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 togetherNeurons

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 SystemsIn 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 AnimationReflex 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 FishLateral 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???

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