The sensorimotor system

Question 1

Types of motor control

Answer 1

Voluntary- running, walking, talking
Goal directed- conscious, explicit, controlled
Habit- unconscious, implicit, automatic
Involuntary- eye movements, facial expressions, tongue, digestion

Question 2

Control architecture

Answer 2

Pain- spinal corn registers this- makes us escape that situation

Looming threat- sensorimotor midbrain processes sensory information - makes us avoid a bad situation

Learned threat- uses the cortex + limbic system- avoid that situation

Question 3

Muscles

Answer 3

Antagonistic arrangement- muscles are arranged in ways that oppose each other e.g. triceps and biceps- word in a coordinated fashion to give a precise movement

Recruitment of muscle fibres

Question 4

Myosin cross-bridge cycle

Answer 4

Myosin head has a neck- attaches to the actin filament and bends it neck and pushes it, then it disconnects and attaches again- this is muscle movement.

Acetylcholine (ATP) is required to break the bond between the myosin head and the actin filament.
Rigor mortis occurs when there is no more ATP is there to break the bond- cant move muscles

Question 5

Motor unit

Answer 5

A single alpha motor neuron + all the muscle fibres that it innervates
Different motor neurones innervate different numbers of muscle fibres
Fewer fibres means greater movement resolution- those innervating finger tips and tongue

Question 6

Fast and slow muscle fibres

Answer 6

Slow- muscles used to sit up for hours
Fast fatigue resistant- walking/running- can do for quite a while- takes longer to tire out
Fast fatigueable- short term explosive releases of force

Question 7

The motor pool

Answer 7

All the lower motor neurone that innervate a single muscle

Question 8

Sensing in muscles

Answer 8

Muscles can be contracted or relaxed to provide movement, but a good control system (CNS) needs to know two things
- How much tension is on the muscle- Golgi tendon organs
- What is the length (stretch of the muscle)- muscle spindles

Question 9

Golgi tendon organs

Answer 9

Within the tendon- where the muscles joins to bone
Mostly sends ascending sensory information to the brain via the spinal cord about how much force there is on the muscle
When there is extreme tension it is possible that GTOs act to inhibit muscle fibres to prevent damage

Question 10

Muscle spindles

Answer 10

Sense the length of muscles- the amount of stretch
When you hit a reflex point (knee cap) you pull the muscle fibres along the muscle and stretch them out- the muscle is contacting as a result of the stretch to return the leg to what it thinks it should be

Question 11

Intrafusal muscle fibres

Answer 11

Sensory part of the muscle- contains the muscle spindles
Detects when the muscle has been lengthened

Innervated separately to extrafusal fibres- gamma motor neurone
They make sure that the intrafusal fibres are kept at a length that can detect stretch

Question 12

Reciprocal innervation

Answer 12

Explains why the contraction of one muscle induces the relaxation of the other
Permits the execution of smooth movements

Question 13

Vestibular righting reflex

Answer 13

Vestibular system detects that the body is not upright, as well as any acceleration due to gravity (falling)
Information from the vestibular system is combines with visual, somatosensory and proprioceptive sensory input in order to specify a pattern of motor activity that will restore ‘uprightness’ and a safe landing
The cerebellum is essential for computing what to do in this situation

Question 14

Cortical motor areas

Answer 14

Motors command originated in motor cortex pyramidal cells
Pyramidal cells axon can project directly or indirectly to spinal cord and onto lower brain stem motor neurone. These axons form the pyramidal tract
Most cortical projections innervate contra lateral motor units- opposite side of the body

Question 15

Upper and lower motor neurons

Answer 15

Upper motor neurons start in the cortex and projects down to the spinal cord

Lower motor neurons pick up the signal from the spinal cord and sends it to the muscles and activates the muscle fibres

Question 16

Spinal cord

Answer 16

Sensory input goes in through the dorsal root, motor output comes out of the ventral root

Question 17

Dorsolateral corticospinal tract

Answer 17

Operate limb muscles on the opposite side of the body- fingers, arms, legs feet

Question 18

Ventromedial cortospinal tract

Answer 18

Central muscle control, like the trunk, innervates both sides at the same time

Question 19

Basal ganglia

Answer 19

Inhibits information so you don’t do things you don’t want to