Central nervous system

the nervous system
• Master control
• Has three overlapping functions
• Sensory receptors
• monitor inside and outside the body
• from PNS to CNS
• Processes and interprets sensory input
• Makes decisions – integration
• Dictates a response by activating effector organs
• Response
• Muscles
• Glands
• From CNS to PNS
1. sensory input
2.integration
3. motor output
central nervous system
brain (gray matter)and spinal cord (white matter)
integrating and command center
gray matter
in the spinal cord
• H-shaped region – surrounds central cavity
• Cell bodies are clustered in the gray matter
• Nucleus vs. ganglia
white matter
in the spinal cord
• External to gray matter
• No neuronal cell bodies, but millions of axons
• Myelin sheath – white color
• Consists of axons running between different parts of the
CNS
• Tracts – bundles of axons traveling to similar
destinations
• vs. nerve
neuronal regeneration
• Neural injuries may cause permanent dysfunction
• If axons alone are destroyed, cells bodies often
survive and the axons may regenerate
• PNS—macrophages invade and destroy axon distal
to the injury
• Axon filaments grow peripherally from injured site
• Partial recovery is sometimes possible
• CNS—neuroglia never form bands to guide regrowing
axons and may hinder axon growth with
growth-inhibiting chemicals
• No effective regeneration after injury to the spinal
cord and brain
peripheral nervous system
outside the CNS
nerves from brain and spinal cord
(cranial nerves, spinal nerves)
peripheral nerves link all regions of the body to CNS
sensory input and motor output
somatic body region & visceral body region
somatic sensory, visceral sensory, somatic motor, and visceral motor
somatic sensory region
Monitors skeletal muscles, joints, skin surfaces, and responsible for touch/pressure/pain/temperature sensation
visceral body region
internal organs, nerves/neurons
somatic sensory
are general senses such as touch, pain, pressure, vibration, temperature and proprioception. Is voluntary because have some control over them and are conscious of them.
visceral sensory
Receives sensory info from viscera (internal organs)
-hunger, taste
somatic motor
(voluntary) – impulses from the CNS that causes contraction of skeletal muscles
visceral motor
Carries signals from CNS to internal organs
-secretion of pancreas, contraction of bladder, contraction of heart
synapses
• Site at which neurons communicate
• Signals pass across synapse in one direction
• Presynaptic neuron
• Conducts signal toward a synapse
• Postsynaptic neuron
• Transmits electrical activity away from a synapse
signals carried by neurons
• Plasma membranes of neurons conduct electrical
signals
• Resting neuron
• membrane is polarized
• Inner, cytoplasmic side is negatively charged
• Stimulation of the neuron–depolarization
action potentials on axons
• Strong stimulus applied to the axon triggers
• Nerve impulse or action potential
• Membrane becomes negative externally
• Impulse travels the length of the axon
• Membrane repolarizes itself
synaptic potentials
• Excitatory synapses
• Leads to an inflow of positive ions
• Depolarizes the postsynaptic membrane
• Drives the postsynaptic neuron toward impulse
generation
• Inhibitory synapses
• Inside becomes more negative
• Action potential less likely
classifications of neurons
• Structural classification
• Multipolar – possess more than two processes
• Numerous dendrites and one axon
• Bipolar – possess two processes
• Rare neurons – found in some special sensory
organs
• Unipolar (pseudounipolar) – possess one short,
single process
functional classifications of neurons
• According to the direction the nerve impulse travels
• Sensory (afferent) neurons -transmit impulses toward the CNS
• Virtually all are unipolar neurons
• Cell bodies in ganglia outside the CNS

• Motor (efferent) neurons
• Carry impulses away from the CNS to effector organs
• Most motor neurons are multipolar
• Cell bodies are within the CNS
• nucleus
• Form junctions with effector cells

• Interneurons (association neurons) – most are multipolar
• Lie between motor and sensory neurons
• Confined to the CNS

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supporting cells
• Six types of supporting cells
• Four in the CNS
• Two in the PNS
• Provide supportive functions for neurons
• Non-excitable
• Maintenance
• Insulation
• Cover nonsynaptic regions of the neurons
• Neuroglia
• Outnumber neurons 10 to 1
• Make up half the mass of the brain
Astrocytes
Glial cells that provide a framework for neurons and supply them with oxygen and nutrition for life
Microglia
Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system
Ependymal cells
Line ventricles of brain and central canal of spinal cord. Form single layer of cuboidal to columnar cells with cilia and microvilli. Modified epithelial cells.
Oligodendrocytes
A cell that holds nerve fibers together and produces the myelin sheath around axons in the central nervous system
Satellite cells
surround neuron cell bodies within ganglia
schwann cells (neurolemmocytes)
surround axons in the PNS
form myelin sheath around axons of the PNS
myelin sheaths
• Segmented structures composed of the lipoprotein
myelin
• Surround thicker axons
• Form an insulating layer
• Prevent leakage of electrical current
• Increase the speed of impulse conduction

1. A Schwann cell envelops an axon.
2. The Schwann cell then
rotates around the axon, wrapping its plasma membrane loosely around it in successive layers.
3.The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath.

Oligodendrocytes
form the myelin sheaths in the
CNS
• Have multiple processes
• Coil around several different axons
multiple sclerosis
Immune system attacks the myelin around axons in
the CNS
Myelin sheaths produced by oligodendrocytes are destroyed.
nerves
• Nerves – cordlike organs in the PNS
• Consists of numerous axons wrapped in
connective tissue
• Axon is surrounded by Schwann cells
reflex arch
sensory receptor > sensory neuron > integrationcenter > motor neuron > effector
monosynaptic reflex
Simplest reflex involving the synapse of a sensory neuron with a motor neuron
polysynaptic reflex
reflex that has at least one interneuron placed between the sensory afferent and the motor efferent, thus having a longer delay between stimulus and responseASEE4sae43q
sensory (afferent) division
carries impulses from skin, skeletal muscles, and joints to the brain
motor (efferent) division
nerve fibers that carry impulses away from the central nervous system
somatic nervous system
Division of the PNS that controls the body’s skeletal muscles.
autonomic nervous system
Regulates events that are automatic, or involuntary, such as the activity of smooth and cardiac muscles and glands.
sympathetic division
A branch of the autonomic nervous system and prepares the body for quick action in emergencies; fight or flight; busiest when frightened, angry, or aroused; increases heart rate, increases breathing rate, enlarges pupils, stops digestion; connects to all internal organs; sudden reaction
parasympathetic division
Branch of the autonomic nervous system; it calms and relaxes the body.
Chemical substances released by the endocrine glands; they help regulate bodily activities
The visceral motor division of the PNS __________.
regulates the contraction of smooth and cardiac muscle and regulates secretion by the body’s many glands
A somatic motor neuron carries
motor commands to the skeletal musculature.
The peripheral nerve fibers that speed up the movement of the digestive tract are classified as
general visceral motor (efferent).
function of synaptic vesicles inside axon terminals
store and release neurotransmitters
This is the site of communication between neurons.
synapse
The ________ of a presynaptic neuron associates with the dendrite of a postsynaptic neuron.
axon terminal
Chemical signals diffuse between neurons at this location.
synapse
This region of the neuron contains a single nucleus surrounded by cytoplasm.
cell body
This neuronal region transmits electrical impulses away from the cell body.
axon
Which of the following is the correct path an impulse takes across a synapse?
axon of presynaptic neuron, synaptic cleft, dendrite of postsynaptic neuron
Action potentials travel along the
axon membrane
The chemical substance that is released at axon terminals is called a
neurotransmitter
most sensory neurons are
unipolar
interneurons
Interneurons are multipolar neurons that are confined to the CNS and are linked together in chains that form complex neuronal pathways.
The majority of neurons in the body are
multipolar
Interneurons are found
only in CNS
What important function could be diminished if the cilia on ependymal cells were absent?
circulation of cerebrospinal fluid
Which cells provide the myelin sheath for neurons in the CNS?
oligodendrocyctes
These glial cells surround the cell bodies of sensory neurons within ganglia of the PNS.
satellite cells
Myelin on axons functions to
speed the rate of impulse conduction and insulate neighboring axons from one another.
Nonmyelinated axons
conduct impulses more slowly than myelinated axons.
A node of Ranvier (myelin sheath gap)
is a bare region of axonal membrane in myelinated axons only.
The difference between myelinated and unmyelinated axons is that
Schwann cells wrap around myelinated axons in concentric layers.
Ciliated neuroglial cells that form an epithelium and play an active role in forming and moving cerebrospinal fluid are
ependymal cells
perineurium
perineurium
The entire nerve is surrounded by a tough fibrous sheath called the
epineurium.
The covering of a fascicle within a nerve is the
perineurium
Which of the following sequences puts the components of a reflex arc in the correct order of their activation?
receptor, sensory neuron, CNS integration center, motor neuron, effector
Ganglia represent
groups of neuron cell bodies.
Which part or parts of the neuron are found in the white matter of the central nervous system?
long axonal processes
How are gray matter and white matter arranged in the CNS?
Gray matter is deep to the superficial white matter in the spinal cord.
White matter represents
myelinated axons traveling together in the CNS.
In the region of the spinal cord, the cell bodies of most interneurons lie in
the dorsal half of the gray matter.
Which structure is responsible for formation of the regeneration tube following injury to an axon?
schwann cells
In what instance is axonal regeneration possible?
If the cell body of a PNS neuron survives when an axon is damaged, axon filaments can extend peripherally from the injured site toward the original target.
x

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