Transcript PSE4U1 - 10.Unit 4

The Nervous System
PSE 4U1
Exercise Science
Unit 4
Suggested Readings/Practice
• Text: p. 95-107
• Workbook: p.84-89
Two Components of the Nervous System
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
The Components of the Nervous
System
Nervous System
Peripheral Nervous System
Cranial Nerves
Spinal Nerves
Forebrain
Central Nervous System
Brain
Hindbrain
Spinal Cord
Midbrain
The Central Nervous System (CNS)
•
Brain
– Cerebrum
• largest part, nerve centres, 4 lobes (frontal, temporal,
parietal, occipital)
– Cerebellum
• second largest region, behind and below the cerebrum,
coordinates muscle movement, controls balance
– Brain stem
• below cerebrum & in front of cerebellum, links cerebrum
with spinal cord, autonomic functions, etc.
The Central Nervous System (CNS)
• Brain (con’t)
– Diencephalon
• thalamus (sensory stimuli to brain, eg. pain) and
hypothalamus (body temp., appetite, emotions)
– Limbic system
• hippocampus, amygdala, pituitary, etc.
• regulates basic drives/emotions (eg. hunger,
aggression, emotional drives)
– Reticular activating system
• directs information to appropriate centres, maintains
consciousness
This is an opposite view of the brain from the previous slide
The Central Nervous System (CNS) Con’t
• Spinal cord
– runs through vertebrae (vertebral column)
– starts at base of brain stem to second lumbar
vertebra
– spinal nerves branch off between each vertebra,
and travel to various organs and tissues
– spinal nerves carry sensory information
TOWARDS the CNS and motor commands
AWAY from the CNS
The Peripheral Nervous System (PNS)
• parts of nervous system that are outside the CNS
• massive road network “carrying traffic”
(information) in and out of the CNS
Composed of…
PNS
- Autonomic
sympathetic
- Somatic
parasympathetic
PNS: The Autonomic Nervous System
•
Controls heart and internal organs
•
Sympathetic system
- prepares the body for emergencies (e.g. increase
heart rate, decreased digestive activity, increased
breathing)
- fight-or-flight responses
- orders release of adrenaline from adrenal gland
•
Parasympathetic
- helps bring body back to “normal state”
- parasympathetic system has opposite effect of
sympathetic system (e.g. decreases HR, increases
digestive activities
Functions of the Sympathetic
Nervous System (in depth)
• Helps us cope with stress by sending impulses
to many internal organs producing widespread
changes:
– Increase in: heart rate, blood pressure, blood
supply to skeletal muscles, secretion of sweat,
secretion by adrenal glands
– Decreased secretion from digestive glands
– Constriction of blood vessels
– Prepares body for strenuous muscular work
(eg exercise)
– Prepares us for FIGHT or FLIGHT response
The Somatic Nervous System
•
Makes us aware of the external environment. Consists
of nerves that convey messages from the sensory
organs to the CNS and from the CNS to the muscles.
Composed of…
•
Afferent nerve fibres
- sends sensory information to the brain
•
Efferent nerve fibres (E=Exit)
- brain sends information through these fibres to instruct
skeletal muscles to react
Reflex Arc Characteristics (p. 99)
Reflex Arc
• pathway (circuit) along which the initial stimulus and
corresponding response message travel
1. the Receptor receives the initial stimulus
2. the Sensory (or Afferent) nerve carries the impulse to
the spinal column or brain
3. the Intermediate nerve fibre (adjustor or interneuron)
interprets the signal and issues an appropriate response
4. the Motor (or Efferent) nerve carries the response
message from the spinal cord to the muscle or organ
5. the Effector organ (e.g. skeletal muscle) carries out the
response
Suggested Work
• Read Textbook p. 95-99
• Complete Workbook Ex. 6.3 (p. 87)
Coverings & Fluid Spaces of Brain
and Spinal Cord
• Brain & spinal cord surrounded with tough,
fluid-containing membrane called
Meninges
• Meninges
– A. the dura mater – tough outer layer
– B. the arachnoid mater – middle cobweb like
fluid filling in its spaces
– C. the pia mater – delicate innermost layer
(look at handout)
Coverings & Fluid Spaces of Brain
and Spinal Cord (Con’t)
• Cerebrospinal fluid
– Forms continually from fluid filtering out of the
blood, which circulated between the arachnoid
and pia mater
– Fills spaces inside of the brain that are called
ventricles (2) – one inside the right half of
cerebrum and one inside the left cerebrum
– CSF moves from ventricles down and around
spinal cord and returns to blood
– Remember: this fluid forms continually from
blood, circulates, and is reabsorbed into the
blood
Cells of the Nervous System
• Two types
– Neurons: nerve cells
– Neuroglia: specialized connective tissue
Neurons
• Consist of 3 main parts
1. Neuron Cell Body
2. Dendrites
- branching projections from neuron cell body
- transmit impulses to the neuron cell bodies
3. Axon
- one elongated projection from the cell body
- transmit impulses away from the neuron cell
bodies
(look at handout)
Neurons (Con’t)
• Are classified according to the direction in
which they transmit impulses
– Sensory neurons: transmit impulses to the
spinal cord and brain from all parts of the
body
– Motor neurons: transmit impulses away from
the brain and spinal cord to muscles and
glands
– Interneurons: conduct impulses from sensory
neurons to motor neurons
Neurons (Con’t)
• Myelin
– A white fatty substance which surrounds the axon
– Good insulator covering the axon between nodes,
allowing transmission to be fast
– Formed by Schwann Cells that wrap around some
axons outside the central nervous system
– Neurilemma is the outer cell membrane of a
Schwann Cell
– Nodes of Ranvier are indentations that exist
between adjancent Schwann Cells
– Saltatory Conduction rapid nerve conduction along
a myelinated axon where impulse jumps from node to
node (look at handout)
Neurons (Con’t)
• Myelin (con’t)
– An interesting note about neurilemma
– Axons in brain and spinal cord have no
neurilemma
– Neurilemma plays an important part in
regeneration of cut and injured axons,
therefore, axons in brain and cord do not
regenerate, but those in nerves do (albeit
slowly)
Nerve Impulses
• On handout
Neuroglia Cells
• Do not transmit impulses
• Special type of connective tissue
• Maintain functioning of neurons by holding them together and
protecting them
• 3 types
– Astrocytes: large, star shaped, threadlike branches attached
to neurons and blood vessels
– Microglia: smaller than astrocytes, stationary, when brain
tissue shows signs of inflammation or degeneration, they
enlarge and move about acting as microbe-eating
scavengers
– Oligodendroglia: hold nerve fibres together, produce fatty
myelin sheath that surrounds neurons in the brain and spinal
cord
The Proprioceptor System
• Proprioceptors:
– Specialized receptors located within tendons,
muscles, and joints
– Provide sensory information (ex. state of muscle
contraction) through the primary use of two sensory
receptors: golgi tendon organs and muscle spindles
• Continuously monitor muscle actions
• “Tell” the nervous system about the state of
muscle contraction
• Act as a kind of safety device allowing the nervous
system to respond accordingly
Golgi Tendons and Muscle Spindles
• Golgi Tendon Organs (GTOs)
- located on the ends of tendons
- detects increased tension exerted on tendon
• Muscle Spindles
- help detect increased muscle length
Golgi Tendon Organs
The Muscle Spindle
Sensory neuron
(two branches within)
Motor neuron
Muscle spindle
within muscle fibre
(magnified)
Muscle fibres
Golgi Tendon Organs & Muscle
Spindles
Golgi Tendon Organs
Muscle Spindles
Location
Where tendon meets
muscle fibre
In belly of muscle fibre
Position
In series with muscle
fibre
Parallel to muscle fibre
Respond to
Changes in
muscle/tendon tension
Changes in muscle
length
Sensory
neurons
1
2
The Stretch Reflex
• Stretch reflex:
– Simplest spinal reflex
– Depends on the single connection between
primary afferent fibres and motor neurons of same
muscle
The Stretch Reflex
• Stretch reflex (con’t):
– Sequence of nerve impulses and motions (e.g.
tapping patella ligament):
• Receptor muscle senses action of hammer
against patella ligament through the muscle
spindle’s sensory neuron
• Message transmitted along afferent nerve axon
to spinal cord
• Afferent neuron synapses with the efferent
pathway of same muscle
• Impulse transmitted along efferent pathways to
muscle
• Motor units contract–brings about knee-jerk
action
Muscle Spindles at Work
Sensory neuron
(two branches within)
Motor neuron
Muscle
fibres
Polysynaptic Reflexes
• Withdrawal reflex:
– Rapid and occurs before brain has time to interpret
the information
– Involves the withdrawal of a body part from a painful
stimulus
– Reflex action involves transferring impulse from a
sensory neuron to a motor neuron through a
connecting interneuron
• Crossed-Extensor Reflex:
– Observed when one leg or arm automatically
compensates for a reflex action in opposing leg or
arm
– Involves multiple synapses and muscle groups
The Withdrawal Reflex and the
Crossed-Extensor Reflex
Disorders & Diseases of the
Nervous System
• Multiple Sclerosis (MS)
– Autoimmune disease in which the fatty myelin sheaths
around the axons of the brain and spinal cord are
damaged, leading to demyelination and scarring
Disorders & Diseases of the
Nervous System
•
•
•
•
•
•
Parkinson’s
Alzheimer’s
Epilepsy
Stroke
Meningitis
Schizophrenia
Spinal Cord and Head Injuries
•
© iStockphoto.com/”caracterdesign”
Spinal cord injuries:
– Damage to the spine can result
in an inability to send impulses
to body parts
– Nerves above injury keep
working, nerves below may not
– Paraplegia:
• Injury prevents use of legs
but not arms
– Quadriplegia:
• Injury prevents movement of
both arms and legs
– Causes:
• Car accidents, Falls, Sports,
Diving
Spinal Cord and Head Injuries
© iStockphoto.com/”AlexKalina”
• Head injuries:
– Most common head
injury is a concussion:
• Occurs when brain
literally hits the skull;
often involves injury
to nerve fibres
• Ranges from mild to
severe
• Symptoms can
include: headaches,
fatigue, dizziness,
memory problems, or
slurred speech