Transcript The Nervous System

The Nervous
System
Lily Silsby & Emily Alesch
Period 3A
Command and Control Center
● ability to sense and react originated billions of years ago with prokaryotes
o affected their ability to detect environmental changes and respond to
them
o to maximize chances for survival and reproductive success
● this mechanism later became more complex when the Cambrian explosion
occurred
Nervous Systems: Circuits of
Neurons and Supporting Cells
● All organisms except sponges have a nervous system
● simplest animals w/ nervous systems are the cnidarians
o nervous system consists of a simple gastrovascular cavity with nerve
nets that allow it to expand and contract
● in more complex animals like humans, there are both nerve nets and
nerves (bundles of fiberlike extensions of neurons)
Nervous Systems: Circuits of
Neurons and Supporting Cells
● behavior became more complex as nervous systems evolved w/
cephalization (clustering of neurons toward the front (anterior) of the
brain)
● central nervous system (CNS): brain and longitudinal nerve cords
● in more complex organisms there are more complicated brains and ventral
nerve cords with segmentally arranged clusters of neurons---> ganglia
o CNS consists of the brain and spinal cord in vertebrates
o spinal cord runs along the back (dorsal) side of the body
● peripheral nervous system (PNS): nerves that connect the CNS with the
rest of an animal’s body
o PNS consists of nerves and ganglia
Information Processing
● 3 stages of information processing by nervous systems: sensory input,
integration, and motor output
● sensory neurons: transmit info from sensors that detect external stimuli
and internal conditions to the CNS
● once at the CNS, interneurons analyze and interpret sensory input
● motor output leaves CNS via motor neurons, which communicate using
effector cells (muscle/endocrine cells)
● information processing is easiest to study w/ reflexes (automatic
responses to stimuli
Information Processing
● neurons organelles, including the nucleus are located in the cell body
● 2 types of extensions from the cell body: dendrites and an axon
● dendrites: highly branched extensions that receive signals from other
neurons
● axon: longer extension that transmits signals to other cells
● axon hillock: conical region of an axon where it joins the cell body, where
the signals that travel down the axon are generated
● axons are enclosed by a layer called the myelin sheath
● the end of the axon usually divides into branches, each ending in a
synaptic terminal
● site of communication between a synaptic terminal and another cell: a
synapse where info is passed from the transmitting neuron (presynaptic
cell) to the receiving cell (postsynaptic cell) by means of chemical
messengers called neurotransmitters
Supporting Cells (Glia)
● Glia: supporting cells essential for structural integrity of the nervous
system and the normal functioning of neurons
● glia outnumber neurons
● in the CNS, astrocytes provide support for neurons and regulate
extracellular concentrations of ions and neurotransmitters
o astrocytes are able to facilitate info transfer by causing blood vessels
to dilate, increasing blood flood to the area and causing the neurons to
obtain glucose and oxygen more quickly
● blood-brain barrier: during development, astrocytes cause tight junctions
to form between the cells that line the capillary border between the brain
and spinal cord
o this restricts the passage of many substances into the CNS
● radial ganglia form tracks along which neurons migrate to from the neural
tube during embryonic development
o this gives rise to the CNS
● radial ganglia and astrocytes can act as stem cells to form neurons and
other specialized glia
Supporting Glia Cells
● Oligodendrocytes (in CNS) and Schwann cells (in PNS) are glia that form
the myelin sheaths around the axons of many vertebrate neurons
● neurons are myelinated during development in which Schwann cells or
oligodendrocytes grow around the axons, creating many layers of lipid
membrane
o provides electrical insulation for the axon as a poor conductor of
electricity
o helps channel the electrical impulse
Ion pumps and ion channels maintain
a neuron’s resting potential
● all cells have a voltage (electrical potential difference) across their plasma
membrane known as the membrane potential
● membrane potential of a cell is usually between -60 and -80 mV (minus
sign indicates that the inside of the cell is negative relative to the outside)
● membrane potential of a neuron that is not transmitting signals is the
resting potential
The Resting Potential
● resting potential is the membrane potential of a neuron that is NOT
transmitting signals
● solutes tend to diffuse down their concentration gradient from an area of
high concentration to an area of low concentration
● there is a higher concentration of K+ and organic anions in the cytosol than
in the extracellular fluid
● extracellular fluid has a higher concentration of Na+ and Cl- than the
cytosol
● membrane channels are selective for K+, so a separation of charge
develops
● K+ diffuses across the membrane to the extracellular fluid, creating an
electrical gradient that opposes the concentration gradient
● once the electrical gradient and concentration gradients are balanced by
the diffusion of K+, when there is no longer any net diffusion of K+ across
the membrane
● magnitude of the membrane voltage at equilibrium is equilibrium
potential (Eion) given by the Nernst equation
https://www.youtube.com/watch?v=YP_P6bYvEjE
The Resting Potential
● the resting potential is steady, so the K+ and Na+ currents are equal and
opposite
● when the membrane’s permeability to particular ions changes, the
membrane potential can change from its resting value
Gated Ion Channels
● ion channels that are always open are said to be ungated
● gated ion channels open or close in response to stimuli
● stretch-gated ion channels are found in cells that sense stretch and open
when a membrane is mechanically deformed
● ligand-gated ion channels open or close in response to the binding of a
chemical or neurotransmitter to the channel
● voltage-gated ion channels open or close in response to changing
membrane potentials
Quiz: Neurons, Supporting Cells,
Ion Pumps, Resting Potential
1. once info is sent to the CNS,
_____ analyze and interpret
the sensory input.
2. behavior is regulated by
more complicated brains and
ventral nerve cords
containing segmentally
arranged clusters of neurons
called _____.
3. axons in the white matter are
enclosed by a layer known
as the ____.
4. bundles of fiberlike
extensions of neurons
5. membrane potential of
neuron that is not
transmitting signals is the
____.
nerves
resting potential
equilibrium potential
Schwann cells
astrocytes
interneurons
blood-brain barrier
myelin sheath
oligodendrocytes
ganglia
radial glia
Quiz: Neurons, Supporting Cells,
Ion Pumps, Resting Potential
6. _____ are found at synapses and
open or close when a specific
chemical, such as a
neurotransmitter, binds to a channel.
7. ____ open or close when the
membrane potential changes
8. there is a greater concentration of
___ in the cytosol of a neuron at
resting potential.
9. there is a greater concentration of
___ in the extracellular fluid at
resting potential
10. cell that receives a signal via
action potential.
effector cells
reflexes
voltage-gated ion channels
ligand-gated ion channels
Na+
K+
postsynaptic cell
Mg2+
Cu2+
presynaptic cell
glia
motor neurons
Action Potentials: Signals
Conducted by Axons
● hyperpolarization: increase in the magnitude of the membrane potential
○ caused by opening of gated K+ channels
● depolarization: reduction of the magnitude of the membrane potential
○ caused by opening of gated Na+ channels
● graded potentials: changes in membrane potential
● threshold: a certain membrane voltage that triggers an action potential
which is an all-or-none phenomenon; signals that carry info along axons
● info is encoded by action potential frequency
● voltage-gated Na+ and K+ channels are opened by depolarizing the
membrane to produce an action potential
● 1. at resting potential Na+ activation gate is closed; inactivation gate is
opened
● 2. depolarization occurs when the activation gate for Na+ quickly opens
and the inactivation gate slowly closes, allows Na+ to diffuse into the
neuron
● 3. K+ only has an activation gate, which is slowly opened by depolarization
https://www.youtube.com/watch?v=7EyhsOewnH4
Production of Action Potentials
● when a stimulus triggers membrane depolarization, Na+ activation gates
open = more Na+ diffuses into the cell
● rising phase: when threshold is crossed membrane potential is brought
close to ENa
● membrane potential never actually gets to ENa b/c the inactivation gates
close, blocking the influx of Na+ AND the activation gates of K+ open
o this brings the membrane potential back toward EK (falling phase)
● undershoot phase: when the membrane potential is closest to EK; closer
than at resting potential
● then membrane potential returns to resting potential after the action
potential is produced
● there is a “downtime” following the production of the action potential in
which a second action potential cannot be stimulated; known as the
refractory period
o this is when the Na+ activation channels remain closed during the
falling phase and the early undershoot phase
Conduction of Action Potentials
● action potentials regenerate themselves along the length of an axon
● the initial Na+ influx during the rising phase depolarizes the axon
membrane
o creates a positive charge inside the axon, enough to cross the
threshold
o recreates the action potential
● when Na+ inactivation channels close, K+ crosses membrane from the
inside of the axon to the extracellular fluid during repolarization
o creates a negative charge within the axon and a positive charge
outside of the axon
● action potential can only move forward, toward the synaptic terminals
Conduction Speed
● larger axon diameter = faster conduction = less electrical current
resistance
● myelin sheath increases action potential conduction speed by insulating
axon membrane
● allows depolarization to spread farther along the axon interior
● brings membrane potential to the threshold sooner
● myelination allows space efficiency
● voltage-gated Na+ and K+ channels are concentrated at myelin sheath
gaps called nodes of Ranvier
● action potentials are regenerated at the nodes of Ranvier because this is
where the axon comes in contact with the extracellular fluid
● saltatory conduction:mechanism in which action potential appears to
jump from node to node
Neurons communicate at the
synapses
● information is transmitted at the synapses
● electrical synapses contain gaps that DO allow electrical current to flow
directly from cell to cell
● most synapses are chemical synapses, involving the release of a
chemical neurotransmitter by a presynaptic neuron
● then presynaptic neuron synthesizes and packages the neurotransmitter
into the synaptic vesicles, within the synaptic terminals
● action potential depolarizes the terminal membrane, triggering voltagegated Ca2+ to diffuse into the terminal buttons
● the rise in Ca2+ concentration causes the synaptic vesicles to fuse with the
terminal membrane through exocytosis
● then neurotransmitter diffuses across the synaptic cleft
https://www.youtube.com/watch?v=LT3VKAr4roo
Direct Synaptic Transmission
● direct synaptic transmission: when neurotransmitters bind to receptors
on the postsynaptic neuron, allowing certain ions to diffuse across the
postsynaptic membrane
● postsynaptic potential: change in the membrane potential of the
postsynaptic cell
o allows Na+ and K+ to diffuse across the membrane
● excitatory postsynaptic potential: depolarization of the membrane
potential toward the threshold (ESPSs)
● when an inhibiting neurotransmitter binds to the postsynaptic channels, the
membrane becomes selective for K+
o causes the membrane to hyperpolarize→ known as inhibitory
postsynaptic potentials (IPSPs)
o membrane potential is moved farther from the threshold
Summation of Postsynaptic
Potentials
● greater the amount of neurotransmitter, the greater the magnitude of the
postsynaptic potential
● postsynaptic potentials DO NOT regenerate, but requires 2 ESPSs to
occur in rapid succession
o has to occur before the postsynaptic neuron potential has returned to
action potential to create temporal summation
● simultaneous ESPSs created by different synapses can add together when
received by the same postsynaptic neuron (spatial summation)
o to cause an action potential to be generated at the postsynaptic
neuron axon hillock
Indirect Synaptic Transmission
● indirect synaptic transmission: when a neurotransmitter binds to a
receptor that is not part of an ion channel
● activates a transduction pathway
Neurotransmitters
● acetylcholine: can be inhibitory or excitatory, depending on the receptor
● reduces the rate and strength of contraction of cardiac muscle cells
● biogenic amines are derived from amino acids
o includes epinephrine and norepinephrine which function as
hormones
o often involved in indirect synaptic transmission
o includes serotonin and dopamine which affect sleep, mood, learning,
and attention
● lack of dopamine in the brain = degenerative illness Parkinson’s disease
● psychoactive drugs such as mescaline and LSD produce their
hallucinatory effects by binding to the same receptors as serotonin and
dopamine
● antidepressant drugs increase concentrations of biogenic amines like
serotonin and norepinephrine
o ie Prozac
Amino Acids and Peptides
● CNS neurotransmitters: gamma aminobutyric acid (GABA), glycine,
glutamate, asparate
● GABA produces ISPSs by increasing postsynaptic membrane permeability
to Cl● neuropeptides are short chains of amino acids that function as
neurotransmitters
● neuropeptide substance P: key excitatory neurotransmitter that mediates
pain perception
● endorphins function as natural analgesics, decreasing pain perception
o produced during times of severe physical or emotional stress
o also produce euphoria and decrease urine output
Gases
● some neurons release dissolved gases, such as NO and CO
● CO regulates hypothalamic hormones (CNS)
o CO functions as a neurotransmitter that hyperpolarizes intestinal
smooth muscle cells
● cells synthsize NO and CO on demand (not stored in the terminal buttons
in vesicles)
o they diffuse into target cells, induce a change, then get broken down
Regionally specialized nervous
system
● spinal cord integrates simple responses to stimuli (like reflexes)
o also conveys info to the brain
● central canal of spinal cord and 4 brain ventricles filled w/ cerebrospinal
fluid (provides nutrients and hormones to brain; important for cushioning)
● white matter: axons in the CNS w/ myelin sheaths
● gray matter: dendrites, unmyelinated axons, cell bodies
Peripheral Nervous System
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PNS transmits info to and from the CNS
cranial nerves: in head and upper body
spinal nerves extend from spinal cord to parts below the head
PNS divided into somatic nervous system and autonomic nervous
system→ work tog to maintain homeostasis
somatic nervous system carries impulses to and from skeletal muscles in
response to external stimuli
autonomic nervous system regulates internal environment by controlling
smooth cardiac muscles and organs of the endocrine, digestive,
cardiovascular, and excretory systems
consists of sympathetic, parasympathetic, and enteric divisions
sympathetic division--fight or flight response; arousal and energy
generation
parasympathetic division--calming and returning of self-maintenance
enteric division--neurons control digestive tract, gallbladder, and
pancreas secretions
Embryonic Development of the Brain
● forebrain, midbrain, and hindbrain become evident as the embryo
develops
● regionalization increases capacity for complex integration
● forebrain: telencephalon and diencephalon develop
● midbrain: mesencephalon develops
● hindbrain: myelencephalon and metencephalon develop
● telencephalon gives rise to cerebrum
● cerebral cortex outer portion of the the cerebrum that develops to
surround much of the brain
● brainstem: consists of midbrain, pons, and medulla
Brainstem
● evolutionarily older
● 3 parts: medulla oblongata, pons, midbrain: all function in homeostasis,
coordinating movement, and conducting info to higher brain centers
● medulla oblongata controls visceral functions like breathing, heart rate,
blood circulation, digestion
● pons regulates breathing centers in the medulla
● axons carry movement instructions from one side of CNS to other in the
medulla
● midbrain: receives, sends, and integrates sensory info
Arousal and Sleep
● reticular formation includes the reticular activating system (RAS) that
regulates sleep and arousal
● sensory filter of info to the cerebral cortex
● melatonin--dietary supplement to treat sleep disturbances
● SLEEP: involved in consolidation of learning and memory
Cerebellum and Diencephalon
● cerebellum develops from metencephalon; involved in coordination and
error-checking
o learning and remembering motor skills
o integrates sensory and motor info to coordinate movement and
balance
● diencephalon develops into epithalamus, thalamus, and hypothalamus
o epithalamus includes pineal gland and choroid plexus (produces
cerebrospinal fluid from blood
o thalamus is input center for sensory and motor info going to and from
the cerebrum
 also regulates emotion and arousal
● hypothalamus--homeostatic regulation; regulates basic survival
mechanisms
Circadian (daily) Rhythms
● biological clock: internal timekeeper; maintains circadian rhythms
● superchiasmatic nuclei (SCN): biological clock which is a pair of
hypothalamic structures, requires external cues
● human biological clock has a cycle length of 24 hrs and 11 min
Cerebrum
● is divided into right and left cerebral hemispheres
● consists of outer gray matter (cerebral cortex), internal white matter, and
groups of neurons known as basal nuclei
● basal nuclei for planning and learning movements
● cerebral cortex: sensory info is analyzed, motor commands are issued,
language is generated
● neocortex: outermost part of the cerebrum w/ a convoluted surface area
● corpus callosum: enables communication b/t right and left cerebral
cortices
Cerebral cortex = voluntary
movement & cog functions
● sensory info directed via thalamus to primary sensory areas
o visual info to occipital lobe
o auditory input to temporal lobe
o somatosensory info to parietal lobe
● cerebral cortex can generate motor commands by producing action
potentials in the primary motor cortex
Lateralization of Cortical
Function
● left hemisphere = language, math, logic, focused perception
● right hemisphere = pattern recognition, spatial relations, nonverbal
thinking, emotional processing, whole context
Language, Speech, Emotions
● Broca’s area: active during generation of speech
● Wernicke’s area: active when speech is heard
● emotions involve limbic system which includes amygdala, hippocampus,
and olfactory bulb
o attaches “feelings” to basic survival functions controlled by brainstem
o emotional bonding
● amygdala recognizes emotional info and emotional meaning of facial
expressions
o preserves emotional memories
● primary emotions like pleasure and fear require prefrontal cortex
o ie Phineas Gage
Memory and Learning
● short-term memory holds info, anticipation, goals in frontal lobes, then
releases if irrelevant
● long-term memory for retaining knowledge, requires the hippocampus
● recall: info fetched from LTM and returned to STM
● process enhanced by rehearsal
● slow learning of new skills and procedures = neurons make new
connections
Cellular Mechanisms of Learning
● long-term potentiation (LTP): increase in synaptic transmission strength
when presynaptic neurons produce brief, high-frequency series of action
potentials
o can last for days/weeks
o occurs in hippocampus when presynaptic neurons release excitatory
neurotransmitter glutamate
 binds to the postsynaptic neuron AMPA and NMDA receptors
 both ligand and voltage gated
 so glutamate must be bound AND membrane must be
depolarized
Consciousness
● broad & subjective
● fMRI allows conscious and unconscious info processing to be compared
Nerve Cell Development
● growing axon is directed and redirected by molecular signposts
● growth cone: responsive region at the leading edge of the growing axon
● signal molecules released by cells along growth route bind to receptors on
plasma membrane of growth cone
o triggers a transduction pathway
o developing axon expresses different genes at different time of
development
Neural Stem Cells
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human brain DOES produce new neurons in adulthood
new neurons come from stem cells
unspecialized cells that continue to divide
goal: to get neural progenitor cells to differentiate into neurons or glia
where and when needed
● goal: transplant cultured neural progenitor cells into damaged CNS
Diseases and Disorders of the
Nervous System
● schizophrenia: severe mental disturbance characterized by psychotic
episodes in which patients lose ability to distinguish reality
● hallucinations & delusions
● 2 types of depressive illnesses: bipolar disorder and major depression
● bipolar disorder: swings of mood from high to low
o manic phase: high self-esteem, increased energy, flow of ideas,
overtalkativeness, recklessness, creativity
o depressive phase: loss of interest, worthlessness
● major depression: low mood
o anit-depressants increase activity of biogenic amines
Diseases and Disorders of the
Nervous System
● Alzheimer’s disease (AD): mental deterioration
o involves confusion, memory loss
o progressive illness
o personality changes
o lose ability to recognize people
o neurons die, brain tissue shrinks
o neurofibrillary tangles: bundles of degenerated neuronal and glial
processes
o senile plaques: aggregates of beta-amyloid (insoluble peptide)
 membrane enzymes called secretases cause beta-amyloid to
accumulate outside neurons and collect in plaques
Disorders and Diseases of the
Nervous System
● Parkinson’s disease: motor disorder characterized by difficulty initiating
movements, slowness of movement, rigidity
o progressive illness
o from death of neurons in the midbrain nucleus known as substantia
nigra
 substantia nigra neurons release dopamine
● lack of substantia nigra = accumulation of alpha-synuclein
protein aggregates
● L-dopa
Transduction of Stimulus Energy and
Transmittance of Signals to CNS
● Information is transmitted through the nervous system by nerve impulses,
or action potentials.
● Sensations are action potentials that reach the brain via sensory
neurons, giving the perception of the stimuli.
● Sensations and perceptions begin with sensory reception (the
detection of a stimulus by sensory cells, called sensory receptors.)
● Exteroreceptors: sensory receptors that detect stimuli coming from
outside the body (heat, light, pressure, chemicals, etc.)
● Interoreceptors: detect stimuli from inside the body (blood pressure,
body position.)
● Stimuli are forms of energy, and sensation is the conversion of this
energy into a change in sensory receptor’s membrane potential,
leading to the change in frequency of the action potentials
transmitted to the CNS.
● During this process, sensory receptors go perform the functions of
sensory transduction, amplification, transmission, and integration.
Transduction of Stimulus Energy and
Transmittance of Signals to CNS
● Sensory Transduction: the conversion of stimulus energy into a change in
the membrane potential of a sensory receptor.
o change in the membrane potential itself is receptor potential
● Amplification: the strengthening of stimulus energy by cells in sensory
pathways.
o amplification may take place in sensory receptors or accessory
structures of a complex sense organ
● Transmission: the movement of the action potentials to the central nervous
system
o the magnitude of a receptor potential affects the frequency of action
potentials that travel as sensations to the CNS.
● Integration: the processing of sensory information, beginning as soon as
the information in received.
o another type of integration is sensory adaptation, the decrease in
responsiveness during continued stimulation.
Transduction of Stimulus Energy and
Transmittance of Signals to CNS
● 5 types of sensory receptors: mechanoreceptors, chemoreceptors,
electromagnetic receptors, thermoreceptors, and pain receptors.
● Mechanoreceptors: sense physical deformation caused by stimuli such as
pressure, touch, stretch, motion, and sound (forms of mechanical energy)
o Bending/stretching of the mechanoreceptors’ plasma membranes
increases the membrane’s permeability to sodium and potassium ions,
resulting in depolarization.
● Chemoreceptors: includes both general receptors that transmit information
about the total solute concentration of a solution and specific receptors that
respond to individual kinds of molecules.
● Electromagnetic Receptors: detect various forms of electromagnetic
energy, such as visible light, electricity, and magnetism.
o Photoreceptors: electromagnetic receptors that detect radiation
(visible light)
● Thermoreceptors: (respond to heat or cold) help regulate body
temperature by signaling both surface and body core temperature.
Transduction of Stimulus Energy and
Transmittance of Signals to CNS
● Pain Receptors: (also called nociceptors) a class of naked dendrites in the
epidermis.
o Chemicals that trigger pain include histamine and acids;
prostaglandins increase pain by sensitizing receptors (lowering their
threshold), aspirin and ibuprofen reduce pain by inhibiting
prostaglandin synthesis.
Mechanoreceptors Involved with
Hearing/Equilibrium
● Hearing and the perception of balance are related in most animals, both
involving mechanoreceptors to produce receptor potentials.
Invertebrates:
● Statocysts: sensory organs that contain mechanoreceptors and function as
invertebrates’ sense of equilibrium.
● Statoliths: grains of sand or other dense granules contained in a layer of
ciliated receptor cells surrounded by a chamber.
● Statoliths settle at the low point of the chamber, stimulating receptors in
that location, which provides the brain with information about the
orientation of the body with respect to gravity.
Mammals: Hearing and equilibrium are closely associated in the ear.
Hearing:
● Vibrating objects create percussion waves in the surrounding air,
causing the tympanic membrane to vibrate with the same frequency
as the sounds
o volume: loudness, determined by amplitude
o pitch: function of a sound wave’s frequency, or number of
vibrations a second
Mechanoreceptors Involved with
Hearing/Equilibrium
Equilibrium:
● Organs in the inner ear of humans and most mammals detect body
position and balance
Other Vertebrates: Fish and aquatic amphibians also have inner ears located
near the brain, except their ears have no eardrums and don’t open to the
outside of the body.
● Fish and aquatic amphibians have a lateral line system, which
contains mechanoreceptors that detect low-frequency waves.
● In terrestrial vertebrates, the inner ear has evolved as the main organ
of hearing and equilibrium.
Senses of Taste and Smell
● Many animals use their chemical senses to find mates, recognize territory,
and navigate during migration.
● The perceptions of gustation (taste) and olfaction (smell) are both
dependent on chemoreceptors that detect specific chemicals in the
environment.
● Taste is the detection of chemicals in a solution and smell is the detection
of chemical carried through the air.
Taste in Humans:
● The receptor cells for taste in humans are epithelial cells organized into
taste buds, which are scattered in several areas of the tongue and mouth.
● Each taste receptor can be stimulated by a broad range of chemicals but is
most responsive to a particular type of substance.
Smell in Humans:
● Olfactory receptor cells are neurons that line the upper portion of the nasal
cavity and send impulses along their axons directly to the olfactory bulb of
the brain.
● When odorous substances diffuse into this region, they bind to proteins
called Odorant Receptors (ORs), generating action potentials.
Vision
Invertebrates
● Most have a light-detecting organ, one of the simplest being the ocellus of
planarians, which provides information about light intensity and direction
but does not form images.
● There are 2 major types of image-forming eyes in invertebrates: compound
eyes and single-lens eyes.
● Compound eyes are found in insects and crustaceans and in some
polychaete worms.
o consists of several thousand light detectors called ommatidia, each
with its own light focusing lens.
o extremely capable of detecting movement
● Single-lens eyes are found in some jellies, polychaetes, spiders, and many
molluscs.
o works on a camera like principal; light enters the pupil, the iris
changes the diameter of the pupil, and a single lens focuses on a
layer of photoreceptors.
o Muscles in an invertebrate’s single-lens eye move the lens back and
forward to focus on objects at different distances.
Vision
Vertebrates
● Similar to the single-lens eye of invertebrates, vertebrates’ eyes are also
camera-like.
● The eyeball consists of a white outer layer of connective tissues called the
sclera and a thin, pigmented inner layer called the choroid.
● The conjunctiva covers the sclera and keeps the eye moist. The sclera
becomes the transparent cornea at the front of the eye. The iris gives the
eye its color.
● The changing of the iris’ size regulates the amount of light entering the
pupil. Inside the choroid, the retina contains the photoreceptors.
● The lens and ciliary body divide the eye into an anterior and posterior
cavity.
● The ciliary body produces the clear, watery aqueous humor that fills the
anterior cavity. The posterior cavity is filled with the jellylike vitreous
humor.
● The human retina contains about 125 million rods and 6 million cones.
● Rods are more sensitive to light but do not distinguish color, whereas
cones can distinguish color in daylight.
● Fovea: center of the vision field
Processing Visual Information
● Processing of visual information begins in the retina, where cones and rods
make synapses with neurons called bipolar cells.
● In the dark, rods and cones depolarize, and continually release the
neurotransmitter glutamate.
● The glutamate release depolarizes some bipolar cells and hyperpolarizes
others.
● In the light, rods and cones hyperpolarize, shutting off glutamate release.
● In response, depolarized bipolar cells hyperpolarize, and those hyperpolarized
by glutamate depolarize.
● Ganglion cells, horizontal cells, and amacrine cells also contribute to the
processing of information in the retina.
● Ganglion cells synapse with bipolar cells and transmit action potentials to the
brain via axons in the optic nerve.
● Horizontal cells and amacrine cells help integrate the information before it is
sent to the brain.
● Lateral inhibition sharpens the edges and enhances the contrast in an image.
This process is repeated by the interaction of the amacrine cells and ganglion
cells and occurs at all levels of visual processing in the brain.
Vision
● Axons in the optic nerves are routed at the optic chiasm (at the base of the
cerebral cortex) such that sensations from the left visual field of both eyes
are transmitted to the right side of the brain, and the sensations from the
right visual field are transmitted to the left side of the brain.
● Point-by-point information in the visual field is projected along neurons
onto the visual cortex.
● At least 30% of the cerebral cortex takes part in formulating what we
actually “see.”
Animal Skeletons and Support,
Protection, and Movement
● Underlying the diverse forms of behavior in animals are common
fundamental mechanisms, they all result from muscles working against
some type of skeleton.
Hydrostatic Skeletons
● consists of fluid held under pressure in a closed body compartment.
● This is the main type of skeleton for most cnidarians, flatworms,
nematodes, and annelids. These animals control their form and
movement by using muscle to change the shape of fluid-filled
compartments.
● Peristalsis is the type of movement on land produced by rhythmic
waves of muscle contractions passing from front to back.
Exoskeletons
● this is a hard encasement deposited on the surface of an animal.
● As the animal grows, it enlarges the shell by adding to the outer edge.
● The jointed exoskeleton is a cuticle, a nonliving coat secreted by the
epidermis.
● 30-50% of the cuticle consists of chitin, a polysaccharide similar to
cellulose.
Animal Skeletons and Support,
Protection, and Movement
Endoskeletons
● consists of hard supporting elements, such as bones, buried within the
soft tissues of an animal.
● Echinoderms have hard plates called ossicles beneath the skin.
● Chordates have endoskeletons consisting of cartilage, bone, or some
combination of these materials.
● The mammalian skeleton is built from more than 200 bones, some
fused together and other connected at joints to facilitate movement.
Locomotion
● Locomotion is the travel from place to place.
● Most animals are mobile and spend a considerable amount of time and
energy actively searching for food, escaping danger, and looking for
mates.
● Locomotion requires an animal to expend energy to overcome gravity and
friction, requiring energy-consuming cellular work.
Swimming
● Most animals are reasonably buoyant in water, allowing them to
overcome gravity better than species on land and in air.
● Water is also more viscous than air, so drag (friction) is a problem, but
a fusiform shape (torpedo-like) is an adaptation of fast swimmers.
● Animals swim in different ways; some insects use their legs as oars,
some squids, scallops and cnidarians are jet-propelled, sharks and
bony fish move their body and tail from side to side, and whales and
other aquatic mammals move by undulating their body and tail up and
down.
Locomotion
Locomotion on Land
● Crawling, walking, running, or hoppings animals must be able to
support itself and overcome gravity, but air poses little resistance.
● An animal’s leg muscles expend energy both to propel it and to keep it
from falling down.
● Maintaining balance is another prerequisite for walking, running or
hopping. Tails help an animal keep balance during movement.
o Bipedal animals, such as humans and birds, keep part of at least
one foot on the ground when walking.
o When running, the momentum allows for all four feet (or 2) to be
off the ground at once.
● A crawling animal must exert energy to overcome friction.
o Ex: earthworms crawl by peristalsis and snakes crawl by
undulating their entire body from side to side.
Flying
● wing shape important for lift to alter air currents and help stay aloft
● light body mass
● fusiform (spindle-shaped) shape reduces drag
Locomotion
Comparing Costs of Locomotion
● swimming is most energy-efficient mode of locomotion
● total amount of expended energy in locomotion is GREATER for larger
animal
● structural and behavioral adaptations that maximize efficiency of
locomotion increase evolutionary fitness
Quiz
Short Answer:
1. Name 3 examples of exteroreceptors.
2. State the differences between statocysts and statoliths.
3. What do compound eyes consist of and what are they capable of doing?
4. What types of cells contribute to information processing in the retina?
5. What is the type of movement produced by muscle contractions?
Matching:
pupil
choroid
vitreous humor
ciliary body
conjunctiva
rods
fovea
cones
aqueous humor
6. white outer layer of connective tissue
7. covers sclera and keeps eye moist
8. divides eye into anterior and posterior cavities
9. clear watery liquid that fills the anterior cavity
10. jellylike substance filling the posterior cavity
iris
cornea
sclera
retina