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Neural Anatomy and Function

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Neural Anatomy
and Function
NERVOUS SYSTEMS
• Central nervous system
• Peripheral nervous system
CENTRAL NERVOUS SYSTEM p. 33
• Brain
– Cerebral Cortex/Cerebrum
• Motor cortex
– Basal Ganglia/Diencephalon – sensory input
– Cerebellum – motor control
– Brain stem – sensory input
• Spinal Cord
PERIPHERAL NERVOUS
SYSTEM
• Somatic
– Sensory (Gamma) Nerves
– Motor (Alpha) Nerves
• Autonomic [FYI]
– Parasympathetic
– Sympathetic
Spinal Nerves p. 35
NERVE ANATOMY
•A single nerve cell is called a neuron
•A bundle or group of neurons make up a
nerve
•A nerve contains both afferent and efferent
nerves
Afferent Neuron
• Carry impulse towards the CNS (e.g. sensory
nerves)
• Synapse
Towards CNS
Efferent Neuron
• Carry impulse away from the CNS (e.g. motor
nerves)
1. Stimulatory
2. Inhibitory
NEURON ANATOMY
• Dendrite
• Cell Body
• Axon
AXON
1.
2.
3.
4.
Conduction
Myelin sheath
Synapse
Neurotransmitter
CONDUCTION
Resting State: Na outside, K inside
CONDUCTION
4. Na K Pump
3. Repolarization
1. Depolarization
2. Propagation
MYELIN SHEATH
SYNAPSE
SYNAPSE
SYNAPSE
•Quick Time Movie
NEUROMUSCULAR
JUNCTION
NEUROMUSCULAR
JUNCTION
MOTOR UNIT
• Motor unit = one motor nerve + all
the muscle fibers it innervates.
• Types
– Fast (alpha -1)
– Slow (alpha -2)
3
1
2
MOTOR UNIT
Fast
Fast
Slow
MUSCLE TENSION or FORCE or
STRENGTH
1. Number of MU
stimulated
2. Frequency of
stimulation to each
MU
3. Type of MU
stimulated
MUSCLE STIMULATION:
How does it begin?
1. Volitional Control
(Motor Cortex)
1. Motor cortex
2. Motor neurons
3. Muscles
2. Reflex Control
1. Afferent neuron
– Sensory
neuron
2. Efferent neuron
– Motor neuron
PROPRIOCEPTION &
KINESTHESIS p. 37
• Proprioception
– The ability to sense the position and location
and orientation and movement of the body
and its parts
• Kinesthesis
– The ability to feel movements of the limbs and
body
PROPRIOCEPTION
• Proprioceptors of the joints and
skin
–Meissner’s corpuscles
–Ruffini’s corpuscles
–Pacinian corpuscles
–Krause’s end-bulbs
PROPRIOCEPTION
• Proprioceptors of the muscles
–Muscle spindles
–Golgi tendon organs
Muscle Spindles
muscle
spindle
Muscle Spindles
• Provide proprioception
• Sense the amount of stretch and the rate of
stretch
• Reflexes involving the muscle spindles is
how we �feel’ a movement was done
correctly
• Spindles are a part of learning; we develop
such reflexes as we practice skills and
movements
Golgi Tendon Organs
Golgi Tendon Organs
• Sensitive to muscle tension and active
contraction
• Protect muscle from excess contraction
force
• Stimulation of GTO an afferent impulse is
sent to the central nervous system
• In turn, efferent impulses are sent to the…
– Agonist muscle causing it to relax
– Antagonist muscle causing it to contract
Neuromuscular Summary
•An example from baseball.
•A pitcher throws a curve ball to
Sammy Sosa
•Sammy’s eyes see the ball coming
towards him and is able to identify
the pitch as a curve ball
•Sensory nerves (afferent) send that
information to the CNS
•In the CNS the sensory nerve
synapses with motor nerves
•The motor nerves in turn stimulates
the muscles (deltoid and pectoralis
major) required to swing the bat in
the proper position to hit the ball
Neuromuscular Summary
•Inside the fibers of the deltoid and
pectoralis major, calcium is
released
•The calcium allows myosin heads
to attach to actin
•When the heads swivel the fibers
of the deltoid muscle will shorten
•The shortening of the fibers will
pull on the humerus causing
Sammy to swing the bat
•The muscle spindles “tell” the
CNS when the arm is in the
correct position
•If all goes as planned, the deltoid
and pectoralis major will move his
arms into a position to hit the ball
Neuromuscular Summary
• An example from weight training.
• A man is having his muscular strength tested on the bench
press
• For his first lift, 50 pounds is put on the bar
• He will be using his pectoralis major muscle with has 500
motor units (300 slow twitch and 200 fast twitch) and his
triceps muscle
• His CNS stimulates 280 motor units leading to his pectoralis
major muscle (180 slow twitch and 100 fast twitch)
• End nerve ending stimulates
a separate muscle fiber
Neuromuscular Summary
• Calcium is released, myosin attaches to actin and
swivels.
• The pectoralis major and triceps muscles shortens
and his arm extends outward raising the bar with
50 pounds on it.
• After a few minutes of rest, 100 pounds is place on
the bar
• This time he stimulates 380 motor units (260 slow
twitch and120 fast twitch)
• The weight is successfully
lifted
• After a few minutes of rest,
150 pounds is place on the
bar
Neuromuscular Summary
• This time he stimulates 460 motor units (280 slow
twitch and 180 fast twitch)
• As the pectoralis major muscle contracts the GTO
in the pectoralis major are stimulated
• They stimulate a sensory nerve leading to the
CNS
• In the CNS, the sensory nerve synapses with a
motor nerve that will inhibit (relax) the pectoralis
major muscle
• The man is unable to
successfully lift the 150
pounds.
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