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There are two major components to the human nervous system.
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The brain and spinal cord make up the central nervous system (CNS).
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The peripheral nervous system (PNS) is responsible for bodily functions. This includes the
beating of the heart, the digestive system, muscular control, and all other voluntary and
involuntary neuromuscular controls.
Central Nervous System (CNS):
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Is divided into 2 parts: The brain and the spinal cord.
a) The Brain:
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It is the main control centre for movement, sleep, hunger, thirst, and virtually every type
of activity necessary for human survival. It acts like the body’s “computer”. It sends out
commands to other parts of the body to perform them. As well, all human emotions are
controlled by the brain.
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The brain has 6 main parts:
1) The cerebrum: This is the largest part of the brain. The outer layer of the
cerebrum (the grey matter) is called the cerebral cortex and it contains all our
neurons. It is responsible for our memory, speech, movement, and intelligence. The
cerebrum is divided into 4 lobes
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The frontal lobe – Responsible for reasoning and judgement
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The temporal lobe – Responsible for visual imagery, touch and pressure sensations
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The parietal lobe – Responsible for hearing, smell, taste, and short term memory
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The occipital lobe – Responsible for vision
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The brain is also divided into 2 hemispheres:
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Left Hemisphere
– Controls the right side of the body.
- Controls speech and language, reasoning, logic,
numbers, and facts
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Right Hemisphere
- Controls the left side of the body.
- Controls music aptitude, facial recognition,
visual imagery, creativity, language tone and
emphasis.
2) The cerebellum: The 2nd largest region of the brain. It below the cerebrum.
Its main function is to coordinate muscle movement, and control balance.
3) The brain stem: Lies below the cerebrum and in front of the cerebellum. It
links the cerebrum with the spinal cord. It houses the brain centres responsible
for autonomic functions (breathing, heart rate, etc), postural control, muscle tone,
and eye movement.
4) The diencephalon: Consists of the thalamus and hypothalamus. It is located
between the cerebrum and the brain stem.
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The thalamus relays most sensory stimuli to the cerebral cortex and
controls primitive awareness of pain, screening of incoming signals,
and focusing attention.
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The hypothalamus controls things such as body temperatures,
appetite, emotions, and various automatic functions.
5) The limbic system: It is composed of a collection of structures within the
cerebral hemispheres that regulate basic drives (hunger, aggression, and emotional
drives) and screens information going to the cerebral cortex.
6) The reticular activating system: This is a network of neurons that fan out
through the cerebral cortex and directs information to appropriate centres for
interpretation. Its functioning is crucial for maintaining consciousness.
b) The Spinal Cord:
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The spinal cord is the main pathway for information connecting the brain and the peripheral
nervous system. The spinal cord runs through the vertebral column. It starts at the base of
the brain stem and travels all the way down to the second lumbar vertebra. In adults, the
spinal cord is an average of 42-45 cm. Spinal nerves carry sensory information towards the
CNS and motor commands away from the CNS.
Peripheral Nervous System (PNS)
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Consists of those parts of the nervous system that lie outside the CNS. It is a massive road
of network carrying traffic (information) in and out of the CNS.
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It includes 12 pairs of cranial nerves that emerge from the brain as well as 31 pairs of spinal
nerves that leave the spinal cord for various parts of the body.
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Motor nerves (aka: efferent nerves) carry information from the CNS to the body’s organs.
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Sensory nerves (aka: afferent nerves) carry information from sensory receptors to the CNS.
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The PNS contains both autonomic and somatic components:
o The Autonomic Nervous System:
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The ANS (Autonomic Nervous System) regulates the involuntary contraction of
our cardiac muscles and the smooth muscles of our internal organs. This subsystem is made up of 2 branches, which tend to act as opposing systems:
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Sympathetic System: Causes localized bodily adjustments to occur (ie:
sweating or cardiovascular changes) and it prepares the body for
emergencies. This involves the release of adrenaline, an increase in
heart rate, a widening of the blood vessels, and similar “fight or flight”
responses to deal with imminent danger.
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Parasympathetic System: Helps return the body to normal after it has
been altered by the sympathetic system.
o The Somatic Nervous System:
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Our SNS (Somatic Nervous System) controls our awareness of our external
environment – and the corresponding motor activity allowing us to cope with it.
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The SNS contains both afferent (sensory) and efferent (motor) nerves that
send instructions to skeletal muscles.
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Through this system, the PNS receives and processes information from
receptors in the skin, in voluntary muscles, tendons, and joints, and gives us the
sensations of touch, pain, heat, cold, balance, body position, and muscle action.
The Reflex Arc
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Reflexes are an automatic and rapid response to a particular stimulation.
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If the command centre for the reflex is located in the brain, it is called a cerebral reflex.
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If the command centre for the reflex is located in the spinal cord, it is called a spinal reflex.
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Autonomic reflexes are mediated by the ANS and involve the activation of smooth muscle, cardiac
muscle, and glands. They regulate such bodily functions as digestions, elimination, blood pressure,
salivation, and sweating.
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Somatic reflexes involve stimulation of skeletal muscles by the SNS and include such reflexes as
the stretch reflex and the withdrawal reflex.
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There are 5 parts to a reflex arc:
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The receptor (which receives the initial stimulus). For example: A pinprick to the skin, or
a loud noise.
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The sensory (or afferent) nerve (which carries the impulse to the spinal column or brain).
For example: the afferent neuron of the muscle spindle or tendon organ.
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The intermediate nerve fibre (the adjustor or interneuron) interprets the signal and
issues an appropriate response.
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The motor (or efferent nerve) which carries the response message from the spinal cord
to the muscle or organ.
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The effector organ itself (example: the skeletal muscle) which carries out the response.
(example: removing the hand or leg away from danger).
PROPRIOCEPTORS
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Specialized receptors located within tendons, muscles and joints that provide sensory information
about the state of muscle contraction, the position of body limbs, and body posture and balance.
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Golgi Tendon Organs (GTO’s): Are sensory receptors that end where tendons join to
muscle fibres. When a muscle stretches, so does the golgi tendon organ. The GTO’s
detect increased tension exerted on a tendon. They help protect the muscle from
excessive tension that would result in damage to the muscle or the joint.
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Muscle Spindles: Are more complex than the GTO’s. Muscle spindles help to maintain
muscle tension and are sensitive to changes in muscle length (rather than tension). They
allow muscles to maintain proper muscle tension or tone (ie: an erect posture).
Golgi Tendon Organs
Muscle Spindles
Location
Where tendon meets muscle fibre
In belly of muscle fibres
Position
In series with muscle fibres
Parallel to muscle fibres
Respond to
Changes in muscle/tendon tension
Changes in muscle length
SPINAL CORD INJURIES
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Reflex testing is an important medical diagnostic tool. Weak, exaggerated, or absent reflex
responses indicate problems with portions of the nervous system. If the spinal cord is damaged,
reflex testing can help to determine the exact area of spinal injury.
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When there is a serious injury to the spinal cord, the nerves above the injury keep working, but
those below the injury may or may not still function.
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Paraplegia: Is when an injury prevents the use of the legs but not the arms.
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Quadriplegia: Is when an injury prevents the use of both the arms and legs.
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There is further classification based on the level of functional loss –an absolute loss of function
in a limb or a set of body parts (complete) or partial levels of such loss (incomplete).
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People involved in sports where there is a possibility of spinal injury (diving, surfing, and football)
can minimize the risk of injury by strengthening the neck and back muscles, and wearing
protective gear.
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Some facts about spinal cord injuries: 80% are male, 50% are paraplegic, and 50% are
quadriplegic. Car accidents account for 35% of all spinal cord injuries, followed by falls at 16.5%.
HEAD INJURIES – CONCUSSIONS
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A concussion results from a blow to the head in which the brain literally shakes within the skull
and often involves injury to nerve fibres.
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You do not need to hit your head to suffer a concussion – if your head moves too quickly back and
forth, the same damage can be done to your brain.
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With a concussion injury, brain cells become abnormal and do not function properly. Some
common symptoms are: headaches, dizziness, light-headedness, fatigue, memory problems,
sensitivity to light, or tiredness. These are called post-concussion symptoms. If someone were
to take another hard hit after having any of these symptoms, there can be a dangerous change in
the brain’s blood supply. This leads to a rapid swelling of the brain that leads to coma and death.
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Changes in behavior to be aware of:
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Inappropriate playing behavior (going the wrong way, shooting at own net)
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Significantly decreased playing ability from earlier in the game.
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Slowness in answering questions or following directions.
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Inability to focus and easily distracted.
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Inability to do normal activities.
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Display of unusual emotions (crying/laughing).
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Changes in personality.
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Irritability and low frustration tolerance.
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Anxiety and depressed mood.
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Sleep disturbance.
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The person will be unaware of time, date, places, period or score of the game; general confusion.
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Feelings and Symptoms of a Concussion:
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Dazed, stunned
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Dizzy
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Like you’re seeing stars or flashing lights
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Ringing in your ears
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Headache
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Sick or nauseous
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Blurred vision
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Poorly coordinated or unbalanced
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Slurred speech