The Nervous System

Objectives

ContentLabel and describe the major divisions of the nervous system

SkillUse models and representations

The command center of the body

The brain contains over 100 billion neurons (nerve cells)Each one of those connected to 100s of othersIncredibly complex MRIs have allowed scientists to “see” into the brain

Have found that certain regions dedicated to certain tasks

Evolution of the Nervous System

All animals (except sponges) have some sort of nervous system

7 Characteristics of Life

CellsDNAGrow and developMaintain homeostasisRespond to the environmentReproductionUse materials and energy

Quick ThinkAll living things are able to RESPOND TO THEIR ENVIRONMENTWith a partner – come up with at least 3 With a partner – come up with at least 3 different organisms and how they different organisms and how they respond to respond to their environmenttheir environmentBe prepared to share

hibernation

estivation

migration

Nervous system in mammals

1. Central Nervous System (CNS)

1. Brain + spinal cord

2. Peripheral Nervous System (PNS)

1. All the nerves that run throughout the body

THE CENTRAL NERVOUS SYSTEM

The BrainCerebrum - 2 hemispheres, controls your senses (seeing, hearing, tasting, feeling, smelling), learning and memory.

Each side has 4 lobes:Frontal TemporalOccipital Parietal

Cerebellum - coordination, decision making, consciousness, awareness of surroundings

Brainstem - Controls breathing rate, arousal & sleep, swallowing, digestion

Quick Think

Identify the 3 major regions of the human brain

Give 1 specific function of each region

Can you identify the lobes of the brain?

1.

2.

3.

4.

Spinal CordControls reflexes

Examples: tickling laughter/twitchingPupil constrictionCough and sneeze reflexInfants grasp and rootWithdraw reflex

Peripheral Nervous System

Somatic nervous system – parts you control

Autonomic nervous system – parts controlled automatically

Sympathetic division - increased heart rate, adrenaline, fight-or-flightParasympathetic division - opposite effect, calming

Quick think

You have to give a speech to a large audience and feel nervous. What parts of the nervous system would be especially active in this case?

Sensory Organs

TasteTastebuds – food molecules trigger a message to the brain

Nose – olfactory bulb sends message to brain

Eyes Compound eyes (insects,crustaceans) - have 1000s of light detectors and lensesSingle lens eye (vertebrates, some inverts)

Pupil - hole in center of irisRetina - contains photorecptor cells

Rods - very light sensitive cellsCones - cells that distinguish color

Optic nerve – exits the eye and creates a blind spot

Your Blind Spot Draw a small X on the right side of your paperMeasure 5 inches from the left of the X and make a dot the size of a pennyHold the paper in front of you and close your right eye. Look at the X. Can you still see the dot?Slowly move the paper, while always looking at the X. When the dot disappears, you have found your blind spot.

Ears

Outer ear – pinna Collects sounds & direct them to tympanic membrane (eardrum)

Middle ear - 3 small bones vibrate(malleus, incus, stapes)

Inner ear - cochlea – tiny hairs vibrate and send message to the brain

Skin – many different kinds of sense receptors

Senses and your brain

Your brain interprets messages – sometimes in a strange way

Neurons – the cells of the nervous system

NeuronsCell body – contains nucleus & organelles

NeuronsDendrites –receive incoming messages

NeuronsAxon – conveys message to the next cell

Myelin Sheath – covers axon and helps messages travel faster

Synapse – the space at the end of the axon where the message is passed with a chemical neurotransmitter

Synapse

Messages always travel in one directionMessage is electrical inside the neuron, then chemical at the synapse

https://www.youtube.com/watch?v=dSkxlpNs3tU

Synapse

Electrical

Neurons

There are 3 types of neuronsThey must work together to pass messages

Neuron #1SENSORY Neuron

Found throughout the bodyTake in information

They “sense”

Examples:Temperature around youTemperature inside youAmount of light in the roomYour blood sugar levelPain Tickles Others?

Neuron #1

SENSORY NeuronWhat information is this neuron sensing?

Draw in a sensory neuron on your diagram in red.Add an arrow to show the direction the message is traveling.

Quick Check

1s answer this question:What does a SENSORY neuron do?

2s answer this question:What are some things it might SENSE?

Answer on whiteboards

Neuron #2

INTERNEURONSINTERNEURONSThese are in the brain and spinal cord They receive the message from the sensory neuron and interpret it

They “think”

Neuron #2

INTERNEURONSINTERNEURONSAdd these neurons in yellow to your diagramAdd a light bulb to show they “think”

Quick Check

What is the role of interneurons in the nervous system?

Fronts tell behinds . Behinds will answer.

Neuron #3

MOTOR NeuronsSend message from brain to an effector cell (muscle or gland)This causes a response in the bodyThe “run the motor” of your body

Neuron #3

MOTOR NeuronsBefore we draw in a motor neuron…Where will it START? Where will it END?Draw in the motor neuron in blueAdd in an arrow to show the direction the message is traveling

Quick Check

What does a motor neuron do?

Everyone answer on whiteboards

3 main types of neurons

Sensory neurons – collect info from inside (blood pressure, blood CO2 levels, etc) & outside the body (light, temperature, taste, etc)

Interneurons – neurons in CNS that analyze & interpret the info from the sensory neuron and connect to motor neurons to elicit a response

Motor neurons – send signals from the CNS to the body

Messages sent to effector cellsEffector cells are muscle cells or gland cells that carry out a particular response

An example of a nerve circuitThe reflex arc – a reflex is a body’s automatic response to stimuli

Sensory neuron receives infoPasses message to spinal cord (interneurons)Message passed to motor neuronMotor neuron signals an effector cellResponse is initiated

Dendrites, cell body, axon, sensory neuron, interneuron, motor neuron, stimulus, effect

How neurons send messages

Part 1: Electrical message within the neuron

Q: What is membrane potential?

All cells maintain an electrical potential difference (voltage) across their plasma membrane

The membrane potential is maintained by a difference in ionic composition on either side of the membraneFor neurons- the resting potential is the membrane potential when the cell is not transmitting a signal

Q: What is membrane potential?

A: A difference in charge between the inside and outside

of the cell membrane

Q: How is this membrane potential created?

Neurons have ion channels in the membraneThe sodium/potassium pump protein (Na+/K+) uses active transport (ATP) to maintain the resting potential

Q: How is this membrane potential created?

A: by proteins in the cell membrane called sodium/potassium (Na+/K+)

pumps

Q: Why “potential”? I get “membrane”…but what does the “potential” part

mean?A: It refers to potential energy – the potential to do work for the

cell

Q: So how do Na+/K+ pumps work?

A: they move 3 Na+ out of cell and 2 K+ into cell so there is an overall negative charge inside the cell

Q: What is “resting” potential?

A: normal voltage (~-70 mV) when a neuron is inactive

A stimulus of some sort affects the permeability of the membrane to certain ions

This gives rise to a nerve impulse we call an action potential

Q: What is an “action” potential?

The Action PotentialAction Potential (aka nerve impulse)

They are the signals conducted by the axonsAn all or none reaction

It starts with a stimulus that causes the depolarization of the neuron Na+ ion channels open and Na+ enters the cell

This reverses the charges (+ inside and – outside)

The action potential ends as Na+ channels are closed and K+ channels are openedThis helps return the neuron to its resting potential

Action potentials move down the axonSaltatory conduction is the jumping of the nerve impulse between the nodes of Ranvier

This speeds up nerve impulses

Q: What is an “action” potential?A: a stimulus opens ion

channels in cell membrane that allow Na+ to rush into cell, reversing electrical potential. This impulse jumps from node of Ranvier to node of Ranvier until it reaches the synapse

Q: How does it all go back to normal?

A: The Na+/K+ pump

How the message is passed to the next neuron

From the axon of one cell to the dendrites of then next through the synapse

Electrical synapse (a few) - electrical current flows from cell to cell via gap junctionsChemical synapse (most) - the release of a neurotransmitter

The Chemical SynapseNeurotransmitter binds to receptors on the plasma membrane of the next neuronThis triggers an action potential in the next neuron