PGY 300 Neurophysiology

Meninges

dura mater, arachnoid mater, pia mater

meningitis

inflammation of the meninges

white matter

in spinal cord, consists of axons carrying info to and from the brain

gray matter

consists of sensory and motor nuceli

dorsal root

carries sensory info to CNS

ventral root

carries motor info to muscles and glands

ascending tracts

carry sensory info to brain

descending tracts

carry commands to motor neurons

interneurons

only in CNS

spinal reflex

initiates a response without input from the brain

shingles

disease of dorsal root ganglion, chicken pox virus dormant but reactivates as rashes along the skin

cerebral spinal fluid (CSF)

provides protection, produced by choroid plexus

hydrocephalus

too much CSF in brain

astrocytes

form blood brain barrier

cerebellum

controls motor, contains almost half of all neurons in brain

cerebrum

largest part of brain, 4 lobes: frontal, parietal, occipital, temporal

pons

sends info between cerebrum and cerebellum, controls sleep and breathing

medulla oblongata

controls cardiovascular and respiration

sensory area

receives sensory input and translates into perception

motor area

direct skeletal muscle movement

association areas

integrate info from motor and sensory areas and direct voluntary behaviors

brocas area

speech production, damage makes person not able to speak

wernickes area

language comprehension, damage makes person talk but not make sense

homunculus

somatosensory map of body parts on cerebral cortex

basal ganglia

control movement in forebrain

limbic system

hippocampus, amygdala, cingulate gyrus

hippocampus

learning and memory

amygdala

emotion and memory (fear associated memories)

cingulate gyrus

emotion

diencephalon

thalamus, hypothalamus, pineal gland, pituitary gland

thalamus

relay and intergrate sensory and motor info

hypothalamus

homeostasis

pineal gland

melatonin

pituitary gland

hormone master gland

corpus callosum

connect hemispheres of brain

MRI

images not degraded by bone

PET

injection of radioactive ligand

EEG

recording of brain waves, sleep thereapy

neuron consists of

dendrites, axon, soma (cell body), synapse

glial cells

supports, nourish and protect neurons, schwann cells, oligodendrocytes, astrocytes

schwann cells

PNS only, myelinated

node of ranvier

gap in myelin sheath, where AP occurs

saltatory conduction

jumping of AP from node to node

axon

connects soma with synapse

dendrite

where inputs to a neuron are found

synapse

site of communication between neurons

voltage

energy to move ions across cell membrane

capacitance

ions needed to change voltage, myelin increases

conductance

ease of flow of ions

excitation

more positive, depolarization, Na enters cell

inhibition

more negative, hyperpolarization, K exits cell or Cl enters

channels

uses concentration gradient, not ATP

carrier

never form open channel, requires ATP, can move against concentration gradient

uniport carrier

one substance

symport carrier

carries 2 or more substances same way

antiport carrier

move substances opposite directions, ex Na-K pump

Na - K pump

moves Na out of cell and K into cell, primary active transport, uses ATP

secondary active transport

uses energy of sodium gradient to move k

selectivity

which ions can pass through

conductance

how fast ions flow

gating

is pore open or closed

voltage-gated

activated when charge changes, ex AP

ligand-gated

molecule binds to another, ex neurotransmitters

mechanically-gated

physical force pops channel open, ex hair cells on inner ear

3rd cytoplasmic loop

forms inactivation gate,

p loop

ion selevtivity

S5 and S6 in voltage-gated channel

form activation gate

NMDA receptor

ionotropic glutamate receptor, blocked by Mg, controls Ca channel

AMPA receptor

ionotropic glutamate receptor, controls Na channel, depolarizes

ionotropic receptors

associated with ligand-activated ion channels, direct link to channel fast

excitatory neurotransmitters

Ach - skeletal muscles, glutamate - brain, selective for Na and K

inhibitory neurotransmitters

GABA - brain, Glycine - spinal cord, selective for Cl

graded potential

occurs in dendrites

strength depends on stimulus

no threshold

longer lasting

involves Na, Cl, and Ca

action potential

all or none

has a threshold

travels farther

involves Na and K

occurs at trigger zone

steps of an AP

1. resting membrane

2. graded potential depolarizes neuron to threshold

3. Na channels open and rapidly depolarizes

4. Na channels inactivate, K channels open

5. K exits the cell and hyperpolarizes until below resting membrane

6. K channels close slowly and returns to resting potential

absolute refractory period

minimum time in-between APs, time required for Na channels to reset, determines spike direction

relative refractory period

determined by K channel after-hyperpolarization

myelin

lowers capacitance, allows APs to travel faster. increases frequency

degenerated myelin sheath

can prevent conduction of AP

Multiple sclerosis

causes loss or myelin and slows conduction

hypokalemia

not enough K in blood, makes neurons less likely to fire ap

hyperkalemia

too much K in blood, makes neurons more excitable

gap junctions

direct cytoplasmic connections

contact-dependent:

require interaction between membrane molecules

autocrine:

act on same cell that secreted them

paracrine:

are secreted by one cell and diffuse to an adjacent one

physiology of a chemical synapse

1. action potential depolarizes axon terminal
2. voltage-gated Ca++ channels opens and Ca++ enters cell
3. Ca++ entry triggers exocytosis of synaptic vesicle contents
4. Neurotransmittters diffuses across synaptic cleft and binds to receptors on postsynaptic cell
5. neurotransmitter binding initiates response in postsynaptic cell

SNARE proteins

attach to presynaptic vesicles

Botulinum toxin (Botox)

blocks release of acetylcholine

Teatnus toxins

disrupts other SNARE proteins, prevent fusion of glycine

synaptotagmin

binds calcium and stimulates vesicle fusion

Synaptic Vesicle life cycle

1. loaded with neurotransmitters and stored away in reserve pool
2. transported to synaptic membrane, docked and primed= ready for release
3. Ca++ enters synapse and binds to synaptotagmin initiating vesicle fusion
4. content is released and vesicle membrane is endocytose to form new vesicle

Acetylcholinesterase

deactivates ACh

Myasthenia gravis

autoimmune attack on AChRs, causes muscle weakness, Acetylcholinesterase can be used as treatment

Cocaine

increases dopamine release, stimulates the reward center

G-protein coupled receptors (GPCRs)

slow muscarinic receptors

7-transmembrane receptors

activate g-proteins inside the cell the g-proteins then stimulate production of second mesengers, enzymes and molecules

cAMP

amplifier enzyme
1. signal molecule binds to g-protein
2. turns on adenylyl cyclase
3. converts ATP to AMP
4. cAMP activates kinase A
5. kinase A phosphorylates other proteins leading to cellular response

big data

100 billion neurons
1000 synapses/neuron
100 trillion synapses

divergent pathway

one presynaptic neuron branches off to affect a larger number of postsynaptic neurons