Download the nervous system

THE NERVOUS SYSTEM
A. Neurons = masses of nerve cells that transmit information to other nerves, tissues or
cells (nerve impulses)
1. Cell Body - contains the nucleus and two extensions
2. Dendrites - receives information carries toward cell body
3. Axons - conducts impulses away from the cell body
B. The nervous system is divided into two parts:
1. Central Nervous System (CNS) - brain and spinal cord
2. Peripheral Nervous System (PNS) - peripheral nerves through the body
Three Basic Functions
1. Sensory Function - gathers info about changes occurring within and around the body Sensory receptors, at ends of peripheral nerves send signals (nerve impulses) to the CNS.
2. Integrative Function - information is "brought together," interpreted, to create
sensations, create thoughts, add to memory, make decisions, etc.
3. Motor Function - responses to signals (impulses). Signals sent from the CNS to
effectors (muscles or glands). The goal is usually to maintain stable conditions
(especially internal) - Homeostasis.
- Somatic Nervous System (skeletal muscles)
- Autonomic Nervous System (smooth muscles, glands)
Neuroglial Cells (neuroglia)
- supportive tissue of the nervous system (more numerous than neurons). Five types
1. Microglial Cells
2. Oligodendrocytes
3. Astrocytes
4. Ependymal Cells
5. Schwann cells *Myelin Sheaths
Identify the Parts of the Neuron
Axon
Dendrite
Myelin
Nodes of Ranvier
Myelinated (white matter) vs Unmyelinated (grey matter)
Classification of Neurons
1. Functional (sensory neurons, motor neurons, interneurons)
2. Structural (multipolar, bipolar, unipolar)
Cell Membrane Potential
Resting Potential / Threshold Potential / Action Potential
1. Neuron membrane maintains resting potential (+ outside - inside )
2. Threshold stimulus is received
3. Sodium channels open
4. Sodium ions diffuse inward, depolarizing the membrane
5. Potassium channels open
6. Potassium ions diffuse outward, repolarizing the membrane
7. The resulting action potential causes a local bioelectric current that stimulates adjacent
portions of the membrane.
8. Wave of action potentials travel the length of the axon as a nerve impulse
Nerve Impulse
*Propagation of action potentials along a nerve axon
Myelinated axons conduct faster than unmyelinated axons
Example: Motor neuron associated with skeletal muscle 120 m/2
Sensory neuron on skin (unmyelinated) travels at .5 m/s
The Synapse
Synapse – junction between two communicating neurons
Nerve pathway – nerve impulse travels from neuron to neuron
To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the
next neuron
Excitatory – increase membrane permeability, increases chance for threshold to be
achieved
Inhibitory – decrease membrane permeability, decrease chance for threshold to be
achieved
Types of Neurotransmitters
Acetylcholine – stimulates muscle contraction
Monoamines – Norepinephrine & Dopamine (sense of feeling good, low levels =
depression)
Serotonin (sleepiness)
Endorphins (reduce pain, inhibit receptors)
Synapses are highly susceptible to drugs and fatigue
Curare (poison used by S. American Indians) and atropine stops Acetylcholine from
depolarising the post-synaptic membrane, i.e. become paralysed.
Strychnine and some nerve gases inhibit or destroy acetylcholinesterase formation.
Prolongs and enhances any stimulus, i.e. leads to convulsions, contraction of muscles
upon the slightest stimulus.
Cocaine, morphine, alcohol, ether and chloroform anaesthetise nerve fibers. (inhibitory)
Mescaline and LSD produce their hallucinatory effect by interfering with nor-adrenaline
& serotonin
Types of Nerves
Sensory Nerves – conduct impulses into the brain or spinal cord
Motor Nerves – carry impulses to muscles of glands
Mixed Nerves - contain both sensory and motor nerve
Nerve Pathways
Reflex arc – simple pathway, includes only a few neurons (reflexes)
Reflex Behavior – automatic, subconscious responses to stimulu
Knee-jerk reflex (patellar tendon reflex
motor nerve spinal cord  sensory nerve stimulus knee
Withdrawal reflex – occurs when you touch something painful
Image Credits: adapted from public domain work found at wpclipart and wikimedia
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