The nervous system
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The Nervous System. Chapter 10. The human nervous system - overview. Generally, the more complex an animal is, the more complex the organisation and coordination of the nervous system. Humans are the most complex.

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The nervous system

The Nervous System

Chapter 10

The human nervous system overview
The human nervous system - overview

  • Generally, the more complex an animal is, the more complex the organisation and coordination of the nervous system.

  • Humans are the most complex.

  • Comprised of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) which are interconnected.

The central and peripheral nervous systems
The central and peripheral nervous systems.

  • The CNS:

    • Includes the nerve cells in the brain and spinal cord and the nerve cells connecting to these to other parts of the body.

    • Is the control centre of the nervous system.

  • The PNS:

    • All other nerve cells that lie wholly in or partially outside the CNS.

Parts and functions of the cns and pns
Parts and functions of the CNS and PNS

Reference: Nature of Biology Book 1; p313

The cns functions
The CNS functions

The CNS:

  • Cerebral cortex

    • Motor activity

    • Sensory input

    • Speech

    • Sight

    • Hearing


  • Information relating to well-being and functions in maintaining homeostasis.

The nervous system


  • Coordination of muscles, posture, balance and movement.


  • Control of the heart, blood vessels and lung ventilation.

  • Stores information

The pns functions
The PNS Functions

  • The motor component can be divided into two sub-systems:

    • Somatic (voluntary) – controls movement which you can control. (e.g. Movement using skeletal muscles).

    • Autonomic (involuntary) – controls movements which you cannot control.

The autonomic nervous system
The autonomic nervous system

  • The autonomic system is involved in unconscious responses:

    • Constriction of the pupils

    • Secretion from glands

    • Changes in heart rate

    • Signals to smooth muscle, the heart and glandular tissues

    • Regulates activities of the digestive, cardiovascular, excretory, respiratory and endocrine systems

Sub dividing the autonomic nervous system
Sub-dividing the autonomic nervous system

  • The autonomic system can be further divided into:

    • Sympathetic:

      • Increases energy use

      • Prepares the body for emergency action by increasing heart and metabolic rate (‘fight or flight’)

    • Parasympathetic:

      • Involved in activities which conserve energy – digestion and slowing heart rate.

    • Enteric:

      • Network of neurons and reflexes within the wall of the stomach.

Neuronal structure1
Neuronal structure

  • Sensory, motor and interneurons have different structures and shape but all comprise of the same parts.

  • Cell body – performs normal cell functions (e.g. Making proteins)

  • Dendrites – projections which carry electrical impulses to the cell body.

  • Axon – transmits impulses from the cell body to the axon terminals

  • Myelin sheath – fatty coating which insulates axon.

The nervous system

Structure of neuron
Structure of neuron one axon.

Nature of Biology Book 1; p314

Different nerve cells
Different nerve cells one axon.

  • Nerve cell = neuron

  • Three types of neurons:

  • Affector neurons:

    • = sensory neurons

    • Receptors detect change in external or internal environment.

    • Transmit information to the CNS through electrical impulses.

  • Effector neurons:

    • = motor neurons

    • Transmit impulses from the CNS to muscle cells or glands triggering a response.

The nervous system

  • Connecting neurons: one axon.

    • = interneurons

    • Normally located in CNS

    • Link sensory and motor neurons

Location of neurons in the cns and pns
Location of neurons in the CNS and PNS one axon.

Reference: Nature of Biology 1; p314

Location and orientation of interneurons sensory and motor neurons
Location and orientation of one axon.interneurons, sensory and motor neurons

(Refer to the diagram on the previous slide.)

  • Sensory neurons:

    • Axon terminals in the CNS

    • Cell body and receptor end in the PNS

  • Interneurons:

    • Normally all in the CNS

  • Motor neurons:

    • Dendrites and cell body in the CNS

    • Axon terminal in the PNS

How the nervous system functions an overview
How the nervous one axon.system functions – an overview

  • A stimulus (a condition or signal) is detected by a receptor (a structure which detects a stimulus or signal).

  • The signal is transmitted by sensory neurones to the CNS.

  • The CNS sends response signals to effectors via motor neurons.

  • Effectors are usually muscles and glands which carry out a response.

Neuronal structure2
Neuronal structure one axon.

  • A single neuron can connect with as many

    10 000 other interneurons.

  • Neurons are bundled together to form nerves – 100’s-1000’s bound together all pointing in the same direction.

Neuronal function
Neuronal function one axon.

  • Three basic steps:

  • Generation of electrical impulse (action potential)

  • Conduction of an impulse along axons

  • Chemical transmission of a signal to another cell across a synapse.

Depolarisation one axon.

  • Sensory neurons respond to stimuli by depolarisation – the inside of the cell becomes less negative than the outside.

  • If depolarisation is large enough an action potential is produced.

The action potential
The action potential one axon.

  • If depolarisation is sufficient Na+ channels in the membrane open and Na+ flood in along the concentration gradient.

     Creates an action potential which moves down the axon.

     The neuron becomes more +

     K+ ions channels open and diffuse out of the cell along concentration gradient causing the neuron to become briefly + and then –

The nervous system

  • Refractory period – one axon.once an action potential is produced, the neuron is inactive for a period of time.

  • Nerve impulse animation

Between neurons
Between neurons one axon.

  • Between the presynaptic terminal of one axon and the postsynaptic region of the adjacent cell is a small gap called the synapse.

  • Electrical signals are passed through the synapse by neurotransmitters.

  • Neurotransmitters bind to specific postsynaptic receptors.

  • They provoke or inhibit activity in the adjoining neuron.

  • Once activated they are either taken up terminal or broken down by enzymes.

Synapses and neurotransmitters
Synapses and neurotransmitters one axon.

Reflex actions
Reflex actions one axon.

Reflex responses
Reflex responses one axon.

  • The simplest type of nervous response (may involve only a few cells) usually to avoid pain, danger or predation.

  • Reflex responses are unconscious and automatic.

  • Reflex arc: The pathway of a reflex impulse.

The knee jerk response
The knee-jerk response one axon.

  • Simplest reflex involving only two neurons. (monosynaptic)

  • A receptor sends a signal via a sensory neuron to the spinal chord which transmits a signal through a motor neuron to the effector muscle.

The withdrawal reflex
The withdrawal reflex one axon.

The withdrawal reflex is triggered by pain receptors in the skin and involves sensory, interneurons and motor neurons.

Other reflex responses
Other reflex responses one axon.

  • Maintaining posture.

  • Homeostatic regulation of systems such as the circulatory system.

  • E.g. Baroreceptor-heart rate reflex helps maintain constant blood pressure.

Interneurons reflexes and complexity
Interneurons one axon., reflexes and complexity

  • When muscles contract, interneurons need to send messages to opposing muscle not to contract. (e.g. Bicep and tricep)

  • Many reflexes are more complex

    • Many movements involve complex balances between opposing muscles.

Sense organs
Sense organs one axon.

Sense organs1
Sense organs one axon.

  • The five senses

  • Sense organs – process sensory information

  • General senses – pressure, pain and joint position

  • Visceral receptors – detect internal states

Types of receptors
Types of receptors one axon.

  • Photoreceptors – vision

  • Chemoreceptors – taste, smell, communication

  • Mechanoreceptors – hearing, balance, pressure, touch

  • Thermoreceptors - heat

The nervous system
` one axon.