1. The Neuron and Action Potential

2. Basic structure of the neuron
Dendrite – Recipient of incoming message
Cell body (soma) – consists of nucleus and most organelles
Axon – carries messages to the axon terminal primarily via the action potential
Because axons are so long, transporting proteins down the axon has developed a special system
Soma to terminal – anterograde transport – uses kinesin protein and microtubule to transport proteins
Terminal to soma – retrograde transport – uses dynein protein and microtubules to transport proteins
Myelin sheath – mostly lipid layer surrounding the axon, made from Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS)
Node of Ranvier – regions of the axon where no myelin sheath found, high concentration of ion channels found here
Axon terminal – action potential triggers the fusion of vesicles containing neurotransmitters to the cell membrane, causing release of neurotransmitters into the synapse
Synapse – region between two neurons where communication occurs

3. Oligodendrocytes and Schwann cells
Forms the myelin sheath
Key differences
Location
Composition of myelin sheath
Number of cells per axon
Schwann cells wrap around one axon
Oligodendrocytes wrap around many

4. The Neuron and Action Potential
The action potential graph shown above is observed when you measure the electrical activity on the INSIDE of a neuron
What is the resting potential voltage?
When a neuron is resting, it is negatively charged.

5. What maintains the resting potential?
Electrostatic pressures
Charges like to remain neutral
Diffusion
Concentrations move from high to low in order to remain balanced
Na+
Na+
Na+
Na+
-70mv
concentration
Sodium/Potassium pump helps maintain resting potential
electrostatic - K+
Na+
Cl-
Na+ +
Cl-
Na+ K+ K+

6. Na+/K+ pump 3 Na+ ions go out 2 K+ ions go in Requires ATP
If 3 positive charges go out, and 2 come in, does the inside of the neuron become more negative or more positive?

7. The Neuron and Action Potential

8. The action potential – the stimulus
dendrite
axon
-70mv
myelin
axon
Na+ NT
synapse

9. Muscle contraction Action potential Muscle cell nAChR
Voltage gated calcium channel
ACh
Acetylcholine binds to nicotinic acetylcholine receptor (nAChR)
Na+ comes through nAChR and causes an action potential (will discuss later)
Voltage gated calcium channel opens and lets through calcium
What does calcium do?

10. The Neuron and Action Potential
If not enough positive charges reach the axon, then you get failed inititiations
If enough positive charges reach the axon, this will cause voltage-gated Na+ channels to open and an action potential will begin. Once threshold occurs, the action potential will fire no matter what.

11. The action potential – threshold to peak
dendrite
axon
-70mv
myelin
axon
Na+
outside
synapse
inside
Once the positive charges reach the axon, that’s when the action potential starts

12. The action potential – peak to hyperpolarization
dendrite
axon
-70mv
myelin
axon
outside
synapse
inside
Na+ K+

13. The Neuron and Action Potential
Resting potential = Na+/K+ pump
Stimulus – neurotransmitter binds
Threshold – Voltage gated sodium channels open
Rising phase – Na+ flows in from voltage gated Na+ channels
Peak – Na+ channels get blocked, K+ channels open
Falling phase – K+ flows out
Hyperpolarization – K+ channels close and neuron returns to resting potential

14. Release of neurotransmitter
Action potential causes voltage-gated calcium channels to open
Calcium comes into the neuron and causes neurotransmitter to be released from vesicles – starts the whole process over

15. Organization of the nervous system
Nervous system divided into two types
Central nervous system = brain and spinal cord
Peripheral nervous system = sensory and motor neurons
Motor neuron – this is what causes muscles to contract (we’ve seen this a couple times now)
Sensory neuron – how we perceive the world around us (retina, nose, cochlea, etc.)
Motor neurons can be divided into two types
Somatic (voluntary) nervous system
Autonomic (involuntary) nervous system
Sympathetic – activated when an animal is stressed
Parasympathetic – opposite of the sympathetic

16. Organization of the nervous system
Cerebrum – where higher thinking takes place
4 lobes
Frontal lobe – motor cortex
Parietal lobe – Somatosensory (touch) cortex
Occipital lobe – visual cortex
Temporal lobe – auditory (hearing) cortex)
Cerebellum – helps with coordinating movement
Hippocampus – looks like a sea horse – involved in learning and memory
Amygdala – what process emotions

17. Organization of the nervous system
Hypothalamus – controls the release of hormones into the bloodstream
Thalamus – process all the sensory information
Brain stem – controls autonomic nervous system – heartbeat, respiration, etc.
Brain stem

18. Reflex
Muscle spindle – sensory receptor that detects stretch in muscle
When a muscle in this type of stretch reflex is stretched, a sensory neuron fires
That sensory neuron synapses with the motor neuron that goes back to the muscle that was originally stretched
Sensory neuron stimulates motor neuron which stimulates the muscle to contract

19. Visual system – the eye Continuous with one another
Cornea – focuses the light entering the eye
Sclera – white part of the eye – protects the eye
Iris – muscle that controls how much light can enter (eye color)
Pupil – opening in the iris where light is let through
Lens – focuses on near or distant objects
Ciliary muscles – attached to the lens, they alter the shape of the lens so it can focus on near or distant objects
Retina – interior lining of the back of the eye where sensory receptors are found (rods and cones – photoreceptors)
Fovea – where most of our acute vision is regulated, only cones found here (part of the retina)
Optic disk – where blood vessels and axons leave the eye, no receptors here so we have a blind spot
Continuous with one another

20. Visual system Sensory receptors of the visual system (photoreceptors)
Rods
Detect only black and white (in other words, light or no light)
help us see in the dark because they are more sensitive to light
More prevalent in the peripheral retina
Cones
Detect color
Daytime vision, higher acuity
More prevalent in central retina

21. The retina Photoreceptor layer Bipolar cell layer Must be invisible
ganglion cell layer
light