The Nervous System

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The Nervous System
-Reflexes
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What is a reflex?

• Automatic and rapid responses to particular
  stimulation

-pain or the threat of pain

• 2 types of reflexes
• 1. Autonomic
• 2. Somatic

-stimulation of skeletal muscle
What signals a reflex?
Reflex arc the pathway along which the stimulus
and response messages travel

• Composed of a(n) 1) receptor
• 2) adjustor
• 3) effector

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Reflex Arc
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From your lab you should have copied down the
function of the 5 parts of a typical reflex arc
Receptor -area of body that receive initial stimulus (often skin)
Sensory (afferent) nerve -carries sensory impulse to spinal column
Interneuron (intermediate nerve fibre) -adjustor ? interprets signal and issues response
Motor (efferent) nerve -carries response impulse from spinal cord to muscle
Effector -area of body that carries out response (often muscle)
Key to a reflex ? it is not the brain that sends
the motor signal to the effector.
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Reflex Arc
-video
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We already discussed how a sensory impulse can
cause a muscle to contract But how does that
muscle fibre know when, how much and who to
contract with?
Proprioceptors
Provide constant sensory information about the
state of muscle contraction
-specialized sensory receptors found in tendons,
muscles and joints

• There are 2 we will be looking at

1. Golgi Tendon Organs (GTO)
-in series where muscles and tendons meet
-when muscles stretch GTOs stretch -therefore
detect TENSION changes
-protect muscle from excessive tension
(damage) -development of power and
strength -overcome GTOs
(1844-1926)
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Golgi Tendon Organs (GTOs)
Change in tension ? impulse sent along sensory
(afferent) neuron to spinal cord ? synapse with
interneuron ? motor (efferent) neuron sends
impulse ? muscle relaxes (preventing injury)
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2. Muscle Spindles
-smaller more specialized muscles fibres
(intrafusal) running parallel to the main muscle
fibres
-help maintain muscle tension (eg. standing erect)
-detect changes in muscle LENGTH

• Change in muscle length ? sensory impulse to
  spinal cord (x2) ? motor
• response ? muscle contracts (remains in proper
  tension)

-video
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Muscle spindles are responsible for one of the
most recognizable reflexes . . .
The Stretch Reflex (Knee Jerk)

• Monosynaptic reflex ? only one connection
  between sensory and motor neuron

Tapping petallar tendon
? Pulls on quad femoris ? excites spindles
(length change) ? sensory to spinal cord ? motor
to contract quad femoris ? knee-jerk
Sudden increase in carrying weight?
1. Stimulus
2. Receptor
Reciprocal Inhibition
3. Sensory impulse
4. Motor impulse
5. Muscle contracts
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(No Transcript)
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But were missing something. What did we say was
the key to a reflex?
Polysynaptic Reflex

• A reflex with one or more interneurons between
  the primary sensory fibres and motor neurons

More more complex slower
Withdrawal Reflex
(Pain sharp/hot)
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1. Stimulus from skin in form of heat (receptor)
2. Sensory impulse generated
3. Interneuron synapse in spinal column
4. Motor impulse generated by interneuron (others
to brain pain)
5. Impulse to proper muscle causing contraction
6. Removal of stimulated area
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But why do we still feel pain when we place our
hand over a flame?

• There is still a sensory impulse sent to the
  brain, but it only reacts to make us feel pain.
• Because it is further away and contains more
  interneurons it is a slower process

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The Nervous System
-Control of Movement
-video
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The Nervous System
An organ system of specialized cells (neurons)
that coordinate the actions of an animal by
transmitting different signals between parts of
the body.
It has 3 main roles

• Assemble information about conditions external
  and internal to the body
• Analyze information
• Initiate response that may be necessary to
  satisfy certain needs of the body

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Even though there are 2 major components to this
system, they are interconnected
"Nervous Breakdown"
Central Nervous system
Peripheral Nervous System
Brain
Spinal Cord
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Central Nervous System (CNS)

• Brain and spinal cord

-main control centre for almost all bodys
activities -receives and interprets signals ?
commands
-the brain consists of 6 main parts (determine
the function of each part pg 95)
-main information pathway -spinal nerves branch
off cord reaching different organs and
tissues -named after where exit Ex. L3 ?
innervates the rectus femoris (extend knee)

• Cerebrum
• Cerebellum
• Brain stem
• Diencephalon
• Limbic system
• Reticular activating system

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Even though there are 2 major components to this
system, they are interconnected
"Nervous Breakdown"
Central Nervous system
Peripheral Nervous System
Autonomic Nervous System
Somatic Nervous System
Brain
Spinal Cord
Sympathetic System
Parasympathetic System
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Peripheral Nervous System (CNS)

• roadway carrying all information towards and
  away from the CNS

• Contains 12 pairs of cranial and 31 pairs of
  spinal nerves

1. Motor (efferent)
2. Sensory (afferent)

2 roots
Autonomic Nervous System

• automatic involuntary contraction
• -cardiac muscles, muscles organs

• 2 opposing branches

• Sympathetic
• localized bodily adjustments
• prepare for emergencies (fight or
  flight)
• adrenaline, increased HR

• Parasympathetic
• returns body to normal state
• decrease HR, rest, digest, etc

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Even though there are 2 major components to this
system, they are interconnected
"Nervous Breakdown"
Central Nervous system
Peripheral Nervous System
Autonomic Nervous System
Somatic Nervous System
Brain
Motor
Spinal Cord
Sensory
Sympathetic System
Parasympathetic System
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Somatic Nervous System

• awareness to external environment
• motor movements to cope

• Afferent
• 2. Efferent

-info from skin, joints, muscles ? touch, pain,
heat, cold, balance, body position

• voluntary movements to respond to stimuli

Look at example on page 97 (fig. 6.2)