Exercise Science Section 6: The Nervous System and the Control of Movement An Introduction to Health and Physical Education Ted Temertzoglou Paul Challen ISBN

The Components of the Nervous System

The Central Nervous System The central nervous system (CNS) is divided into two parts: –The vertebral column and the spinal cord: Main pathway for information connecting the brain and peripheral nervous system –The brain: Main control centre Receives and interprets endless signals Has six main parts: (Cerebrum, Cerebellum, Brain stem, Diencephalon, Limbic system, Reticular activating system)

The Peripheral Nervous System Peripheral nervous system (PNS): –Consists of those parts of the nervous system that lie outside the CNS –Carries information in and out of the CNS (Includes: -12 pairs of cranial nerves - 31 pairs of spinal nerves) –Contains both autonomic and somatic (sensory) components

The Autonomic Nervous System Autonomic nervous system (ANS): –Comprised of two systems: Sympathetic system: –Causes localized bodily adjustments to occur –Prepares body for emergencies (i.e. releases adrenaline, increases heart rate) Parasympathetic system: –Returns body to normal (after it’s been altered by the sympathetic system) –Both systems work in unison

Somatic Nervous System Somatic nervous system: –Handles the muscles in our extremities –Contains both afferent and efferent nerve fibres: Afferent (sensory) nerves: –Send information to the CNS Efferent (motor) nerves: –Send instructions to skeletal muscle –PNS receives and processes information

Autonomic and Somatic Nervous Systems

Reflex arc:  Pathway in which the initial stimulus and the corresponding response message travel The Reflex Arc (pg 87) –Five parts to a reflex arc: Sensory Receptor Sensory (or afferent) neuron Intermediate nerve fibre (Interneuron) Motor (or efferent) nerve Effector organ OUCH!!

Answers - Page 87 1.Receptor receives initial stimulus ie. Pin prick 2.Sensory (afferent) neuron carries impulse to spinal cord 3.Interneuron interprets signal 4.Motor (efferent) neuron carries response to muscle/organ 5.Effector Organ carries out response (remove hand from danger!)

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 Tendon Organs (Page 88)

Answers - Page 88 1.Receptor senses increase in muscle tension. 2.Message sent along sensory neuron to spinal cord 3.Afferent neuron synapses with motor neuron of same muscle 4.Impulse is sent along the motor neuron to the muscle 5.Motor units contract

Golgi Tendon Organs & Muscle Spindles Golgi Tendon OrgansMuscle 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 12

The Stretch Reflex Stretch reflex: –Simplest spinal reflex –Depends on the single connection between primary afferent nerves and motor nerves of same muscle –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 to spinal cord Afferent neuron synapses with the efferent pathway of same muscle Impulse transmitted along efferent nerves to muscle Motor units contract–brings about knee-jerk action

Muscle Spindles at Work

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

Answers – Page 89 1.Stimulus (tack) detected by receptors in the skin 2.Receptors send nerve impulses along sensory nerves 3.Impulse reaches spinal cord – sensory terminals synapse with interneurons 4.Some interneurons synapse with motor neurons and travel to effector organ 5.Knee flexors withdraw from danger zone/extensors are inhibited 6.Other sensory neurons synapse with interneurons affecting motor neurons in opposite leg, causing these muscles to come into action

The Withdrawal Reflex and the Crossed-Extensor Reflex (pg 89) RIGHT LEG LEFT LEG Bend knee Stimulates hamstrings Inhibits quadriceps Takes the weight Inhibits Hamstrings Stimulates Quadriceps

Spinal 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

Spinal 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, memory problems, or slurred speech