3) Organization of PNS

membrane of soma/cell body

• called plasmalemma or neurilemma

  • hydrophobic (keeps water out)

  • binds together a cytoplasm

    • cuytosol, the aqueous part of the cytoplasm

nucleus of soma/cell body

• nucleolus at the center

• chromosomes for coded production of proteins

ER of soma/cell body

• function: lipid and protein synthesis

  • RER = protein

  • SER = lipid

• tubes that isolate, modify, store, and transport the proteins and lipids

lysosomes of soma/cell body

• digest compounds

• glycogen → glucose

• part of axoplasmic transport system

Golgi apparatus of soma/cell body

• stores the formed proteins and lipids

microtubules of soma/cell body

• axonal transport

• relays structures such as neurotransmitter vesicles down the axon to the output zone

2 functions of axons (nerve fiber)

• transmission of information

• transportation of metabolically important materials to and from some to axonal end

transmission of information

• propagation of action potential (electric potentials)

• from soma to output region to propagate

transportation of metabolically important materials to and from some to axonal end

• axonal transport system

• anterograde (from some to output region (axon) like neurotransmitter vesicles)

• retrograde: from axonal end back to soma

myelinated axons

In the PNS, schwann cells myelinate axons by investing them w up to 300 concentric layers to form the myelin sheath

unmyelianted axons

do not have a myelin sheath but are associated w and enveloped by Schwann cells which provide trophic support

electric and physical principles of neuronal cell membrane

• two hydrophobic phospholipid layers

• tries to maintain the outside of the cell away from inside of the cell

• proteins form channels for ions to pass through

positive than the negative inside and more extracellular

the outside of the cell is more

negative than the positive outside and more intracellular

the inside of the cell is more

high sodium and chlorine concentrations

the outside of the cell has

high potassium and protein concentrations

the inside of the cell has

1. electrostatic force

2. diffusion force

what are the two types of force that guide movement of ions

electrostatic force

liek charges repel each other

diffusion force

ions tend to move from high to low concentration and are stronger than electrostatic forces

ion channels

• proteins to control rate of transport of specific ions

• specific to types like sodium and potassium (more passive)

active mechanisms

• sodium potassium pump (tries to get back to normal/resting)

• requires ATP

ligand gated

• made of multiple proteins

• ligand (ACh) attaches to the receptor and opens channel

• ions (Na+) can now move through to inside

mechanically gated

opens in response to any mechanical stimulus such as a pressure or stretch to get the ions to come through

voltage gated

• opens when membrane potential reaches threshold

• Na+ channels open at -55mV and close at +30mV

leakage

• open randomly at rest

• ions can pass in either direction

• More K+ than Na+ leakage

active mechanisms

• sodium potassium pump

  • transports three Na+ ions from interior of the cell to the exterior and two K+ ions from exterior to interior

    • transport is against diffusion gradient of Na and K

    • requires ATP

resting membrane potential

RMP

membrane is polarized and carries negative charge on the inside

depolarization

inside becomes less negative

hyper polarization

inside becomes more negative

postsynaptic potentials (PSP)

• “graded” potential = excitatory and inhibitory

excitatory snaps (EPSP)

inside becomes more (+) than resting; the membrane becomes depolarized

inhibitory synapse (IPSP)

inside becomes more (-) than resting; the membrane becomes hyper polarized

step 1

steps 2 & 3

steps 4 & 5

step 6

propagation of action potential

how do axons conduct information?

propagation of action potential

• occurs in both directions

• speed is different for different axons

  • dependent on:

  • diameter of axon

  • myelination

functions of myelin sheath

1. it acts as an electrical insulator for parts of the axons, thus preventing action potential from developing

2. it allows accumulation of charge at the nodes of ranvier

3. it speeds up the conduction of action potential

motor nerve fibers

• myelinated

• large

• muscle control

sensory nerve fibers

• myelinated, large, touch/vibration/position perception

• thinly myelinated, medium, cold perception & pain

• unmyelianted, small, warmth perception & pain

autonomic nerve fibers

• thinly myelinated or unmyelinated

• very small

• heart rate/blood pressure/sweating/GIT/GUT function

faster conduction velocity

larger axon diameter =

faster conduction velocity

myelinated =

synapses

• Average neuron: 1000–10,000 synapses

• Synapse (Sherrington)

  • Presynaptic axon terminal

  • Zone of apposition (cleft)

  • Postsynaptic cell

• Chemical or electrical

• Can be enhanced or diminished—plasticity

plasticity

NS can adapt in response to info coming in

direction of information flow in synapses

• In one direction: neuron to target cell (chemical synapses)

• First neuron: presynaptic neuron

• Target cell: postsynaptic neuron

glutamine or acetylcholine

excitatory neurotransmitters

GABA

inhibitory neurotransmitters

receptor that they bind to (ex: dopamine can be either depending on what binds to it)

some neurotransmitters can be excitatory or inhibitory depending on the

electrical & chemical

types of synapses

principles of chemical synaptic transmission

• Neurotransmitter synthesis

• Load neurotransmitter into synaptic vesicles

• Depolarization—vesicles fuse to presynaptic terminal

• Neurotransmitter spills into synaptic cleft

• Binds to postsynaptic receptors

• Biochemical/electrical response elicited in postsynaptic cell

• Removal of neurotransmitter from synaptic cleft

direct chemical transmission

transmitter binds, things flow through

indirect chemical transmission

being transmitted then a different pathway that allows the channel to open

simple glutamate receptors

just glutamate… more likely to be impacted or affected of glutamate is inhibited

complex glutamate receptors

a whole lot of things less likely to be impacted or affected of glutamate is inhibited

NMDA vs AMPA receptors

simple vs complex

effects on postsynaptic neuron

Excitatory and inhibitory postsynaptic potentials

EPSP

transient postsynaptic membrane depolarization by presynaptic release of neurotransmitter

IPSP

transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter

neurotransmitter recovery and degradation

• diffusion

• reuptake

• enzymatic destruction

• desensitization

• synaptic fatigue

diffusion

away from synapse

reuptake

neurotransmitter re-enters presynaptic axon terminal

enzymatic destruction

inside terminal cytosol or synaptic cleft (destroyed)

desensitized

no affect anymore (cleaves itself to inactive state)

synaptic fatigue

occurs if the presynaptic vesicles are released at a faster rate than reuptake can recycle them (too fast and just shut down?)

purposes of nervous system

• coordination of all body activities = allows for communication and integration

• voluntary and involuntary movement of our bodies

• cognition

• respond and adapt to demands (internal and external)

CNS - spinal cord

• conveys sensory input from the body and most of the viscera (organs)

• contains fibers and cells that control the motor elements of the body and viscera

CNS - brainstem

• midbrain

• pons

• medulla oblongata

midbrain

eyes and auditory

pons

some reflex actions such as chewing and tasting

medulla oblongata

heart rate, respiration, blood pressure

CNS - cerebellum

• coordination

• balance

• posture

CNS - diencephalon

• main processing center for info to the cerebral cortex from ascending sensory pathways

• thalamus

• hypothalamus

thalamus

sends sensory information to the cerebrum

hypothalamus

regulates temp, thirst, appetite, sleep, BV dilation/constriction

CNS - cerebrum

• largest part of brain

• cortex

• white matter

• basal ganglia

cerebral cortex

layers of cells with specific function (4 lobes: frontal, parietal, temporal, occipital)

white matter

• white from myelination

• allows info to pass through (sends info)

basal ganglia

important in controlling movement (parkinson’s)

PNS

• spinal nerves

• cranial nerves

• autonomic ganglia and autonomic nerves to viscera and glands (autonomic system)

everything coming off of brain, brainstem, and spinal cord (everything that is peripheral)

spinal nerves

have both motor (out) and sensory (in) components

autonomic ganglia and autonomic nerves to viscera and glands

regulates HR, peristalsis, digestion, & more

CNS

brain and spinal cord

PNS

nerves branching off of CNS

communicating, integrating, & processing

NS core functions

spinal peripheral nerves - structural anatomy

• spinal cord (CNS)

• dorsal root - sensory

• ventral root - motor

• input to the cord is sensory/afferent

• output from the cord is motor/efferent

• spinal nerve - mix of motor and sensory

• the spinal nerves then split into rami (dorsal and ventral ramus)

• go into a plexus (structure in the form of a network (braid))

plexus

big collection of things that branch out to help control other things

brachial plexus

C5-T1

5 roots (ventral rami)

3 trunks

6 divisions

3 cords

5 branches

CT layers of a spinal nerve

• epineurium

• perineurium

• endoneurlium

epineurium

perineurium

endoneurium

fascicle