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Information processed in the nervous system occurs in 3 stages:
nerve cells that transfer (receive, transmit, regulate) information within the body.
transmit information from the senses (light, sound, touch, heat smell, taste) or from internal conditions (blood pressure, carbon dioxide level) to the brain. In the brain
integrate the signals and then
transmit the signals.
Central Nervous System (CNS):
where integration takes place. Includes the neurons, brain, and longitudinal nerve cord
Peripheral Nervous System (PNS):
neurons that carry information to and from the CNS.
A neurons organelles are located in the
are branched extensions that receive signals from other neurons.
is a long extension that transmits the signals.
Axons transmit information to other cells at a
are used to pass information.
Neuron sending signal is the
Neuron receiving signal is the
the difference in voltage across the plasma membrane.
When a neuron is not sending a signal, its
is about -70 mV.
Potassium and sodium pumps are used for transport.
When the electrical and chemical gradients are are balanced it is at
Membrane potential changes in responses to stimuli. It is
gated ion channels
that open or close in response to stimuli.
An increase in magnitude of membrane potential is called
Ex: Gated K+ channels open, allowing K+ to diffuse out makes the cell's inside more negative.
A decrease in the magnitude of membrane potential is called
Ex: Na+ channels are opened and Na+ diffuses into the cell.
Generation of Action Potentials
a shift in membrane potential where the magnitude of the change varies with the stimulus strength.
the result of a massive change in membrane potential.
Arise due to
voltage gated ion channels
which respond to changes in membrane potential.
Ex: Depolarization in the membrane causes Na+ channels to open, as Na+ diffuses into the cell it increases the depolarization which causes more Na+ channels to open.
Occurs when a stimulus causes the membrane voltage to cross the
(about -55mV in mammals)
This image shows the role of voltage-gated ion channels in the generation of an action potential.
During the falling phase Na+ channels remain inactive, during this
another action potential cannot occur.
Conduction of Action Potentials
Action potentials travel long distances by regenerating on the axon.
Steps of conduction:
As Na+ flows inward across the membrane action potential is generated.
Depolarization of the action potential spreads to neighboring regions, re-initiating action potential there. The region the was previously depolarized is then re-polarized as K+ flows out.
The depolarization-repolarization process if repeated in the membranes next region. Carrying the action potential along the length of the axon.
A larger axon diameter will result in a quicker action potential.
insulate the axons of vertebrates. They cause action potential's speed to increase.
Myelin sheaths are made up of gila:
in the CNS
in the PNS
Action potentials only occur at
nodes of Ranvier
(gaps in the myelin sheath where there are voltage-gated Na+ channels).
Action potentials use
to move between nodes of Ranvier.
Neurons Communicate with other Cells at
electric current flows from neuron to neuron.
a chemical neurotransmitter carries information across the gap junction.
The majority of synapses are chemical.
Sequence of events to chemically transmit an impulse:
An action potential arrives, depolaraizing the presynaptic membrane. The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles.
An influx of Ca2+ is triggered by the triggering to open voltage-gate channels.
The neurotransmitter is released into the synaptic cleft and received by the postsynaptic cell.
The same neurotransmitter can produce different results in different cells.
There are five major classes of neurotransmitter:
Excitatory postsynaptic potential (EPSP):
depolarization that brings the membrane potential towards threshold.
when two EPSP's occur at a single synapse in rapid succession that the postsynaptic neuron's membrane potential has not returned to resting potential, so the two EPSP's add together.
when two EPSP's occuring at different synapses reach the postsynaptic neuron together, causing the two EPSP's to be added together.
Inhibitory postsynaptic potential (IPSP):
hyperpolarization that brings the membrane potential further from the threshold.
As a general rule simpler organis
ms have simpler nervous systems and more complex organisms have more complex nervous systems.
Singled-celled organisms can respond to stimuli
Animals respond to stimuli using neuron systems
The simplest nervous systems are in cnidarians who's nerves are arranged in a
, or a series of interconnected nerve cells.
More complex animals have
which are bundles that consist of multiple nerve cells axons.
Bilaterally symmetrical animals show cephalization, or the clustering of sensory organs at the front end of the body.
Simple cephalized animals have a CNS
Annelids and arthropods have ganglia, which are segmentally arranged clusters of neurons.
In vertebrates the CNS is the brain and spinal cord and the PNS is nerves and ganglia.
Vertebrates Nervous System
Vertebrates have a dorsal spinal cord.
Information is conveyed to and from the brain through the spinal cord.
The spinal cord can also independently to produce
or the body's automatic response to a stimulus.
Ex: Knee-jerk reflex
During development the CNS develops from the hollow dorsal nerve cord.
The nerve cord gives rise to the narrow
of the spinal cord and the
of the brain.
fills the canal and ventricles.
The fluid is filtered from blood and provides nutrients, removes waste, and cushions the brain and spinal cord.
The brain and spinal cord contain:
neuron cells bodies, dendrites, unmyelinated axons
bundles of myelinated axons
Predominantly on the inside, reflects the role of signaling between neurons and the brain.
are present throughout the brain and spinal cord.
Nourish, support, and regulate neurons
Radial glia help in development by forming tacks along which new neurons migrate.
Astrocytes then induce cells lining capillaries in the CNS to form tight junctions.
Results in a blood-brain barrier and restricts substances entry to the brain
The Peripheral Nervous System
Transmits information to and from the CNS.
Has two efferent components:
carries signals to skeletal muscles and is voluntary.
autonomic nervous system:
regulates smooth and cardiac muscles and is usually involuntary. This system has three divisions:
regulates arousal and energy generation ("fight or flight")
promotes calming and a return to self-maintenance functions.
controls gallbaldder, pancreas, and digestive tract activity.
The Vertebrate Brain is Regionally Specilized
Specific brain structures arise during embryonic development.
The limbic system
The brainstem and cerebrum control arousal (state of awareness) and sleep (state in which external stimuli are received but not consciously perceived).
A network of neurons called the
is found at the core of the brianstem. Its purpose is to regulate the type and amount of information that reaches the cerebral cortex.
Melatonin is released by the pineal gland and plays a role in sleep cycles.
Sleep is essential to learning and memory.
Daily sleep and wakefulness cycles rely on a
, a molecular mechanism that directs periodic gene expression.
Typically synchronized to light and dark cycles but can maintain the cycle in the absence of environmental cues.
suprachiasmatic nucleus (SCN)
is a group of neurons in the hypothalamus that coordinates circadian rhythms.
is made up of the amygdala, hippocampus, and parts of the thalamus. Its function is in motivation, behavior, emotion, and memory.
Emotion generation and experience requires the limbic system and sensory areas of the cerebrum.
Emotional experiences are stored as memories in the
, a mass of nuclei near the cerebrum's base.
The cerebrum (largest structure in the human brain) is essential for awareness, language, cognition, memory, and consciousness.
There are four lobes that serve as landmarks for function:
Broca's area is active when speech is generated
Wernicke's area is active when speech is heard
There are two hemispheres which function differently. This difference is called
is adept in language, math, logic, processing sequences.
is adept at pattern recognition, nonverbal thinking, and emotional processing.
The two hemispheres communicate through corpus callosum fibers.
Cerebral cortex receives input from sensory organs and somatosensory receptors.
Somatosensory receptors provide information on touch, pain, pressure, temperature, and limb/muscle position.
The thalamus directs different inputs to distinct locations.
Integrated sensory information passes to the prefrontal cortex, which helps plan actions and movements.
Neurons are arranged according to the part of the body that generates input or receives commands in the somatosensory cortex and motor cortex.
Frontal lobes have an effect on executive functions.
Frontal lobe damage can impair decision making and emotional responses but intellect and memory will remain intact.
Neural connections in memory and learning
The nervous system is established during embryonic development but can change after birth. The capacity for the nervous system to be modified after birth is called
These changes can strengthen or weaken signaling at a synapse.
Autism is a result of a disruption of activity-dependent remodeling at synapses.
Memory formation is an example of neural plasticity.
information held and released once it become irrelevant, is accessed via the hippocampus.
retains knowledge longer, it is used with recollection, is stored in the cerebral cortex.
Memory consolidation may occur during sleep.
Long-term potential (LTP)
is a form of learning that involves an increase in the strength of synaptic transmission.
For LTP to occur there must be a high-frequency of action potential in the presynaptic neuron. The action potential must arrive at the same time as the postsynaptic cell receives a depolarizing stimulus at another synapse.
Involves glutamate receptors.
Pg. 1078 shows LTP in the brain, I couldn't find this online to put in here.
Stem cells are in the adult human brain, they play an essential role in learning and memory.
Nervous System Disorders
Genetic and environmental factors contribute to diseases of the nervous system
Affects about 1% of the world's population
Patients have a distorted perception of reality
hallucinations, delusions, etc
Treatments focus on brain pathways that use dopamine as a neurotransmitter
Two broad forms of depression:
Major depressive disorder
is periods of lack or interest or pleasure in most activities.
is characterized by mood swings from high (maniac) to low (depressive).
Treatments increase the activity of biogenic amines in the brain.
Addiction is defined as compulsive consumption and an inability to control intake.
Drugs become addictive because they increase activity of the brain's reward system.
Cocaine, heroin, alcohol, tobacco, and amphetamine are all addictive.
Addictive drugs enhance the activity of the dopamine pathway.
Addiction leads to lasting changes in the reward circuitry that lead to craving for the drug.
A mental deterioration characterized by confusion and memory loss.
Caused by neurofibrillary tanges and amyloid plaques in the brain.
There is no cure.
A motor disorder caused by the death of dopamine-secreting neurons in the midbrain.
Symptoms include: muscle tremors, flexed posture, shuffling gait
There is no cure, but deep brain stimulation and certain drugs can help manage symptoms.
Sensory receptors begin with stimuli (represented in forms of energy) and convert it to a change in membrane potential, thereby regulating the output of action potentials to the CNS.
Stimulus may cause a simple or elaborate motor response to be generated.
Sensory pathways have four basic common functions:
detection of stimuli by sensory receptors.
Beginning of the sensation.
direly interact with stimuli inside and outside the body.
the conversion of stimulus energy to a change in membrane potential of a sensory receptor.
is the change in membrane potential. Their magnitude varies with stimulus strength.
after energy has been transducted, some sensory cells generate transmission of action potentials to the CNS.
Some sensory receptors are specialized neurons, others are specialized cells that regulate neurons.
Sensory neurons produce action potentials, their axons extend into the CNS.
begins as soon as information is received.
Response of a sensory receptor varies with stimuli intensity.
Neuron receptor: larger receptor potential results in more frequent action potentials.
Non neuron receptor: larger receptor potential causes more neurotransmitters to be released.
are the brain's construction of stimuli.
is the strengthening of stimulus energy be cells in sensory pathways.
is a decrease in responsiveness to continued stimulation.
Types of Sensory Receptors:
sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound.
General chemoreceptors transmit information about the total solute concentration of a solutoin.
Specific chemoreceptors respond to individual kinds of molecules.
detect electromagnetic energy such as light, electricity, and magnetism.
detect heat and cold.
Help regulate body temperature.
a class of naked dendrites in the epidermis that detect stimuli that can reflect harmful conditions.
Hearing and Equilibrium
Invertebrates maintain equilibrium using mechanoreceptors located in organs called
Statocysts contain mechanoreceptors that detect the movement of granules called
Vertebrates sensory organs for hearing and equilibrium are associated in the ear.
Vibrating objects create waves in the air that cause the tympanic membrane to vibrate. The 3 bones of the middle ear transmit vibrations to the oval window, in the cochlea the vibrations create pressure waves that travel through the vestibular canal causing the basilar membrane to vibrate and bend its
. This bending depolarizes the membranes of mechanoreceptors and send action potentials to the brain via the auditory nerve. The waves dissipate when they strike the
t the end of the tympanic canal.
Volume is the amplitude of the sound wave.
Pitch is the frequency of the sound wave. Distinguished by the cochlea.
perceive position with respect to gravity or linear movement. The chambers contain a sheet of hair cells projected into a gelatinous material. In this gel are small calcium carbonate particleas called otoliths. Movement causes the otoliths to press into the hairs, this change is transformed to an output of sensory neurons that signal the brain telling it your heads at an angle
Fish: have one pair of inner ears near the brain.
lateral line systems
along both sides of their body that contain mechanoreceptors with hair cells that detect and respond to water movement.
Light detectors range from simple cell clusters to complex organs, but all contain
cells that contain light-absorbing pigment molecules.
Invertebrates have a light-detecting organ. One of the simplest is ocelli (eyespots) located near the head region. These allow movement away from light and helping to find shaded locations.
Insects and crustaceans have
which consist of up to several thousand light detectors called
Compound eyes are effective at detecting movement.
Jellies, polychaetes, spiders, and many molluscs have
They have a small
through which light engers and an
to change the diameter of the pupil, thus controlling light entry.
Vertebrate eyes detect color and light but we perceive the information as an image. Transduction begins when light induces the conversion of cis-retinal to trans-retinal, which activates a G protein, leading to hydrolysis of cyclic GMP. GMP breakdown causes Na+ channels to close, hyperpolarizing the cell. Information processing begins in the retina. In the dark rods and cones release glutamate into synapses with
These neurons are hyperpolarized or depolarized in response to glutamate. In the ligh, rods and cones hyperpolarize, shutting of the release of glutamate. Axons of ganglion cells form optic nerves that transmit signals to the brain. In the brain ganglion cell axons lead to the
lateral geniculate nuclei
which have axons reaching to the
primary visual cortex
in the cerebrum.
Ganglion cells transmit signals from bipolar cells to the brain.
Horizontal and amacrine cells integrate visual information before it is sent to the brain.
Interaction among different cells results in
or an enhanced image contrast.
Color Vision: most vertebrates have good color vision. Humans see color based on red, green, or blue cones.
Taste and Smell
In terrestrial animals
(taste) is dependent on the detection
(smell) is dependent on the detection of
There is no distinction between taste and smell in aquatic animals.
Insects have sensory hairs for tast receptors.
Mammals have receptor cells called
that can perceive sweet, sour, salty, bitter, and umami. Olfactory receptors are neurons that line the nasal cavity, when odorant molecules bind to receptors a signal transduction pathway is triggered, sending action potentials to the brain.
Skeletal muscle moves bones and the body.
Skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle.
Each muscle fiber is a bundle of smaller
consist of two strands of actin and two strands of regulatory protein.
are staggered arrays of myosin molecules.
Nervous systems (ch. 48-50)
Neuron organization (overview of cnidarians, echinoderms, flatworms, annelids, arthropods, mollusks, and vertebrates)
Neuron structure and function
Resting and action potentials, conduction of action potentials
Synapse structure and function, neurotransmitters
Organization of vertebrate nervous system
Brain structure and function
Neural connections, memory, and learning
Nervous system disorders: schizophrenia, depression, addiction, Alzheimer’s, Parkinson’s
Sensory receptors (general structure and function)
Types of sensory receptors
Hearing in humans vs. other vertebrates
Vision/light reception in vertebrates vs. other organisms
Taste and smell
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