Lecture 7: Nervous System - Part I
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IB
Curriculum Objectives: Nerves, Muscles, Movement (Includes some Skeletal)Lab: Reflex Arc
Questions:
Study
Questions (Vid) – 2009 NEW
Terms for Brain
Dissection Quiz
Unit Questions - IB
Unit Questions
- Regular
Slides and Figures:
Motor Neuron (Slide)
Motor Neuron (Figure)
Neuralmuscular Junction
Spinal Cord
Reflex Arc
Activity:
Reflex Arc Activity
Crosswords:
Nervous
System – NEW 2009
Ear
Eye
I. Introduction
1.Nervous System is one of the body's principal control and integrating centers. Other is endocrine system.
2. Nervous system has 3 broad functions:
Sensory-sensing
changes within body and in outside environment.
Integrative - Interprets changes.
Motor - Responds to interpretation by initiating
action: muscular contractions or glandular secretions.
3. N.S. is quicker of control systems. Both maintain homeostasis.
4. Neurology is branch of medical science dealing with nervous system.
5. Change in environment (internal or external) is Stimulus.
6. Response is bodies reaction to stimulus.
7. In order to have a nervous response 3 parts are required:
Receptors - detect stimuli (Smell, taste, see, skin -
pressure, pain, temp, touch.)
Conductors - transmit impulses (action potentials) -
neurons.
Effectors - responding organs, muscles or glands.
II. Organization
1. N.S. is divided into 2 major parts:
CNS - (Central Nervous System): Control of entire
nervous system. Brain and spinal cord. All body sensations are relayed from
receptors to CNS. Most motor responses are relayed through CNS.
PNS - (Peripheral Nervous System): Nerves that connect
CNS with receptors, muscles and glands.
2. PNS is subdivided into afferent system and efferent system.
3. Afferent neurons (sensory neurons) convey information from receptors to CNS.
4. Efferent (motor neurons) convey information from CNS to muscles and glands.
5. Efferent system is subdivided into somatic nervous system and autonomic nervous system.
6. Somatic ns consists of efferent neurons carrying impulses from CNS to skeletal muscles - voluntary control.
7. Autonomic ns consists of neurons carrying impulses from CNS to smooth muscle tissue, cardiac muscle, and glands.
8. Autonomic ns is further subdivided.
9. Sympathetic - prepare for emergencies. In general, stimulates (accelerator nerve - heart).
10. Parasympathetic - In general, slows down (vagus nerve - heart).
III. Nerves
1. Nerves are composed of individual cells called neurons.
2. The axon portion is the nerve fiber.
3. A bundle of nerve fibers is a nerve.
4. Cranial nerves are PNS nerves which come from brain.
5. Spinal nerves are PNS nerves which come from spinal cord.
IV. Neurons.
1. There are basically 3 types of neurons.
Sensory neurons (afferent) bring impulse from
receptors to CNS.
Motor neurons (efferent) take impulse from CNS to
effectors.
Association or interneurons which connect sensory and
motor neurons and are located in CNS.
V. Neurons
1. Click here for Motor Neuron - Figure 12.3
2. Cross reference in text: Pages 371-372.
3. Soma - cell body
4. Perikaryon - cytoplasm
5. Dendrites - receive impulses
6. Axon - Usually long process conducting impulse away and to synapse. Also called nerve fiber.
7. Neurofibrils: Long, thin fibrils. Function in support and transportion of nutrients.
8. Axon Hillock: Small conical elevation from cell body.
9. Axon collaterals: side branches of axons.
10. Axon terminals (telondendria): branches of fine filaments at distal end of axons.
11. Synaptic end bulbs: Contain synaptic vessicles which contain neurotransmitters. Neurotransmitters will carry impulse across synapse to postsynaptic cell. See synapse - below.
12. Many axons outside CNS are surrounded by
multilayered, white, phospholipid, segmented covering called the myelin sheath.
13. Myelin sheath increases the speed of the
nerve impulse and insulates axon. Impulse speeds up at nerofibral nodes (nodes of Ranvier).
14. Myelin sheat is produced by flattened cells,
called neurolemmocytes or Schwann cells.
It is white and accounts for white matter in nerves, brain, and spinal cord.
15. Multiple sclerosis and Tay-Sachs
disease are related to destruction of myelin sheath.
16. Cell wraps around axon many times.
17. Inner layer is called myelin sheath.
Outer layer is called neurolemma or
neurilemma (sheath of Schwann).
18. Neurolemma is found only in PNS and assists
in regeneration of injured axons and dendtrites by forming a tube in which a
regenerating aon or dentrite grows.
19. Myelination of CNS is accomplished by
oligodendrocytes, but there is no neurolemma, and therefore no
regeneration.
VI. Synapse
1. Site of intercellular communication
2. Presynaptic cell - sends message. Postsynaptic cell - receives message.
3. Transmission of message due to neurotransmitters such as acetylcholine and noradrenaline.
4. Neurotransmitters are located in synaptic vesicles in synaptic terminals (end bulbs) of presynaptic fibers.
5. Neuroeffector junction: motor neuron connects with other type of cell.
6. 2 types are neuroglandular junction
and neuromuscular junction.
7. The effect of a transmitter is determined by
postsynaptic fiber. Vagus nerve (acetylcholine) inhibits. Accelerator nerve
(noradrenaline) stimulates. Both are autonomic NS.
VII. Neuron Classification
1. Anaxonic neurons - all processes look allike. Brain and sense organs.
2. Bipolar neurons -2 distinct processes. 1 dendrite and 1 axon process. Short (30 mm). Located in sense organs.Relay info about sight, smell, hearing from receptors to neurons.
3. Unipolar neurons - Dendrite and axon are continuous. Most sensory neurons of peripheral ns. May be a meter or more with synapses inside CNS.
4. Multipolar neurons - several dendries and single axon. Most common in CNS. Motor neurons controlling skel musc.
VIII. Neruoglia
1. Companion cells. Outnumber neurons and account for 50% of volume.
2. Know: Table 12-2, page 376
