Form 5 Biology Chapter 3 Body Coordination (a)

Organisation of the Nervous System

1. The whole human nervous system can be divided into two

subsystems:

(a)the central nervous system (CNS)

i. consist of brain and spinal cord

ii. processes sensory information, making decisions and initiating

responses

(b) the peripheral nervous system (PNS)

i. is responsible for the communication between the CNS and the

rest of the body

ii. consists of:

12 cranial nerves to carry nerve impulses to and from the

brain

31 spinal nerves to carry nerve impulses to and from the

spinal cord

(c)whose nerves carry nerve impulses from the sense organs to the

CNS are called afferent nerves

(d) whose nerves carry nerve impulses from the CNS to the

effectors (organs, muscles and glands) are called efferent nerves

2. The nervous system performs three main functions: sensory,

integrative and motor.

3. The sensory function involves the sensory receptors.

4. Sensory receptors

detect stimuli from internal and external environment

initiate nerve impulses that carry information to the CNS.

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Form 5 Biology Chapter 3 Body Coordination (a)

5. CNS

process and integrates the information by analysing and

storing

make decisions to initiate suitable responses.

6. Motor commands from the CNS are transmitted to the effector,

the muscles or glands, to carry out the responses.

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Form 5 Biology Chapter 3 Body Coordination (a)

The Brain and Its Functions

Cerebrum

Interprets information from receptors, control voluntary actions

such as learning and thinking, store information, analyses

speech, hearing and sight. The cerebrum is the largest part of the

brain.

It is highly folded to increase the surface area, so it can contain

more neurons.

Responsible for personality, memory and also emotion.

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Form 5 Biology Chapter 3 Body Coordination (a)

Thalamus

Integrates information from afferent neurons and sends it to the

cerebrum for further processing.

Responsible for sorting incoming information.

Hypothalamus

Control centre of the temperature and the blood osmotic

pressure (homeostasis) as well as the coordination of the

nervous system and the endocrine system.

Cerebellum

Coordination of muscle contraction and body balance control

Medulla oblongata

Controls involuntary actions such as heart beat, breathing,

peristalsis and control (cranial) reflex actions such as coughing

and sneezing.

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Form 5 Biology Chapter 3 Body Coordination (a)

Neurones

1. The nervous system is made up of millions of nerve cells called

neurones.

2. Neurones:

(a)are the basic units of the nervous system

(b) transmit electrical impulses called nerve impulses

(c)each has these basic structures: cell body, axon and dendrites

3. A nerve is a bundle of axons or dendrons (nerve fibres) grouped

and wrapped in connective tissue.

4. There are three main types of neurone:

(a)afferent or sensory neurone

(b) efferent or motor neurone

(c)interneurone or intermediate or relay neurone

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Form 5 Biology Chapter 3 Body Coordination (a)

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Form 5 Biology Chapter 3 Body Coordination (a)

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Form 5 Biology Chapter 3 Body Coordination (a)

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Form 5 Biology Chapter 3 Body Coordination (a)

Spinal Cord

1. Two main functions of the spinal cord:

(a)It relays nerve impulses into and out of the brain

(b) It is responsible for most of the reflex (involuntary)

actions of the body.

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Form 5 Biology Chapter 3 Body Coordination (a)

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Form 5 Biology Chapter 3 Body Coordination (a)

Transmission of Information Along the Neurone

Mode of Transmission along the Neurone

1. Conduction of nerve impulses:

(a)involves changes of charges on the inside and the outside of a

neurone.

(b) involves ions of which the most important are sodium (Na+)

and potassium (K+)

2. Key processes which occur before, during and after an impulse

passes along a neurone

(a)when at rest, the surface membrane of a neurone is polarised

(b) an impulse starts when a stimulation causes this polarised

membrane to depolarise section by section down the neurone.

(c)Repolarisation occurs (just behind the depolarised section)

soon after.

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Form 5 Biology Chapter 3 Body Coordination (a)

Synapse

1. A synapse is a gap (called synaptic cleft) across which a nerve

impulse passes from an axon terminal to another neurone (muscle

or gland cell).

2. Function of synapse:

(a)transmits information from one cell to another: from nerve to

nerve or from nerve to muscle

(b) causes nerve impulses to travel in one direction only, to

specific effectors

3. When an impulse reaches a synapse, the ending of the axon

(synaptic knob) produce and release a neurotransmitter.

4. Examples of neurotransmitter are acetylcholine, dopamine,

glutamate, aspartate, serotonin and noradrenaline.

5. The neurotransmitter binds to the receptor of postsynaptic

membrane and induces the impulse production.

6. Transmission of information across a synapse (Figure 3.13):

(a)electrical signals is converted into chemical signals in the form

of neurotransmitter

(b) chemical signal is reconverted back into electrical signals at

the postsynaptic membrane

7. Then, the neurotransmitter is quickly broken down by enzymes

to ensure the travel of nerve impulses in one direction and to

specific effectors.

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Form 5 Biology Chapter 3 Body Coordination (a)

8. Transmission of nerve impulses across synapses is an active

process which requires energy. This is why synaptic

knob/terminal contains abundant mitochondria.

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Form 5 Biology Chapter 3 Body Coordination (a)

The Effect of Drug on Synapse

1. Drug such as cocaine block the reuptake of dopamine which causes

the accumulation dopamine in the synaptic cleft.

2. This enhance the impulse stimulation at postsynaptic membrane to

generate impulse.

3. Some drugs block the receptor of postsynaptic membrane,

preventing the neurotransmitter binds to the receptor.

4. Therefore, no impulse is produced at postsynaptic membrane. These

types of drugs usually have inhibitory in center nervous system such

as painkiller.

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Form 5 Biology Chapter 3 Body Coordination (a)

Voluntary and Involuntary Action

Voluntary action Involuntary action

Nature of the control of action

Involves thought and free will.

Allows us to consciously control our skeletal muscle

Does not involve thought

Not under the control of the will.

Cannot control such activities, eg: pumping of the heart and peristalsis

Controlled by Cerebrum which:a)Coordinates incoming

information and then initiate impulses which are sent to the effectors

b)May spontaneously initiate actions without any sensory stimulation.

Spinal cord (spinal reflex action)

Hind-brain (cranial reflex action), example, blinking of the eyes.

Parts of the nervous system involved

Inteneurones (ascending and descending fibres) in the spinal cord

Always involve the cerebrum

Reflex arc: afferent neurons to intermediate neurons in spinal cord and out through efferent neurons (to effectors)

Hind-brain (in cranial reflex action)

Receptors involved An action may be initiated by the stimulation of a receptor, or by the

A receptor is always involved

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Form 5 Biology Chapter 3 Body Coordination (a)

conscious will of the brain itself.

Inborn or learned Voluntary actions are learned

Reflex actions are inborn

Role To respond with the benefit of experience

To respond quickly to avoid danger

Speed of action Slow response, as the cerebrum needs time to “think” before an action is carried out

Rapid response, as the cerebrum is not involved.

Response to the same stimulus

The same stimulus may produce various responses; example, when you are hungry, you may decide to eat or not to eat, or just need to drink water

The same stimulus always results in the same response; e.g. the knee jerk

Examples Raising your hand to answer a question

Decide to stand up

Involuntary action (reflex action involving skeletal muscle:

(a)Knee jerk

Involuntary actions involving

(a)Smooth muscles

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Form 5 Biology Chapter 3 Body Coordination (a)

(b)Cardiac muscles(c)Glands, example,

normal blood pressure

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Form 5 Biology Chapter 3 Body Coordination (a)

Reflex Arc

1. Involuntary actions are reflex actions that are being carried out

through a nervous pathway known as reflex arc.

2. Reflex arc consist of:

Receptor, sensory (afferent) neurone, interneurone (maybe

absent in some reflex arc), motor neurone and effector.

3. Reflexes are important because:

(a)provide a means of an immediate withdrawal from dangerous

stimuli.

(b) coordinate rapid automatic responses without the need for

instructions from the brain.

4. Most reflexes involve the spinal cord, however, some reflexes

involve the brain (E.g. the opening and the closing of the pupil of

the eye.), it is an automatic response whereby we have no

control over.

5. Examples are:

(a)Hand withdrawal reflex involve three types of neurones: the

afferent neurone, interneurone and efferent neurone

(b) Knee-jerk reflex involve only two types of neurones: the

afferent neurone and the efferent neurone.

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Form 5 Biology Chapter 3 Body Coordination (a)

Knee jerk reflex

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Form 5 Biology Chapter 3 Body Coordination (a)

Withdrawal Reflex

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Form 5 Biology Chapter 3 Body Coordination (a)

Transmission of Information in Involuntary Action Involving

Smooth Muscles, Cardiac Muscles and Glands

1. The autonomic nervous system

(a)controls involuntary actions involving the glands, the cardiac

muscles of the heart and the smooth muscles of the internal

organs such as the intestines.

(b) connects the medulla oblongata and hypothalamus with

the internal organs and regulates the internal body processes

that require no conscious effort.

2. Therefore, involuntary action does not involve the cerebral

cortex.

3. Autonomic nervous system can be divided into

(a) the sympathetic division

(b) the parasympathetic division

4. Both division work together, but act in opposition to maintain

homeostasis.

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Form 5 Biology Chapter 3 Body Coordination (a)

Sympathetic Nervous System

Promotes a " fight or flight " response, corresponds with arousal

and energy generation, and inhibits digestion

Diverts blood flow away from the gastro-intestinal (GI) tract

and skin via vasoconstriction

Blood flow to skeletal muscles and the lungs is enhanced

Dilates bronchioles of the lung, which allows for greater

alveolar oxygen exchange

Increases heart rate and the contractility of cardiac cells

(myocytes), thereby providing a mechanism for enhanced blood

flow to skeletal muscles

Dilates pupils and relaxes the ciliary muscle to the lens,

allowing more light to enter the eye and far vision

Provides vasodilation for the coronary vessels of the heart

Constricts all the intestinal sphincters and the urinary sphincter

Inhibits peristalsis

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Form 5 Biology Chapter 3 Body Coordination (a)

Parasympathetic Nervous System

Promotes a "rest and digest" response, promotes calming of

the nerves return to regular function, and enhances digestion

The parasympathetic nerves dilate blood vessels leading to the

GI tract, increasing blood flow (this is important following the

consumption of food, due to the greater metabolic demands

placed on the body by the gut)

The parasympathetic nervous system can also constrict the

bronchiolar diameter when the need for oxygen has diminished

During accommodation, the parasympathetic nervous system

causes constriction of the pupil and contraction of the ciliary

muscle to the lens, allowing for closer vision

The parasympathetic nervous system stimulates salivary gland

secretion, and accelerates peristalsis, mediating digestion of

food and, indirectly, the absorption of nutrients

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