Lecture 9 (4b) - Neurons, Glia, and Nervous Systems Flashcards
Nervous systems can vary in
size and complexity
• ganglia larger and fuse in more complex organisms
• ganglia - cluster of neurons
Cnidarians have simple networks of neurons called
nerve nets
• there is little or no processing of signals
In more complex animals, neurons are organized into clusters called
ganglia
• complex animals must process and integrate larger amounts of information
In bilaterally symmetrical animals
the ganglia are often paired
Ganglia may be enlarged and fused at the anterior end to form
a brain
Squid
signal eye (sensory) --> brain (integration ) --> mantle (motor output to propel)
The human brain contains … neurons
10^11 neurons
One given neuron can have … synapses
1,000 synapses
10^11 x 10^3 = 10^14 synapses
- the number of combinations of possible networks is almost infinite
- the incredible ability of the human brain to process information, learn, solve complex tasks, have emotions…
Neural networks are for
information processing
3 stages for information processing
- sensory input
- integragion
- motor output
Integration
central nervous system of brain and spinal cord
sensory input and motor output
- integration
vertebrates have a central nervous system including the brain and spinal cord - the sites of most of the information processing, storage, and retrieval
- sensory input and 3. motor output are carried in and out of the CNS by
the peripheral nervous system
• includes sensory and effector (motor) neurons
Sensor to effector
sensory --> sensory input (PNS) --> integration (CNS) --> motor output (PNS) --> effectore
Afferent neurons
Arrive sensory information to the brain
• carry sensory info to the nervous system
• sensory neurons - internal or external stimuli
Efferent neurons
information arrives at the Effectors
(eg motor neurons)
• carry commands to effectors such as muscles, glands
• motor neurons
Information processing is supported by neural networks
- afferent neurons
- efferent neurons
- interneurons
Example of a simple neural network - the knee-jerk reflex
- afferent (sensory) axons in a spinal nerve inter the spinal cord through the dorsal rot
- efferent (motor) axons leave through the ventral root
• cell body in dorsal root
- long axon not in cell body
• dorsal = afferent
• ventral = efferent
Gray matter
rich in neural cell bodies
White matter
contains myelinated axons
Matter inside/outside
gray matter inside, white matter outside
- other way around in the brain
Spinal reflex
conversion of afferent to efferent information in the spinal cord without participation of the brain
Limb movements are coordinated by
antagonistic sets of muscles - flexors and extensors
• 1 muscle excites and 1 muscle contracts
(bc antagonist muscles opposite)
The coordination of antagonistic muscles is achieved by
an interneuron, which makes an inhibitory synapse onto themotor neuron of the antagonistic muscle
- 1 contracts/flexes
- 1 extends
Information processing in the spinal cord
- interneuron decides flexor or extensor
* encode, process, store info to regulate physiological/behavioral
What cells are unique to the nervous system?
- CNS includes the forebrain and spinal cord
- nervous system has 2 types of cells
- • neurons
- • glia, or glial cells
Neurons/nerve cells
• excitable - they generate and transmit electrical signals called ACTION POTENTIALS
Glia/glial cells
modulate neuron activity and provide support
Action potentials are
unidirectional
• dendrite –> axon
Action potentials are integrated in
the hillock
• integrates action potentials
The brain is mostly
interneurons
The neuron’s structure depends on
function
Neurons have 4 regions
- cell body
- dendrites
- axon
- axon terminals
Cell body
contains the nucleus and organelles
Dendrites
bring information to the cell body
• receive information from other neurons
Axon
carries information away from the cell body
Axon terminal
at the tip of the axon
• synapse with a target cell
Axons carry informatoin as
ationpotentials
away from the originating cell body (presynaptic cell) to the receiving target cell (postsynaptic cell)
UNIDIRECTIONAL
The plasma membranes of all neurons can
generate and conduct action potentials
Action potentials can travel at speeds up to
100 m/sec (360 km/hr)
The axon terminal comes extremely close to the membrane of
the target cell, forming a SYNAPSE
Dendrites in the retina are
small
• information comes from a local area
• doesn’t need to store information for a long time
Some neurons branch over
a broad area
Axons with fewer dendrites
process fewer inputs
Bushy dendrites collect information from
many other cells
Some neurons communicate
over long distances via long axons
Electrical synapses allow the action potential to pass
directly between 2 neurons
Synapses can be
electrical or chemical
In vertebrates, most synapses are
chemical
The action potential arriving at the terminal causes it to release
neurotransmitter chemicals which diffuse to the receptors on the target cells
Glial cells outnumber neurons in the human brain by
10x
In the brain and spinal cord, glial cells are called
oligodendrocytes
Oligodendrocytes
wrap around neuron axons, forming the concentric layers of insulating plasma membrane
For the nerves (not CNS), glia is called
Schwann cells and wrap the axons
Insulating plasma membrane is
myelin
• myelin is not continuous = nodes of Ranvier
(jump makes faster)
Oligodendrocytes and Schwann cells produce
myelin that covers axons
Some diseases affect
myelin and impair conduction of action potentials
Multiple sclerosis
- an autoimmune disesase
- antibodies to proteins in myelin in the brain and spinal cord are produced (motor impairment)
- oligodendrocytes myelin
Disease that attacks Schwann cells myelin
Giullain-Barre syndrome
Glia that contribute to the blood-brain barrier
astrocytes
The blood-brain barrier
protects the brain from toxic substances in the blood
Astrocytes
- blood-brain barrier
- take up and release neurotransmitters, and alter the activities of neurons
- plasticity (memory)
Astrocytes store
glycogen that can be broken down to supply neurons with fuel
• aid in repair and regeneration of neurons
• make contact with both blood vessels and neurons, and can signal changes in the composition of the blood
Projections of 1 astrocyte may make contact with more than
100,000 synapses
Tripartite synapse
the idea that a synapse includes the pre- and postysynaptic neurons as well as connections from astrocytes
The blood-brain barrier typically prevents
antibodies form entering the brain and spinal cord
Microglia act as
macrophages and mediators of inflammatory responses, thus providing the nervous system with immune defenses
• microglia = antibodies of the brain
The whole nervous system initially comes from
the ectoderm
The ectoderm gives rise to the
epidermis and neural plate
The neural plate will give rise to the
neural tube and the neural crest cells
The neural crest cells
lead the development of the connections between the CNS and the rest of the body
Nervous system process
The whole nervous system initially comes from the ECTODERM
that gives rise tot he EPIDERMIS and the
NEURAL PLATE.
The NEURAL PLATE gives rise to the NEURAL TUBE and the NEURAL CREST cells that lead the development of the connections between the CNS and the rest of the body.
Future CNS =
forebrain + spinal cord
