View
229
Download
0
Category
Tags:
Preview:
Citation preview
Unit 12: Nervous Control
Chapter 25
The Role of the Nervous System
Which characteristic of life is an organism’s nervous system related to?
Nervous Response
4 requirements before nervous response can occur:1. Detection of stimulus
by sensory receptors2. Transmission of
impulse along neurons3. Interpretation &
analysis of impulses in coordination center▪ brain or spinal cord
4. Response by effectors▪ muscles or glands
Nerve TissueNerve
many neurons bundled together
Neurons specialized cells that
transmit nerve impulses through body▪ different types▪ sensory neurons▪ interneurons▪motor neurons
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
Neuron Structure dendrites
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
Neuron Structure
cell body (soma) axon
terminal buttons (end branch)
cytoplasmnucleus
dendrites
myelin sheathnodes of Ranvier
Transmitting Impulses Along a Neuron
nerve impulse or “action potential” results from
changes in ion concentration inside/outside neuron plasma membrane
Transmitting Impulses from Neuron to Neuron
between each neuron is a synapse small fluid-filled
spaceneurotransmitters (chemicals) help impulse across synapse
Nervous Systems
In bilaterally symmetrical animals the nervous system is divided into 2 parts central nervous system (CNS)
peripheral nervous system (PNS)
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
3 Major Parts of the Brain
cerebrum speech, reasoning,
emotionscerebellum
controls balance, posture, muscle tone
medulla (oblongata) controls involuntary
actions of internal organs▪ heart rate, breathing rate,
peristalsis, etc.
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)
Reflexes: Initial Response & Reflex Arc
Reflex arc1. Receptors activated2. Sensory neuron
transmits impulse towards spinal cord
3. Impulse crosses synapse to interneuron in spinal cord
4. Impulse crosses synapse to motor neuron & leaves spinal cord
5. Impulse activates effectors which respond appropriately
Does NOT involve brain
Reflex Arc Animation
Reflex Arc Animation 2
2. Sensory neuron
transmits impulse towards
spinal cord
3. Impulse crosses synapse into
interneuron where interpreted &
analyzed
4. motor neuron transmits impulse
away from spinal cord
1. Sensory receptor activated (receives stimulus)
5. Impulse received by
effector (which responds
appropriately)
Interneuron = association nerve
ReflexArc
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!”
Comparison of Nervous Systems
Euglena Light-sensitive structure
under the “eye-spot”▪ Allows Euglena to swim in
direction of lightParamecium
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
Nervous Systems in Unicellular Organisms
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
Other bilaterally symmetric animals also have brains Ex. earthworm▪ cerebral ganglia
(slightly larger ganglia) Ex. grasshopper▪ Brain divided into
specialized areas▪ protocerebrum▪ deutocerebrum
Nervous Systems in Invertebrates
Nervous System in Fish
Lateral line system can sense the
slightest movements (vibrations) in water
Electrical sense Ampullae of Lorenzini▪ sense changes in
electrical fields
Questions to Ponder& Extras
How do we see unity within diversity in relation to nervous control???
How does form follow function???
Kid’s Health website http://
kidshealth.org/PageManager.jsp?lic=1&article_set=59295&cat_id=20607
Recommended