Name:_________________________
THE NERVOUS SYSTEM
9.1 Introduction
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 - shorter, more numerous, receive information
3. Axons - single, long fiver which 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
- includes 31 pairs of spinal nerves
- includes 12 pairs of cranial nerves
9.2 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. Sensory Neuron
2. Integrative Function - information is "brought together," interpreted, to create
sensations, create thoughts, add to memory, make decisions, etc. Association neuron
or interneuron
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. Motor neurons.
- Somatic Nervous System (skeletal muscles)
- Autonomic Nervous System (smooth muscles, glands)
C. Neurons: Nerve cells. Unique structure - cell body with many extensions or
processes (nerve "fibers") which conduct impulses. There are two types of processes:
1. Dendrites - shorter, more numerous. These, along with the cell body, form the
receptive surfaces of neurons.
2. Axons - single, long "fiber" which conducts impulse away from the cell body.
Sometimes it is "branched" (collaterals). End has many fine branches.
Name:_________________________
9.3 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
9.4 Neurons
Axon
Dendrite
Neurofibril
Chromatophilic substance
Myelin
Nodes of Ranvier
Myelinated (white matter) vs Unmyelinated (grey matter)
Name:_________________________
Classification of Neurons
1. Functional (sensory neurons, motor neurons, interneurons)
2. Structural (multipolar, bipolar, unipolar)
9.5 Cell Membrane Potential
Resting Potential / Threshold Potential / Action Potential
1. Neuron membrane maintains resting potential
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
9.6 Nerve Impulse
*Propagation of action potentials along a nerve axon
Impulse Conduction – speed of an impulse proportionate to diameter of axon (greater
diameter = faster impulse)
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
A: Neuron (Presynaptic)
B: Neuron (Postsynaptic)
1.
2.
3.
4.
5.
6.
7.
8.
Mitochondria
Synaptic vesicle full of neurotransmitter
Autoreceptor
Synaptic cleft
Neurotransmitter receptor
Calcium Channel
Fused vesicle releasing neurotransmitter
Neurotransmitter re-uptake pump
Name:_________________________
9.7 The Synapse
Synapse – junction between two communicating neurons
Nerve pathway – nerve impulse travels from neuron to neuron
Synaptic Transmission
Dendrite  cell body  along axon  synapse (gap)
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
9.8 Impulse Processing
Neuronal pool – groups of neurons that make hundreds of synaptic connections and
work together to perform a common function
Name:_________________________
9.9 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
9.10 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
stimulus knee  sensory nerve  spinal cord  motor nerve
Withdrawal reflex – occurs when you touch something painful
Name:_________________________
Neuron Label
Name:_________________________
Nerve Cells Coloring
Oligodendrocytes (purple)
Astrocyte (green)
Ependymal Cells (orange)
Body of Neuron (blue)
For each of the cells above, color the nucleus a darker shade of purple, green, blue,
orange
Myelin sheaths (pink)
Capillary (red)
Microglial cells (yellow)
Nodes or Ranvier and the Axon (brown)
What is the function of:
1) Oligodendrocytes
______________________________________________________________
2) Astrocytes
____________________________________________________________________
3) Microglial cells
________________________________________________________________
4) Myelin sheaths
_______________________________________________________________
5) Trace the path of a nerve impulse in a neuron:
_________________________________________
Name:_________________________
Nervous System Review
1. The skeletal muscles are controlled by the ___________________________nervous
system.
2. The smooth muscles and glands are controlled by the _______________________
nervous system.
3. Neurons are composed of a network of fine threads called ____________________
4. The nervous system consists of two parts, the brain and spinal cord make up the
______________ nervous system, and the nerves throughout the body make up the
___________ nervous system.
5. ______________________________are cells found between neurons and blood
vessels.
6. Neurons consist of a cell body, axons, and _________________________, which
receive information.
7. Neurons that have a single process extending from the cell body are classified as
_________, if they have two processes, they are classified as _____________
8. White matter is composed of axons that are sheathed in ______________________
9. Two ions necessary to create an electric current in a nerve fiber are potassium and
______________.
10. The ______________________ function of the nervous system refers to information
being interpreted so that the brain can make decisions.
11. The junction between two communicating neurons is called the ________________
12. Acetylcholine, serotonin and endorphins are all forms of ___________________
13. The _________________________arc refers to a simple nerve pathway that would
be involved with involuntary actions (like knee-jerk, or withdrawal)
14. Groups of neurons that perform a common function, such as the storing of
procedural memory (tying your shoe) are called neuronal __________.
15. __________________________________cells help destroy bacterial cells and
cellular debris.
16. There are 31 pairs of ____________________________ nerves.
17. These types of neurotransmitters increase membrane permeability, thus increasing
the chance that threshold will be achieved.
18. When a threshold is achieved, an event called the __________________ potential
occurs.
19. Gaps in the myelin sheath are called Nodes of
_________________________________
20. These support cells are responsible for secreting the myelin sheaths:
_________________________
21. A nerve impulse is received by the dendrites and then travels down the
___________________
22. There are twelve pairs of ________ nerves.
23. This neurotransmitter stimulates the muscles to contract. __________________
24. These cells form a membrane that covers specialized brain parts: ___________
25. These cells have the same function as oligodendrocytes, but are packed within the
myelin: _________________
Locate words from the Review on the Word Search:
Name:_________________________
Nervous System Review Word Search