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The Nervous System (2) Rachel Muheim Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi The Nervous System A) What are nerves and neurons? B) The electrical nature of neurons C) The nervous systems of invertebrates D) The nervous systems of vertebrates Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi C) The nervous systems of invertebrates Cephalization Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Whole body response in organisms lacking organization Sponges (Porifera) • Specialized pinacocytes, contractile cells called myocytes, control the flow of water • Myocytes have electrical synapses (gap junctions) to synchronize the contractions • Slow contractions at 0.26 cm/s! Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Nerve nets with simple sensory cells • Simplest nervous system with extensive network in and under the epidermis • Nerve signals conducted in all directions through two-directional synapses • No myelin sheaths on axons • No sensory, motor or interneurons • Can still be found in advanced animals as nerve plexus Sea anemones, jellyfish, hydra, comb jellies Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Nerve nets in Cnidaria Section of epitheliomuscular cells: Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi True sense organs in medusae Active locomotion favored cephalization and evolution of sense organs! Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Bilateral nervous systems in flatworms (Platyhelminthes ) • Simplest bilateral nervous system • Two anterior ganglia lead to two main nerve trunks • Lateral branches form a ladder appearance • Simplest system to have a PNS and a CNS Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Evolution of sense organs in planarians Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Segmental nervous systems in Annelids • CNS and PNS • Segmental ganglia: – local control of segmental muscles – local reflexes involving the first true afferent and efferent pathways • Neurosecretory cells that secrete neurohormones • Sensory organs: tactile receptors, statocysts, chemoreceptors, eyespots or well-formed lens eyes Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi CNS in Annelids – Fused pair of cerebral ganglia (brain) – Paired ventral nerve cord – Fused ganglion in each segment along the ventral nerve cord Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Reflex arc controlling locomotion in Annelids Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Specialized nervous system of arthropods • Segments are specialised and each is devoted to specific tasks • Ganglia are larger and sense organs better developed than those of annelids • Elaborate social behaviour • Examples of learning Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Increasing degree of cephalization in more advanced arthropods Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Specialized nervous systems of insects Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Highly cephalized nervous systems in molluscs • Huge, well-defined ganglia, with a large brain • Ganglia divided in sub-parts of enormous complexity • Highly developed sense organs, complex behaviour, and learning abilities • Ability to think, intelligence ? Sea hare Aplysia Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Cephalopod nervous system: pinnacle of the invertebrates • CNS: large brain and optical lobes • PNS: neurons with a few ganglions • mostly concerned with motor control • neurons without myelin sheets • giant neurons for fast transmission Cuttlefish Sepia officinalis Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Octopus vulgaris: highest developed brain of all invertebrates Adult Octopus have about 520 Mio. neurons! • brain has 40 Mio. cells • optic lobes have 130 Mio. cells • nerve cords and ganglia have 350 Mio. cells Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi D) The nervous system of vertebrates Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Development of the vertebrate brain Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Evolution of the vertebrate brain encephalization expansion and addition of more and more functions to the cerebrum Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Lampreys and fish Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Amphibians, reptiles, birds and mammals Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Evolution of the vertebrate brain • Brain has changed dramatically • Ancestral vertebrate brain of fish has become a deeply fissured intricate brain of mammals • Ratio of weight of brain to spinal cord provides a scale of intelligence • Fish and amphibians: 1:1 • Humans: 55:1 encephalization increase and elaboration in size of the brain Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi The human brain Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Human forebrain Neocortex Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi CNS: Spinal cord Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Reflex arcs as fundamental units of neural operations Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Peripheral nervous system (PNS) Division of PNS by: 1. Anatomy: spinal nerves vs. cranial nerves 2. Function: sensory (afferent) nerves vs. motor (efferent) nerves 3. Connection: somatic nerves (from sensory cells; to muscle cells) vs. visceral nerves (to and from inner organs) Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Division of PNS by anatomy: spinal vs. cranial nerves 43 pairs of nerves in humans: •12 pairs of cranial nerves some only afferent or only efferent fibers •31 pairs of spinal nerves all with both afferent and efferent fibers Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Spinal nerves in humans • 8 pairs of cervical nerves (hals/nacknerver; C1-C8) • 12 pairs of thoracic nerves (bröstnerver ; T1-T12) • 5 pairs of lumbar nerves (ländnerver ; L1-L5) • 5 pairs of sacral nerves (korsbensnerver ; S1-S5) • 1 pair of coccygeal nerves (svansbensnerv; CO1) Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Cranial nerves in humans Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Division of PNS by function: sensory (afferent) vs. motor (efferent) neurons Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Sensory (afferent) vs. motor (efferent) neurons Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Division of PNS by connection: somatic nerves vs. visceral nerves Somatic nerves: voluntary nerves from sensory cells and to muscle cells) Visceral nerves: involuntary (autonomous) nerves to and from inner organs) • sympathetic nervous system • parasympathetic nervous system Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi Autonomic NS Lund University / Faculty of Science / Department of Biology / BIO B02 – Zoologi