The Nervous System and the Control of Movement

“He’s got what you might call a control problem. The guy has a million-dollar arm, but only a ten-cent brain.” - line from the baseball movie Bull Durham

Learning Goals: • I will be able to….

– Describe and explain the various components of the nervous system

– Explain how the nervous system functions to transmit sensory and motor signals throughout the body

– Explain how different types of reflexes work

The Nervous System• Gathers information from outside (external)

and inside (internal) the body, interprets and analyzes the info, then initiates a response

• Works as a basic feedback loop:– Sensor– Interpreter– Responder

Two Components of the Nervous System

• Central Nervous System (CNS)• Peripheral Nervous System (PNS)

The Central Nervous System (CNS)• Divided in 2 parts:

1. Brain2. Spinal Cord

• Brain • Main control center; “computer”• Sends out commands

• Spinal Cord• Main pathway for information• Connects brain and peripheral

nervous system • Carries sensory info to CNS and motor

commands away from the CNS

The Peripheral Nervous System (PNS) • Parts of the nervous system other than the brain and

spinal cord • Communication lines between the CNS and the rest of

the body• 12 pairs of cranial nerves and 31 pairs of spinal nerves

Composed of…– Somatic nervous system– Autonomic nervous system

• Sympathetic system • Parasympathetic system

The Somatic Nervous System

• Voluntary - skeletal muscle • Processes info from receptors in skin, muscles,

joints, etc. and give us sensations of pain, heat/cold, body position, muscle action, etc.

Composed of…• Afferent nerve fibers “sensory nerves”

- sends sensory information to the CNS

• Efferent nerve fibers “motor nerves” - CNS sends information through these fibers to instruct skeletal muscles to react

The Autonomic Nervous System

• Involuntary – cardiac and smooth muscle

• Sympathetic system- prepares the body for emergencies- fight-or-flight responses- increases HR, BP, breathing rate, etc. - release of adrenaline

• Parasympathetic- helps bring body back to “normal state”- decreases HR, BP, breathing rate, etc. - parasympathetic system has opposite effect of sympathetic system- release of acetylcholine

Neurons

• “nerve cells” • Transmit signals or

nerve impulses

Cross-Section of Spinal Cord

Check Your Understanding…• How does the nervous system relate to what you have

learned about muscles, bones, joints, etc.?

• Create a graphic organizer to help you organize and understand the structure of the nervous system

• Compare and contrast afferent and efferent nerves.

• How do the sympathetic and parasympathetic systems work together?

• What is an example of a body function controlled by the somatic nervous system? Autonomic nervous system?

Nervous System Jigsaw Activity • Each person will be assigned to learn and summarize a

component of the nervous system

• Summarize your information in a few points

(What is it? How does it work? Why is it important?)

• You may include diagrams

• Everyone needs their own note!

• Each person will present material to the group

• You are responsible for knowing all info!

Topics

• Reflex arc

• Golgi Tendon

• Muscle spindle and stretch reflex

• Polysynaptic reflexes

Reflexes • Reflex: rapid, automatic response to stimulation

– Can occur in the brain (cerebral reflex) or in the spinal cord (spinal reflex)

• Autonomic reflexes – autonomic nervous system– Smooth and cardiac muscle, glands – Digestion, elimination, blood pressure, salivation,

sweating

• Somatic reflexes – somatic nervous system– Skeletal muscle – Eg: pain, withdrawal reflex, stretch reflex

The Reflex Arc

• Five parts of the Reflex Arc:

• Receptor – receives initial stimulus

• Sensory (afferent) nerve – carries impulse to spinal cord or brain

• Intermediate nerve fibre (adjustor or interneuron) – interprets signal

• Motor (efferent) nerve – carries response to the muscle or organ

• Effector organ (skeletal muscle) – carries out the response

Pathway of the initial stimulus and the response message

Components: Sensory receptor Adjustor (CNS) Effector organ

Proprioreceptors and the Control of Movement

• Proprioreceptors are specialized receptors located throughout the body that provide sensory information regarding position of limbs, body posture, balance, etc.

• Proprioception: Awareness of one’s body position

• Uses 2 sensory receptors– Golgi Tendon Organs– Muscle Spindles

Golgi Tendon Organs (GTOs)

located on the ends of tendons detects increased tension exerted on tendon

Tension Reflex: when tension is detected in GTOs an impulse is send along afferent nerves to the CNS which send a signal to efferent nerves causing the muscle to relax to prevent injury

The Muscle Spindle Located in the belly of muscle fiber Help maintain muscle tension (body posture) but

detects increases in muscle length More sensitive than GTOs (2 sensory nerves) Involved in the Stretch Reflex

Stretch Reflex

Sequence of nerve impulses:

1. Muscle spindle’s sensory neuron senses stretch of patellar ligament

2. Afferent nerve transmits signal to the spinal cord

3. Afferent neuron synapses with efferent neuron in spinal cord

4. Impulse transmitted along efferent nerve to muscle

5. Muscle contracts to reduce the stretch (knee-jerk reaction)

The simplest reflex – one connection between afferent and efferent neurons (monosynaptic)

Eg: Knee-jerk reflex (patellar ligament)

Reciprocal Inhibition • While tapping on the patellar ligament

causes the quadriceps to contract, reciprocal inhibition causes the antagonist (opposing) muscle group (hamstrings in this case) to relax

• Makes it easier for the quadriceps to contract

• Allows constant adjustment between the two muscle groups

Polysynaptic Reflexes

• As opposed to monosynaptic reflexes• i.e. more than one interneurons lie between the

sensory and motor neurons • More complex and slower reflexes

Withdrawal Reflex- Withdrawal of a body part from a painful stimulus- Still very rapid, but involves more interneurons

Crossed-Extensor Reflex - When one arm or leg automatically compensates for a

reflex action in the opposing arm or leg- The reflex involves multiple synapses and muscle

groups

Videos• Spinal Reflex intro/reflex arc

http://www.youtube.com/watch?v=8EmCV-aVQOQ&feature=related • Reflex arc

http://www.youtube.com/watch?v=Y5nj3ZfeYDQ • Stretch reflex

http://www.youtube.com/watch?v=HfuhVWK8C0U&feature=related • Tension reflex

http://www.youtube.com/watch?v=lT9XhORYHJ8&feature=related • Withdrawal reflex • http://www.youtube.com/watch?v=RLe9koPfVoo&feature=related • Crossed extensor reflex • http://www.youtube.com/watch?v=iaXVUtS8Y4I&feature=related

What’s working? • Removing your hand from a hot pot

– Withdrawal reflex • Being able to touch your finger to your knee with your eyes closed

– Proprioreceptors • Stepping on a tack and immediately stand on your other foot

– Crossed-extensor reflex • A doctor taps your patellar ligament to test your reflexes

– Muscle spindle – stretch reflex • Your muscle relaxes after being stretching too much

– Golgi Tendon Organs – tension reflex • When your biceps contracts, your triceps are inhibited

– Reciprocal inhibition • You are able to stand on one foot, any changes to muscle length are

detected and corrected– Muscle spindle

Spinal Cord Injuries

• Each person researches one spinal cord injury or technological advancement and will present it to the class

– Paraplegia – Quadriplegia– Concussions– MRI Technology

Careers Involving the Nervous System

• Neurologist - An M.D. who diagnoses and treats disorders of the nervous system.

• Neuroradiologist- Uses imaging methods such as X-ray, MRI, CT and angiography to diagnose diseases of the nervous system.

• Psychologist- Studies the neural basis of behavior

• Psychiatrist - M.D. who diagnoses and treats mental disorders.

• Electroneurodiagnostic Technician - Records electrical activity from the brain (electroencephalograms; evoked potentials) and spinal cord.

• Chiropractor, physical therapist, massage therapist, physiotherapist, etc.

• Spinal Cord Injury Research/Clinic at Brock University (pdf article)