KIN 103 (Chp: 13) Flashcards
What is a reflex?
A reflex is an involuntary response to the activation of a sensory receptor.
Monosynaptic reflexes
Monosynaptic reflexes- a single synapse between afferent and efferent neurons.
Polysynaptic reflexes
Polysynaptic reflexes- two or more synapses in the CNS
Proprioceptors
are located in skeletal muscles, joints, ligaments and the skin (muscle spindles, Golgi tendon organs, joint receptors, cutaneous receptors)
“proprius”- latin for “ones own”
Alpha motor neurons are always what?
Somatic motor neurons carry output signal (Alpha motor neurons)- always excitatory
Muscle spindles (What do they do?)
Muscle spindles provide information about static muscle length (position) and the rate of change of muscle length (velocity, acceleration).
Extrafusal muscle layer (What is it made of)
- Extrafusal muscle fibers
- Alpha motor neurons (invertebrates exfsal)
Intrafusal muscle layer (what is it made of)
- Intrafusal muscle fibers
- Gamma motor neurons (control from CNS)
(It is also found in muscle spindles)
Muscle spindles (Tonic firing)
- extrafusal muscle fibers are at rest
- sensory neuron is tonically active
- spinal cord integrates function
- alpha motor neurons to extrafusal fibers receive tonic input from muscle spindles
- extrafusal fibers maintain a certain level of tension even at rest
Muscle spindle reflex (What is it?)
The addition of a load stretches the muscle and the spindles creating a contraction
Muscle spindle reflex (What kind of loop is it?
The stretch reflex is a negative feedback loop that helps overcome unexpected disturbances and bring the limb back into position.
The muscle spindle reflex (when the muscle contracts what happens to the afferent signal?)
- the firing rate of the afferent neuron will decrease therefore causing negative feedback to occur
Alpha-gamma co-activation (What is it?)
Alpha-gamma co-activation maintains the sensitivity of the spindle when the muscle shortens voluntarily and the spindle might otherwise fall slack and become unresponsive to externally applied stretches.
Microneurography (What is it?
Using microneurography you can record action potentials as they travel along single human axons.
Patellar tendon reflex (What is it?)
- a monosynaptic stretch reflex
- accompanied by reciprocal inhibition of the antagonistic muscle.
Golgi tendon organs (What do they do?)
- Are located in the musculotendinous junction
- Golgi tendon organs discharge during contractions and provide information about contraction force
- Information from Golgi tendon organs is integrated in the CNS to help control movement
Cutaneous mechanoreceptors (What are they?)
Cutaneous mechanoreceptors provide information about tactile stimuli and limb movement.
Flexion and crossed extensor reflexes (What are they?)
essentially that when someone steps on something there will be a reflex that reaches the spinal cord only to activate an inverse response that pulls the individual away from the painful stimulus
Kinesthesia (What is it?)
Kinesthesia: the ability to consciously perceive the position and movement of the body segments without the aid of vision.
- Thought that muscle spindles are the cause of this
Muscle spindles and vibration
- Muscle spindles are highly sensitive to vibration
Illusions of movement- vibrate tendon on one side, subject matches any perceived movement with opposite limb
Reflex (characteristics)
stimulus: external sensory receptors
complexity: least complex
voluntary movement (characteristics)
stimulus: external stimulus or at will
complexity: most complex (cereberal cortex)
rhythmic movement (characteristics)
stimulus: initiation/termination voluntary
complexity: spinal cord but higher input required
Role of thalamus and cerebellum
Thalamus: contains relay nuclei that pass message to cerebral cortex
cerebellum: monitors output signals from motor areas and adjusts signals
Central patter generators (where are they?)
The spinal cord also houses central (locomotor) pattern generators, that generate the basic motor output from the spinal cord to muscles to produce walking
Central pattern generators (what are they?)
Rhythmic movements are controlled by CPGs flying, breathing, swallowing, vomiting, locomotion.
Half center model of CPGs
- “Half-centres” receive a descending signal from the brain to move
- Each half Centre reciprocally inhibits the other, keeping one “off” while the other is “on”
What can CPGs be used for in rehabilitation?
spinal cord injury rehabilitation
Control of voluntary movements (Planning movement components)
Cerebellum, cortical association areas, and basal ganglia
Control of voluntary movements (Initiating movement components)
Motor cortex
Control of voluntary movements (Executing movement components)
Cerebellum
Frontal lobe (what does it do?)
Coordinates information from other association areas, controls some behaviors
Parietal lobe (what does it do?)
Sensory information from skin, musculoskeletal system, viscera and taste buds
Gustatory cortex (what is it?)
Sense of taste area
The corticospinal tract (what is it?)
Most important descending motor pathway in humans (~1 million fibres)
Originates in motor cortex and crosses over in the brainstem
Makes mono- and polysynaptic connections with motor neurons
BCI’s (What are they?)
BCI’s are essentially interfaces that allow a machine to control the body’s movements through an implant in the brain
Parkinson’s disease background
- In 1817 Dr. James Parkinson published “Essay on the Shaking Palsy”
- in the 1920’s the brains of Parkinson’s patients were found to have extensive degeneration in the basal ganglia
- 1960s learnings (less dopamine = less movement)
Parkinson’s symptoms (resting tremor)
. Resting tremor- tremor at rest (4-6 Hz)
- often starts with “pill-rolling” tremor (hand)
- eventually tremor on one or both sides of the body
- tremors reduced during movement
Parkinson’s symptoms (Rigidity)
- increased co-contraction around joints leads to increased resistance to stretch
- results in reduced arm swing during walking and “mask-like” (emotionless) face
Parkinson’s symptoms (Bradykinesia)
- slowness of movement, increasing difficulty in generating voluntary movements
Parkinson’s symptoms (Akinesia)
inability to initiate movement (freezing)
Parkinson’s symptoms (postural instability)
Postural instability- impaired balance and coordination, progressively flexed posture
Parkinson’s symptoms (Festination)
small quick steps
Parkinson’s 7 symptoms (all together)
- Resting tremor
- Rigidity
- Bradykinesia
- Postural instability
- festination
- Akinesia
- mood and others
What causes Parkinson’s
Loss of dopaminergic neurons in SN
What does a Parkinson’s patient brain look like?
Brains of people who had Parkinson’s have a characteristic pale color on post-mortem
(although the substantia nigra region turns a dark colour)
At what point does Parkinson’s set in?
Symptoms of PD appear after 60-70% of dopaminergic cells in SNpc are lost, typically occurs over 5-10 years.
How long is life expectancy after the symptoms appear?
life expectancy is 15-25 years after symptoms appear
What happens in the motor cortical areas of a PD patient?
- loss of dopamine cells in substantia nigra
- less dopamine = less movement
- increased inhibitory output of basal ganglia = less excitation of motor cortical areas
(HYPOkinetic movement)
Parkinson’s disease rehabilitation (main target?)
- Increase dopamine in substantia nigra
- L-DOPA - Disrupt excessive output
- surgical lesions
- deep brain stimulation
L-DOPA (What is it?)
L-DOPA crosses the blood brain barrier and is converted to dopamine in the substantia nigra
L-DOPA (What effects does it have?)
- Often a dramatic reduction of symptoms in the first year (read/see Awakenings)
- effects decline with use
- less improvement is seen over the years
- can no longer offset the death of dopaminergic neurons in striatum
Surgical treatments for Parkinson’s disease (2 of them)
- Subthalamic nucleus lesion
- Globus pallidus lesion pallidotomy
- small (pearl sized) lesion is burned into the part using electrical stimulation
- the effects can be long lasting without negative effects
Deep brain stimulation (DBS)
Stimulation of different regions of the basal ganglia can be effective at reducing Parkinsonian symptoms
- they locate the target area by listening to characteristic discharge of the cells as the electrode advances
