1. TRANSMISSION OF SIGNALS FROM THE MOTOR CORTEX TO THE MUSCLES Motor signals are transmitted directly from the cortex to the spinal cord through the corticospinal tract and indirectly through multiple accessory pathways that involve the: Basal ganglia Cerebellum Various nuclei of the brain stem
2. Pathways for PAIN
2.1. NEOSPINOTHALAMIC TRACT Neo=New=Modern=Better=FAST therefore Neo>FAST PAIN
2.1.1. A-delta fibers-----Transmits fast pain, MECHANICAL/ACUTE THERMAL.
2.1.2. ACTUAL PATHWAY-Info from A-delta fibers that terminate in lamina I of the dorsal horns → cross the anterior commissure → proceed to anterolateral pathway→ somatosensory cortex.
2.1.3. ★ Probable neurotransmitter is glutamate (excitatory transmitters in the CNS).
2.2. PALEOSPINOTHALAMIC TRACT Paleo=Prehistoric period=Old=Slow, therefore Paleo>SLOOOOOWWWW PAIN
2.2.1. type C pain fibers transmits slow type of pain of the MECHANICAL,THERMAL,AND CHEMICAL KIND but may also transmit some signals from A-delta fibers.
2.2.2. ACTUAL PATHWAY: C fibers terminate in laminae II and III of the dorsal horn (collectively known as substantia gelatinosa) → synapse with Lamina V → cross the anterior commissure → proceed to anterolateral pathway → brainstem (reticular nuclei, tectal area and periaqueductal gray area) → thalamus.
2.2.3. Probable neurotransmitter for slow chronic pain is substance P, lots of this=more pain sensitivity= Hyperalgesia .
2.2.4. “10-25% of the fibers are terminated at the somatosensory cortex when the paleospinothalamic tract is used.”
3. PAIN SUPRESSION/ANALGESIA SYSTEM
3.1. Pain Tolerance or Killer System
3.1.1. The capacity of the brain to suppress pain signals to the nervous system by activating its descending pain control system.
3.2. Components: Periaqueductal gray and periventricular areas of midbrain and upper pons → Raphe magnus nucleus and nucleus reticularis paragigantocellularis located in the lower pons and medulla → Pain inhibitory complex in the dorsal horns of the spinal cord.
3.3. ACTUAL PATHWAY Periventricular nuclei of the midbrain release enkephalin. 1 Enkephalin excites the periaqueductal gray of the midbrain. 2 Sends signal to the nucleus raphe magnus in the lower pons and releases enkephalin. 3
3.3.1. 4Makes AP in the medulla. 5Synapse with the pain inhibitory complex in the dorsal horn of spinal cord and release serotonin. 6Activates the inhibitory interneuron and releases enkephalin.
3.3.1.1. Anterolateral pathway will NOT bring signal to the cortex = NO PAIN
3.4. Enkephalin - believed to cause both presynaptic and postsynaptic inhibition of incoming type C and type Aδ pain fibers where they synapse in the dorsal horns.
3.5. Analgesia system can block pain signals at the initial entry point to the spinal cord. It can also block many local cord reflexes that result from pain signals, especially withdrawal reflexes.
4. Motor Pathways/Descending (in general)
4.1. First Order Neuron Cell body in the cerebral cortex
4.2. Second Order Neuron Internuncial neuron situated in the anterior gray column of the spinal cord
4.3. Third Order Neuron Lower motor neuron in the anterior gray column, with its axon innervating the skeletal muscle through the anterior root and spinal nerve
4.4. • Pyramidal Tract /Corticospinal tract Most important output pathway from the motor cortex Fibers originate from giant pyramidal cells, called Betz cells from layer V of the primary motor cortex, excitatory cell, only inhibitory are the Purkinje cells
4.4.1. Originates: 30% from the primary motor cortex 30% from the premotor and supplementary motor areas 40% from the somatosensory areas
4.4.1.1. Passes through the posterior of the internal capsule between the striatum → down thru the brain stem, forming the pyramids of the medulla → most of the pyramidal fibers then decussate in the lower medulla down the lateral corticospinal tracts (80%) of the cord → terminates principally on the interneurons in the intermediate regions of the cord gray matter
4.4.1.1.1. Few of the fibers do not cross to the opposite side in the medulla but pass ipsilaterally down the cord in the ventral/anterior corticospinal tracts (20%)
4.4.2. Pathway for voluntary, discrete, skilled movements, especially those of the distal parts of the limbs
4.5. CORTICOBULBAR TRACT From areas of motor cortex related to the head and face Descending motor pathway that terminates in the pons and Medulla Composed of fibers that pass from the motor cortex to motor neurons in the trigeminal, facial, and hypoglossal nuclei
4.5.1. Cranial equivalent of the corticospinal tract Responsible for voluntary movement of cranial muscles
5. Descending Pathways from Brainstem (The Reticulospinal Tracts)
5.1. Pontine Reticulospinal Tract
5.1.1. Stimulation has generalized activating effect on both flexor and extensor muscles, with its predominant effect on extensors
5.1.1.1. Stimulation activates extensors, axial and antigravity muscles of the body
5.2. Medullary Reticulospinal Tract
5.2.1. Counterbalances the pontine reticulospinal tract and predominantly inhibits the extensors of the body
5.3. Medial VESTIBULOSPINAL TRACT/Descending Medial Longitudinal Dasciculus
5.3.1. It descends bilaterally through the brainstem and travels in the anterior white columns of the spinal cord where in it terminates on LMN circuit neurons of cervical and upper thoracic levels
5.3.1.1. influences motor neurons controlling the neck muscles, is responsible for stabilizing the head while moving and also plays a role in coordinating head movements with eye movements
5.4. (LATERAL) VESTIBULOSPINAL TRACT
5.4.1. descends ipsilaterally in the anteromedial area of the brainstem and travels in the anterior white column of the spinal cord
5.4.1.1. terminate at all levels of the ipsilateral spinal cord to facilitate the activity of the extensors and inhibit the activity of the flexors
5.4.1.1.1. This tract serves to mediate postural adjustments to compensate for movements and changes in position of the body and to coordinate the orientation of the head and body in space
5.5. RUBROSPINAL TRACT close function with corticospinal tract= lateral motor system when mixed with corticospinal tract.
5.5.1. Originates in the red nucleus in the midbrain and crosses to the opposite side in the lower brainstem before projecting to the spinal cord interneurons and alpha motor neurons
5.5.1.1. Facilitates the activity of flexors and inhibits the activity of extensors
5.5.1.1.1. May play a role in the posture typical of decorticate rigidity.
5.5.2. Serves as an accessory route for transmission of discrete signals from the motor cortex to the spinal cord
5.6. TECTOSPINAL TRACT
5.6.1. travel bilaterally through the brainstem and in the spinal cord and project to the cervical spinal cord where they innervate motor neurons responsible for neck movements
5.6.1.1. for orienting the head and neck during eye movements,
6. BASAL GANGLIA PATHWAYS Direct[Excitatory] Indirect [Inhibitory]
6.1. Direct Pathway
6.1.1. “double negative” in the pathway between the striatum and GPi and the GPi and thalamus, the net result of exciting the direct pathway striatal neurons is to excite motor cortex
6.2. Indirect Pathway
6.2.1. The GPe neurons make inhibitory connections to cells in the subthalamic nucleus, which in turn make excitatory connections to cells in the GPi then the GPi neurons make inhibitory connections to thalamus, then inhibit the motor cortex
7. Input nuclei =striatum Output nuclei =GPI and SNPR All structures in the BG are inhibitory and thus produce GABA EXCEPT SN which is excitatory and produces Glutamate Cortex and thalamus are generally excitatory
8. regulate the vegetative and endocrine functions of the body as well as emotional behavior
8.1. Cardiovascular Regulation stimulation in the posterior and lateral hypothalamus ups arterial pressure and heart rate stimulation in the medial preoptic area downs heart rate and arterial pressure
8.2. Body Temperature Regulation Posterior preoptic area Blood Temp up= ups activity of temp-sensitive neurons Blood Temp down=downs activity of temp-sensitive neurons
8.3. Body Water Regulation Thirsty, Controlled by ADH/Vasopressin secreted by supraoptic nuclei Uterine Contractility and Milk ejection by paraventricular nuclei- oxytocin
8.4. Gastrointestinal and Feeding Regulation lateral hypothalamic area (LAMON) ventromedial nuclei [Butsog] mamillary bodies [feeding reflexes]
8.5. Hypothalamic Control of Endocrine Hormone Secretion by the Anterior Pituitary Gland
9. DORSAL COLUMN-MEDIAL LEMNISCAL PATHWAY
9.1. Phasic sensations (vibratory sensations) ⇨ Sensations that signal movement against the skin ⇨ Proprioception from the joints ⇨ Pressure sensations related to fine degrees of judgment of pressure intensity •Consists mainly of group I and II nerve fibers (large myelinated nerve fibers). Super fast conduction when myelinated and THICC
9.2. 1st order neurons: Dorsal root ganglion
9.2.1. fasciculus gracilis (lower body) or the fasciculus cuneatus (upper body).
9.3. 2nd order neurons: Nucleus gracilis and nucleus cuneatus of the medulla
9.3.1. Nucleus gracilis = G “graceful legs” → lower body Nucleus cuneatus = C “cute arms” → upper body Fascicles – collection of axons of nucleus cuneatus. !!!!!!Axons then decussate to the opposite side and ascend as the medial lemniscus.
9.4. 3rd order neurons: VPL of thalamus
9.5. 4th order neurons: Postcentral Gyrus or Primary Somatosensory Cortex
10. ANTEROLATERAL SPINOTHALAMIC TRACT
10.1. ⇨ Lateral spinothalamic tract – transmits pain, temperature, crude touch, pressure, tickle, and itch. ⇨ Anterior spinothalamic tract – transmits sexual sensation. • Consists mainly of group III and group IV nerve fibers (small myelinated - A delta (Aδ) and unmyelinated nerve fibers - Type C).
10.2. 1st order neurons: Dorsal root ganglion
10.3. 2nd order neurons: Dorsal horn laminae
10.3.1. Only Different part, but identical paths for 1,3 and 4th order neurons
10.4. 3rd order neurons: VPL of thalamus
10.5. 4th order neurons: Post-central Gyrus or Primary Somatosensory Cortex
11. Somato Sensory Complex: Anterior half of the parietal lobe is concerned almost entirely with reception and interpretation of somatosensory signals.
11.1. Signals from all modalities of sensation terminate in the cerebral cortex immediately posterior to the Rolandic fissure
12. SOMATOSENSORY AREAS
12.1. Primary Somatosensory Cortex: BA 3, 1, 2 Somatosensory area I have a high degree of localization of the different parts of the body.
12.1.1. Somatosensory Cortical Representation the somatic cortex(other term for somatosensory cortex—the lips the greatest of all, followed by the face and every part of the hand—whereas the torso and lower part of the body are represented by relatively small areas.
12.2. Somatosensory area II: BA 5 & 7A localization is poor Receives input from the primary somatosensory cortex, thalamus, visual and auditory cortex (to refine the sensation).
13. Cerebral Layers
13.1. Layer I (Molecular Layer)
13.1.1. mostly axon terminals and synapses on dendrites.
13.2. Layer II (External Granular Layer)
13.2.1. mostly stellate cells function as interneurons
13.2.1.1. Found in layers II and IV.
13.2.1.2. “Lola mong superstar na G na G” Superstar (stellate), granny (granular), and G na G (which stands for GABA and glutamate).
13.3. Layer III (External Pyramidal Layer)
13.3.1. Mostly small pyramidal cells.
13.3.1.1. Pyramidal Cells are most abundant 75%
13.3.1.1.1. Excitatory (glutamate and aspartate). Found in layers III, V, and VI.
13.4. Layer IV (Internal Granular Layer)
13.4.1. Mostly excitatory stellate cells
13.5. Layer V (Internal Pyramidal Layer)
13.5.1. Lots of large pyramidal cells
13.5.1.1. main source of cortical efferent to most subcortical regions.
13.6. Layer VI (Multiform Layer)
13.6.1. pyramidal, fusiform,important origin of cortical efferent, those that target thalamic nuclei.
13.7. ------Layers I, II, and III – for intracortical association functions. ------Layers IV – where most incoming sensory signals terminate. ------Layers V and VI – where most of the output signals leave the cortex going to the brainstem and spinal cord (Layer V) and going to the thalamus (VI).
14. Cerebral Dominance
14.1. Right-handed individuals - the left hemisphere is dominant in 90 to 95%. Left-handed individuals The left hemisphere is still dominant 60% of the time. There is co-dominance in about 15%.
14.1.1. Dominant hemisphere functions: Handedness (“Left hemisphere is responsible for right side and vice versa because of decussation”) Perception of language (Wernicke) Speech (Broca) Mathematical ability (Broca)
14.1.1.1. The right hemisphere is dominant in facial expression, intonation, body language, and spatial tasks.
14.1.1.2. The left hemisphere is usually dominant with respect to language, even in left-handed people. Lesions of the left hemisphere cause aphasia.
14.1.1.2.1. The left cerebral hemisphere is dominant for language in almost all right-handed persons and in more than two-thirds left-handed persons.
14.1.2. Nondominant hemisphere functions: Spatial perception Recognition of faces, forms, and body images Music interpretation
14.2. Classification of Memory
14.2.1. Short-term (now)
14.2.1.1. Continuous sensation, reading a notepad then dictating the content
14.2.2. Intermediate (recent)
14.2.2.1. Reviewing for an exam
14.2.2.1.1. Chemical change
14.2.3. Long-term ( past)
14.2.3.1. Pointing out that you used to ride a bike
14.2.3.1.1. Explicit: Episodic (Autobiographical) Semantic (factual)
14.2.3.1.2. Implicit: Classical Conditioning
14.2.3.1.3. Procedural: Muscle Memory
14.2.3.1.4. ACTUAL PHYSICAL CHANGE Increased transmitter vesicles released. Increased presynaptic terminals. Dendritic spine structure changes that permit transmission of stronger signals.
14.2.3.2. Retrograde Amnesia, Can form new memories, can't remember old ones due to DAMAGE TO THALAMUS since its job is retrieving memory
14.2.3.3. Anterograde Amnesia, Procedural Memory Intact, "Stuck in the PAST" due to Damage to HIPPOCAMPUS which converts SHORT-TERM into LONG-TERM
15. Hypothalamus
16. Reticular Activating System
16.1. Mediates consciousness and the waking state
16.1.1. Non-REM sleep (NREM sleep) o Stage 1 (5%) Theta rhythm o Stage 2 (45%) Sleep Spindles and some high-voltage K waves o Stage 3 [delta rhythm] & 4 (25%) [LARGE WAVES] Rapid Eye Movement Sleep (REM sleep) (25%)
16.1.1.1. REM Sleep, absent if super sleepy, Every 90 mins and lasts for 5-30mins
16.1.1.1.1. more rested=longer REM less slow wave sleep and more REM towards the morning
16.1.1.1.2. Autonomic changes
16.1.1.1.3. Postulated that large acetylcholine neurons in the reticular formation might be responsible
16.1.1.1.4. Paradoxical sleep, according to EEG similar to EEG of an awake person with alpha and beta waves, difficult to wake them up