (aiding in plasticity)

cranial meninges

CT surrounding brain, protecting it and anchoring it to the cranial cavity

dura mater

“tough mother” outer layer fuses with periosteum of skull (not spinal cord) inner layers fold in cranial cavity creating sinuses.

arachnoid mater (web)

spaces for blood vessels, subarachnoid space filled with CSF.

pia mater

thin protective layer of tissue covering nerves and neruoglia

composition of cerebrospinal fluid (CSF)

plasma filtrate

glucose, O2, Na+, K+, Mg2+, other ions

functions of CSF

cushioning/shock absorption, maintain stable chemical environment, exchange nutrients and wastes.

where does CSF form?

the ventricles of the brain (1-4), numbered according to flow, and after the 4th one is emptied into the central canal of spinal cord.

choroid plexus

network of blood vessels formed from pia mater, forms CSF via filtration

CSF recycling

arachnoid granulations where CSF is absorbed back into circulatory system as fast as it produced.

what is resting membrane potential

the baseline electrical condition of all cells in the body

• greater negative charge outside of the cell

• greater positive charge inside the cell

with energy of 1 ATP, the Na/K ATPase pump can:

3 Na out of the cell

2 K in to the cell

what does the Na/K ATPase pump maintain?

the concentration gradients for both Na and K

at rest, the membrane is permeable to ___ through ______.

K+; potassium leak channels

what is the average resting membrane potential?

-70mV

movement of K+ ions is influenced by two competing forces:

• electrical gradient (running IN to cell)

• concentration gradient (running OUT of cell)

how can we change the membrane potential?

changes in membrane permeability produce large changes in the membrane potential. opening gates permits ions to move.

how do we make the membrane more permeable to K?

open K+ channels

how do we make membrane more permeable to Na?

open Na channels

what allows cells to generate electrical signals?

regulation of channel-mediated ion permeability

ion channels

• integral membrane proteins

• selective for certain ions

• can be opened or closed

  • some are routinely open (ion leak channels - which are unregulated)

name this specific ion channel

chemically-gated (ligand-gated) ion channels

name this specific ion channel

mechanically-gated ion channels

name this specific ion channel

voltage-gated ion channels

voltage-gated ion channels open when..

when the membrane potential gets less negative (depolarized)

mechanically-gated ion channels open when…

when the membrane get stretched

chemically-gated (ligand-gated) ion channels open when…

a signal molecule binds to the channel protein (e.g. ACh)

what do excitable cells do to generate an electrical signal?

change their membrane potential.

what is the principle mechanism of generating an electrical signal?

opening and closing of voltage-gated Na+ channels.

ligand gated and mechanically gate ion channels found where in relation to nervous tissue?

dendrites and cell body.

voltage gated ion channels found where in relation to nervous tissue?

axon, axon branches, and synaptic end bulbs

what does this graph represent?

a neuronal action potential

what are the 4 steps of generating an action potential?

1. local depolarization

2. depolarization to threshold & voltage gated Na+ channels open

3. voltage gated Na+ channels open

4. voltages gated K+ channels open

depolarization

less negative

repolarization

more negative, back to resting

hyperpolarization

most negative, past resting potential

break down of step 1 of generating an AP

local depolarization

• graded potentials

  • local changes in cells membrane potential

    • 2 different types

two types of graded potentials are…

IPSP (inhibitory postsynaptic potential)

EPSP (excitatory postsynaptic potential)

IPSP (inhibitory postsynaptic potential)

hyper polarizing, taking it further from an AP

EPSP (excitatory postsynaptic potential)

depolarizing, bringing it closer to excitation and AP

break down of step 2 of generating an AP

depolarization to threshold

• graded potentials produce enough depolarization to reach threshold

  • opens voltage-gated Na+ channels

    • increased Na+ permeability

  • occurs in axon hillock

• there is no turning back, action potential begins and travels all the way to the end of the axon

break down of step 3 of generating an AP

Na+ Channels Close

• shortly after they open, they spontaneously close (become inactive)

break down of step 4 of generating an AP

K+ Channels Open

• depolarization opens K+ channels

  • K rushes out making it repolarize (more negative)

    • brings membrane back down toward resting value

after-hyperpolarizing phase what occurs?

after repolarization but before returning to resting membrane potential

• cell overshoots resting membrane potential (gets more negative)

refractory period

period when it is difficult or impossible to generate a 2nd AP

absolute refractory period

absolutely not

• membrane cannot be re-stimulated to produce another AP

• involves resetting of Na+ channels

relative refractory period

• new AP could be produced but doing so requires a larger than normal stimulation

• resetting the K+ channels

why are refractory periods important?

• establishes maximum rate of AP’s

• influences characteristics of AP propagation

  • ensures forward propagation

what is this graph showcasing?

all of the periods of an AP plus the refractory period.

if potassium channels open in a neuron what happens?

potassium rushes out of the cell, causing the inside of the neuron to repolarize

what is the threshold line at for an action potential to take place?

-55mV

at rest, na and k channels and permeability is what?

both channels are closed and the permeability is low for both.

when the neuron is depolarizing what is happening to the na and k channels and permeability?

the na channel is open and has high permeability, rushing INTO the cell. k channel is closed and has low permeability.

when the neuron is repolarizing what is happening to the na and k channels and permeability?

na channel is closed and has low permeability, k channel is open with high permeability of ions rushing OUT.

which graded potential is hyperpolarizing?

inhibitory post-synaptic potential (IPSP), it is becoming more negative, taking it further away from the threshold that shoots off an action potential.

electrical signaling occurs where and does what?

occurs in the axon and propagates info through changes in Vm.

after electrical signals, it goes to chemical signaling, where does this occur and what happens?

chemical signaling occurs in the synapses, there is a release of neurotransmitters that help transmit the info.

propagation of an action potential

entry of Na produces a local current, which spreads laterally to depolarize adjacent areas of membrane. after one action potential, the adjacent membrane area is depolarized to threshold, opening Na channels in the new region of the membrane.

once initiated, an action potential moves along the membrane of the neurons ___ until it reaches the _________.

axon; synaptic end bulbs.

what is the orientation of the propagation of an action potential?

it carries all the way to the end. Na goes first, K always follows after. Only ever moves in one direction.

why do action potentials only move in one direction?

because of refractory periods, establishing the frequency of the AP, and ensures the AP goes from the axon hillock → axon terminal

what is electrotonic conduction?

the passive spread of an electrical charge (voltage change) along a neuron's membrane or through the cytoplasm without the generation of new action potentials

what affects the velocity of propagation for an AP?

1. Size (in axon diameter)

2. myelination (insulation)