Lesson 18 Flashcards
reflexes
quick, involuntary, stereotyped reaction of glands or muscle to stimulation; controlled by the spinal cord alone
what do reflexes require? (4)
require stimulation, quick, involuntary, stereotyped
somatic reflexes
reflexes involving the somatic nervous system, innervating skeletal muscle
visceral reflexes
reflexes involving organs such as heart and intestines
reflexes generally _____ original stimulus, what is this called?
opposes; negative feedback
somatic reflex arc (5)
- somatic receptors in skin, muscle, or tendons
- afferent nerve fibers carry information from receptors to posterior horn of the spinal cord or the brainstem
- integrating center: a point of synaptic contact between neurons in gray matter of the spinal cord or brainstem
- effect nerve fibers carry motor impulses to muscles
- effectors the muscles that carry out the response
four classification of reflexes
- development
- type of motor response
- complexity of neural circuit
- site of information processing
innate reflexes (3)
- formed before birth
- basic neural reflexes
- withdrawal from pain, chewing, sucking, tracking objects with eyes
acquired reflexes (3)
- learned motor patterns
- rapid, automatic
- riding a bike, pressing breaks when cut off
motor response
nature of resulting motor response
somatic reflexes (3)
involuntary control of the nervous system
1. superficial reflexes of the skin and mucous membranes
2. stretch or deep tendon reflexes
visceral reflexes
aka autonomic reflexes
- control systems other than muscular system
- smooth/cardiac muscles, glands, adipose tissue
monosynaptic reflex
sensory neuron synapses directly onto motor neurons
polysynaptic reflex
at least one interneuron between the sensory and motor neurons
spinal reflexes
occur in the spinal cord
cranial reflexes
occur in the brian
intersegmental reflex arcs
- many spinal segments interact producing highly variable motor responses
monosynaptic reflex arcs (3)
- little synaptic delay
- very prompt response
- knee-jerk reflex
reciprocal inhibition
reflex phenomenon that prevents muscles from working against each other by inhibiting antagonist when agonist is excited
stretch (myotatic) reflex (3)
when a muscle is stretch it “fights back” and contracts
- helps maintain equilibrium and posture
- stabilizes joints
what is the stretch reflex primarily mediated by?
the brain, but it’s spinal component can be more pronounced if muscle is suddenly stretched by a tendon tap (like knee jerk)
muscle spindles (4)
stretch receptors embedded in skeletal muscles
- serve as proprioceptors
- inform brain of muscle length and body movement
- enable brain to send motor commands back to the muscles and control coordinated movement
intrafusal fibers
modified muscles fibers within a muscle spindle
extrafusal fibers
muscle fibers outside the muscle spindle that generate force
gamma motor neuron
innervates the ends of an intrafusal fiber and keeps it taut, allowing the CNS to adjust sensitivity to the spindle; allows voluntary contraction to NOT trigger the reflex
where is the gamma motor neuron located?
the anterior gray horn of the spinal cord
what do alpha motor neurons innervate?
extrafusal fibers (aka normal muscles)
the _____ of the intrafusal fiber contains sensory nerve fibers
midportion
primary afferent fibers in muscles
monitor fiber length and speed of length changes
secondary afferent fibers
monitor length only
postural reflex
a type of stretch reflex, helps keep you upright when standing on a boat
steps of the patellar reflex (7)
- tap on patellar ligament excites nerve endings of muscle spindle in quadriceps
- stretch signals travel to spinal cord vis primary afferent fiber and dorsal root
- primary afferent neuron stimulates alpha motor neuron in spinal cord
- efferent signals in alpha motor nerve fiber stimulate quads to contract
- at the same time, a branch of the afferent nerve fiber stimulates inhibitory motor neuron in the spinal cord
- that neuron inhibits alpha motor neurons that supply hamstrings
- hamstring contraction is inhibited so hamstrings do not antagonize quads
five general characteristics of polysynaptic reflexes
- involves pools of interneurons
- involve reciprocal inhibition
- have reverberating circuits
- are intersegmental in distribution
- several reflexes cooperate
polysynaptic reflex arc
pathway in which signals travel over many synapses on their way to the muscle
flexor reflex
the quick contraction of flexor muscle resulting in the withdrawal of a limb from an injurious stimulus
reciprocal inhibition
relaxation of the extensors in a limb which is undergoing a reflex
tendon organs
proprioceptors in a tendon near its junction with a muscle; involved in the tendon reflex
tendon reflex
response to excessive tension on the tendon by inhibiting muscle from contracting strongly
crossed extension reflex
contraction of extensor muscles in the limb opposite to the one that is withdrawn
ipsilateral reflex arc
stimulus and response are on the same side of the body
contralateral reflex arc
input and output are on opposite sides of the body
intersegmental reflex
one in which the input and output occur at different levels or segments of the spinal cord
reinforcement of spinal reflexes (3)
higher centers reinforce spinal reflexes by stimulating excitatory neurons in the brain stem or spinal cord
- EPSPs
- facilitating postsynaptic neurons
Jendrassick maneuver
hooks fingers together to try and pull hands apart, reinforces the knee jerk reflex
inhibition of spinal reflexes (3)
higher centers inhibit reflexes by:
- stimulating inhibitory neurons
- creating IPSPs
- suppressing postsynaptic neurons
Babinski’s sign
displayed by infants normally, but may indicate CNS damage in adults
neural pools
functional grouping of neurons; each pool consists of thousands of interneurons concerned with a particular body function
diverging circuit
one nerve fiber branches and synapses with several postsynaptic cells
converging circuit
input from many different nerve fibers can be funneled to one neuron or neural pool
reverberating circuit
positive feedback; neurons stimulate each other in linear sequence but one or more of the later cells re-stimulates the first cell to start the process all over again
parallel after-discharge circuit
input neuron diverees to stimulate several chains of neurons
what does after-discharge mean?
continuation of firing after the stimulus stops; staring at a bright light, then closing your eyes and still seeing it
serial processing
neurons and neural pools relay information along pathways in relatively simple linear fashion
how many flows of info can serial processing, process?
just one, you cannot really multitask
parallel processing
information is transmitted along diverging circuits through different pathways that act on it simultaneously for different purposes; think all the things that go into driving
complete transection
complete severance of the spinal cord
complete transection of the spinal cord above what vertebra poses a threat of respiratory failure?
C4
what comes from complete transection?
intermediate loss of motor control below level of injury
paraplegia
paralysis of both lower limbs
quadriplegia
paralysis of all four limbs
hemiplegia
paralysis on one side of the body
paresis
partial paralysis or weakness of the limbs
