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The Nervous System
Transcript of The Nervous System
Vertebrate Nervous System
Soooooo what is a neuron???
Neuron: A nerve cell; the fundamental unit of the nervous system, having structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its cell membrane. :)
Types of Neurons:
1. Sensory Neurons
3. Motor Neurons
A nerve cell that receives information from the internal and external environments and transmits the signals to the central nervous system (CNS).
An association neuron; a nerve cell within the central nervous system that forms synapses with sensory and motor neurons and integrates sensory input and motor output.
A nerve cell that transmits signals from the brain or spinal cord to muscles or glands.
Nick Astalos &
THANKS FOR WATCHING :D
Basic Anatomy of a Neuron:
Divisions of the Nervous System:
Central Nervous System (CNS):
Peripheral Nervous System (PNS):
In vertebrate animals, the brain and spinal cord.
The sensory and motor neurons that connect to the central nervous system.
One of usually numerous, short, highly branched processes of a neuron that convey nerve impulses toward the cell body.
A typically long extension, or process, from a neuron that carries nerve impulses away from the cell body toward target cells.
The part of a neuron that houses the nucleus and other organelles.
The conical region of a neurons axon where it joins the cell body; typically the region where nerve signals are generated.
In a neuron, an insulating coat of cell membrane from Schwann cells that is interrupted by nodes of Ranvier, where saltatory conduction occurs.
A bulb at the end of an axon in which neurotransmitter molecules are stored and released.
-The locus where one neuron communicates with another neuron in a neural pathway; a narrow gap between a synaptic terminal of an axon and a signal-receiving portion (dendrite or cell body) of another neuron or effector cell. Neurotransmitter molecules released by synaptic terminals diffuse across the synapse, relaying messages to the dendrite or effector.
The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. In neurons the membrane potential is typically between -60 and -80 mV.
The membrane potential of a neuron that is not transmitting signals. This resting potential is reliant on the ionic gradients that exist across the plasma membrane.
Gated Ion Channels:
-Stretch-gated ion channels: found in cells that sense stretch; open when the membrane is mechanically deformed.
-Ligand-gated ion channels: found at synapses; open/close when a specific chemical (neurotransmitter) binds to the channel.
-Voltage-gated ion channels: found in axons, dendrites, and cell body; open/close when membrane potential changes.
A membranous sac containing neurotransmitter molecules at the tip of the presynaptic axon.
An electrical state in which the inside of the cell is more negative relative to the outside than at the resting membrane potential. A neuron membrane is hyperpolarized if a stimulus increases its voltage from the resting potential of −70 mV, reducing the chance that the neuron will transmit a nerve impulse.
An electrical state in an excitable cell whereby the inside of the cell is made less negative relative to the outside than at the resting membrane potential. A neuron membrane is depolarized if a stimulus decreases its voltage from the resting potential of −70 mV in the direction of zero voltage.
A local voltage change in a neuron membrane induced by stimulation of a neuron, with strength proportional to the strength of the stimulus and lasting about a millisecond.
The potential an excitable cell membrane must reach for an action potential to be initiated.
A rapid change in the membrane potential of an excitable cell, caused by stimulus–triggered, selective opening and closing of voltage–sensitive gates in sodium and potassium ion channels.
The short time immediately after an action potential in which the neuron cannot respond to another stimulus, owing to an increase in potassium permeability.
Conduction of an action potential:
A narrow gap that separates the presynaptic neuron from the postsynaptic cell.
Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin–sheathed regions of membrane.
In a myelinated axon, the depolarizing current during an action potential at one node of Ranvier spreads along the interior of the axon to the next node (blue arrows), where it re–initiates itself. Thus, the action potential jumps from node to node as it travels along the axon (red arrows).
Direct Synaptic Transmission:
-A neurotransmitter binds directly to an ion channel, causing the channel to open.
-Generally results in a postsynaptic potential (a change in the membrane potential of the postsynaptic cell).
Excitatory Postsynaptic Potential (EPSP)
An electrical change (depolarization) in the membrane of a postsynaptic neuron caused by the binding of an excitatory neurotransmitter from a presynaptic neuron cell to a postsynaptic receptor; makes it more likely for a postsynaptic neuron to generate an action potential.
Inhibitory Postsynaptic Potentials
An electrical charge (hyperpolarization) in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more difficult for a postsynaptic neuron to generate an action potential.
Action Potentials vs Postsynaptic Potentials
-Postsynaptic potentials vary in magnitude due to many factors (ex. amount of neurotransmitter released by the presynaptic neuron)
-Postsynaptic potentials do not regenerate themselves as they spread along membrane of cell--they become smaller with distance from the synapse
-A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron
-But if 2 EPSP's occur in rapid succession at a synapse, the second EPSP may begin before the postsynaptic neuron's membrane potential has returned to the resting potential after the first EPSP--the EPSP's add together = Temporal Summation
EPSP's produced simultaneously by DIFFERENT synapses on the SAME postsynaptic neuron add together = Spatial Summation.
Through summation, an IPSP can counter the effect of an EPSP
Indirect Synaptic Transmission:
-A neurotransmitter binds to a receptor that is not part of an ion channel, activating a signal transduction pathway involving a second messenger in the postsynaptic cell.
-The effects are slower but last longer compared to the postsynaptic potentials produced by direct synaptic transmission.
Action: Alertness/attentiveness, motivation, triggers muscle contractions
Too much= Convulsions & spasms
Too little= Alzheimers
-Can be inhibitory or excitatory
-Excitatory to vertebrate skeletal muscles
Secreted in CNS, PNS, vertebrate neuromuscular junctions (synapse between motor neuron & skeletal muscle cell)
At the vertebrate neuromuscular junction, acetylcholine released by the motor neuron binds to receptors on ligand-gated channels in the muscle cell = producing an EPSP via direct synaptic transmission.
Tracts of axons within the CNS.
Regions of dendrites and clusters of neuron cell bodies within the CNS.
Biogenic Amines: Norepinephrine
Action: affects learning, memory and mood
too much= mania [uncontrollable excited mood]
too little= depression
-Excitatory or inhibitory
-Secretion sites= CNS; PNS
The Peripheral Nervous System:
Biogenic Amines: Serotonin
-Cranial Nerve: A nerve that leaves the brain and innervates an organ of the head or upper body.
-Spinal Nerve: a nerve that carries signals to or from the spinal cord.
-Somatic Nervous System: The branch of the motor division of the vertebrate peripheral nervous system composed of motor neurons that carry signals to skeletal muscles in response to external stimuli.
-Autonomic Nervous System: A subdivision of the motor nervous system of vertebrates that regulates the internal environment; consists of the sympathetic, parasympathetic, and enteric divisions.
-Sympathetic Division: One of three divisions of the autonomic nervous system of vertebrates; generally increases energy expenditure and prepares the body for action.
-Parasympathetic Division: One of three divisions of the autonomic nervous system; generally enhances body activities that gain and conserve energy, such as digestion and reduced heart rate.
-Enteric Division: Complex networks of neurons in the digestive tract, pancreas, and gallbladder; normally regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system.
Action: Calming, promotes sleep, pacifies hunger & pain, euphoria
Too much= Lethargy, sleepy
Too little= Insomnia, depression, aggressive behavior
-Secretion site= CNS
-Production is affected by light, stimulated by antidepressants
Biogenic Amines: Dopamine
Embryonic Development of the Brain:
In all vertebrates, three bilaterally symmetrical, anterior bulges of the neural tube—the forebrain, midbrain, and hindbrain— become evident as the embryo develops.
Action: attention/memory, emotions, feelings of elation, pleasure; key addiction molecule
Too much= Schizophrenia [over-stimulation causing disturbances in thought, perception, emotion, delusions, hallucinations,false sensory perceptions]
Too little= Parkinson's Disease [voluntary muscles fail to respond, uncontrollable shakes, memory lapses]
-Generally excitatory; may be inhibitory at some sites
-Secretion sites= CNS; PNS
Amino Acids: GABA (gamma aminobutyric acid)
Action: Coordinates muscle movement, soothes aggression, eating
Too much= eating disorders and anxiety
Too little= Rigid movements, convulsions, alcoholism
-Secretion sites= CNS; invertebrate neuromuscular junction
-Reticular Formation: A system of neurons, containing over 90 separate nuclei, that passes through the core of the brainstem.
*also regulates sleep and arousal*
Other Amino Acids:
-Secretion site= CNS
-Secretion sites= CNS; invertebrate neuromuscular junction
-Secretion sites= CNS
Action: help regulate emotional behaviors [anxiety, fear, tension, pleasure, pain], depress respiration, decrease urine output, decreases pain perception
-Secretion sites= CNS, PNS
Neuropeptides: Substance P
Action: Mediates perception of pain
-Secretion site= CNS
-Some neurons of the PNS and CNS release dissolved gases, notably nitric oxide (NO) and carbon monoxide (CO), as local regulators.
-CO regulates the release of hypothalamic hormones. In the PNS it acts as an inhibitory neurotransmitter that hyperpolarizes intestinal smooth muscle cells.
-NO and CO are not stored in cytoplasmic vesicles--cells synthesize them on demand.
A chemical messenger released from the synaptic terminal of a neuron at a chemical synapse that diffuses across the synaptic cleft and binds to and stimulates the postsynaptic cell.
Part of the vertebrate hindbrain located dorsally; functions in unconscious coordination of movement and balance.
Organization of some nervous systems:
Modeling a Mammalian Neuron:
Each beaker is divided into two chambers by an artificial membrane. (a) The membrane is selectively permeable to K+, and the inner chamber contains a 30–fold higher concentration of K+ than the outer chamber; at equilibrium, the inside of the membrane is 92 mV relative to the outside. (b) The membrane is selectively permeable to Na+, and the inner chamber contains a ten–fold lower concentration of Na+ than the outer chamber; at equilibrium, the inside of the membrane is +62 mV relative to the outside.
Synaptic terminals on the cell body of a postsynaptic neuron (colorized SEM):
-Nerve Nets: A weblike system of neurons, characteristic of radially symmetrical animals, such as hydra.
-Nerve: A ropelike bundle of neuron fibers (axons and dendrites) tightly wrapped in connective tissue.
-Nerve Cord: A ropelike arrangement of neurons characteristic of animals with bilateral symmetry and cephalization.
-Ganglia: A cluster (functional group) of nerve cell bodies in a centralized nervous system.
A muscle cell or gland cell that performs the body's responses to stimuli; responds to signals from the brain or other processing center of the nervous system.
An automatic reaction to a stimulus, mediated by the spinal cord or lower brain.
-At most synapses, information is passed from the transmitting neuron (the presynaptic cell) to the receiving cell (the postsynaptic cell) by means of chemical messengers called neurotransmitters.
Supporting Cells (Glia):
-Supporting cells that are essential for the structural integrity of the nervous system and for the normal functioning of neurons.
-Astrocytes: A glial cell that provides structural and metabolic support for neurons. During development, astrocytes induce the formation of tight junctions between cells that line the capillaries in the brain and spinal cord. The result is the blood–brain barrier, which restricts the passage of most substances into the CNS, allowing the extracellular chemical environment of the CNS to be tightly controlled.
-Radial Glia: In an embryo, supporting cells that form tracks along which newly formed neurons migrate from the neural tube; can also act as stem cells that give rise to neurons and other glia.
-Oligodendrocytes: A type of glial cell that forms insulating myelin sheaths around the axons of neurons in the central nervous system.
-Schwann Cells: A type of glial cell that forms insulating myelin sheaths around the axons of neurons in the peripheral nervous system.
-Equilibrium Potential (Elon): The magnitude of a cells membrane voltage at equilibrium; calculated using the Nernst equation.
A gated channel for a specific ion. When ion channels are opened or closed, the membrane potential of the cell is altered.
Central Canal: The narrow cavity in the center of the spinal cord that is continuous with the fluid–filled ventricles of the brain.
A space in the vertebrate brain, filled with cerebrospinal fluid.
Blood–derived fluid that surrounds, protects against infection, nourishes, and cushions the brain and spinal cord.
-Medulla Oblongata: The lowest part of the vertebrate brain, commonly called the medulla; a swelling of the hindbrain dorsal to the anterior spinal cord that controls autonomic, homeostatic functions, including breathing, heart and blood vessel activity, swallowing, digestion, and vomiting.
-Pons: Portion of the brain that participates in certain automatic, homeostatic functions, such as regulating the breathing centers in the medulla.
Functions in homeostasis, coordination of movement, and conduction of information to higher brain centers.
-Beatrice the Biologist
-The embryonic diencephalon develops into three adult brain regions: the epithalamus, thalamus, and hypothalamus.
-Epithalamus: A brain region, derived from the diencephalon, that contains several clusters of capillaries that produce cerebrospinal fluid.
-Thalamus: One of two integrating centers of the vertebrate forebrain. Neurons with cell bodies in the thalamus relay neural input to specific areas in the cerebral cortex and regulate what information goes to the cerebral cortex.
-Hypothalamus: The ventral part of the vertebrate forebrain; functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems; secretes hormones of the posterior pituitary and releasing factors that regulate the anterior pituitary.
-Biological Clock: An internal timekeeper that controls an organisms biological rhythms. The biological clock marks time with or without environmental cues but often requires signals from the environment to remain tuned to an appropriate period.
WHEN THE BIOLOGICAL CLOCK IS OFF...
The cerebrum is divided into right and left cerebral hemispheres. Each hemisphere consists of an outer covering of gray matter, the cerebral cortex; internal white matter; and groups of neurons collectively called basal nuclei located deep within the white matter.
A cluster of nuclei deep within the white matter of the cerebrum.
In the mammalian brain, the outermost region of the cerebral
Corpus Callosum: The thick band of nerve fibers that connect the right and left cerebral hemispheres in placental mammals, enabling the hemispheres to process information together.
CNS Injuries :(
-Unlike the PNS, the mammalian CNS cannot fully repair itself when damaged or assaulted by disease.
-Surviving neurons in the brain can make new connections and thus sometimes compensate for damage, as in the remarkable recoveries of some stroke victims.
-Generally speaking, however, brain and spinal cord injuries, strokes, and diseases that destroy CNS neurons, such as Alzheimer′s disease and Parkinson′s disease, have devastating effects.
-Current research on nerve cell development and the discovery of neural stem cells enhance our fundamental knowledge of the nervous system and may one day make it possible for physicians to repair or replace damaged neurons.
Nerve Cell Development:
Growth Cone: Responsive region at the leading edge of a growing axon.
Diseases and Disorders of the Nervous System:
-Schizophrenia: Severe mental disturbance characterized by psychotic episodes in which patients lose the ability to distinguish reality from hallucination.
-Bipolar Disorder: Depressive mental illness characterized by swings of mood from high to low; also called manic–depressive disorder.
-Major Depression: Depressive mental illness characterized by experiencing a low mood most of the time.
-Alzheimer's Disease: An age–related dementia (mental deterioration) characterized by confusion, memory loss, and other symptoms.
-Parkinson's Disease: A motor disorder caused by a progressive brain disease and characterized by difficulty in initiating movements, slowness of movement, and rigidity.
Microscopic signs of Alzheimer′s disease. A hallmark of AD is the presence in brain tissue of neurofibrillary tangles surrounding senile plaques made of β–amyloid (LM).
Nerve Cell Development:
-Most sensory information coming into the cortex is directed via the thalamus to sensory areas within the lobes.
-Cerebral cortex may generate motor commands that cause specific behavior (ex. moving a limb).
-Commands consist of action potentials produced in the primary motor cortex.
Axons--brainstem/spinal cord-- motor neurons--skeletal muscle cells
Lateralization: Segregation of functions in the cortex of the left and right hemispheres of the brain.
-Serial Processing of sequences of info
-Skeletal muscle control
-Simultaneous processing of many kinds of info
Language & Speech
-Broca's Area: Speech production
-Wernicke's Area: Comprehension of words
-Mediates primary emotions that manifest themselves in behaviors such as laughing and crying
-Responsible for for behaviors that separate mammals from most reptiles and amphibians (such as extended nurturing of infants)
-Structures form early in development and provide a foundation for higher cognitive functions that appear during the development of neocortical areas.
Short-term memory= frontal lobes
Long-term memory= Hippocampus
Long-term potentiation (LTP)
-Def: Responsiveness to an action potential (nerve signal) by a receiving neuron
-Lasts days to weeks--may be a fundamental process by which memories are stored or learning takes place.