3.2 ANALYSING ANALYSING THE ROLE OF THE ROLE OF

THE HUMAN NERVOUS THE HUMAN NERVOUS SYSTEMSYSTEM

THEME: PHYSIOLOGY OF LIVING THINGSLEARNING AREA: 3.0 COORDINATION AND RESPONSE

LEARNING OBJECTIVE: 3.2 ANALYSING THE ROLE OF THE HUMAN NERVOUS SYSTEMLEARNING OUTCOMES:

• state the role of nervous system,• draw and label a diagram to show the organisation of the nervous system,• name the main parts of the brain and state their functions,• draw and label a diagram of a cross section of the spinal cord,• state the main functions of the spinal cord,•label the structure of an efferent neurone,•Identify and discuss the function of the three types of neurone.•identify the type of the neurone from diagrams given,•state the function of each type of neurone,•state the mode of transmission of information along the neurone,•describe briefly the pathway of transmission of information from receptors to effectors,

draw and label a simple diagram of a synapse,•describe the transmission of information across synapses,•state the role of the synapse in transmission,•give examples of voluntary action,•give examples of involuntary action,•outline the transmission of information in voluntary action,•outline the transmission of information in involuntary action,•draw a schematic diagram showing a reflex arc,• give examples of nervous system related diseases.

Role of the nervous system• It is a communication network

– It receives information from receptors and then transmits and interprets the information

– It then formulates appropriate responses to be sent to the effector organs

• It also controls and coordinates functions throughout the body and helps maintain homeostasis

THE HUMAN NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM (CNS)

PERIPHERAL NERVOUS SYSTEM (PNS)

ORGANISATION OF THE NERVOUS SYSTEM

THE HUMAN NERVOUS SYSTEM

SPINAL CORD

BRAIN

ORGANISATION OF THE NERVOUS SYSTEM

HUMAN NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM

[CNS]

PERIPHERAL NERVOUS SYSTEM

[PNS]

BRAIN SPINAL CORDCRANIAL NERVES[12 pairs]

SPINAL NERVES[31 pairs]

Links receptors & effectors to CNS : relays signals between CNS & rest of

body

• Performs 3 functions:

• …..sensory

• …..integrative

• …..motor

THE ROLE OF THE NERVOUS SYSTEM

AN OVERVIEW OF THE FUNCTIONS OF THE NERVOUS SYSTEM

Sensory receptors detect stimuli from int. & ext. environments & initiate nerve impulses carrying

information to CNS

CNS processes &

integrates information by

analysing & storing some of it, & then

make decisions to

initiate suitable

responses

Motor commands from CNS transmitted to effectors [muscles or glands] to carry out responses

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THE HUMAN BRAINHUMAN BRAIN

HYPOTHALAMUS

THALAMUS

MEDULLA OBLONGATA

CEREBELLUM

CEREBRUM

THE HUMAN BRAIN

SKULL

MEDULLA OBLONGATA

CEREBELLUM

CEREBRUM

VERTEBRASPINAL CORD

PITUITARY GLAND

THALAMUS

HYPOTHALAMUS

THE BRAIN

Medulla oblongata

Pons

Brainstem

Cerebellum

Cerebrum

Thalamus

Hypothalamus

STRUCTURE OF THE BRAIN

• The cerebrum is the largest and most complex part of the brain.

• It is divided into two halves called the cerebral hemispheres.

• The left hemisphere controls the movements on the right side of the body.

• The right hemisphere controls the movements on the left side of the body.

• The cerebrum is the centre which receives the sensory input and carries out integrative functions before initiating appropriate motor responses.

• It also coordinates the activities of the other parts of the brain.

• The outer region of the cerebrum is the cerebral cortex.• The cerebral cortex is a structure with many folds which

increases the surface area.• The cerebral cortex directs voluntary muscle

movements, which result in a sensory perception that is, when a person becomes aware of what he sees, hears, smells, tastes or touches.

• It is also responsible for many mental abilities such as learning, memorising, reasoning, language skills, speech. mathematical skills, imagination, artistic talent and personality traits.

• Brain damage from trauma, a stroke or a tumour can result in specific defects, such as speech impairment. reading difficulty, or the paralysis of certain parts of the body.

CEREBRUM

• The cerebellum is located below the cerebrum near the top of the spinal cord.

• The cerebellum is the coordinating centre for body movement

• The cerebellum receives information from the sensory receptors on the positions of different parts of the body; and, from the cerebrum, an indication of the need to move.

• The cerebellum evaluates the information and relays the need for coordinated movements back to the cerebrum.

• The cerebrum then sends appropriate commands to the muscles

• The cerebellum controls voluntary muscles, posture, balance and the coordination of walking, running and playing sports

CEREBELLUM

MEDULLA OBLONGATA

•The medulla oblongata regulates the internal body processes that do not require conscious effort, that is, automatic functions such as the heartbeat, breathing and vasoconstriction

•It is also the reflex centre for vomiting, coughing. sneezing, hiccupping and swallowing.

NOTE: THE BRAINSTEM [connects the brain & spinal cord]- MADE UP OF PONS & MEDULLA OBLONGATA

HYPOTHALAMUS

•The hypothalamus plays an important role in homeostatic regulation. It acts as a major coordinating centre for regulating sleep. hunger, thirst, body temperature, water balance and blood pressure.

•It is also the control centre of the endocrine system.

• The pituitary gland secretes hormones that influence other glands and body functions.

• The hypothalamus controls the release of several hormones from the pituitary gland and thereby serves as an important link between the nervous

and endocrine systems.

PITUITARY GLAND

THALAMUS

•The thalamus is responsible for sorting the incoming and outgoing information in the cerebral cortex.

•It also integrates the information from the sensory receptors to the cerebrum by enhancing certain signals and blocking others

THE SPINAL CORD AND ITS MAIN FUNCTIONS

INTERNEURONE DORSAL ROOT

DORSAL ROOT GANGLION

AFFERENT NEURONE

RECEPTOR

EFFECTOR

EFFERENT NEURONE

CENTRAL CANAL

GREY MATTER[ contains

cell bodies]

SPINAL NERVE

WHITE MATTER {contains myelin-coated axons]

VENTRAL ROOT

CROSS SECTION OF THE SPINAL CORD

Spinal cord in cross section showing the position of the vertebral column

CROSS-SECTION OF THE SPINAL CORD

CENTRAL CANAL DORSAL ROOT GANGLION

WHITE MATTERGREY MATTER

VENTRAL ROOT OF SPINAL NERVE

SPINAL NERVE

DORSAL ROOT 0F SPINAL

NERVE

• The spinal cord is contained within the vertebral column• The spinal cord is surrounded by cerebrospinal fluid which

acts as a shock absorber and provides the spinal cord with nutrients.

• It consists of white matter and grey matter.• (a) In cross section, the grey matter looks like a butterfly

or the letter H.• (b) The grey matter consists mainly of cell bodies of

neurones.• (c) The grey matter is surrounded by the white matter.• (d) The white matter comprises myelin-coated axons of

neurones that extend the whole length of the spinal cord.

THE SPINAL CORD AND ITS MAIN FUNCTIONS

The spinal nerves emerge from the spinal cord through two short branches or roots.(a) The dorsal root contains the axons of the afferent neurones which conduct nerve impulses from the sensory receptors to the spinal cord.(b) The cell bodies of the afferent neurones are clustered in the dorsal root ganglion(c) The ventral root contains the axons of the efferent neurones which conduct nerve impulses away from the spinal cord to the effectors.(d) The dorsal and ventral roots join to form a spinal nerve.

FUNCTION: The spinal cord(a) processes certain types of sensory information and sends out responses via the efferent neurones.(b) contains neurones that convey signals to and from the brain,(c) contains the neural pathway for reflexes

THE NEURONE

• The nervous system is made up of millions of nerve cells called neurones

• Neurones transmit nerve impulses to other nerve cells, glands or muscles.

• There are three types of neurones

THE NEURONE

Carry sensory information from receptors cells to the brain & spinal cord

Structure of an afferent (sensory) neurone

Structure of an efferent (motor) neurone

Carry sensory information from brain & spinal cord to the effectors

[muscle / gland cells]

Structure of an interneurone

• Convey nerve impulses between the various parts of the brain and spinal cord

• Transmit nerve impulses between the afferent neurones and efferent neurones

• Transmit nerve impulses from one side of the spinal cord to the other side, or from the brain to the spinal cord and vice versa

• Many of the neurones that carry out integrative functions are the interneurones and the efferent neurones respond to these integrative signals

STRUCTURE OF AN EFFERENT NEURONE

• Dendrites are fibres that receive information or signals from other neurones or from the external environment and conduct them towards the cell body. • Dendrites of afferent neurones have special membrane adaptations that allow them to produce signals in response to specific stimuli from the external environment such as pressure, light or heat.

• A long, thin fibre called the axon extends outward from the cell body.• The axon conducts the nerve impulses away from the cell body.• The axons are usually bundled together into nerves

•Nerve impulses are conducted along the axon and finally reach the synaptic terminals [swellings at the branched ends

of the axons] located at the far end of each axon.• The synaptic terminals then transmit these signals to the muscle cells, gland cells or the dendrites of another neurone.

• The electrical signals or nerve impulses then travel along the dendrites and converge on the cell body of the neurone.• The cell body has a nucleus and other organelles which are found in cells.• The cell body integrates the signals and coordinates the metabolic activities.

•Some axons are insulated by a thick coat of material called a myelin sheath.•This sheath protects and insulates the axons, and helps to speed up the transmission of the nerve impulses.

dendrite

Cell body

Myelin sheath

Muscle fibre

(effector)

Synaptic terminals

axon

Direction of nerve impulse

nucleus

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THE TRANSMISSION OF INFORMATION ALONG THE NEURONE

•The transmission of information along the neurone is through electrical signals known as nerve impulses.

•An impulse is a wave of positive charges that travel along the axon to the synaptic terminal.

•A neurone will not transmit an impulse unless the stimulation is strong enough.

•Once the magnitude or size of the stimulation reaches a threshold level, a full-sized impulse is generated to travel the entire length of the axon.

The transmission pathway of information

Reception of stimuli by receptors

Response by the effectors

From the CNS to the effectors

Integration & interpretation by

the central nervous system

From receptors to the central

nervous system

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Afferent neurone

Efferent neurone

Interneurone 1 5

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3

2

6

Receptors in the ear

Muscles in the arm

Receptors in the ear pick

up the ringing of the

doorbell.

The nerve impulses pass from the afferent neurones to the interneurones in the brain

The receptors trigger nerve impulses in the afferent neurones.

From the interneurones, nerve impulses are transmitted to the efferent neurones andthen to the muscles

The brain interprets the nerve impulses from many interneurones that the doorbell is ringing. The brain also decides that the door should be opened

The muscles in the arm carry out the response and open the door

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The transmission pathway of information

The transmission of nerve impulses along the three types of neurones

Synaptic terminaldendrites

axon

dendrite

Cell body

receptor in skin

axon

myelin sheath

Synaptic terminal on muscle fibre

Cell body

Cell body

axon

myelin sheath

Efferent neurone

synaptic terminal

Afferent neurone

Interneurone

AFFERENT NEURONE EFFERENT NEURONE

Long dendrite, short axon

Short dendrite, long axon

Cell body at the side of the neurone [not at the end]

Cell body at the end of the neurone

Begins with receptor Ends with effector

DIFFERENCE BETWEEN STRUCTURE OF AFFERENT NEURONE & EFFERENT NEURONE

TRANSMISSION OF INFORMATION ACROSS SYNAPSES

What is a SYNAPSE?

The synapse is the site where two neurones, or a neurone and an effector cell communicate

•A nerve impulse is conducted along the axon of a neurone until it reaches the synaptic terminal.

•Beyond the synaptic terminal is a narrow space known as the synaptic cleft that separates the synaptic terminal from the dendrite of a receiving neurone, a muscle cell or a gland cell.

•The synapse is the site where two neurones, or a neurone and an effector cell communicate.

•The electrical signals carrying a message must be transmitted across the synaptic cleft to an adjacent cell.• (a) A synaptic cleft is the space between the presynaptic

membrane and the postsynaptic membrane.• (b) The transmission of nerve impulses across the synaptic cleft

occurs via a chemical process.

• (c) This process requires the actions of certain chemical substances

known as neurotransmitters.

• (d) Neurotransmitters are stored in small synaptic vesicles clustered at the

tip of a synaptic terminal

• The transmission of information across a synapse (a) involves the conversion of electrical signals into chemical signals in the form of neurotransmitters (b) the reconversion of the chemical signals into electrical signals at the postsynaptic membrane

• (c) The transmission of nerve impulses across synapses is an active process which requires energy. (d) The synaptic terminal contains abundant mitochondria to generate energy for the transmission of nerve impulses across the synapse.

• After the neurotransmitter has relayed its message, (a) it is rapidly broken down by enzymes, or (b) taken up again by the synaptic terminal and recycled. (c)This ensures that the effect of a neuro transmitter is brief and precise.

•Some examples of neurotransmitters are acetylcholine, noradrenaline, serotonin and dopamine.

• (a) controlling and integrating the nerve impulses transmitted by the stimulated receptors

• (b) allows the transmission of nerve impulses in only one direction. A nerve impulse cannot go backward across a synapse. Synaptic vesicles are only present in the synaptic terminals. Only the presynaptic membrane can discharge neurotransmitters. In contrast, receptors are only present in the postsynaptic membrane. This means that only the postsynaptic membrane can receive a chemical signal.

The role of synapse in transmission

NEURONES COMMUNICATE WITH ONE ANOTHER THROUGH SYNAPSES

Axon

Synaptic cleft

mitochondria

Presynaptic membranePostsynaptic membrane

[plasma membrane of the cell body or dendrite of a

neighbouring neurone]

Receptor

Dendrite

Synaptic vesicle

Synaptic terminal

Direction of transmission of nerves impulses

TRANSMISSION OF CHEMICAL SIGNALS ACROSS THE SYNAPSE

When an electrical impulse reaches the presynaptic membrane, it triggers the synaptic vesicles to release neurotransmitters into the synaptic cleft

The neurotransmitters diffuse across the synaptic cleft and bind to specific proteins or receptors which are attached to the postsynaptic membrane

The binding of the neurotransmitters to the receptors leads to the generation of new electrical signal

VOLUNTARY ACTION & INVOLUNTARY ACTION

TYPES OF NERVOUS ACTIONS

VOLUNTARY ACTION

INVOLUNTARY ACTION

Involves skeletal muscles

[eg raising your hand to answer

a question]

Involves skeletal muscles

[eg knee jerk]

Involves smooth muscles, cardiac

muscles or glands

[eg normal blood pressure]

VOLUNTARY ACTION & INVOLUNTARY ACTION

•The peripheral nervous system (PNS) has two main functions. (a) It transmits signals to the central nervous system (CNS) for processing. (b) It transmits responses from the CNS to the rest of the body.

These responses are either voluntary or involuntary actions.

1. VOLUNTARY ACTION INVOLVING SKELETAL MUSCLES

•Voluntary actions such is walking and talking are under conscious control.•Voluntary control of the skeletal muscles is governed by the cerebral cortex of the cerebrum•Information that reaches the cerebral cortex or the conscious level results in a perception of the external environment.

RECEPTOR

EFFECTOR

SENSORY (AFFERENT) NEURONE

MOTOR (EFFERENT) NEURONE

INTERNEURONE

STIMULUS

RESPONSE

CEREBRUM

THE PATHWAY OF TRANSMISSION OF INFORMATION IN VOLUNTARY ACTION

2. INVOLUNTARY ACTION INVOLVING SKELETAL MUSCLES: THE REFLEX ARC

•Involuntary actions that involve skeletal muscles allow immediate action that does not require conscious effort•For example, if a finger touches a hot stove or is pricked with a sharp pin, the reaction is to pull the finger away immediately without having to think about it.•In such circumstances when the responses to stimuli are involuntary, they are called reflexes.

•A REFLEX ACTION IS AN AUTOMATIC RESPONSE THAT OCCURS VERY RAPIDLY AND WITHOUT CONSCIOUS CONTROL [involves the contraction of the skeletal muscles and the spinal cord only]

•Reflexes are rapid, automatic or involuntary responses to stimuli.•The nerve pathway involved in a reflex action is called a reflex arc.•A simple reflex arc involves communication between the neurones in the peripheral nervous system and the spinal cord

A reflex arc involving 3 types of neurones and the spinal cord

NB: brain not involved

Afferent neurone

4.Efferent neurone

Grey

The knee-jerk ---------A reflex arc involving 2 types of neurones and the spinal cord

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afferent

efferent

The rubber hammer hits a tendon that connects the quadriceps

muscle in the thigh to a bone in the lower leg

As the rubber hammer strikes the knee, the force stretches the

quadriceps muscles and stimulates the stretch receptors in

the muscles, triggering nerve impulses

Afferent neurones transmit the information to the efferent neurones

in the spinal cord

The efferent neurones transmit this information to

the quadriceps muscle, and the muscle contracts,

jerking the leg forward

The knee-jerk ---------A reflex arc involving 2 types of neurones and the spinal cord

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3. INVOLUNTARY ACTION INVOLVING SMOOTH MUSCLES, CARDIAC MUSCLES OR GLANDS

• 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.

• Since the information for involuntary actions does not involve the cerebral cortex of the cerebrum, no perception is generated. Therefore, we are not aware of the responses.

•This means the autonomic nervous system permits vital functions such as the heartbeats and blood circulation to continue even during states of unconsciousness such as sleeping or fainting when voluntary actions have ceased.

•The autonomic nervous system can be divided into (a) the sympathetic division (b) the parasympathetic division

•These divisions work together, usually with one activating and the other inhibiting the actions of the internal organs.

•Both systems innervate the same organs or are connected to the same organs and act in opposition to maintain homeostasis

Sympathetic division

•Prepares the body for stressful situations or an emergency, in which the responses are associated with ‘fight or flight’ •Increases the pulse rate, blood pressure, and breathing rate•Slows down the digestive system so that more blood is available to carry oxygen to the vital organs such as the brain, heart and muscles

Parasympathetic division

•Prepares the body during ordinary situations or brings on the responses associated with a relaxed state•Decreases the pulse rate, blood pressure, blood pressure and breathing rate•Stimulates the digestive system to continue breaking down food

THE AUTONOMIC NERVOUS SYSTEM

DISEASES OF THE NERVOUS SYSTEM

DISEASE EXPLANATION

Parkinson’s disease

•Parkinson’s disease is a progressive disorder of the CNS that typically affects victims around the age of 60 years onwards.

•Parkinson’s disease affects muscular movements, causing tremors or trembling of the arms, jaws, legs and face.

•Patients also have difficulty in maintaining normal postures and

experience impaired balance and coordination.Alzheimer’s disease

•Alzheimer’s disease is a neurological disorder which affects victims around the age of 60 years onwards, causes the loss of reasoning and the ability to care for oneself.

•The cause of this disease is still unknown but factors such as genetic, environmental or the aging process itself can lead to Alzheimer’s disease.

•Individuals with Alzheimer’s disease often become confused, forgetful, and lose their way although they are in places which are familiar to them.

•As their minds continue to deteriorate, patients may lose the ability to read, write, eat, walk and talk.

•Taking care of patients with Alzheimer’s and Parkinson’s diseases requires a lot of patience and understanding.

•As such, we should empathise and show compassion towards patients with Alzheimer’s and Parkinson’s diseases.

•We should visit homes for the aged, senior citizens or patients with Alzheimer’s or Parkinson’s diseases