Nervous System

ZNerve cells (neurons) transmit information much faster than hormones. ZThey communicate by transmitting nerve impulses from cell to cell.

Neuron structure ZEach neuron has the same 3 parts: Z 1 Dendrites - receive information from other cells. Z 2 Cell body - collects information from dendrites. Z 3 Axon - conducts the nerve impulse.

ZMany neurons have insulation wrapped around them. ZThis myelin sheath allows impulses to travel faster. ZThe sheath allows the impulse to jump over nodes (gaps) along the axon.

ZThere is a difference in electrical charge across the neuron membrane. ZThis difference is membrane potential and results from ions moving in and out of the cell.

ZWhen the neuron is not conducting an impulse, it is at resting potential (~ -70mV) ZThe inside of the cell is negative with respect to the outside.

ZWhen the neuron is conducting, it triggers an action potential. ZThis occurs when the inside of the neuron becomes positive (~ +40 mV). ZThis occurs because sodium ions rapidly flow into the axon.

ZAfter the action potential has passed, the sodium gates close and the sodium ions stop flowing into the axon. ZThe resting potential must return to normal before another action potential can be triggered.

ZWhere a neuron meets another neuron, there is a gap (synapse) ZThe action potential cannot travel across this gap; instead, it is converted into molecules that can cross this gap (neurotransmitters)

ZNeurotransmitters do not stay in the synapse forever. ZThey have to stop transmitting the signal so that the signal does not continue indefinitely. ZThey can be reabsorbed (reused), or broken down.

Structures of the System ZThe nervous system is divided into 2 systems. ZThe central nervous system consists of the brain and spinal cord; the peripheral system consists of the nerves.

Central Nervous System ZThe brain is the body’s processing center (~100 billion neurons) ZThere are 3 major parts of the brain. Z 1 Cerebrum - largest part of the brain; responsible for learning, memory, perception, and intellect.

Z 2 Cerebellum - located at the posterior base of the brain. ZIt regulates balance, posture, and movement. ZThis part of the brain takes the input from the cerebrum and creates movements.

Z 3 Brain stem - base of the brain. ZThe lower part consists of the pons, medulla oblongata, and the midbrain. ZThis part regulates homeostasis (breathing rate, heart rate, temperature and sleep)

ZThe upper brain stem consists of the thalamus (sensory processing - relays information to the appropriate parts of the cerebrum) and the hypothalamus (helps medulla regulate hunger, temperature)

ZThe other part of the CNS is the spinal cord. ZIt extends from the medulla to right below the ribs. ZSend messages from the brain to the rest of the body. ZAlso functions in reflexes (involuntary contractions)

Peripheral Nervous System ZThere are 31 pairs of spinal nerves and 12 pairs of crainial nerves. ZThe system is divided into 2 separate systems.

Somatic Nervous System ZMotor neurons (responsible for movement) are part of this system. ZMost are voluntary (responsible for skeletal muscle movement) ZReflexes (involuntary) fall under this system.

Autonomic Nervous System ZThis system is involuntary. ZIt includes the nerves that regulate heart rate, digestion, etc. ZThe parasympathetic part (usually active) is rest and digest. ZSympathetic - fight or flight

Stimuli Reception ZSpecialized neurons detect sensory stimuli (pressure, temperature, light, etc) ZThe cerebrum is divided into different processing centers that interpret this stimuli.

ZOccipital lobe (in the back) processes sight. ZTemporal lobe (side of head) carries out sound.

Eyes ZThe eye is lined in the back with the retina where light is focused when it enters. ZThere are 2 photoreceptors (capture light). ZRods respond to dim light. ZCones respond to bright light and give us color vision.

Ears ZSound enters the ear and strikes the tympanic membrane (eardrum) ZBehind the eardrum are 3 bones (hammer, anvil, stirrup) that transfer vibrations to cochlea (chamber with fluid)

ZThe cochlea has tiny hair cells that are stimulate in different sequences according to vibrations that interpret the sound (by nerve impulses) ZHair cells in the semicircular canal (also in inner ear) are responsible for balance.

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