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Organization of the Nervous System

• The nervous system is divided into the central nervous system and the peripheral nervous system
• The central nervous system consists of the encephalon (brain, brainstem, cerebellum) and the spinal cord
• The peripheral nervous system includes the sensory and motor peripheral nerves
• The autonomic nervous system controls the body's autonomic functions like heart rate, breathing, digestion, and urination, sharing fiber tracts with both the CNS and PNS
• The sympathetic nervous system increases autonomic functions, associated with "fight or flight"
• The parasympathetic nervous system decreases autonomic functions

Functional Organization

• The functional organization includes sensory, integrative, and motor divisions
• The sensory division (receiver) receives sensory information such as tactile, proprioceptive, visual, auditory, olfactory, gustatory, and vestibular, reporting the body's state and its environment
• The integrative division (processor) integrates sensory input and motor output to cause desired responses, providing higher order brain function including perception, decision making, thinking, attention, language, emotion, and memory
• The motor division (effector) responds to orders of other divisions, controlling bodily activities

Levels of the Central Nervous System

Spinal Cord Level

• The spinal cord level acts as an intersection, conducting sensory and motor signals bidirectionally between the PNS and CNS
• The spinal cord is the center for processing basic motor and sensory information
• Reflexes at the spinal cord level can work without the need for higher level processing
• Motor reflexes include the stretch reflex, Golgi tendon reflex, and withdrawal reflex
• Reflexes that control internal organ function are also processed at this level, these relate to blood vessels, gastrointestinal functions, and urination

Subcortical Level (Lower Brain)

• The subcortical level controls subconscious body activities such as equilibrium, movement modulation, arterial pressure, respiration, heart beats, feeding reflexes, body temperature, wakefulness, sleep, and hormonal regulation
• The subcortical level contains the brainstem (medulla and pons), mesencephalon, thalamus, hypothalamus, basal ganglia, and cerebellum

Cortical Level (Higher Brain, Telencephalon, Cerebral Cortex)

• The cerebral cortex is the superficial layer of grey matter, 2-4mm thick
• The cortex rarely functions alone, usually in association with lower centers (subcortical and spinal cord)
• The cerebral cortex is key for the most complex and sophisticated functions of the nervous system, such as information processing, memory formation, decision making, thoughts, and emotions
• The cerebral cortex is divided into two hemispheres (left and right)
• Each hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital
• The frontal lobe handles motor functions (precentral gyrus) and higher mental functions like executive function and attention
• The parietal lobe area handles somatosensory functions (postcentral gyrus) and higher mental functions, giving a sense to sensory information
• The temporal lobe is the area of auditory functions and memory formation and storage
• The occipital lobe is the area of visual functions

Somatosensory Axis of the Nervous System

• The somatosensory system transmits somatic (body) information from the body's periphery (skin, muscle, bone) to the CNS
• Somatic information is transmitted to the spinal cord, brainstem, cerebellum, thalamus, and cerebral cortex (somatic areas)

Motor Axis of the Nervous System

• The motor system responds to integrative and sensory divisions
• It controls body motor activities, both skeletal (striated) and smooth muscles (internal organs, heart, stomach)

Neuron Structures

• A neuron is the basic functional unit of the nervous system
• There are more than 100 billion neurons in the nervous system
• It is an electrical cell, generating and transmitting electricity
• Neurogenesis is the formation of new neurons, which is possible but slow
• Components of a neuron: -Cell body (soma): It's the main body of the neuron where the nucleus is found and it is responsible for signal processing -Dendrites: Projections of the soma that act as signal inputs -Axon: Extends from the soma to the synaptic terminals and provides signal outputs, sending signals to other neurons

Types of Neurons - Anatomy

• Multipolar Neurons:
  • Multiple processes with several dendrites and one main axon on different sides of the soma
• Most common cell type (motoneuron, purkinje cell)
• Bipolar Neurons:
• Two processes with one main dendrite and one main axon on different sides
• Found in the retina, inner ear, and olfactory system
• Unipolar Neurons:
• One process with a dendrite and axon on the same side
• Photoreceptors in the retina (rods and cones)
• Pseudo - unipolar neurons:
• One process with a dendrite and axon developing on the same process but on opposite sides
• Sensory neurons of the spinal cord

Types of Neurons - Functions

• Afferent Neurons:
• Send signals to the spinal cord and brain; sensory input = sensory neurons
• Efferent Neurons:
• Send electrical signals from the brain and spinal cord to the periphery; motor output = motor neurons
• Interneurons: Located in local circuitry between sensory and motor neurons (integration)
• Neurons are interconnected; each neuron is connected to up to 1000 neurons = neural network
• A synapse is the point of communication between two neurons

Glial Cells

• They don't participate directly in electrical signaling or synaptic transmission
• They have supportive functions, helping define synaptic contacts, maintain signalling abilities, and defend neurons
• Types of Glial Cells:
• Astrocytes: Maintain a good chemical environment for neuronal signalling and secrete substances that influence the formation of new synaptic connections
• Oligodendrocytes: Produce myelin around the axon in the CNS to maintain signaling abilities of the neuron
• Schwann Cells: Produce myelin around axon in the PNS to maintain signaling abilities of the neuron
• Microglia: Responsible for immune function, consuming cellular debris, bacteria, and dead cells, and secreting signalling molecules that modulate local inflammation and influence cell survival and death

Electrical Potentials of Neurons

• The generation of electricity is a specific feature of neurons (also found in muscles)
• Neurons have a high density of ion channels that allow them to control the flow of different ions and generate action potentials (potential difference)
• Neurons generate electrical potentials (signals) to transmit information throughout the brain and body

Four Types of Membrane Potential

• Resting Membrane Potential (Vm): At a resting state (no stimulus); results from a polarization of the plasma membrane (potential difference); always negative (-90 mv to – 70 mv)
• Action Potential: Results from transient changes in the membrane potential of a stimulated neuron; an electrical signal that travels along the axons; long range transmission of information within the nervous system
• Receptor Potential: Results from transient changes in the membrane potential of a receptor of sensory neurons by external stimuli (receptor is stimulated)
• Synaptic Potential: Results from the communication of signals between neurons at the synaptic contact; recorded at the postsynaptic neuron by the stimulation of the presynaptic neuron

Resting Membrane Potentials

• At rest the neuron is polarized; the inside (intracellular) of the membrane is more negative than the outside
• The recorded potential is between -90 and -70 mv, which is the resting membrane potential (voltage)
• Vm is caused by a difference in the concentration of ions outside the cell and inside the cell
• At the resting state, all voltage gated sodium (Na+) channels and most voltage gated potassium (K+) channels are closed
• At the Resting State: the Na+/K+ pump transports Na+ ions out of the cell and K+ ions into the cell, keeping the inside of the cell more negative; the intracellular fluid is filled with negatively charged proteins

Action Potential (Spike, Impulse, Firing)

• Is a very rapid shift in the membrane potential from “- “to “+” values and return back to its initial resting potential level "-"
• Three Phases: Depolarization Phase (“- “to “+”); Repolarization Phase (back to “- “); Hyperpolarization Phase (below Vm)
• These phases of the AP are caused by the activation of 2 special types of ion channels on the nerve membrane: Voltage Gated Sodium (Na+) Channels and Voltage Gated Potassium (K+) Channels

Depolarization Phase of AP

• Initial increase in the membrane potential can be caused by a mechanical, electrical, or chemical stimulation
• If the membrane potential rises, some of the voltage gated sodium channels will open
• The Na+ will start to flow inside of the cell, making it more positive inside the cell
• The potential rises further to reach the threshold level (65 mV), this causes more sodium channels to open, and creates a positive feedback cycle
• The potential than reaches the overshoot level (above 0 mV)

Repolarization Phase of AP

• The return of the membrane potential toward the resting level (back to negative)
• Caused by the activation of the voltage gated potassium channels and the deactivation of the voltage gated sodium channels
• K+ channels are activated when the membrane potential increases above 0mV; K+ gates open slowly at the same time as the Na+ gates close
• K+ ions flow outside of the cell and Na+ ions are blocked from flowing inside, making the inside of the cell more negative
• The membrane potential returns towards the resting state of -90 mV

Hyperpolarization Phase of AP

• K+ channels remain open for a few seconds after the repolarization state is complete, excess K+ flows out of the cell, and the membrane potential becomes more negative than the resting state

Back to Resting Stage

• K+ channels gate close and the membrane potential comes back to resting stage (-90 mV)

Threshold of AP

• Is the level of the membrane potential at which the Na+ channels start to open one another in a positive feedback cycle
• Preceded by a sub threshold potential (no AP yet)
• Occurs when amount of Na+ entering neuron is greater than how much K+ is leaving the neuron. -55 mV if Vm is -70mV. -65mV for a Vm of -90mV

"All or None" Principle

• AP is said to be all, or none signal, since either is occurring fully, or it does not occur at all.
• No 1/2 AP, 1/4 AP, just 1AP
• If the threshold level is reached, the Action Potential occurs
• The amplitude (voltage) of an AP is not dependent of the intensity of the stimulus that it evokes

Amplitude and Frequency of Stimulus

• Distance of peak has nothing to do with the intensity of the stimulus

Frequency of Stimulus

• The frequency of the firing (number of AP) is dependent on the intensity of the stimulus; more we stimulate the greater number of AP are generated

Propagation of Action Potential

Unmyelinated Nerve Fibers (adjacent propagation)

• The Action Potential travels along the neuron's axons and fibers
• AP excites adjacent portions of the membrane resulting in propagation of the AP
• Na+ ions flow to adjacent area, opening more voltage gated Na+ channels, increasing voltage of adjacent area to reach threshold level, initiating a new AP in the adjacent area
• This adjacent propagation occurs if AP occurs in unmyelinated axons
• Conduction velocity/speed is slow = 0.25 m/s

Myelinated Nerve Fibers (saltatory conduction)

• Axon surrounded by myelin sheath (fatty white substance) and Myelin forms wrapping layers around the axon
• Myelin is produced as an extension of Glial Cells (Schwann cells in PNS and Oligodendrocytes cells in CNS)
• About once every 1-3mm, myelin sheath is interrupted by a Node of Ranvier
• Ions cannot flow significantly through the thick myelin sheath, which insulates the nerve fiber

Saltatory Conduction in Myelinated Nerve Fibers

• Action potential can only occur at the Node of Ranvier (where the voltage gated channels are located) and is conducted from node to node
• Saltatory = jump
• Fast conduction: conduction velocity increases 5 to 50 folds = 100 m/s compared to unmyelinated fibers 0.25 m/s
• Saltatory conduction conserves energy for the axon, with little metabolism being required to activate ion channels

Principles of Action Potential Propagation

• All or none principal:
• If conditions are right it is a full AP propagation; if not, a "stop" AP propagation
• Initial point of generation of AP:
• An action potential does not begin near the soma or dendrite, but at the initial segment of the axon known as the Axon Hillock, where AP begins
• Direction of the propagation:
• The action potential travels from the Axon Hillock towards the Synaptic Terminal of the axon, and cannot go in the reverse direction

Functions of Action Potential

• Transmitting Information
• Transferring all sensory information from the PNS to CNS
• Transferring all motor information for the CNS to PNS -Transferring information between different parts of the CNS
• Encoding Information (neuronal language)
• Encoding in the form of AP and the frequency of AP defines the code
• Rapid Transmission over Distance: Speed of transmission depends on the fiber size and if it is myelinated

Multiple Sclerosis: Blockage of AP Conduction

• MS is an immune deficiency disease causing demyelination of neuronal fibers in the central nervous system (CNS)
• Manifests through symptoms such as progressive muscle weakness, loss of sensation, loss of vision, and ultimately death
• Demyelination causes the blockage in the conduction (propagation) of AP and is a result of "all or none" principle

Synaptic Transmission

• In neuronal communication, information is transmitted within a neuron by an action potential (electrical signal) and information is communicated between neurons by a synapse (point of communication between two neurons)
• A synapse is the contact point between two neurons, characterized by a presynaptic neuron (sending neuron) and postsynaptic neuron (receiving neuron),
• Between both neurons is a space known as the synaptic cleft (200 – 300 angstrom)

Types of Synapses

• Synapses fall into two classes: electrical synapses (electrical signal) and chemical Synapses (chemical signal)
• Can be distinguished based on their structures and the mechanism they use to transmit signals from the presynaptic to the postsynaptic element

Electrical Synapses

• Electrical synapses permit direct passive flow of electrical current from one neuron to another
• Electrical current flows through intracellular continuities called connexons (channel bridges), and these connexons are grouped in small areas called gap junctions
• Transmission is very fast because the current flow across connexons is virtually instantaneous
• Transmission is bidirectional, allowing electrical synapse to synchronize electrical activity among the population of neurons (pre to post or post to pre)
• Electrical synapses are a minority (in the brain) and are mostly inhibitory synapses

Chemical Synapses

• There are no connexons (no intracellular continuity) between the two neurons (only synaptic cleft = empty space)
• At the presynaptic terminal, there are synaptic vesicles containing chemical substances known as neurotransmitters
• Synaptic transmission is initiated when an AP invades the presynaptic terminal and causes the release of the neurotransmitters into the synaptic cleft
• The binding of neurotransmitters into the postsynaptic receptors causes the activation of the postsynaptic receptors and thus a change in the membrane potential

Synaptic Transmission – Neurotransmitter (Ligand)

• A neurotransmitter is a chemical substance that is synthesized and packaged in the presynaptic terminal
• Released into the synaptic cleft by the arrival of a nerve impulse (AP)
• Binding to its specific receptor, the neurotransmitter causes the transfer of the impulse to the postsynaptic neuron

Types of neurotransmitters

Based on the action on the postsynaptic neuron:

Excitatory Neurotransmitters

• Excite (depolarize) postsynaptic membrane (i.e., more likely to generate AP)
• Glutamate (Glu), synthesized by Glutamatergic neurons
• Acetylcholine (ACh), synthesized by Cholinergic neurons Dopamine (DA), synthesized by Dopaminergic neurons
• Serotonin (5HT), synthesized by Serotonergic neurons -Norepinephrine (NE), synthesized by Norepinephregic neurons

Inhibitory Neurotransmitters

• Inhibit (hyperpolarize) postsynaptic membrane (i.e., less likely to generate AP):
• GABA, synthesized by GABAergic neurons
• Glycine, synthesized by Glycinergic neurons
• Each neurotransmitter has their specific postsynaptic receptor (e.g., key and lock)

Types Based on Size and Speed of Action

• Small Molecule, Rapidly Acting Transmitters include: -Glutamate (Glu) -GABA, Glycine -Dopamine (DA) -Norepinephrine (NE) -Acetylcholine (ACh) -Serotonin (5HT) -Nitric oxide
• Large Molecules, Slow Acting Transmitters, Neuropeptides include: -Hypothalamic-releasing hormones -Pituitary peptides -Peptides that act on the gut and brain -Peptides from other tissues

Synaptic Transmission

• Action of Neurotransmitter on Postsynaptic Neuron, there are two types of postsynaptic receptors:
• lonotropic receptors
• Metabotropic receptors
• Both receptors contain two components:
• A binding component, which binds the neurotransmitter -An active component, activated by the binding of the neurotransmitters -lonotropic receptors: the active component is an ion channel -Metabotropic receptors: the active component is a second messenger activator (G-protein)

Synaptic Transmission – Ionotropic Receptors

• In ionotropic receptors, the ion channel (active component) is an integrated part of the receptor
• Once the neurotransmitter binds into the receptor, the ion channels are activated
• Two types of Ion Channels:
• Cation Channels: allow cations (+ ions) (Na+, Ca2+, K+) to pass as to excite (depolarize) the postsynaptic neuron; make inside the cell positively charged (glutamate receptor) -Anion Channels: allow anions (-ions) (Cl-) to pass, inhibit (hyperpolarize) the postsynaptic neuron; make inside the cell negatively charged (GABA receptors)
• Ionotropic receptors open and close rapidly, providing very rapid control of postsynaptic neurons and enabling fast synaptic transmission

Synaptic Transmission – Metabotropic Receptors

• The active component is not an integrated part of the receptor, but a protein structure “second messenger activator” that causes prolonged changes in the neurons (minute to months) by activating substances inside the postsynaptic neuron enabling slow synaptic transmission
• The most common type of second messenger activator uses G – proteins as an active component, a protein complex (α, β, γ sub-units) attached to the interior portion of the binding component
• The binding of the neurotransmitter on the receptor activates the G – protein, which initiates a cascade of events leading to alternation in the cellular activity
• Upon the activation of the G-protein complex, the a sub-unit detaches from the complex and activates multiple functions inside the cell (e.g., opens ion channels, activates membrane enzymes, activates intracellular enzymes, activates gene transcription)
• This slow synaptic transmission causes prolonged changes in the neurons (up to months)

Electrical Events in the Postsynaptic Membrane

• The binding of the neurotransmitter on the post-synaptic receptor opens ion channels and increases the permeability of ions
• Causes the postsynaptic membrane potential to shift from the resting state (Vm) and the new potential is called the postsynaptic potential (PSP)

Excitatory postsynaptic potential (EPSP)

• The membrane potential moves towards less negative values (> Vm, depolarization)
• Increased permeability to Na+ and/or Ca2+ (more positivity inside)
• Caused by the activation of excitatory receptors
• EPSP favorites the generation of AP (depolarized membrane)

Inhibitory postsynaptic potential (IPSP)

• The membrane potential moves towards more negative values (< Vm, hyperpolarization)
• Increased permeability to Cl- and/or K+ (more Negativity inside)
• Caused by the activation of inhibitory receptors
• IPSP blocks the generation of AP (hyperpolarized membrane)

Characteristics of postsynaptic potentials

• Sub-threshold potentials (below threshold of AP)
• Do not obey the All-or-none principle (i.e. more stimulus, higher the amplitude)
• EPSP favorites the generation of AP (signal transmission)
• IPSP blocks the generation of AP (no signal transmission)
• Different PSPs can be combined through Spatial & Temporal summation

Summation of Postsynaptic Potentials – Spatial Summation

• Spatial Summation: different presynaptic terminals (E1 & E2) stimulate the same postsynaptic neuron, their respective EPSPs summate (i.e., superpose)
• If the postsynaptic neuron receives an Excitatory stimulus (E1) or an Inhibitory stimulus (I), the 2 stimuli cancel each other (i.e. (+1) + (-1) = 0)
• The membrane potential may reach the threshold to generate an action potential

Summation of Postsynaptic Potentials – Temporal Summation

• Temporal Summation: a postsynaptic neuron receives, in a very short period of time, successive stimulations from the same presynaptic terminal (e.g., E1)
• The 2nd EPSP will generate before the recovery of the 1st one, thus both EPSPs can summate Rapid successive discharges from the same synaptic terminal can summate to reach the threshold for firing AP

Synaptic Plasticity

• Is the ability of a synapse to change (strengthen or weaken) over time, in response to increase or decrease in its activity
• Can result from a change in in the quantity of neurotransmitters released, a change in the number of postsynaptic receptors, or a change in the response of the postsynaptic neuron to presynaptic stimulation (EPSP & IPSP)
• Types of synaptic plasticity: -Synaptic potentiation (enhancement): Increase in the efficacy of the synapse
• Synaptic depression: Decrease in the efficacy of the synapse
• Short-term plasticity: lasts from few milliseconds to minutes -Long-term plasticity: lasts from minutes to months (even years)
• Synaptic plasticity is an important neurochemical mechanism of learning and memory (Hebbian theory: "cells that fire together, wire together”)

Drugs and Synaptic Transmission

• Drugs modulate synaptic transmission to affect brain activity: -Medication (e.g., Antidepressants, Antipsychotics...)
• Recreational drugs (e.g., Ecstasy, Cocaine, Opiates, Cannabis...)

Effect of Ecstasy on Serotonin transmission

• In a healthy brain, serotonin is rapidly reuptake from the synaptic cleft by the Reuptake Transporter
• In the presence of Ecstasy, the transporter blocks the job of the Reuptake Transporter, Serotonin stays longer in the synapse and over stimulates the postsynaptic neuron
• Ecstasy causes euphoric sensation, increased heart rate, panic attacks, blurred vision, nausea, vomiting, convulsions, and death (overdose)
• It's very addictive even with low doses

Somatosensory Axis of the Nervous System

• Transmits somatic (body) sensations from the body receptors to the CNS
• Information is transmitted to the spinal cord, brainstem, cerebellum, thalamus, and cerebral cortex
• Three important elements are sensory receptors (reception), sensory pathways (transmission), and sensory centers (processing)

Classification of Somatic Sensations

• Mechanoreceptive Sensations are stimulated by mechanical displacements (tissue deformation): tactile and proprioceptive
• Tactile Sensation (skin)
• Touch
• Pressure
• Vibration
• Tickle and itch
• Proprioceptive Sensations (muscle and joints): muscle condition sense and joints position sense
• Nociceptive Sensations: detect pain, being stimulated by any factor that damages the tissue
• Thermoreceptive Sensations: detect temperature (heat and cold), being stimulated by the change in temperature

Classification of Somatosensory Receptors

• Classified based on the type of sensation they detect
• Mechanoreceptors detect tissue deformation like skin tactile recepters and muscle receptors
• Nociceptors detect pain (tissue damage), including pain receptors such as specialized free nerve endings
• Thermoreceptors detect changes in temperature and include specialized free nerve endings such as cold receptors and warmth receptors

Receptor Potential

• Resting membrane potential happens at a resting state with no stimulus
• Action potential results from transient changed in the resting membrane potential of a stimulated neuron
• Electircal signal that travels along axons, including long range transmission of Information within the nervous system
• Receptors Potential results from transient changed in the resting membrane potential in the receptor of sensory neurons by an external stimulus
• Synaptic Potential results from the communication between neurons at synaptic contacts and recorded at the postsynaptic neurons stimulated by the presynaptic neuron

Receptor Potential

• When a stimulus (touch, pain) excites the receptor, the electrical potential of the receptors membrane changes and creates a receptor potential (like EPSP)
• Stimulation causes opening of ion channels (Na+, Ca2+), depolarization of the membrane
• Mechanism of Stimulation of the Receptor -Mechanical deformation stretches the membrane (mechanoreceptors)
• Application of chemicals (acid, alcohol, drugs) -Change in temperature (thermoreceptors) -Tissue damage (pain receptors)

Transduction of Sensory Stimulus

• The receptor potential rises the membrane potential of the nerve fiber attached to the receptor, and if the threshold is reached, an action potential appears in the nerve fiber
• Action potential travels through the nerve fiber to reach the brain and transmits encoded sensory information to the brain)
• The greater the intensity of the stimulus the greater the receptor potential amplitude and thus the greater rate of action potential

Adaptation of Receptors

• When a continuous sensory stimulus is applied, the receptors respond at a high impulse rate at first stimulus and then progressively slow down their rate of response until many of them no longer respond as a result of adaptation, like the adaptation of cold water
• The speed of adaption varies with the type of receptors -Slowly Adapting Receptors decrease their rate of response slowly (Pain receptors, Merkel's discs, and Ruffini's organ)
• Rapidly Adapting Receptors rapidly reduce their rate of response (Thermoreceptors, Pacinian corpuscle, Hair receptors, Meissner's corpuscle)

Examples of receptors and their rate of adaptation

• Pacinian corpuscle adapts very rapidly
• Hair receptors adapt rapidly
• Joints capsule and muscle spindle receptors adapt slowly

Adaptation of Receptors: Mechanism of Adaptation

• Accommodation of the Receptor,the receptor potential appears at the onset of the stimulus (compression) but disappears rapidly even though the stimulus continues, like how the receptor still reacts under compression, squeezed it all
• Accommodation of the Nerve Fiber comes as a decrease in the firing of AP that is caused by the inactivation of the Na+ channels, saturation of ions channels
• Tactile Receptors and Sensations

Six Types of Receptors

• Free Nerve Endings are found everywhere in the skin, are connected with small unmyelinated sensory nerve fibers, detect crude touch and pressure sensations, and follow slowly adapting receptors
• Meissner's Corpuscle are elongated encapsulated nerve endings, are connected with large unmyelinated sensory nerve fibers, are located in the superficial layers of the skin, detect fine touch and low frequency vibrations, and follow rapidly adapting receptors
• Merkel's Discs are located in the superficial layer of the skin, detect touch and light pressure, and follow slowly adapting receptors
• Hair end-organ is in contact with the root of the skin hair, detects hair movement, and follows rapidly adapting receptors
• Ruffini's end-organ are encapsulated endings located in the deeper layers of the skin, detect heavy touch and deep pressure signals, and follow slowly adapting receptors
• Pacinian Corpuscles are encapsulated endings located in the deeper layers of skin, detect tissue vibration and other rapid changes in the mechanical state of the tissue, and follow rapidly adapting receptors

Pain Sensation

• Occurs whenever tissue is being damaged, in accordance with a protective mechanism for the body that causes the body to remove the painful stimulus
• The two types of pain are fast and slow pain: Fast Pain occurs within less than a second of the stimulus and is displayed as a sharp character
• Slow Pain begins after a second or more, is throbbing and aching in nature, like a headache and toothache

Pain Receptors

• They're specialized free nerve endings
• Widespread in many locations of the body such as superficial layers of the skin, internal tissues, bones, joints and muscle surfaces, arterial walls, but NOT the brain
• Can be stimulated by mechanical, chemical, thermal, and inflammation
• Pain receptors are slow adapting receptors for a protective mechanism to remove painful stimulus
• Thermal Sensation

Thermal Sensation: They can be graduated

• Thermal gradations are discriminated by 3 types of sensory receptors that can be specialized free nerve endings like how -Cold receptors can be sensible to cold temperatures -Warm receptors can be sensible to hot temperatures -Pain receptors can be sensible to extreme temperatures There ate more cold than hot receptors Freezing cold and burning hot are the same sensation and a sign of stimulation of pain receptors
• Thermal receptors are rapidly adapting receptors, like a swimmer's response in cold water

Transmission of Somatosensory Information from the Receptor to the Brain

• The somatosensory receptor is the peripheral end of the processes neurons, in the form of pseudo unipolar neurons, that transmits the sensory Information to the central nervous system, spinal cord
• The cell body of the sensory neuron is in the sensory ganglion (spinal cord0
• Each type of somatic sensation (sensation modality) is transmitted by its specific sensory nerve, described as the labelled line principle- Velocity depends on fiber diameter and fibre myelinization; the largerthe diameter, the faster the information
• Velocity depends on fiber diameter and fibre myelinization; the largerthe diameter, the faster the Information

Nerve Fiber Classification

• Type A—myelinated fibers of varying sizes
• Type C—unmyelinated fibers

Sensory Transmission: In the spinal path ways

• Each part of the body is connected to segments of the spinal cord.
• This makes sensory transmissions important for the spine

Somatosensory pathway for face

• Somatosensory information moves through the brainstem to the trigeminal system
• Three neurons will send to the brainstem to cortex

Primary Somatosensory Cortex

• Primary station of pathways is called the somatosensory
• High amount of orientation on postcentral gyrus, parietal lobe
• Cortex will receive information related each part of the body There has to be communication between sides
• Lips will have the most sensory points

The Cellular Organization of the Primary Somatosensory Cortex: six layers in the Somatosensory area

• Within the layer will organize vertical columns, and signals in the columns
• Different columns must be able to communicate with each other

Somatosensory Association Cortex

• The somatosensory center is located in Somatosensory cortex in parietal lobe
• The location receives input from the thalamus and primary cortex
• Allows the body to recognize objects

Modality of Sensation

• The brain determines sensation
• The modality will sense light touch

Anatomy of the Human Eye

• Fluid filled with a layered structure
• Composed of sclera, choroid and retina
• Has fluid compartments- The aqueous and vitreous humors
• Lense refracts light

The Sclera

• White tissue on outside and allows rays to reach

Choroid

• Intermediate that nourish in central region

Ciliary Body

• Consist of vascular and muscular region- Ciliary muscle leads shape for lense and is for the zonule fibers

Iris

• Two different sets of muscle for size adjustment
• Controls the Lens that lets the eye generate high focus

Retina

Inner eye layer and transmits into brain -Photosensitive and allows vision to send info

Accommodation for Lens

These depend on the ciliary muscles for refractive power for the eye.

• Distant vision is thin and and allows little refractive power for the eye.
• Near Vision is round and has most refractive power for the eye, all thanks to ciliary
• Emmetropia is lens that allows right accomodation for the eye.

Myopia

• Lense over accomodates in the from tof retina
• Objects are hard to see
• To fix can use diverge lenses

Hyper Opia

• Lense will not accomodate enough, and vision cannot be fully processed
• Difficult to see by and are adjusted with converge lenses

Rods and Cones

Vision depends from sensory in the eye

• Lowest illuminations means, more rods are in eye
• Starlight allows cones to be set on eye

Structure on the Retina

• Cells need light to be functional
• Photosensitive cells will have these cells to be functional
• Ganglion cells transfer info

On and off-switch function

• Depending on how the cells function, the field is changed

What happens when info reaches retina

• Retinital vision allows the person to transfer visual context
• Inverted vision for the retinal surface

Visual field

• Eye processes both fields and has to focus for any overlapping
• Includes lateral and medial fields through nasal
• Hem fields will be displayed for retina as well

Central Pathways- vision

• Comes through optic nerve in the ganglion cells
• 60 percent crossing and has an effect with contralateral

Visual - Brain

• The vision can help control the pupillary of legiht
• Optic nerves and and the leg innervation
• Leg and eye musscle in eye

The Visual Area Brain

• Contains primary vision and basic information
• Retina is mapped through visual cortex welll . Sensory information will be translated to the brains vision in HD

Organization of the primary cortex

• 6 layers and layers will input information
• Vertical columns will receive information
• These area has ocularity

Consequence of Damage at different brain levels

• High number of sensory is the tumor and causes other side vision to be affected
• Pituitary level can hurt the eye

Vistabular System

• Located behind the brain stem in the ear- Controls motion, position and gravity
• Helps stablize the head, gaze and posture
• Relies on hairs

Inside Vistabulator

Consists of 2 organs that

• Connect from the cranial nerve Have epitical cells for shape

Types of movements they detect linear and translation movement

This is for the tilt with gravity relative to the axis

Central System

• nerves transfer fibers to vestibular levels in brainstem
• Brain will have multiple sources to help connect

Pathway to the Cortex

Nerves create signals from the canals Then will proceed through to the vestibular location

• Help maintain balance and equilibrium thanks to cerebellum

Vestibular - Ocular Reflex (VOR)

• Can maintain stable gaze If head turns, VOR helps adjust balance and direction
• The left horizontal will send signal of the canal.

Cervical Reflex -

• Adjust position for head to help move semi canals. The Upper canal adjusts positions to stay balanced and avoid any collision

The Spinal - Verticular Reflexes

Stabilizer and protects any falling Axons from nuclear send it down vertibculal spinal direction

Cerebral Pathway

Work together to coordinate balance and equilibrium. Adjust and adapt to different ranges

System Analysis:

• the brain relies on certain sources to help know more, and is related to visual senses

Motor System Function

• Upper motor neuron The Brain will then modulate to stimulate spinal cord
• Then modulate for the function/stimulation

Central System

• Spinal cord and intersections will process with basal motor and vision. Will work without intersections.
• Controls interrnal organ functions from blood flow (bladder, gastrointestinal system)
• Sensory Neuron of Spinal Cord

3 important items for spinal code

• Sensory with somatic relations
• Motor and connection in spinal cord to give better
• Neurons in the posterior sections , help with functions
• Inhibitory and exhibitory to make the spinal movements

Sensory Receptors

• Senses the change of tention levels (contraction)
• Stimulates the area the tension levels

Muscle Spindle

• Changes size in myosin and tension
• Sensory ending travels over fibers to change fiber size (either fast or slow)

Golgi Tendon

• Encapsulates sensory to connect tendon fibers
• helps the neuron release the tension for contraction

Lower Motor Neuron

• Cell are in anterior of spinal cord and is needed for muscle contraction and support
• Alpha and beta fibers needed for skeletal contraction

Motor Unit

Muscles connect to the motor of the motor neuron for contraction.

• Most muscle rely on this system
• Help with balance and coordination for the body.

Multiple Fiber Summation is also how to modulate the rate of the brain.

• Help the muscles work together for balance and motion.
• Will continue to have muscles to adjust

Rate of Summation

. Individual parts will touch to modulate rate

• . At a critical state it allows total one contraction known as the Tetanization

Cord Reflexes

• Use all systems for all response needed for reaction

Tendon Organ

. Helps with muscle tension for protection (prevent pain) . The activation is helpful and allow the muscles to relax when they are over stretched

Neuron

. Connect with nerves or tension point, Then connect with spindle area