The Brain

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Responding to the environment - The brain

The Brain:

Cerebrum: Divided into 2 hemispheres which are connected via the corpus callosum.

Controls the higher brain functions including:

  • Conscious thought and emotion.
  • Features associated with intelligence e.g. reasoning and judgement.

Cerebral cortex is sub-divided into sensory, motor and association areas

Sensory areas:

  • Receive impulses indirectly from the receptors. 

Association areas:

  • Compare input with previous experiences in order to interpret what the input means and judge an appropriate response. 
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Motor areas:

  • Send impulses to effectors (muscles and glands). 


  • Involved with coordinated motor response.
  • Neurones carry impulses to the motor areas so motor output to effectors can be adjusted appropriately in relation to the requirements. 
  • Plays a key role in coordinating balance, fine movement and posture. 

Processes information from:

  • The retina,
  • Balance organs in the inner ear,
  • Specialised fibres in muscles (spindle fibres) which give information about muscle tension and the joints. 

The hypothalamus:

  • Controls the autonomic nervous system and endocrine glands.
  • Controls most of the body's homeostatic mechanisms.
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The brain

  • Sensory input from temperature receptors and osmoreceptors is received by hypothalamus and leads to initiation of automatic responses that regulate body temperature and blood water potential. 

Medulla Oblongata:

  • Controls action of smooth muscle in gut wall and controls breathing movements and heart rate.
  • Controls non-skeletal muscles (i.e. cardiac and involuntary), which means it is in control of the autonomic nervous system.
  • Regulatory centres for a number of vital processes are found here, including the cardiac centre which regulates heart rate and the respiratory centre which controls breathing and regulates the rate and depth of breathing. 

Organisation of the Nervous System:

Nervous system --> Peripheral nervous system --> Autonomic OR Somatic nervous system -->

Sympathetic OR Parasympathetic nervous system. 

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Nervous systems

Central Nervous System:

  • Made up of the brain and spinal cord.

Peripheal Nervous System:

  • Made up of neurones that carry impulses into and out of the CNS. 

Vagus nerves:

  • Serve the abdominal organs and regulate heart rate. 

Cranial nerves:

  • These form part of the nervous system.

Spinal nerves:

  • 31 pairs of spinal nerves. Either SOMATIC and mainly supply the skin and voluntary muscles or they are VISCERAL and supply the gut, glands and involuntary muscles.
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Somatic VS Autonomic Nervous System

SOMATIC Nervous System: 

  • Motor neurones of the somatic nervous system transmit impulses away from the CNS to the skeletal muscles.
  • Sensory neurones of the somatic nervous system transmit impulses to the CNS from generalised sensory receptors such as touch and taste. 

AUTONOMIC Nervous System:

  • Consists mainly of efferent visceral motor neurones which are bundled into motor fibres.
  • Motor neurones of the autonomic nervous system transmit impulses from the CNS to smooth muscle, cardiac muscle and glands. 
  • The few sensory neurones of the autonomic nervous system transmit impulses from visceral (internal organs) receptors into the CNS.
  • Motor portion is divided into sympathetic and parasympathetic motor neurones.
  • Motor system of the autonomic pathway consists of 2 neurones - a PREGANGLIONIC neuron (myelinated) with it's cell body within the CNS and a POSTGANGLIONIC neurone (non-myelinated) with it's cell body in a ganglion outside of the CNS. 
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