Brain

• Brain


  • Primary integration and control centre of the body
  • Weighs around 1.36 kg
  • Requires a large and constant energy supply (consumes 20% of body's oxygen, and 15% of its blood glucose)
  • Hollow and expanded anterior end of the spinal cord
  • Receives information from sense organs in the head via specific sensory nerves and from other body organs via the ascending fibres of the spinal cord
  • Communicates with other organs via the cranial nerves, the descending fibres of the spinal cord, and through regulation of endocrine secretions via the pituitary gland
  • Utilises many neurotransmitters including dopamine, serotonin, histamine, GABA and endorphins

  
• Sections of the brain

  • Forebrain
  • Midbrain
  • Hindbrain
• Evolutionary development of the brain

  • Increase in size relative to body size, being largest in mammals
  • Cerebrum size (part of forebrain) increased leading to more complex behaviour
  • Specialisation of forebrain, midbrain and hindbrain areas
• Ventricles


  Four hollow cavities located in the brain that produce and store CSF
• Brain stem


  • One of the three largest parts of the brain along with the cerebellum, and the cerebrum
  • Consists of a stalk and swellings at the anterior end of the spinal cord and includes the mesencephalon, pons, and medulla oblongata

  
• Cerebrum


  • The vastly expanded anterior end of the brain
  • Governs intelligence, reasoning, personality, learning, emotions and will
  • Consists of two cerebral hemispheres connected together by the corpus callosum
  • Each hemisphere controls the opposite half of the body
  • Are not perfectly symmetrical, hence some abilities are predominantly controlled by only one hemisphere
• Cerebral cortex


  • The outer 2-4 mm of the cerebrum
  • Consists of the grey matter of the brain (located on the outside) and hence contains the cell bodies of millions of neurons
  • Highly folded into characteristic convolutions which increase the surface area available to accommodate more cell bodies
  • Beneath it is the white matter which contains the myelinated axons arising from the cell bodies found in the cortex
• Lobes of the brain cortex

  • Frontal lobe
  • Temporal lobe
  • Parietal lobe
  • Occipital lobe
• Frontal lobe


  • Located at the very front of the brain
  • Most of this lobe is an association area which deals with thinking and planning
  • Neurons in the part of frontal lobe just in front the central sulcus control the muscles in specific regions of the body (primary motor cortex)
  • At the base of the frontal lobe resides the olfactory area – a sensory area which receives smell sensory impulses
• Parietal lobe

  • The primary somatosensory cortex is located just behind the central sulcus
  • Receives impulses from receptors in the skin, muscles and joints
  • Receives information through the thalamus
  • Responsible for the sensations of temperature, touch, pressure and pain
• Occipital lobe


  • Located behind the parietal lobe and just above the cerebellum
  • Receives and processes visual information (makes sense of images and coverts images into words)
• Temporal lobe


  • Beneath the frontal and parietal lobes
  • Receives and processes auditory information
  • Involved in the recognition, identification and naming of objects (including faces)
  • Important for understanding the written word (reading)
• Types of areas within each lobe

  • Sensory areas
  • Association areas
  • Motor areas
  • Silent areas
• Sensory areas

  Receives sensory information from the relevant sensory organs. The processing of this information then takes place in the association areas.
• Association areas


  • Integrate incoming information from several receptors and associating it with stored information in the memory area. This leads to interpretation of information and the passing on of instructions to the motor areas.
  • Involved in memory, learning and reasoning and thus intelligence.
  • Generally, found close to the relevant sensory areas.
• Motor areas


  Initiate and control the movement of voluntary muscles.
• Silent areas


  Associated with personality and moral judgement.
• Thalamus


  • The primary site of relay and sensory integration in the brain.
  • Receives visual, auditory and somatosensory information which is processed by the association neurons.
  • This information is transmitted to the appropriate sensory area in the cerebrum.
• Hypothalamus


  • Located below the thalamus.
  • The main coordination and control centre for the autonomic nervous system.
  • Receives information from all the receptors of the autonomic nervous system as well as those of taste and smell receptors.
  • Controls complex instinctive behaviour such as sexual response, mating behaviours and fight or flight responses.
  • It is connected to and controls the pituitary gland via hormonal secretions.
  • Contains the centres which control mood and emotions, thirst, hunger, satiety and body temperature. It monitors metabolite ionic and hormone levels (not glucose) in the blood. Thus the hypothalamus helps to maintain homeostasis.
• Midbrain


  • The smallest part of the brain forms part of the brainstem.
  • Receives and integrates information from the optic and auditory systems.
  • It controls the reflex movements of the eye muscles as well as many other visual and auditory reflexes.
  • The pineal gland projects dorsally from the mid-brain and secretes the hormone melatonin.
  • The floor of the midbrain contains nerve fibre tracts connecting the spinal cord to the cerebrum.

  
• Cerebellum


  • Found at the back of the brain under the cerebral hemispheres.
  • Consists of two complexly folded hemispheres.
  • Co-ordinates movement, enabling accurate and smooth movement of muscles.
  • Enables activities such as walking, swimming, typing, riding a bike etc., to become automatic and executed without conscious thought.
  • Maintains balance.
  • Receives information from the balance sensors in the ears, the motor centres of the cerebral cortex and the receptors of joints, muscles and tendons.
  • Enlarged in birds and controls the flight muscles.
• Pons


  • Located immediately beneath the midbrain.
  • Manages the transition between sleep and wakefulness.
  • Controls the rate and depth of breathing.
  • Controls inhalation and exhalation.
  • Contains nuclei which relay impulses from the forebrain to the cerebellum.
• Medulla oblongata


  • The last part of the brain and the part closest to the spinal cord.
  • Controls vital processes: breathing, heart rate and the force of the heartbeat, blood pressure, vasoconstriction and vasodilation, sneezing, coughing, swallowing, salivation and vomiting.
  • Nerves leaving the medulla oblongata form part of the autonomic nervous system (actions are therefore under involuntary control).
  • Ascending and descending nerve fibers cross over at this point. i.e. right side of brain controls much of the movement by the left side and vice versa.
• Reticular system

  1. Sensory information comes into brain

  2. Passes through the reticular system (a diffused collection of neurons located in brain stem)

  3. System distributes to relevant parts of brain