Nervous System Introduction to the Nervous System

Dr. Rufus B. Weaver with Harriet Examine This Image: What body system is shown? Dr. Rufus B. Weaver with Harriet Once Hahnemann Medical College had an extensive museum, now reduced to a few interesting showcases. The centerpiece of the modest display at the entrance to the school's library is one of the world's most fascinating and unusual medical specimens. What seems like a weird example of string art in human form is all that is left of Harriet Cole, an African-American scrubwoman at the medical school who died in 1888. Apparently, the cleaning lady was interested in anatomy and willed her body to the school.

Harriet Donated Her Body to Science Dr. Rufus B. Weaver, the school's foremost anatomy professor had a special project in mind for Harriet — a project many colleagues thought impossible. Weaver spent five exhausting months — working eight to 10 hours a day — painstakingly removing every bit of bone and flesh from the cadaver leaving only the nervous system and eyes. During the dissection each strand was wrapped in gauze and kept moist with alcohol and finally preserved with white lead-based paint and shellac. The exposed nervous system was then mounted on a board with hundreds of tiny pins. Harriet was displayed at the 1893 Colombian Exposition in Chicago where it was awarded a gold medal and blue ribbon. Life Magazine published a nice photo essay on Harriet in 1960. She was also featured in Time Magazine and a number of medical books. You can see Philadelphia's most famous bundle of nerves near the 15th and Vine streets school entrance.

Today’s Essential Knowledge statement 3.E.2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. This is the essential knowledge statement from the curriculum framework. Detect---process---response Image: Hillis, Principles of Life

Role of the nervous system The nervous system interacts with sensory and internal body systems to coordinate responses and behaviors. The diagram references a Pavlovian response. Students may be familiar with this example. If so, allow them to explain it. Feature detectors are individual neurons – or groups of neurons – in the brain which code for perceptually significant stimuli. Early in the sensory pathway feature detectors tend to have simple properties; later they become more and more complex as the features to which they respond become more and more specific.

What trends do you notice? What trends do you notice? Students should see an increased presence in the nervous system as you move up the evolutionary ladder from hydra to jelly fish. They will also notice the increased presence of ganglia and increased presence of brain tissue. Carefully note that the sea star is evolutionarily misplaced in this trend-revealing graphic. (exception to the evolutionary trend)

Noteworthy Trends In Development Increase in ganglia Increase in sensory reception Increase in cephalization Cephalization is the concentration of nervous tissue in the anterior region of the organism. Students may have prior knowledge of these terms. Ask them to define each term. In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism. Cephalization is defined on the slide.

What would be the advantage of having cephalization? Cephalization supports anterior and sensory input. Is there are relationship between cephalization and symmetry? (yes with adult echinoderm exception) Bilateral symmetry and increased anterior cephalization are evolutionarily tied together.

Human Nervous System -two main systems Note the cephalization of the human nervous system. Our nervous system is divided into two main categories; the central (composed of brain and spine) and then the Peripheral system composed of the nerves and ganglia out side the brain and spine. Which system do you think would be more involved in detection, CNS or PNS? (PNS) Point out that nerves are composed of bundles of neuron (cell) projections called axons.

Consider this image. Ask students the following questions: Which portion indicates where detection of a stimulus is occurring? Processing? Responding? Our body continually detects stimuli from inside and outside our body. What are you detecting right now? (accept answers like the amount of light, hot/cold, pressure, etc) What receptors are you using? Try to lead them to the 5 senses

Describe the flow of communication through the reflex arc showing that this pathway includes sensory input, integration/process and response. A reflex pathway includes the central nervous system and the peripheral nervous system in the pathway.

Neuron Defined The basic structure of the nervous system that reflects function. The structure of the neuron allows for the detection, generation, transmission, and integration of signal information. Trivia: 30,000 neurons can fit into a pinhead Image from Hillis, Principles of Life

Take a moment to analyze the similarities and differences between each type of neuron. (next slide)

There are three main types of neurons: Sensory neurons Interneurons Neurons are highly specialized for the function of conducting impulses. There are three main types of neurons: Sensory neurons Interneurons Motor neurons Refer back to the reflex pathway to show the locations of the sensory neurons, interneurons, and motor neurons (next slide)

Where are the neurons in this reflex arc? Label the diagram with the class as you describe the flow of information through the pathway. A = sensory receptor, B = sensory neuron, C = interneuron, D = motor neuron, E = effector.

Choose the correct pathway of information flow through neurons while taking a test, starting with reading the question and ending with marking an answer. a. interneurons  motor neurons  sensory neurons  effectors b. effectors  sensory neurons  interneurons  motor neurons c. sensory neurons  interneurons  motor neurons  effectors d. interneurons  sensory neurons  motor neurons  effectors Expect them to answer this question on their own. Answer: c

Neuron What are some notable differences between this cell compared to a “typical” animal cell? Always take the opportunity to train students to discuss what is “alike” and what is “different” when answering compare and contrast questions. Don’t let them get away with discussing only what is “different”. Students should notice the cell extensions/processes including the dendrites, a long, cylindrical axon, a triangular axon hillock, and the terminal branches that end in a synaptic terminal.

A typical neuron has a cell body, axon and dendrites. Neuron Anatomy A typical neuron has a cell body, axon and dendrites. Describe the features of the neuron. Dendrites receive incoming stimuli. Notice there are several dendrites on the single neuron. The cell body contains organelles including the nucleus. The triangular axon hillock is the location in which the action potential will be generated. Once the action potential is generated, the signal will travel down the axon toward the synapse. The cell prior to the synapse is called the presynaptic neuron, the one occurring after the synapse is called the post synaptic neuron. Neuron transmitters will be released in the space or synaptic cleft.

Identify The Numbered Structures 1 = dendrites 2 = nucleus 3= axon 4= axon hillock 5 = cell body

Neuron A typical neuron has a cell body, axons and dendrites. Many axons may have a myelin sheath that acts as an electrical insulator. Some neurons have myelin sheaths produced by Schwann cells surrounding the axon.

Nucleus of Schwann cell Axon Myelin sheath Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nodes of Ranvier Nucleus of Schwann cell Axon Myelin sheath Schwann cells and the myelin sheath. Notice the location of the Schwann cell on the exterior of the axon. What cellular process must occur at high levels in order for the Schwann cell to perform its function of myelin production? (protein synthesis) 0.1 m 21

Saltatory Conduction Saltatory conduction. Notice that the conduction along a myelinated axon can occur quickly as large spaces can be skipped and impulse propagation occurs only at the nodes of Ranvier. Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon Notice that the conduction along a myelinated axon can occur quickly because large spaces can be skipped and occurs only at the node of Ranvier. Saltare is Latin for “to leap” and that is why conduction on a myelinated sheath is called saltatory conduction. What would you expect would happen when a disease such as multiple sclerosis causes demyelination? 22

Putting It All Together How are the nerves you saw in Harriet’s picture related to neurons? How are they alike? How are they different? Ask students to think to themselves or write their answers on the edge of their notes. After a few seconds, ask them to share out loud. Build a T-chart (alike vs. different) on the board to show relationships. Nerve larger, multicellular, composed mostly of axons…

Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals called neurotransmitters

There is enough electrical current in the brain to power a flashlight The use of neurotransmitters causes an electrical current There is enough electrical current in the brain to power a flashlight

Anatomy of the Brain Cerebellum : at base of brain -Responsible for: - Muscle coordination - Balance - Posture

Anatomy of the Brain Brain Stem : connects brain to spinal cord -Responsible for: - Breathing - Swallowing - Heartbeat - Blood pressure

Central Nervous System Spinal Cord : Column of nerves from brain to tailbone – protected by vertebrae of spine Responsible for: - Conducting impulses between the brain and the rest of the body *Impulses may travel as fast at 268 miles/hr

Problems of the Nervous System Concussion A temporary disturbance of the brain’s ability to function due to a hard blow to the head

Paralysis A loss of sensation and movement of part of the body due to an injury of the spinal cord or brain

Parkinson’s Disease The brain does not produce enough of the neurotransmitter that transmits messages from the brain to the muscles Symptoms: tremors, rigid muscles, shuffling walk, and loss of facial expression Red areas show where chemical is stored

Alzheimer’s Disease A gradual shrinking of the neurons in the cerebrum Symptoms: memory loss, emotional disturbances, inability to function on own, death

Epilepsy Abnormal transmission of messages between the neurons in the brain Symptoms: seizures