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Equine Nervous System - Horse Anatomy (view source)
Revision as of 09:02, 22 November 2012
, 09:02, 22 November 2012→Vasculature of the Brain
===Vasculature of the Brain===
===Vasculature of the Brain===
====Circle of Willis====
Blood is supplied to the brain from a ventral arterial supply in all species; from a circle of arteries called the Circle of Willis (also called the ''cerebral arterial circle'' or ''arterial circle of Willis'') which lies ventrally to the hypothalamus where it forms a loose ring around the '''infundibular stalk'''. Blood is supplied to the brain by the '''internal carotid artery''' in horses. The Circle of Willis is made up of five main pairs of vessels:
*Rostral Cerebral Arteries: supply the medial aspect of the cerebral hemispheres.
*Middle Cerebral Arteries: supply the lateral and ventrolateral aspects of the cerebral hemispheres.
*Caudal Cerebral Arteries: supply the occipital lobes.
*Rostral Cerebellar Arteries: supply the rostral aspects of the cerebellum
*Caudal Cerebellar Arteries: supply the caudal and lateral aspects of the cerebellum.
The arrangement of the Circle of Willis means that if one part of the circle becomes blocked or narrowed (stenosed), or one of the arteries supplying the circle is stenosed, blood flow from the other blood vessels can continue to provide a continuous supply of blood to the brain.
The main blood supply to the circle is via the paired '''internal carotid arteries''' and the '''basilar artery'''. The basilar artery receives blood from the '''ventral spinal artery''' and the '''vertebral artery''' (the vertebral artery is a branch of the subclavian artery running through the vertebral foramina of C1 - C6). The maxillary artery does not contribute to the arterial circle in the horse, but it does supply the meninges. In horses, the vertebral artery can also supply the internal carotid artery via the '''occipital artery''' but this can be bypassed so that the vertebral artery can directly supply the internal carotid artery via a ramus to the internal carotid directly from the vertebral artery.
====Rete Mirable====
The brain is particularly susceptible to increased blood temperature and to protect the brain from any potential heat stress a number of species have developed protective mechanisms with the ability to selectively cool the brain. This protective system is often referred to as the Rete Mirable. The Rete Mirable is a complex network of arteries and veins lying very close to each other and depends on a countercurrent blood flow between the arterioles and venules (blood flowing in opposite directions). It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient.
====Venous Sinuses====
Venous sinuses drain the brain, meninges, and surrounding bone as well as participate in cerebrospinal fluid resorption; they are arranged into two systems. The dorsal system is within the dura
mater of the cranium and drains the cerebral cortex, the cortex of the cerebellum, the deeper telencephalon, part of the diencephalon, and the tectum of the midbrain. The ventral (basilar) system lies on the floor of the cranial vault and drains the brainstem. The dorsal and ventral systems have minimal connection between them, but each communicates with the extracranial venous system. The dorsal system begins where several dorsal cerebral veins converge in the area of the '''crista galli''' of the '''cribriform plate'''. The '''dorsal sagittal sinus''' arises from this convergence and runs caudally along the dorsal midline; surrounded by the falx cerebri as it lies against the skill bones. Along its course, it receives '''cerebral veins''', '''meningeal veins''', and '''diploic veins''' from the skull.
The dorsal sagittal sinus of the horse, is incompletely divided by a septum and bifurcates rostral to the '''osseous tentorium'''. Just before reaching the osseous tentorium, the dorsal sagittal sinus
receives a single sinus that drains the '''medial cortex''', '''corpus callosum, '''basal ganglia''', and part of the '''diencephalon'''. The '''transverse sinuses''' run ventrally from the '''osseous tentorium''' to the '''retroarticular foramen''', where they exit to join the '''extracranial venous system'''.
===Spinal Cord===
===Spinal Cord===
The '''spinal cord''' is constructed of the ''[[Spinal Cord - Anatomy & Physiology#Marginal layer|marginal layer]] ''which has axons and white matter, the ''[[Spinal Cord - Anatomy & Physiology#Mantle|mantle]]'' which contains cell bodies and grey matter and the ''[[Spinal Cord - Anatomy & Physiology#Spinal Canal|spinal canal]]''. This canal conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain, conducts motor information from the brain to various effectors and acts as a minor reflex center. The spinal cord can be divided to several regions:
The '''spinal cord''' is constructed of the ''[[Spinal Cord - Anatomy & Physiology#Marginal layer|marginal layer]] ''which has axons and white matter, the ''[[Spinal Cord - Anatomy & Physiology#Mantle|mantle]]'' which contains cell bodies and grey matter and the ''[[Spinal Cord - Anatomy & Physiology#Spinal Canal|spinal canal]]''. This canal conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain, conducts motor information from the brain to various effectors and acts as a minor reflex center. The spinal cord can be divided to several regions: