Brain

·         The sulcus limitans divides the alar plate, from which sensory regions of the spinal cord and brainstem are formed, and a basal plate, from which motor regions of the spinal cord and brainstem are formed.

·         Major excitatory transmitters: Substance P, acetylcholine, and excitatory amino acids

Major inhibitory transmitters: GABA, enkephalin, and glycine.

·         Major ascending tracts of the spinal cord and their functions include:

1. Dorsal columns. Mediates conscious proprioception, two-point discrimination, and some tactile sensation ipsilaterally to the dorsal column nuclei and then contralaterally from the dorsal column nuclei to the postcentral gyrus from the VPL of the thalamus.
2. Lateral spinothalamic tract. Mediates pain and temperature inputs contralaterally to the VPL and posterior complex of the thalamic nuclei and then to the postcentral gyrus.
3. Anterior spinothalamic tract. Mediates tactile impulses contralaterally to the VPL and then to the postcentral gyrus.
4. Posterior spinocerebellar tract. Mediates unconscious proprioception from muscle spindles and Golgi tendon organs of the lower limbs through the inferior cerebellar peduncle ipsilaterally to the anterior lobe of the cerebellar cortex.
5. Cuneocerebellar tract. Mediates unconscious proprioception from muscle spindles and Golgi tendon organs of the upper limbs from the accessory cuneate nucleus through the inferior cerebellar peduncle to the anterior lobe of the cerebellar cortex.
6. Anterior spinocerebellar tract. Mediates unconscious proprioception from the Golgi tendon organs of the lower limbs bilaterally to the anterior lobe of the cerebellar cortex. This tract initially crosses in the spinal cord and then crosses again through the superior cerebellar peduncle.

·         Major descending tracts of the spinal cord and their functions include:

1. Lateral corticospinal tract. Mediates voluntary control of motor functions from the contralateral cerebral cortex to all levels of the spinal cord.
2. Rubrospinal tracts. Mediates descending excitation of flexor motor neurons at both the cervical and lumbar levels of the contralateral spinal cord.
3. Reticulospinal tracts.

 The lateral reticulospinal tract arises from the medulla and descends bilaterally to the cervical and lumbar levels of the spinal cord, mediating inhibition upon the spinal reflexes, mainly of extensors;

 the medial reticulospinal tract arises from the pons and descends mainly ipsilaterally to the cervical and lumbar levels of the spinal cord and facilitates extensor reflexes.

4. Vestibulospinal tracts. The lateral vestibulospinal tract arises from the lateral vestibular nucleus and descends ipsilaterally to the cervical and lumbar levels of the spinal cord, mediating powerful excitation of the extensor motor neurons; the medial vestibulospinal tract arises from the medial vestibular nucleus and descends mainly to the cervical levels of the spinal cord, mediating postural reflexes of the head and neck.

·         The principles of an excitatory focus-and-surround inhibition, as well as that of a somatotropic organization are present within a given receptor system and form the functional basis for discriminative functions in a number of the sensory systems, including the auditory circuit.

The auditory pathways are complex and involve the following synaptic connections:

first-order root fibers of the spiral ganglion, which originate in the cochlea (organ of Corti), synapse in the cochlear nuclei of the upper medulla;

second-order neurons, which project through lateral lemnisci, terminate bilaterally in the inferior colliculus;

 third order neurons project to the medial geniculate nucleus; and

 fourth-order neurons project to the superior temporal gyrus (primary auditory cortex).

·         The following arteries make up the circle of Willis:

· Anterior cerebral artery (left and right)

· Anterior communicating artery

· Internal carotid artery (left and right)

· Posterior cerebral artery (left and right)

· Posterior communicating artery (left and right)

The basilar artery and middle cerebral arteries, though they supply the brain, are not considered part of the circle.

·         CNs that lie medially at brain stem: III, VI, XII. 3(×2) = 6(×2) = 12

·         Only CN with myelination by oligodendrocyte is OPTIC NERVE.

·         Medial Leminiscus is crossed 2^nd order neuron of dorsal column tract.

STT is analogus to medial leminiscus as its also crossed 2^nd order neuron of Anterior sensory system.

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Sympathetic anatomy

o    Preganglionic efferent

§  Lateral column cell body --> ventral root --> white ramus communicans --> sympathetic trunk --> synapse in trunk or other ganglia or adrenal

o    Postganglionic

§  May ascend or descend in the trunk, rejoin all spinal nerves via grey rami communicantes or leave in direct branches to vessels or viscera

o    Distribution

§  Cranial

§  Internal carotid plexus arises from superior cervical ganglion and accompanies carotid into the cranium and along anterior and middle cerebral arteries and ophthalmic artery

§  Cervical

§  Sympathetic chain condenses usually into three ganglia on each side: superior (C2-3), middle (C6) and cervicothoracic (stellate, T1) cervical ganglia

§  Cardiac plexus

§  Derived from T1-4 (and X) via cervical and thoracic ganglia

§  Surrounds heart, great vessels and coronaries

§  Pulmonary plexuses

§  Coeliac plexus

§  Two ganglia opposite T12-L1 with large condensation of autonomic fibres

§  Gives rise to phrenic, splenic, hepatic, left gastric, intermesenteric, suprarenal, renal, gonadal, superior and inferior mesenteric plexuses which accompany arteries to their target organs

§  Superior hypogastric plexus

§  Inferior hypogastric plexus

§  Supplies hindgut, ureter, bladder, gonads, sex organs

        

        

Parasympathetic anatomy

o    III

§  Edinger-Westphal nuclei --> oculomotor n. --> n. to inferior oblique --> ciliary ganglion --> short ciliary nn. --> ciliary muscle and sphincter pupillae

o    VII

§  Superior salivatory nucleus --> nervus intermedius --> facial n. --> chorda tympani --> lingual n. --> submandibular ganglion --> submandibular and sublingual glands

§  Geniculate ganglion --> greater petrosal n. --> pterygopalatine ganglion --> zygomatic and lacrimal nerves to lacrimal gland and nasal and palatine branches to nasal mucosa

o    XI

§  Inferior salivatory nucleus --> glossopharyngeal nerve --> tympanic plexus --> lesser petrosal n. --> otic ganglion --> auriculotemporal n. --> parotid gland and oral mucosa

o    X

§  Dorsal nucleus of vagus --> vagus n. --> minute ganglia in respiratory tract, heart, kidneys and gastrointestinal viscera from oesophagus to mid transverse colon. Most vagal fibres are afferent, there is a very large ratio of postganglionic to preganglionic efferent fibres.

o    S2-4

§  Anterior rami --> sacral spinal nerves --> pelvic viscera and pelvic plexus --> bladder, erectile tissue, gonads, uterus and uterine tubes, hindgut from mid transverse colon to rectum