2.11 Brainstem Networks Flashcards
What are all the neuroanatomical directional terms
Anterior:In front of or toward the face
Posterior:Behind or toward the back
Superior:Above or toward the head
Inferior:Below or toward the feet
Medial:Toward the middle
Lateral:Toward the edge
Dorsal:Toward the top of the brain or the back of the spinal cord
Ventral:Toward the bottom of the brain or the front of the spinal cord
Rostral:Toward the front of the brain or the top of the spinal cord
Caudal:Toward the back of the brain or the bottom of the spinal cord
Describe the brainstem
The brainstem connects the cerebrum to the spinal cord, it is made up of the midbrain then the pons then the medulla. It gives a pathway for tracts running between higher and lower neural centers. It is deep grey matter surrounded by white matter fibre tracts and its structures are responsible for a lot of the automatic behaviours necessary for survival.
What are the functions of the midbrain
vision, hearing and motor control
What is the function of the pons
pneumotaxic centre (regulating respiration and vascular tone)
What are the functions of the medulla oblongata
cardiac, respiratory, vasomotor and vomiting
Describe the different pathways within the brainstem
sensory ascending pathways (dorsally located) - there are relay nuclei and tracts
motor descending pathways (ventrally located) - come down through motor cortex, through motor nuclei in the brain stem and down tracts in the spinal cord
cerebellar pathways - cerebellar afferent and efferent nuclei and tracts
cranial nerve sensory and motor tracts - cranial nerve nuclei, nerve entry and exit points
CPG (central pattern generator) networks - rhythmic chewing, respiration, cardiovascular regulation and gain adjustments for reflexes
modulatory systems with chemically coded nuclei: locus coeruleus, raphe & substantia nigra
Describe the structure of the midbrain
The midbrain is located between the diencephalon and the pons. It has 2 cerebral peduncles on it’s ventral side and these peduncles have descending fibres that go to the cerebellum via the pons as well as descending pyramidal tracts. There is a hollow cerebral aqueduct running through the midbrain which connects the 3rd and 4th ventricles of the brain. The roof of this aqueduct (tectum) contains the corpora quadrigemina which has 2 superior colliculi that controls the reflex movements of the eyes head and neck in response to visual stimuli and 2 inferior colliculi controlling reflex movements of head neck and trunk in response to auditory stimuli.
What are 2 structures on each side of the midbrain
on each side of the midbrain theres a red nucleus and substantia nigra
red nucleus- has many blood vessels and receives info from cerebrum and cerebellum and issues subconscious motor commands concerned with muscle tone and posture
substantia nigra- is lateral to the red nucleus, is a dopamine high area that secretes dopamine to inhibit the excitatory neurons of the basal nuclei
What are the 2 dopaminergic pathways projecting from the midbrain
nigrostriatal pathway - projects from the substantia nigra to the corpus striatum of the basal nuclei (affecting motor coordination)
mesolimbic pathway - projecting from the VTA to the nucleus accumbens (affecting behavioural reward)
Describe the pons
The pons is the bridge between the midbrain and the medulla. It contains lots of nuclei and tracts that process and relay information to and from the cerebellum. These include respiratory nuclei such as apneustic and pneumotaxic centres that work with the medulla to maintain respiratory rhythm as well as the sensory and motor nuclei for cranial nerves 5-8. It has ascending, descending, and transverse tracts that interconnect other portions of the CNS.
Describe the structure of the medulla oblongata
The medulla oblongata is the most inferior brainstem region, it becomes the spinal cord at the level of the foramen magnum (open of the base of the skull). Ventrally, the 2 medullary ridges (formed by the large motor corticospinal tracts) are visible, most of these fibres cross over (aka decussate) right above the medulla/spinal cord junction.
Describe the nuclei within the medulla
Nuclei within the medulla are associated with autonomic control, cranial nerves, and motor/sensory relay.
Autonomic nuclei include;
Cardiovascular centers- alter the rate and force of cardiac contractionsand alter the tone of vascular smooth muscle
Respiratory rhythmicity centers- receive input from the pons
Additional Centers- emesis, deglutition, coughing, hiccupping, and sneezing
The medulla also has the sensory and motor nuclei of cranial nerves 8-12
The medulla also has relay nuclei such as;
-nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus
-Olivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex.
What are the ascending sensory pathways in the brainstem
Fine discriminative touch, conscious proprioception:
-Fasciculus gracilis: Terminates in the nucleus gracilis (medulla)
-Fasciculus cuneatus: Terminates (medulla) in the cuneate and accessory cuneate nuclei
Sensations of pain and temperature:
-Lateral Spinothalamic Tract
-originà dorsal horn cells of the gray matter
-Fibers cross contralaterally through the anterior commissure and ascend to the VPL nucleus
Transmits sensations of touch:
-Ventral Spinothalamic Tract
-originà cells of the posterior horn
-Fibers cross to the opposite side in the anterior commissure
What are the descending motor pathways in the brainstem
Voluntary movement:
- Lateral Corticospinal Tract
- Originates in large pyramidal cells (precentral gyrus)
- cross to the opposite side of the cord at the pyramidal decussation & terminate in the dorsal horn cells
- Ventral Corticospinal Tract
- Originates in the pyramidal cells (motor area of the cortex)
Impulses related to equilibrium and antigravity reflexes:
- Vestibulospinal Tract
- Fibers originate in the vestibular nuclei of the medulla and terminate at level of the sacral spinal nerves
-connects the vestibular complex and head and eye movement coordination center in medulla
-contains both ascending and descending fibres
Describe reticular formation in the brainstem
An extensive network of neurons going through the medulla and projecting to the thalamic nuclei that influence large areas of the cerebral cortex. They function as a filter for sensory input, allowing important stimuli through and filtering out repetitive stimuli
