Neurons, Nervous System, and Action Potentials

What is the function of the nervous system?

To coordinate the actions of complex organisms via the transmission of electrochemical signals

What cells transmit signals in the nervous system?

Neurons

What is the basic function of a neuron?

To send and/or receive electrical signals

What is the function of dendrites?

Receive electrical signals

What is the function of the axon?

Propagate (continue) electrical signals toward the axon terminal and synapse

What is the function of the cell body?

Contains the nucleus and organelles

What are the two main divisions of the nervous system?

Central nervous system and peripheral nervous system

What makes up the central nervous system (CNS)?

Brain and spinal cord

What makes up the peripheral nervous system (PNS)?

All peripheral nerves linking the CNS to receptors and effectors

What are the three main types of neurons?

Sensory neurons, relay neurons, and motor (effector) neurons

What is the role of sensory neurons?

Transmit information from receptors to the CNS

What is the role of relay neurons?

Interpret and transmit signals within the CNS

What is the role of motor neurons?

Transmit signals from the CNS to effectors

How does information flow through the nervous system?

PNS sends sensory input to CNS, CNS activates effectors via motor neurons

What is an anatomical dermatome?

A region of the body innervated by nerves from a specific spinal segment

Why are cervical spinal injuries most severe?

They affect a larger portion of the body

What is the effect of C1–C4 spinal injuries?

Impaired normal breathing

What is resting potential?

The voltage difference across a neuron's membrane when it is not firing

What is the value of the resting potential?

-70 millivolts

What creates and maintains resting potential?

The sodium–potassium pump

What does the sodium–potassium pump do?

Pumps sodium ions out and potassium ions into the neuron

Why is the sodium–potassium pump energy-dependent?

It uses ATP to move ions against their concentration gradients

Sodium-potassium pump 1

Three sodium ions bind to sites on the sodium-potassium pump

Sodium-potassium pump 2

A phosphate group is transferred to the pump via the hydrolysis of ATP

Sodium-potassium pump 3

The pump undergoes a conformational change, moving sodium across the membrane.

Sodium-potassium pump 4

The conformational change exposes two potassium (K+) binding sites on the extracellular surface of the pump.

Sodium-potassium pump 5

The phosphate group is released, which causes the pump to return to its original conformation.

Sodium-potassium pump 6

This translocates the potassium across the membrane, completing the ion exchange

What is a nerve impulse?

A signal that moves along an axon as a wave of depolarisation

What is an action potential?

a rapid, temporary change in memebrane volatge of a neurons axon

What causes depolarisation

Opening of sodium channels allowing Na⁺ to enter the neuron

why does sodium enter the neuron during depolarisation

because of the high sodium concentration outside the cell

what causes repolarisation

opening of potassium channels allowing K⁺ to leave the neuron

what is the purpose of repolarisation

to restore the resting potential