Animal Physiology

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Unit 3

Animal Physiology
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Structure and Function of the Brain

• The brain is a complex organ consisting of
  several different regions.
• The CEREBRUM is the largest part of the brain and
  is divided into 2 connecting hemispheres.
• The CEREBELLUM
• The MEDULLA
• The HYPOTHALAMUS

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Structure and Function of the Brain
cerebrum
cerebellum
medulla
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Structure Function
Cerebrum Site of conscious thought and higher mental faculties such as reasoning, imagination, creativity, conscience and memory
Cerebellum Centre of balance and coordination of movement/muscular co-ordination
Medulla Site of vital centres such as breathing and heart rate.
Hypothalamus Contains centres that regulate water balance and temperature
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Structure and Function of the Brain
front
rear
Key motor area sensory area
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• The cerebrum has discrete areas which perform
• their own functions distinct from the others
• Sensory area
• Receives information as sensory impulses
• from the bodys receptors e.g. sense organs.
• It then passes on to other parts of the brain
• to be analysed and interpreted.
• Motor area
• Consists of motor neurones which send out
• impulses to bring about appropriate
• voluntary movements of skeletal muscles.

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Structure and Function of the Nervous System

• The human nervous system is composed of 3 parts
  - Brain, nerves and spinal cord.
• The CENTRAL NERVOUS SYSTEM (CNS) is made up of
  just the brain and spinal cord.
• Nerves carry electrical impulses from the senses
  to the CNS and electrical impulses from the CNS
  to the muscles.
• Nerves are made of bundles of fibres. Each nerve
  fibre is a part of a nerve cell or neurone.
• - Stick the diagram into your jotter.

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• Types of Nerves
• 1) Sensory neurone
• Carries electrical impulses to the CNS from the
  sense organs
• 2) Motor neurone
• Carries electrical impulses from the CNS to the
  muscles and glands
• 3) Relay neurone
• Found in the spinal cord to connect sensory and
  motor neurones.
• Stick in the diagram of the nerves

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Flow of information
Sensory nerves

• The sense organs (receptors) detect a stimulus
  and send information to the CNS along sensory
  nerves. The brain sorts this information and
  sends instructions along motor nerves to the
  muscles (effector) to respond to that information

Motor nerves
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Reflex Arc

• A reflex arc is the arrangement of the 3
  different types of neurone.
• .starting with receptor sensory neurone relay
  neurone, motor neurone and effector.
• Stick in the diagram of a reflex arc

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Reflex Action

• Transmission of a nerve impulse through a reflex
  arc results in a reflex action.
• A reflex action is a rapid, involuntary,
  automatic response to a stimulus
• A reflex action protects the body from damage.
• They do not need conscious thought by the brain.

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Examples of reflex actions

• Limb withdrawal (stimulated by touching something
  sharp or hot), blinking, knee jerk, iris reflex
  and sneezing.

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Arm extended at start
Arm bends at end of reflex action
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• 1) Heat is detected by pain receptors in the skin
• 2) An impulse is immediately sent up the fibre of
  the sensory neurone.
• 3) In the grey matter of the spinal cord, the
  impulse crosses its 1st synapse (gap)
• 4) ..and passes through the relay neurone
• 5) The impulse crosses a 2nd synapse and passes
• into the motor neurone.
• 6) It then moves into the muscle (effector),
• chemicals are released and the muscle
• contracts moving the arm out of harms way.

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Regulation of Body Temperature

• The hypothalamus contains the bodys
  temperature-monitoring centre.
• It receives nerve impulses from heat and cold
  receptors in the skin. The skin also acts as an
  effector.
• It also has its own central thermoreceptors which
  monitors the temperature of the blood.
• The central thermoreceptors
• detect changes in the bodys core
• temperature.
• The hypothalamus responds to this info by sending
  motor nerve impulses to effectors.

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• The body core is the brain, lungs, gut and other
  vital organs
• this is normally at 37C.
• The body shell is the skin, limbs, fat and
  skeletal muscle this
• is normally at around 33C.

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Overheating

• The skin helps to correct overheating of the body
  by doing the following-
• Increased rate of sweating
• By sweating a lot this lowers the body
• temperature
• Vasodilatation
• The arterioles leading to the skin become
  dilated which allows a large volume of blood to
  flow through capillaries near the skin surface.
  Heat can be lost as radiation.

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Vasodilation
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Overcooling

• The skin helps to correct overcooling of the body
  by doing the following-
• Decreased rate of sweating
• The rate you sweat reduces and stops
• the temperature from lowering any further.
• Vasoconstriction
• The arterioles leading to the skin become
  constricted which allows only small volume of
  blood to flow through capillaries near the skin
  surface. Little heat is lost by radiation.
• Contraction of erector muscles
• This is when the hairs on the skin are raised
  by the erector muscles contracting. It traps a
  wider layer of air between the body and the
  environment. Provides insulation.

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Vasoconstriction
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• Shivering (nothing to do with the skin)
• When the hypothalamus detects a drop in body
  temperature, nerve impulses to the skeletal
  muscles cause them to undergo brief repeated
  contractions shivering.
• This generates heat energy and helps to return
  the body temperature to its normal level.

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Negative Feedback Control

• Regulation of body temperature is a further
  example of negative feedback control. (remember
  water balance is too)
• The mechanisms of temperature regulation of the
  skin are involuntary and are controlled at a
  subconscious level by the hypothalamus.

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Motor nerve impulses to skin
VASODILATION, INCREASED SWEATING
THERMORECEPTORS IN HYPOTHALAMUS
Increase in body temperature
Decrease in body temperature
No change in body temperature temperature remains
at set point
NORMAL BODY TEMPERATURE (37C)
NORMAL BODY TEMPERATURE (37C)
Increase in body temperature
Decrease in body temperature
THERMORECEPTORS IN HYPOTHALAMUS
VASOCONSTRICTION, DECREASED SWEATING
Motor nerve impulses to skin
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No change in body temperature temperature remains
at set point







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No change in body temperature temperature remains
at set point