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The Nervous System and
the Control of Movement
Two Components
1. CNS (Central Nervous System)
• brain and spinal cord
2. PNS (Peripheral Nervous System)
• 12 pairs of cranial nerves and 31 spinal
nerves
CNS
The brain: receives and interprets signals sent from other
parts of the body
6 major parts
Cerebrum
• Largest
• sensory and motor activities AND intelligence
• Divided into frontal, temporal, parietal and occipital lobes
Cerebellum
• 2nd largest
• movement and balance
Brain Stem
• Link between spinal cord and cerebellum
• Posture, muscle tone, eye movement
(autonomic functions)
Diencephalon
• Between cerebrum and brain stem
• Thalamus and hypothalamus
Thalamus: pain, screens signals, attention
Hypothalamus: body temp., appetite, emotions
other automatic function
Limbic System
• Structures in cerebral hemispheres
• Regulates drives (hunger, aggressions
etc.)
Reticular Activating System
• Network of neurons
• Maintaining consciousness
The Spinal Cord: main pathway for
messages and connects brain to PNS
• Travels down vertebral column to 2nd
lumbar vertebrae
• Adults 42cm-45cm long
• Spinal nerves exit between vertebrae
• Carries sensory info. to brain and motor
info. away from brain
PNS
Recall;
31 pairs of spinal nerves and 12 pairs of
crainial nerves
- nerves have two roots
1. anterior root: carries motor
nerve fibres (efferent)
2. posterior root: carries sensory
nerve fibres (afferent)
PNS 2 Components
1.
•
•
Autonomic Nervous System
Controls involuntary contraction
2 Subsystems
1. Sympathetic System
- causes localized body
adjustments to occur (sweating
or cardiovascular changes)
- prepares the body for
emergencies (fight/flight)
2. Parasympathetic System
- returns body to normal after
sympathetic response
2.
•
•
•
•
•
Somatic Nervous System
Awareness of external environment
Afferent and efferent nerve fibres
Info from receptors in the skin, voluntary
muscles, tendons and joint
Gives sensations in touch, pain, heat….
Movement
See pg. 97 Figure 6.2
Reflex Arc
Reflexes: automatic and rapid responses to
particular stimulation
Reflex Arc: the pathway along which the
initial stimulus and the correcting response
message travel
cerebral reflex- command center in brain
spinal reflex- command center in spinal
cord
Autonomic reflexes
- mediated by autonomic division of nervous
system
- Smooth muscle, cardiac muscle, glands
Somatic reflexes
- mediated by somatic division of nervous
system
- Stretch and withdrawal reflex (ways the
body responds to unexpected
5 Parts of a Reflex Arc
1. Receptor: receive the initial stimulus
(pinprick/loud noise)
2. Sensory (afferent) nerve: sends
impulse to spinal cord or brain (afferent
neuron of muscle spindle or tendon
organ)
3. Intermediate Nerve Fibre: interprets the
signal and issues an appropriate
response (interneuron)
4. Motor (efferent) nerve: carries response
from spinal cord to muscle organ
5. Effector organ: carries out the response
(skeletal muscle moves)
Proprioceptors and Control of
Movement
• Provide sensory information about the
state of muscle contraction, the position of
body limbs, body posture and balance
• Located in tendons, muscles, and joints
• Two sensory receptors:
– Golgi tendon organs
– Muscle spindles
Golgi Tendon Organs
- sensory receptors that terminate where tendons join to muscle
fibres
- Used to detect tension exerted on tendon
- 1 sensory nerve, 1 motor nerve
- Play a part is strength and power development
Muscle Spindles
- sensory receptors that lie parallel to main muscle fibres
- Send constant signals to spinal cord
- 2 sensory nerve, 1 motor nerve
- Help maintain tension and sensitive to muscle length
- Play a part in all physical movement as they constantly and
automatically adjust to the changing demands placed on them
The Stretch Reflex
- Simplest spinal reflex
- Monosynaptic reflex
- e.g knee jerk
1. Receptor muscle sense the action (e.g hammer on
knee)
2. Message sent along afferent nerve axon to spinal cord
3. Afferent synapses with efferent of same muscles
4. Impulse in transmitted along efferent pathway
5. Motor unit contracts (e.g. knee jerk occurs)
Reciprocal Inhibition:
- when one agonist muscle contracts,
antagonist muscle is simultaneously
inhibited
Provides constant adjustment
Polysynaptic Reflexes
• One of more interneurons lie between
primary sensory fibres and motor neurons
• Increased complexity and slower
• e.g. withdrawal reflex
– From pain
– Sensory neuron to interneuron to motor neuron
Homework:
From last nights reading,
1. Outline the sequence the Polynaptic
Cross-Extensor Reflex
2. Complete exercise 6.6 and be ready to
discuss tomorrow