Transcript Epilepsy & Membrane Potentials

Epilepsy & Membrane Potentials
EEG WAVEFORM
Ca2+
Neural Recording
Excessive Calcium influx leads to a depolarized Resting Membrane
Neurophysiology
Anatomy of the Neuron
Dendrites
Axon Hillock
= Trigger Zone
Cell Body
(organelles)
Direction of
Action Potential
Axon
Terminals
Schwann cells and Nodes of Ranvier
Schwann cells make MYELIN
MYELIN is an electrical insulator
Action Potential “jump” down myelinated axons by SALTATORY CONDUCTION
Peripheral Nervous System: Support Cells
CNS Support Cells = Neuroglia
Action potential propagation along neurons
How does the action potential move from the terminal of neuron 1
to the dendrites of neuron 2?
Direction of
Action Potential
SYNAPSE
2 main types:
electrical and chemical
Electrical SYNAPSE
Gap Junction
Action potential moves DIRECTLY between neurons
EXAMPLES:
Smooth Muscle
Cardiac Muscle
Gap junction
between adjacent
cardiac cells
Chemical SYNAPSE
Presynaptic Terminal
Synaptic CLEFT
Postsynaptic membrane
Chemical SYNAPSE: Function
1) Action potential down axon to terminal
2) Ca2+ Channel open;
Ca2+ influx
3) Vesicles of Neurotransmitters release
into synaptic cleft
- 4) Neurotransmitter diffuse into synaptic cleft
- Bind to LIGAND-gated ion channels
on post-synaptic membrane
Chemical SYNAPSE: Signal types on post-synaptic membrane
1) EPSP: Excitatory post-synaptic potential
Mechanism
Ligand-gated Na+ channels OPEN
Importance
Increases likelihood of AP in
postsynaptic cell
If ENOUGH
neurotransmitters are
released….AP
Local Anesthetics: Novacain, Lidocaine, etc.
Lidocaine
Painful stimulus
Action potential
Sensory Neuron
Blocks LIGAND-gated NA+ channels
NO EPSP……no Action potential on post-synaptic cell……no perception of PAIN
Chemical SYNAPSE: Signal types on post-synaptic membrane
2) IPSP: Inhibitory post-synaptic potential
Mechanism
Ligand-gated K+ or CL- channels
OPEN on post-synaptic membrane
Importance
Decreases likelihood of AP in
postsynaptic cell
Presynaptic INHIBITION and FACILITATION:
Neuromodulators
Can modulate the ability of a neuron to release neurotransmitter
Neuron
Collateral Neuron
INHIBITION of neurotransmitter release
at
POST-SYNAPTIC membrane
Clinically important
neurotransmitters & neuromodulators
Cocaine
Alcohol
Caffeine
Nicotine
Heroin
Morphine
Viagara
Marijuana
Anti-depressants: Prozac
Crystal Meth
Strychnine
LSD
We will cover how some of these drugs work
Neural Summation
Spatial
Axon hillock
Temporal
Spatial &
Temporal
SUMS EPSP & IPSP
Functional Organization of Nervous System
Central Nervous System
Brain & Spinal Cord
Peripheral Nervous System
Spinal Nerves & all other nerves
Sensory
Motor
Sensory Physiology
Sensory Physiology
• Perception of sensation involves
1) External physical signals
2) Converted by physiological process
3) To neural signals (graded & action potentials)
Light
Eye
Phototransduction
1
Action Potential
in Optic Nerve
3
General senses
Perceive touch, pressure, pain, heat, cold,
stretch, vibration, changes in position
Located on skin and in joints/muscles
Cutaneous Somatic Receptors
Muscle spindle: stretch receptor
Golgi Tendon Organ: Tendon stretch receptor
Sensory Neurons
Collagen Fibers within Tendon
Physiology of Cutaneous Receptors
1.
Stimulus (Vibration, Pressure, Temperature, Stretch, etc)
2.
Mechanical and/or biomolecules cause opening/closing of ion
channels (K+, Ca2+, Na+) on receptor membrane =
Graded Receptor Potential
3.
If receptor membrane depolarizes to threshold =
ACTION POTENTIAL
Functional classifications of sensory receptors
Sustained Pressure
Pain
Vibration
General sensory neural pathways
Dorsal Column
thalamus
Tertiary Neuron
Proprioreception,
Vibration,
Pressure
Secondary Neuron
Primary Neuron
Anterolateral System
Tertiary Neuron
Touch,
Itch,
Pain,
Temperature
Secondary Neuron
Primary Neuron
Blocking Pain Perception
Pressure, Vibration
Dorsal Column
Pain
Anterolateral system
2) Triggered by BRAIN (endorphins)
Via Blood
Heroin & Morphine can trigger
1) Triggered by Massage, Exercise
:
Presynaptic inhibition of 2nd Neuron in Anterolateral System
Sensory Perception in Brain
Somatosensory Cortex (Postcentral Gyrus)
Area on cortex = sensitivity of body part =
# of sensory receptors on that part of body
Special senses
(located in the head region)
1)
2)
3)
4)
Vision
Hearing and equilibrium
Olfaction
Taste
We will ONLY cover Vision as an example of a Special Sense!
Eye: Basic Anatomy
Lens
Pupil
Optic Nerve
Retina
Rod & Cones
Bipolar Cells
Ganglion Cells
Retina
Pupil
Lens
Disk
Rhodopsin
Rhodopsin
Transducin (G-protien)
cGMP
cGMP-gated Na+/Ca2+ Channel
K+ channel
Glutamate
DARK
Bipolar Cells
-Rhodopsin: inactive
-Transducin: inactive
-Intracellular cGMP levels HIGH
-Ion channels are OPEN
-Membrane potential = -40 mV
-Glutamate release high onto
Bipolar cells!
Retinal
Activated Transducin (G-protien)
decreases Intracellular cGMP
1
Rhodopsin
BLEACHES
2
cGMP-gated Na+/Ca2+ Channels CLOSE
cGMP
3
K+ channel
LIGHT
5
Glutamate
decreases
Photoreceptor
Membrane potential (mV)
Opsin
-40
-70
4 HYPERPOLARIZATION
Time
Bipolar Cell
6
Cones: Color & Day Vision
Rod: Night Vision
Optic Nerve
Neural pathway to
optic nerve & brain
Rod & Cones
Bipolar Cells
Ganglion Cells
Neural Layer
of Retina
Neural Pathway in Brain
Optic Chiasm
Optic Cortex
Optic Nerve
Neural Processing in Brain
V4
V3
V2
V1
Layers of signal processing
V1 sends projections Dorsal & Ventral
Dorsal Stream: “Where” & “How” Pathway
Ventral Stream: “What” Pathway
Color Vision: 3 cone types
Retina
Distribution of Rod vs. Cones
# of photoreceptors
Position on Retina
Processing Visual Stimuli
Retinal Processing:
Convergent Neural Network!
125 million photoreceptors!
Amount of convergence
1 million ganglion cells!
200:1
1:1
Position on Retina
Neural Networks
Brain Commands to Muscle
(Motor Output)
Vision
Circadian Rhythms:
Why you get tired when its dark!
Melanopsin
Rhodopsin
Suprachiasmatic Nucleus (SCN)