1. Nervous system

2. Nervous System Central Nervous System (CNS):
brain and spinal cord
relays messages, processes and analyzes information
Peripheral Nervous System (PNS)
peripheral nerves: cranial and spinal (outside CNS)
connects sense organs to CNS
connects CNS to muscles and glands

3. Peripheral Nervous System
Sensory division (from receptors to CNS)
Motor division (from CNS to effectors)
Somatic: voluntary
Autonomic: involuntary
Sympathetic: “fight or flight”
Dilates pupil/relaxes lens
Inhibits digestion
Increases heart rate
Dilates bronchioles
Stimulate liver: glycogen → glucose
Relaxes bladder
Parasympathetic: opposite - conserves energy (“rest and digest”)

4. Neurons Specialized cells that carry electrical impulses Motor Neuron
node of Ranvier
Motor Neuron

5. Neurons under a microscope

6. Nerve bundle
Myelin sheath is made of Schwann cells wrapped around the axon
Myelin: insulating material
Demyelination = myelin is destroyed
e.g. multiple sclerosis

7. Spinal cord

8. Types of Neurons
Sensory Neuron
Sensory Neurons: transmit electrical impulses from sensory receptors to the CNS
Relay Neurons (Interneurons): move impulses inside the CNS
Motor Neurons: take impulses from CNS to effectors (glands/muscles)
Motor Neuron

9. Reflex

10. How the impulse is transmitted
Impulse begins when a neuron is stimulated by another neuron or by the environment
Electrical impulse moves in one direction:
Dendrites → Cell Body → Axon
Synapse: gap between 2 neurons
Neurotransmitters send the signal to the following neuron
No myelin = 5-25m/s
With myelin = m/s

11. How the impulse is transmitted
Neuron not transmitting an impulse: membrane has an electrical potential (voltage) called resting potential
Caused by the imbalance of K + and Na + across the membrane (Na + /K + pumps) = polarization
Electric difference (voltage): -70mV

12. When there is a stimulus...
Na+ gates open = Na + enter the cell
Electrical potential of the cell changes
depolarization (normal charge is reversed) = +30mV
Action potential is recorded
Na + channels close
K + channels open
repolarization occurs (charges back to normal)
K + channels stay open longer
hyperpolarization = -85mV (refractory period = prevents one impulse to catch up with another)
Stimulus = self-propagating

15. The Synapse Synapse = gap between neurons
Action potential cannot cross gap: neurotransmitters carry the impulse
Neurotransmitters: stored at the end of axons in vesicles(glutamate, GABA, acetylcholine, norepinephrine, dopamine, serotonin, nitric oxide, etc)
Voltage Ca+2 gated ions open → calcium flows inside neuron (presynaptic membrane)
Calcium help vesicles fuse with membrane → neurotransmitters are released (presynaptic membrane)
These bind with neuroreceptors (post synaptic membrane
Voltage gated ions are activated = depolarization
Impulse is passed on to post-synaptic neuron
Neurotransmitters = broken by enzymes and reabsorbed by pre-synaptic neuron