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What to flashcard
flashcard objectives and specifics
Overall objectives
- Identify the external features of the brainstem and cerebellum and understand the functional significance
- Identify the cranial nerves and understand the general function
- Identify the external features of the forebrain and understand general function of each lobe
- Understand localisation and lateralisation of brain function
- Define the dominant hemisphere and describe some of the major effects of dominant vs nondominant hemisphere stroke
- Understand motor and sensory systems and describe the pathways
- Understand and describe the visual and auditory pathways.
Cranial nerves
The cranial nerves are in the division of the PNS and innervate various tissues and organ in the head + neck (with the exception of the vagus nerve)
They are:
| Nerve | Function | Description |
|---|---|---|
| 1. Olfactory nerve | Special sense of smell | Synapses with the olfactory bulb where nerve endings pass through the cribriform plate of ethmoid bone |
| 2. Optic nerve | Special sense of vision | optic canal → optic chiasm → optic tract → some go to superior colliculi some go to the thalamus |
| 3. Oculomotor nerve | Motor to all extraocular muscles except lateral rectus and superior oblique Motor to intrinsic motors of the eye | Midbrain origin. Exits cranium via the superier orbital fissure |
| 4. Trochlear nerve | Motor to superior oblique muscle | Midbrain origin. Only does 1 muscle so small. originates from dorsal surface of brainstem. As it goes to the eye it exits via the superior orbital fissure |
| 5. Trigeminal nerve | Somatic sensation of face and cavities Motor to muscles of mastication | Pons origin. Fat nerve. 3 divisions which exit at different places. Exits at superior orbital fissure, foramen rotundum, foramen ovale. |
| 6. Abducens nerve | Motor to lateral rectus muscle | Pons origin. As it goes to the eye it exits via the superior orbital fissure |
| 7. Facial nerve | Motor to muscles of facial expression Taste on anterior tounge | Pons origin. Exits via the internal auditory meatus & facial canal |
| 8. Vestibulocochlear nerve | Special senses of hearing and balance | Pons origin. Exits via the internal auditory meatus |
| 9. Glossopharangeal nerve | Major nerve for taste Sensation on posterior tongue and pharynx | Medullary origin. Exits via jugular foramen |
| 10. Vagus nerve | motor and sensory to viscera and thorax and abdomen Motor to muscles of Pharynx and larynx | Medullary origin. Exits via jugular foramen |
| 11. Accessory nerve | Motor to sternomastoid and trapezius msucles | Medullary origin. Exits via jugular foramen |
| 12. Hypoglossal nerve | Motor to all muscles of tongue | Medullary origin. Exits via Hypoglossal canal |
Brainstem and cerebellum
Features of the brainstem
The brainstem is a channel for signals to get to and from the spinal cord, cerebellum and cerebrum. It is split into 3 main zones which are the midbrain pons and medulla
Midbrain
Midbrain has a few structures
- Cerebral peduncles Crus Cerebri - little feet of peduncles NOT cerebellar peduncles these are fibres descending from the cores to the brainstem and spinal cord. They also help anchor the cerebrum to the brainstem.
- Corpora quadrigemia Quadruplets This is a group of 4 colliculi (hills), a pair of superior colliculi which deals with certain visual signals and the inferior colliculi which deals with reflexive responses to noises which startle you.
- Substantia nigra Black substance These are neurons which contain melanin, as it is a chemical precursor to dopamine. They are involves with dopamine release and are thus atrophied in parkinsons disease. It is functionally linked to the basal nuclei
- Red nucleus This has extensive blood supply, leading to its red colour. it is a relay nucleus in some motor pathways
- Cerebral aquaduct
- superior cerebellar peduncles
- Cranial nerves
Pons
- 4th Ventricle
- Middle cerebellar peduncle
- Cranial nerves
- Trigeminal
- Abducens
- Facial
- Vestibulocochlear
- Composed of sensort and motor tracts (pontine nuclei)
- Pneumotaxic centre (Along with medullary centre)
Medulla
- Pyramids
- olives
- 4th ventricle
- inferior cerebellar peduncles
- Cranial nerves
- Glossopharangeal
- Vagus
- Accessory
- Hypoglossal
- Cardiovascular centre
- Respiratory centre
- Other reflex centres
The Cerebellum
The cerebellum contains the cortex, white matter and deep nuclei. it is connected to the brainstem by cerebeller peduncles which also transmit information. The main functions of the cerebellum are to coordinate somatic motor function, control muscle tone and maintain balance. It needs to recieve sensory information to do this but is not involved in conciousness. Volentary movement can proceed without cerebellum but are unrefined.
Functional divisions of the cerebellum (& Deep nuclei)
The medial half of the cerebellum controls the posture and movement of the trunk and limbs. It is called the spinocerebellum.
The cerebrocerebellum are the lateral hemispheres and is involved in planning movement.
The vestibulocerebellum is concerned with balance head and eye movements. It is composed of the flocculi and the nodulus.
There are deep nuclei in the cerebellum called the dentate nuclei, interposed nuclei and fastigial nuclei.
Cerebellar signal flow
The Superior cerebellar peduncle is mainly efferent informartion to the cerebrum whereas the MCP is mainly afferent. The ICP does both.
Input
To do its job the cerebellum needs to get motor information from the cerebral cortex to figure out intended movements, sensory information conveying muscle length, joint position and movement to figure out actual movement. it combines these to figure out how to refine movement, as well as corrections to issue to the body.
Output
The ICP transmits processed information back to the brainstem and spinal cord which allows it to directly influence motor control.
The SCP allows the processes motor information plans to be relayed to the motor areas in the thalamus and brainstem. it helps refine movements.
Cerebellum and motor control (Actual processing)
the cerebellar cortex is involved with comparing sensory data to motor data but the movement refinement, on the go correction as well as learning is chiefly handled by the DCN.
Cerebellar dysfunction
Some symptoms of cerebellar dysnfucntions are loss of cooridination in muscle activity which can present as:
- Ataxia Inaccuracy in the speed force and distance of a movement.
- Tremor Involuntary oscillation of the limbs or trunk
- Nystagmus Rhythmic involuntary oscillation of the eyes
- Headache & vomiting
Localisation & Lateralisation of brain function
The localisation of brain function essentially describes how different areas of the brain have specific things they deal with.
Focusing on the cerebral cortex there can be:
- Motor areas (example: primary motor cortex) Voluntary motor functions
- Sensory areas (example: primary somatosensory cortex) Conscious sensation
- Association Areas (example: prefrontal cortex) Integrating a number of diverse info for action
Specific sites and functions
there are many but some specific examples are:
- Brocas area, made of opercular and triangular gyri Deals with spoken speech
- Prefrontal cortex This deals with intellect complex learning, cognition, recall anbd personality. it is heavily dependant on social environment. damage can result in mental and personality disorders
- Supramarginal gyrus This deals with tactile sensory data and in involved with spacial perception and limb spacial awareness
- Primary visual cortex This is the gyri forming the walls of the the calcarine sulcus.
- Visual association area
- uncus
- Amygdala
- Wernickes area deals with listening to communications
- primary auditory cortex
- right hippo campus - spatial representation.
- Insular lobe Function is unknown. visceral sensation effected as well as general sensory and mtoro function. A case study apparently found the left insular lobe was involved in the normal emotional processing of music.
- pineal gland
- thalamus
- hypothalamus
Somatotopy
This is the idea each point in the body has a point in the cerebrum for motor and for sensory. this is where we get the motor and sensory homonculi
Lateralisation
This the idea that the different hemispheres have different things they do. in 90% of people the left hemisphere is dominant which means that the brocas and wernickes areas are only found on the left side
Motor and sensory pathways
Motor pathways
The corticospinal tract starts with the Primary motor, premotor and sensory cortices and then the tract follows through the internal capsule, to the midbrain pons and medulla. most of the fibres (90%) decussate in the medulla and travel down the lateral corticospinal tract on other side of the body to the origin (contralateral). The endpoint is the cell bodies in the ventral horn of the spinal cord which then link to the effector.
Role of the cerebellum.
The cerebellum receives inputs form the motor cortex which relays the intended movements as well as inputs from the somatosensory neurons. The DCN will do comparative calculations and sends corrections to the motor neurons as well as brain stem nuclei.
Role of the Basal nuclei in motor control.
The role of the BN are to recieve inputs from all cortical areas and project back to premotor cortex as well as the prefrontal cortex. it is involved in more abstract (complex) parts of motor control for example broadly inhibiting during rest or stillness and then coordinating motions when the motor centers are release from forementioned inhibition.
Somatosensory pathways
There are 2 main types of pathway to the somatosensory cortex.
The discrimative pathway relates fine touch, vibration and conscious proprioception to the SSC with the first neuron being in the spinal root ganglion, second order neuron being in the medulla where decussation happens, and 3rd order being in the thalamus.
The difference is the nondiscriminatory pathway (which relates pain pressure and temperature) has the decussation and second order neuron in the dorsal horn of the spinal cord.
Spinocerebellar tract
This is a tract which does not contribute to somatic sensation but just sends data to the cerebellum for processing there. first order neuron is in the dorsal root ganglion and the second order neuron is in the dorsal horn with NO DECUSSATION. It is an ipsilateral pathway so right arm position sent to right cerebellar cortex
Audio visual pathways
Visual pathway
The retinal cells get excited and send information to the optic nerve where a decussation happens at the optic chiasm. Then optic tract travel to the lateral geniculate nucleus of the thalamus where processing occurs. After this visual information is relayed to the visual cortex. The superior colliculus is involved in tracking fst moving object and startling imagery.
the PVC provessing basic visual information, and conscious perception of visual information.
visual association areas process visual information concerned with form colour and movement.
complec visual proccessing occurs in ventral parts of the temporal lobe, parietal cortex and frontal corex.
- ventral temporal lobe identifies what the object is
- parietal lobe assesses where the location is
- frontal cortex uses visual information to guide movements.