BISC 221 - Nervous System Part 1 (Topic 8) - Midterm 3

What are neurons?

nerve cells that transfer information within the body

What types of signals do neurons use to communicate?

electrical signals (long-distance) and chemical signals (short-distance)

What are dendrites?

highly branched extensions that receive signals from other neurons

What is the axon?

typically a much longer extension that transmits signals to other cells at synapses

What is the axon hillock?

the cone-shaped base of an axon

What does the synaptic terminal do?

passes information across the synapse in the form of chemical messengers called neurotransmitters

What is a synapse?

a junction between an axon and another cell

Where are most of a neuron's organelles located?

in the cell body

What is a presynaptic cell?

a neuron that sends the signal

What is a postsynaptic cell?

a neuron, muscle, or gland cell that receives the signal

What direction is information transmitted?

from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)

What are glia (glial cells)?

cells that support most neurons

What are the three stages of nervous system information processing?

sensory input, integration, and motor output

What do sensors do?

detect external stimuli and internal conditions and transmit information along sensory neurons

Where is sensory information sent?

to the brain or ganglia

What do interneurons do?

integrate the information

What does motor output do?

leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity

What are the three classes of neurons?

sensory neuron, interneuron, motor neuron

What is the central nervous system (CNS)?

where integration takes place; this includes the brain and a nerve cord

What is the peripheral nervous system (PNS)?

carries information into and out of the CNS

What do bundled PNS neurons form?

nerves

What do ion pumps and ion channels establish?

the resting potential of a neuron

What is membrane potential?

Every cell has a voltage (difference in electrical charge) across its plasma membrane

What is the resting potential?

the membrane potential of a neuron not sending signals

What do changes in membrane potential do?

act as signals, transmitting and processing information

Where is the concentration of K+ highest in a resting neuron?

inside the cell

Where is the concentration of Na+ highest in a resting neuron?

outside the cell

What do sodium-potassium pumps use energy from?

ATP

What do sodium-potassium pumps maintain?

K+ and Na+ gradients across the plasma membrane

What do concentration gradients represent?

chemical potential energy

What are these gradients used for?

used by neurons for signaling

What does the opening of ion channels convert?

chemical potential to electrical potential

What channels are mostly open at resting potential?

many open K+ channels and fewer open Na+ channels

What happens to K+ at resting potential?

K+ diffuses out of the cell

What causes the buildup of negative charge within the neuron?

K+ diffusing out of the cell

What is the major source of membrane potential?

the buildup of negative charge within the neuron

What is the resting potential due to?

the asymmetric distribution of Na+ and K+ ions and the selective permeability of the neuronal membrane to K+

What are action potentials?

the signals conducted by axons

What are gated ion channels?

ion channels that open or close in response to stimuli

What happens when the gate is closed?

No ions flow across membrane

What happens when the gate is open?

Ions flow through channel

Why do changes in membrane potential occur?

neurons contain gated ion channels that open or close in response to stimuli

What are graded potentials?

changes in polarization where the magnitude of the change varies with the strength of the stimulus

What produces hyperpolarizations?

stimuli that increase membrane permeability to K+

What produces depolarizations?

stimuli that increase membrane permeability to Na+

What triggers an action potential?

a depolarization that reaches the threshold

What happens if depolarization shifts membrane potential sufficiently?

it results in a non-linear change in membrane voltage called an action potential

What are characteristics of action potentials?

constant magnitude, are all-or-none, and transmit signals over long distances

Why do action potentials arise?

some ion channels are voltage-gated, opening or closing when the membrane potential passes a certain level

At resting state, what is the condition of voltage-gated Na+ and K+ channels?

Most voltage-gated sodium (Na+) and potassium (K+) channels are closed

What happens during depolarization?

Voltage-gated Na+ channels open first and Na+ flows into the cell

What happens during the rising phase of the action potential?

the threshold is crossed, and the membrane potential becomes positive

What happens during the falling phase of the action potential?

voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell

What happens during the undershoot?

membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close and resting potential is restored

What is an action potential considered as?

a series of stages