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NERVOUS SYSTEM BIOLOGY
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Brief notes on nervous system, clearly explained and easy to grasp subject using these notes, useful for medicos and medical field people
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The Nervous SystemFunctions of the Nervous System
1. Gathers information from both inside and outside the body - Sensory Function
2. Transmits information to the processing areas of the brain and spine
3. Processes the information in the brain and spine – Integration Function
4. Sends information to the muscles, glands, and organs so they can respond appropriately – Motor
Function
It controls and coordinates all essential functions of the body including all other body systems
allowing the body to maintain homeostasis or its delicate balance.
The Nervous System is divided into Two Main Divisions: Central Nervous System (CNS) and
the Peripheral Nervous System (PNS)
Divisions of the Nervous System
1
, Basic Cells of the Nervous System
Neuron
• Basic functional cell of nervous system
• Transmits impulses (up to 250 mph)
Parts of a Neuron
• Dendrite – receive stimulus and carries it impulses
toward the cell body
• Cell Body with nucleus – nucleus & most of
cytoplasm
• Axon – fiber which carries impulses away from cell body
• Schwann Cells- cells which produce myelin or fat layer in the Peripheral Nervous System
• Myelin sheath – dense lipid layer which insulates the axon – makes the axon look gray
• Node of Ranvier – gaps or nodes in the myelin sheath
• Impulses travel from dendrite to cell body to axon
Three types of Neurons
o Sensory neurons – bring messages to CNS
o Motor neurons - carry messages from CNS
o Interneurons – between sensory & motor neurons in the
CNS
Impulses
• A stimulus is a change in the environment with sufficient
strength to initiate a response.
• Excitability is the ability of a neuron to respond to the stimulus and convert it into a nerve impulse
• All of Nothing Rule – The stimulus is either strong enough to start and impulse or nothing happens
• Impulses are always the same strength along a given neuron and they are self-propagation – once it
starts it continues to the end of the neuron in only one direction- from dendrite to cell body to axon
• The nerve impulse causes a movement of ions across the cell membrane of the nerve cell.
Synapse
o Synapse - small gap or space between the axon of one neuron and the dendrite of another - the
neurons do not actually tough at the synapse
o It is junction between neurons which uses neurotransmitters to start the impulse in the second
neuron or an effector (muscle or gland)
o The synapse insures one-way
transmission of impulses
Neurotransmitters
Neurotransmitters – Chemicals in
the junction which allow impulses to
be started in the second neuron
2
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