Why Do Animals Need a Nervous System?

• Because the world is always coming at you!

Many animals have nervous tissue, but mammals have the most organized and efficient nervous system.

• Central nervous system– brain & spinal chord

• Peripheral nervous system– nerves from senses– nerves to muscles

Nervous System cerebrum

cerebellum

spinal cord cervicalnerves

thoracicnerves

lumbarnerves

femoral nerve

sciatic nerve

tibialnerve

Nerve Cells• Neuron

–  building blocks of the nervous system– sends signals so your body can respond to the

environment

Labeling A Nerve Cell1. Cell Body

2. Nucleus

3. Dendrites

4. Axon

5. Schwann cell nucleus

6. Schwann cell

8. Myelin Sheath .10. Synaptic knobs

7. Node of Ranvier

9. Terminal branch

Fun Facts about Nerve Cells

• Most specialized cell in animals

• Longest cell– blue whale neuron

• 10-30 meters

– giraffe axon• 5 meters

– human neuron• 1-2 meters

Nervous system allows for 1 millisecond response timeNervous system allows for 1 millisecond response time

myelin coating

Myelin Coating

• Axon coated with insulation made of myelin cells– controls speed of signal

• signal hops from node to node

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

Synapse• Junction between nerve cells

– Can be electrical or chemical

Each axon may have synapses with up to 1000

other neurons

Synapse• A chemical synapse

involves release of a neurotransmitter.

• Neurotransmitters are removed from a synapse by enzymes, or they are reabsorbed from the pre-synaptic neuron.

• This is where drugs effect the system.

Reflexes

• Now that we know about neurons…how do they work in the system as a whole?

• They work by reflexes, or automatic response

Sensory Neuron - RECEPTORS

• Sensory Neuron - neurons activated by sensory input (vision, touch, hearing, etc.), which send external stimuli to the central nervous system 

• A receptor is a structure which receives something

Interneuron

• A neuron that forms a connection between other neurons.

• These neurons receive signals in the brain and spinal cord.

Motor Neuron - EFFECTORS

• Neurons that receive signals from the brain to perform motor functions. – Movement– Twitch– Run/Walk/Etc

• The effectors are the organs which respond to the signals

sensory neuron(from senses)

interneuron(brain & spinal cord)

motor neuron(to muscle)

Simplest Nerve Circuit• Reflex, or automatic response

rapid response automated

signal only goes to spinal cord no higher level

processingadvantage

essential actions don’t need to think or

make decisions about blinking balance pupil dilation startle

Testing Your Reflexes - Video

Nerve Potential

• Nerve cells use IONS to function.

Nerve Potential

• Membrane Potential – difference in electrical charge (caused by ions) across cell membrane.

• How many ions on each side?

• Action Potential – causes a nerve impulse – uses ions

• Resting Potential – membrane potential of a neuron at rest, neuron not working – but can when needed (all or none response).

Human Brain

Primitive Brain

• The “lower brain”– medulla oblongata– pons– cerebellum

• Functions– basic body functions

• breathing, heart, digestion, swallowing, vomiting

– homeostasis– coordination of movement

People in “vegetative” states

only use their primitive brain.

Higher Brain

• Cerebrum– 2 hemispheres– left = right side of body– right = left side of body

• The right side of your brain perceives and controls the left side of your body

• Left side of brain perceives and controls right side of your body

Higher Brain

• Corpus callosum– connection

between 2 hemispheres

– When your corpus callosum is severed, you can use each half of the brain independently

These two sides work together. It’s difficult to use only one side of the brain. For example: Have your right hand tap your head while your left hand rubs

your stomach

Division of Brain Function• Left hemisphere

– “logic side”– language, math, logic

operations, vision & hearing details

– fine motor control

• Right hemisphere – “creative side”– pattern recognition, spatial

relationships, non-verbal ideas, emotions, multi-tasking

Activity – Left or Right Test

• Clockwise = Right Dominant

• Counter-Clockwise = Left Dominant

• Lets take a Paper Test to see if this is TRUE…

Cerebrum Specialization

frontal

temporal

• Regions specialized for different functions• Lobes

– frontal• speech,

control of emotions

– temporal• smell, hearing

– occipital• vision

– parietal• speech, taste

reading occipital

parietal

55555 Test

Limbic SystemControls basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory

Memory Loss and Amnesia is due to

Limbic System Damage

Speaking of Memory….

• Do you really pay attention? How much stuff do you miss when you think you’re observing carefully…

• Your ears convert sound waves into electrical signals that are interpreted by your brain

• The cochlea is the auditory portion of the inner ear. It is shaped like a snail shell.

 • Bones of the ear:

– Anvil– Hammer– Stirrup

The Ear

• Eyes enable us to see in color and to distinguish fine details and movement.

• The retina is the lining on back inner surface of the eye – consists of photoreceptors.

• The optic nerve exits the back of the eye and connects in the brain to the thalamus. It contains many neurons that process visual information.

•  – Rods - respond to dim light and black and white shading.– Cones- respond to bright light and enables the sight of the

colors.

The Eye

The Eye

Lens

Cornea

Iris

Pupil

The Tongue