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1/3/2013

BSC 2086L

Anatomy & Physiology
Lab II

Chap 22: Human Reflex Physiology
Chap 23: General Sensation

Chap 22: Reflex Physiology
Reflex Arc: mediated by neural paths (connections
of neurons) to yield rapid involuntary muscle
response to stimuli
Two main groups of reflexes:
1) Autonomic: mediated thru autonomic nervous sys
(smooth muscles in digestion, glands in sweating)
2) Somatic: involve sensory stimulation that causes
skeletal muscles to react (withdrawal reflex from
pain)

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Components of Reflex Arc
1. Receptor: site of stimulus
2. Sensory neuron: transmits
afferent impulse to central
nervous system (CNS)
3. Integration center: one or
more synapses in CNS
4. Motor neuron: conducts
efferent impulse to effector
5. Effector: muscle/glands
respond to impulses

Monosynaptic & Polysynaptic Spinal Reflex
Arcs
Spinal reflexes: initiated & completed at spinal cord
level without involvement of higher brain centers.
Remember, these are somatic reflexes.
Knee-jerk reflex: utilizes a 2 neuron (sensory and
motor neurons)
Flexor reflex: utilizes sensory and motor neurons
connected by interneurons
arc.

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Somatic Reflexes (cont)
Spinal reflex:
1. Stretch reflex: maintains posture/balance &
locomotion; tendon stretch causes agonist
muscle contraction and antagonistic relaxation.
e.g. Patellar (knee jerk) reflex

2. Crossed extensor reflex: flexion of one limb
followed by extension of opposite limb.
3. Superficial cord reflex: result from pain and
temperature changes. e.g. Plantar reflex

Somatic Reflexes (cont)
Cranial Nerve Reflex
1. Corneal reflex: a function of cranial nerve V
(trigeminal). Touching of the cornea causes
blinking to occur.
2. Gag reflex: a function of cranial nerves IX
(glossopharyngeal) & X (vagus). Touching of
the uvula causes gag reflex.

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Autonomic Reflexes
Pupillary reflexes: reflex caused by light stimulation
of cranial nerve II (optic) causing iris constriction
by cranial nerve III (oculomotor)
1. Pupillary light reflex: pupil constricts due to
light stimulus
2. Consensual reflex: light stimulation of one eye causes
pupil constriction in contralateral (opposite side) eye

Ciliospinal reflex: stimulation of back of neck causes
ipsilateral (same side) pupil dilation

Salivary reflex: food odor detection causes salivation

Chap 23: General Sensation
General senses: general sensory receptors respond to
touch, pressure, pain, heat, cold, stretch, vibration,
& body position. Found throughout body
Special senses: localized in groups; receptors for
sight, hearing, equilibrium, smell, & taste
Types of Receptors that can detect stimuli:
Exteroceptors: react to external stimuli
Interoceptor/visceroceptor: react to internal stimuli
Proprioceptor: detects body/limb position

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General Sensory Receptors
Structures:
Free/naked nerve endings:
Tactile (Merkel) disc: detects light touch
Hair follicle receptor: detects light touch

Encapsulated nerve endings:

Lamellated (Pacinian) corpuscle: detects deep
pressure/high frequency vibrations

Receptor Physiology
Four qualities of cutaneous sensations: touch, heat,
cold, & pain. They are non-uniformly distributed
throughout the body (hands have more touch
receptors than arm, etc). Distribution based on the
importance of the area and the need for those
receptors.

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Receptor Physiology (cont)
Stimulus detection terminology:
Two-point threshold: smallest distance 2 points of contact
can be perceived (use a vernier caliper for this activity)

Tactile localization: determining which point on skin has

been stimulated
Adaptation: sensory receptor discharge from stimulus slows
causing the perception of stimulus to decrease
Referred pain: perception of pain from one area of body
when another area is actually receiving the noxious stimulus

How to use/read a vernier caliper

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