Unit 3 -NEUROBIOLOGY AND

IMMUNOLOGYDivisions of the Nervous System &

Neural Pathways

Key area 3.1

REVISION

• What are the two parts of the Central Nervous System?

• What two types of nerves are involved in a nerve pathway?

• Why are reflex reactions necessary?

The Structure of the Nervous System

NERVOUS SYSTEM

CENTRAL

NERVOUS

SYSTEM (CNS)

PERIPHERAL

NERVOUS

SYSTEM (PNS)

BRAIN SPINAL

CORD

Glow

Learning Intention

• State the main structure of the central nervous system.

• State the main structure of the peripheral nervous system.

The function of the Nervous System

• The nervous system analyses sensory information from the body and the external environment.

• Some of the information is stored and decisions are made to ensure appropriate response and behaviour.

• Motor responses are brought about which either initiate muscular contractions or glandular secretions.

STRUCTURE & DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM

SOMATIC NERVOUS

SYSTEM

AUTONOMIC

NERVOUS SYSTEM

SYMPATHETIC

SYSTEM

PARASYMPATHETIC

SYSTEMSensory

neuronsMotor

neurons

The function of the Peripheral Nervous System

• The SNS controls the voluntary movement of skeletal muscles

• The ANS controls the involuntary movement of skeletal muscles – egsmooth muscle, cardiac muscle and glands to control

Somatic Nerve Pathway

CNS

receptors

(e.g. sense organs)

effectors

(e.g. muscles and glands)

STIMULUS (BURGER)

SENSORY NERVE (from retina to the brain)

CNS – information sorted and compared with

previous experiences

MOTOR NERVE to arm and hand

EFFECTOR – Muscles contract

NOM NOM

The Sympathetic fibres of the ANS

• Sympathetic fibres act as ‘accelerators’, and if they gain an upper hand, the body is prepared for action.

• It increases the expenditure of energy. Heart rate and blood pressure increase.

• Blood supplies are diverted to skeletal muscles, rate of perspiration increases .

• This is due to the release of the hormone Epinephrine (adrenaline).

• This is known as flight or fight.

Parasympathetic fibres of the ANS

• Parasympathetic fibres act as ‘brakes’ on activity and when they gain an upper hand, the body is able to rest and perform activities such as the digestion of food.

• This is known as ‘rest and digest’.

• The body goes into a calming state, energy expenditure slows down, heart rate and blood pressure drops.

Quick Questions

Q1: What are the main functions of the Central Nervous System?Q2: What are the components of the Central Nervous System?Q3: Describe two responses that can be stimulated by motor nervesQ4: What two systems comprise the Peripheral Nervous System?Q5: What is the main function of the Somatic Nervous SystemQ6: What types of nerves are involved in the Somatic Nervous System?Q7: Describe the pathway of a somatic nervous responseQ8: What two types of reactions are involved in the Autonomic Nervous System?Q9: What does the sympathetic system prepare the body for?Q10: What does the parasympathetic system prepare the body for?

1. Receive information from the senses, process information and

bring about an appropriate response.

2. The brain and the spinal cord

3. Muscle Contraction or Glandular Secretion

4. The Autonomic and the Somatic

5. Controls the skeletal muscles

6. Motor and Sensory nerves

7. stimulus- sensory nerve- CNS- motor nerve- effector

8. Sympathetic and Parasympathetic

9. Fight or Flight

10. Rest and Digest

Quick Question (answers)

The Antagonistic Actions of the Sympathetic and Parasympathetic System

SYMPATHETIC PARASYMPATHETIC

HEART RATE

BREATHING RATE

PERISTALSIS

INTESTINAL SECRETIONS

Increased contraction of

cardiac muscles – increases

cardiac output

Decreased contraction of

cardiac muscles –

decreases cardiac output

Smooth muscle wall of

bronchioles relaxed- increased

intake of air

Smooth muscle wall of

bronchioles contracted-

decreased intake of air

Rate of contraction of

smooth muscle in digestive

tract decreased- decreases

rate of peristalsis

Rate of contraction of

smooth muscle in digestive

tract increased- increased

rate of peristalsis

Activity of the secretory

glands inhibited – decreased

production of intestinal

secretions

Activity of the secretory

glands stimulated –

increased production of

intestinal secretions

Peripheral Nervous System Summary

• The sensory and motor neurons of the somatic nervous system (SNS) control the voluntary movement of skeletal muscles.

• The autonomic nervous system (ANS) conduct involuntary impulses to smooth muscle, cardiac muscle and glands through sensory neurons and motor neurons.

• The antagonistic action of the sympathetic ‘fight or flight’ and parasympathetic ‘rest and digest’ have an effect on heart rate, breathing rate, peristalsis and intestinal secretions.

Describe the antagonist nature of the two branches of the autonomic nervous system. Expand you answer by including the control of heart rate and peristalsis (6)

Autonomic Nervous System Answers

• Works automatically, without conscious thought.

• Associated impulses originate in the medulla in the brain.

• It regulates the bodies internal environment.

• It is made up of two systems: sympathetic and parasympathetic.

• These two systems are antagonistic in action.

• The sympathetic system prepares the body for fight or flight.

• The parasympathetic system prepares the body for rest and digest.

S vs P 1. The ANS works automatically / without conscious control.

2. Impulses originate in the medulla (region of the brain)

3. The sympathetic system prepares the body for fight or flight.

4. The parasympathetic system prepares the body for rest and digest.

5. Sympathetic nervous system increases HR whereas parasympathetic decreases HR

7. Sympathetic nervous system decreases rate of peristalsis whereas parasympathetic increaseses rate of peristalsis

8. Sympathetic nervous system decreases intestinal secretions whereas parasympathetic decreases intestinal secretions

Learning Intention

• Describe the structure and function of:

–Converging

–Diverging

–Reverberating neural pathways

Complex Neural Pathways

• Neurones are found to be connected to one another in many different ways in the CNS

• Examples of neural pathways are:

DIVERGING NEURAL PATHWAY

CONVERGING NEURAL PATHWAY

REVERBERATING NEURAL PATHWAY

Converging Neural Pathways

• To converge means to come together and meet at a common point.

• Converging path ways are where two or more neurones feed impulses to one neurone

• Converging neural pathways increase the sensitivity to excitatory or inhibitory signals.

Converging Neural Pathways

• Rods are visual receptors present in the retina of the eye. They contain pigments which break down in the presence of light.

• In each case, this breakdown forms a chemical which triggers off nerve impulses along a pathway of neurones

Converging Neural Pathways

• The nerve impulse transmitted by one rod is weak. It would mean not enough neurotransmitter would be released to carry on the impulse.

• Several rods converge to one rod biploar cell to allow enough neurotransmitter to be released.

Diverging Neural Pathways

• In a diverging neural pathway, the route along which an impulse is travelling divides

• Diverging neural pathways mean that an impulse in one neurone can have a simultaneous effect in many parts of the body

• An example of diverging pathways is fine motor control in the fingers

Reverberating Pathway

• Reverberation means a sound that occurs repeatedly, as in an echo

• In reverberating pathway neurones later in the pathway posses axon branches which synapse with earlier neurones sending the impulse back through the circuit

Neural Pathways Summary

• Converging neural pathways increase the sensitivity to excitatory or inhibitory signals.

• Diverging neural pathways influence several neurons at the same time.

• In a reverberating pathway neurones later in the pathway synapse with earlier ones sending the impulse back through the circuit.