Neurons and innervation of the orbit

What are the 3 functions of a neuron?

1. RECEPTION: taking in info from neighboring neurons
2. CONDUCTION: integrating these signals
3. TRANSMISSION: passing signals to other neurons

What are sensory neurons?

Detect info from physical world and pass that info to the brain generally via the spinal cord

Are sensory neurons afferent or efferent neurons?

Afferent - carrry info TO BRAIN

Define somatosensory

= sensations experienced within the body
- sensory nerves that provide info from muscles

How do motor neurons function

- Produce movement by direction muscles to contract or relax

Are motor neurons afferent or efferent?

Efferent - transmit signals from brain to muscles throughout the body

How do interneurons function?

- Communication with other neurons in a local or short distance circuit.

Where are interneurons typically found?

In a specific brain region

What are the 8 main components of a neuron?

1. Dendrites
2. Soma/cell body
3. Nucleus
4. Axon hillock
5. Axon
6. Myelin sheaths
7. Nodes of Ranvier
8. Terminal buttons
9. Synapse/synaptic cleft

Describe a dendrite: (3)

- Branch-like structure
- receives messages from other neurons
- allows the transmission of messages to the cell body

What does the soma contain?

Soma contains cell body with
- nucleus
- Golgi apparatus
- endoplasmic reticulum
- mitochondria
- other organelles.

What occurs in the soma?

information received from thousands of neurons is collected and processed.

What is an axon hillock?

- Where the axon arises from the soma/cell body

What shape is the axon hillock?

- triangular and cone shaped region

What is the purpose of an axon hillock?

- assists in distinguishing the axon from a dendrite in microscopy since it doesn't have large cytoplasmic organelles lke Nissl granules and golgi complexes
- Has high conc. of ion channels
- Acts as neurons primary integrative zone, receiving various excitatory and inhibitory stimuli

What does the axon hillock determine?

- determine if the sum of all of the incoming signals warrants the propagation of an action potential and transmission of a signal

What is a terminal bouttons?

small nodules at the end of an axon
-receive electrical impulses from the axon and release chemicals to the synapse to be detected by a neighboring neurons

What are myelin sheaths?

- Fatty material made up of glial cells that encases and insulates the axon
- Allows electrical signlas to travel quickly down the axon

How do myelin sheaths grow?

- Grow along the axon in short segments

What are the nodes of Ranvier?

- small gaps of exposed axon without myelin sheath

What is the purpose of nodes of ranvier?

- Located at these nodes are ion channels which allow cations and anions to pass in and out of the cells when the neuron is transmitting signals down the axon

What makes up the Central Nervous System?

Brain and Spinal Cord

What makes up the Peripheral Nervous System?

Spinal and cranial nerves

What are the 2 subsections of the PNS and are they voluntary or involuntary?

Autonomic Nervous System - involuntary

Somatic Nervous System - voluntary

What is the Autonomic Nervous System broken down into:

Sympathetic Nervous System

Parasympathetic Nervous System

Enteric Nervous System

What does the sympathetic nervous system do?

Mobilisation of energy stores for increased activity

What does parasympathetic nervous system do?

Conservation of energy stores

What is the enteric nervous system?

neurons intrinsic to the GI tract

What is the somatic nervous system?

Voluntary motor fibres to skeletal muscle.

What is the largest part of the brain?

cerebrum

What is the cerebrum made up of?

2 cerebral hemispheres: right and left

What is a gyrus?

a ridge in the cerebrum, which is a highly folded sheet of neuron

What is a sulcus?

A furrow in the cerebrum, which is a highly folded sheet of a neuron

What is the cerebral cortex?

External layer of the brain that’s made up of grey matter

What is grey matter?

a grouping of cell bodies

What is white matter?

A group of axons

what is the corpus callosum?

Largest commissure that connects the left and right hemispheres, allowing them to communicate.

What are the 4 cerebral lobes?

Frontal

Parietal

Temporal

Occipital

What is the cerebellum made of?

2 hemipsheres

Has numerous deep and superficial fissures

Function of cerebellum?

muscle coordination and postural control

Which components are in the brainstem?

midbrain

pons

medulla oblongata

Which nerves are found in the brainstem?

• Nuclei of CN’s

• Autonomic fibres

• Reticular nuclei for vital centres (cardiac, respiratory, consciousness)

What is the function of the Cranial Nerves?

Transmit sensory info from head and neck to the brain

Control actions of the head and neck

What does a CN consist of?

central nucleus in brain and peripheral nerve fibre

What are the 3 sensory CNs

olfactory

optic

vestibulocochlear

what are the 5 motor CNs?

oculomotor

trochlear

abducent

accessory

hypoglossal

what are the 4 sensory and motor CNs?

trigeminal

facial

glossopharyngeal

vagus

What is an acronymn to remember the 12 CNs?

Oh - olfactory

Oh - optic

Oh - oculomotor

To - trochlear

Take - Trigeminal

A - Abducens

Family - Facial

Vacation - Vestibulocochlear

Go - Glossopharyngeal

Vegas - Vagus

After - Accessory

Hours - Hypoglossal

What is an acronymn to remember if a CN is sensory, motor or both?

some

say

marry

money

but

my

brother

says

big

business

makes

money

Where is the origin of CNII - Optic Nerve

Ganglion cells of the retina

What is the course for CNII - Optic Nerve

pass from posterior globe through optic canal, decussating at the optic chiasm, emerging at optic tract

What are the central connections of CNII- Optic Nerve

Lateral geniculate nucleus of thalamus, pretectal area of midbrain

What is the function of CNIII - Oculomotor nerve (1)

Movement of eye

Elevation of upper lid (motor)

What are the central connections for CNIII - Oculomotor nerve for eye movement and elevation of sup lid?

Ocular motor nucleus

What is the course of CNIII-Oculomotor nerve for eye movement and elevation of sup lid?

Emerges from anterior midbrain, runs forward along lateral cavernous sinus, enters orbit through superior orbital fissure.

Which structures does the CNIII - Oculomotor nerve innervate (1)?

Superior, inferior, medial rectus

Inferior oblique

Levator palpebrae superioris

What is the function of CNIII - oculomotor nerve (2)

Is it motor or sensory?

Is it sympathetic or parasympathetic?

pupillary constriction and accommodation

motor

parasympathetic

Where is the central connections for CNIII - Oculomotor nerve (2)

accessory oculomotor (Edinger-Westphal) nucleus

What is the course for CNIII - oculomotor nerve (2)

Follow oculomotor fibres to orbit, synapse cilliary ganglion, travel as short cilliary nerves to sphincter and cilliary muscle

Which structures are innervated by CNIII-oculomotor nerve (2)

sphincter pupillae and ciliary muscle via cilliary ganglion

Explain CNIII-oculomotor nerve in terms of how it splits up into superior and inferior divisions:

CNIII divides into superior and inferior divisions before entering superior orbital fissure.

Enters within common tendinous ring

Superior division innervates the superior rectus and levator

Inferior division innervates the medial and inferior recti, inferior oblique

What is the function of CNIV - trochlear nerve

movement of the eye (motor)

What is the central connections for CNIV - trochlear nerve?

trochlear nucleus

What is the course of CNIV - trochlear nerve?

Only CN to leave posterior brain stem, decussates and runs forward along lateral cavernous sinus, enters orbit through superior orbital fissure superior to common tendinous ring

What structures does CNIV - trochlear nerve innervate?

superior oblique muscle

What are the 3 branches of CNV - trigeminal nerve?

V1 - opthalmic

V2 - maxillary

V3 - mandibular

Is V1 opthalmic branch of CNV - trigeminal nerve sensory or motor?

sensory

Is V2 maxillary branch of CNV - trigeminal nerve sensory or motor?

sensory

Is V3 mandibular branch of CNV - trigeminal nerve sensory or motor?

motor and sensory

What is the origin/target of V1-opthalmic branch of CNV - trigeminal nerve?

Sensation from forehead, scalp,eyelids, nose, and eye (cornea and conjunctiva)

What is the central connections of V1 - opthalmic branch of CNV - trigeminal nerve?

trigeminal ganglion

What is the origin/target of V2 - maxillary branch of CNV-trigeminal nerve

skin of anterior temporal and upper cheek, below eye, palate, teeth, maxillary sinus

What is the central connections of V2 - maxillary branch of CNV - trigeminal nerve?

trigeminal ganglion

What is the origin/target of V3 - mandibular branch of CNV-trigeminal nerve

Masticatory muscles. Sensory to anterior 2/3 of tongue, skin, posterior temporal, cheek, chin, teeth and lower jaw

What is the central connections of V3 - mandibular branch of CNV - trigeminal nerve?

trigeminal ganglion

trigeminal motor nucleus

What is V1 - opthalmic branch of CNV - trigeminal nerve further divided into?

frontal nerve

lacrimal nerve

nasocilliary nerve

Where does CN V1 - frontal nerve enter through?

superior orbital fissure outside common tendinous ring

What does CN V1 - frontal nerve branch into and innervate?

SUPRAORBITAL NERVE: innervates skin and conjunctiva of upper lid and forehead

SUPRATROCHLEAR NERVE:

• communicates with infratrochlear branch of nasociliary nerve.

• skin and conjunctiva of upper lid and forehead

Where does CN V1 - lacrimal nerve enter through?

Enters through superior orbital fissure outside common tendinous ring

What does CN V1 - lacrimal nerve innervate?

receives parasympathetic fibres from zygomatic nerve and stimulates the lacrimal gland

Where does CN V1 - nasocilliary nerve enter through?

superior orbital fissure inside common tendinous ring - passes forward to become the anterior ethmoidal nerve

What does the anterior ethmoidal nerve branch into and what does it innervate?

RAMUS COMMUNICANS: to ciliary ganglion then short posterior ciliary nerves

LONG POSTERIOR CILIARY NERVES: ciliary body, iris and cornea

INFRATROCHLEAR NERVE: lacrimal sac, conjunctiva and skin of medial lower eyelid and lateral nose

What is the function of CNVI - abducens nerve?

movement of eye (motor)

What are the central connections of CNVI - abducens nerve

abducens nucleus

What is the course of CNVI - abducens nerve?

runs forward inferolateral to internal carotid artery, enters orbit through superior orbital fissure within the common tendinous ring

What structures doe CNVI - abducens nerve innervate?

lateral rectus muscle

What is the sensory function, origin/target and central connections of CNVII - facial nerve

Sensory

Proprioception from facial muscles. Taste from anterior 2/3 of tongue.

Geniculate ganglion

What is the parasympathetic function, origin/target and central connections of CNVII - facial nerve?

origin/target: lacrimal gland and mucuous membranes of nasal and oral cavities and salivary glands, causing secretion.

Central connections: superior salivatory nucleus

What is the MOTOR origin/target and central connections of CNVII - facial nerve?

origin/target: muscles of facial expression

central connections: facial nucleus