422
UNIT 3
Regulation and Integration of the Body
11
pathways from receptors to the brain are also examples. Because
reflexes are the functional units of the nervous system, it is im-
portant that you understand them early on.
Reflexes
are rapid, automatic responses to stimuli, in which
a particular stimulus always causes the same response. Reflex
activity, which produces the simplest behaviors, is stereotyped
and dependable. For example, if you touch a hot object you jerk
your hand away, and an object approaching your eye triggers a
blink. Reflexes occur over neural pathways called
reflex arcs
that
have five essential components—receptor, sensory neuron, CNS
integration center, motor neuron, and effector
(Figure 11.24)
.
Parallel Processing
In
parallel processing
, inputs are segregated into many pathways,
and different parts of the neural circuitry deal simultaneously
with the information delivered by each pathway. For example,
smelling a pickle (the input) may cause you to remember pick-
ing cucumbers on a farm; or it may remind you that you don’t
like pickles or that you must buy some at the market; or perhaps
it will call to mind
all
these thoughts. For each person, parallel
processing triggers unique pathways. Te same stimulus—pickle
smell, in our example—promotes many responses beyond sim-
ple awareness of the smell. Parallel processing is not repetitious
because the circuits do different things with the information, and
each pathway or “channel” is decoded in relation to all the others
to produce a total picture.
Tink, for example, about what happens when you step on
something sharp while walking barefoot. Te serially processed
withdrawal reflex causes you to remove your foot immediately
from the sharp object (painful stimulus). At the same time, pain
and pressure impulses are speeding up to your brain along par-
allel pathways that allow you to decide whether to simply rub
the hurt spot to soothe it or seek first aid.
Parallel processing is extremely important for higher-level
mental functioning—for putting the parts together to under-
stand the whole. For example, you can recognize a dollar bill in
a split second. Tis task takes a serial-based computer a fairly
long time, but your recognition is rapid because you use parallel
Input
Input 1
Input
Input
Input 2
Input 3
Output
Output
Output
Many outputs
(a) Diverging circuit
• One input, many outputs
• An
amplifying
circuit
Example:
A single neuron in
the brain can activate 100 or
more motor neurons in the
spinal cord and thousands of
skeletal muscle fibers
(b) Converging circuit
• Many inputs, one output
• A
concentrating
circuit
Example:
Different sensory
stimuli can all elicit the same
memory
(c) Reverberating circuit
• Signal travels through a chain
of neurons, each feeding back
to previous neurons
• An
oscillating
circuit
• Controls rhythmic activity
Example:
Involved in
breathing, sleep-wake cycle,
and repetitive motor activities
such as walking
(d) Parallel after-discharge
circuit
• Signal stimulates neurons
arranged in parallel arrays that
eventually converge on
a
single output cell
• Impulses reach output cell at
different times, causing a burst
of impulses called an
after-
discharge
Example:
May be involved in
exacting mental processes
such as mathematical
calculations
Figure 11.23
Types of circuits in neuronal pools.
1
2
3
4
5
Receptor
Sensory neuron
Integration center
Motor neuron
Effector
Stimulus
Response
Spinal cord (CNS)
Interneuron
Figure 11.24
A simple reflex arc.
Receptors detect a change in
the internal or external environment that elicits a rapid stereotyped
response. Effectors are muscles or glands.
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