Chapter 13 Notes
Receptors
Classification of receptors by stimulus:
Mechanoreceptors
Respond to
mechanical force
(Touch, pressure,
vibration , and
stretch
Thermoreceptors
Respond to
changes in
temperature
Photoreceptors
Respond to light
energy
Chemoreceptors
Respond to
chemicals in
solution.
Nociceptors
Respond to
potentially
damaging stimuli
that results in
pain. Extremes
(heat, cold,
pressure,
inflammatory
chemicals
Classification of receptors by location
Exteroceptors
Sensitive to stimuli coming from
outside to body. Most are
located at or near the surface of
the body. Touch, pressure,
pain, temperature,, and most of
the special senses.
Interoceptors (visceroceptors)
Respond to stimuli from inside
the body. (visceral organs and
blood vessels) monitor chemical
changes, tissue stretch, and
temperature. Feel pain, hunger,
etc.
Proprioceptors
Respond to internal stimuli,
located in skeletal muscles,
tendons, joints, ligaments and
coverings of bones and muscles.
Respond to stretch.
Classification of receptors by structural complexity
Simple receptors
Most are simple.
Complex receptors
Sense organs - collections of cells associated with
the special senses.
Unencapsulated –free nerve endings of sensory
neurons, modified free nerve endings (merkel
Discs) Hair follicle receptors.
Encapsulated – Meissner’s corpuscle, Pacinian
Corpuscle, Ruffini endings, muscle spindles, Golgi
Tendon Organs, Joint kinesthetic receptors
What makes up a nerve?
Axons are wrapped in endoneurium (connective tissue) and then bundled together and wrapped in
perineurium. These bundles are called fascicles. Fascicles are then bundled together with blood vessels
and wrapped together with Epineurium.
Nerves that only contain axons that signals travel toward the CNS are sensory (afferent) nerves, signals
that travel away from the CNS are motor (efferent) nerves, but most nerves are mixed. This means that
within a nerve, there are axons that are sensory (afferent) and axons that are motor (efferent).
Peripheral nerves are classified as Spinal or Cranial depending on where they originate from.
Cranial Nerves - 12 pairs
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Olfactory – nasal
Optic – actually a brain tract, eyes
Oculomotor – eye mover
Trochlear – eye mover
Trigeminal - Largest, three branches, sensory for face, motor for chewing
Abducens – eye mover (abducts)
Facial – facial expression
Vestibulocochlear – sensory for hearing and balance
Glossopharyngeal – tongue and pharynx
Vagus – “wanderer” cranial nerve that extends into the thorax/abdomen
Accessory – accessory to the vagus nerve
Hypoglossal – “under the tongue” tongue
Spinal Nerves - 31 pairs
All are mixed nerves. Each nerve leaves the spinal column inferior to the vertebra they are named after.
8 pairs are cervical nerves (C1-C8)
12 pairs are Thoracic nerves (T1-T12)
5 pairs of Lumbar nerves (L1-L5)
5 pairs of Sacral nerves (S1-S5)
1 pair of Coccygeal nerves (Co1)
The spinal nerves have Rami which are “branches” that combine neurons from both the dorsal root and
ventral roots. This is why they are mixed nerves, when the roots themselves, are not mixed. Ventral
Rami are larger and form plexuses. Plexuses are interlacing nerve networks.
Cervical plexus – neck
Brachial Plexus – upper chest, shoulder, arm
Lumbosacral plexus – lumbar and sacral plexuses converge and connect together. Hip, abdomen,
buttock and leg.
Sacral plexus – (L4-S4) – sciatic nerve comes from this. It is the longest and thickest nerve in the body.
Reflex arcs
Parts of a Reflex arc – Receptor, sensory neuron, integration center, motor neuron, effector.
Reflexes are somatic if they activate skeletal muscle, and autonomic if they activate visceral effectors.
Stretch reflex
Golgi Tendon reflex
Ensures that the
muscle stays at the
length that the brain
sets. If it stretches, the
reflex is to contract the
muscle to shorten it
back to the set length.
(ie. Patellar or knee
jerk reflex)
When a muscle
endures a substantial
increase in tension
during contraction or
passive stretching, the
result is inhibition on
the contracting muscle,
and the antagonist
muscle is activated.
Flexor and crossed
extensor reflexes
Flexor is the
withdrawal reflex from
a painful stimulus. The
crossed-extensor reflex
often accompanies the
flexor reflex. It helps
maintain balance. If
you step on a sharp
object, you have Flexor
reflex to remove from
pain, and crossed
extensor to balance on
one foot.
Superficial reflexes
Plantar reflex – curling
of the toes after a
stimulus to the sole of
the foot.
Abdominal reflexes –
stimulus to skin of
abdomen results in
abdominal muscle
contraction.
Chapter 14 - Autonomic nervous system
The autonomic nervous system (think automatic – you do not need to process and decide consciously
what to do, it automatically is done for you) is broken down into the parasympathetic and sympathetic
nervous systems.
Both of the following charts are represented as one chart in your text page 538
The parasympathetic and sympathetic work together to help us operate/function. One of the main
reasons this can happen is the release of different neurotransmitters and their partnering receptors.
Some neurotransmitters have an excitatory effect, and some have an inhibitory effect. (Remember
from Chapter 11 chart)
What controls the ANS? Hypothalamus is responsible for most control. The brainstem, spinal cord,
limbic system of Cerebral cortex also are involved.
Diseases –
Hypertension – too much control of the sympathetic nervous system causing vasoconstriction.
Raynaud’s disease – exaggerated vasoconstriction of the digits, resulting in lack of blood flow to the
fingers/toes, and can result in cell death.
Autonomic dysreflexia – life threatening lack of control of the autonomic neurons. Resulting in over
filling of a visceral organ, skyrocketing blood pressures, too much pain in skin.