Nervous System

An Introduction:

Do you take your nervous system for granted? Have you ever pondered the multitude of processes that are made possible because of the central nervous system? We’ll give you a better understanding of the complexities of the nervous system as we step through some of its major parts. We’ll start with a real life story that might help you understand how important this system is. Then, we’ll look at the brain, the spinal cord and nerves. We’ll see how each of the senses work, such as sight, hearing, touch, taste and smell. Finally, we’ll explore some interesting questions related to the nervous system.

But first, we’ve created this short video about Rob’s experience with surgery. Anesthetics seriously affect your nervous system and Rob is no exception.

Football and your Nervous System:

The wide receiver dashes down the field towards the end zone. As he turns back he sees the quarterback throwing a bomb to the end zone. His mind concentrates on the flight path of the ball, integrating information from his eyes and ears and communicating actions to his muscles. Without direct mental input, his heart beats faster and adrenaline hormones are being pumped through his blood stream. As he catches the ball, he sees an opposing player for a split second and then blackness.

While all body systems are extremely important to this player, we can take a closer look at how the nervous system plays an important role in this scenario.

The nervous system controls all the actions the player makes as he catches the football. Some of them are conscious movements, such as running, catching, jumping. Others, such as his heart rate and breathing are not conscious. He uses many different sensory mechanisms, such as touch, sight and sound. Nerves that connect his muscles to his brain are telling him about his surroundings. Different parts of the brain are working at the same time to then communicate the needed directions to catch the ball.

You may never realize quite how important your nervous system is until it gets damaged. When a player blacks out, it is often caused because there is damage to the brain, the main control central of your nervous system. Lets give you a better idea of how the nervous system works by examining each piece in this complex puzzle.

The Neuron:

The building blocks of the nervous system are our neurons.  Our nerves run through our body and help us
interpret the outside world via thousands of neurons. These neurons connect end to end and transmit messages throughout the body. This message relay system is made possible via small electrical pulses that travel down the length of the cell. When it reaches a new cell, chemicals called neurotransmitters take over.

This diagram helps show what happens at the synapse between neurons.  At the synaptic cleft, or the junction between neurons, the "message" is transferred as packages full of neurotransmitters are released into the cleft.  These neurotransmitters, then bind to receptors on the new neuron. This binding action helps open ion channels.  These channels let ions move in or out of the neuron, starting a new action potential to continue the "message'.

To understand the basics of the electrical impulse, lets look at how this action potential is formed …

Action Potential or Nerve Impulse:

A nerve impulse works because the neuron is able to change the electrical charge along the length of the cell. Its not a magical phenomenon but it does take energy input from the cell. The entire process is set in motion because protein pumps along the cell membrane change the concentration of sodium and potassium in the cell. These sodium potassium pumps move one potassium ion into the cell as it moves one sodium ion out.  A huge concentration gradient is set up. Sodium wants in and potassium wants out. Both ions are positively charged though, so there is no electrical potential. However, since some of the potassium is able to leak out of the cell, the entire cell ends up having a negative charge.This voltage differential is approximately -70 millivolts (mV) and is known as the resting potential.

A neuron keeps its resting potential until an outside stimulus is large enough to trigger a nerve impulse. These nerve impulses are driven by a sudden reversal of the resting potential on the cell. Gated sodium channels open allowing positively charged sodium into the cell. This switches the charge. Other gated sodium channels open in front of the impulse. However, as soon as the cell becomes positively charged, the gated sodium channels close and gated potassium channels open. Positively charged potassium rushes out of the cell. The cell returns to a negative charge. In the meantime, sodium-potassium pumps work to keep the
gradient of sodium and potassium unequal within the cell. This way the cell is ready for the next impulse – sometimes refereed to simply as the action potential

Peripheral Nervous System:

All our nerves are part of either the peripheral nervous system or the central nervous system. Most scientists classify the brain, spinal column, and the nerves associated with these masses of ganglia as part of the central nervous system. That leaves the peripheral nerves that control muscles, and our senses. These nerves make up the peripheral nervous system. The two major divisions of this system are the sensory division (nerves sending impulses from sensory organs) and the motor division (nerves controlling muscles).

Motor Division

It’s fairly easy to visualize nerves sending impulses to our muscles when we tell them to move. We move our fingers to type on the computer and we control where we walk. Yet, there are lots of muscles that are sent impulses without us even thinking about it. Muscles in our stomach move without use even knowing it. The motor division of the peripheral system also sends impulses to glands. We divide up the moto division into two classes – the autonomic nervous system and the somatic nervous system.

Somatic Nervous System:

The somatic nervous system consists of muscles that are controlled concoiusly. When we move our skeletal muscles we do this all consciously. Most of the time we have full control over our muscles. Only during times of stress might the nervous system take over. When you touch something hot for instance, its sometimes hard to stop yourself from pulling away. Your blinking reflex is another example. Try not blinking when you sneeze for instance.

- Autonomic Nervous System:

The autonomic nervous system controls bodily functions that are not under conscious control. The movement of our digestive system would be part of this system. Most of the glands in our body are controlled by our nervous system yet we never know about it. The autonomic nervous system is further divided up into two more systems, the sympathetic nervous system and the parasympathetic nervous system. Just as a hang-glider controls his altitude by pushing or pulling on the bar in front of him, these two systems work to push and pull against each other, and thus maintain homeostasis. The control of heart rate is a classic example. The sympathetic nervous system increases heart rate and the parasympathetic nervous system decreases it. There are many other examples of how these two systems work in tandem, but the take home point is that both work together to help maintain equilibrium in the body.

Sensory Systems:

The human boy has the ability to sense the environment and respond to it. We can sense chemicals in our food. They give us smells and tastes. Cells in the back of the eye respond to light and help us produce images of the world around us. Cells in the skin respond to pressure, and allow us to feel objects. Our ears allow us to detect sound waves and aid in our balance. Each of these systems is complex, but they all work because of mechanisms that send stimuli to our central nervous system. The following are but a few of the senses and sense organs that help send information to the brain.
Touch – The Skin
Smell – The Nose
Taste – Taste Buds
Hearing – The ear
Sight – The Eye

Central Nervous System:

The central nervous system serves as the processing system for the nerve impulses received from the peripheral nervous system. All of our sense organs send information to the spinal chord and the brain. Both of these areas are responsible for complex task management.The spinal chord does less processing, but is the root for most of our reflexes (automatic responses to stimuli). The brain on the other hand, is divided up into many regions, which control different parts of the body.

The Brain: Thinking Headquarters

Almost all nerve processing takes place in the major regions of the brain – the cerebrum, cerebellum, and brain stem. Each of these regions controls a different part of the body. But the brain does more than just command the ever changing body. It also changes with time depending on environmental conditions. We’ve outlined the major regions of the brain below. Scroll over each section to learn about what it does.

The Spinal Chord:

The spinal chord is the main communication link between the brain and the rest of the body. The spinal chord is different from the vertebral column. It resides inside and is protected by the bony vertebral column. Because the spinal chord acts to combine nerves from several regions around the body, damage to the spinal chord can result in loss of communication from the brain to that bodily region. This is often what happens when someone becomes paralyzed.