Proprioception and Intro to the Brain Flashcards
Archeocortex- the main structures of the limbic system
What is the most caudal part of the brain? What does it expand to form?
Medulla oblongata. It expands to form the pons.
What is the cavaria? What bones make up the cavaria?
Cranial vault aka the roof of the skull.
Occipital, parietal, frontal temporal, sphenoid, and ethmoid bones.
What does the pituitary gland lie within?
Hypophyseal fossa
What does the petrous temporal bones house?
Cochlea and vestibular apparatus- sensory structures for hearing and head position/ movement (balance)
How do the lateral ventricles communicate with the third ventricle? How does the third ventricle communicate with the fourth ventricle?
Interventricular foramen and the mesencephalic aqueduct
What is the obex?
The fourth ventricle narrows at the obex to form the central canal of the spinal cord.
What are the general functions of the telencephalon? What does the telencephalon comprise?
Voluntary control of movement, sensory perception, cognition (the process of learning by integrating sensory input with other behaviours such as memory), behaviour, personality, language, consciousness (awareness of the external environment and in some species of self)
* Telencephalon comprises the right and left cerebral hemispheres that are separated dorsally by the longitudinal fissure. The surface of the hemispheres is composed of grey matter.
What are the basal nuclei?
Accumulations of grey matter dorsal to the rhinencephalon, deep within the hemispheres. The claustrum and amygdala are associated with the limbic system. The caudate nucleus and lentiform nucleus (globus pallidus and putamen) act together with the cerebral cortex and the thalamus in a complex feedback loop to control voluntary posture and movement. These nuceli act by:
1) inhibiting muscle tone
2) selecting and maintaining purposeful motor activity, suppressing useless/ unwanted patterns of movement
3) Helping monitor and coordinate slow sustained contractions, especially those related to posture
What is the thalamus?
Part of the diencephalon.
The thalamus has numerous nuclei and thus forms an important relay and integration centre of the brain.
* Primary site of relay for sensory pathways to the cerebral cortex (except olfaction)
* As well as relay of feedback from the cerebellum and basal nuclei to the cortex, relay of input fromt he limbic system, and from the reticular formation
* It receives modulatory input from the cerebral cortex and other areas.
* It also filters the information that it transmits e.g. via inhibitory interneurons
What is the epithalamus?
* On the dorsal aspect of the thalamus, includes the habenula and the pineal gland.
* The pineal gland secretes melatonin in a circadian rhythm associated with day/night cycle.
* important role in many species in triggering hibernation, sexual maturation, seasonal sexual activity.
What is the subthalamus?
* Located in the lateroventral wall of the third ventricle on either side of the hypothalamus
* Subthalamic nucleus acts as a relay station on the extrapyramidal motor pathway
* Other nuceli link the limbic system with the somatic and visceral motor systems
* Role in posture and movement including rhythmic movement
What is the hypothalamus?
* In the wall of the third ventricle medial to the subthalamus, it has the optic chiasm (CN II) on its ventral surface rostrally and it extends caudally to include the tuber cinerium and mamillary bodies.
* The tuber cinereum gives rise to the infundibulum that attaches the pituitary gland (hypophysis)
* It is a major output control pathway of the limbic system that has connections with the forebrain (other limbic structures), the autonomic nervous system (mainly via reticular areas of the brainstem) and the pituitary gland and controls
1) most vegetative functions- body processes concerned with the maintenance of life- include regulation of heart rate and BP, temperature, body water (thirst, excretion), GI functions (hunger, satiety, feeding reflexes), lactation and uterine contractions
2) Most endocrine functions- through control of the pituitary gland
3) Many aspects of emotional behaviour- rage/fighting, fear, sexual drive
What is the tectum? What does it do?
Comprises the paired rostral and caudal colliculi (corpora quadrigemina) and their tracts.
* The paired colliculi are reflex centres that are responsible for stimulating orientation of the eyes, ears, and head towards the source of visual (rostral colliculus) or auditory (caudal colliculus) stimulus
What makes up the tegmentum? What does it do?
Structures include: white matter tracts, tracts and nuclei of the reticular formation, nuclei of cranial nerves III and IV, the red nucleus (red due to vascularity), substantia nigra (cells are dark due to accumulated pigment)
* Outputs from the red nucleus include the rubrospinal tract, an indirect corticospinal tract (extrapyramidal tract) and the main tract for voluntary movement in domestic species
* Substantia nigra- part of the motor feedback loops between basal nuclei and thalamus- acts to reduce motor activity
What is the crus cerebri?
White matter fibres on the ventral aspect, continuing from the internal capsule of the telencephalon to become longitudinal fibres of the pons (then to pyramids of the myelencephalon)
What is the reticular formation?
A centrally located and extensive network of nuclei through the length of the brainstem. These nuclei are interconnected by ascending, descending, and transverse white matter tracts.
* Also has connections with the telencephalon and spinal cord
* It has connections with all afferent and efferent projection systems and all major integration centres of the brain and is believed to play a role in influencing the activity of these centres
* Ascending reticular activating system- when activated causes arousal/increased alertness, reduced activity, induces lethargy or sleep.
* Descending reticular formation is involved in numerous activities including Upper Motor Neuron function, ANS activity, and reflexive behaviour such as coughing, swallowing, and vomiting
What is the caudal cerebellar peduncle?
What is the middle cerebellar peduncle?
What is the rostral cerebellar peduncle?
caudal cerebellar peduncle- both afferent and efferent fibres- connects cerebellum with vestibular apparatus, hindbrain, and spinal cord
* middle cerebellar peduncle- has afferent fibres only- continuation of transverse fibres of pons from pontine nuclei into cerebellum. Input is from cerebral cortex and rostral caudal colliculi
* Rostral cerebellar peduncle- mainly efferent fibres that project to motor control centres
What is the caudal medullary velum?
The roof of the fourth ventricle on the dorsal aspect
What is the fasciculus gracilis and the fasciculus cuneatus?
Fasciculus gracilis- information from caudal half of the body- runs on either side of the caudal part of the 4th ventricle
* Lateral to this fasciculus is the fasciculus cuneatus- from thoracic limb and neck
* These carry somaesthetic information (e.g. proprioception) and their nuclei will relay this sensory information to the thalamus via the medial lemniscus and also the cerebellum
What are the olivary nuclei?
Relay information from motor centres of the forebrain and brainstem to the cerebellum. Nuclei of the extrapyramidal system project via these nuclei (e.g. pyramidal system projects via pontine nuclei in pons)
What are the vestibular nuclei?
Role in maintaining balance (equilibrium)- receive input from vestibular N (CN VIII), cerebellum, and spinal cord and project to cerebellum (proprioceptive information) eye muscles (vestibuloocular reflexes for eye position) and spinal cord (vestibular reflexes concerned with position of head and body).
What are the cranial nerve nuclei and tracts?
Whilte the point of emergence of each of the cranial nerves can be localized to a particular division of the brain, their nuclei may lie within more than one division.
Certain nuclei of similar function may contribute fibres to more than one cranial nerve. e.g. Nucleus ambiguus- contributes somatic efferent (motor) fibres to IX (glossopharyngeal), vagus (striated muscles of pharynx, larynx, and oesophagus), and accessory/ XI (certain neck muscles)
* Cranial nerves with more than one function receive fibres from more than one nucleus e.g. Oculomotor nerve (III) comprises somatic efferents to certain eyes muscles as well as PS (visceral efferent) fibres to the pupil (pupillary light reflex)
How is proprioceptive sensory information conveyed?
Along long neural tracts from receptors in the limbs and trunk to cerebellum and the cerebrum. The receptors are concerned with body position sense and include the muscle spindles, GTOs, joint angle receptors, tactile and pressure receptors. The impulses are conveyed on peripheral nerves into the spinal cord then to the myelencephalon (via fasciculus gracilis and cuneatus, spinocerebellar tracts). Pathways then split with some going to the ipsilateral (same side of the body) cerebellum for unconscious proprioception. The rest continue up through the brain stem to the thalamus and the sensory cortex of the contralateral cerebral hemisphere for conscious proprioception.
** input from muscle spindles, GTOs, and joints go to the cerebellum and convey info about body posture, muscle tension and length, joint angle- UCP of centre of balance and normal posture
** info the sensory/somesthetic cortex is more concerned with precise knowledge of where and how the limbs are positioned e.g. that the foot is weight bearing on its palmar/plantar surface. The somesthetic cortex receives info in a somatotopic manner. E.g. there are 2 rows of 7 groups of nuclei in the somesthetic cortex of the rat that represent the 14 whiskers on its face. And there are greater numbers of neurons in those parts of the cortex that receive info from areas of the body with particularly important sensory information (SENSORY homunculus)
What is neuron 1 in the corticospinal pathway (pyramidal system)?
* Neuron 1: cell body lives in the primary motor cortex of the cerebral hemisphere- just next to the primary somatic sensory area. (from the cell body the axon passes through the internal capsule into the crus cerebri- the crus cerebri also contains axons of the corticopontocerebellar feed back pathway), the axons of the pyramidal system are divided into the corticonuclear axons (controlling muscles of the head) and corticospinal axons (controlling skeletal muscles of the body), the remaining axons continue to the pyramid after passing underneath the transverse fibres of the pons, then decussate at the level of the medulla oblongata and cross to the opposite side of the spinal cord to form the lateral corticospinal tract)
* Neuron 2: short interneuron within the base of the dorsal horn GM of the spinal cord. IN the case of cranial nerve nuclei this interneuron lives within the nuclei of the CN. In primates sometimes this neuron is missing- to allow more rapid transmission.
* Neuron 3: Cell body is either in the nuclei of a cranial nerve (III, IV, V, VI, VII, or IX) or in the ventral horn grey matter of the spinal cord. Typically this cell is the gamma motor neuron (or fusimotor neuron) but it can sometimes be the alpha motor neuron.
