1) sensory receptor that transduces stimulus Σ

2) sensory/afferent neuron carrying APs from receptor to

3) integrating centers (grey matter) of CNS

4) LMN carrying APs from integrating centre to the effectors

5) effectors: mm or glands responding to motor neuron signals

What word defines a fast, predictable sequence of involuntary actions

(ie: muscle contractions or glandular secretions, which occurs in response to certain stimuli)

Respiratory movements

Digestion

Posture

Defensive movement

Walking

*reflexes form basis of all CNS activity*
*occur at brain and SC*

True or False?

We are aware or every single one of our reflex acts.

False

Some reflex acts are conscious while other occur without our knowledge

Which types of reflexes involve integration of activity (at many levels) of the spinal cord and allow coordination of motor activity among the limbs and axial muscles?

Intersegmental reflex: involve integration of activity (at many levels) of the spinal cord and allow coordination of motor activity among the limbs and axial muscles?

*intersegmental reflex is  a complex spinal reflex*

Convergence

*allow a single site to serve as a summing point for activity originating from several other places*

Different sources competing for the final common pathway/convergence at the same time will be dominated by source that reinforce each other. Which sources will take precedence if no one source is compatible?

Painful stimuli (ie: protective reflexes) will take precedence over any other sources if not one source is compatible with one another

Supraspinal reflexes

*complex motor reflexes mediated by centers in the brainstem, cerebellum, BG, and other areas of the brain*

Vestibular reflex:  assist in the maintenance of overall posture and balance

What are results of abnormalities in vestibular reflexes?

the Vestibulospinal tract/indirect

*helps to maintain an upright and balanced posture by stimulating extensor motor neurons in the legs*

tectospinal tract: coordinates head and eye movement

*part of the extrapyramidal/indirect tract*

True or False?

The tectospinal tract is part of the exrapyramidal/indirect tract.

Complete the sentence

Spinal nerves are cell body located in motor nucleus of...

Complete the sentence

cranial nerves are cell body located in motor nucleus of...

Complete the sentence

Upper motor neurons are cell body in....

What is innervated by the lateral corticospinal tract?  What directs it? Where does it decussate?

Lateral corticospinal tract

Innervate: skeletal mm

Directed by: motor cortex

Decussate: medullar pyramids

*lateral corticospinal tract makes up 90% of tracts*

Corticobulbar tract

Innervate: muscles of the head/neck/face (CN7)

Directed by: motor cortex

Decussate:  only some

True or False?

The lateral corticospinal tract and corticobulbar tract are both extrapyramidal pathways

False

Lateral corticospinal and corticobulbar tract are both direct/pyramidal/corticospinal pathway

*direct pathway = 2 neuron system*

Indirect/extrapyramidal pathway

* multi-neuron system*

> Rubrospinal (involuntary tract)

> Vestibulospinal (involuntary tract)

> Tectospinal (involuntary tract)

Rubrospinal pathway

Innervates/directs:

> muscles of the shoulder and arm

> facilitates flexion and inhibits extension in the upper extremities

Directed by: red nucleus in midbrain

Which pathway innervates/directs: 

> correct position of head and neck

> vestibular reflexes; maintain upright and balanced posture by stimulating extensors/antigravity mm

Vestibulospinal pathway:

> correct position of head and neck

> vestibular reflexes; maintain upright and balanced posture by stimulating extensors/antigravity mm

*Directed by: brainstem*

Tectospinal pathway

Innervates/directs: coordination of head and eye mvmts

Directed by: brainstem

Decorticate posturing = damage to

> cerebral hemisphere

> internal capsule

> thalamus

*Damage above rubrospinal tract = abnormal flexion/ decorticate rigidity*

Complete the sentence

Lesions above the red nucleus cause.... of the red nucleus which results in the .... of the rubrospinal tract.

abnormal posturing = severe brain injury

*agonist and antagonists become unbalanced*

*e.g.: decorticate rigidity/flexor posturing: arms are flexed on the chest while the legs are extended*

stretch reflex/myotatic reflex/deep tendon reflex (DTR)

> involuntary contract of mm in response to a stretching force due to stimulation of m spindles?

*m spindle = stretch receptor*

What does each muscle spindle contain?

Each muscle spindle contains intrafusal fibres

*small m fibers enclosed in a CT capsule*

Gamma motor neurons (small motor neurons): regulate the sensitivity of the spindle to stretch

* intrafusal fibers are innervated by gamma motor neurons in the anterior horn of the SC*

shortening of the intrafusal fiber increases tension in the m spindle

*shortening of intrafusal fibers increases sensitivity to stretch*

*lowers the threshold for depolarization/fire of the 1a fibres*

What is innervated by large Alpha motor neuron/LMN/final common pathway?

Deep tendon reflex/DTR is procuted by tapping a tendon with a reflex hammer.  It causes:

> brief fast stretch of muscle including m spindles

Excitation of m spindle receptors results in:

> Contraction of the stretched m

> Relaxation of its antagonist (reciprocal inhibition/reciprocal innervation)

> Facilitation of motor neurons of synergistic mm

True or False?

The deep tendon reflex and the Golgi tendon reflex are the same reflexes

Complete the sentence:

The greater the degree of gamma activity, the .... the set length

The greater the degree of gamma activity, the shorter the set length

*when a m contracts, it shortens*

> set muscle length: determined by extent of gamma motor neuron activity

Stretch reflex: returns the stretched m back to its original length

*maintain a "set m length" against any change in load*

no stretch reflex = little resistance to mvmt, little tone, muscle is flaccid (limp, without tone)

*lack of constant feedback from m spindle = m gets flaccid*

Which descending fibers control Gamma motor neurons?

Gamma motor neurons are controlled by input from:

> descending fibers from suprasinal centers ie: BG via extrapyramidal tracts

True or false?

The stretch reflex also plays a role in maintaining an upright posture.

> Erector spinae/sacrospinales/superficial paraspinals

*there is little adaptation (↓ in sensivitiy to long lasting stimulus) = stretch reflex contraction can be sustained as long as stretch is imposed*

Dynamic stretch reflex

*can be done at a variety of joints*

damage in supraspinal centers = changes in reflex threshold, amplitude, and/or pattern

*emotion, stress and other factors also play a role*

patellar reflex = L2, L3, L4 (tests the circuit)

*sit on a chair on edge of table with legs crossed at the knee. find patella with finger and tap patellar tendon below the patella. check for responses BL*

Achilles reflex tests the circuit of S1, S2

*partner kneel on a chair, hold the back of the chair while the feet hang over the front edge. feet are relaxed. passively dorsiflex/extend the toes to ↑ tension on gastrocs. tap achilles tendon*

Flexion reflex

*noxious = painful*

Babinski Sign = damaged in corticospinal tract (except in infants)

*toe extension instead of flexion (plantar reflex) is a primitive reflex in infants*

*baby's toes fan out and great toe dorsiflex as SC is not fully myelinated*

*disappears at 12-18 mths*

Tonic neck reflex

*appears at 2 mths and disappears at 6 mths*

Placing a finger on an infant's open palm causes the infant's hand to close around the finger.  Trying to remove the finger will cause the grip to tighten.  What do you call that reflex?

Persistance of this reflex suggests what dysfunction?

Grasp reflex

> persistance of grasp reflex suggests cerebral dysfunction

*disappears after 4 mths*

Stroking an infant's right cheek will cause the infant to turn towards the right and make sucking motions

> rooting reflex

> Galant reflex

> stroking along the left side of the spine causes the infant to laterally flex towards the left side

*rules out brain damage at birth*

> Blinking before eyes are touched/when sudden bright light appears

> Gag reflex: gag when throat or back of mouth is stimulated

> Cough reflex:  coughs when airway is stimulated