Nervous system Biology by Campbell & Reece, chap 48.1 Invertebrate zoology by Barnes, Ruppert and Fox, part of the introduction chapters+ text to figures Sense cells and organs Biology by Campbell & Reece, chap 49 Invertebrate zoology by Barnes, Ruppert and Fox, part of the introduction chapters+ text to figures
Nerve cells and tissue All animal except Porifera have some type of nervous system Nerve tissue: secondary tissue (as muscle tissues) Nerve cells or neurons evolved in conjunction with muscle: For animals to move in response to stimuli, they must coordinate their body movements through muscle contraction
dendrite nucleus Neurons Cell body axon synaps respond to stimuli (dendrite) transmit information (nerve impulse (action potential): a rapid wave of depolarization along the neuron membrane (axon) to the target cell: next neuron or to an effector (muscle or endocrine cell) Transmission nerve impulse: A) gapjunction or B) synaps: release and diffusion of neurotransmitters
Evolution of neuromuscular system
Three different types of neurons to process information Sensory neuron (Peripheral nervous system PNS): transmit information from sensors (external or internal) Sensory input Interneuron (Central nervous system (CNS)): Integrate (analyze and interpret) the sensory input Motor neuron (PNS): Communicate with effectors cells Motor output PNS: somatic (external) and somatogastric (internal) nervous system
Nerve cord (nervstam) Nerve cell body Neurite: axon or dendrite Simple nerve cord Segmented nerve cord arranged in clusters Ganglion (neuromere): arranged cluster of neurons (cell bodies, axons (neuropil), glial cells)
Organization of nervous system Different animals group: different organization of neurons (nerve cells) into circuite
Nervous system Nerve nets: Cnidaria polyps A pair of nerve nets of interneurons interposed between a series of sensory cells and effector cells Nerve nets, nerve rings and ganglia: Cnidaria medusae Nerve nets and nerves (no ganglia): Echinodermata (sea star) bundle of fiber-like extensions of neurons
Fig 48.2 C&R
Sensory neuron direct connected to cnidocyte
Connected by gap junction to coronal muscle
CNS (central nerve system): nerve ring and 5 radial nerves PNS (peripheral nerve system): two intraepithelial nerve nets (sensory and motor)
Nervous system Cephalization: Brain (cerebral ganglia) and several longitudinal nerve cords (CNS) (flatworm) Nerve cord interconnected by transverse commissures (kummisur) Brain and one or two longitudinal nerve cords with ganglia (CNS and peripheral nervous system PNS) (annelida, arthrophoda)
Brain (no other ganglia) Nerve cords Nerve nets Platyhelminthes
Fig 48.2 C&R
CNS: Annelida Brain in prostomium clitellata:shifted posteriorly =A pair of suprapharyngeal ganglia A pair of subpharyngeal ganglia (svalgganglier) with a commissure A pair of circumpharyngeal connectives (svalgkonnektiv) A ventral par of nerve cords -oligocheata fused to one -have giant axons (larges in animal kingdom) Segmented ganglia with commissure and (segmental nerves) Fig 13.6a 13.62OH
CNS: Arthropoda Similar to CNS of Annelida Brain: a syncerebrum: two-three cerebrums -protocerebrum: the paired ganglia (neuromeres) of the acron -deutocerebrum: second pair of neuromeres -triocerebrum: third pair of neuromeres Fig 16-10 OH
Lockespindlar, daddy-long legs CNS: highly cephalized
Fig 48.2 C&R
Aplysia, sea hare (type of sea slug, Mollusca) Used in neurobiology research
Fig 12-17 OH CNS: Mollusca Several pairs of ganglia Brain (cerebral ganglia): -receive sensory nerves from eyes, tentacles and statocysts -linked with connective with different ganglia Buccal ganglia: muscle from radula Pedal ganglia: foot muscles Pleural ganglia (not connected): mantle The ganglia of any pair are connected by commissure Ganglia of different pairs are connected by connectives
CNS: Mollusca Visceral nerve cords: a pair of connective between pleural ganglia and visceral ganglia Visceral ganglia: organs in the visceral mass Esophageal ganglia: on the visceral nerve cord (gills ) Cerebral and pedal ganglia with their connectives from a circumesophageal nerve ring A pair of pedal nerve cords extends from the pedal ganglia into the foot Two visceral nerve cords run from the nerve ring to the visceral ganglion
Nerve cords in Mollusca
Sense cells and organs Living organism: more successful if they respond appropriated to environmental variations Animals: obtain a dynamic picture of environment by using sensory structures Sensory structures are specialized to detect a particular type of stimulus: -electromagnetic energy (light) -mechanical energy (sound, vibrations, touch, pressure, gravity) -chemical stimuli (taste, smell)
Chemoreceptive sensory neuron direct connected to cnidocyte Simplest case
Extreme case The entire body can respond to a complex pattern of stimuli Photoreceptive cells can be grouped together with other cells to form an eye The of some animals contains accessory structures, such as lens, which can focus an image on sensory neurons The sensory neurons encode and transmit the image data as impulses to optic neurons Optic neurons convey the information to CNS CNS decode the information and project it as a mental image and an adaptive response can be based
Direction and distance to the source of stimuli Two important sensory determinations Eumetazoan animals have receptors for all three classes of stimuli that provide direction and distance information (vision, smell, hearing) All three in many animals-one dominant
Evolution of the receptor neurons Ciliated epithelial cell Sensory surface are typically modifications of cilia or microvilli Simplest: individual receptor neurons Later, groups of photoreceptor or chemoreceptors neurons become locally concentrated in patches and cuplike depressions in the epithelium
Sense organs Organs: functionally specialized structures composed of two or more different tissues First organs: gravity receptors and eyes (gonads) Nervous and somatic (nonnervous) tissues
Five categories of sensory receptors Mechanoreceptors Chemoreceptors Electromagnetic receptors (photoreceptors) Thermoreceptors Pain receptors
Gravity receptors Statocysts: hollow capsule lined by mechanoreceptive cells Has a dense particle, the statolith Sense the changes of the orientation of the animals in correlation to the gravity Fig 49.6 C&R
Statocysts Fig 7.6OH 7.52,48 OH crayfish
Other mechanoreceptors An insect ear: tympanic membrane -over an air chamber -vibrates in response to sound waves -mechanoreceptors attached to the inside Fig 49.7 C&R
Other mechanoreceptors Many animals: hair or seta -receptors sense movements of hair -touch, sound, vibrations - Example spider trichobothrium (hårkopp) Fig 18-8e OH
Chemoreceptors Detect chemicals from distant (by smell or taste) Bombyx mori: sensory seta that have chemoreceptors
Gustatory sensilla on feets and mouthparts: taste
In arthrophods: Require a thin permeable or perforated cuticula that permit passage of chemical to the membrane of a chemosensory neuron Chemoreceptive sensilla- modified setae Fig 16-12C 18-8 c OH -hemosensory peg organs Fig 16-12a OH
Other receptors Thermoreceptors Thermo-hygroreceptive sensillum Insects 2-70 of them Hollow cuticular peg with three sensory cells Hygroreceptors Endoreceptors