The Nervous SystemHASPI Medical Anatomy & Physiology 11aLab Activity

BackgroundThe Nervous SystemThe nervous system is an incredibly complex network of tissues that are capable of carrying information throughout the human body. The two primary cells of the nervous system are neurons, that actually carry and storeinformation, and glial cells that support the neurons. The nervous system is broken up into a few systems depending on the function and location. Central Nervous SystemThe central nervous system, or CNS, is made up of the brain and spinal cord. The retina of the eye is also considered part of the central nervous system. The brain is the control center of the body and is housed within the protective hard skull. Layers of tissues called meninges and cerebrospinal fluid also protect the CNS. The spinal cord extends from the brainstem through the vertebral column. There are 31 segments to the spinal cord, and a pair of spinal nerves extends from each segment into the body. Peripheral Nervous SystemThere are 43 pairs of nerves that connect the central nervous system to the rest of the body, and they make up the peripheral nervous system or PNS. The PNS is made up of sensory neurons that are capable of receiving stimuli, and motor neurons that are capable of responding to stimuli. For example, sensory neurons in the eye are capable of receiving light stimuli and motor neurons are attached to muscles that can create movement. The PNS is broken down into the somatic and autonomic nervous systems, and the autonomic is further broken down into the sympathetic and parasympathetic nervous systems. Diagram A summarizes the relationship between these systems. The somatic NS is the voluntary system that can be controlled consciously, such as movement of muscles. The autonomic NS is the involuntary system and controls unconscious impulses such as the heartbeat. The sympathetic and parasympathetic systems work opposite of one another. For example, the sympathetic system speeds up the heart rate while the parasympathetic system slows down the heart rate.

The NeuronThe neuron is the functional cell of the nervous system. It can send and receive nerve impulses. There are billions of neurons in the body, with more than 100 billion on the surface of the brain alone. Even so, approximately 90% of cells in the brain are supportive glial cells and only 10% are actualneurons. Neurons are made up of a cell body, dendrites, an axon, and axon terminals. When

Name(s): ________________________

Period: _________ Date: ___________

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Diagram A

something stimulates a dendrite, the nerve impulse travels through the dendrite, to the cell body down the axon and axon terminals, where the impulse will be passed to the dendrites of the next neuron to perpetuate the impulse. Sensory neurons have a single specialized dendrite to receive stimuli while motor neurons have many dendrites. Axons are covered with a lipid-based myelin sheath created by Schwann cells that is capable of drastically speeding up the nerve impulse.

When you touch a hot pan, sensory neurons at the ends of the fingertips start a chain reaction that is passed through neurons from the fingertip all the way to the brain. The brain is then capable of interpreting this reaction, most likely as “pain” or “hot”, and will immediately send a response back through motor neurons capable of immediately moving the finger away from the hot pan. This is an extremely fast process.

The Synapse & Nerve ImpulseNeurons pass impulses from the axon terminal of one neuron to the dendrite of another neuron at the synapse. The message is actually passed between two neurons through chemicals called neurotransmitters. Different neurotransmitters can relay different messages. For example, serotonin is a neurotransmitter that regulates appetite, sleep, and mood. The following steps outline the process of a nerve impulse at the synapse and correlates with Diagram B.

Nerve Impulse at the SynapseStep 1 The nerve impulse travels down

the axon to the synapse

Step 2The impulse opens channel proteins on the membrane of the synapse that allows calcium (Ca2+) to enter

Step 3Ca2+ prompts synaptic vesicles to release neurotransmitters into the synaptic cleft

Step 4The neurotransmitter binds to receptors on channel proteins of the NEXT neuron and opens them

Step 5Na+ molecules can now travel through the open channel protein into the dendrite of the next neuron

Step 6 Na+ builds up in the next dendrite and starts an electrical impulse

Step 7The impulse travels down the dendrite, through the cell body, and through the axon to the next neuron

Kendal, E., Schwartz, J., and Jessel, T. 2000. Nerve Cells and Behavior. Principles of Neural Science, McGraw-Hill.

Mandal, A. 2012. What is the Nervous System? News Medical, www.news-medical.net.

Diagram B

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Station 1: The Nervous SystemThe Nervous System – Using “The Nervous System” chart, identify the labeled A-X in Table 1 below. If there are any that you cannot identify, use a textbook or online resource. A smaller version of this chart is included here for later review.

The Neuron – Using “The Neuron” chart, identify the labeled A-J in Table 3 below. If there are any that you cannot identify, use a textbook or online resource. A smaller version of this chart is included here for later review.

Table 1: The Nervous SystemA MB NC OD PE QF RG SH TI UJ VK WL X

Table 3: The NeuronA F

B G

C H

D I

E J

The Nerve Impulse – Using “The Nerve Impulse” chart, record the steps 1-8 of a nerve impulse in Table 4 below. A smaller version of this chart is included here for later review.

Station 2: Nerve DamageThe nervous system is responsible for muscular contractions that produce heat, and therefore sweat. When the nerve toa specific muscle is damaged, it will not send the signal to contract to that portion of muscle, and no sweating will occur in that area. Nerve damage can result from any type of injury in which the actual nerve fibers are disrupted. This could be caused by something as simple as a laceration, or as severe as third-degree burns. Nerve damage is placed into three categories:

Neurotmesis – The most severe nerve damage resulting in complete loss of function and ability of the nerve to send an impulse. Can result from tearing, stretching, or bruising.

Axonotmesis – Results when the nerve is placed under too much pressure and/or crushed. The axon of the nerve is damaged preventing the nerve from sending impulses, but it is possible for the axon to regenerate. This regeneration can take months to years.

Neurapraxia – The least severe nerve damage that allows for complete recovery within a few months. Can result from constant pressure or lack of blood supply to the nerve.

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Table 4: The Nerve ImpulseStep 1

Step 2Step 3Step 4Step 5Step 6Step 7Step 8