Objectives

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3.5.3 Responses in the Human Nervous System
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Objectives What you will need to know from this
section

• Outline the nervous system components central
  nervous system (CNS) and the peripheral nervous
  system (PNS)
• Receptor messages are carried through these
  systems by nerve cells or neurons.
• Outline the structure function of the neuron
  includingcell body, dendrites, axon, myelin
  sheath, schwann cell, and neurotransmitter
  vesicles synaptic cleft
• Outline impulse movement synapse.
• Explain activation inactivation of
  neurotransmitter.

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• The structure and function of a neuron
  variation in size and shape.
• Neuron -- Three part structuregt dendrite(s)
  receive information and carry it towards the
  cell body,gt the axon conducts nerve impulses
  away from the cell body,gt the cell body
  contains the nucleus and other organelles and
  produces neurotransmitter chemicals.
• Explain the role position of 3 types of neuron
  -- sensory/motor/inter
• Movement of nerve impulse.(Detailed knowledge of
  electrochemistry not required.)
• Knowledge that the conduction of nerve impulses
  along a neuron involves movement of ions
  (details not required).

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• Outline the senses with the brain as an
  interpreting centre.
•  Outline the CNS, brain spinal cord.

• State location function of cerebrum /
  hypothalamus / pituitary gland / cerebellum /
  medulla oblongata
• Label /or draw diagrams of spinal cord (cross
  section) indicating white matter, grey matter,
  central canal, 3 layer protective
  tissue-meninges.
• Spinal nerves containing dorsal and ventral
  roots that project from the spinal cord

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• Outline disorders from NS disorders
  paralysis/Parkinson's including Cause/Prevention/
  Treatment
• Outline PNS including the location nerve fibres
  cell bodies.
• State the role, structure mechanism of the
  Reflex arc/action.
• The sense organs contain receptors, with the
  brain as an interpreting centre for received
  information.
• Knowledge of the five senses and related organs.
• Study the eye and the ear recognition and
  fuction of the main parts. 
• Corrective measures for long and short sight or
  for a hearing defect.

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The Nervous System

• Organisms must be aware of what is happening
  around them,as this affects their survival
  chances.

• Co-ordination of an organisms activities is
  carried out by the nervous system and the
  endocrine system.

• A nervous system allows an organism to detect and
  respond to stimuli in its internal or external
  environment.

• A stimulus is any change in your environment

e.g. a flash of light, a noise, a fly landing on
your nose.
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• The nervous system relies on electrical signals,
  carried byspecialised cells neurons, and is
  involved in fast responses.

• The central nervous system (CNS) is your brain
  and spinal cord.

• The brain keeps a check on internal organs and
  activities, such as the level of carbon dioxide
  or water in the blood.

• The peripheral nervous system (PNS) is the nerves
  branchingfrom the CNS to all parts of the body.

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Comparison of the endocrine and nervous systems
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Comparison of the endocrine and nervous systems
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Endocrine Nervous
Cells involved Gland Sense receptor
Message Chemical (Hormone) Electrical(Impulse)
Carried by Blood Nerve cell
Message sent to Cells throughout the body A specific cell or tissue
Received by Target organ Effector (muscle or gland)
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Comparison of the endocrine and nervous systems
-- 2
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Comparison of the endocrine and nervous systems
-- 2
Endocrine Nervous
Speed of transmission Usually slow Rapid
Effects Can be widespread Localised usually
Duration long-lasting (hours) Usually brief (seconds)
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LEARNING CHECK

• Co-ordination of an organisms activities is
  carried out by what 2 body systems?
• Distinguish between the CNS and PNS.
• What is a neuron?
• What is an impulse?
• List the main differences between the endocrine
  and nervous systems.

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NS ----- Co-ordination Response

• A stimulus is any change in your environment

• A receptor is a nerve cell that detects the
  stimulus

• A neuron is a specialised cell that carries
  electrical messages(impulses) around the body.

• An impulse is an electrical message that is
  carried along aneuron.

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Neuron structure

• The cell body contains the nucleus and other
  organelles andproduces neurotransmitter
  chemicals.

• A dendron is a short fibre that receives
  information and carries it towards the cell body.

• The axon is a very long fibre that conducts
  impulses away from the cell body.

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• A dendron is a short fibre that receives
  information and carry it towards the cell body.

• Dendrites are small branches of a dendron.

• Many Schwann cells wrap their fatty cell
  membranes around an axon, forming a myelin sheath.

• The myelin sheath insulates the neuron from
  electrical impulses flowing in other neurons.

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There are three types of Neuron

• Sensory neuron carries messages from the sense
  organ to the central nervous system (CNS).

• Interneuron connects sensory and motor neurons
  and so carries messages within the CNS.

• Motor neuron carries impulses from the CNS to
  muscles and glands.

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• Synapseregion where two neurons come into close
  contact.

• Synaptic cleftthe gap between two neurons,
  bridged by chemicals (neurotransmitters).

• Neurotransmitterchemical released across a
  synaptic cleft tocarry a signal from one neuron
  to another.

• The chemical is then destroyed or removed

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LEARNING CHECK

• What is a stimulus?
• What is a receptor?
• Name the main parts of a neuron and give one
  function of each.
• Distinguish between a sensory and motor neuron.
• Distinguish between synapse and synaptic cleft.
• What are neurotransmitters?

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The Brain

• The brain is composed of over 100 billion
  neurons, eachreceiving messages simultaneously
  from thousands of otherneurons.

• The brain is protected by the skull bones,
  meninges (three membranes) and cerebrospinal
  fluid.

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• The cerebrum is our conscious brain, with
  different parts havingdifferent jobs to do.

cerebrum
hypothalamus
pituitary

• The hypothalmus is the centre for the regulation
  of the internal organs.

• The pituitary master gland secretes hormones
  that stimulateother glands to release their
  hormones.

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Conscious actions
A conscious action is one where the brain makes a
considered response. Heres what happens
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• The cerebellum co-ordinates processes that we
  have learned to do automatically, such as
  speaking.

cerebellum

• The medulla oblongata co-ordinates involuntary,
  automatic processes such as breathing,
  heartbeat.

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LEARNING CHECK

• Name the 3 main parts of the brain and one
  function of each.
• How is the brain protected?
• What is meant by conscious action?
• What does the term involuntary mean?
• Distinguish between the cerebrum and the
  cerebellum.

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• The spinal cord is well protected by the
  vertebrae, meninges (three membranes) and
  cerebrospinal fluid.

• It transmits impulses to and from the brain and
  controls many reflex actions.

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• A cross-section through the spinal cord shows a
  small central canal, filled with cerebrospinal
  fluid, surrounded by an area of grey matter,
  shaped somewhat like the letter H.

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• Grey matter contains cell bodies and dendrites
  (regions of a neuron that have no white myelin
  covering).

• Outside the grey matter, the spinal cord consists
  of white matter (containing axons only).

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• In humans, 31 pairs of spinal nerves branch off
  from the spinal cord.

• Each spinal nerve has a dorsal root and a ventral
  root.

• The dorsal root consists of nerve fibres carrying
  information into the spinal cord from the senses.

• The dorsal root ganglion is a swelling that
  consists of the cell bodies of the sensory
  neurons.

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• The ventral root consists of nerve fibres
  carrying information out from the spinal cord, to
  the muscles and glands.

• The cell bodies of the motor neurons are
  positioned within the grey matter of the cord.

• The spinal cord transmits impulses to and from
  the brain and controls many reflex actions.

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REFLEX ACTION --- The Reflex Arc

• A reflex action is a quick, automatic response to
  a particular stimulus.

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REFLEX ACTION --- The Reflex Arc
Suppose you touch a hot flame.

• Almost instantly you pull your hand away.

• In this brief instant, a message has been carried
  by a sensory neuron from pain receptors in the
  skin to the spinal cord.

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• In the spinal cord, the message is passed on to
  an interneuron and then to a motor neuron, and so
  into muscles that respond by contracting and
  pulling your hand from the flame.

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• This response saves the body from injury.

• The response is called a reflex action, as it
  does not involve conscious control, and is
  predictable and automatic.

• Many of the activities of the body, such as
  breathing and keeping our balance, are regulated
  by reflex actions.

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LEARNING CHECK

• How is the spinal cord protected?
• Distinguish between grey and white matter.
• Distinguish between dorsal and ventral root
• What is meant by reflex action?
• Give some examples of reflex actiongt
• What is an interneuron?
• Distinguish between cell bodies and ganglions.

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Nervous System Disorder

• Parkinsons disease is a nervous system disorder,
  normally seen in older people, in which muscles
  become rigid and movement is slow and difficult,
  with persistent tremors shaking.

• It is caused by the brain reducing the normal
  amount of dopamine that it makes.

• There is at present no means of preventing it,
  but giving L-dopa (which the body changes into
  dopamine) can relieve the symptoms in many
  patients.

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SENSE ORGANS

• Animals have specialised senses to provide them
  with information about their environment.
• The five senses are sight, hearing, touch, taste
  and smell.

• A receptor is a cell that can detect a stimulus
• A stimulus is any change in your environment,
  e.g. light, sound.

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The EYE

• Eyelids can cover and protect the eyes.

Conjunctiva
Cornea

• Conjunctiva thin transparent lining protecting
  the cornea.

• Corneafront transparent part of the sclera. It
  focuses light rays on the retina.

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Sclera

• Scleratough fibrous outer layer the white of
  the eye it maintains the shape of the eyeball.

Choroid
Retina

• Choroidcontains blood vessels supplying food and
  oxygen to the cells of the eye.

• Retinathe innermost layer that contains the
  receptor cells rods and cones.

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• The fovea is where our best vision is mainly
  cones

• The front region of the choroid is specialised
  into the iris

Iris

• Iriscontains blood vessels and melanin giving
  us our eye colour, and controls the amount of
  light entering the eye through the pupil.

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Pupil

• In bright light, pupil constricts.

• In dim light, the pupil dilates.

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• Ciliary body muscle thickened edge of the
  choroid that controls the shape of the lens

Ciliary muscle

• Suspensory ligaments hold the lens in place.

Suspensory ligaments
Lens

• Lenslike a magnifying glass, it focuses the
  light rays on the retina.

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• Lensfocuses the light rays on the retina.

• Accommodation is the ability of the lens to
  change its shape (focal length) to form a clear
  image.

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LEARNING CHECK

• Name the 5 senses and the organs involved.
• Name the 3 main layers of the eye and the
  function of each.
• What is the function of the a iris, b lens,
  c cornea, d fovea
• What is accommodation?

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Close Vision

• For close vision, the ciliary muscle contracts,
  the suspensory ligaments relax, the lens becomes
  thicker.

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Distant Vision

• When the eye is at rest, the lens is thin, has a
  long focal length and is adapted for seeing
  distant objects.

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• Accommodation is the ability of the lens to
  change its shape (focal length) to form a clear
  image.

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Seeing things at different distances
For distant objects, the ciliary muscle relaxes
and so the suspensory ligaments pull tight,
pulling the lens thinner the light doesnt bend
as much.
For close objects the ciliary muscle contracts,
allowing the lens to go fat, thus bending the
light more.
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• Aqueous humourwatery liquid that supplies the
  lens and cornea with nutrients and helps keep the
  shape of the cornea and lens.

Aqueous humour
Vitreous humour

• Vitreous humourgel that helps maintain the shape
  of the eye.

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• When light rays focus on the retina, receptor
  cells are stimulated and impulses are carried
  along the optic nerve to the brain.

Optic nerve
Blind Spot

• Blind spotwhere the optic nerve fibres pass
  through the retina and there is no room for
  receptors.

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Eye Defects

• Long-sighted You are long-sighted if you can
  clearly see objects a long way off, but you
  cannot see things close by.
• Reading glasses convex lenses can correct the
  problem.

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Eye Defects

• Short-sightedYou are short-sighted if you can
  clearly see objects close to you, but you cannot
  see things in the distance.
• Glasses with concave lenses can correct the
  problem.

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LEARNING CHECK

• Explain how the ciliary body and suspensory
  ligaments alter the lens.
• What is the function of the a humours, b
  optic nerve?
• If you are longsighted, what does it mean?
• What could be a possible cause?
• What type of lens can rectify it?

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The EAR

• Pinnaouter visible ear, funnels sound into the
  ear canal.

• Ear canal tube leading to the ear drum. It has
  hairs and wax glands to trap dirt and germs.

Eardrum

• Eardrummembrane of skin that vibrates when sound
  waves hit it.

Pinna
Ear Canal
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Middle Ear

• Middle earair-filled cavity containing three
  small bones ossicles and the Eustachian tube

Ossicles

• Ossicles 3 small bones hammer, anvil and
  stirrup, that amplify the sound.

• Eustachian tubekeeps air pressure equal on each
  side of the eardrum.
• It opens when we swallow, cough, etc.

Eustachian tube
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• Inner earcontains a coiled, fluid-filled tube
  called the cochlea and the semi-circular canals.

Inner Ear
Semi-circular canals

• Cochleacontains nerves that convert sound
  vibrations into electrical impulses.

• Semi-circular canalshelp us keep our balance and
  posture.

Cochlea
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• The pinna (ear lobe) channels the sound
  (vibrations in the air) towards the eardrum,
  which then vibrates.

• In turn, this vibrates the hammer, anvil and
  stirrup bones, which amplify the sound.

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• The stirrup pushes on the oval window of the
  cochlea, moving the liquid inside.

• Special hairs on 30,000 receptor cells detect the
  movement and send signals to the brain along the
  auditory nerve.

• The brain interprets these as sounds, and we
  hear.

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• Semi-circular canalshelp us keep our balance and
  posture.

• The three semicircular canals are curved tubes,
  each about 15mm long and filled with fluid.

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• Head movements are detected by nerves inside the
  canals.

• The brain responds by sending messages through
  the cerebellum, which trigger reflex actions in
  our muscles.

• This helps us keep our whole body balanced as we
  move.

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Ear Defects

• Deafness
• Deafness can be caused by long exposure to a high
  level of noise, drugs, or ear infections.
• Damage to the eardrum, ossicles bones, and
  cochlea, which can be caused by loud sounds,
  produces incurable deafness.

• Workers exposed to prolonged sounds of over 90
  decibels dB are obliged by law to wear ear
  protection.

• Any exposure to 140 dB causes immediate damage to
  hearing.

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The SKIN as a Sense Organ
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LEARNING CHECK

• What is the function of the a pinna, b 3
  ossicles, c cochlea, d semi-circular canals,
  e eustachian tube?
• Outline how vibrations in the air are eventually
  heard by our brain.
• Name a common ear defect.
• Give some possible causes treatments.
• How might you reduce your risks of this defect?