Transcript pp08-cns - Welcome to the EvoS Consortium!

Biological Bases of Behaviour.
Lecture 8: Central Nervous System.
Learning Outcomes.
• At the end of this lecture you should be able to:
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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.
Divisions of the Nervous System.
NERVOUS SYSTEM
Peripheral Nervous System
Autonomic
Nervous
System
Somatic
Nervous
System
Forebrain
Central Nervous System
Brain
Midbrain
Spinal
cord
Hindbrain
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).
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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.
Anatomical
directions
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
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.
Blood Supply Continued..
Basilar artery
Middle cerebral
artery
Internal
carotid artery
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.
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.
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.
The Ventricular System.
Lateral ventricles
Fourth ventricle
Third ventricle
Cerebral aqueduct
The Central Nervous System.
• The CNS is split into 3 sections.
Forebrain
Midbrain
Hindbrain
1. The Forebrain.
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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'.
Telencephalon (continued).
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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.
The Lobes of the Brain.
Longitudinal fissure
Central sulcus
Lateral fissure
Sagittal View of the Brain.
Central sulcus
Corpus callosum
Cerebellum
Pons
Medulla
Subcortical Divisions of the
Telencephalon.
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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
Amygdala
Hippocampus
Mamillary
bodies
ii) Basal Ganglia.
• A collection of nuclei located in the forebrain under the anterior
portion of the lateral ventricles. They are involved in movement.
Thalamus
Globus
pallidus
Caudate
nucleus
Putamen
Amygdala
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.
Thalamus.
Motor cortex
Frontal cortex
Somatosensory
cortex
Occipital
cortex
Thalamic nuclei
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.
Hypothalamus and
Surrounding Structures.
Cingulate gyrus
Thalamus
Fornix
Hypothalamus
Mamillary bodies
Amygdala
Hippocampus
2. The Midbrain.
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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.
Tectum.
Thalamus
Superior colliculus
Inferior colliculus
Pons
Medulla
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 coordinates 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.
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.
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.
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.