Brain Lobes and Nervous System

• This is a summary of the brain and nervous system

Left Brain / Right Brain

• The "Spinning Dancer" visual Illusion is a popular but inaccurate test to determine brain dominance.

Brain Lobes and White Matter Tracts

• Lobes are external gray areas of the brain.
• White matter tracts include commissural, association, and projection tracts.
• Commissural tracts link the right and left hemispheres.
  • The corpus callosum is the largest commissural tract.
  • The Corpus Callosum is sexually dimorphic and wider in females than in males.
• Association tracts link anterior to posterior areas, connecting sensory and motor regions within a hemisphere.
• Projection tracts link the cortex to the lower brain.

Basal Nuclei

• Basal Nuclei are the old name of the Basal Ganglia.
• Basal Nuclei are responsible for muscle control and steadying movements.
• They facilitate or inhibit motor functions, aiding in the start, stop, and steadying of movements.
• They smooth out muscle movements, suppress involuntary movements, and coordinate changes in posture.
• Parkinson's Disease is caused by a loss of dopaminergic neurons in the basal nuclei.
• Huntington's Chorea results from an overproduction of dopamine by neurons in the basal nuclei.

Diencephalon: Thalamus and Hypothalamus

• Both are dense with nuclei and have many connections.

Thalamus

• Functions as the relay center, receiving all sensory input except for olfaction.
• Performs crude integration, channeling input to the appropriate areas of the cortex.
• Discrimination occurs at the cerebral cortex.
• All of the cerebral cortex communicates with the thalamus.
• The hippocampus, a nucleus associated with memory, crosstalks with cortical association areas.

Hypothalamus

• The visceral center of the brain.
• Links the neural and endocrine systems.
• It functions as the highest CNS regulator of the autonomic nervous system.
• It is also the highest regulator of the endocrine system.
• Hypothalamic neurons make up the posterior pituitary gland.
• Hormones released by hypothalamic neurons cause the anterior pituitary to release hormones.
• The Hypothalamic Nuclei include control over the circadian rhythm, hunger and satiety, thirst, body temperature regulation.
• It also controls phobic centers which regulate aversion to new experiences.
• It is also regulates Aggression, Sexual Behavior (reproduction), Maternal Behavior including care, defense, and close contact

Limbic System

• It’s The "emotional" brain
• It's a series of nuclei that span the thalamus and the hypothalamus
• Integrates the emotional content of sensory information.
• It's the area that controls basic survival instinct behaviors and puts an emotional overlay on these behaviors.
  • Including fear, jealousy, anger/rage, and love.
• It has intimiate connection with the autonomic nervous system.
• Emotions can override reason because of intimate connection with the autonomic system
• Mechanisms responsible are Norepinephrine, Dopamine, and Serotonin.
• High blood pressure and heart burn are results of these systems being overstimulated
• Emotion induced illnesses are called psychosomatic
• Schizophrenia is an excess of dopamine in the limbic system.
• Drugs treat this by blocking dopamine receptors.
• Depression can be caused by too little norepinephrine or serotonin in the limbic system.
• PROZAC blocks deactivation of serotonin and is called a selective serotonin reuptake inhibitor (SSRI).

Midbrain

• It serves as a relay area
• The Tectum (roof) contains a nucleus at the start of the tectospinal tract.
  • This nuclei controls head and eyeball movements to stimuli.
• The red nucleus is at the start of the rubrospinal tract.
  • This nuclei coordinates muscle and posture

Pons

• It contains the transverse tract connecting the pons and cerebellum.
• Both ascending and descending tracts to/from cerebrum pass through it.
• Also contains respiratory nuclei which control respiration (basic rhythms).

Medulla

• Ascending and descending tracts pass through the medulla.
• Vital centers in this area includes cardiac and vasomotor centers, and the respiratory center.
• Nucleus gracilis which receive fine touch and pressure and proprioception.
• Nucleus cuneatus which synapse points for the fasciculi gracilis and fasciculi cuneatus.
• Vestibular Nuclei connects to the vestibulospinal tract.
• The Reticular Formation controls consciousness, arousal and start of reticulospinal activity.
• The cortex is aroused and brought to the conscious level, so awaking occurs first in reticular formation then cortex.

Cerebellum

• It is known as the mini-me muscle brain.
• It contains 1/2 of the neurons of the brain
• The cerebellum consists of two hemispheres.
• Characterized by a thin layer of gray matter over white matter.
  • It forms wrinkles, gyri and sulci

Cerebellum Function

• Integration of proprioception to coordinate muscle movement
• Inferior part is for sensory input
• A middle "cortex" integrates information.
• The superior part is for motor output.
• Receives instructions from and sends instructions to the thalamus
• It always knows the actual body state.
• Gets a duplicate copy of corticospinal output.
• Compares this to the actual state of the body in updated time.
• Sends accompanying info to muscles on how to effect the desired movement.
• Results in smooth, coordinated movement.

Meninges

• Meninges are membranes that cover the CNS.
• There are 3 layers external to the brain and spinal cord.
• Meninges protect the CNS and its blood vessels, and hold the CSF.
• The dura mater (outermost layer).
• The arachnoid mater is the middle layer.
• The pia mater (innermost layer that comes in contact with the CNS.)

Dura Mater

• The dura mater is tough
• dura mater adheres tightly to the cranium
• Dura mater is a protective sheath of dense connective tissue.
• At the brain, the dura mater has a 2 layered sheet
• The two layers of the Dura Mater are:
  • Periosteal layer (= periosteum of cranial bones).
  • Meningeal layer.
• These 2 layers sometimes split at certain places of the brain.
• Dural sinuses are blood filled sinuses.
• Arachnoid villi project into the sinuses to drain CSF into the venous system.

Spinal Cord Meninges

• At the spinal cord, the dura mater has only 1 layer.
• The epidural space contains fate connective tissue and blood vessels.
• The subdural space is serous.
• The subarachnoid space which contains CSF.
• The arachnoid layer (mater) a net-like (web-like) membrane with no blood vessels

CSF and Choroid Plexus

• Choroid Plexus consists of ependymal cells & pia mater cells
• It is located in the ventricles and produces CSF
• If CSF doesn't drain hydrocephaly occurs which is blockages of the ducts
• Hydrocephaly can occur due to continuous production of CSF needs to drain to venous circulation
• In baby's skulls soft , hydrocephaly can result in bulge of the head
• If there is brain injury cutting off section of skull so bulge out rather than crushing delicate nervous tissue inward
• The spinal cord runs from the brain stem to the 2nd lumbar vertebra.
• It is enlarged (expanded out at bit) at areas of the cervical vertebrae and lumbar vertebra.
• The spinal cord at its end is called the conus madullaris

Spinal Cord Endings

• Coming off the area of the conus medullaris is the cauda equina (Spanish for horse's tail)
• it is the splaying out of the sacral spinal nerves

Peripheral Nervous System

• It made of spinal nerves and cranial nerves
• There are cranial nerves 12 pair which project from Brain
• Spinal nerves that project from Spinal column are 31 pairs
• There are 12 cranial nerves(PR)
  • 10 prs originate on -Brain stem
  • 2 prs originate on brain (CN I and II)

Cranial Nerves

• SOME CN are only sensory function (CN I, II, VIII)
• OTHERS CN primarily motor (USED TO BE THOUGHT TO BE ONLY MOTOR THOUGH NOW CLASSIFIED PRIMARILY AS BECAUSE THERE ARE ILL-DEFINED SENSORY INPUT - e.g. PROPRIOCEPTION/CHEMORECEPTOR/BARORECEPTOR INPUT) (CN III, IV, VI, X, XI, XII)
• OTHERS CN are truly MIXED (WELL-DEFINED SENSORY INPUT AND MOTOR OUTPUT)

Cranial Nerves Functions

I. OLFACTORY (Only Sensory) - olfaction - directly to cortex-temporal lobe II. OPTIC (Only Sensory) – vision –thalamus – occipital lobe III. OCULOMOTOR - (primarily motor) moves eyelid and eye muscle- parasympathetic output - iris with some odd proprioception from eyeball muscle IV. TROCHLEAR - (primarily motor) moves eyeball with some odd proprioception from eyeball muscle V. TRIGEMINAL -truly mixed (LARGEST CN WITH THREE BRANCHES) - Motor Output: action of chewing muscles VI. Trigeminal Sensory Input- Conveys Touch, Pressure, Temperature, Pain (somatosensory) from your eye, most of your face, teeth and tongue (thalamus -parietal lobe) VII. ABDUCENS -primarily motor - moves eyeball - some odd proprioception from eyeball muscle VIII. FACIAL –truly mixed - Controls muscles of facial expression and secretion of tears and saliva (this latter is parasympathetic output); Sensory Input – Taste IX. VESTIBULOCOCHLEAR - only sensory- Equilibrium or hearing to thalamus and then to temporal lobe X. GLOSSOPHARYNGEAL - truly mixed - Output- -Control of muscles of throat and larynx (swallowing) and saliva secretion (parasympathetic) Sensory Input: Taste : Perception of ventilation and BP????? + proprioception: XI. VAGUS - primarily motor - visceral muscle Movement (parasympath). Smooth muscle contraction and relaxation of several visceral structures (airways, esophagus, stomach, small intestine); Decrease HR + secretion Digestive Fluids +sensory Sensations from visceral organs (chemo & BARO) XII. ACCESSORY --primarily motor- swallowing + movements of Head ; proprioception XIII. HYPOGLOSSAL - primarily motor- tongue Movement during Speech and Swallowing; Proprioception

• Spinal Nerves- 31 Pairs
• Project from spinal Column
  • 8 Cervical (C1-C8)
  • 12 Thoracic (T1-T-12)
  • 5 Lumbar (L1-L5)
  • 5 Sacral (S1-S5)
  • 1 Coccygeal (Co1)

Spinal Nerves

• Has sensory Input and Motor output
• Somatic Branches (Anterior & Posterior Branches - both carry Somatomotor output / somatosensory input)
• Anterior Branch– to /from front part of body and appendages
• Posterior Branch –to/ from back part of body
• Autonomic Branch (carries visceromotor and viscerosensory)
• Meningeal Branch-- back and forth from meninges
• Every spinal nerve anterior branch innervates a dermatome except C.1
• Dermatome is an area of skin supplied with afferent nerve fibers going to a single spinal dorsal root All Spinal Nerves have efferent soma to innervate

Receptor Sensory Physiology

• Receptors design of receptor to specific kind of Stimuli
• 1. Receptor Types-
• Mechanoreceptors – sensitive to mechanical Stimulation
• Chang shape and send impulses
• Stretch receptors and BP Regulation
• Organ of corti (ear)- hairs wiggle in response to sound waves
• Thermoreceptors receptors in hypothalalmus and skin stimulated by
• Nociceptors Stimulated by damage done to the receptors and pain
• Photoreceptors– Comes and Rod
  • 5.) electromagnetic Receptors – radiation- light and magnetic field
• Chem receptors – 02, C02, H Na. 7) osmorecepters
• Olfactory
• Act in an example called Weber or Fecher principal
• As magnitude of stimil gets greater the receptors potential
• Gets greater (agraded Potential)
• Feed login and create in stimulus Changes of generate an arthimetic changes in receptor receptor responses graded potentially It change the frequency action Putentials and ands going to the brain

Frequency of Action Potential and Receptors

• Frequency of action potentials reaching the brain determines the amount of the sensation
• Receptor adaptation with impulses from afferent Neurons -Phasic –-Get used to it Same Stumulus over time- responds repidly after does not respond - you get used to use touch your clothes the smells around u. -Tonic –Doesn't get used to it- don't adopt and rapidly

Example of Sensory Synapse Points

• Primary Somatosensory Cortex -Axons of Third order Neurons Thalamus Cerebrum
  • Medial Leuniscus track (Axons of second order eurors)
• Nucleus gracilis
• Nucleus Ceuneats Mediate Oblanga