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