Transcript 6.1 The Nervous System - Blyth-Exercise

The Nervous System
and the Control of Movement
“He’s got what you might call a
control problem. The guy has a
million-dollar arm, but only a
ten-cent brain.”
- line from the baseball movie Bull Durham
Learning Goals:
• I will be able to….
– Describe and explain the various
components of the nervous system
– Explain how the nervous system functions
to transmit sensory and motor signals
throughout the body
– Explain how different types of reflexes
work
The Nervous System
• Gathers information from outside (external)
and inside (internal) the body, interprets
and analyzes the info, then initiates a
response
• Works as a basic feedback loop:
– Sensor
– Interpreter
– Responder
Two Components of the Nervous System
• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)
The Central Nervous System (CNS)
•
•
Divided in 2 parts:
1. Brain
2. Spinal Cord
Brain
• Main control center; “computer”
• Sends out commands
• Spinal Cord
• Main pathway for information
• Connects brain and peripheral
nervous system
• Carries sensory info to CNS and
motor commands away from the CNS
The Peripheral Nervous System (PNS)
• Parts of the nervous system other than the brain and
spinal cord
• Communication lines between the CNS and the rest of
the body
• 12 pairs of cranial nerves and 31 pairs of spinal nerves
Composed of…
– Somatic nervous system
– Autonomic nervous system
• Sympathetic system
• Parasympathetic system
The Somatic Nervous System
• Voluntary - skeletal muscle
• Processes info from receptors in skin, muscles,
joints, etc. and give us sensations of pain,
heat/cold, body position, muscle action, etc.
Composed of…
• Afferent nerve fibers
“sensory nerves”
- sends sensory information to the CNS
• Efferent nerve fibers
“motor nerves”
- CNS sends information through these fibers to
instruct skeletal muscles to react
The Autonomic Nervous System
•
Involuntary – cardiac and smooth muscle
•
Sympathetic system
- prepares the body for emergencies
- fight-or-flight responses
- increases HR, BP, breathing rate, etc.
- release of adrenaline
•
Parasympathetic
- helps bring body back to “normal state”
- decreases HR, BP, breathing rate, etc.
- parasympathetic system has opposite
effect of sympathetic system
- release of acetylcholine
Neurons
• “nerve cells”
• Transmit signals or
nerve impulses
Cross-Section of Spinal
Cord
Check Your Understanding…
• How does the nervous system relate to what you have
learned about muscles, bones, joints, etc.?
• Create a graphic organizer to help you organize and
understand the structure of the nervous system
• Compare and contrast afferent and efferent nerves.
• How do the sympathetic and parasympathetic systems
work together?
• What is an example of a body function controlled by the
somatic nervous system? Autonomic nervous system?
Nervous System Jigsaw Activity
• Each person will be assigned to learn and summarize a
component of the nervous system
• Summarize your information in a few points
(What is it? How does it work? Why is it important?)
• You may include diagrams
• Everyone needs their own note!
• Each person will present material to the group
• You are responsible for knowing all info!
Topics
• Reflex arc
• Golgi Tendon
• Muscle spindle and stretch reflex
• Polysynaptic reflexes
Reflexes
• Reflex: rapid, automatic response to stimulation
– Can occur in the brain (cerebral reflex) or in the spinal
cord (spinal reflex)
• Autonomic reflexes – autonomic nervous system
– Smooth and cardiac muscle, glands
– Digestion, elimination, blood pressure, salivation,
sweating
• Somatic reflexes – somatic nervous system
– Skeletal muscle
– Eg: pain, withdrawal reflex, stretch reflex
The Reflex Arc
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
Pathway of the initial stimulus and the
response message
Components:
 Sensory receptor
 Adjustor (CNS)
 Effector organ
•
Five parts of the Reflex Arc:
•
Receptor – receives initial stimulus
•
Sensory (afferent) nerve – carries impulse to spinal cord or brain
•
Intermediate nerve fibre (adjustor or interneuron) – interprets signal
•
Motor (efferent) nerve – carries response to the muscle or organ
•
Effector organ (skeletal muscle) – carries out the response
Proprioreceptors and the
Control of Movement
•
Proprioreceptors are specialized receptors
located throughout the body that provide sensory
information regarding position of limbs, body
posture, balance, etc.
•
Proprioception: Awareness of one’s body
position
•
Uses 2 sensory receptors
– Golgi Tendon Organs
– Muscle Spindles
Golgi Tendon Organs (GTOs)



located on the ends of tendons
detects increased tension exerted on tendon
Tension Reflex: when tension is detected in GTOs an
impulse is send along afferent nerves to the CNS
which send a signal to efferent nerves causing the
muscle to relax to prevent injury
The Muscle Spindle




Located in the belly of muscle fiber
Help maintain muscle tension (body posture) but
detects increases in muscle length
More sensitive than GTOs (2 sensory nerves)
Involved in the Stretch Reflex
Stretch Reflex



The simplest reflex – one connection between afferent and
efferent neurons (monosynaptic)
Eg: Knee-jerk reflex (patellar ligament)
Sequence of nerve impulses:
1.
Muscle spindle’s sensory neuron
senses stretch of patellar ligament
2.
Afferent nerve transmits signal to the
spinal cord
3.
Afferent neuron synapses with
efferent neuron in spinal cord
4.
Impulse transmitted along efferent
nerve to muscle
5.
Muscle contracts to reduce the
stretch (knee-jerk reaction)
Reciprocal Inhibition
• While tapping on the patellar ligament
causes the quadriceps to contract,
reciprocal inhibition causes the
antagonist (opposing) muscle group
(hamstrings in this case) to relax
• Makes it easier for the quadriceps to
contract
• Allows constant adjustment between the
two muscle groups
Polysynaptic Reflexes
•
•
•
As opposed to monosynaptic reflexes
i.e. more than one interneurons lie between the
sensory and motor neurons
More complex and slower reflexes
Withdrawal Reflex
- Withdrawal of a body part from a painful stimulus
- Still very rapid, but involves more interneurons
Crossed-Extensor Reflex
- When one arm or leg automatically compensates for a
reflex action in the opposing arm or leg
- The reflex involves multiple synapses and muscle
groups
Videos
• Spinal Reflex intro/reflex arc
http://www.youtube.com/watch?v=8EmCV-aVQOQ&feature=related
• Reflex arc
http://www.youtube.com/watch?v=Y5nj3ZfeYDQ
• Stretch reflex
http://www.youtube.com/watch?v=HfuhVWK8C0U&feature=related
• Tension reflex
http://www.youtube.com/watch?v=lT9XhORYHJ8&feature=related
• Withdrawal reflex
• http://www.youtube.com/watch?v=RLe9koPfVoo&feature=related
• Crossed extensor reflex
• http://www.youtube.com/watch?v=iaXVUtS8Y4I&feature=related
What’s working?
• Removing your hand from a hot pot
– Withdrawal reflex
• Being able to touch your finger to your knee with your eyes closed
– Proprioreceptors
• Stepping on a tack and immediately stand on your other foot
– Crossed-extensor reflex
• A doctor taps your patellar ligament to test your reflexes
– Muscle spindle – stretch reflex
• Your muscle relaxes after being stretching too much
– Golgi Tendon Organs – tension reflex
• When your biceps contracts, your triceps are inhibited
– Reciprocal inhibition
• You are able to stand on one foot, any changes to muscle length are
detected and corrected
– Muscle spindle
Spinal Cord Injuries
• Each person researches one spinal
cord injury or technological
advancement and will present it to the
class
–
–
–
–
Paraplegia
Quadriplegia
Concussions
MRI Technology
Careers Involving the Nervous System
• Neurologist - An M.D. who diagnoses and treats disorders of
the nervous system.
• Neuroradiologist- Uses imaging methods such as X-ray, MRI,
CT and angiography to diagnose diseases of the nervous
system.
• Psychologist- Studies the neural basis of behavior
• Psychiatrist - M.D. who diagnoses and treats mental disorders.
• Electroneurodiagnostic Technician - Records electrical activity
from the brain (electroencephalograms; evoked potentials) and
spinal cord.
• Chiropractor, physical therapist, massage therapist,
physiotherapist, etc.
• Spinal Cord Injury Research/Clinic at Brock University (pdf
article)