Chapter 10

Question 1

Is it possible to move voluntarily without somatosensation?

Answer 1

Yes, it would be uncoordinated (cerebellum is not doing its job so it isn’t making necessary changes, It cannot tell what we are really doing)

Question 2

Somatosensation

Answer 2

Allows for us to investigate the world (two point discrimination)

• Move accurately (perception- how I am moving in space)
• Avoid or minimize injury (helps detect stimulus that may cause injury)

Question 3

Cutaneous (somatosensation)

Answer 3

Touch, nociception (pain), and temperature. (cutaneous-under surface of skin)

Proprioception and nociception. (deep- in muscle bell and at tendon)

We have receptors in the muscle belly, at the tendon, and under the surface of the skin there are a series of receptors which gives us both superficial and deep sensation that tells us about touch and movement)

Bulbs are peripheral somatosensory cells that are located in the dorsal root ganglion.

Question 4

Three neuron pathway

Answer 4

general pathway for somato sensation.
First order (first in line)- pseudounipolar (peripheral to the body and central to the brainstem) from receptor in the body somewhere to the spinal cord.

Second in line (chapter 11)
Third in line (chapter 11)

Question 5

Sensory receptors

Answer 5

• Mechanoreceptors (nociceptors- high threshold) modality gated channels (depolarizes peripheral sensory axons) detect mechanical stimuli that could hurt us and alert us to get away.
• Chemoreceptors (nociceptors- high threshold) free nerve ending that detect chemical environment of ECF, and especially active during the inflammation response during injury. detect chemical environment that is potentially damaging..
• Thermoreceptors (nociceptors-high threshold) free nerve endings that respond to temperature. detect danger of damaging you.

Question 6

Tonic receptors and phasic receptors

Answer 6

• Tonic receptors (slow adapting)- slow to adapt/doesn’t adapt to a stimulus, it stays active.
• Phasic receptors (fast adapting)- Really respond to changes, once there has been a change they wait for the next change)

Touch shoulder- phasic detect change in a touch and then shut down waiting for the next change, Tonic lets us know that the hand is still on our shoulder and is still being touched. when the hand leaves, the phasic receptors then tell us that the hand is gone and no longer on our shoulder (a change on the skin).

Question 7

First order neurons (classified by diameter)

Answer 7

Scheme 1-
Ia
Ib
II
III
IV

Scheme 2-
A-beta
A-delta
C

Classified on diameter and the function that they serve. (what modality an axon carries)
bigger diameter and thicker myelin are in order from highest to lowest in ascending order.

Scheme 1 has a thicker coating than scheme 2

Ia- a proprioceptive receptor

Question 8

Receptive field

Answer 8

The area of skin that is innervated by one peripheral sensory axon and all its terminal branches= sensory receptive fields.
Sometimes sensation can fall into two different receptive fields.
We have a lot more sensory axons distally than we have proximally (more in hand, feet, and mouth).
More axons in the hand means there is more brain area devoted to decoding sensation in the hand.
Ends up in the post central gyrus and in the parietal lobe.
Smaller fields distally and larger proximally and there are a greater density of receptors distally and less density proximally.

Question 9

Sensations- Light (discriminative touch)

Answer 9

A-beta (all messages sent to the nervous system on sensory fibers that are of class A-beta)

Specialized receptor

• touch
• vibration
• pressure
• hair movement
• stretch

can describe the touch and locate it on the body (light and discriminative are the same) superficial sensory system.

Question 10

Sensations- Coarse touch (non-discriminative)

Answer 10

A-delta and C

• free nerve ending
• axons with terminal branches but no specialized receptors at nerve endings (detect coarse touch but cannot describe it very well) we know we are being touched through modality gated channels but cannot describe or locate it well.

Question 11

Sensations- Nociception (non-discriminative)

Answer 11

free nerve endings that detect painful mechanical stimulation (high threshold) and carry messages of pain on A-delta and C fibers

Question 12

Sensations- Temperature (non-discriminative)

Answer 12

free nerve endings that detect hot and cold. messages sent on class A-delta and C fibers.

Question 13

Peripheral vs. dermatomal innervation

Answer 13

different distribution in the body.
The brachial plexus is a mixer and an unmixer (combines peripheral nerves into spinal nerve) and unmixes spinal nerves into peripheral nerves.

Three different named peripheral nerves have the same sensation as one dermatome (spinal nerve) area. 3 peripheral nerves have the same sensation of spinal nerve C7. If lost sensation of C7 then would lose sensation in the entirety of the green 3 areas. But in patients with peripheral nerve injuries it is possible to lose only part of the sensation of the C7 dermatome.

Spinal nerve issue could be a bulging disc.

Critical that OT knows the difference between spinal nerve and peripheral nerve damages due to loss of sensation patterns.

Question 14

Muscle spindles

Answer 14

Deep sensation- a deep sensor that detects proprioception.
Buried deep in a muscle, responds to what is the length of the muscle (stretched or unstretched) and how fast the length is changing, by knowing those two things it can keep you coordinated. Fusiform=spindle shape

always in line with the muscle

Question 15

Intrafusal

Answer 15

Inside the spindle

Question 16

Extrafusal

Answer 16

Outside the spindle

Question 17

Sensory receptors (muscle spindles)

Nuclear bag and nuclear chain

Answer 17

mechanoreceptors- sensory receptors in bulgy part of spindle are sensitive to stretch (as the muscle is stretched and unstretched the receptors are deformed and create action potentials).

Nuclear bag fibers-Bulgy (detects the rate of change of length)

-Nuclear chain fiber- slim- detects the length of a muscle (how long is the muscle)

Together=

• what is the length of muscle?
• is length changing?
• How fast is length changing?

Question 18

muscle spindles- Primary endings

Answer 18

-Primary endings-sensory- action potentials on Ia fibers. biggest diameter neuron and most heavily myelinated neuron in body (fastest transmission) the importance of knowing where you are in space is the highest. endings pick up messages from nuclear bag and nuclear chain (tell the brain what is the length and how fast is it changing). sends messages generated by middle of each sensor of the muscle spindles.

Question 19

Muscle spindles- secondary endings

Answer 19

Secondary endings- sensory- action potentials sent on II fibers- smaller and thinner than type Ia. messages just from the chain (only messages on length).

Question 20

muscle spindles- baseline potentials

Answer 20

when we are at rest- they are constantly sending action potentials- when we are quiet and not doin anything there is a baseline signal coming from every muscle spindle so the brain always knows the position of the body at every moment in time.
-When muscle and spindles get stretched the number of action potentials goes up. When they get unstretched the action potentials go down (how the brain knows the muscle is changing in length)

Question 21

Associated motor neurons- A-alpha

Answer 21

muscle fibers of contraction are extrafusal (shorten the overall muscle) brain sends messages to them on axons of class A-alpha, are efferent (are messages of movement from the spinal cord out to the muscle) action potentials depolarize muscle membrane and contraction occurs (voluntary contraction). Move the actual muscle.

Question 22

Associated motor neurons- A-gamma

Answer 22

buried deep inside the muscle fibers (from the spinal cord out to the muscle spindle and they make the little muscles of the muscle spindles contract- when active they don’t cause big muscles to shorten, they just cause the muscles of the small spindles to shorten.
-purpose is to keep the muscle sensitive to unexpected stretch throughout movement. (efferent) tighten up the muscles to keep the muscles sensitive. keep the brain sensitive to positioning during contractions.

A-gamma keeps the spindle sensitive to A-alpha contraction and shortening of the muscle.-when muscles contract due to A-alpha, there can become slack in A-gamma which can no longer sense the position of the body (loses sensitivity)
A-gamma then has to shorten so that the spindle is able to stay sensitive to the change in length so brain always knows.

Question 23

quick stretch

Answer 23

stretch the spindle, when you stretch spindle really quickly (# of action potentials goes up) feeds into spinal cord and facilitates same motor neuron that facilitates that muscles. Spindles signal for auto facilitation of a muscle.

Question 24

Golgi Tendon Organs

Answer 24

Mechanoreceptors that are buried in the tendon origin and insertions of the muscles. Job is to sense tension/physical stress. They are active whether the tension is due to active contraction or if it is due to passive tension.

• Send signals on Ib sensory neurons
• GTO inhibition would prevent muscle from damaging during contraction.

Question 25

Deep tendon pressure

Answer 25

Aims for the GTOs of the muscle fiber tendons- will autoinhibit muscle it is attached to that allows you to stretch muscle out.

Question 26

Joint receptors- Specializes capsule receptors

Answer 26

send signals on class II sensory neurons. in the joint capsule that detect movement and position of the capsule. (if it is taut or slack or if capsule is changing its position) information on position of the joint- adds to the information of length of a muscle.

Question 27

Joint receptors- Ligament receptors

Answer 27

• Sends messages on class Ib sensory neurons.

- tells about the tension on a ligament that supports a joint .

Question 28

Joint receptors- Free nerve endings

Answer 28

• Sends messages on class A-delta and C sensory neurons
• transduce pain and inflammation, damaging stimuli and the inflammation of injury. A-delta (fast pain) and C (slow pain)

Question 29

Large diameter (myelinated)

Answer 29

Muscles, tendons, and joints (Ia, Ib)

Question 30

Medium diameter (myelinated)

Answer 30

• Muscle spindles (II)

- Specialized cutaneious receptors (a-beta)

Question 31

Small diameter (myelinated)

Answer 31

Free nerve endings (fast pain and temp) (A-delta)

Question 32

Small diameter (unmyelinated)

Answer 32

Free nerve endings (slow pain and temp) (C)

Question 33

Peripheral nerve lesions

Answer 33

sensory loss with compression in order

• Conscious proprioception and light touch
• Cold
• Fast nociception (sharp, stinging pain)
• Heat
• Slow nociception (dull, ache)

sensation returns in reverse order.

Question 34

Ataxia- sensory

Answer 34

sensory input to the cerebellum is messed up (if sensory system is broken then the cerebellum never knows what the body is doing.)

• sway indicates that pt does not have good sensation from feet and ankles.
• Romberg test tests ataxia due to sensory complications

Question 35

Ataxia-Cerebellar

Answer 35

Cerebellum is broke and doesn’t know what you meant to do and what you are really doing so it cannot compare and make corrections, due to damage to cerebellum.

Question 36

Ataxia- Vestibular

Answer 36

inner ears facilitate two powerful groups of muscles for balance (vestibulospinal) hold us up against gravity. Damaged inner ear may have bad activation of system and are uncoordinated as a result.

Question 37

Ataxia

Answer 37

Perfectly strong but still uncoordinated. inability or difficulty planning movements.