Difference between revisions of "Midbrain - Anatomy & Physiology"

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==Introduction==
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The midbrain or mesencephalon represents the connection between the brain stem and the higher centres of the brain and is involved in most body systems including sleep/conciousness, vision, hearing and temperature regulation. The midbrain is located between the diencephalon and the hind brain, or brain stem. More specifically it can be found ventral to the cerebral cortex and between the cerebral pedicles of the diecncephalon and the pons. It is a relatively short portion of the upper brain stem and connects higher brain centres with the lower centres and the spinal cord. In most species the midbrain is found most centrally to the cranial cavity.
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==Midbrain Development==
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The midbrain arises from the [[CNS_Development_-_Anatomy_%26_Physiology#Development_of_the_Brain|mesencephalon]]. One of the key roles of this area of the brain during development is the maintainence of a patent cerebral aqueduct to facilitate the appropriate development of higher brains structures including the cerebral hemispheres.
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==Midbrain Structure & Function==
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The midbrain has a stratified structure comprising various layers including the tectum, tegmentum and cerebral peduncle. These structures are found in a dorsoventral sequence. The tectum lies dorsally to the cerebral aqueduct and it has four major rounded surface swellings; colliculi (see below).
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===Oculomotor Nerves===
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The oculomotor nerves [[Cranial_Nerves_-_Anatomy_%26_Physiology|(Cranial Nerve III)]] have their superficial nuclei within the midbrain.
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===Cerebral Aqueduct===
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Within the lumen of the midbrain lies the cerebral aqueduct which acts as a simple passage between the spinal cord and the third and fourth ventricles.
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===Colliculi===
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The tectum (roof) has four [[#Colliculi|colliculi]], two rostral and two caudal. The caudal colliculi are widely spaced and are joined by a substancial commissure. The caudal colliculi act as integration centres for auditory pathways. The caudal colliculi also have a further connection to the thalamus via the 'ipselateral medial geniculate body'. This body is effectively a swelling of the thalamus.
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Also known as: '''''Mesencephalon'''''
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Cranial nerves III and IV have their nuculi within the midbrain.
  
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==Introduction==
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==Structure and Function==
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[[File:Human brain midsagittal cut description.JPG|thumb|right|300px|Human brain midsagittal cut description]]
 
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The midbrain or mesencephalon represents the connection between the [[Hindbrain - Anatomy & Physiology#Hind Brain Structures & Functions|brain stem]] and the higher centres of the brain and is involved in most body systems including '''sleep/consciousness, vision, hearing and temperature regulation'''.
 
  
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The midbrain is located between the diencephalon and the hind brain, or brain stem. More specifically, it can be found ventral to the [[Cerebrum|cerebral cortex]] and between the cerebral pedicles of the diencephalon and the pons. It is a relatively short portion of the upper brain stem and connects higher brain centres with the lower centres and the spinal cord. In most species the midbrain is found most centrally within the cranial cavity.
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{| style="width:75%; height:200px" border="1"
  
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==Midbrain Development==
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!
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The midbrain arises from the mesencephalon. One of the key roles of this area of the [[CNS Development - Anatomy & Physiology#Development of the Brain|brain during development]] is the maintainance of a patent cerebral aqueduct to facilitate the appropriate development of higher brains structures including the cerebral hemispheres.
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!'''Structures Present'''
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!'''Function'''
  
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==Midbrain Structure & Function==
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|-
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The midbrain has a stratified structure comprising various layers including the '''tectum, tegmentum '''and '''cerebral peduncle'''. These structures are found in a dorsoventral sequence. The tectum lies dorsally to the cerebral aqueduct and it has four major rounded surface swellings; colliculi (see below). The tegmentum is the core of the midbrain and a large proportion of it is made up by the [[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation (Spinoreticular Tract)|reticular formation]].
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| '''Midbrain (Mesencephalon)'''
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| '''[[#Colliculi|Colliculi]]'''
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'''[[#Occulomotor Nuculi|Occulomotor Nuculi]]'''
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| '''[[#Colliculi|Colliculi]]''' - Processing visual and auditory information.
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'''[[#Occulomotor Nuculi|Occulomotor Nuculi]]''' - Eyeball mm., more cranial nerves.
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|
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|}
  
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===Cranial Nerve Nuclei===
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===Colliculi===
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The major cranial nerve nuclei within the midbrain are the mesencephalic nuclei of the [[Cranial Nerves - Anatomy & Physiology|trigeminal nerves (V)]], the trochlear nuclei (IV), the principle and parasympathetic oculomotor nuclei [[Cranial Nerves - Anatomy & Physiology|(Cranial Nerve III)]], the 'red nuclei' (so named due to its pronounced vascularity) and the periaqueductal gray nuclei. The periaqueductal gray nucleus is a core of gray nervous tissue located adjacent to the cerebral aqueduct. The oculomotor nerve emerges from the mid brain rostral to the pons.
 
  
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===Cerebral Aqueduct===
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===Oculomotor Nuclei===
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Within the lumen of the midbrain lies the cerebral aqueduct which acts as a simple passage between the spinal cord and the third and fourth ventricles.
 
  
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===Colliculi===
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*See [[CNS Vasculature - Anatomy & Physiology|blood suppply to the brain]] and the [[CNS Vasculature - Anatomy & Physiology#Species Differences|relevent species differences.]]
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The tectum (roof) has four colliculi, two rostral and two caudal.  
 
  
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====Caudal Colliculi====
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*The cerebral (mesencephalic) aqueduct is a ventricular tube running through the midbrain which connects the third and fourth ventricles. It contains [[Cerebral Spinal Fluid - Anatomy & Physiology|cerebral spinal fluid]] which offer it immunological protection.
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The caudal colliculi are widely spaced and are joined by a substantial commissure. The caudal colliculi act as '''integration centres for auditory pathways'''. The caudal colliculi also have a further connection to the thalamus via the 'ipsilateral medial geniculate body'. This body is effectively a swelling of the [[thalamus]].  
 
  
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====Rostral Colliculi====
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See [[Immunology|immunology]].
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The rostral colliculi are placed closer together in comparison to the caudal. The rostral colliculi are also joined to the thalamus, but by the 'lateral geniculate bodies' rather than the medial. The rostral colliculi help to '''integrate the visual pathways''' and also are involved in '''somatic reflexes''' that are caused by visual cues. The rostral colliculi have also been suggested to be involved in spatial integration.
 
  
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===Substantia Nigra===
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==Species Differences==
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The substantia nigra is a prominent area of the mid brain and is identifiable on cross sections by its darker pigmentation. This pigmentation is due to the gradual accumulation of pigmentation of neurons and is associated with basal nuclei within the tissue. The ''substantia nigra'' nuclei are involved in the '''control of voluntary movement'''.
 
  
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===Crura Cerebri===
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* Other than size the brain of most species is fairly consistant.
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These are visible on the ventral surface of the mid brain and consist of fibre tracts that are in passage between the telencephalon and the brain stem. The oculomotor nerves (see above) also emerge in this region of the mid brain, directly rostral to the pons.
 
  
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==Links==
  
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{{review}}
 
  
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{{unfinished}}
 
[[Category:Nervous System - Anatomy & Physiology]]
 
[[Category:Nervous System - Anatomy & Physiology]]
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[[Category:A&P Done]]
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[[Category:To Do - A&P]]

Revision as of 16:17, 6 August 2011

Introduction

The midbrain or mesencephalon represents the connection between the brain stem and the higher centres of the brain and is involved in most body systems including sleep/conciousness, vision, hearing and temperature regulation. The midbrain is located between the diencephalon and the hind brain, or brain stem. More specifically it can be found ventral to the cerebral cortex and between the cerebral pedicles of the diecncephalon and the pons. It is a relatively short portion of the upper brain stem and connects higher brain centres with the lower centres and the spinal cord. In most species the midbrain is found most centrally to the cranial cavity.

Midbrain Development

The midbrain arises from the mesencephalon. One of the key roles of this area of the brain during development is the maintainence of a patent cerebral aqueduct to facilitate the appropriate development of higher brains structures including the cerebral hemispheres.

Midbrain Structure & Function

The midbrain has a stratified structure comprising various layers including the tectum, tegmentum and cerebral peduncle. These structures are found in a dorsoventral sequence. The tectum lies dorsally to the cerebral aqueduct and it has four major rounded surface swellings; colliculi (see below).

Oculomotor Nerves

The oculomotor nerves (Cranial Nerve III) have their superficial nuclei within the midbrain.

Cerebral Aqueduct

Within the lumen of the midbrain lies the cerebral aqueduct which acts as a simple passage between the spinal cord and the third and fourth ventricles.

Colliculi

The tectum (roof) has four colliculi, two rostral and two caudal. The caudal colliculi are widely spaced and are joined by a substancial commissure. The caudal colliculi act as integration centres for auditory pathways. The caudal colliculi also have a further connection to the thalamus via the 'ipselateral medial geniculate body'. This body is effectively a swelling of the thalamus.


Cranial nerves III and IV have their nuculi within the midbrain.

Structure and Function

Structures Present Function
Midbrain (Mesencephalon) Colliculi

Occulomotor Nuculi

Colliculi - Processing visual and auditory information.

Occulomotor Nuculi - Eyeball mm., more cranial nerves.

Colliculi

Oculomotor Nuclei

  • The cerebral (mesencephalic) aqueduct is a ventricular tube running through the midbrain which connects the third and fourth ventricles. It contains cerebral spinal fluid which offer it immunological protection.

See immunology.

Species Differences

  • Other than size the brain of most species is fairly consistant.

Links


 This article is still under construction.


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