The Nervous System Juliana Paz Bio 490 Dr. Smith May 20, 2010 Overview Irritability: The capacity of cells and the whole organism to respond in a characteristic fashion to stimuli. Specific responses for specific stimuli. The nervous system is made up of interconnecting fibers that communicate via nerve impulses. Sensory (Afferent) Impulses Motor (Efferent) Impulses Central Nervous System (CNS) Phylogenetic Development Cnidara Slender Sensory Cells Afferent apparatus Nerve Net Ex: Hydra Ctenophora Nerve Net Localized differentiation Oral ring Ex: Jelly Combs
Platyhelminthes Evident Organization Brain made of nerve tissue Nerve Cord Extension of the brain tissue Ex: Flatworm Mollusca Increased cephalization Ganglia Increased number of knots on the nerve cell body. Ex: Snails and Clam Annelida Sensory cells on the head Two ganglia Double fused nerve cord Ex: Earthworms Arthropoda Simple sense organ on head Ventral surface Motor coordination Ex: Insects Neuron A specialized cell Composed of: Dendrites Cell Body Axon Myelin Sheath Glial Cells Neuroglia: support cells of the Central Nervous System (CNS). Schwann Cells: Support cells of the Peripheral Nervous 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 by two factors: imperablity to Na and the Na/K pump. Creates a negative charge because of their interactions. 2) Action Potential The start of neuron stimulation. The cell membrane become suddenly permeable to Na Leads to depolarization Action Potential: the shift in the charge that creates the neural impulse.
3) Repolarization Occurs when action potential reaches a +40mV and the membrane becomes impermeable to Na + K+ is also pumped out to 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 Principle Each 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 like acetylcholine (Ach), norepinephiren, γ-aminobutynic acid (GABA), and Serotonin. Action potential reaches the synaptic knobs Synaptic vesicles rupture and release neurotransmitters. Excitatory Postsynaptic Potential (EPSP) Temporal summation Spatial summation Some neurotransmitters can inhibit GABA and the inhibitory postsynaptic potential (IPSP) Excitatory synapse
Reflex Arc The functional unit of the nervous system and has an unchanging, automatic response. Simple reflex arc is the physical pathway of the impulse as it moves from the receptor of the afferent neuron to the effectors of the motor neuron. Receptors and Effectors Receptors: modified dendrite endings of sensory nerves that respond to specific kinds of stimuli. Muller s Doctrine of Specific Nerve Energies Based of the specificity of the receptor, it must have a 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 and cones, bipolar cells, optic neuron), optic nerve. Sound Ears, pinna, auditory canal, eardrum, three contiguous bones, cochlea (oval window and round window, perilymph, organ of Corti (basilar membrane and tectorial membrane)) cochlear nerve.
Gravity and Motion Vestibular apparatus (saccule, utricle, and semicircular canals), macula (otoconia), ampullae cupula) Taste and Smell Chemorecepetors: taste buds and nasal epithelium. Touch and Pressure Meissne s corpuscles and free nerve endings, hair, pacinian corpuscles. 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, mechanical processes. Midbrain Connector Assists in visual and auditory processes. Forebrain Cerebrum split into four lobes Location of complex activities.
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 the impulse toward motor neurons within the spinal cord. 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 association area 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 impulse begin at a motor neuron and meet at the ganglion. SNS-chain along the spine