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)

Cranial Nerves Spinal Nerves

Peripheral Nervous System

Forebrain Hindbrain Midbrain

Brain Spinal Cord

Central Nervous System

Nervous System

The Components of the Nervous The Components of the Nervous SystemSystem

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

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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 - Somatic

sympathetic 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)

• 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

Coverings & Fluid Spaces of Brain and Spinal Cord (Con’t)

Cells of the Nervous System

• Two types– Neurons: nerve cells– Neuroglia: specialized connective tissue

Neurons

• Consist of 3 main parts1. Neuron Cell Body2. 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)

• 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)

Neurons (Con’t)

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 SystemThe 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 OrgansGolgi Tendon Organs

The Muscle SpindleThe Muscle Spindle

Motor neuron

Sensory neuron(two branches within)

Muscle spindle within muscle fibre (magnified)

Muscle fibres

Golgi Tendon Organs & Muscle Golgi Tendon Organs & Muscle SpindlesSpindles

Golgi Tendon Organs Muscle Spindles

LocationWhere tendon meets muscle fibre

In belly of muscle fibre

PositionIn series with muscle fibre

Parallel to muscle fibre

Respond toChanges in muscle/tendon tension

Changes in muscle length

Sensory neurons

1 2

The Stretch ReflexThe Stretch Reflex

• Stretch reflex:– Simplest spinal reflex– Depends on the single connection between

primary afferent fibres and motor neurons of same muscle

The Stretch ReflexThe 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 WorkMuscle Spindles at Work

Motor neuron

Sensory neuron(two branches within)

Muscle fibres

Polysynaptic ReflexesPolysynaptic 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 The Withdrawal Reflex and the Crossed-Extensor ReflexCrossed-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 InjuriesSpinal Cord and Head Injuries• 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

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Spinal Cord and Head InjuriesSpinal Cord and Head Injuries

•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

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tockphoto.com/”A

lexKalina”