Lecture 15 - Spinal Cord + Motor Cortex

Question 1

Motor cortex

Answer 1

planning, initiating, directing voluntary movements

Question 2

Brainstem Centers

Answer 2

basic movements, postural control

Question 3

What is the basal ganglia?

Answer 3

gating proper initiation of movement

Question 4

What is the cerebellum?

Answer 4

sensory motor coordination of ongoing movment

Question 5

What are the spinal cord and brainstem circuits

Answer 5

• local circuit neurons

- motor neuronpools

Question 6

What does SAME-DAVE stand for?

Answer 6

sensory-afferent
motor-efferent
dorsal-afferent
ventral-efferent

Question 7

What is a motor unit?

Answer 7

group of muscle fibers that receive input from a single motor neuron

Question 8

What are lower motor neurons?

Answer 8

-motor neurons that innervate proximal mucles

Question 9

Smaller (S) alpha motor neurons

Answer 9

• conduct slowly

- innervate muscle fibers that generate small, lasting contractions (EX: postural muscles like soleus)

Question 10

Larger (FF) alpha motor neurons?

Answer 10

• fast

- innervate larger groups of muscle that generate larger forces (EX muscles for jumping)

Question 11

Intermediate (FR) alpha motor neurons

Answer 11

-innervate muscles with intermediate properties

Question 12

What is the motor pool? What can it comprise?

Answer 12

• group of motor neurons that innervate a single muscle

- can comprise more thane one type of motor unit

Question 13

What are golgi tendon organs?

Answer 13

capsules encasing group 1b afferents

-embedded in tendons that connect muscle to bone

Question 14

What do golgi tendon organs signal?

Answer 14

• information about force

- afferent atvity is greatest when muscle contracts

Question 15

What is the monosynaptic stretch reflex?

Answer 15

maintains muscle length(classical reflex induced with hammer to the knee)

Question 16

What does the golgi tendon organ reflex do?

Answer 16

maintains tension via negative feedback

Question 17

Where are upper motor neurons?

Answer 17

brainstem and cortex

Question 18

Where are lower motor neurons?

Answer 18

in spinal cord or brain stem

Question 19

Dorsal horn

Answer 19

inputs from sensory cells, somas of local circuit neurons

Question 20

Dorsal roots

Answer 20

contain somas of sensory neurons who axons travel out to peripheral sensor receptors and to the cord (afferent)

Question 21

ventral horn

Answer 21

somas of lower motor neurons

Question 22

ventral roots

Answer 22

contains axons of lower motor neurons that travel out toward muscles (efferent)

Question 23

medial white matter

Answer 23

carries fibers from brainstem

Question 24

what are the 4 regions of the spinal cord?

Answer 24

1. cervical
2. thoracic
3. lumbar
4. sacral

Question 25

What does each spindle contain? What are they called?

Answer 25

two types of special muscle fibers (intrafusal fibers)

Question 26

How are intrafusal fibers arranged?

Answer 26

in parallel with extrafusal fibers

Question 27

What are nuclear bag fibers?

Answer 27

sensitive to rate of change in muscle length (velocity)

Question 28

What are nuclear chain fibers?

Answer 28

sensitive to muscle length

Question 29

What are Group 1a sensory afferents? When are they most active?

Answer 29

- wrap around the bag and chain fibers | - most active when muscle length changes (EX stretching)

Question 30

What are group II sensory afferents? When are they most active?

Answer 30

- wrap around chain fibers only | - most active when muscle is stretched

Question 31

What are intrafusal fibers innervated by?

Answer 31

gama motor neurons

Question 32

What do gama motor neurons do?

Answer 32

- regulate sensitivity of the muscle spindle - pull at both ends of bag and chain fibers - stretching regions where afferent endings are wrapped

Question 33

What Betz cells?

Answer 33

- very large - stout axons form most fibers in descending and corticobulbar tracts - example of upper motor neuron

Question 34

What are the 2 descending motor tracts that originate in the motor and premotor cortices?

Answer 34

1. corticobublar (ends in brainstem) | 2. corticospinal (ends in spinal cord)

Question 35

The corticobulbar tract is ______ while the corticospinal tract _____ at the _____

Answer 35

- uncrossed | - crosses, midline

Question 36

What is the lateral cortico-spinal tract?

Answer 36

- comprises most of corticospinal tract | - originates from premotor cortex + primary motor cortex

Question 37

Where do most fibers cross?

Answer 37

- at the pyramidal decussation | - terminate on lateral motor neurons (those that move distal muscles like fingers and toes)

Question 38

What is the anterior (ventral) corticospinal tract?

Answer 38

- crosses at the cord | - makes bilateral + polysynaptic connections with medial motor neurons that are used to maintain posture

Question 39

supplementary and premotor cortex

Answer 39

movement planning

Question 40

motor cortex

Answer 40

movement execution

Question 41

How are cells organized in cortices?

Answer 41

arranged in columns that perform common functions

Question 42

What are the 3 steps to the monosynaptic stretch reflex?

Answer 42

1. agonist muscle is stretched, leads to increase in discharge by 1a afferents 2. monosynaptic excitation of a-motoneuron in lateral horn 3. disynaptic relaxation of antagonist, 1a afferent synapses with inhibitory interneuron in dorsal horn

Question 43

What kind of diameters do the 1a fibers and a-fibers have? What does this mean?

Answer 43

- large diameters - conduct quickly - reflex is fast

Question 44

What are the 3 steps of the Golgi tendon organ reflex?

Answer 44

1. agonist contracts, muscle tension increases, 1b afferents fire hard 2. 1b afferents synapses with inhibitory interneuron 3. muscle relaxes, tension decreases

Question 45

How are motor neurons (in ventral horn) arranged?

Answer 45

somatically

Question 46

What does it mean that motor neurons (in ventral horn) are somatically arranged?

Answer 46

- motor neurons that innervate proximal muscles are medial | - those that innervate distal muscles are lateral