Chapter 15 Nervous System Organization & Biological Clocks Flashcards
Organization
- Two major divisions
1. Central nervous system - Brain and spinal cord
2. Peripheral nervous system - All processes & soma located outside of the CNS
- Afferent branch – carries input to CNS
- Efferent branch – carries CNS output
- Somatic nervous system: controls skeletal muscle
- Autonomic branch: controls smooth muscle, cardiac muscle, and glands
- sympathic branch- fight or flight
- parasympathic branch- any other time
Organization of the Nervous System
The nervous system evolved from a simple reflex arc that can be divided into 3 parts:
- Stimulus (sensory reception)
- Processing (sensory filtering/past experience/other input/patterned neuronal activity)
- Behavior (motor output)
- In the cockroach, stimulation of wind receptors stimulate a jump
Types of Reflex Arcs
Nervous System Evolution
- There is little direct knowledge of nervous system evolution as it is rarely preserved in fossils
- Theories are based on anatomy and molecular genetics of living animals
- Risky since all are highly evolved & none represent a primitive condition
- Neurons differ in form, but are quite similar in function
- All use the same voltage-gated channels and synaptic communication
- Nervous system evolution is mainly a change in complexity
Principles of Nervous System Evolution
- All are based on one cell type, the neuron.
- Organization evolved through elaboration of one fundamental pattern, the reflex arc.
- There is a trend toward the gathering of neurons into a CNS.
- Complex organisms have more neurons than simpler organisms.
- As complexity increased, new structures were added to older ones. Old structures were not replaced.
- The relative size of each brain region is related to the importance of the sensory input or motor control for species survival.
- Many brain regions are organized into topographical maps.
Evolution of the Nervous System
- The tissues of most phyla originate with 3 embryonic tissues: ectoderm, mesoderm, and endoderm
- All of these except Cnidarians and sponges have nervous systems originating from the ectoderm
- The nervous systems of different animal groups reflect this phyletic scheme
- At one point, these relatively complex animals split into protostomes and deuterostomes
- Protostomes include- annelids, arthropods, and molluscs
- Deuterostomes include- echinoderms and vertebrates
Sponges
The only multicellular animals that do not have neurons.
Electrical path, trabecular reticulum, made up of connected cells.
Movement of flagella stops if the sponge is disturbed.
Nerve Nets
- The simplest form of a nervous system
- There is a thin layer of (randomly) dispersed neurons
- No nerves or CNS
- Found in:
- Cnidarians: jellyfish, anemones
- Hydra
- Also form subsets of more complex nervous systems
- Primarily in the PNS
- Usually in invertebrates (molluscs: local reflex paths), but also found in the vertebrate GI tract (nerve plexus)
- Simplest forms are unpolarized: bidirectional communication
- There is a thin layer of (randomly) dispersed neurons
Nerve Nets: Cnidarian Nervous Systems
- Cnidarians have radial symmetry
- No front or back
- While these animals may have areas with more neurons than others, they do not have brains.
- Unpolarized – make synapses at all junctions
- Nerve net allows for synchronized contraction of umbrella musculature
Nerve Rings: Echinoderms and Swimming Cnidarians
- More complex, providing more complex behavior
- Sensory structure cover 360°
- May have 2 rings
- Some have groups of neurons called ganglia
- Gap junctions & bidirectional chemical synapses
- Waves of activity
- Synapses are replicated at many points on the ring
Bilateral Symmetry
Two major trends are observed in bilaterally symmetric animals
- Centralization – The organization of integrating neurons into a particular area
- Longitudinal nerve cords (transverse) to coordinate activity
- Peripheral nervous system containing nerves
- Cephalization – The coalescence of neurons at the anterior end of an animal where many sensory receptors are typically concentrated
Both are found in flatworms
A More Complex Ganglionic CNS: Arthropod Nervous Systems
- Ganglionic CNS is found in protostomes
- Found in arthropods and some aspects are in annelids and molluscs
- CNS is ventral and solid
- Chain of segmental ganglia
- Ganglia are linked together by connectives
- Nerve a bundle of processes within the PNS
- Molluscan nervous sytems can be asymetric and nonsegmental (see aplysia).
Rind – The outer area of the arthropod ganglia which contains neuronal soma
Inner core
- Neuropile – A region of synapses between axons and dendrites
- Tracts – bundles of axonal processes within the ganglion
- Commissure: a tract that crosses from one side to the other
The Vertebrate CNS
- Columnar CNS found in vertebrates and deuterostomes
- Dorsal and hollow
- The human central nervous system shows segmentation and cephalization of the CNS as with arthropods
Arthropod and Vertebrate Nervous Systems
Five Principles of the Functional Organization of MammalianBrain
- Brain function is somewhat localized
Five Principles of the Functional Organization of MammalianBrain
- Brains have maps
Five Principles of the Functional
Organization of Mammalian Brain
- Size matters
- Neuron number
- Invertebrates (nematodes): 300
- Cephalopods: 108
- Large mammals: 1011
- Humans: 9x1010
- Elephants: 1.8x1011
- Intelligence is not related to the number of neurons!
- Intelligence is due to:
- Neuronal connections/networks
- Ratio of brain to body size
Five Principles of the Functional Organization of MammalianBrain
- Vertebrate brain evolution has involved repeated expansion of forebrain areas
- Neural circuits are plastic
Vertebrate Nervous System Organization
The Autonomic Nervous System
- Two main divisions: Sympathetic and parasympathetic (also enteric).
- Named based on anatomy, not physiology
- Generally act in opposition
- Parasympathetic system dominates in sleep
- Sympathetic dominates during activity/fright
Structure of the Autonomic Nervous System
- Preganglionic neuron somata in the thoracic and lumbar spinal cord segments.
- Preganglionic neurons synapse onto postganglionic neurons in the sympathetic chain ganglia.
- The postganglionic neurons extend a long distance (usually) to the target organs.
Structure of the Autonomic Nervous System
- Preganglionic neuron somata in the brain and sacral spinal cord.
- Preganglionic neurons synapse onto postganglionic neuron ganglia near or in the target organs.
- The postganglionic neurons do not extend a long distance to the target organs.
Neurotransmitters of the Autonomic Nervous System
Receptor Class Agonist Antagonist
Nicotinic Nicotine Curare
Muscarinic Muscarine Atropine
Autonomic Nervous System Structure
The Autonomic vs. Somatic Nervous System (Essay)
Biological Clocks
- Endogenous (in body) physiological timing mechanisms
- Provide temporal organization
- Period – Amount of time between one part of the cycle and the same part of the next cycle
- Circadian rhythm – about a day (happens everyday)
Free-Running Rhythms
Free-Running Rhythms
entrainment- light resets it
25 hours
Cellular Mechanisms of Circadian Clocks
Cellular Mechanisms of Circadian Clocks
