Unit 17: Nervous Control
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Unit 17: Nervous Control
Chapter 15 Nervous & Chemical Control (sec. 1 & 2)
The Role of the Nervous System
What is the nervous system? a system that lets an animal
detect changes & respond to them▪ nerve cells, sense organs, & brain
Which characteristic of life is an organism’s nervous system related to? response to stimuli
How many parts is the human nervous system divided into? two▪ 1. central nervous
system (CNS)▪ brain▪ spinal cord
▪ 2. peripheral nervous system (PNS)▪ body nerves
The Human Nervous System
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
cerebellum
medulla (brain stem)
spinal cord
How do the PNS & CNS Work Together in Nervous Response?1. Detection of stimulus
by sensory receptors2. Transmission of
impulse along nerve (PNS)
3. Interpretation & analysis of impulses in control center (CNS)
4. Transmission of impulse along nerve (PNS)
5. Response by effector muscle, gland, organ
What is a nerve? many
neurons bundled together
can be compared to a cable
Nervesbundle of neurons
Neurons
What is a neuron? specialized cell
that transmits nerve impulses (carries messages) through the body
can compare to electrical wires
What are the main parts of a neuron? dendrites▪ receive impulses & move
them toward cell body cell body (soma)▪ nucleus & cytoplasm
axon▪ carries impulses away from
cell body towards end branch▪ terminal buttons/end branch of
axon▪ help send impulses to next neuron or
effector (muscle, organ, gland)
Neurons
Terminal buttons/end branch of axon
What are the other parts of a neuron? myelin sheath▪ fatty layer surrounding axon
that protects it & allows impulses to move quickly
Schwann cells▪ make myelin
Nodes of Ranvier▪ sections of axon between
Schwann cells not covered in myelin sheath▪ help transport impulses
quickly
Neurons
cell body (soma)
terminal buttons/end branch of axon
Dendrites
Direction of impulse
Neurons
How do messages move along a neuron? an electrical
charge moves along the axon▪ in one direction from
dendrites to the end branch of the axon▪ So, there are 2
different pathways… sensory receptor to control
center control center to effector
(muscle, gland, organ)
The Pathway of Impulses
Do neurons touch each other? No, they are separated by
a synapse.▪ small, fluid-filled space▪ between end branch of axon (of
one neuron) and dendrites of next neuron
So, how do messages get from one neuron to the next?▪ neurotransmitters▪ chemical messengers that help
impulse cross synapse
The Pathway of Impulses
What are the types of neurons involved in the pathway of impulses? sensory neurons▪ transmit incoming impulses (stimuli)▪ from receptors to control center
interneurons ▪ transfer impulses within control
centers (brain & spinal cord)▪ from sensory to motor neurons
motor neurons▪ transmit outgoing impulses▪ from control center to effectors
muscles, glands, organs
Sensory neuron
Motor neuron
interneuron
Stimulus
response
interpretation
The Pathway of Impulses
Reflexes What is a reflex?
involuntary/automatic response to stimuli▪ Involve CNS, but
does NOT require conscious control or decision making b/c determined by fixed pathways▪ some through brain
(ex. blinking)▪ others through spinal
cord (ex. touch cactus & respond) known as reflex arc
interneuron
5 Steps of the Reflex Arc & the Initial Response
Reflex arc1. Receptors detect stimulus & are
activated2. Sensory neuron transmits
impulse towards spinal cord3. Impulse crosses synapse to
interneuron in spinal cord4. From spinal cord impulse crosses
synapse to motor neuron & leaves spinal cord
5. Impulse activates effectors (muscle, gland, organ) which responds 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 in spinal cord where interpreted & analyzed
4. impulse crosses synapse from spinal cord motor neuron & leaves spinal cord
1. Sensory receptor receives stimulus & is activated.
5. Impulse received by effector (which responds appropriately)
interneuron
5 Steps of the Reflex Arc & the
Initial Response
Interneuron = association nerve
ReflexArc
The Secondary Response: After the Reflex ArcSince reflex actions (arcs) don’t
involve the brain, how does your brain become aware? Some spinal cord interneurons that
receive sensory impulses connect w/ the brain▪ This path is slower than the reflex arc▪ So, brain becomes aware of what has happened after your body has already responded. secondary response… You yell, “Ouch!”
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