Nervous Systems
Nervous Systems
Evolution of the Nervous
System
• Nerve Net
– Cnidarian, Ctenophora
• Nerve Ring with radial nerves
– Echinodermata
• Bilateral Nervous Systems
– Cephalization (ganglia or brain)
– Nerve cord
Evolution of the Nervous
System
• Bilateral Nervous Systems
– Ganglia and two or more longitudinal nerve
cords
• platyhelminthes, some mollusca
– Ganglia (brain) and ventral nerve cord
• annelida, arthropoda, some mollusca
– Brain and dorsal nerve cord
• chordata
Overview of a Nervous
System
Overview of a Nervous System
• Sensory Input
– conduction of signals from sensory
receptors
– PNS
• Integration
– environmental information is interpreted
– CNS (brain and spinal cord)
• Motor Output
– conduction of signals to effector cells
– PNS
Neurons
Neurons
• Cell body
– nucleus and organelles
• Dendrites
– short and branched
– toward cell body
• Axons
– long and unbranched
– away from cell body
Axons
• Myelin Sheath - insulating layer
• Node of Ranvier - gaps between Schwann
Cells
• Synaptic Terminals - neuron ending
Clusters of Neurons
• Ganglion
– Cluster of nerve cell bodies in the PNS
• Nuclei
– Cluster of cells in the brain
Supporting Cells
• Glia (glue)
– Astrocytes (structural support)
• Creates tight junctions and forms the blood-brain barrier
– Radial Glia
• Form tracks for new neurons formed in the neural tube
– Oligodendrocytes
• Form myelin sheath in brain
– Schwann Cells
• Form myelin sheath in the PNS
Reflex
• Sensory
neuron
to a
motor
neuron
Neural Signals
• Membrane Potential
• Sodium-Potassium Pump
Threshold Potential
Resting State
• Both sodium
and
potassium
activation
gates are
closed
• Interior of
cell is
negative
Depolarization State
• Sodium
activation
gates are
opened on
some
channels
• Interior of
cell
becomes
more
positive
Rising Phase of Action Potential
• Most sodium
activation
gates are
opened
• Potassium
activation
gates are still
closed
Falling Phase of Action Potential
• Inactivation
gates on
sodium
channels are
closing
• Activation
gates on
potassium
channels are
opened
• interior of cell
becomes more
negative
Undershoot
• Both gates to
sodium
channels are
closed
• Potassium
channels are
closing
• Membrane
returns to its
resting state
Propagation of
the Action
Potential
• Localized event
• First action
potential’s
depolarization sets
off second action
potential
• Travels in one
direction due to
refractory period
Salatory Conduction
• Action Potential jumps from node to node
• Speeds up signal from 5 m/sec to 150
m/sec
Communication Between
Synapses
• Electrical Synapses
– gap junctions allow for direct transfer of action
potential (used during escape responses)
• Chemical Synapses
– uses neurotransmitters
Chemical Synapse
Chemical Synapses
• Action potential triggers an influx of calcium
• Synaptic vesicles fuse with presynaptic
membrane
• Neurotransmitter released into synaptic cleft
• Neurotransmitters bind to receptors and
open ion channels on postsynaptic
membrane which sets off new action
potential
• Neurotransmitters are degraded by enzymes
or removed by a synaptic terminal
Neurotransmitters
Postsynaptic Potentials
Postsynaptic Potentials
• Subthreshold
– doesn’t reach threshold
• Temporal Summation
– two signals do not reach threshold level but
occur close enough to set off action
potential
• Spatial Summation
– two signals are set off at the same time
setting off an action potential
• Spatial Summation with an inhibitor
– doesn’t reach threshold
Vertebrate
Nervous
System
Central Nervous System
• Ventricles (4)
– Cerebrospinal
fluid
• White Matter
– Made up of
axons
• Gray Matter
– Made up of
dendrites
Peripheral Nervous System
Peripheral Nervous System
• Autonomic Nervous System regulates the
internal environment (usually involuntary)
• Somatic Nervous System regulates the
external environment (usually voluntary)
Autonomic Nervous System
Autonomic Nervous System
• Sympathetic Division
– Flight or fight response
• Parasympathetic Division
– Rest or digest response
Brain
The Brainstem
• The Medulla Oblongata and
the Pons controls breathing,
heart rate, digestion
• The Cerebellum controls
coordination of movement
and balance
The Midbrain
• The Midbrain receives,
integrates, and projects
sensory information to the
forebrain
The Diencepholon
• Forebrain
– Epithalamus
• Includes the pineal gland and the
choroid plexus
– Thalamus
• conducts information to specific areas of
cerebrum
– Hypothalamus
• produces hormones and regulates body
temperature, hunger, thirst, sexual
response, circadian rhythms
The Telencepholon
• Cerebrum
– with cortex and
corpus callosum
• higher thinking
Cerebrum
Cerebrum
Cerebrum
Limbic System
• Regulates
emotions
– Association
with different
situations is
done mostly
in the
prefrontal
lobe
Memory
• Short Term
– Done in the
frontal lobe
• Long Term
– Frontal lobes
interact with
the
hippocampus
and the
amygdala to
consolidate
Sensory Receptors
•
•
•
•
•
Mechanoreceptors
Pain Receptors
Thermoreceptors
Chemoreceptors
Electromagnetic Receptors
Sensory Receptors
• Mechanoreceptors
• Pain Receptors
• Thermoreceptors
Sensory Receptors
• Chemoreceptors
Sensory Receptors
• Electromagnetic receptors
Evolution of the
Eye
• Complex eyes
have developed
many times
Evolution of the
Eye
•
All light-sensitive organs
rely on photoreceptor
systems employing a
family of proteins called
opsins. Further, the
genetic toolkit for
positioning eyes is
common to all animals:
the PAX6 gene controls
where the eye develops
in organisms ranging
from mice to humans to
fruit flies
Photoreceptors
• Eye cups
(ocelli) - light
detection
• Genetic basis
that started as a
light detector
600 mya
• During the
Cambrian
explosion
around 540 mya
two types of
eyes arose
Photoreceptors
• Compound Eyes made up of
ommatidia that helps
detect movement
Photoreceptors
• Camera Type Eyes
– Evolved several
times
– Hagfish eye
– Lamprey eye
– Jawed vertebrate
eyes
Single Lens Eye
•
•
•
•
•
•
•
•
Sclera (white)
Cornea (clear)
Choroid (pigmented)
Iris (color of eye)
Retina (rods and cones)
Pupil
Fovea (focal point)
Blind spot
Photoreceptors
Scars of Evolution
1. inside out retina
that forces light to
pass through the
cell bodies and
nerves before
hitting the retina
2. blood vessels
across the retina
that cause
shadows
3. nerve fibers that
exit causing a blind
spot
Focusing
• Near vision
– ciliary muscle
contracted
– lens becomes
more spherical
• Distance vision
– ciliary muscle
relaxed
– lens becomes
flatter
Visual Problems
• Near-sightedness (myopia)
– eyeball too long / focal point in front of fovea
• Far-sightedness (hyperopia)
– eyeball too short / focal point behind fovea
• Astigmatism (blurred vision)
– misshapen lens or cornea
Hearing and Equilibrium
Hearing Organ
• Outer Ear
– pinna and the auditory canal
– tympanic membrane
• Middle Ear
– malleus, incus and stapes
– oval window
• Inner Ear
– cochlea with the Organ of Corti
• with a basilar membrane and hair cells
• Eustachian Tube
Sound
• Volume
– amplitude of sound wave
– vibrates fluid in ear and bend hair cells which
generates more action potentials
• Pitch
– frequency of sound wave
Equilibrium
• Utricle and Saccule
• Semicircular Canals
– used to detect body position and movement
Lateral Line
System
• Similar to inner ear
• detects movement of
current, moving
objects
Statocysts
• Equilibrium
• contain
statoliths
Sound Systems in
Invertebrates
• Body hairs that vibrate
– mosquitoes
• Tympanic Membranes
– crickets
Chemoreception
• Taste Buds
– sweet (tip), salty
(behind), sour (sides),
bitter (back of tongue)
Chemoreception
• Olfactory receptors cells
– upper portion of nasal cavity
The Cost of Locomotion
The Cost of Locomotion
• Locomotion must overcome two forces:
– gravity
– friction
• Swimming is more efficient than running
– runner must overcome gravity
• Larger animals travel more efficiently than
smaller animals
• Flight is the most costly (per minute)
Skeletal Structures
• Hydrostatic Skeleton
– (cnidaria, ctenophora, platyhelminthes,
nematoda, annelida)
• Exoskeletons
– mollusca, arthropoda
• Endoskeletons
– chordata
Cooperation of Muscles and
Skeletons
• Muscles always
contract
• Muscles
attached in
antagonistic
pairs
Skeletal Muscles
• Muscles are made up of
muscle fibers
• Fibers are made up of
myofibrils
• Myofibrils are made up of
myofilaments
– thin filaments (actin)
– thick filaments (myosin)
Sliding Filament
Model
• Sacromeres (basic
functioning unit)
– Z lines (border of
sacromeres)
– H zone (center of
sacromere)
– I band (only thin filaments)
– A band (length of thick
filaments)
Sliding Filament
Model
• During contraction, thin
and thick filaments slide
past each other
– I band and H zone
decreases in size
• Caused by myosin
head creating cross
bridge with actin fiber
and then moves by
using ATP
Muscle
Control
• Tropomyosin
blocks
myosin
binding sites
• Calcium ions
allow cross
bridges to
form
Muscle Fibers
• Fast Muscle Fibers
• Slow Muscle Fibers
– rapid, powerful
contractions
– flight muscle
– sustain, long
contractions
– adductor muscles
Invertebrate Muscles
• Flight muscles in insects are capable of
independent contractions
– wings beat faster than action potentials
• Clam muscles contain paramyosin that
allows them to remain contracted with little
energy
• Nematodes only have longitudinal muscle
that gives them their characteristic
movements