Topic 1: Relexes and Release Signs

Question 1

Main contributors to proprioception? (3)

Answer 1

Muscle spindles
Cutanious input
Visual input

All combined.

Question 2

Post injury/ potential affect on proprioception?

Answer 2

Often a deficit in ppriceptive ability; can leave a person prone to re-injury; often mistaken for mm weakness.

Question 3

Def: reflex

Answer 3

A fast, predictable sequence of involuntary actions

Question 4

List the basic components of a reflex arc (5)

Answer 4

1. A receptor that transduces (converts) stimuli to APs
2. An afferent neuron that carries APs to …
3. Interneurons
4. Efferent neurons that carry APs to…
5. Effectors (mms or glands)

Question 5

‘Reflexes form the basis of all _____ ____ _____.’

Answer 5

CNS motor activity

Question 6

Reflexes occur at which level(s) of the CNS?

Answer 6

All levels

Question 7

The stretch reflex- aka? (2)

- Define

Answer 7

Myotatic reflex; deep tendon reflex (DTR)

An involuntary muscular contraciton in response to a fast stretch

Question 8

Stretch reflex: what is stretching & how is the stretch occuring/which types of cells/structures/neurons involved?

Answer 8

A brief, fast stretch of the mm and its spindle.

APs travelling along the 1a neuron/LMN reflex arc, causing the mm to contract

Question 9

Alpha motor neuron

• AKA? (2)
• Innervates what

Answer 9

AKA LMN; final common pathway

Innervates/goes to a muscle/’motor’ movement/efferent

Question 10

1A fiber: def

Answer 10

A unipolar neuron that comes from a mm spindle (sensory)

Question 11

Patellar reflex: which nerve is involved; what structure do you tap?

Answer 11

Femoral nn

Tap the patellar ligament/patellar tendon

Question 12

Achilles reflex: which nn is involved? How do you evoke it?

Answer 12

Tibial nn

Relax feet; dorsiflex the toes; tap Achilles tendon lightly

Question 13

Triceps reflex: which nn is involved? How do you evoke it?

Answer 13

Radial nn

Us. patient seated; gently tap triceps brachii tendon

Question 14

A spindle is ‘fusiform’, meaning…?

Answer 14

..it’s wide in the middle and tapers at both ends.

Question 15

Intrafusal fibers are innervated by which type of neuron? Located in which part of the SC?

Answer 15

Gamma motor neurons, located in the anterior horn

Question 16

Extrafusal fibers: what are they composed of and what type of neuron innervates them?

Answer 16

Composed of normal, skeletal mm fibers

Innervated by alpha motor neurons (LMNs).

Question 17

Gamma motor neurons: fxn & how they do this.

Answer 17

Regulate the sensitivity of the spindles to stretch. They do this by controlling the length of the intrafusal fibers

Question 18

What happens when the intrafusal fibers are shortened? (3)

Answer 18

• tension in the spindle increases
• this increases sensitivity to the stretch
• this makes the 1a neuron more likely to depolarize

Question 19

Gamma m. neurons are mainly controlled by ___ ___, coming from ___ ___.

Answer 19

descending tracts; supraspinal centers (ex: basal ganglia)

Question 20

How does abnormal gamma activity affect the body?

Answer 20

By significantly distorting mm tone and fxn (‘I’m tense’)

Question 21

Every unipolar neuron is attached to __ __ __.

Answer 21

a sensory receptor

Question 22

Stretch reflex: 2 main roles in overall motor control?

Answer 22

1. It informs the CNS of the rate of change in mm length. The stretch rflx returns the stretched mm back to its original length and protects it from injury.
2. It maintains a set mm length against any change in load.

Question 23

What is the ‘set mm length’ is moderated by?

Answer 23

gamma m. neuron activation

Question 24

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

Answer 24

shorter

Question 25

What is the stretch reflex’s response to long-lasting activity?

Answer 25

It shows little adaptation- there is little decrease in sensitivity during long-lasting stimulus. Thus, stretch reflex contraction an be sustained as long as the stretch is imposed.

Ex: standing upright: the stretching force elicits a sustained reflex contraction on the quads. It assists in the maintenance of extension at the knee and thus upright posture. The stretch reflex is well developed in other anti-gravity mms.

Question 26

What do things look like in the absence of the stretch reflex?

Answer 26

Since it is a primary, but not the sole source of mm tone, the absence of this reflex results in:

little resistance to movement
little tone
mm is flacid

Question 27

Stretch reflexes are subject to strong regulation (modulation) by __ __.

Answer 27

Supraspinal centers

Question 28

What changes might you see following a supraspinal lesion, in relation to stretch reflexes? Explain why.

Answer 28

Changes in reflex threshold, amplitude (strength) and/or patterns. Because your reflexes are wrong all the time, but are filtered by the supraspinal centers and controlled, unless you get a pathology of those centres.

Question 29

Vestibulo-ocular reflex (VOR): fxn and what kind of reflex is it?

Answer 29

Fxn: keeps you vision stabilized when you move your hea, esp. when you are walking or running.

It is a supraspinal reflex

Question 30

Def: Central pattern generators (CPGs); list some examples.

Answer 30

Clusters of neurons that coordinate mm recruitment with fixed action patters to reduce the computational load of repetitive movements on the brain. CPGs produce an instantly recognizable and predictable pattern of human motion.

Ex’s - control chewing, swallowing, breathing, walking

Question 31

Frontal release signs: define

Answer 31

Primitive reflexes that are normally present in infancy. Us. disappear as the CNS matures, however, if the reflex remains or re-occurs, it is called a ‘frontal release sign’

Question 32

How do frontal release signs occur?

Answer 32

Certain areas (us. in frontal lobe) inhibit these (baby) reflexes as the brain develops, and they eventually disappear.

However, if a disease process disrupts these inhibitory pathways/the parts of the brain responsible for them, the reflex is ‘released’ from inhibition (disinhibition) and returns, and is now called a ‘frontal release sign’.

Question 33

The tonic neck reflex- elicited by what? What happens?

Answer 33

Elicited when head of a relaxed infant, lying on its back, is rotated to the side. The arm toward which baby is facing ‘punches’ outwards, away from the body, w/ the hand partially open. Arm on opposite side is flexed w/ fist clenched tightly. Turning the face the opposite direction will cause a reverse of the position.

A frontal release sign if seen in adults.

Question 34

The grasp reflex - elicited by what? what happens?

Answer 34

By placing a finger on the baby’s open palm. Hand will close around the finger, attempting to remove finger will cause grip to tighten. You can almost lift baby up.

*reflex most clearly associated with frontal lobe dxfxn (ex in severe dementia).

A frontal release sign if seen in adults.

Question 35

The rooting reflex: elicited by what? What happens?

Answer 35

Elicited by stroking the cheek

Baby turns towards the side that was stroked and begin to make suckling motions with its mouth; us. only present in ppl with severe dementia.

A frontal release sign if seen in adults.

Question 36

The Galant reflex: elicited by what? What happens?

Answer 36

Elicited by holding the newborn in ventral suspension and stroking along the one side of the spine.

The normal reaction is for the newborn to laterally flex toward the stimulated side. Used in newborns to rule out damage at birth.

A frontal release sign if seen in adults.

Question 37

Snout reflex: Describe.

Answer 37

Involved in suckling; gentle px on the philtrum invokes pouting or pursing of the lips (resembles a snout)

A frontal release sign if seen in adults.

Question 38

Palmo-mental reflex: Describe

Answer 38

Reason unknown. When thenar eminance is stroked, ipslilateral mentalis mm contracts (chin twitch). May indicate possibility of cerebral pathology, but ‘normal’ ppl may demonstrate it too.

A frontal release sign if seen in adults.

Question 39

Glabellar tap reflex: describe

Answer 39

May protect eyes in certain situations.

In most people when this area is tapped repetitively, at one second intervals, the blink response extinguishes after a short number of taps.

Absent glabellar reflex may be present in individuals with extrapyramidal disorders such as Parkinson’s

A frontal release sign if seen in adults.

Question 40

Babinski sign: Is a frontal releases sign if ____.

Answer 40

Is a FRS if (in an adult), if, when lateral aspect of the sole of the foot is stimulated/stroked with pencil, the pig toe becomes dorsiflexed/extended and the other toes fan outward.

Normal, adult response if to plantar flex all toes.

Question 41

Why/how is the Babinski sign ‘normal’ in babies/as a primitive reflex?

Answer 41

In infants, is called the extensor reflex. This happens because the corticospinal pathways are not fully myelinated at this age, so the reflex is not inhibited by the cerebral cortex.

Question 42

Which type of neurons often control/inhibit reflexes?

Answer 42

Upper motor neurons

Question 43

Neuroimaging: 3 types?

Answer 43

1. Magnetic Resonance Imaging (MRI)
2. Functional Magnetic Resonance Imaging (fMRI)
3. Diffusion Tensor Imaging (DTI)

Question 44

How does MRI work?

Answer 44

It creates a structural ‘snapshot’ of the brain, incl. bone, tissue, blood vessels, tumours, infection, damage or bleeding (such as from a stroke)

Question 45

How does fMRI work?

Answer 45

It measures the rate of blood flow, chemical activity and electrical impulses in the brain during activity; there are often false positives.

Question 46

What does DTI show?

Answer 46

Miswiring of the brain or connectopathies.

Ex- the brain of a person who died from Alzheimer’s or Parkinson’s shows clear evidence of degenerating and dying neurons. For people with schizophrenia, the neurons may look healthy/no visible neuropathology but the neurons may be connected in an abnormal way.