Lecture Objectives for: Motor Control, Reflexes, Smooth Muscle

Question 1

Provide a general description of the function of 4 motor nuclei of the extrapyramidal motor system

Answer 1

• Reticular nuclei: maintain balance and posture (Reticulospinal tract)
• Vestibular nuclei: receive input from the equilibrium apparatus of the ear and cerebellum (Vestibulospinal tract)
• Red nuclei: control flexor muscles (Rubrospinal tract)
• Superior colliculi: orient head and eyes to stimuli (Tectospinal tract)

Question 2

List 3 brain structures in the regulatory motor system and explain why damage to structures in this system rarely produce paralysis

Answer 2

Cerebellum, basal ganglia, and thalamus.
Paralysis doesn’t result from disruption of the regulatory region these regions do not have access to the alpha neuron responsible for pathways as sensory and motor information cannot be relayed to other areas or appropriately controlled by the brain

Question 3

List the components of a monosynaptic reflex arc and describe the function of these components within the patellar tendon refle

Answer 3

• Receptor: intrafusal fibers of muscle spindles function as mechanoreceptors- detects changes in length (sensor)
• Afferent Innervaton: flower spray and annulospiral afferent nerves (integrator)
• Efferent Innervation: Alpha motorneurons (integrator)
• Effector: extrafusal fibers (regular myofibers)

Question 4

Pre-motor cortex

Answer 4

patterning of learned motor skills, specifically externally generated movements. Guided by sensory input from the posterior parietal cortex

Question 5

Supplemental motor area

Answer 5

patterning of learned motor skilled, particularly internally generated movements

Question 6

What motor systems of the CNS have direct access to the alpha motor neurons

Answer 6

Pyramidal (primary motor cortex)

Extrapyramidal (reticular formation and other motor nuclei, multi-synaptic and inhibitory)

Question 7

Describe the somatotopic mapping of the motor homunculus

Answer 7

For the primary motor cortex, the motor homunculus demonstrate a reversed orientation of the body in the regions of the cortex. The things that are at the bottom of our body are represented at the top of our brain and vice versa. Also, the more devoted an area is to the motion of a particular area of our body is enlarged.

Question 8

Cerebellum does what

Answer 8

recieves input from the primary and secondary motor cortex, as well as feedback from the somatosensry and vestibular system to integrate this information for coordination and adjustment of movements

Question 9

Secondary motor cortex

Answer 9

planning and initiation of movement

Question 10

Basal Ganglia does what?

Answer 10

Inhibits effects to decrease muscle tone and suppress unwanted movements. Initiates sustained receptive movements

Question 11

Thalamus does what?

Answer 11

The sensory relay station, receives sensory afferent input and re-route it to appropriate higher brain centers. It does positive reinforcement of movement.

Question 12

Flaccid paralysis

Answer 12

damage to the descending excitatory pathways leads to hypo-activity in the muscle as they cannot be excited

Question 13

Spastic paralysis

Answer 13

Damage to the inhibitory pathways of the motor nuclei- causing hyper-activity in the muscle

Question 14

What does the secondary (flower-spray) endings of afferent fibers do?

Answer 14

Nuclear chain fibers: detects extent of change (how big a change in length)

Question 15

What does the primary (annulospiral) endings of afferent fibers do?

Answer 15

Nuclear bag and chain fibers: detects rate of change (how fast the length changes)- for predictability of reaction

Question 16

Describe the function of an inhibitory interneuron in the disynaptic reflex that results in the reciprocal inhibition of antagonist muscles

Answer 16

The interneuron, which sits on the horn of spinal cord, causes a ISP to be sent to the motor neurons of the as the other motor neuron for the other muscle receives a ESP so that an antagonist muscle may relax and allow the contraction of the other muscle without interference.

Question 17

Differentiate single unit and multi-unit smooth muscle with respect to locations in the body, mode of excitation, and innervation patterns

Answer 17

Multi-unit: large vessels, airways, the iris and hair follicle; neurogenic- ANS input is required to initiate APs, discrete units can function independent because of the low number of Gap junctions
Single-unit:
walls of hollow organs, pacemaker cells initate an AP and communicate to other cells through gap junctions

Question 18

In Smooth Muscle, how does Calcium trigger contractions?

Answer 18

Calcium forms a calcium-calmodulin complex, which activates the myosin light chain kinase. When the kinase is dephosphorylated, relaxation occurs

Question 19

Force modulation in smooth muscle is accomplished by?

Answer 19

Graded calcium release and altering the response to calcium

Question 20

How come smooth muscle reacts differently to a single neurotransmitter?

Answer 20

Look at the receptor subset at the muscle (adrenergic receptor subsets)