brainstem and cranial nerves Flashcards
what does the brainstem connect
The brainstem connects the spinal cord to the forebrain
what are the three functions of the brainstem
- cranial nerve functions
- conduit function
- integrative functions
describe the three functions of the brainstem
- Cranial nerve functions
- The brainstem contains functional centers associated with 11 of the 12 pairs of cranial nerves - Conduit function
- it contains ascending and descending pathways that transmit sensorimotor information to and from the cortex. - Integrative functions
- e.g. respiratory and cardiovascular activities, consciousness, sleep, and wakefulness that occur via the reticular formation that runs throughout length of brainstem.
what does damage to the brainstem result in
- results in sensorimotor dysfunction accompanied by abnormalities in cranial nerve function
what are the main parts of the brainstem
- midbrain
- pons
- medulla
what is the most rostral part of the brainstem
- midbrain
what is the most caudal part of the brainstem
- medulla
then does the brainstem become the foramen magnum
beyond the foramen magnum
what is the midbrain associated with
- auditory
- visual
- pupillary reflexes
- eye movements
- Crainal nerves II to IV
what is the pons associated with
- cranial nerve V-VII.
- mastication (V)
- eye movement (VI)
- facial expression, blinking and salivation (VII)
- equilibrium and audition (VIII).
what is the medulla associated with
- cranial nerves VIII-XII
- equilibrium
- audition
- deglutition
- coughing
- vomiting
- salivation,
- tongue movement
- respiration & circulation.
how is the brainstem organised
- into 3 sections in the dorsal ventral axis
- they receive input from all the parts of the nervous system and exert widespread influences on CNS functions
describe what is in the dorsal part
in the dorsal part are located the cranial nerve nuclei;
describe what is in the ventral part
in the ventral part are located fibres of descending pathways
describe what is the middle part
in the middle part (which is often called the tegmentum) are located the ascending pathways and various nuclei associated with the reticular formation
- it runs the length of the brainstem and receives input from all parts of the nervous system
name the divisions of the 12 cranial nerves
- purely sensory (I, II VIII)
- purely motor,(III,IV, VI, XI XII)
- mixed (V,VII, IX, X) nerves
where do sensory nerve nuclei tend to be located compared to motor nuclei
sensory nerve nuclei tend to be located in the lateral brainstem, while motor nuclei tend to be located medially.
describe the origins of mixed nerves from the brainstem
= nerves that have both sensory and motor fibres have more than one nucleus of origin - they have ne sensory and one motor therefore they tend of be located in between
more than one nerve will…
will originate from a single nucleus
- for example, the sense of taste is spread across at least two nerves but merges into a single nucleus
where are the sensory receptor bodies
- located just outside the CNS in an ganglion
what is the brainstem organised
- Neurons with similar functions are brought into close proximity to reduce the amount of neural wiring needed.
- Different functions are affected by local damage depending on whether the lesion is lateral or near the mid-line.
what can brainstem disorders by analysed by
- Is it LATERAL or MEDIAL
2. What is the LEVEL of the LESION - specific cranial nerves delineate the actual level
what is cranial nerve I
olfactory nerve
why is the olfactory nerve unique
- it is the only sensations that projects directly into the cortex
- does not go through the brainstem or thalamus
describe the structure of the olfactory nerve
- The olfactory receptors are located within the upper nasal mucosa and detect chemical stimuli.
- very short
- central axons pasS through the cribiform plate to connect with mitral cells in the olfactory bulb
- The axons of the mitral cells form the olfactory tract and connect either with cells of the anterior olfactory nucleus or pass directly to the ipsilateral primary olfactory cortex (piriform cortex), which includes the amygdala and uncus regions of the temporal lobe
how is smell and taste linked
connections are made with the olfactory nerve and with the reticular formation nuclei that influence visceral functions such as salivation, gastric secretion and peristalsis. = In this way smell and taste are linked.
what does the anterior olfactory nucleus do
they transmit the smell to the contralateral cortex
what does damage to the olfactory nerve cause
anosmia - loss of smell
how do you test the olfactory nerve
Ask the patient to close both eyes and 1 nostril and identify different smells such as coffee, soap, herbal aromas presented to the open nostril.
- Do not use volatile substances such as alcohol or ammonia as these stimulate the chemical receptors of the trigeminal nerve that innervate the nasal mucosa.
what nerve is CNII
optic nerve
where does optic nerve originate from
The optic nerve is in fact a CNS tract originating in the diencephalon
what happens if the optic nerve is damaged
it does not regerneate
describe the structure of the optic nerve
- The rods and cones are the receptors for vision while retinal ganglion cell axons (RGC) make up the optic nerve.
- RGCs from the nasal side of each eye cross each other at the optic chiasm to run in the contralateral optic tract whereas those from the temporal retina do not.
where does the optic nerve terminate
- A small proportion of fibres leave the tract to terminate in midbrain nuclei to participate in visual reflexes.
- The majority of optic tract axons terminate in the lateral geniculate nucleus of the thalamus in an orderly manner termed retinotopy.
what does lesions of the visual pathway cause
lesions of the visual pathway cause predfictable deficits in the visual field and the nature of the deficit identifies the site of lesion in the pathway.
how do you do an examination of the optic nerve
- Pupillary reflexes- checks pupil reactions
- Visual acuity – test ability to distinguish objects, usually letters.
- Visual fields – assesses peripheral and central retina, and the visual pathway.
- Colour vision – assess function of retinal cones and optic nerve.
- Fundoscopy – checks retinal vessels.
what do cranial nerves II, IV AND VI do
- they innervate the muscles that control voluntary eye movements and pupillary size
what are the two types of voluntary eye movements
- conjugate
- vergence
