Transcript nervous system - De Anza College

NERVOUS SYSTEM
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Two major divisions
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
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Three specific functions
1. Receives sensory input
2. Performs integration of all input
3. Generates motor output
Nervous Tissue
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Contains two types of cells
1. Neuroglial cells(make up more than half the
brain)
2. Neurons
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Neuroglial cell function
1. Structural and protective
2. Support and nourish neurons
3. Insulation and development guide
(myelin sheath)
Nervous Tissue (cont’)
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Neurons
1. Three types of neurons
a. Sensory neurons – transmit nerve impulses
from stimulus to the CNS
b. Interneurons – in central nervous system
c. Motor neurons – instructions away from to
muscles or glands.
2. Parts of a neuron: dendrites, cell bodynucleus, axon, myelin sheath & nodes of
Ranvier
Myelin Sheath
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In the PNS, the neuroglial cells responsible
for myelination are called Schwann cells
In the CNS, Schwann cells are absent,
therefore myelin is provided by
oligodendrocytes
Speeds signal conduction
Made of lipids and phospholipids
Guides nerve regeneration
Attacked by immune system in multiple
sclerosis
The Nerve Impulse
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All cells have a membrane potential or
voltage (electrical charge) across their plasma
membrane
At rest, when no nerve impulse is being
received, the potential is about - 65mV
1. Potential due to difference in Na+
and K+ concentration across the axon
membrane
2. K+ able to cross axon membrane, Na+not
The Nerve Impulse cont’
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3. Build up of neg. charge results inside
axon and more pos. charge outside, hence
membrane potential = -65mv
When the axon receives an impulse, the membrane
potential changes
1. When the membrane potential reaches – 40Mv
(threshold level), Na+ channels open
2. Influx of Na+ causes depolarization of the
membrane to occur
3. When the membrane potential reaches +40mV,
K+ channels open – repolarization occurs
4. Inside of axon reverts to pre-dominant neg chg.
The Nerve Impulse cont’
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When an impulse has passed a section
of an axon, a refractory period begins
(period following an action potential
when a neuron can’t conduct another
impulse) as the sodium channels are
unable to open.
This keeps the impulse running down
the axon in the same direction
The Synapse
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Synapses separate one neuron form another
Neurons physically do not touch one another
A synapse is a gap that separates neurons
Neurotransmitters released from the terminal bulb
enter into the synapse and move across the space
(called the synaptic cleft) by diffusion
Neurotransmitters leave the presynaptic neuron and
diffuse toward the postsynaptic neuron, where they
settle on receptors and initiate a reaction
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Neurotransmitters carry the message
across the synapse
Neurotransmitters are chemicals that
carry an impulse across the synaptic
cleft
The Central Nervous System
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The brain has four main parts
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Brain stem + midbrain
Diencephalon
Cerebellum
Cerebrum
The entire brain is involved in the integration of
sensory input and motor responses.
Each section has a slightly different role
Brain cont’
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Brain stem – medulla oblongata and pons and
midbrain
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Regulates heart rate, breathing and blood
pressure
Portion of the brain (anatomically and
physiologically) closest to the spinal cord
Cerebellum
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Maintains muscle tone, posture and balance, and
fine-tuning conscious and unconscious movement
Portion of the brain posterior to the brain stem
Brain cont’
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Diencephalon
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Functions mainly as a relay center for
sensory information from the body and
motor responses from the cerebrum
(including centers for visual and auditory
startle reflexes)
The thalamus and hypothalamus are
located in the diencephalon
Brain cont’
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Cerebrum
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Largest portion of the brain, integrates
information and generates appropriate
responses
The center of the brain responsible for
learning, remembering and planning
activities
Spinal cord
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Extends from the brain into the
vertebral column
It is the main route of communication
between the brain and the body
The spinal cord connects to almost
every organ
Protection and Support
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Meninges:3 layers around brain and spinal
cord
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Three connective tissue membranes
Inflammation is meningitis
Cerebrospinal fluid
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Absorbs shocks and nourishes neurons
There are four ventricles (cavities) in the brain
filled with CSF – circulates around spinal cord
Reabsorbed in brain; if not working, hydrocephaly
Protection and Support
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The axial skeleton provides bony
protection for the CNS
What separates the CNS from the axial
skeleton?
Meninges and Cerebrospinal fluid
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Damage to neurons in the CNS is
generally not repaired
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The oligodendrocyte retreats and leaves no
tube (myelin sheath) or pathway to aid in
axonal regrowth
In the PNS, neurons can recover from
some damage because the Schwann cell
axonal tube remains
CNS - review
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The brain (skull) and spinal cord (vertebral
column) are encased in the skeleton and are
covered by meninges
It is the main integration center of the body
Sensory information enters the CNS, where it
is analyzed and an appropriate
response is generated
Motor information leaves the CNS and brings
about the body’s response.
Peripheral Nervous System
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The neurons of the PNS are arranged in
bundles called nerves
Nerves can be motor, sensory or mixed
depending on the neurons they contain
Information traveling to and from the CNS
must go through the PNS
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The PNS picks this information by:
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Special senses receptors: enable us to see,
hear, taste, and smell
General sensory receptors: found in our
skin and inform us about temperature, light
touch, pressure, and pain
Visceral receptors: monitor proprioception
(help control movement and awareness of
limb position) and organ functioning
The Autonomic Nervous System
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This division of the PNS governs our
body’s responses to subtle changes in
homeostasis
There are 2 subdivisions
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Sympathetic – includes the nerves that
control the body when it is actively moving
and burning energy – also called the
“Fight, Flight, Fright” system.
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Parasympathetic is responsible for
digestion, energy storage, and relaxation.
“Rest and Digest” system.