Exam 4, Chapter 13b - Somatic Motor (Part 2) Flashcards
- Receptor
- Sensory neuron
- Integration center
- Motor neuron
- Effector
Reflex Arcs
Five Components of
site of stimulus
Reflex Arcs
Receptor
transmits the afferent impulse to the CNS
Reflex Arcs
Sensory neuron
either monosynaptic or polysynaptic region within the CNS
Reflex Arcs
Integration center
conducts efferent impulses from the integration center to an effector
Reflex Arcs
Motor Neuron
muscle fiber or gland that responds to the efferent impulse
Reflex Arcs
Effector
For skeletal muscles to perform in a normal coordinated fashion, the nervous system needs
___ types of information:
Reflex Component Anatomy
2
Length of the muscle: provided by the
Reflex Component Anatomy
muscle spindles
Amount of tension in the muscles: provided by the
Reflex Component Anatomy
Golgi tendon organs (proprioceptors)
Composed of modified muscle fibers called intrafusal muscle fibers that are wrapped in a
connective tissue capsule (the spindle = fusal) and serve as receptive surfaces.
Muscle Spindles
Only the ends of the ___ are contractile & are innervated by gamma (gamma) efferent fibers
Muscle Spindles
Contractile skeletal muscle fibers are extrafusal fibers & are innervated by alpha (α) efferent fibers
Muscle Spindles
signals from the brain cause the muscle spindles to be more taut (greater force of extrafusal contraction can be anticipated; e.g. high vertical jump) or to be
less taut, as the situation demands
Operation of the Muscle Spindles
Gamma / efferent
Stretching the muscles also activates the ____, which then sends afferent impulses to the spinal cord
Muscle spindles
The greater the rate and degree of stretch, the ___ the impulse frequency
Muscle spindles
higher
Stretch Reflex
Patellar Reflex Example
Tapping the patellar tendon quickly - stretches the quadriceps and starts the reflex action
yes
Stretch Reflex
Patellar Reflex Example
The ___ is activated and sends afferent impulses to the spinal cord (dorsal horn)
-Two components!
muscle spindle
synapses with an alpha (alpha) motor neuron in the ipsilateral
ventral horn causing immediate contraction of the quadriceps, with resultant knee extension
Monosynaptic component
the muscle spindle afferent simultaneously synapses with an inhibitory interneuron which subsequently synapses with the ventral horn α-motor neuron for the antagonist muscle (in this case, the hamstrings)
Polysynaptic component
While the quadriceps muscles are contracting, the hamstrings are inhibited and unable to resist the contraction.
Net result: Reciprocal Inhibition:
Stretch Reflex and Muscle Tone
The brain sends commands to _____ neurons, effectively setting a muscle’s length (or
tone).
gamma motor neurons
The stretch reflex assists in maintaining this “set point” for muscle tone, especially in
the postural muscles of the trunk
ex:
knees don’t buckle during squat (stretched quadriceps muscle triggers a stretch reflex, which causes the quadriceps to contract, preventing a fall)
activate skeletal muscles
Somatic (voluntary) reflexes: activate skeletal muscles
activate visceral effectors
Autonomic Reflexes
smooth muscle, cardiac muscle, glands
Autonomic Reflexes
Effectors
these are used as neurotransmitters
Autonomic Reflexes
Acetylcholine
Norepinephrine
Autonomic motor endings and visceral effectors are ___ than somatic junctions
Autonomic Reflexes
simpler
Visceral responses are faster?/slower? than somatic responses
Autonomic Reflexes
slower
Produces the opposite effect of the stretch reflex
Golgi Tendon Reflex and Flexor Withdrawal
are located in the muscle tendons and are activated during a significant increase in muscle tension (e.g.: carrying a dangerously heavy load)
Golgi Tendon Reflex and Flexor Withdrawal
Golgi Tendon Organs (GTO)
Helps prevent muscles and tendons from tearing when they are subjected to a damaging
stretching force
Golgi Tendon Reflex and Flexor Withdrawal
-The GTO afferent travels to the dorsal horn and synapses with an inhibitory
interneuron.
-This interneuron synapses with the ventral horn α-motor neuron for the
contracting muscle.
-The GTO afferent also synapses with an excitatory interneuron.
-This interneuron synapses with the ventral horn α-motor neuron for the antagonist muscle.
Golgi Tendon Reflex and Flexor Withdrawal
(contracting muscle relaxes & antagonist activates)
Golgi Tendon Reflex and Flexor Withdrawal
Net Result: Reciprocal Activation
-reflex is initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part
Flexor Withdrawal Reflexes
-Polysynaptic and ipsilateral
Flexor Withdrawal Reflexes
-overrides other spinal pathways and other reflexes
Flexor Withdrawal Reflexes
Protective
Can be overridden by descending signals from the brain (not pulling away from a needle
during a blood draw)
Flexor Withdrawal Reflexes
Protective
includes the flexor withdrawal component plus The contralateral side is extended
(opposite arm swing when you pull one back)
THINK DISCUS
Crossed Extensor Reflex
initiated by firmly/sharply stimulating the lateral aspect of the sole of the foot, moving medially at the metatarsal heads
Plantar reflex
normal response is downward flexion of all toes (including the hallux)
Plantar Reflex
abnormal plantar reflex where the hallux extends and pedal digits 2-5 fan laterally
Babinski’s sign
Indirectly tests for corticospinal tract functioning (Indicates an UMN lesion)
Babinski’s sign
