The Nervous System

Communication Center• Central Nervous System (CNS):

system of nerves, the spinal cord, and the brain that receives signals from environment and sends out responses to those signals

• Neurons: nerve cell; 3 sections– Dendrites: fan like branches that

receive impulses– Cell body: main area of cell– Axon: long extension that sends

impulses on to other neurons or body cells

Basic Structure of Information• What are the parts of a negative

feedback system?• Stimuli information about environment• Receptor something that can sense stimuli (input)• Integrator thinking part; uses set point

– Also called coordinator• Effector sends the response to the stimuli (output)

• What does the nervous system run on?– SAME THING!

• Stimuli comes in through receptor• Input moves on to integrator• Integrator activates effector• Effector causes response

Regions of the Brain• 3 main sections:

1) Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from

2) Cerebellum- back of your brain; controls balance, senses, and coordination

3) Brain stem- connection between brain and spinal cord

a) Medulla oblongata- controls involuntary activities

b) Midbrain- responds to signals and sends them to regions of the brain

c) Hypothalamus- connection between nervous and endocrine system

Layers of the Nervous System• Peripheral Nervous System

(PNS): nerves that carry messages to and from the CNS

• Two system in the PNS:1) Somatic Nervous System:

- 12 nerves in the brain- 31 nerves in the spine- send information for all

voluntary movement Reflex: automatic response to

set stimuli so to quickly minimize damage

- pulling back when burned

Layers of the Nervous System2) Autonomic Nervous System:

- send impulses to organs in the body- control involuntary

movementsTwo systems in the ANS:1) Sympathetic Nervous System:

- controls organs during times of stress

- release of epinephrine2) Parasympathetic Nervous System:

- controls organs during times at rest

Layers of the Nervous System

Types of Neurons• Sensory neurons: receive

signals from the environment and send impulses to the spinal cord and brain

• Interneurons: nerves that make up the brain and spinal cord; process impulses and send response impulses to motor neurons

• Motor neurons: react to impulses from brain and spinal cord; activate glands, muscles, etc..

They Mighty Reflex• I throw a ball at you. What

nerves first take in the input?– Sensory nerves in eyes

• The input to the brain quickly calculates distance, speed, angle, etc… to conclude if the ball will hit him. What nerve cells to this?– Intermediate neurons

• What is your reaction? What caused this?– Muscles move body away from

ball; Motor neurons (effector neurons)

• If input is strong enough, you don’t even need his brain!

They Mighty Reflex• Where are intermediate neurons

located? – Brain AND Spinal Cord

• Reflex action:– When input is significantly higher/lower

than set point, spinal cord sends response before brain even gets input

– Cuts only fractions of a second off but can save your life

• Reflex arc:– Sensory impulse travels to intermediates

in spine, set point comparison causes response on effector neurons

• Explains why we can feel temp, text, etc… BEFORE we feel pain (Brain is too slow)

How Neurons Send Impulses• Ion channels allow the inward

flow of K+ and limit the flow of Na+

• Concentration difference between Na+/K+ is made greater by Na+/K+ Pump

• Membrane is polarized:– Inside has negative charge– Outside has positive charge– About -70mV difference (resting

potential)• Impulse is sent as swift of K+

and Na+ across the membrane change the polarity of the cell (action potential)

Na+/K+ Pump• Concentration gradient of Na+ and K+ most be large so

the flow of ions is fast• Na+/K+ Pump uses ATP to pull in K+ and push out Na+

1 ATP= 2 K+ in; 3 Na+ out• Also helps to repolarize membrane after impulse

All About Speed!• Signals can “jump” down

axon by traveling to pockets between myelin sheaths

• Myelin sheaths increase signal transmission

• Heavily myelinated nerves have a white color– Inner areas of the brain– Spinal cord nerves

• Regular nerves have gray color– Outer areas of the brain– Body nerves

Neuron to Neuron Signals• Nerve cells don’t touch;

signal “wave” has to be passed from cell to cell

• Synapse: small space (10-20 nm) between neurons

• Neurotransmitter: chemical signals that travel from axon of one neuron to the dendrite of the next neuron; triggered by Ca+ channels

Nerves and Muscles • Antagonistic Muscles– System of paired muscles that

allow all our complex movement• Contraction of Bicep1) Bicep muscles fibers shorten

(contract) while triceps muscle fibers relax

2) Tendons pulls lower arm3) Ligaments allow elbow joint to

end• Triceps and Biceps are

antagonsitic pairs – If one contracts the other must

relax

The Senses

The 5 Major Senses• Smell• Taste• Touch• Hearing• Sight

• How our brain/body takes in stimulus from the environment

• How we learn about the world

Smell• Breathing air through your

nose pulls in particulate matter (chemicals floating in the air)

• Olfactory:– collection of receptors in top

of the nose– Chemicals bind to receptors,

and signals are sent to the brain along a cranial nerve

– Brain interprets good and bad smells based on what chemicals are detected

• Why have a sense of smell?

Good Smells vs. Bad Smells• Things smell good because

they are good for the body or the mind:Meat- smell of fats and proteinsFlowers- smell triggers release of hormones that relax usFruits- smell of sugars and vitamins

• Things smell bad because they might kill us:Waste material- contain bacteria; no usefulmaterialRotten Food- contain bacteria; bad for digestion

Taste• Smell and taste are strongly

linked• Taste buds:

- receptors for each of the 5 tastes:

salty, sweet, sour, bitter, umami- Chemical reacts with receptor and signals are sent to the brain

Why do things taste good? Why do they taste bad?

Hearing• Sound travels as waves

through media (air, water, etc…)

• Eardrum:– Vibrates to changing pressure

from sound waves– Vibrations travel through the

body’s smallest bones(Malleus, Incus, and Stapes)

• Cochlea:– Vibrations from travel into fluid– Fluid activates hire-like receptors

which send impulses to the brain– Ear as a hair for different

frequencies

Hearing (Balance)• Cochlea as 3 semicircular

canals filled with fluid and motion receptors (hair-like)

• Movement in the fluid triggers impulses that tell the brain direction and orientation

• Small Ca+ stones inside also push down on the hairs

Why?-Feel which way is up/down

Touch• A collection of different

receptors:– Temperature– Pressure– Pain

• Different parts of the body have higher concentration of touch sensors– Eyelids, fingers, feet, tongue,

etc…• Some receptors fire faster

than others:– You can feel the texture of an

object before its temperature

Sight• Sight is detecting the photons of light

bouncing of objects– 80% of all you know comes from sight

• Conjunctiva: protective layer; cleaned by lysosome filled tears

• Cornea: transparent cover over eye• Pupil: opening into the eye• Iris: colored membrane that changes

size due to light intensity• Lens: focuses the light to clear the

image; made of clear cells• Retina: special part of the eye that

reacts to photonsImages passing through the lens are flipped and our brain learns to flip them back

Light Level and Depth• Iris muscles circular and

radial muscles change diameter to iris– Low light radial contract to

make wide pupil (dilated)• Need more light

– Bright light circular contract to make narrow pupil (constricted) • Need less light; may damage

receptors in eyes

• Two eyes = two sets of information– Brain compares sets to produce

3D image (depth perception)

Seeing Colors• To see clearly, light must be focused

on the fovea– Center point on the back of the retina;

has most receptors• Rod cells:

detect low levels of light (black and white)• Cone cells:

detect high levels of light (color)S- detect blue lightM- detect green lightL- detect red light

Overlapping signals from cones create the other colors

Accommodation• Focusing the eye so objects at different

distances are clear• Lens elastic clear fluid sac that changes

shape with ciliary muscles • Distant objects:

1) Ciliary relax2) Pressure in eye pulls lens into a thin

elliptical (oval) shape3) Light focused on fovea

• Near objects:1) Ciliary contract2) Lens pulled into thick spherical shape3) Light focused on fovea

• Optic nerve main nerve that send images to the brain– Creates a blind spot cause no receptors

there

Extra Senses• Echolocation: use

sound waves to find objects

• Infrared vision: can see heat of an object

• UV vision: see UV signals

• Electroreception: can sense electric fields

• Magnetoreception: can sense magnetic fields