AP Bio- Communication 5: Sensation, Integration, Response

Integration

The Brain

Structure

Development of the human brain

One Glial Cell

Fundamentally, the Brain consists of

• Glial cells (astrocytes)
• 100 billion neurons- perhaps 500 trillion synapses

Like an onion!

EMG of Cerebral Cortex

Brainbow staining of neurons

one neuron

Gray matter = cell bodies, nerve terminals, dendrites

White matter = axons

Brain Damage?

Roughly: It is still hard to predict the effect that brain damage will have on an individual.

Phineas Gage:

lived for 12 years following this injury

Though his personality changed drastically

Evidence of neural stem cells in a mouse hippocampus.

Plasticity!

Microscopic image of human cerebral cortex showing the delineation between gray matter and white matter.

Function

Alzheimer's Disease: Associated with destructive protein plaques in the brain.

Is it "brain damage"?

The Brain Has Specific Sections

?

Different Regions of the Brain Are Active for different tasks

Human vs. Avian Brain

Medulla/Pons- Autonomic System

Cerebellum- Balance, coordination

Cerebrum- "Higher order" functions

Lots of "Black Boxes" left:

fMRI showing word-related brain activity

2 "hemispheres" of the brain

Diencephalon: Seat of Endocrine Control

Different cerebral regions participate in different functions

Mental Illness?

Learning/Memory?

Roughly: Disruptions in normal neurotransmitter release and reuptake contributes to mental illness.

Some mental illnesses seem to have a genetic component.

Much better understanding & treatment than 50 years ago!

Roughly: The more used a synaptic pathway is, the more firm that pathway becomes

Synapses are plastic (meaning "flexible")!

Long Term Potentiation: A lasting synaptic connection.

Amygdala-

involved in emotional response

Nucleus Accumbens-

involved in reward response

Somatosensory & Motor Cortexes route from/to different regions of the body.

Dolphins sleeping one hemisphere at a time

The Nervous System

Human Nervous System

Response

Sensation

Reflex Actions Do Not Require CNS Processing (only relay)

Why?

How To Respond?

Muscle Structure

Evolutionary Progression of Nervous System complexity.

• Nerve net: No CPU
• Development of Central Nervous system, & Brain
• Cephalization of sensory organs.

Touch

What is Sense?

Typical Muscle Structure:

Major animal Response:

• Muscle!

Major divisions:

• Central vs. Peripheral
• Afferent vs. Efferent
• Autonomic vs. Motor
• Parasympathetic vs. Sympathetic

Fundamentally, sensation requires three things:

1. A stimulus must be detected by a sensory receptor.

2. The sensor must translate the stimulus into a nervous signal (an action potential).

3. The signal must be interpreted by the central nervous system (the brain).

All sensory apparatus have these three things in common!!!

Touch sensations are mediated by receptors in the skin.

There are many kinds of receptors in the skin:

• temperature receptors
• pain receptors
• pressure receptors
• hair movement receptors.

These are what people mean by

"nerve endings".

3 Kinds:

• Skeletal- voluntary motion
• Smooth- lines organs, involuntary
• Cardiac- heart, independent

Only skeletal is under conscious control!

Each muscle is bundle of muscle fibers

Each fiber is a bunch of multinucleated cells.

Each cell has a collection of myofibrils

Each myofirbril is packed with actin (thin) and myosin (thick) filaments, arranged in "sarcomeres"

Skeletal muscles are arranged in "antagonistic" pairs.

• Extensor & Flexor

Muscle cells do two things:

• Contract
• Relax

That's it!

Since action potentials are binary, the spatial and temporal pattern of signals is what determines the sensation

The sensory receptor is either:

• the first ("afferent") neuron in the signaling pathway

• or it regulates the afferent neuron through neurotransmitter release.

Muscle fiber (nuclei in blue)

Muscle fiber (nuclei in purple)

Human Skeleton

Muscle Function

Sight

Sound

The "Sliding Filament" Model

Sight is mediated by photoreceptors in specialized organs ("eyes")

Sound is mediated by receptors that vibrate in response to sound waves

Big Questions:

Why Can We Run So Fast?

The Mammalian Ear

Eyespots in Planaria

Calcium ions must be present in the sarcomere, and bonded to tropomyosin for myosin to bond to actin.

Calcium is stored in a region of the sarcomere called the "sarcoplasmic reticulum"

The Vertebrate Eye

ATP is hydrolyzed to move myosin between active (high energy) and inactive (low energy) conformations

Active: Myosin bonds to actin (forming a "cross bridge") and pulls it towards the middle of the sarcomere.

Inactive: Myosin remains attached to actin until ATP hydrolysis occurs again.

"Sliding fillament": Actin and myosin slide past each other.

Very primitive.

The planarian brain drives movement as long as light is shining on either eyespot (ocellus).

This causes negative phototaxis (movement away from light).

The ocellus only allows light from above to interact with neurons

The ear consists of a canal to direct soundwaves, and a series of bones and organs that interpret those waves as heard sound.

Much of hearing is due to hair cells that line the cochlea and vibrate at particular frequencies.

These vibrations stimulate afferent neurons.

The human skeleton is an endoskeleton made of bone tissue.

During early life, bones grow.

Bones are awesome!

Living Bone is constantly broken down and reformed by populations of bone stem cells.

Some bone tissue ("marrow") is also the site of blood cell production.

Joints: Connections between bones.

How do nervous systems help animals coordinate and control their physiology?

How is the structure of the brain related to its functions?

Why do most responses in animals rely upon the skeletal/muscular system?

The nervous system interfaces with muscle tissue at modified synapses called "neuromuscular junctions".

The release of Acetylcholine into the NMJ is responsible for calcium ion release into the sarcomere.

"Motor neruons" terminate at NMJ's

Total muscle contraction ("Tetanus") is only initiated when enough motor units are activated ("twitch summation")

Compound Arthropod Eye

Hair cells and ear anatomy are also involved in the detection of spatial positioning of the body and subsequently balance

Each eye contains many individual facets.

Each facet has one fixed lens and one photoreceptor

Light is focused by a lens onto the retina lining the back of the eyeball.

The retina translates light into nervous signals.

Information from each eye is routed to both hemispheres of the brain

Normal hearing range occurs over a logarithmic scale of frequencies, with lower frequency vibrations being interpreted as lower pitch sounds.

Rods interpret the presence/absence of light

Cones respond to different wavelengths of light

Stonefish venom induces involuntary tetanus.

Wear your Flip Flops!

A motor neuron and its NMJ's are called a "motor unit"

UV illumination of some flowers suggests adaptation for arthropod pollinators

Schematic of retina

Arthropod hearing is typically mediated by tympanic membranes on the the forelegs of the organism

Make Sure You Can

Any Questions?

Other Senses

Chemicals

Movement

Other Skeletons

Animals have three options

There are many examples of senses that are present in other animals but are absent in humans

All Vertebrates have endoskeletons.

Advantage: Internal-grows with the organism

Disadvantage: Interntal- soft flesh on top

Chemoreception in animals is mediated through taste and smell

Most animals sense the environment predominantly through chemoreception

Many reptiles have infrared radiation receptors

Compare the major sensory apparati used by mammals and other animals.

Explain the relationships between the major divisions of the mammalian nervous system.

Explain the relationships between the major divisions of the human brain

Explain the causes of nervous system disruptions and how disruptions of the nervous system can lead to disruptions of homeostasis.

Explain how the skeletal-muscular system functions at the system and cellular levels.

Explain the sliding filament model of muscle contraction

Explain the causes of sensory and motor system disruptions and how those disruptions can affect homeostasis

There are energy considerations

The lateral line system in fish detects energy signatures (currents, sound, etc) in water

Smell

Taste

Arthropods and molluscs have exoskeletons ("shells")

Advantage: Protects all soft tissue beneath.

Disadvantage: Doesn't grow with the organism, must be periodically shed ("molting")

Taste is mediated by taste buds in the tongue

Fly

Run

Swim

I'ma get my molt on

Chitin!

Calcium Carbonate!

Taste buds interpret different molecules as different tastes

"Food" tastes "good"

Bats and cetaceans use sonar systems

Smell is interpreted when molecules ("odorants") interact with receptors on the cell membranes of chemoreceptors that protrude from the olfactory bulb of the brain.

Human sense of smell is vastly less pronounced than that of typical mammals.

Smell is important for taste as well, as odorants are released into the nasal cavity when food is chewed.

Annelids have a hydostatic skeleton.

No Bones (good for squishiness)

Structure is maintained by internal pressure.

Many insects have chemoreceptors on their antennae which are particularly sensitive to mating pheromones

Genetic variance is demonstrated to be responsible for some differences in taste preferences.