1. The Nervous System
YuHui Lee
Cindy Tsai

2. The nervous system
Nerve net: the simplest nervous system found in hydra; a network of nerve cells
Ganglia: clumps of nerve cells
Neurons: more specialized nerve cells in complex organisms

4. Types of neurons
Sensory neuron: receives impulses from the environment and bring them to the body
Motor neuron: transmits the impulse to muscles/ glands to produce a response
Interneuron: links between sensory neurons and motor neurons (found in brain and spinal cord)

5. Parts of brain

7. The Central Nervous System
Receives information from sensory neurons and interprets it
Brain:
Cerebrum: controls all voluntary activities; receives and interprets sensory information; largest part of human brain
Cerebellum: coordinates muscle activity and refinement of movement
Midbrain: center for visual and auditory reflexes
Hypothalamus: regulates homeostasis and secretes hormones; regulates pituitary gland
Thalamus: conducting information and between the spinal cord and cerebrum
Pons: connects parts of brain with one another and contains respiratory center
Medulla: controls involuntary actions such as breathing, swallowing, heartbeat, and respiration
Spinal Cord:
Associated with reflex

8. Peripheral Nervous System
Somatic Nervous System
Associated with voluntary actions
Autonomic Nervous System
Associated with involuntary actions
Sympathetic nervous system: promotes a “fight or flight” response
Parasympathetic nervous system: promotes a “rest or digest” response

9. HOW NERVE IMPULSES ARE TRANSMITTED

10. Resting potential Not always transmitting signals
Transmission of impulse depends on the ionic gradients across the axonal membrane
The concentration of K+ ions is higher in the cytosol than the concentration of Na+.
The inside of a neuron is more negative than the outside, around -70 mV
Many K+ channels open but only small no. of Na+ channels are open  diffusion of Na+ and K+ through ion channels

11. Resting Potential (cont.)
Na+K+ ATPase : Pumps two K+ into the neuron for every three Na+  net loss of positive charge
Leaky protein channels : slow diffusion of K+

13. Action Potential
rapid change in polarity across a portion of an axonal membrane
An action potential is generated only after a stimulus larger than the threshold
All-or-none response : have to reach the threshold
Gated channel proteins
One channel protein suddenly allows sodium to enter the cell
Another channel protein allows potassium to leave the cell

14. Depolarization and Repolarization
Cell is more positive inside than outside
From -70mV to +35mV
Sodium Channels close, Potassium channels open
K+ rush out of the cell
Repolarized : charge returns to original

16. The Refractory Period
Ions are on the wrong side of the axonal membrane
Sodium Potassium pump will kick 3 Na+ and bring in 2 K+

17. When a small area is depolarized  action potential spread out to the rest of the axon
Reaches the axon bulb  release neurotransmitter into synapses
Synapses : space in between a axon terminal of a neuron and the dendrite of the another
Transmission
Sudden rise in calcium in the axon terminal of one neuron
Calcium stimulates synaptic vesicles to merge with the pre synaptic membrane
Neurotransmitter molecules are released into the synaptic cleft

18. Myelin Sheath Schwann cells wrap around the axon
Forms myelin sheath and create spaces
Nodes of Ranvier
Impulses jumps from one node to the next until it reaches the terminal
Increase the speed