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uitgebreide Samenvatting hoofdstuk 11 silverthorn human physiology
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Fleur sam ch 11To go in less than 1 second from state of quiet rest to panic: reflex flight-or-fight reaction. Which is
integrated and coordinated through the CNS, then carried out by efferent division of the PNS.
Efferent neurons carry rapid commands from the CNS to the muscles and glands of the body through
nerves, or bundles of axons. Some nerves, called mixed nerves, also carry sensory info through
afferent fibers.
The efferent division of the PNS can be subdivided into:
- Somatic motor neurons, which control skeletal muscles. Voluntary division of nervous
system.
- Autonomic neurons, which control smooth muscle, cardiac muscle, many glands and some
adipose tissue. Involuntary division of nervous system.
Voluntary vs involuntary distinction is not always true. Most movement controlled by somatic
pathways require conscious thought, but some skeletal muscle reflexes, like swallowing and knee-
jerk reflex, are involuntary.
Autonomic reflexes are mainly involuntary, but person can use biofeedback training to learn to
modulate some autonomic functions such as heart rate and blood pressure.
Autonomic division of efferent nervous system (or autonomic nervous system) is also known in older
writings as the vegetative nervous system, reflecting the observation that its functions are not under
voluntary control. Also known as visceral nervous system, bc of control over internal organs.
Autonomic division is subdivided into sympathetic and parasympathetic branches. Sympathetic and
parasympathetic branches can be distinguished anatomically, but there is no simple way to separate
the actions of the 2 branches on their targets.
If you are resting, parasympathetic branch is dominant, taking the command of quiet activities, day-
to-day living like digestion. Rest and digest functions.
Sympathetic branch dominates in stressful situations, like potential threat.
Bv. Of sympathetic action is the flight-fight response, in which the brain triggers massive
simultaneous sympathetic discharge throughout the body. Heart speeds up, blood vessels to
muscles/arms/legs/heart dilate, liver produces glucose to provide energy for muscle contraction.
Digestion low priority. Blood diverted from gastrointestinal tract to skeletal muscles.
Massive sympathetic discharge that occurs in flight-or-fight situations is mediated through the
hypothalamus and is total-body response to a crisis.
Most sympathetic responses are not the all-out response of a flight-flight reflex, however, activating
one sympathetic pathway does not automatically activate them all. Role of sympathetic nervous
system in daily activities is as important as flight-fight response. Bv. Sympathetic branch controls
blood flow to the tissues.
Most of the time, autonomic control of body function seesaws back and forth between sympathetic
and parasympathetic branches as they cooperate to fine-tune various processes.
Autonomic nervous system works closely with the endocrine system and the behavioral state system
to maintain homeostasis in the body. Sensory info from somatosensory and visceral receptors goes
, to homeostatic control centers in the hypothalamus, pons and medulla. These centers monitor and
regulate important functions like blood pressure, temp control, water balance.
Hypothalamus also contains neurons that act as sensors, such as osmoreceptors, which monitor
osmolarity, and thermoreceptors, which monitor body temp.
Motor output from the hypothalamus and brain stem creates autonomic responses, endocrine
responses, behavioral responses like drinking, food-seeking, temp. regulation. These behavioral
responses are integrated in brain centers responsible for motivated behaviors and control of
movement.
Sensory info integrated in the cerebral cortex & limbic system can create emotions that influence
autonomic output.
Emotional influences on autonomic functions, bv. Blushing, fainting at the sight of a hypodermic
needle, butterflies in the stomach.
Understanding the autonomic and hormonal control of organ systems is the key to understanding
the maintenance of homeostasis in every system of the body.
Some autonomic reflexes can take place without input from brain. These spinal reflexes include
urination, defecation, penile erection- body functions that can be influenced by descending pathways
from the brain but do not require this input. Bv. People with spinal cord injuries that disrupt
communication between brain and spinal cord may retain some spinal reflexed but lose ability to
sense or control them.
Sympathetic and parasympathetic branches of autonomic nervous system display all 4 of walter
cannon’s properties of homeostasis:
1. preservation of the fitness of the internal environment
2. up-down regulation by tonic control
3. antagonistic control
4. chemical signals with different effects in different tissues.
Many internal organs are under antagonistic control, in which one autonomic branch is excitatory
and other branch is inhibitory. Bv. Sympathetic innervation increases heart rate, parasympathetic
decreases it. So heart rate can be regulated by altering the relative proportions of sympathetic and
parasympathetic control.
Exceptions to dual antagonistic innervation include sweat glands and smooth muscle in most blood
vessels. Those tissues are innervated only by sympathetic branch and rely only on tonic (up-down)
control.
2 autonomic branches are usually antagonistic in their control of a given target tissue, but they
sometimes work cooperatively on different tissues to achieve common goal. Bv. Blood flow for penile
erection is under control of parasympathetic branch, while muscle contraction for sperm ejaculation
is directed by sympathetic branch.
In some autonomic pathways, the neurotransmitter receptor determines the response of the target
tissue. Bv. Most blood vessels contain 1 type of adrenergic receptor, that causes smooth muscle to
contract. But some blood vessels contain a second type of adrenergic receptor that causes smooth
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