Biological Bases of Behaviour. Lecture 8: Central Nervous System.

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Biological Bases of Behaviour. Lecture 8
Central Nervous System.
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Learning Outcomes.

• At the end of this lecture you should be able to
  
• 1. Understand key anatomical terms.
• 2. Describe the gross organisation of the CNS.
• 3. Identify key structures of the CNS.
• 4. Briefly describe the functions of key CNS
  structures.

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Divisions of the Nervous System.
NERVOUS SYSTEM
Peripheral Nervous System
Central Nervous System
Autonomic Nervous System
Somatic Nervous System
Spinal cord
Brain
Forebrain
Hindbrain
Midbrain
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Terms of Reference.

• When describing the CNS we use directional terms
  described relative to an imaginary line drawn
  through the spinal cord and the front of the
  brain (neuraxis).
• Anterior (or rostral) front part of a structure.
• Posterior (or caudal) back part of a structure.
• Dorsal Pointing out of the back.
• Ventral Pointing towards the ground.
• Lateral towards the sides.
• Medial towards the middle.
• Ipsilateral on the same side of the body or
  brain.
• Contralateral on the opposite side of the brain
  or body.

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Anatomical directions
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Anatomical Planes.

• Horizontal a slice parallel to the ground.
• Sagittal a slice perpendicular to the ground,
  parallel to the neuraxis.
• Transverse (coronal) a slice vertical from front
  to back

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Blood Supply.

• The brain receives 20 of the blood flow from the
  heart.
• The brain cannot store glucose nor can it extract
  energy without oxygen, so continuous blood flow
  is essential.
• A 1-second interruption in blood flow will use up
  all of the brains resources, a 6-second gap
  produces unconsciousness. Permanent brain damage
  occurs after a few minutes.
• Two major sets of arteries serve the brain
• 1. The vertebral arteries (serving the caudal
  portion) enter at the base of the skull.
• 2 The internal carotid arteries (serving the
  rostral portion) ascend the left and right sides
  of the neck.
• These join to form the basilar artery.
• There is overlap between the arterial systems so
  that if a vessel becomes blocked (a stroke),
  potential damage is minimised.

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Blood Supply Continued..
Basilar artery
Middle cerebral artery
Internal carotid artery
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Blood-Brain Barrier.

• Nutrients such as oxygen and glucose are
  delivered to the brain, and waste products such
  as carbon dioxide are extracted.
• Molecules over a certain size cannot enter the
  brain, this blood-brain barrier preserves the
  brain from harmful substances in the blood.
• The barrier is relaxed in the area postrema where
  the chemoreceptor trigger zone (CTZ) responds to
  toxic chemicals in the blood to initiate the
  vomit reflex.

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Meninges.

• The brain and spinal cord are protected by tough
  protective tissue called the meninges,
  consisting of three layers
• i) Dura mater The thick and tough but flexible
  outer layer.
• ii) Arachnoid membrane The soft and spongy
  weblike middle.
• iii) Pia mater The lower layer closely attached
  to the skull and spine.
• Between the pia mater and the arachnoid membrane
  lies the subarachnoid space through which
  cerebrospinal fluid (CSF) passes.
• Inflammation of the meninges in the brain or
  spine caused by viral or other means is called
  meningitis.

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The Ventricular System.

• The brain is encased in a protective bath of CSF,
  manufactured by the choroid plexus.
• The brain contains a series of 4 hollow
  interconnected chambers called ventricles which
  are filled with CSF.
• The largest are the 2 lateral ventricles.
• These are connected to the third ventricle
  located in the middle of the brain.
• This is connected to the fourth ventricle via the
  cerebral aqueduct.
• If the flow of the CSF is interrupted (e.g. by a
  tumour) then this increases pressure in the
  ventricles and they will expand producing
  hydrocephalus.

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The Ventricular System.
Lateral ventricles
Third ventricle
Fourth ventricle
Cerebral aqueduct
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The Central Nervous System.

• The CNS is split into 3 sections.

Forebrain Midbrain Hindbrain
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1. The Forebrain.

• This region is split into the 2 major components.
• a) The Telencephalon.
• The hemispheres are separated by the longitudinal
  fissure.
• They are covered by cortex.
• A deep cleft is referred to as a fissure, and a
  shallow one is called a sulcus, each ridge is
  called a gyrus. Two thirds of the surface of the
  cortex is hidden in these grooves.
• Because cells predominate in the cortex, the
  cortex has a grey appearance and is referred to
  as 'grey matter'.
• Beneath the surface of the cortex run axons
  covered by the myelin sheath which is referred
  to as 'white matter'.

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Telencephalon (continued).

• The most prominent features of the cortex are
• Lateral fissures.
• Central sulcus.
• Longitudinal fissure.
• These clear divisions are used to help define the
  different lobes of the brain.
• The surface of the hemispheres is divided into
  four lobes frontal, temporal, parietal and
  occipital.
• The central sulcus divides the frontal lobe from
  the parietal lobe, and the lateral fissure
  divides the temporal lobe from the frontal and
  parietal lobes.
• The hemispheres are connected by a bundle of
  verve fibres called the corpus callosum.

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The Lobes of the Brain.
Longitudinal fissure
Central sulcus
Lateral fissure
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Sagittal View of the Brain.
Central sulcus
Corpus callosum
Cerebellum
Pons
Medulla
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Subcortical Divisions of the Telencephalon.

• i) The Limbic system.
• The hippocampus crucial for learning and
  memory.
• The amygdala is important for emotion and
  motivation.
• Other parts of the limbic system include the
  mamillary bodies and cingulate gyrus.

Cingulate gyrus
Thalamus
Mamillary bodies
Amygdala
Hippocampus
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ii) Basal Ganglia.

• A collection of nuclei located in the forebrain
  under the anterior portion of the lateral
  ventricles. They are involved in movement.

Caudate nucleus
Thalamus
Putamen
Globus pallidus
Amygdala
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b) The Diencephalon.

• This region surrounds the third ventricle and
  consists of the following structures
• i) Thalamus.
• Separate but interconnected nuclei receive
  information from the sensory systems, and relay
  this information to sensory processing areas in
  the cortex.
• It is a relay system and can thus influence
  almost the whole of the brain.
• It may also play a role in learning and memory.

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Thalamus.
Somatosensory cortex
Motor cortex
Frontal cortex
Occipital cortex
Thalamic nuclei
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Diencephalon continued..

• ii) The Hypothalamus.
• Comprises 22 nuclei and the pituitary gland.
• These control the autonomic nervous system and
  the endocrine system.
• Key aspects of behaviour are co-ordinated from
  here including feeding, sex, sleep, temperature
  regulation, and emotional behaviour.

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Hypothalamus and Surrounding Structures.
Cingulate gyrus
Thalamus
Fornix
Hypothalamus
Mamillary bodies
Amygdala
Hippocampus
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2. The Midbrain.

• This consists of two major regions
• a). Tectum This contains two main structures
• Superior colliculus part of the auditory system
• Inferior colliculus part of the visual system.
• b). Tegmentum This includes the rostral portion
  of the reticular formation, 90 interconnected
  nuclei involved in sensory processing, sleep,
  arousal, attention, muscle tone, movement and
  reflexes.
• Two key structure of the tegmentum are the red
  nucleus and the substantia nigra which are
  important components of the motor system.

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Tectum.
Thalamus
Superior colliculus
Inferior colliculus
Pons
Medulla
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3. The Hindbrain.

• This consists of two main divisions
• a) The Metencephalon Consists of two main
  structures
• i) The cerebellum Receives information from
  sensory systems, the muscles, and the vestibular
  system. It co-ordinates this information to
  produce smooth movements.
• Damage to the cerebellum (which occurs in such as
  cerebral palsy) impairs walking, balance,
  posture, and skilled-motor activity.
• ii) The pons A large bulge on the brain stem
  involved in sleep and arousal.

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Divisions of the Hindbrain.

• b) The Myelencephalon.
• This contains one major structure called the
  medulla oblongata which is the most caudal part
  of the brain stem and it borders the spinal cord.
  
• It contains part of the reticular formation and
  contains nuclei that control vital functions such
  as control of breathing and skeletal muscle tone.
  

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4. Spinal cord.

• This is located within the vertebrae of the
  spinal column and it communicates with the sense
  organs and muscles below the neck.
• It consists of two fibre pathways
• Dorsal roots process sensory information
• Ventral roots process motor information.

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Summary of CNS organisation.

• A convenient way to visualise how the brain is
  organised is to imagine it as three structures
  each increasing in the complexity of the
  functions they subserve.
• At the core is the medulla-brainstem which
  controls basic aspects of behaviour (breathing,
  swallowing, digestion, urination etc). Alongside
  is the cerebellum which controls movement and
  posture.
• Wrapped around this core is the limbic system, a
  primitive region responsible behaviours essential
  to basic survival - pain, pleasure, fear, eating
  and sex.
• The outer layer of the brain is the cerebral
  cortex - a thin sheet of neurons dealing with
  higher-order functions such as perception,
  planning, problem solving thinking, consciousness
  etc.