Epineurium The structure indicated is the epineurium of a nerve. Nerves are surrounded by three layers of connective tissue: Endoneurium Perineurium Epineurium The endoneurium is a delicate layer of connective tissue which surrounds individual axons.  Collections of axons are known as nerve fascicles; the perineurium surrounds each nerve fascicle, and consists of several concentric layers. The epineurium is the outermost layer of connective tissue which encloses the whole nerve. It is composed of dense irregular connective tissue and encloses all the nerve fascicles together with any blood vessels which supply the nerve.

Vestibulocochlear Nerve

Vestibulocochlear Nerve The structure indicated is the vestibulocochlear nerve (cranial nerve VIII). The vestibulocochlear nerve consists of a vestibular branch and a cochlear branch. The vestibular branch is responsible for balance, and the cochlear branch is responsible for hearing. It originates laterally in the cerebellopontine angle and passes together with the facial nerve into the internal acoustic meatus of the temporal bone.   Cochlear nerve Bipolar sensory neurons in the organ of coorti pass impulses from the hair cells of the cochlear via the peripheral axonal process to the spiral ganglia (this is the collection of cell bodies of the …

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vestibulocochlear nerve

Synaptic Vesicle

Synaptic Vesicle The structure indicated is a synaptic vesicle located in a presynaptic bouton. Synaptic vesicles are structures found at synaptic terminals which contain various different types of neurotransmitter, the chemicals which mediate neurotransmission. Synaptic vesicles are contained within pools within the nerve terminal. There are three types of pools: Readily releasable pool Recycling pool Reserve pool Release of synaptic vesicles is mediated by voltage-gated calcium channels. When an action potential arrives in the synaptic bouton, voltage-gated calcium channels are opened causing calcium influx into the synaptic terminal. This influx then permits fusion of vesicles to the presynaptic membrane and …

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Synaptic Vesicle

Optic Tract

Optic Tract The structure indicated is the optic tract. The pathway of light from the retina to the occipital cortex is as follows: Retina Optic nerve Optic chiasm Optic tract Lateral geniculate body Optic radiation Occipital cortex There are two optic tracts, a right and a left optic tract. The optic tract is an extension of the optic nerve, conveying information from the optic chiasm to the lateral geniculate nucleus. The optic tracts convey information from the opposite visual field – the right optic tract will convey information from the left visual field, and vice versa. The right optic tract …

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Optic Tract

Gray Ramus Communicans

Gray Ramus Communicans The structure indicated is the gray ramus communicans (known collectively as the gray rami communicantes). The spinal nerves at each level receive this branch, the gray ramus communicans, conveying postganglionic nerve fibres from the sympathetic nervous system. In the same picture, parallel to the gray ramus communicans, the branch which conveys the preganglionic sympathetic fibres into the paravertebral sympathetic ganglia is known as the white ramus communicans. The preganglionic nerve fibre which passes through the white ramus communicans has three potential outcomes: Synapse in the paravertebral ganglion. Travel up or down a level in the sympathetic chain …

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Gray Ramus Communicans

Abducent Nerve

Abducent Nerve The structure indicated is the abducent nerve (cranial nerve VI). The abducent nerve (cranial nerve VI), provides general somatic efferent fibres (motor function) to the lateral rectus muscle of the eye. There are three cranial nerves which are responsible for innervating the extrinsic muscles of the eye: Oculomotor nerve (cranial nerve III) Trochlear nerve (cranial nerve VI) Abducent nerve The oculomotor nerve supplies the superior, inferior and medial rectus muscles, as well as the inferior oblique muscle and the levator palpebrae superioris. The trochlear nerve supplies the superior oblique muscle. It originates between the pons and the medulla …

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Abducent nerve