NERVOUS SYSTEM

NERVOUS SYSTEM

RECEPTORS & EFFECTORS

RECEPTORSReceptors are groups of specialized cells. They can detect changes in the environment, which are calledstimuli, and turn them into electrical impulses. Receptors are often located in thesense organs, such as the ear, eye and skin. Each organ has receptors sensitive to particular kinds of stimulus.

SENSE ORGAN RECEPTORS SENSITIVE TO SKIN TONGUE NOSE EYES EARS Receptors SENSE ORGAN RECEPTORS SENSITIVE TO SKIN Touch, pressure, pain & temperature

TONGUE Chemicals in food

NOSE Chemicals in the air

EYES Light

EARS Sound and head position

Effectors

An effector is any part of the body that produces the response. Here are some examples of effectors:a muscle contracting to move the arma muscle squeezing saliva from the salivary glanda gland releasing ahormoneinto the blood

The nervous system is divided into:

Central nervous system: this includes the BRAIN and the SPINAL CORD. Peripheral nervous system: this includes the nerves that connect the spinal cord to the body.

The brain, the spinal cord and the nerves are made of nerve cells or NEURONS.

Neurons are nerve cells. They carry information as tiny electrical signals.

The diagram in the next slide shows a typical neuron - in this case, a motor neuron. It has tiny branches at each end and a long fiber carries the signals.

NEURONES

Label the Neurons

DENDRITE Fine hair-like extensions on the end of a neuron.Function: receive incoming stimuli.CELL BODY OR SOMA The control center of the neuron. Function: Directs impulses from the dendrites to the axon. NUCLEUS Control center of the Soma. Function: Tells the soma what to do.AXON Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron.MYELIN SHEATH An insulating layer around an axon. Made up of Schwann cells.NODES OF RANVIER Gaps between schwann cells. Function: Saltatory Conduction (Situation where speed of an impulse is greatly increased by the message jumping the gaps in an axon).

There arethree different types of neurons, each with a slightly different function.

Sensory neuronscarry signals fromreceptorsto the spinal cord and brain.Relay neuronscarry messages from one part of theCNSto another.Motor neuronscarry signals from theCNSto effectors.

Types of neurons

TYPES OF NEURONSBased on: Mader, S., Inquiry Into Life, McGraw-Hill15Main Idea(s) of This Slide -

There are three primary types of neurons in the nervous system. Sensory neurons carry impulses to the brain and spinal cord (CNS).Interneurons (in the brain and spinal cord) process and interpret the incoming information.Motor neurons then carry impulses from the CNS to the effectors throughout the body.

Note a nerve is a bundle of many sensory or motor neurons wrapped together in a sheath of connective tissue.

Nerve fibers, Nerves and TractsA nerve is a bundle of nerve fibers, located outside the brain and spinal cord, that connect various parts of the body.Sensory nerves carry messages to the CNS (brain) and the motor nerves carry messages away from the CNS.Groups of nerve fibers within the CNS are known as tracts.Telling the difference

How can your brain tell the difference between a strong chocolate smell and a faint chocolate smell?If a stimulus is strong, then a greater number of impulses will be sent out. This is because more nerve cells will be stimulated and transmit their messages to your brain. If the smell was faint, then fewer impulses would be sent out and fewer nerve cells would be stimulated. In this way the brain is able to detect differences.

What if a stimulus is applied for a long time?If you ate chocolate all day long, for example, the sensory receptors would stop reacting to it and eventually you would not taste it anymore. We say the sensory receptors have adapted. Similarly, when you put jeans on fi rst thing in the morning, you feel the material against your skin. But soon you dont notice the material is there because your skin receptors have adapted to its presence.SYNAPSES

Where two neurons meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neuron releases the chemical into the gap. The chemical diffuses across the gap and makes the next neuron transmit an electrical signal.

SynapsesNeurotransmitter being released into synapse and attaching to receptors on dendriteBased on Harvard Medical School Family Health Guide20Main Idea(s) of This Slide -

This slide depicts the synapses between the axon of one neuron and the dendrite of another.

Here is a close-up view of the synapse between two adjacent neurons. The axon of the neuron at the top of the slide terminates in what is called an axon bulb. Inside the axon bulb are synaptic vesicles that contain neurotransmitters. The neurotransmitters are responsible for exiting the axon bulb and entering into the synapse. Once inside the synapse (space between the neurons), the neurohormones bind to the adjacent neurons postsynaptic membrane and cause a new depolarization wave to begin.This image on the right depicts the neurotransmitter (neurohormone) being released from the synaptic vesicle into the synapse where it can then bind to receptors on the adjacent neuron.

50 Known NeurotransmittersExamples include:AcetylcholineDopamineSerotonin21Main Idea(s) of This Slide -

There are over 50 known neurotransmitters today. This slide lists three commonly discussed neurotransmitters; acetylcholine, dopamine, and serotonin. Acetylcholine is the neurotransmitter that is responsible for carrying a nerve impulse from a motor neuron, across a synapse, to a muscle cell (the effector) and causing the muscle to respond by contracting. Insufficient levels of acetylcholine or disruption in its ability to work can cause neuromuscular problems.Seratonin is a neurotransmitter that is responsible for filtering sensory information coming into the brain. Some recreational drugs such as ecstasy create imbalances in the levels of serotonin resulting in hallucinations and mood changes. Other drugs called SSRIs (selective serotonin re-uptake inhibitors) elevate serotonin levels in the brain resulting in mood elevation and are prescribed as anti-depressants.Dopamine is considered the master molecule of addiction. It is a neurotransmitter that is released by brain cells that causes a feeling of well being in response to pleasurable activities such as sex and eating. Elevated levels of dopamine cause a euphoric high and are associated with many recreational drugs.

Why do we need a neurotransmitter like dopamine?22Main Idea(s) of This Slide -

Here is a good time to generate some discussion with the students. Ask them to come up with ideas as to why neurotransmitters like dopamine are needed based upon their reading.Human behavior is controlled by natural chemical reward systems in the body

For example, we like to eat fatty foods because it make us feel good

It is the release of dopamine that is the chemical reward system responsible for the good feeling

Dopamine reinforces behaviors essential to our survival.Importance of Dopamine23Main Idea(s) of This Slide -

Dopamine reinforces behaviors that are essential to human survival such as eating and procreating. When humans engage in these behaviors, some brain cells release dopamine resulting in good feelings.

Dopamine is released bycellsof the nervous system during pleasurable activities such as eating or havingsex. Once released, dopamine travels across a gap between nerve cells, called asynapse, and binds to areceptoron a neighboring nerve cell (also called a neuron). This sends a signal to that nerve cell, which produces a good feeling. Under normal conditions, once the dopamine sends that signal it isreabsorbedby the neuron that released it. This reabsorption happens with the help of a protein called thedopamine transporter.Cocain interrupts this cycle. It attaches to the dopamine transporter, preventing the normal reabsorption process. As dopamine builds up in the synapse, it continues to stimulate the receptor, creating a lingering feeling of exhilaration or euphoria in the user.http://health.howstuffworks.com/wellness/drugs-alcohol/crack.htm/printable

(Somatic) REFLEX ACTIONS

When a receptor is stimulated, itsends a signal to the central nervous system, where the brain co-ordinates the response. But sometimesa very quick response is needed, one that does not need the involvement of the brain. This is a reflex action.

Reflex actions are rapid and happen without us thinking. For example, you would pull your hand away from a hot flame without thinking about it. The animation below allows you to step through each stage of the reflex arc.