Ch 48-49 Obj - Neurons and Nervous System

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Course objectives for Ch48 andCh49: Neurons and Nervous Systems

• Name the three stages in the processing of information by nervous systems.

o Sensory Input: sensory neurons transmit information from external stimuli (light, sound, touch, heat, smell, and taste) and internal conditions (blood pressure, blood, CO2 level, and muscle tension, for example). This info is sent to the CNS for processing.

o Integration: In the CNS, interneuron analyze and interpret the sensory input taking into account the immediate context and what happened in the past. The CNS then decides how to respond.
o Motor Output: leaves the CNS via motor neurons to effector cells which can be either muscle cells or endocrine glands, which then do something (move or release hormones, for example)

• Distinguish among sensory neurons, interneurons, and motor neurons.

o Detect external stimuli and transmit information to the CNS
o CNS and ganglia receives information and makes the integration or decision.
o Information from CNS and ganglia heads to the motor neurons and triggers muscle and gland activities.

• List and describe the major parts of a neuron and explain the function of each.

o Cell body (and nucleus inside)
o Dendrites: senses the stimulus
o Axon: signal direction
o Synaptic terminals: attaches to other neurons and releases neurotransmitters.

• Describe the functions of glia.

o Glia nourishes and supports the neurons, and insulates their axons (aka the myelin sheets)

• Define a membrane potential and a resting potential.

o Membrane potential = voltage (difference in electrical charge) across plasma membrane
o Resting potential = membrane potential of a resting neuron. Does not send signals.

• Describe the factors that contribute to a membrane potential.

o -the ion's electrochemical gradient (driving force)
o -the ion's permeability

• Distinguish between gated and ungated ion channels and among ligand-gated ion channels, and voltage-gated ion channels.

• Gated and ungated ion channels open and close in response to stimuli. Ungated remain close.
• Ligand-gated = changes in response to a ligand that binds to the channel.
• Voltage-gated = Responds to change and membrane potentials.

• Describe the characteristics of an action potential. Explain the role of voltage-gated ion channels in this process.

• Action potentials are signals conducted by axons. As the signals travel down the axon, gated-ion channels open in response to change in potentials: with hi number of NA+ going inside the cell, and K+ going outside cell.

• Explain how an action potential is propagated along an axon.

• When depolarization reaches threshold, action potentials then gets propagated along an axon.

• Define the refractory period.

• That's like between the falling stage and the undershoot. The short time immediately after an action potential in which the neuron cannot respond to another stimulus, owing to the inactivation of voltage-gated sodium channels.

• Explain why the action potential cannot travel back toward the cell body.

• b/c the inflow of K+ after action potentials deactivate the NA+ ion channel.

• Describe the factors that affect the speed of action potentials along an axon and describe adaptations that incr speed of propagation. Describe saltatory conduction.

-> Speed of action potential incr. with axon diameter. Axons are insulated by myelin sheets (made by glial cell), which causes an action potential speed to incr.
-> Action potential jumps from node to node as it travels along the axon, b/c when it jumps to the next node it depolarize the membrane and regenerate the action potential.
(see fig 48.13)

• Distinguish between an electrical synapse and a chemical synapse.

Electrical synapses allow electrical current to flow from one neuron to another.
Chemical synapses send neurotransmitters across gap junctions of neuron.
Most synapses are chemical synapses.

• Describe the structures of a chemical synapse and the events that lead to the release of neurotransmitters into the synaptic cleft.

Chemical synapses includes:
the synaptic cleft (the junction btw presynaptic membrane and postsynaptic membrane)
Synaptic vesicles (the balls containing the neurotrans.)
CA2+ channel and ligand-ion channels for the NA+ and K+

-> Action potential depolarize plasma membrane of synaptic terminal
-> Depolarization causes CA2+ ion channel to open and lets CA2+ ions flow into the presynaptic membrane.
-> Ca2+ flow causes the synaptic vesicles (the balls containing the neurotransmitters) to land on the presynaptic membrane and releases the neurotransmitters to the synaptic cleft, where...
-> ... they bind to the ligand-gated ion channel
-> The ligand-gated ion channels open up and let NA+ and K+ ions flow on their merry ways

• Explain how excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) affect the postsynaptic membrane potential.

When excited, EPSPs move the membrane potential toward threshold. Depolarized
When quiet, IPSPs move the membrane potential away from threshold. Hyperpolarized

• Define summation and distinguish between temporal and spatial summation. Explain how summation applies to EPSPs and IPSPs.

Summation is when synapses occur at the same time.
Temporal summation happens on the same synapses but occurs at the same time.
Spatial summation happens on two different synapses but occurs at the same time.

• Describe the specific properties of the neurotransmitters acetylcholine and biogenic amines.

Acetylcholine is a common neurotransmitter in vertebrates and invertebrates
In vertebrates it is usually an excitatory transmitter

Biogenic amines include epinephrine, norepinephrine, dopamine, and serotonin
They are active in the CNS and PNS



1. Compare and contrast the nervous systems of the following animals and explain how variations in design and complexity relate to their phylogeny, natural history, and habitat: hydra, sea star, planarian, insect, squid, and vertebrate.

a. Hydra have a nerve net
b. Sea star have a nerve ring
c. Planarian and insect and squid have brain and ganglia (or nerve cord)
d. Vertebrate have a CNS (the brain and the spinal cord), and a PNS (ganglia and spinal nerves and cranial nerves)

2. Compare the structures and functions of CNS and PNS

a. CNS (brain and spinal cord) - spinal cord sends info to brain, and sometimes acts independently to brain and causes reflexes.
b. PNS (ganglia and spinal nerves and cranial nerves) - brain sometimes transmits info to the PNS.

3. Explain how the spinal cord produces reflex movement.

a. Reflex is auto response to certain stimuli. The knee-jerk reflex. When a doctor hammers your knee and your knee jumps.

i. Sensory neuron detects hammer. Info travels down to the motor neuron and the motor neuron makes an auto response.

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