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).