The Nervous System YuHui Lee Cindy Tsai

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

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)

Parts of brain

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

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

HOW NERVE IMPULSES ARE TRANSMITTED

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

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+

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

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

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+

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

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