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The Control of Movement
(Text pg 95-102)
The main role of the nervous system is to:
a. assemble information coming from internal and external stimuli
b. analyse this information
c. initiate a response to satisfy the need.
The Nervous System Works using a Basic Feedback Loop
(Figure 6.2 of text book Pg 97)
• Three components of the Feedback loop
o Sensor (receives input/stimulus)
o Interpreter (Brain or spinal cord)
o Responder (carries out the reaction/output)
There are Two Main Divisions of the Nervous System
• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)
Two Main Components to the CNS
1. The Brain:
• Mainframe which controls everything (sends, interprets & receives signals)
• Three Parts Associated with Movement and Exercise:
a. Cerebrum: (the two hemispheres)
o Motor and sensory cortex are located here
b. Cerebellum: (the back of the brain)
o Coordinates muscle movement and balance
c. Brain Stem: (Connects cerebrum to spinal cord)
o Controls autonomic functions (breathing, heart rate, posture, eye movement)
2. The Spinal Cord:
• Highway for communicating between CNS and PNS
• Spinal nerves branch off between vertebrae (PNS begins here)
• Spinal nerves are named according to the vertebrae level they exit.
E.g. C6 = deltoid; L3 & L4 = Rectus
femoris (See figure below)
• Below T12-L1 level is an extension of the spinal cord called the cauda
equina (which means “horses tail” in Latin).
There are Two Main Divisions of the PNS
The Peripheral Nervous System are parts of the nervous system that lie outside the Central Nervous
system (Brain and Spinal Cord).
1. Autonomic Nervous System (ANS):
• Involuntary control over cardiac and smooth muscle (two opposing systems).
a. Sympathetic Nervous System:
o Fight or flight response (Release of Adrenaline,  HR,  BP, etc.)
b. Parasympathetic Nervous System:
o Establishes Homeostasis (Opposes sympathetic system by regulating HR, BP, and
Adrenaline Levels)
2. Somatic Nervous System (SNS):
• Voluntary control over skeletal muscle
• Two types of nerves
a. Afferent Nerves (posterior root)
o Sensory nerves: Periphery → CNS
b. Efferent Nerves (anterior root)
o Motor nerves: CNS → Periphery
The Reflex Arc
Reflexes are automatic and rapid responses to a particular stimulation. Most reflexes are not dependent of
a conscious intervention by a high centre of the brain, rather a quick response by an unexpected stimulus.
2 types of reflex arcs:
Autonomic reflexes involve quick activation of smooth muscle, cardiac muscle and glands
Somatic reflexes involve stimulation of skeletal muscle which include the withdrawal reflex
Five parts to the Reflex Arc
The Receptor: Receives initial stimulus (extreme heat on finger)
The Sensory Nerve (afferent): carries impulse to spinal column
Intermediate Nerve Fiber: interprets the signal and issues an appropriate response.
The Motor Nerve: Carries the response message from the spinal cord to the muscle or organ.
Effector organs: Organs that carry out the response (removal of hand when in danger)
How does a muscle fibre know how much to contract, when to relax and how to coordinate with
other muscles?
• Consists of sensory organs (specialized receptors called PROPRIOCEPTORS) in the muscles, tendons
and joints
• Allows us to maintain our posture & balance.
• Is a safety mechanism ensuring appropriate muscle responses
• Provides feedback regarding:
o The state of muscle contractions
o Where our limbs are in space
Two Types of Proprioceptors
1. Golgi Tendon Organs (GTO’s)
• Located in series within the tendon (musculotendenous junction)
• Sense changes in muscle tension (when stretched)
• Afferent nerve synapses directly with efferent nerve from same
muscle. Efferent nerve sends a “relax” signal to that muscle.
• Protects muscle/joint from damage.
• May interfere with development of strength/power.
2. Muscle Spindles
• Located parallel to muscle fibres (intrafusal muscle fibres)
• Sense changes in muscle length
• Two afferent nerves synapse with spinal cord to allow for proper response
(very sensitive).
• Critical role in maintaining muscle tension/contraction to regulate posture &
balance. E.g. Knee Jerk Reflex:
• Spindle senses quads lengthen, spindle sends signal to contract quads.
E.g. Weight dropped into hand:
• Spindles sense muscle lengthen causing biceps to contract. GTO inhibits