Action Potential: Refractory Periods

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Action Potential Refractory Periods
SupraThreshold Stimulus can produce 2nd AP
K activation gates OPEN
Na activation gates open
No stimulus can produce 2nd AP
Guarantee that each AP can undergo its
Depolarization/Repolarization Phase
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Functional Organization of Nervous System
Central Nervous System Brain Spinal Cord
Peripheral Nervous System Spinal Nerves all
other nerves
Motor
Sensory
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Sensory Physiology
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Sensory Physiology

• Perception of sensation involves
• 1) External physical signals
• 2) Converted by physiological process
• 3) To neural signals (graded action
  potentials)

Eye
Light
Phototransduction
Action Potential in Optic Nerve
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3
2
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General senses

• Perceive touch, pressure, pain, heat, cold,
  stretch, vibration, changes in position
• Located on skin and in joints/muscles

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Cutaneous Somatic Receptors
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Muscle spindle stretch receptor
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Physiology of Cutaneous Receptors

• Stimulus (Vibration, Pressure, Temperature,
  Stretch, etc)?
• Mechanical and/or biomolecules cause
  opening/closing of ion channels (K, Ca2, Na)
  on receptor membrane graded receptor potential
• If receptor membrane depolarizes to threshold
  ACTION POTENTIAL

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Functional classifications of sensory receptors
Sustained Pressure
Vibration
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Exam 1 Grade Distribution
Credit 30, D or E Credit 47, C or E

• Mean 77
• Median 77
• Grade of total
• A (90-100) 15 13
• B (80-89) 41 35
• C (70-79) 27 23
• D (63-69) 12 10
• F (0-62) 14 12

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General sensory neural pathways
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Dorsal Column
thalamus
Tertiary Neuron
Proprioreception, Vibration, Pressure
Secondary Neuron
Primary Neuron
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Anterolateral System
Tertiary Neuron
Touch, Itch, Pain, Temperature
Secondary Neuron
Primary Neuron
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Blocking Pain Perception
Pressure, Vibration
Pain
Dorsal Column
Anterolateral system
2) Triggered by BRAIN (endorphins) Heroin
Morphine can trigger
Via Blood
1) Collateral Branch

• Triggered by Massage, Exercise

Presynaptic inhibition of 2nd Neuron in
Anterolateral System
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Sensory Perception in Brain
Somatosensory Cortex (Postcentral Gyrus)
Area on cortex sensitivity of body part of
sensory receptors on that part of body
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Special senses (located in the head region)?

• Vision
• Hearing and equilibrium
• Olfaction
• Taste

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Eye Basic Anatomy
Lens
Optic Nerve
Pupil
Retina
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Retina
Pupil
Lens
Ganglion Cells
Rod Cones
Bipolar Cells
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Disk
Rhodopsin
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Rhodopsin
Transducin (G-protien)
cGMP-gated Na/Ca2 Channel
K channel
Glutamate
DARK

• -Rhodopsin inactive
• -Transducin inactive
• Intracellular cGMP levels low
• Membrane potential -40 mV
• Glutamate release high
• Bipolar cells!

Bipolar Cells
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Retinal
Activated Transducin (G-protien) increases
Intracellular cGMP
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Opsin
Rhodopsin BLEACHES
cGMP-gated Na/Ca2 Channels CLOSE
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cGMP
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K channel
-40
LIGHT
Photoreceptor Membrane potential (mV)
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Glutamate decreases
-70
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HYPERPOLARIZATION
Time
Bipolar Cell
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