1. Unit 12: Nervous Control
Chapter 25

2. The Role of the Nervous System
Which characteristic of life is an organism’s nervous system related to?
Receives information from internal and external stimuli – and responds (by sending a message to an “effector” such as a muscle or gland)

3. Nervous Response 4 requirements before nervous response can occur:
Detection of stimulus by sensory receptors
Transmission of impulse along neurons
Interpretation & analysis of impulses in coordination center
brain or spinal cord
Response by effectors
muscles or glands
4 requirements must be met before nervous response can occur:
Detection of stimulus by sensory receptors (Ex. touch-sensitive cells in skin or cells that form part of sense organ such as eye or ear) convert input into electrical impulse
Ex. Touch hot stove & sense too much heat
Transmission of impulse to other parts of body along network of neurons (which are specialized cells for conducting nerve impulses)
Ex. signal sent along sensory neurons to brain or spinal cord
Interpretation & analysis of impulses which take place in coordination center (brain or spinal cord)
Ex. brain or spinal cord interprets & processes signal in interneuron
Appropriate response by effectors (Muscles or glands that cause the actual response to the stimulus.)
Ex. motor neurons transmit outgoing impulses to the effectors which respond (pull hand away from hot stove)

4. Nerve Tissue Nerve Neurons many neurons bundled together
specialized cells that transmit nerve impulses through body
different types
sensory neurons
interneurons
motor neurons
Different types of neurons differ in structure & direction in which they carry impulses

5. Different Types of Neurons
Sensory neurons
transmit impulses from receptors to coordination center
Interneurons
transfer impulses from sensory to motor neurons
in brain & spinal cord
Motor neurons
transmit outgoing impulses to effectors
Sensory neurons transmit incoming impulses from receptors to a coordination center where impulses are interpreted
Interneurons transfer impulses from sensory to motor neurons (in brain & spinal cord)
Motorneurons once incoming impulses have been analyzed, the brain or spinal cord will send out a response… motor neurons transmit outgoing impulses to effectors

6. Neuron Structure dendrites cell body axon
conduct impulses toward cell body
cell body
resembles other types of cells
contains nucleus & cytoplasm
axon
carries impulses away from cell body
often covered with myelin sheath
end branch
dendrites highly branched fibers; receive impulses from end brush of previous neuron; conduct impulses toward cell body
cell body portion of neuron that most resembles other types of cells…. contains nucleus & cytoplasm
Axon long, narrow portion of cell; carries impulses away from cell body… to end brush (end of axon that divides into many filaments… then impulse travels to dendrites of next neuron or to effector). Axons are often covered with myelin sheath (insulating lipid material).
Myelin allows impulse to move very rapidly… consists of many layers… made of Schwann cells wrapping around & around axon… Schwann cells help provide nourishment to the axon & aids in axon regeneration. Between Schwann cells the axon is left uncovered. These bare areas are called nodes of Ranvier & help transport impulses quickly b/c the impulse is able to move from node to node instead of continuously along membrane.

7. Neuron Structure dendrites terminal buttons (end branch) nucleus
cell body
(soma)
axon
terminal buttons (end branch)
cytoplasm
nucleus
dendrites
myelin sheath
nodes of Ranvier

8. Transmitting Impulses Along a Neuron
nerve impulse or “action potential”
results from changes in ion concentration inside/outside neuron plasma membrane

9. Transmitting Impulses from Neuron to Neuron
between each neuron is a synapse
small fluid-filled space
neurotransmitters (chemicals) help impulse across synapse
Virtually all nerve impulses must travel through many neurons before reaching their targets
Impulse is transmitted in only one direction

10. Nervous Systems
In bilaterally symmetrical animals the nervous system is divided into 2 parts
central nervous system (CNS)
peripheral nervous system (PNS)
CNS serves as control centers… info brought from PNS analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS
PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons

11. Coordination between the PNS & the CNS
receptors in PNS gather info about animal’s environment
impulses along the PNS’s sensory neurons travel to CNS
in CNS (brain & spinal cord) impulses are interpreted & analyzed
impulses leaving CNS by motor neurons of PNS are carried to effectors
which carryout response
CNS serves as control centers… info brought from PNS (sensory neurons) analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS
PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons

13. 3 Major Parts of the Brain
cerebrum
speech, reasoning, emotions
cerebellum
controls balance, posture, muscle tone
medulla (oblongata)
controls involuntary actions of internal organs
heart rate, breathing rate, peristalsis, etc.
Cerebrum… sensory inputs are interpreted & motor impulses started
Cerebellum… coordinates impulses sent out from cerebrum think of Belle dancing w/ the Beast…. Her balance, posture, muscle tone….
Medulla oblongata… part of brain stem…

14. What are reflexes?
reflexes = involuntary/automatic responses to stimuli
Involve CNS, but require no conscious control or decision making b/c determined by fixed pathways
some through brain (ex. blinking)
others through spinal cord (ex. touch hot iron & respond)

15. Reflexes: Initial Response & Reflex Arc
Reflex Arc Animation
Reflex Arc Animation 2
Reflex arc
Receptors activated
Sensory neuron transmits impulse towards spinal cord
Impulse crosses synapse to interneuron in spinal cord
Impulse crosses synapse to motor neuron & leaves spinal cord
Impulse activates effectors which respond appropriately
Does NOT involve brain
Reflex arc
Receptors activated (ex. feel excess heat)
Sensory neuron transmits impulse towards spinal cord
Impulse crosses synapse to interneuron in spinal cord
Impulse crosses synapse to motor neuron & leaves spinal cord
Impulse activates effectors which respond appropriately (ex. pull hand away)
Does NOT involve brain
Takes a fraction of a second

16. 1. Sensory receptor activated (receives stimulus)
2. Sensory neuron transmits impulse towards spinal cord
4. motor neuron transmits impulse away from spinal cord
3. Impulse crosses synapse into interneuron where interpreted & analyzed
Reflex arc
Receptors activated (ex. feel excess heat)
Sensory neuron transmits impulse towards spinal cord
Impulse crosses synapse to interneuron in spinal cord
Impulse crosses synapse to motor neuron & leaves spinal cord
Impulse activates effectors which respond appropriately (ex. pull hand away)
CNS serves as control centers… info brought from PNS (sensory neurons) analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS
PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons
5. Impulse received by effector (which responds appropriately)

17. Reflex
Arc
Interneuron = association nerve

18. Reflexes: Secondary Response
Since reflex actions (arcs) don’t involve the brain, how does your brain become aware?
Some spinal cord interneurons that receive sensory impulses connect w/ other neuron pathways leading to the brain
Brain becomes aware of what has happened
Secondary response occurs
You yell, “Ouch!”

19. Comparison of Nervous Systems

20. Nervous Systems in Unicellular Organisms
Euglena
Light-sensitive structure under the “eye-spot”
Allows Euglena to swim in direction of light
Paramecium
Can respond to obstacles in path
Turns 30 & moves forward again…
Continues to do this until passes object
Seems to be mainly under chemical control

21. Nervous Systems in Invertebrates
Radially symmetrical organisms have no center for nervous control
Many short neurons form nerve net
No definite nerve pathways
Ex. Hydra
Bilaterally symmetric animals have a primitive control center(s) (ganglia) & specific nerve pathways
Ex. Planaria

22. Nervous Systems in Invertebrates
Other bilaterally symmetric animals also have brains
Ex. earthworm
cerebral ganglia (slightly larger ganglia)
Ex. grasshopper
Brain divided into specialized areas
protocerebrum
deutocerebrum
In arthropods such as the grasshopper, the brain is divided into specialized areas, including the protocerebrum (controlling vision) and the deutocerebrum (processing antenna signals). The stomatogastric system regulates digestion.

23. Nervous System in Fish Lateral line system Electrical sense
can sense the slightest movements (vibrations) in water
Electrical sense
Ampullae of Lorenzini
sense changes in electrical fields
Being highly complex life forms fish need a brain and a nervous system to control their body's actions. The nervous system of fish, much like ours, is composed of a central co-ordinating brain, a spinal cord and many, many nerves.
The Brain:- Generally speaking fish have small brains in relationship to their overall body weight. Elasmobranchs (Sharks and Rays) in general have a slightly larger brain for the same body mass as Teleosts (Bony Fish), however there is great variety within the teleosts scientists have learned something quite surprising about the Elephantnose Fish (Gnathonemus petersii).

24. Questions to Ponder & Extras
How do we see unity within diversity in relation to nervous control???
How does form follow function???
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