Nervous system: comprised of neurons and glial cells Glial cells:
-Schwann cells and oligodendrocytes : produce myelin sheath around axons
-Astrocytes : cellular conduit between CNS neurons and blood, BBB
-Microglia : ameboid, “clean up” cells, immune-like function Neurons: transmit
information
-Soma : cell body; includes organs for metabolism
-Dendrites : large contact area to receive signals from other neurons
-Axon : carries rapid nerve impulse signals to other neurons, often long distances
-Axon terminal : transmit signals from one neuron to another/to responding cells
-Synapses : connections between neurons
Cnidaria (jellies, anemones, corals) have a nerve net versus a defined system
Animals with bilateral symmetry have a central and peripheral nervous system
CENTRAL NERVOUS SYSTEM:
-Ganglia : aggregations of interconnected neurons and neural components
-Cephalization : large clusters of neurons for processing and integrating incoming
information from environment and coordinating behavior
-Afferent (sensory) neurons: carry input from sensory structure TO the CNS
-Efferent (motor) neurons : carry signals AWAY from CNS to muscles/responding organs
PERIPHERAL NERVOUS SYSTEM:
Divided into:
-Sensory somatic (voluntary) nervous system : connects CNS to sensory structures
associated with external environment and effector organs
-Autonomic (visceral) nervous system : connects CNS to sensory structures and internal
organs associated with internal environment to control homeostasis
NERVOUS SYSTEM OF INVERTEBRATES
Organized as ganglia close to sensory structures, organisms w/ segmentation have ganglia in a
chain-like pattern down ventral portion of body
Connectives: connections between ganglia in different body segments
Commissurae: connectives between ganglia in the same segment NERVOUS SYSTEM IN
MOLLUSCS:
Generally made up of buccal, cerebra, pleural, pedal, parietal, and visceral ganglia
Invertebrate “brain”: comprised of cerebral, parietal, and pedal ganglia
Cephalopods have well-defined brain; octopus have largest and mostcomplex of any
invertebrate
NERVOUS SYSTEM IN ARTHROPODS:
“Ladder-type” CNS—paired ganglia in each segment ventrally
Supraesophageal ganglia: is the arthropod brain, three pairs of ganglia fused together
-Protocerebrum : innervates eyes and processes visual information
-Deutocerebrum : processes sensory information from antennae
-Tritocerebrum : innervates upper lip of mouth; integrates info from other parts of brain
and connects it to stomatogastric nervous system
CENTRAL NERVOUS SYSTEM OF VERTEBRATES:
Brain and spinal cord: comprise central nervous system in all vertebrates Spinal cord: made up
of grey and white matter w/ a central canal
-Grey matter: high density of neuron cell bodies, dendrites, and unmyelinated axons
-White matter : myelinated fibers
-Dorsal horn : mostly sensory neurons w cells bodies found in dorsal root ganglia
-Ventral horn: mostly motor neurons CNS covered in impermeable membrane:
-Meninx : single layer, in fish (primitive meninx)
-Meninges : two layers, in amphibians, reptiles, and birds (dura mater and secondary
meninx)
-Meninges : three layers, in mammals (dura mater, arachnoid, pia mater)
Cerebrospinal fluid: fluid between CNS tissue and meninges, functions as a cushion for CNS and
a pathogen-free extracellular environment for neurons
Brain: organized in 3 parts
-Hindbrain : medulla, pons, cerebellum
Medulla: subconscious (respiration, heart rate modification)
Cerebellum: motor control in equilibrium, posture, movement
-Midbrain : sensory and motor region called tectum and tegmentum
-Forebrain : diencephalon (thalamus, hypothalamus, and pituitary gland) and cerebrum
Hypothalamus: sets thirst, hunger, body temp, ADH and CRH production
Cerebrum: motor and sensory areas, higher thought process
Reticular formation: a mesh of neurons and their fibers, as neural circuits, involved in diverse
functions (regulates sleep-wake cycle, filters out background noise, maintains muscle tone,
posture, and balance, relays visual and acoustic signals to cerebellum for postural equilibrium,
coordinates autonomic functions like breathing and HR, modulates pain signals)
Brain divided into two hemispheres (left and right) and four lobes:
Frontal
Parietal
Temporal
Occipital
PERIPHERAL NERVOUS SYSTEM OF VERTEBRATES:
Consists of:
-Cranial nerves : emerge in pairs bilaterally from brain, 12 pairs
-Vagus nerve : longest in body, controls almost all thoracic and abdominal organs
(viscera) plus epiglottis, larynx, and pharynx
-Spinal nerves: emerge in pairs from spinal cord
Sensory somatic system: controls animals’ activities in the environment by carrying information
from sensory structures CNS and from CNS somatic tissues
Autonomic/visceral system: controls body’s homeostasis by connecting CNS w/ sensory
structures and internal organs
-Sympathetic division: fight/flight response o Increase HR and BP
o Dilates coronary and skeletal muscle blood vessels o Dilates
bronchi and pupils o Stimulates adrenal gland o Mobilizes
glucose from glycogen stores in liver o Causes release of extra
RBC’s from spleen o Inhibits activity of digestive tract
-Parasympathetic division: rest/repose response (does opposite of sympathetic
division)
Both sympathetic and parasympathetic consist of pre-ganglionic and postganglionic nerve
fibers, ganglia in parasympathetic system are closer to target organs
Neurotransmitters:
- Preganglionic fibers: acetylcholine for both sympathetic and parasympathetic nerves -
Postganglionic fibers:
Parasympathetic division: acetylcholine
Sympathetic division: norepinephrine or epinephrine
-Enteric system: regulates activity of digestive tract—mesh-like network of neurons
imbedded in lining of gastrointestinal tract, has more neurons than spinal cord,
communicates w/ CNS via sympathetic and parasympathetic nervous systems,
essentially a “second brain.”
Ionic basis for electrical activity in neurons
RESTING MEMBRANE POTENTIAL
An electrical potential at rest across a neuron cell membrane is usually between -60 and -70mV
Membrane permeability ratio: determines membrane potential based on the ratio of Na and K,
membrane more permeable to K at rest than Na Depolarize:
Hyperpolarize:
Voltage-activated Na channels:
- Activation gate that opens when depolarized - Inactivation gate that closes
slowly when depolarized Voltage-activated K channels:
- Activation gate which opens when depolarized (slower than Na gate)
Tetrodotoxin: found in pufferfish, some salamander and newt secretions. It block Na
channels/impulses.
GENERATING AN ACTION POTENTIAL
Action potentials: stereotyped all-or-none response of the membrane potentials in neurons, it
is triggered by a membrane depolarization above a threshold.
Threshold: “point of no return” level of change from resting potential in which an action
potential will be generated Refractory period: prevents backflow
-Absolute refractory period: happens during an AP in which no stimulus can generate
another action potential, no matter how strong.
-Relative refractory period: if a stimulus greater than the original one is applied then
another action potential can be generated (this happens during hyperpolarization) Post-
inhibitory rebound excitation:
- Some neurons are more sensitive to excitability after hyperpolarization
- When these neurons depolarize following hyperpolarization they exceed the condition
for threshold and automatically generate another action potential
- This is a continual, rhythmic activity called central pattern generators and do not require
sensory feedback
PROPOGATION OF ACTION POTENTIALS
AP’s can only be conducted in one direction, known as refractory period Large diameter
axons conduct AP’s faster. Insulation increases propagation velocity
- Myelin sheaths: insulates most vertebrate axons
-Nodes of Ranvier : gaps between sheaths, only place where AP’s can be generated and
they “jump” between nodes called saltatory conduction
- Membrane depolarization can occur several nodes ahead of AP
Pacemaker cells: generate spontaneous oscillations in their membrane potential, can be caused
by release of neurotransmitters, hormones, or even changes in PCO2. They don’t have a RMP
because they are never at rest.
Pacemaker potential can be:
-Spiking oscillations – triggering an AP
-Non-spiking oscillations – neurons that have graded changes in their membrane
potential without producing the action potential “spikes”
How Neurons communicate with each other
ELECTRICAL SYNAPSES
Gap junctions: tight junctions with a thin gap between the two neurons and connected by
channels. The depolarization/hyperpolarization of one neuron can cause
depolarization/hyperpolarization in the other neuron as well. The signal can move in either
direction.
CHEMICAL SYNAPSES
- Signals are transmitted more slowly in one direction from a presynaptic neuron to a
post-synaptic neuron via the release of a neurotransmitter.
-Neurotransmitters are stored + carried by vesicles, release of the neurotransmitter is
generated by depolarization from an AP
- Synaptic knob has VGCaIC
- When you generate an AP in the postsynaptic cell an AP in the presynaptic membrane
triggers the calcium channels to open, it then flows into the knob and triggers synaptic
vesicles to release, they bind w/ the membrane and release contents into the synaptic
cleft via exocytosis.
Neurotransmitter binds to receptor molecules.
-Ionotropic receptor: ligand-gated ion channels
-Metabotropic receptor: coupled to G-proteins and form second messengers which alter
ion channel properties
EXICTATORY AND INHIBITORY SYNAPSES
Excitatory synapse: moves membrane potential of postsynaptic neuron closer to threshold.
Ligand gated ion channels are permeable to monovalent cations (Na or K).
Inhibitory synapse: moves the membrane potential of the postsynaptic neuron further from
threshold. Ligand gated channels are permeable to monovalent anions (Cl).
SYNAPTIC INTEGRATION
Integration: takes place @ axon hillock, which is where the axon emerges from the neuron
body
Temporal summation: two+ electrical signals which are both below threshold trigger an AP if
they are quick in succession
Spatial summation: two+ electrical signals generated in different locations on the post-synaptic
neuron sum to trigger an action potential
Long term potentiation: plays a key role in memory function, a process that leads to
strengthening due to increased stimulation of an excitatory synapse.
Central pattern generators: circuits made of neurons can generate rhythmic patterns without
sensory stimulation. They play a central role in the coordination of complex body movements.
How animals sense their environments
Senses: how the world is perceived by animals
Sensory receptors: how environmental sensory information is captured, and they act as
selective amplifiers for stimuli.
Stimuli: detectable factors in the external or internal environment that are associated with
particular forms of energy.
Sensitivity: the ability of an organism to respond to stimuli at low levels of energy.
Stimulus modalities: what the animal perceives after the stimulus (light, sound, smell, taste,
etc.)
Interoceptors: monitor variations within the body of the animal
Exteroceptors: monitor variations in the external environment
Information carried by specific stimuli is converted into electrical signals in the form of receptor
potentials and then into action potentials by a process called sensory transduction.
Logarithm of stimulus intensity: has a linear relationship to the frequency of AP’s generated in
sensory neurons, it allows animals to sense a very large range of stimulus intensities in their
environment.
PHOTORECEPTION: the ability of organisms to interpret their surroundings by acqu8iring and
processing information contained within the electromagnetic radiation spectrum.
Photopigments: contained by photoreceptor cells, they change configuration when they absorb
energy. They consist of a chromophore like
1. retinal (a derivative of vitamin A) and
2. opsin protein when a photopigment absorbs a photon, opsin is activated and triggers a
cascade of events:
- retinal changes shape: photoisomerization – 11-cis-retinal (bent form) is converted to
11-trans-retinal, an intermediate (straight) form.
- G proteins activated
- Generates receptor potential
- Alters neurotransmitter release
Photoreceptor cells can be one of two types:
-Ciliary photoreceptors: depolarized in the dark and hyperpolarized in the light
(vertebrates)
-Rods (noncolor vision, contain rhodopsin which is a photopigment consisting of
the chromophore retinal and the protein scotopsin, much more sensitive to light
than cones but respond more slowly)
-Cones (color vision, also contain retinal but different photopsins which are
specific to narrow wavelength bands which are colors)
Color vision is based on the presence of at least 2 classes of cone:
-Trichromatic : 3 classes of cones (humans, primates, marsupials)
-Tetrachromatic : 4 classes of cones (fish, reptiles, birds, amphibians)
-Dichromatic : 2 classes of cones (terrestrial mammals, like dogs) - Monochromatic : 1
type of cone (marine mammals)
-Rhabdomeric receptors: polarized in the dark and depolarized in the light (arthropods)
- Several groups of invertebrates have both.
Eye: most common photoreceptive organ, varies in complexity
In vertebrates: retina is inverted, photoreceptor cells are not located on the side facing the
incoming light. All vertebrates have vesicular eyes, characterized by a lens focusing on the
image on the retina.
Tapetum lucidum: found in crepuscular and nocturnal vertebrates, it is a highly reflective layer
that allows them to see it the dark by reflecting light back through the photoreceptors.
Invertebrate visual systems:
-Vesicular eye with spherical lens
-Vesicular eye with cornea optics
-Flat sheet eye
-Cup-shaped eye
-Pinhole eye
-Concave mirror eye
-Compound eye ( in arthropods, complex convex eyes consisting of many units called
ommatidia, which are organized in a dome-like structure, each ommatidium can
perceive light of a certain wavelength and intensity which allows them to have color
vision)
(these are drawn on iPad)
Circadian clocks: photoreception plays a huge part in these.
CHEMORECEPTION: the ability of animals to interpret their environment by acquiring smells.
Olfaction: smell.
Olfactory receptors: in vertebrates they are located in the upper part of the nasal cavity, and in
insects/invertebrates they are located in olfactory hairs called sensilla
Pheromones: a special class of chemicals secreted by animals to communicate with their own
species
Vomeronasal organ: the organ with which amphibians, reptiles, and nonprimate mammals use
to detect pheromones.
Gustation/taste
Taste chemoreceptors play an important role in determining if things are edible or toxic
Taste buds: where taste receptor cells in vertebrates are located. Sensitive to salt, sweet,
umami, acidic, bitter.
MECHANORECEPTION:
Stretch sensitive ion channels: where mechanical stimuli act upon, they are on receptor cells
and convert the stimulus to depolarizing receptor potentials and action potentials.
Hearing: perceiving sound by detecting vibrations
Vertebrate ear has a cochlea, sound waves transmitted to tympanum and move ossicles. The
basilar membrane flexes w/ sound waves, higher frequencies vibrate near the base closer to
the oval window while lower frequences vibrate closer to the tip or further from the oval
window. Hair cells in organ of Corti transmit to the acoustic nerve.
Hari cells w/ mechanoelectrical ion channels involved in:
-Sound transduction in vertebrate ear
-Balance and special orientation in vertebrates and invertebrates
- Multifunctional lateral line system in fish
Infrasound: lower frequencies used by some animals like elephants to communicate long
distances
Ultrasound: higher frequency sounds that animals like dogs and bats can detect.
Echolocation: emit sounds and ears pick up returning sounds at slightly different times and
intensities, can detect higher frequencies with thicker sections of cochlea.
Hearing in other organisms:
Basilar papilla: an auditory apparatus in a blind-ended tubular structure, for birds, reptiles, and
amphibians.
Saccule of vestibular organ: sensory cells for hearing in the saccule, for amphibians that lack a
basilar papilla
Utricle: where the sensory cells of bony fish are located, and their lateral line transduces sound
waves to electrical signals
Tympanal organs: in arthropods, tympanum stretched over a chamber w/ internal
mechanoreceptor organ called chordotonal organ.
BALANCE AND SPATIAL ORIENTATION
Vestibular organ: made of 3 semicircular canals and two chambers:
utricle and saccule. Used by most vertebrates.
-Cristae in semicircular canals and maculae in saccule and utricle: sensory structures
that contain hair cells
-Otoliths : calcium carbonate particles embedded in gelatinous matrix
- Utricle and saccule are sensitive to orientation and linear acceleration
- Semicircular canals are sensitive to angular acceleration
Fish have a lateral line system consisting of neuromast organs which
- Maintain balance
- Navigate
- Detect sound and other fish
Aquatic invertebrates have statocysts: a mineralized mass called the statolith surrounded by
hair cells.
TOUCH:
Hair follicle receptors: sense hair movement
Free nerve endings: pain and temperature
Tonic touch receptors (constant stimuli)
-Ruffini’s corpuscles —stretch receptor
-Merkel’s discs —hi-res touch
Phasic touch receptors (when pressure applied and removed)
-Pacinian corpuscles —deep touch
-Meissner’s corpuscles —light touch and low frequency vibrations
INTERNAL MECHANORECEPTION
Proprioception: ability to “feel” the relative position of their different body parts and the
strength of contractions. Receptors in:
- Muscles – muscle spindles: provide info on muscle length
- Tendons – Golgi tendon organs: provide info on force produced
- Joints: Pacinian and Ruffini’s corpuscles give joint angle In insects:
Touch and proprioception is mediated by the chordotonal organ which is attached to structures
on body surface and in antennae (Johnston’s organ)
Baroreception: ability to sense pressure (vertebrates have these in their blood vessels, part of a
fast negative feedback reflux to short-term regulate BP).
the ability to detect temperature on the body
surface and in body tissues.
- Protects from damaging temps.
- Different temp. thresholds for different organisms
-Capsaicin : chemical in chili peppers, burning sensation
-Menthol : gives cooling sensation
NOCICEPTION: the ability to perceive noxious/damaging stimuli to avoid damage.
- Behavioral reactions can be conscious or unconscious
-Pain involves a conscious behavioral response with an emotion experience, it involves
the brain.
ELECTRORECEPTION: the ability of some animals to sense electric fields in the environment.
Passive electroreception: sensing field generated by external sources
(prey/predator detection)
-Ampullae of Lorenzini: sharks, skates, rays
THERMORECEPTION:
- Bees and flowers (paper) Active electroreception:
-Electric organs in electric fish generate strong (prey stunning) or weak (navigation)
electric fields.
MAGNETORECEPTION: the ability of some animals to detect geomagnetic fields and use them
for orientation and navigation.
Three potential mechanisms have been proposed, though no specific sensory receptors have
been identified in any animal (maybe add, depending on what the real study guide says lol)
MUSCLES AND MOVEMENT
Animal movement is powered by the pulling force to produce contracting muscles
Striated muscles: transverse striations of light and dark
-Skeletal muscle: muscles connected to skeletal, voluntary muscles
-Cardiac muscle: hear muscle, involuntary muscles
Smooth muscle (non-striated) uniform appearance
- Involuntary muscles found in sheets around blood vessels, organs/eyes, also called
visceral muscles
Invertebrates don’t have distinctions between muscle appearance and type
- Soft bodied invertebrates have obliquely striated muscles
Contractile apparatus: composed of two types of myofilaments
- Myosin filament: thicker filament with myosin molecules that act as a motor to convert
energy into mechanical work
- Actin filament: thinner filament with actin molecules with which the myosin interact
GENERAL STRUCTURE OF MYOSIN MOLECULE:
- Each molecule has two myosin heads each w/ an actin binding site and a myosin ATPase
site
- M. heads connected w/ long tail w/ hinge region
-Bipolar : myosin filaments in striated muscles are made up of several hundred myosin
molecules w/ tails intertwined and heads facing outward on each side
-Side-polar : in vertebrate smooth muscle, myosin heads are oriented in one direction on
one side of the sheet and the opposite direction on the other side of the sheet
- In invertebrates, the myosin filament also contains paramyosin, which is a protein
GENERAL STRUCTURE OF ACTIN MOLECULE
- Two chains of globular actin monomers wrapped around each other in a double helix
-Tropomyosin : elongated protein covering the actin active sites
- Vertebrate striated muscle have a troponin complex of 3 globulin proteins:
1. Troponin C – Ca binding site
2. Troponin T – tropomyosin binding site
3. Troponin I – inhibitory troponin subunit
STRUCTURE AND BANDED PATTERN OF STRIATED MUSCLE
- muscle held to bone via tendons made of collagen
- Skeletal muscle is covered by a thick layer of connective tissue called epimysium
-fascicles : bundles of muscle fibers
-perimysium : covers fascicles
-endomysium : surrounds muscle fibers
- muscle fibers (muscle cells) are further made up of myofibrils
-A-band : thicker myosin filaments make a darker band
-I-band : thinner acter filaments make a thinner band
-Z band/disc : midpoint of where I band, and where the myosin filaments are anchored
-Titin : an elastic protein that anchors the myosin filaments
-M-line : midpoint of the A-band and myosin filament, holds the myosin filaments
together
-Sarcomere : function unit of the contracting muscle, measured from Z line to Z line.
Muscle fibers are sensitive to calcium concentrations
- In vertebrates, the calcium regulatory system is associated with the actin filament
- Striated muscles in bivalve mollusks have a myosin-filamentlinked calcium regulatory
system
- Striated muscles in arthropods have calcium regulatory systems of both actin and
myosin, so both systems must be activated for muscle contraction
Voluntary muscle fibers
NEURAL CONTROL
Neuromuscular junctions: chemical synapses between motor neurons and voluntary muscle
fibers. The synapses become activated by action potentials in the motor neuron.
- As an AP descends down the motor neuron axon, it triggers voltagesensitive Ca ion
channels in the synaptic knob
- As Ca floods in, it triggers synaptic vesicles to bind to the cleft region and release
neurotransmitter (Ach)
- Muscle fibers have Ach receptors that are ionotropic receptors that allow Na and K to
enter sarcolemma (muscle cell membrane)
The majority of skeletal muscle fibers are all twitch fibers, and only have a single
neuromuscular junction in the middle of the fiber
The AP spreads outward, resulting in a contraction or twitch.
Tonic muscle fibers have multiple neuromuscular junctions across their length
