Sensory Systems Flashcards
Medial Lemniscal System Pathway General Information
Several Pathways
Merge into 1 large pathway
Point to Point somatotopic organization
Ascending Reticular Formation General Information
Primitive
Base of everything in nervous system
Input from all receptors
Important for arousal and deep pain
Four Aspects of a Stimulus
Modality- What kind of stimulation is it (Mechano, thermal, etc.)
Intensity- Conveyed by temporal summation (increased impulse frequency) and spatial summation (increased number of nerve fibers)
Duration- How long
Location- Where (somatotopic)
Proprioceptive Mechanoreceptors
Provide information about the effect of gravity on muscles as well as the differences between actual & intended movements
Provide feedback critical for appropriate CNS control of LMNs
Two types of muscle proprioreceptors
Muscle Spindle- Responds in change to length (Buried within muscle)
Golgi Tendon Organ- Responds to tension (on tendon)
Muscle Spindle Receptors
Stretch receptor present in most skeletal muscles
Sends information that is processed by the cerebrum via multiple tracts to determine position of body parts and the cerebellum via the spinocerebellar tracts to provide proprioceptive feedback on the position of body in space to help with coordination of movement. Also goes to reflex pathways
Coordinated Movement via Cerebellum
To achieve this cerebellum needs information:
Position of limbs via muscle spindles
Position of head and body in space via vestibular system
Intended movement via motor system
Muscle Spindle Anatomy
Composed of 4-8 intrafusal muscle fibers enclosed in a fibrous capsule that run in parallel with extrafusal muscle fibers
Extrafusal Muscle Fibers
Big muscle fibers (like in quadriceps)
Innervated by alpha motor neuron
Motor unit consists of extrafusal muscle & alpha motor neuron
Intrafusal Muscle Fibers
Innervated by gamma motor neuron
Fibers themselves are a proprioceptor. Detect static (chain fibers) and dynamic (bag fibers) changes in length.
Walled off by a fusiform collagen sheath
Ends are contractile area, middle is receptor. Stretch of the ends or extrafusal fibers cause stimulation of receptor.
Muscle Spindle Reflex
Muscle is stretched, lengthening intra and extrafusal fibers in parallel
Primary a1 afferent neuron discharges
Monosynaptic reflex arc causes firing of LMN alpha motor neuron in spinal cord
Muscle is shortened and spindles are shut off
So the result of reflex is muscles contraction
Function: Smooths and stabilizes movement
Tendon Reflex
Same exact thing as muscle spindle reflex used for neurological exam
Tapping tendon causes rapid/transient muscle stretch
Voluntary Movement
Mostly mediated indirectly through gamma motor neuron
Called gamma alpha loop
Gamma motor neuron is tonic
Golgi Tendon Organ
Connected in series with muscle fibers
Deformed with muscle contraction or stretch, firing 1b afferent neuron to ascending pathways for proprioception or segmentally for reflex
Golgi Tendon Organ Reflex
Safety mechanism for too much tension, relaxes muscle.
Polysynaptic reflex with inhibitory interneuron to inhibit muscle and cause relaxation. Also stimulates antagonistic muscle through a separate interneuron and efferent neuron