BIOL 225 Lecture Notes - Lecture 48: Peripheral Nervous System, Cnidaria, Information Processing
14 May 2018
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Chapter 48
Notes
• Jellyfish move through ocean using pulses of their umbrella-shaped body
• Cnidarian→ simplest animals lacking true tissues
• The giant ring axon is a collection of neurons that receives information from
tentacles and the edge of the bell (umbrella shaped body)
• Ring axon may send signals to the tentacles to trigger a switch
• Depending on route of signal the bell may contract in a slow way or fast way
• Allows the animal to glide through water→ escaping the predator
• Communication by neurons consists of long-distance electrical signals and
short distance chemical signal
• Specialized structures of neurons allows them to use pulses of electric
current: Receive, transmit and regulate the flow of information along
distances of the body
• N transmits sensory info→ control heart rate, hand & eye corrdination,
generate dreams….
• More complex animals → higher order processing is carried out largely in
groups of neurons organized in braun or simpler clusters called ganglia
48.1) Neuron organization and structure reflect function in information transfer
Information Processing
• Information processing by a nervous system occurs in 3 stages:
1) Sensory input
2) Integration
3) Motor output
• N that carry out integration are organized in a CNS (brain and
longitudinal nerve cord)
• N carry that info into & out of the CNS constitute the peripheral
nervous system (PNS)
• N bundle together form neurons
• Sensory neurons→ transmit info from eyes & other sensors that
detect external stimuli (light, sound, heat, smell & taste) or internal
conditions (BP, blood carbon dioxide levels & muscle tension)
• This info sent to processing centres in the brain or ganglia
• There they are integrated (analyze & interpret) the sensory input
• Majority of neurons in brain are interneurons →form the local circuits
connecting neurons in brain
• Motor output relies on neurons that extend out of the processing
centres& trigger muscle or gland activity
find more resources at oneclass.com
find more resources at oneclass.com
Neuron structure and Function
• Most of a neuron’s organelles, include its nucleus, are located in the
cell body.
• Has numerous highly branched extensions called dendrites (receive
signals from other neurons)
• A neuron has a single axon (extension that transmits signals to the
cells)
• Axon longer than dendrites
• Cone shaped base of axon, the axon hillock is typically where the
signals travel down the axon are generated
• Space between the end of the axon, the axon terminal, and the target
cell is called a synapse
• Most synapses, chemical messengers called neurotransmitters→ pass
info from the transmitting neuron to the receiving cell.
• Transmitting neuron as he presynaptic cell and the neuron, muscle or
gland that receives the signal as the postsynaptic cell
• Neuron supporting cells called glial cells
48.2) Ion gradients and ion channels establish the resting membrane potential of a
neuron
• High concentration of K+ inside the cell & high concentration of Na+
outside the cell
• Therefore, ion gradients and channels→ minor differences in charge
do exist, and when these interact across the thin membrane, they
create a source of electrical potential energy→ this vharge difference
or voltage is called membrane potential.
• MP of an inactive neuron is its resting membrane potential 60-80 mV
• Stimuli causes changes in MP
• Membrane potential of -70 mV means that the inside of the cell
membrane is more negative than the outside
• Any membrane potential different from zero is considered polarized.
• Ion movement may increase the membrane potential →
hyperpolarization
• Or decrease it→ depolarization
• Some ions like potassium and sodium may be allowed to pass through
the membrane, however other membranes may need an active
transport to do so
• Cell membrane potential depends on both gradients of ions across the
membrane and the permeability of the membrane to ions
• Cell membrane resting potential determined by: cytoplasm has high
concentration of proteins and other macromolecules that posses a net
negative charge & cannot move across the membrane
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
48. 1) neuron organization and structure reflect function in information transfer. Information processing by a nervous system occurs in 3 stages: sensory input, integration, motor output, n that carry out integration are organized in a cns (brain and longitudinal nerve cord) Hyperpolarization and depolarization: exploring how membrane potential changes, what happens when potassium channels that are closed in a resting neuron are then open, opening k+ channels increases membrane"s permeability to k+. Na+ diffuses into cell along its concentration gradient causing a depolarization to shift towards +62 mv. Immediately behind the traveling zone of depolarization caused by na+ inflow is a zone of repolarization caused by k+ outflow. Inward current that depolarizes the axon membrane ahead of ap and cannot produce another ap behind it. Evolutionary adaptations of axon structure: usually the smaller the diameter of axon, the slower it goes. Therefore the larger diameters means the signal would travel faster.
