Download The Nervous System (2)

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