Download Nervous system Sense cells and organs

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
Neurons
nucleus
dendrite
axon
synaps
Cell body
• 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)
Platyhelminthes
Brain (no other ganglia)
Nerve cords
Nerve nets
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
CNS: highly cephalized
Lockespindlar, daddy-long legs
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)
Simplest case
Chemoreceptive
sensory neuron
direct connected to
cnidocyte
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