the nervous system - california state university, bakersfieldpsmith3/teaching/paz.pdf · the...
TRANSCRIPT
Juliana PazBio 490
Dr. SmithMay 20, 2010
The Nervous System
Overview Irritability: The capacity of cells and the whole
organism to respond in a characteristicfashion to stimuli.
Specific responses for specific stimuli. The nervous system is made up of
interconnecting fibers that communicate via nerveimpulses. Sensory (Afferent) Impulses Motor (Efferent) Impulses
Central Nervous System (CNS)
Phylogenetic Development
Cnidara Ctenophora
Slender Sensory Cells Afferent apparatus
Nerve Net Ex: Hydra
Nerve Net Localized
differentiation Oral ring Ex: Jelly Combs
Platyhelminthes MolluscaMollusca
Evident Organization Brain made of nerve
tissue Nerve Cord
Extension of the braintissue
Ex: Flatworm
Increased cephalization Ganglia
Increased number ofknots on the nerve cellbody.
Ex: Snails and Clam
Annelida Arthropoda
Sensory cells on thehead
Two ganglia Double fused nerve
cord Ex: Earthworms
Simple sense organ onhead
Ventral surface Motor coordination Ex: Insects
Neuron A specialized cell Composed of:
Dendrites Cell Body Axon Myelin Sheath Glial Cells
Neuroglia: support cellsof the Central NervousSystem (CNS).
Schwann Cells: Supportcells of the PeripheralNervous System (PNS).
Nerve Impulse Early Theories:
Axon was the passive portion of the impulse Nerve impulse decrease voltage The location of the electrical conductor
Nerve Impulse Resting State The neuron is at
resting potential(RP)
RP is maintained bytwo factors:imperablity to Naand the Na/K pump.
Creates a negativecharge because oftheir interactions.
2) Action Potential The start of neuron
stimulation. The cell membrane
become suddenlypermeable to Na
Leads todepolarization
Action Potential: theshift in the charge thatcreates the neuralimpulse.
3) Repolarization Occurs when action
potential reaches a+40mV and themembrane becomesimpermeable to Na+
K+ is also pumped outto balance Na
4) Refractory Period Restoration of the
Na+/K+ gradient. Incapable of creating
a new impulse until at-60mV. The impulse is
recreated on the axon
Sodium/Potassium Pump The channels are guarded by voltage sensitive
proteins. Potassium has only one channel opening, while
sodium has two channel openings Activation Gate Inactivation Gate
All or None PrincipleEach neuron has a threshold, where the minimum
strength is needed to initiate depolarization.
Saltatory Conduction Aided by the Myelin Sheath and the Nodes of
Ranvier The impulse is transmitted as an electrical current
rather than a chemical process.
Synapse The point at which the axon and dendrite
associate Invertebrate nerve nets have the axons and
dendrites touch each other Simpler vertebrates have a discrete neural
pathway. Vertebrates have a unique characteristic of
moving in one direction. Movements across the Synaptic Cleft is a chemical
event mediated by neurotransmitters likeacetylcholine (Ach), norepinephiren, γ-aminobutynicacid (GABA), and Serotonin.
Action potentialreaches the synapticknobs
Synaptic vesiclesrupture and releaseneurotransmitters.
ExcitatoryPostsynaptic Potential(EPSP)
Temporal summation Spatial summation
Someneurotransmitters caninhibit
GABA and theinhibitory postsynapticpotential (IPSP)
Excitatory synapse
Reflex Arc The functional unit of
the nervous systemand has anunchanging,automatic response.
Simple reflex arc isthe physical pathwayof the impulse as itmoves from thereceptor of theafferent neuron to theeffectors of the motorneuron.
Receptors and Effectors Receptors: modified dendrite endings of sensory
nerves that respond to specific kindsof stimuli.Muller’s Doctrine of Specific Nerve Energies
Based of the specificity of the receptor, it must havea low threshold and send only one kind of
message to the CNS. Exteroceptors Proprioceptors Interoceptors
Effectors: Specific response
Sensory Organs Light
Eyeball, cornea, pupil,iris, retina (rods andcones, bipolar cells,optic neuron), opticnerve.
Sound Ears, pinna, auditory
canal, eardrum, threecontiguous bones,cochlea (oval windowand round window,perilymph, organ ofCorti (basilar membraneand tectorialmembrane)) cochlearnerve.
Gravity and Motion Vestibular apparatus
(saccule, utricle, andsemicircular canals),macula (otoconia),ampullae cupula)
Taste and Smell Chemorecepetors: taste
buds and nasalepithelium.
Touch and Pressure Meissne’s corpuscles
and free nerve endings,hair, paciniancorpuscles.
Heat and Cold Ruffini corpuscles and
Krause end bulbs.
Brain and Spinal Cord Protected by the bony skull ,three meninges, and
cerebrospinal fluid (CSF). The brain has three regions: hindbrain, midbrain,
and forebrain.
Hindbrain Medulla oblongata,
pons, celebellum Control the
involuntary,mechanicalprocesses.
Midbrain Connector Assists in visual and
auditory processes. Forebrain
Cerebrum split intofour lobes
Location of complexactivities.
Limbic system Hypothalamus: hormone regulation and body
regulator. Thalamus: A series of cerebral nuclei (basal
ganglia). Reticular formation: region of nuclei in close
association. Mood regulator? The hippocampus, amygdala, and
cingulate are apposed with the olfactory nerve.
Spinal Cord a thick, dorsal neural tract extending from the brain
stem to the lower back. Protected by bone. Consists of ascending tracts that conduct impulses
to the brain and descending tracts that carries theimpulse toward motor neurons within the spinalcord.
Gray matter houses the central canal. Ventricles hold CSF. Process sensory impulses from the PNS.
Dorsal root ganglia Ventral horn
Brain Specialization The brain hemispheres can specialize in
something. Left hemisphere controls speech and the right
hemisphere can regulates spatial perceptions. Corpus callosum allows communication. The neocortex is quick to create new synapses
By means of central circuits and the associationarea of the parietal lobe.
Short term and long term memory Learning occurs in two ways:
Engrams Modification of the neural apparatus.
Autonomic Nervous System Sympathetic Nervous
System Preparation for
emergencies Parasympathetic
Nervous System Lie near the target
organ Restoration functions
Both effector impulsebegin at a motor neuronand meet at theganglion. SNS-chain along the
spine PNS- in the target organ
(Ach).