13. CNS-1-GM_2024-25

Main Features of Structure and Function of the Nervous System

• The nervous system has two principal cell types: Neurons and Supporting cells.

Cell Structure

• Neurons' structural makeup includes dendrites, perikaryon, cell body, nucleus, axon, and telodendria.
• Perikaryon is the cytoplasm surrounding the nucleus in a neuron.
• Dendrites receive information.
• Axons transmit information.

Neurons - Body

• Body contains cell organelles
• Body is the site of metabolic processes

Neurons - Dendrites

• Receive information
• Modulate postsynaptic potential

Neurons - Axon

• Transmit information away from the neuron's body
• Axon has an initial segment
• Transport of substances to the distal axon
• Can be myelinated
• There is a synaptic knob -- an expanded area containing synaptic vesicles

Neuron Types - Structural

• Neurons vary structurally dependent on the number of processes extending from the cell body.
• Bipolar neurons have two processes (one dendrite, one axon), are rare, and exist in special sensory organs.
• Multipolar neurons have many processes and make up 99% of neurons.
• (Pseudo)unipolar neurons have one process and are associated with DRG and sensory ganglia.

Neuron Types - Functional

• Sensory neurons are afferent and transport impulses to the CNS. They're mostly unipolar, sometime bipolar, and dendritically release neurotransmitters.
• Interneurons, also called link neurons, are association or internuncial neurons. Multipolar, they are located in the CNS.
• Motor Neurons are efferent and transport impulses from the CNS to effectors. These are multipolar.

Neuron Relations

• Connection, or the transmission of information, between neurons occurs at a synapse.
• Divergence is when one neuron axon diverges into multiple nerve endings, making synapses with several neurons to spread stimulation.
• Convergence occurs when multiple axons converge on a single postsynaptic neuron, summing contributions of presynaptic elements.

Impulse Transmission Regulation

• Spatial summation, presynaptic (increased released mediator), and postsynaptic activity can all facilitate impulse transmission.
• Presynaptic (decreased released mediator), postsynaptic, and feedback activity can inhibit impulse transmission.

Impulse Transmission Regulation - Recurrent Inhibition

• Recurrent inhibition, or feedback inhibition, protects the neuron (or effector) from excessive activity.
• A collateral connects to an inhibitory interneuron, which suppresses a presynaptic neuron.
• An example is the motor neuron which has an inhibitory Renshaw cell

Impulse Transmission Regulation - Forward Inhibition

• Forward inhibition is when a collateral connects to an inhibitory interneuron, which suppresses a postsynaptic neuron.

Impulse Transmission Regulation - Reciprocal Innervation

• Reciprocal innervation involves simultaneous agonist activation and antagonist inhibition, or vice versa.

Impulse Transmission Regulation - Reverber Circuit

• Reverber circuits cause recirculation of action potential with prolonged stimulus and memory trace.

Supporting Cells in Nervous System

• Neuroglial cells include astrocytes, oligodendrocytes, microglia, and ependymal cells.
• Supporting cells make up half the volume of the nervous system, are nonexcitable, and they control the chemical environment and segregate and insulate neurons.
• Supporting cells provide supportive scaffolding for neurons, promote health and growth, and guide young neurons to connections.
• Supporting cells are essential to the survival and function of neurons. They vary in the CNS and PNS.

Supporting Cells in CNS

• These include astrocytes, oligodendrocytes, microglia, and ependymal cells.
• Astrocytes are supporting cells in the CNS.
• Oligodendrocytes myelinate CNS neurons.
• Microglia clean up pathogens and cellular debris.
• Ependymal cells line the cerebral ventricles.

Astrocytes

• Astrocytes make up 20-40% of all supporting cells.
• There are more astrocytes than neurons in the cortex.
• Astrocytes have local subpopulations.
• They make up part of the BBB
• Regulate CSF composition
• Function in glucose metabolism.
• Astrocytes maintain a stable environment
• They play a role in the pathophysiology of several diseases, such as multiple sclerosis and Alzheimer's disease.

Astrocytes and Neurotransmission

• Astrocytes electrically insulate neurons.
• With a tripartite synapse, astrocytes provide a barrier against spread of transmitters, and recycle transmitters.
• Astrocytes express receptors that detect synaptic activity of neurons.
• They release substances that modulate the excitability of neurons, both pre- and post-synaptic

Astrocytes and Potassium Spatial Buffering

• Astrocytes are part of the mechanism for the regulation of extracellular concentration of K+ in the brain.
• Electrical activity of neurons increases the K+ concentration in the extracellular fluid.
• Excess K+ is taken via membrane channel to via gap junction to other astrocytes, to perivascular spaces or to area with lower neuronal activity.
• They keep extracellular K+ at levels preventing interference with normal propagation of an action potential.

Astrocytes and CNS Metabolism

• Glucose goes through the capillary endothelium into astrocytic end feed
• Lactate is generated in astrocytes and shuttled into neurons
• Glucose is stored in the form of glycogen.
• Glucose and lactate exchange occurs between glial cells through gap junctions.

Supporting Cells in PNS

• Schwann cells form comprise myelin sheath and cover a small segment of the axon and envelop unmyelinated axons.
• Satellite cells are present in ganglia and regulate the chemical environment.

Components and Divisions of the PNS

• The PNS is divided into Afferent and Efferent divisions.
• Afferent includes somatic, visceral, and special sensory.
• Efferent includes somatic and autonomic motor, with the autonomic including sympathetic, parasympathetic, and enteric systems

Peripheral Nervous System

• The PNS transmits signals between the CNS and receptors and effectors.
• The PNS includes ganglia (sensory, autonomic) and nerves (axons grouped into bundles).
• 43 pairs - 31 pairs of spinal nerves and 12 pairs of cranial nerves
• Spinal nerves contain both afferent and efferent fibers.
• Cranial nerves contain mostly afferent fibers

Spinal Nerve Anatomy

• Dorsal (posterior) horn location.
• Lateral horn contains preganglionic parasympathetic or sympathetic neurons.
• Ventral (anterior) horn contains motor neurons.

Cranial Nerves - I - VII

• CN I, the olfactory nerve, is sensory for olfaction.
• CN II, the optic nerve, is sensory for vision.
• CN III, the oculomotor nerve, is motor for eye, pupil, and lens movements.
• CN IV, the trochlear nerve, is motor, and rotates the eye downward.
• CN V, the trigeminal nerve, is mixed, for biting and chewing movements plus sensory data from the palate, teeth, gums, face, and cornea.
• CN VI, the abducens nerve, is motor, for lateral eye movements.
• CN VII, the facial nerve, is mixed, for facial expression and salivary gland secretion, taste and sensory data from the external ear.

Cranial Nerves IX - XII

• CN IX, the glossopharyngeal nerve, mixed, for speech, swallowing, salivation of the parotid gland, blood pressure of the carotid sinus, blood gases from carotid body, taste, and sensory data from tongue and external ear.
• CN X, the vagus nerve, is mixed, innervating speech, swallowing, heart rate, stomach motility, abdominal and thoracic visceral sensation, blood pressure of the aortic arch, blood gases from the aortic body, taste, and sensory data from tongue and external ear.
• CN XI, the spinal accessory nerve, is motor, for head movement.
• CN XII, the hypoglossal nerve, is motor, and controls tongue movement

Somatic vs Autonomic Nervous Systems

• The Somatic Nervous System (SNS) controls skeletal muscles and the body's conscious and subconscious movements.
• The Autonomic Nervous System (ANS) mostly controls visceral functions largely outside our awareness.

SNS vs ANS: Neuron Chains

• SNS has one neuron chain from the CNS to effector organs whereas ANS has has two neuron chain from the CNS to effector organs

SNS vs ANS: Effector Organs and Effects

• The SNS innervates skeletal muscle, using ACh to activate stimulatory effects.
• The ANS innervates smooth muscle, glands, and cardiac muscle; the effects vary dependent on type of neurotransmitter and receptors on effector organs.

CNS Components

• The brain and spinal cord are components of the CNS.
• Brain regions include the brainstem, diencephalon, cerebellum and cerebrum
• The spinal cord runs vertically and the CNS. Brain sits at the top

Spinal Cord

• The spinal cord is located within the bony vertebral column.
• The spinal cord contains grey and white matter. Grey in the shape of a butterfly, central

Spinal cord - Grey Matter

• Grey matter is butterfly shaped, contains interneurons, cell bodies of efferent neurons, and entering axons of afferent neurons and glial cells.

Spinal cord - White Matter

• White matter surrounds the gray matter.
• Transmits information between brain and periphery
• Site of spinal cord reflexes
• Generates rhythmic movement

White Matter in Spinal Cord

• Fibers run ascendly, descendly, and transversely
• Divided into posterior, lateral and anterior funiculi (columns)
• Each funiculus contains multiple fiber tracts named after their origin and destination and also are composed of axons of similar functions
• Pathways decussate
• Exhibiting somatotopy, or precise spatial relationships
• Pathways are paired

Spinal Cord Pathways - Afferent

• Afferent pathways includes Dorsal, Cuneate and Gracile Fasciculus tracts
• Cuneate fasciculus -- Discriminative touch and proprioception from the upper body
• Gracile fasciculus -- Discriminative touch and proprioception from the lower body

Spinal Cord Pathways - Efferent

• Lateral and Anterior Corticospinal Tracts
• Lateral horns for Origin of preganglionic sympathetic fibers
• Motor neurons in the ventral horn
• Vestibulospinal Tract that stimulates extensors of trunk and lower limb as well as flexors of the upper limbs.
• Reticulospinal Fibers are crossed and uncrossed for both unskilled and involuntary movements

Organization of Spinal Cord

• Inner segment is somatotopically organized meaning there is a precise spatial relationship of each of fibres going to the spinal cord tract.

Brain Information

• The brain contains almost 97% of the body's neural tissue, with the average weighing about 1.4 kg.

Brain Regions

• Four Key regions include: Brainstem, Diencephalon Cerebellum and Cerebrum

Brain - Brainstem

• Medulla houses sensory afferent nuclei, the reticular activating system, and visceral control centers.
• Pons and midbrain house the reticular activating system and visceral control centers.

Brain - Diencephalon

• Diencephalon structures: thalamus and hypothalamus.
• Neuroendocrine control (statins and liberins; ADH and oxytocin)
• Hypothalamus includes regulations for hunger, food intake, thermoregulation etc

Diencephalon - Thalamus

• Thalamus information: relays information between cerebral cortex and midbrain, has several nuclear groups, and also has functions including sensory and motor signaling

Thalamus - Nuclear Groups

• Specific sensory relay nuclei
• Nuclei concerned with efferent control mechanisms.
• Nuclei concerned with complex integrative functions
• Nonspecific projection nuclei

Thalamus - Specific Sensory Relay Nuclei

• Relay and process sensory information, with every system represented except olfaction.
• The visual system relays to lateral geniculate nucleus, with fototopic organization, leading to visual cortex.
• Auditory system relays to media geniculate nucleus and is the Key relay point between the inferior colliculus of the midbrain and primary auditory cortex.
• Somatosensory system has a ventral basal complex sending touch and proprioceptive information to the cortex, including VPL from medial lemniscal and spinothalamic pathways, and VPM from the trigeminothalamic tract.
• Taste relays parts of the VPM, receives inputs from the solitary nucleus, and projects to the far lateral aspect of postcentral gyrus bordering the Sylvian fissure.
• Vestibular relays take parts of the VPM or VPL nucleus then relayed to the postcentral gyrus.

Thalamus - Efferent Control Mechanisms

• The ventral anterior and ventrolateral nucleus - concerns motor function.
• Receives inputs from the cerebellum and basal ganglia and also have outputs to primary motor cortex, premotor cortex and supplementary area
• Essential for normal motor functions; loss of feedback results in motor dysfunctions

Thalamus - Integrative Functions

• Lateral posterior thalamic nucleus.
• Receives input with the parietal lobe and gives outputs to superior parietal lobe in areas 5 and 7 of the brain
• Allows for complex sensorimotor integration
• Helps program the sequences of motor responses involved in complex motor processes

Thalamus - Nonspecific Functions

• Receive Inputs: RF or Reticular Formation
• Outputs with specific and association thalamic nuclei and wide regions of the cerebral cortex
• Projections that are not topographically organized
• Function: modulation of the activity of cortical neurons and alteration of cortical excitability levels.

Thalamus Relationships

• Association and nonspecific thalamic nuclei share reciprocal connections with the cerebral cortex and this is a basis for feedback mechanism
• These basis from the cortex to the thalamus helps to control the amount of information that reaches a specific region of cortex at any given moment

Brain - the Cerebrum

• Cerebrum Basal ganglia
• Cerebral cortex
• Composed of primary motor and premotor areas and the motor and prefrontal areas
• Cerebrum + diencephalon allows for the forebrain which supports primary olfactory, lateral sulcus, auditory, and sensory speaking functions

Nervous System Principle Functional Unit

• The reflex is the basic functional unit
• Response of organism to receptor stimulation
• Mediated by a reflex arc movement or activity of the body performed automatically and without conscious decision

Reflex Arcs

• The reflex arc includes the receptor, afferent neuron, center, efferent neuron, and effector.

Classifications of Reflexes

• Number of synapses (monosynaptic, polysynaptic)
• Receptor includes exteroceptive, proprioceptive, and interoceptive
• Effector consists of somatic and visceral (autonomic)

Cerebrospinal Fluid System (CSF)

• This system includes all of the body and components of CSF
• Helps in bodily functionality

Characteristics of Cerebrospinal Fluid

• CSF: clear, sterile, colorless fluid
• Volume: 150 ml
• Surrounds and bathes the CNS
• Ventricles of the brain, the central canal of the spinal cord, and the subarachnoid space.
• The brain floats in it!

Cerebrospinal Fluid Production(CSF)

• Produces 500ml per day
• At the choroid plexus (70%) and brain parenchyma
• Process consists of the choroid plexus allowing fluid to filter of into plasma ultrilfiltrate, the process which allows the sodium to actively transfer across the choroidal cells into the CSF which then allows for water to carry-on through the transfer
• Cholinergic stimulation increases production
• Adrenergic stimulation decreases production

CSF Composition

• Na+: CSF (150 mmol/l), plasma (140 mmol/l)
• K+: CSF (2-3 mmol/l), plasma (4.8 mmol/l)
• Ca++: CSF (1.1-1.25 mmol/l), plasma (2.3 mmol/l)
• Mg++: CSF (2.3 mmol/l), plasma (1.1 mmol/l)
• Cl-: CSF (115-130 mmol/l), plasma (108 mmol/l)
• Lactate: CSF (1.1-2.0 mmol/l), plasma (1 mmol/l)
• Proteins: CSF (0.1-0.4 g/l), plasma (63-83 g/l)
• Glucose: CSF (2.2-4.2 mmol/l), plasma (3.3-5.6 mmol/l)

CSF Functions

• Maintains homeostasis as a chemical buffer and transport for all substances.
• Mechanical protection for CSF, preventing brain compressive gravity against the skull
• Allows shock absorbance
• Allows intracranial volume changes

CSF Circulation

• The CSF has circulation
• It moves through the different parts of the brain

CSF Absorption

• Done so by: Arachnoid villus - a diverticulum of the subarachnoid
• Which is thin cellular layer covered by the endothelium of the venous sinus and has project dural venous sinuses
• And grouped together it forms arachnoid granulations

Collection of CSF

• Via lumbar puncture
• Where cerebral spinal fluid is collected

Blood Brain Barrier (BBB)

• Maintains a stable environment for brain
• Includes: small molecules (H2O, O2, CO2, NH3, ethanol), lipid soluble molecules (steroid hormones)
• Utilizes Transport such as: Glucose
• Prevents waste, proteins from entering brain tissue

Blood Brain Barrier (BBB): Properties

• Continuous endothelium and tight junctions.
• Reduces pinocytosis
• Utilizes the "feet" of the astrocytes
• Includes thick basal lamina

Circumventricular Organs

• Has extensive vasculature and highly permeable capillaries
• BBB-free areas are located in brain
• Control through compositions of zone control called chemoreceptor zones and hormones to be transferred
• Includes functions subfornic to pineal gland.

Blood-Cerebrospinal Fluid Barrier

• At the choroid plexus
• Similar to BBB
• More permeable than BBB
• allows movement of all substances allowed by BBB.

Metabolism of the CNS

• Glucose is the basis for aerobic metabolism
• Extraordinary sensitivity to oxygen support
• Big intensity (brain weight - 2% of t. b. w., energetic turnover 20%)
• For Sustaining synaptic transmission, neuronal survival and information processing

Energetic Substrate

• Main Energetic Substrate of CNS includes: Glucose and some metabolic intermediates which shuttle into neurons
• After Starvation (weeks)-Ketone bodies in CNS allow astrocytes of ketone bodies.
• Neurons require support to be converted

Electrical Activity of the Brain and Neocortex Organization

• Outer layer cerebral hemispheres. Has grey matter (neuronal cell bodies & unmyelinated fibres). and with two types of neurons (excitatory pyramidal neurons = ∼ 80% neocortical neurons & inhibitory interneurons = ∼ 20%).

Neocortex Organization and Layers Information

• There are six labeles from I outward to innermost layer VI
• The neocortex Is the largest part of the cerebral cortex ( along with the archicortex & paleocortex - cortical parts of the limbic system)
• In humans, higher functions

Neocortex Activity Recording

• Through Electroencephalogram (EEG) and Functional magnetic resonance imaging (fMRI)

EEG

• Electroencephalogram (EEG) :Means of recording cortical activity for electrical waves.

EEG - Recorded Summation

• Is the summation of the postsynaptic potentials that is from a large number of neurons (this will determine what electrical activity to the cerebral cortex

EEG Recording Assessment Leads

• Can have unipolar or bipolar Electrodes and on the scalp, or ECo in cerebral cortex Variables Includes: Amplitude and Frequency

Properties of Amplitudes

• Measured in Microvolts or higher
• Vary from 0.5 to 100
• Indicates how much electrical activity of the type a signal may carry for a given instance of a recording

Frequency

• Frequency can vary and measure in Hertz

EEG Rhythms

• Alpha Theta Delta , beta and theta levels of activity in the brain determines what these signals are based on each actual person.

EEG Rhythm - Attention

• The greater the person's attention ( lower Alpha activity), the more EEG increases to
• The greater the mental effort, the higher the delta increase activity

EEG Recordings when measuring for different functions

• EEG stable, tested variable with flex under specific circumstances.

EEG - Waking State Alpha Rhythm

• In a relaxed state with closed eyed adults, waves measured between 8 -13 hartz to 5-100mV

EEG - Alerts and Rapid Movement Beta Waves

• Alert states that includes rapid eye movement measures with a fast rate. Frequency >14 Hz, amplitude 2-20 mV. Is the most prominent in frontal region

Delta Waves

• Slow and low Hz (0.5-4), with high Amplitude (20 uV)., during deep sleep
• (Physiological Present, 1-3 old , sleepy) Brain Oedema.
• (Pathological present, during epilepric stroke)

Theta Rhythm

• Medium waves, with 5 -7 Hz, Amplitude for sleep or high levels frustration.

Open Brain and Arousal

• Opening of the eyes, leads to concentrations of mental focus where alpha is placed.

Evoked Cortical Potentials

• This tests electrical function of the brain -Includes testing different cortical functions such as: Sensors and the Motor movements in function.

Clinical Uses of EEG

• Diagnose conditions of Brain: Tests like: -Coma -Brain Death -Encephalitis

Consciousness and Behavior

• The phenomenon that includes: - Full Attention levels ,Purposefully for every activity.

Consciousness Components of Awareness

• Includes - Awareness that includes: - Imaginations/Internal Thoughts + External Senses" And Arousal as states

Arousal (Levels states of Conciousness)

• Physiological - Transcendent: -States such as : Comas and Drug/Medicine levels"

Glasgow Coma Scale

• Evaluates a patient ability to have an eye, motor and verbal response

Wakefulness

• Involves activation from reticular formation and is regulated from transition

RF Reticular Formations

• Helps discriminate information which is key or irrelevant.

Rf controls and Functions in the Somatic system

Includes functions that is a central signal for rhythms: Functions with the eye signals in relation to movement and the signals in which allow for you to breather rhythmically.

Functions of Rf includes for Cardiovascuar System and Pain

Includes both - The Cardio function for Medusa of brain + Allowing pain

Coma to Levels of Consiocusness

• Levels Include : Normal Sleep Cycle / Lethargic Stupor, that leads to Comatose States.

Sleep Function

• Altered state of cycles, which allows you to restore.

The EEG for Sleep

EEg is slower with high frequency with high amplitude,

Sleep Types of REM

• Includes No REM + Fast and high functions

Non Rem, Slow waves, High Low Frequency

• Slow wave cycles without fast eyes, with 4 states including what is around us"

- Sleep and stages in REM

"Sleep Cycles: Fast functions and fast cycles ( Low Thresh, Fast Frequency, Inaccurate Muscle and Brain. )"

REM sleep Cycle information

• Allows 20%, with long irregular waves that have fast activation
• "Erection and arousal during the process" and "High thresh"

Sleep Onset

• " "Neurons ,promoting " ( Preoptic- Lateral Hypothalamus)

Arousing Functions during sleep

• Activation during sleep, is known to stop those arousal during REM , as sleep states

REM Information for Brain

" Allows brain, for REM activity "Allows the body to recover with the process of memorization and resting the cycle for it"

EEG Information on sleeping states (Types in table)

• Beta (Alert)
• Alpha (Relax)
• Theta- Delta (Low sleep states)
• Rem ( Brain alert)

"Normal sleeping, cycle pattern information"

• Allows REM to cycle in the middle of each state and start back from the start"and cycles in 30-45 Allows baby to sleep, where senior with old age, may need more cycles"

Sleeping Habits for Elderly

• Older citizens do not get as much sleep, so it changes with age levels

Functions of Sleep cycle

"Includes Internal and External, cycles, that have connection to all levels of functions

"

Biological Function

• Helps stabilize the rhythm in cycles and hormones of certain parts for levels of hormone signals"

Melatonin Functions

"" Hormones, low with high activity and helps the cycles to signalize body to function. Has low- High cycles

"

Problems in Cycling in Brain"

• Creates disruption in brain
• Can cause illnesses due to changes in the hormones"

Cognition and Sensories

"Process and focus on memory by using : --Sensory --- Integrations --Motor skills ""

Levels Of Cognition

• Process and use: attention, memory, reason for decisions."

Cognition levels of learning "Includes

• Attention , Learning+ memory , thought"

Limbic , Learning Information

• Process , emotions with information"

Unimodal Association Areas

• Close and sensory information functions and associations of unimodal"

Associations between Memory

• Brain has junction links between them

What makes us know what is around us and information

• This is processed with all tools we have that functions Memory
• Can vary: (Spatial and Naming)"

Area destruction and Information

• Can't focus, Can't understand and process memory, and make conclusions."

Networks of the Brain for connections

"" Includes -Cortical
Comissional"

Cognitive Processing

• In the symbolic process, uses memories and instruments to formulate with memory for : : Processing information" plan and think" language"

Memory Impairment

-Includes: Inability for recall memory processes+ memory levels"

Cognition - Loss of Memory

-Can't be identified- as information lost or the connection/ path ways"

Agnoisa (Inability for Processing Information. )

" Includes faces names or not knowing what is really"

Neglect"

Neglects: The Hemisphere and awareness of body and envioroment

-Deficit of attention with lack of body and movement.

Apraxia "

• No Memory to move and do what is asked with no sensory information"

Damage with Functions related to information

""

Brain and Frontal Destruction Functions

"- Destruction Impairs the function to respond to spatial activity"

Spatial Response destruction and Cognitive activity

"" Has a domino effects, that leads to other cognitive effects Brain is limited and connected to these systems"

Distruption or Damage for Frontal

• Schizophrenia and disorders that impair dopamenergic transmmiton

What is Dominant with brain hemispheres:

• One sides function over comes another for right function than the left. for all types of functioning"

Morpohoglic Brain Asymettry

• Brain shape - planum shapes for more use for side"

Asymmetrical functions

Functions : Analysis + Creativity for the art and music side

Symmetry Asymmetry & Differences

Hemisphere side of functioning controls functions over other handers side"

Hemmishpere Dominancy

• Most 96% population functions with left for right body funtions.

"

Primary Language Area for function

• Limbic and prefrontal lobes function before and after the brain "

Area of the Brain during Language" And Functions

• Includes BOCA for Motor - Wernike for process" - and Auditory function and how the brain hears it."

Damage to Memory

"Boca - Hard to speak,

wernicke- Hard to process what's said"

Memory Loss"

• Includes - Memory process

"

What happens to the process with brain Damage "

Loss of the ability and how we remember (Memory process)"

Alxeia

• Inhibit of brain and understanding writting.

Angorphia

Inhibit of writing with hands for what functions.

Learning " - Deficits.

: Inhibit with dyslexia and other skills"

Emotions

• How we show expressions and thoughts.