Download Chapter 7: The Nervous System

Chapter 7: The Nervous System
The Communication System of the Body
Nervous System
• Master controlling and communicating system of the
body
The Nervous System : communication
A. Neurons = masses of nerve
cells that transmit information
Two processes:
1. Dendrites – shorter, more
numerous, receive
information
2. Axons - send information
Central Nervous
System (CNS): brain
and spinal cord.
Peripheral Nervous
System (PNS): nerves
of the body
-- Includes 31 pairs of spinal nerves
-- And 12 pairs of cranial nerves
Three Basic Functions of Nervous System
•Sensory function: gathers info
•Integrative function: bring the info together
•Motor function: responds to signals
Neuroglial cells (neuroglia) – supportive tissue of the
nervous system (more numerous than neurons)
• 5 Types of Cells:
•
•
•
•
•
Microglial cells
Oligodendrocytes
Astrocytes
Ependymal cells
Schwann cells
Microglial cell – digest debris or bacteria
Respond to immunological alarms
Oligodendrocytes – makes the myelin sheath
that provides insulation to the axon
Astrocytes – connect blood vessels to neuron
Ependymal cell- forms a membrane
Schwaan cells – forms the insulating myelin
sheath around a neuron
Neuron (nerve cell) structure:
• Axon – long section, transmits impulses
• Dendrite – extend from the cell body; receive
information
• Neurofibril – fibers within the impulse
• Chromatophilic substance (rough ER) – transport
system
• Myelin – insulation surrounding axons
• Nodes of Ranvier – gaps in the insulation
*Myelinated vs.
Unmyelinated
Myelinated (white matter) –
myelinated axons
Unmyelinated (grey matter) unmyelinated
Facts about Neurons
• Longevity: can live and function for a lifetime
• Do not divide: fetal neurons lose their ability to
undergo mitosis; neural stem cells are an
exception
• High metabolic rate: require abundant amounts
of oxygen and glucose
Classification of Neurons
Functional
Sensory – receives information from
senses
Motor – sends information to
muscles, glands, organs
Interneuron – relays information
Structural
Bipolar
Unipolar
Multipolar
Cell Membrane Potential
Resting Potential / Threshold Potential / Action Potential
Nerve Impulse = weak electric current
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
Nerve Impulse
Speed of an impulse is proportionate to the DIAMETER of the
AXON.
Greater diameter = faster speed
**Myelinated Axons conduct faster than unmyelinated ones**
The Synapse
A: Neuron (axon)
B: Neuron (dendrite)
1.Mitochondria
2.Vesicle
3.Receptor
4.Synapse
5.Receptor
6.Calcium Channel
7.Releases neurotransmitter
8.Re-uptake
Synapse - junction between two communicating
neurons
Nerve pathway - nerve impulse travels from neuron to
neuron
Dendrite → cell body → along axon -> synapse (gap)
→ dendrite
To complete the signal, a NEUROTRANSMITTER is
released in the gap to signal the next neuron. They can
be two types:
• 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 in Humans
Acetylcholine - stimulates muscle contraction
Monoamines - Norepinephrine & Dopamine (sense of
feeling good, low levels = depression)
Serotonin (sleepiness) and mood
Endorphins = reduction of pain, good mood
Nerves – bundles of axons common to a
section of the body
• Types of Nerves:
• Sensory: conduct impulses into the brain and spinal cord
• Motor: carry impulses to muscles or gland
• Mixed: contains both sensory and motor
Nerve Pathways
• Reflex Arc: simple pathway, only includes a few neurons (involuntary,
instantaneous)
• Reflex behavior
• Knee-jerk reflex: maintains uprightness
• Withdrawal reflex: avoids painful stimuli