Week 6 - finished Flashcards
What is the oldest and most primitive part of the brain?
The brainstem
What is the main function of the brainstem?
Maintenance of homeostasis
CN nuclei are interspersed with the fibers of the reticular formation to form the origins of the CN’s
Contains nuclei which give rise to some of the descending motor pathways
Provides a thoroughfare for fibers passing between the brain, spinal cord and cerebellum
What do cranial nerves do?
They innervate somatic structures of the head and neck with motor and sensory supply
They mediate the special senses
They provide PSNS supply to the viscera, heart, GIT, Resp system and vasculature
Where do each of the CN’s exit the brain?
I - cortex II - diencephalon CN’s III – XII exit the brainstem surface III & IV from the midbrain V & VI from the pons VII & VIII from the pontomedullary junction IX, X, XI & XII from the medulla XI picks up some Cx fibers also
What CN’s tend to exit medially from the brain stem?
Those that have predominantly motor function
What CN’s nuclei sit medially?
Motor nuclei
What is the 4th ventricle continuous with?
The 3rd ventricle above via the cerebral aqueduct
What makes up the core of the brainstem?
The reticular formation
Foramen of Lushka is what?
The end of the lateral recesses there CSF can exit the fourth ventricle and surround the spinal cord
What is larger, the cuneate or gracile tubercle?
The cuneate (as there is more sensation in the upper limbs
What is the reticular formation?
A diffuse network of neurons and glial cells that is interspersed between the CN nuclei and tracts that traverse through the brainstem.
Its function is very poorly understood. Possibly some kind of primitive motor centre.
What are the key functions of the reticular formation?
Coordinates arousal for the adjustment of conscious perception of our environment for sleep & variations in alertness
Controls our habituation to ‘insignificant’ sensory information
Modulation of pain sensation
Regulation of motor function for muscle tone, balance & posture
Relays audiovisual information to the cerebellum for integration into motor control systems
Coordination of autonomic function and rhythmic pattern generation for breathing & swallowing
What art the primary neurotransmitters in the reticular formation nuclei?
Noradrenaline
Serotonin
Dopamine
What is noradrenaline? Where is it made? Where does it usually exert its effects? What does it contribute to?
Largely produced by the locus coeruleus
Exerts its affect on:
- Hippocampus & Amygdala
- Cingulate gyrus & Neocortex
- Thalamus & Hypothalamus
- Striatum
- Cerebellum
- Spinal cord
Contributes to:
- autonomic regulation
- behavioural arousal (to control alertness & vigilance)
- Is a key ‘stress’ hormone
Where is the majority of the bodies serotonin produced and found? How much is found here? What is its function here?
The GIT.
90%
The function is to regulate GIT motility
Where is the other 10% of serotonin found in the body (not in the GIT?). What is its function here?
In the CNS.
Its function is to regulate mood, appetite and sleep.
Serotonergic neurons from the raphe nuclei spread their influence to almost every CNS structure to influence:
- ascending nociceptive pathways
- memory & learning
- Its roles as a vasoconstrictor & in clotting are also thought to have implications in migraine
What is the tegmentum?
The structures derived from the ventral part of the neural tube
What are the 3 distinct dopaminergic pathways?
Mesostriatal fibres project to the diencephalon to influence voluntary movement
Mesolimbic fibres project to the limbic cortex
Mesocortical fibres project to the frontal cortex - The function of the these pathways are not understood but thought to influence emotional and cognitive behavior
What does injury to the brain stem usually result in?
Ipsilateral cranial nerve affects
Contralateral somatic and sensory disturbance
UMN weakness contralaterally
May involve paralysis of the larynx, pharynx and irregularities in breathing and heart rhythm
What is the medulla oblongata? what does it contain?
It is a continuation of the spinal cord, with ascending sensory tracts and descending motor tracts.
Cardiovascular center
Cardiac contractility & HR
Blood vessel diameter
Respiratory center
Rhythmicity area sets basic rhythm of breathing
Centers for cough, sneeze & swallow reflexes
Nuclei for CN’s
What structures are found on the ventral surface of the medulla?
The pyramids:
- largest motor tract
- decussation of most fibres
The olives:
- key cerebellar input for precision movement
- proprioceptive and motor signals
What is found on the dorsal surface of the medulla
- Gracile & cuneate tubercles
- Relay DCML sensation to contralateral thalamus
What cranial nerves arise from the medulla
8-12
Where does CN 12 arise from? Describe CN 12 function and where it receives input from.
Arises: Hypoglossal nucleus
Controls tongue muscles (except palatoglossus) for speech & swallowing
Injury causes tongue to deviate to the injured side when protruded
Primarily motor
Receives input from the corticobulbar tract
Describe the function of the 2 portions of CN 11
Cranial portion
- From the medulla
- With CN IX/X supplies skeletal mm of throat & soft palate
Spinal portion
- cervical spinal cord
- SCM & trap mm.
What are the 3 key nuclei of CN 10 and what are their functions?
Functions via 3 key nuclei:
Dorsal nucleus for parasympathetic motor supply of the thoracic & abdominal viscera
Nucleus Ambiguus for the parasympathetic output to the heart and LMN supply to the skeletal muscle of the pharynx & larynx
Solitary nucleus for primary afferents from the pharynx, ear & viscera
(CNVII/IX also terminate here)
Describe CN 9 function
Somatic motor supply to Stylopharyngeus mm.
Parasympathetics to the parotid gland to regulate secretion
Somatic sensation & taste post.1/3 of tongue
Somatic sensation from the tonsils and middle ear
Visceral sensation from the carotid body and sinus
Describe the functions of the different parts of CN 8
Cochlear portion for audition
- begins in medulla
- Hair cell receptors in cochlea
- deafness or tinnitus produced in dysfunction
Vestibular branch for equilibrium
- begins in pons
- Mechanoreceptors in vestibular apparatus
- vertigo & ataxia produced in dysfunction
How long is the pons?
approx 1 inch long
What is the function of the pons?
Holds fiber tracts, both ascend & descend
Pneumotaxic & apneustic areas to control breathing
Cerebellar peduncles carry info to the cerebellum
Is the area where cranial nerves 5-7 exit
What are the functions of CN 7?
Motor portion
- facial muscles
- Salivary, nasal & oral mucous glands & tears
Sensory portion
- taste buds ant. 2/3 tongue
Has unique UMN/LMN presentations-
The UMN is in the cortex and synapses at the thalamus.
The LMN is from the thalamus to the facial muscles.
The UMN supply the contralateral side of the face, except the muscles of the face on the upper part of the face e.g. the muscles around the eye, are also supplied by a branch from the facial nerve of the ipsilateral side. This is for self preservation in the instance that the facial nerve is damaged, they will still be able to see and open the eyes on both sides.
So therefore if there is a UMN lesion, they will have a saggy lower contralateral side of the face, but an in tact upper part of that contralateral side of the face
If there is a LMN lesion, you will see a loss of function/ you will see saggy whole side of that contralateral face
Describe the function of CN 6
LMNs to Lateral rectus mm.
Has a long path from the brainstem to the orbit and has several common points of compromise making it a frequent indicator of intracranial pathology
Describe the 4 key nuclei of CN 5. What are the peripheral divisions of this nerve?
4 key nuclei:
- Motor nucleus: Somatic motor to muscles of mastication
- Mesencephalic nucleus: Proprioception from the TMJ, oral cavity and mucous membranes .
- Principal nucleus: Tactile sensation
- Spinal nucleus: Pain & temperature
Peripheral divisions:
- ophthalmic branch
- maxillary branch
- mandibular branch
Where does the midbrain sit?
Between the pons and the mesencephalon
What travels through the mid brain?
The cerebral aqueduct
What is located on the dorsal surface of the midbrain? What does it do?
Corpora quadrigemina = superior & inferior colliculi
coordinate eye movements with visual stimuli
coordinate head movements with auditory stimuli
What is the functions of CN 4. What is special about it?
LMN’s to Superior oblique mm. of the eye
Smallest CN
Only one to exit dorsally
Only CN that has decussation of LMN’s
What are the 2 nuclei? of CN 3? What is the function of the 2 parts of CN 3?
Oculomotor nucleus:
- Levator palpebrae raises eyelid (ptosis)
- 4 extrinsic eye muscles
Edinger-Westphal nucleus:
- 2 intrinsic eye muscles:
- accommodation for near vision
- constriction of pupil
What is the only CN to have decussation of LMN?
Trochlear (CN 4)
