Nervous System Grade 10

What is the Nervous System? In the simplest form, the nervous system is an organ system specifically designed to sense the environment and to produce a response to changing conditions

How Does the Nervous System Sense its Surroundings? The nervous system has a number of receptors designed to accumulate information about the environment Examples of these receptors include: taste buds, rods and cones on the retina, pressure sensors in the skin

How Does the Nervous System Transmit Information from One Part of the Body to the Next? The nervous system transmits signals from one part of the body to another (taste to brain) by using neurons

How Does the Nervous System Interpret the Information? The brain acts as the main filter for information coming from all over the body The brain then has to prioritize information that is more important than others The brain has to then decide upon a set of actions to respond the environment

What type of Responses can the Brain Direct? The brain can cause a multitude of reactions to respond to the environment such as: the movement of a muscle to avoid a moving object the increase of heart rate to escape from a bear the increase in pupil sight to see in the dark

What is a Neuron? A neuron is the smallest unit of the nervous system Every part of the nervous system is composed of specialized neurons

Parts of the Neuron The Cell Body is the center of the cell. Here most chemical reactions occur, DNA is in the nucleus, most of the organelles are located here

Neuron Continued Dendrites receive information. This can come from two sources, other neurons or specialized receptors (like taste buds)

Neuron Continued The axon transmits the message along the rest of the neuron to the next neuron

Electrical Impulses Electrochemical impulses transmit signals to other parts of the nervous system. There is an all or none response to stimulus (either the nerve cell decides to send a message, or it remains inactive) There is no difference in the strength of the impulse Once it decides to send a message, the message cannot be recalled

Axon Although the stregth of an impulse cannot be changed, it can become faster Sometimes Schwann Cells wrap around the axon and produce a Myelin Sheath These nerve cells are called Myelinated The myelin sheath in conjunction with the Nodes of Ranvier speeds up the electrochemical impulse Schwann Cells Node of Ranvier

Why do Some Things Hurt More Than Others? Because the number of nerve cells that receive the stimulus increase The more nerve cells that send an impulse, the greater the sensation of pain

How Does the Impulse go From one Neuron to the Next? The axon of the first neuron is connected to the dendrites of a second neuron by a space called the SYNAPSE Chemicals called NEUROTRANSMITTERS send a signal to the second neuron asking it to continue sending the information

Neurotransmitters Neurotransmitters are transported to the edge of the synapse by synaptic vessicles Many drugs that target the brain affect the transmissions of singals across the synaptic cleft

Divisions of the Nervous System CNS- the central nervous system includes the brain and spinal cord PNS- the peripheral nervous connects the CNS with the rest of the body

Divisions of the Nervous System Somatic Nervous System- voluntary control of functions Autonomic Nervous System- involuntary control for automatic functions

Reflex Arc In a reflex arc, your body responds to a stimulus without the direct intervention of the brain This is because sending information to your brain and waiting for a decision to be made would take too much time

Reflex Arc A reflex arc is made up of three different types of neurons: 1.Sensory Neurons- Brings information to the Central Nervous System (Brain and Spinal Cord) 2.Association (Interneurons) Neurons- Found only in the Central Nervous System (CNS) 3.Motor Neurons- Carries impulses from the CNS to effectors (muscles or glands)

Reflex Arc A Reflex Arc must always contain the following: 1.Receptor (ex. pain receptor) 2.Sensory Neuron 3.Interneuron 4.Motor Neuron 5.Effector (Muscles)

Diseases of the Nervous System Multiple Sclerosis (MS)- Deterioration of the myelin sheath (slower impulses) Scar tissue builds up on the axon No impulse transmission Impared neural functioning (loss of co-ordination, tremors, paralysis) Cause remains unknown

Diseases of the Immune System Isaacs Syndrome: Rare Involuntary muscle contractions May interfer with speech and breathing