Chapter 48 Nervous System The Nervous System http

Chapter 48 ~ Nervous System

The Nervous System http: //outreach. mcb. harvard. edu/animations/synaptic. swf n n n n Neurons Glial cells Soma Axon Dendrite Synapse Neurotransmitters Action potential n n n Motor neurons Interneurons Sensory neurons Myelin sheath Schwann cells Reflex arc

Nervous systems n Effector cells~ muscle or gland cells n Nerves~ bundles of neurons wrapped in connective tissue n n Central nervous system (CNS)~ brain and spinal cord Peripheral nervous system (PNS)~ sensory and motor neurons

Structural Unit of Nervous System n n n n Neuron~ structural and functional unit Cell body~ nucelus and organelles Dendrites~ impulses from tips to neuron Axons~ impulses toward tips Myelin sheath~ supporting, insulating layer Schwann cells~PNS support cells Synaptic terminals~ neurotransmitter releaser Synapse~ neuron junction

Simple Nerve Circuit http: //msjensen. cehd. umn. edu/1135/Links/Animations/Flash/0016 -swf_reflex_arc. swf n n n Sensory neuron: convey information to spinal cord Interneurons: information integration Motor neurons: convey signals to effector cell (muscle or gland) Reflex: simple response; sensory to motor neurons Ganglion (ganglia): cluster of nerve cell bodies in the PNS Supporting cells/glia: nonconductiong cell that provides support, insulation, and protection

Neural signaling http: //bcs. whfreeman. com/thelifewire/content/chp 44/4403 s. swf http: //outreach. mcb. harvard. edu/animations/actionpotential. swf n n Membrane potential (voltage differences across the plasma membrane) Intracellular/extracellular ionic concentration difference K+ diffuses out (Na+ in); large anions cannot follow…. selective permeability of the plasma membrane Net negative charge of about -70 m. V

http: //bcs. whfreeman. com/thelifewire/content/chp 44/4402 s. swf Neural signaling http: //www. mind. ilstu. edu/curriculum/neurons_intro/flash_electrical. php? mod. GUI=232&comp. GUI=1827&item. GUI=3158 n n n Excitable cells~ cells that can change membrane potentials (neurons, muscle) Resting potential~ the unexcited state of excitable cells Gated ion channels (open/close response to stimuli): photoreceptors; vibrations in air (sound receptors); chemical (neurotransmitters) & voltage (membrane potential changes)

Neural signaling n n n Graded Potentials (depend on strength of stimulus): 1 - Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more negative 2 - Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative

Neural signaling n n n n n Threshold potential: if stimulus reaches a certain voltage (-50 to -55 m. V)…. The action potential is triggered…. Voltage-gated ion channels (Na+; K+) 1 -Resting state • both channels closed 2 -Threshold • a stimulus opens some Na+ channels 3 -Depolarization • action potential generated • Na+ channels open; cell becomes positive (K+ channels closed) 4 -Repolarization • Na+ channels close, K+ channels open; K+ leaves • cell becomes negative 5 -Undershoot • both gates close, but K+ channel is slow; resting state restored Refractory period~ insensitive to depolarization due to closing of Na+ gates

Neural signaling n n n “Travel” of the action potential is self-propagating Regeneration of “new” action potentials only after refractory period Forward direction only Action potential speed: 1 -Axon diameter (larger = faster; 100 m/sec) 2 -Nodes of Ranvier (concentration of ion channels); saltatory conduction; 150 m/sec

Synaptic communication n n n Presynaptic cell: transmitting cell Postsynaptic cell: receiving cell Synaptic cleft: separation gap Synaptic vesicles: neurotransmitter releasers Ca+ influx: caused by action potential; vesicles fuse with presynaptic membrane and release…. Neurotransmitter

Signal transmission http: //www. bayareapainmedical. com/neurtrns. html

Neurotransmitters http: //www. blackwellpublishing. com/matthews/neurotrans. html n n Acetylcholine (most common) • skeletal muscle Biogenic amines (derived from amino acids) • norepinephrine • dopamine • serotonin Amino acids Neuropeptides (short chains of amino acids) • endorphin

Nervous System n Central Nervous System q q n Crainial Nerves Spinal Nerves Peripheral Nervous System q Sensory (afferent) Division n n q Sensing external environment Sensing internal environment Motor (Efferent) Division n Autonomic Nervous System q Sympathetic Nervous System § q Parasympathetic Nervous System § n increase energy consumption conservation of energy Somatic Nervous System q voluntary, conscious control, muscles

Vertebrate PNS

The Brain n n n Meninges Cerebrospinal fluid Ventricles Brain Stem Medulla oblongata Pons midbrain n Diencephalon Thalamus Hypothalamus n Cerebellum n n

The Vertebrate Brain n Forebrain q q • cerebrum~memory, learning, emotion • cerebral cortex~sensory and motor nerve cell bodies q • corpus callosum~connects left (analytical) and right (creative) hemispheres q q q n • thalamus (main input/output from cerebrum); hypothalamus (hormone production) Midbrain • inferior (auditory) and superior (visual) colliculi Hindbrain • cerebellum~coordination of movement • medulla oblongata/ pons~autonomic, homeostatic functions

Pituitary Gland Corpus Callosum

Cerebrum n n n Cerebral hemispheres Cerebral cortex—”gray matter” Convolutions Cerebral lobes Frontal lobe—conscious thought and muscle control. n n n Parietal Lobes—receive information from skin receptors. Occipital Lobe— receives visual input. Temporal Lobe—has areas for hearing and smelling.