Coordination in Mammal

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Coordination in Mammal

• coordination is the way in which receptors detect
  stimuli, and then nerve impulses are sent to the
  effectors
• in mammals, coordination is carried out through
  the activities of nervous system and the
  endocrine system

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• nervous coordination is brought about by
  transmission of nerve impulses between receptors
  and effectors through nerve fibres

• endocrine coordination is brought about by
  hormones secreted from endocrine glands

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What is Nervous Coordination ?

• nervous system of mammal consists of central
  nervous system(CNS) and peripheral nervous system
• CNS includes brain and spinal cord and the
  peripheral nervous system includes cranial nerves
  and spinal nerves

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Structure of Neurones

• neurones make up nervous system in mammal
• each neurone has a cell body and nerve fibres
• cell body is a mass of cytoplasm with nucleus
  inside and it is called ganglion
• nerve fibres are cytoplasmic processes of
  neurones and there are two types, one is dendron
  and the other is axon

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• dendron transmits nerve impulses towards cell
  body while axon transmits nerve impulses away
  from cell body

• nerve fibres may be protected by a fatty layer
  which serves as an insulator to prevent the
  spread of nerve impulses and help to speed up the
  rate of transmission

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Types of Neurones

• there are three types of neurones sensory
  neurone, motor neurone and association neurone

- sensory neurone transmits nerve impulses
from receptor to the central nervous system
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- motor neurone transmits nerve impulses
from central nervous system to effectors. The
axon branches at its end to form many motor end
plates which are attached to muscle fibres
- association neurone connects the sensory
neurone to the motor neurone and also the
neurones in the central nervous system
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Nerve

• bundles of nerve fibres
• usually myelinated and surrounded by a sheath of
  white connective tissue

nerve
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• impulses do not jump from one fibre to another
  because of the presence of fatty substance in
  nerve

• in sensory nerves, there may be ganglia where the
  cell bodies are situated
• nerve fibres found inside the central nervous
  system do not have insulating fatty layers

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Nerve Impulses Transmitted in Nerve Fibre

• stimulation of the receptors
  may initiate nerve impulses
  and this follows
  
  All-Or-None principle

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• ALL impulses are alike regardless of the site
  from which they are fired off

• impulses travel very quickly in one direction
  from dendron to axon of the same neurone

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Nerve Impulses Transmitted across the Synapse

• neurones are not in direct contact with each
  other. A small gap called synapse exist between
  two neurones
• impulses need to jump across the synapse as to
  travel from one end of axon to dendron of another
  neurone

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• ending of axon secretes a
  chemical which diffuses
  into synapse and stimulates
  the next neurone to
  pass
  on the impulse
• the chemical is unstable
  and will be destroyed
  later

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• presence of synapse enables nerve impulses to
  travel only from axon of one neurone to dendron
  of another neurone

• it also allows higher level of nervous
  coordination as one neurone can be linked with a
  number of other neurones

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Central Nervous System

• includes brain and spinal cord in higher animal

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Protection of Central Nervous System

• brain is enclosed in cranium of
  skull while spinal cord is enclosed
  in vertebral column
• CNS is also enveloped in three layers
  of meninges and between the inner
  two layers is a cavity filled with cerebrospinal
  fluid

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Functions of Cerebrospinal Fluid

• act as a cushion for absorbing external shock
• nourish neurones inside as it enables diffusion
  of oxygen and food to the nerve cells
• it also filled up cavity called ventricle in
  brain and in the central canal of spinal cord
• it also helps in preventing collapse of CNS

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Parts of Brain
brain is divided into three main parts cerebrum,
cerebellum and medulla oblongata
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Brain--Cerebrum

• lies in the front part of brain and divided into
  two cerebral hemispheres connected by nerve
  fibres
• surface of cerebrum is highly folded to increase
  area for coordination
• centre of thinking, memory, reasoning,
  imagination, learning and voluntary actions

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• divided into three functional areas

- sensory areas receive impulses from
receptors - motor areas send out impulses to
effectors - association area correlates impulses
from different receptors and assists in
producing appropriate responses
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Brain--Cerebellum

• lies below the back part of cerebrum
• centre for muscular coordination and involved in
  control of body balance
• damage of cerebellum will lead to a loss of
  ability to maintain balance

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Brain--Medulla Oblongata

• lies at the floor of cerebellum
• reflex centre for controlling involuntary actions
  such as breathing, heartbeat, swallowing,
  coughing, sneezing and salivation
• damage of medulla oblongata may lead to death

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Internal Structure of Cerebrum and Cerebellum

• outer layer is made up of gray matter which
  consists of nerve cell bodies
• inner layers consist of nerve fibres and is white
  in colour and is called white matter

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Internal Structure of Medulla
Oblongata

• outer layer is made up of white matter while
  inner layer is made up of grey matter

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Internal Structure of Spinal Cord

• arises from medulla oblongata and runs through
  backbone of mammal
• internal distribution of nerve cell bodies is
  similar to medulla oblongata which the outer
  cortex contains white matter while the inner
  cortex is in H-shaped and contains grey matter

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• in the central region of grey matter is
  central canal and filled with cerebrospinal fluid

• reflex centre for controlling involuntary actions
  and it also transmits impulses to and from brain

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Grey White Matters
spinal cord medulla oblongata
cerebrum cerebellum
grey matter (cell body)
outer region
inner region
white matter (nerve fibre)
outer region
inner region
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Peripheral Nervous System

• consist of cranial nerves
  and spinal nerves
• these nerves leave CNS
  and run out to every part
  of the body

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Cranial Nerves and Spinal Nerves

• Cranial Nerve
• - twelve pairs of cranial nerves in mammal
• - most of cranial nerves arise from lateral
  sides of medulla oblongata
• Spinal Nerve
• - there are 31 pairs of spinal nerves in human

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- all are mixed nerve carrying both sensory
and motor neurones
- each spinal nerve has a dorsal root and
ventral root - dorsal root contains
ganglion which contains nerve cell bodies
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- cells in dorsal root ganglion are sensory
neurones and impulses travel through dorsal root
to spinal cord from spinal nerve
- ventral root carries motor nerve fibres and
their cell bodies are found in H-shaped grey
matter of spinal cord
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Investigation 15.3
Experiment to Initiate Knee Jerk Reflex
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What happens to the leg immediately after tapping?
Ans It kicks up at once.
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Does the same action occur again if the knee is
tapped the second time?
Ans Yes.
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Reflex Action

• simple reflex action is a quick, inborn and
  automatic response of an animal to a stimulus and
  cerebrum does not involve in the response
• protective in function and need not be learnt
• same stimulus initiates the same responses at
  different times
• examples like withdrawal from hot objects,
  blinking, coughing, sneezing and pupil size

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Reflex Arc

• neural pathway between receptor and effector
  involved in a reflex action
• example is knee jerk reflex

Knee Jerk Reflex

• At the Receptor

• receptor receives stimulus. In this case, tapping
  stimulates tendon of knee cap

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• At the Sensory Neurone

• from ending of dendrons of sensory neurones,
  nerve impulses fired off

• Across the Synapse to the Motor Neurone

• through dorsal root of spinal nerve, impulses are
  carried to spinal cord

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• impulses jump across synapses to motor neurones
  in grey matter but in other reflex action,
  association neurones may involve

• To the effector

• impulses are further transmitted through ventral
  root to effector to produce responses

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• in knee jerk, effector is muscles in upper leg
  which it will contract when impulses are received
  so the leg jerks up and it is an example of
  spinal reflex action as only spinal cord is
  involved

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Reflex arc sensory, association, motor neurones
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• spinal reflexes can occur in deep sleep and do
  not depend on awareness but impulses can still
  pass form sensory neurones up the spinal cord to
  brain

• other reflex actions like blinking, coughing and
  sneezing are cranial reflex action and take place
  in medulla oblongata

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Voluntary Actions

• conscious response to a certain stimulus
• involves cerebrum of brain and mammals are aware
  of all the steps of the response
• may differ from time to time as mammals can gain
  experiences and store them in cerebrum so they
  can choose how to response to the same stimulus

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Neural Pathway of Voluntary
Action
receptor receives stimulus
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Comparison between Reflex Voluntary
Actions
pathway taken by nerve impulses
not involving cerebrum
automatic, not under control of the will
voluntary, under control of the will
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speed of response
different, depend on learning from previous
experiences
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Investigation 15.4
To measure your Reaction Time
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Does your reaction time improve with practice ?
Ans Yes.
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Was your reaction time quicker with or without
the ruler touching your hand?
Ans The reaction time was quicker without ruler
touching the hand.
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Explain.
Ans It is because the sensory pathway from eye
to brain is much shorter than that from
finger-tips to the brain.
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Endocrine Glands

• ductless glands in body
• secrete chemical messengers called hormones which
  diffuse directly into the blood
• hormones are
  carried to target
  
  organs by
  bloodstream

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Specificity and Effect of Endocrine Glands

• usually, target organ
  respond to a particular
  hormones only so
  hormones are
  specific
• hormonal coordination is slow and takes a longer
  time for response to appear but its effect can
  last for a long period of time

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Comparison between Nervous Hormonal
Coordination
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Locations of Endocrine Glands

• pituitary gland locate below cerebrum and it
  controls many
  other endocrine
  glands activities in body
• thyroid glands in neck
• islets of Langerhans in pancreas
• adrenal glands above kidney
• ovaries in females abdominal cavity
• testes in males scrotal sacs

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Sites of Six Main Endocrine Glands in Human
Body
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Negative Feedback Mechanism

• secretion of hormones follows negative feedback
  mechanism which means that any decrease in the
  level of a factor switches on a series of
  corrective actions to restore the factor to
  normal level and vice versa
• an example is insulin which is secreted by islets
  of Langerhans in pancreas to liver through blood
  vessels to control blood glucose level

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Effect of Sex Hormones

• puberty occurs between the ages of 11-14 years
  when a child become sexually mature
• ovaries in females and testes in males become
  functional and secrete sex hormones for
  development of secondary sexual characteristics
  which are physical changes for sexual awareness

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Secondary Sexual Characteristics
Boys
Girls
growth of pubic hair and hair on face (facial
hair) and in armpits (axillary hair)
growth of pubic hair
growth and development of breasts
breaking of voice and enlargement of larynx
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Boys
Girls
widening of hips(pelvic girdle)
muscle development
more fat deposits under skin
widening of shoulders
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