5 - somatic nervous system

What is the motor cortex responsible for and what is it driven by?

planning, initiating, and directing voluntary movements

basal ganglia

What are brainstem centers responsible for and what is it driven by?

basic movement and postural control

cerebellum

Where are upper motor neurons located?

just the CNS

Where are lower motor neurons located

extend out to skeletal muscles

What do upper motor neurons do?

control the muscles and the interneurons that affect them

Outline the 5 divisions of the somatic reflex arc

1. sensor (receptor)

2. afferent pathway - to the spinal cord or the brainstem

3. intergrating centre - grey matter of the spinal cord or brainstem synapse

4. efferent pathway - to the muscles

5. effector muscle gives response

Outline the 4 steps of the patellar reflex

1. striking patellar ligament stretches tendon and quadriceps femoris muscle

2. spindle is stretched, activating sensory neuron

3. sensory neuron activates α motorneuron

4. α motorneuron stimulates extrafusal muscles to contract

List 2 reasons as to why the patellar reflex is so fast

• doesn’t require conscious thought

• there is only 1 synapse between afferent and efferent neurons

What does the afferent neuron extend to within the integrating centre (2 points)

• efferent neuron (leads to muscle contraction)

• interneuron that’s inhibitory to the hamstring muscle, creating a negative-feedback reflex arc

What maneuver is used to relax someone?

Jendrassik maneuver

Outline the Jendrassik maneuver (2 points)

• patient clenches their teeth and tries to pull apart their interlocked fingers

• occupies enough of the CNS that it doesn’t interfere with the patellar reflex

Define proprioception

how you know where your body is at any given time

State 2 ways that proprioception is detected

• muscle spindles

• golgi tendon organs

How do muscle fibres detect movement

when intrafusal muscle fibres contract, nerve fibres are stretched, sending information forward

Approximately how many muscle fibres are connected to each golgi tendon organ?

10-15

How do golgi tendon organs detect movement (2 points)

• sensory dendrites of afferent nerves are interwoven with collagen fibres

• when the muscle contracts, the collagen fibres are pulled tight, activating the afferent neuron

How does the golgi tendon organ act as a failsafe (2 points)

• the golgi organ has a disynaptic (inter neuron) connection to its own neuron

• if a muscle is subject to so much tension that itt’l be damaged, it produces a powerful activation of that inhibitory inter neuron that stops the lower motor neuron firing