Neuro Midterm

Synapses

• Synapses are connection points between a nerve cell and another cell
• They facilitate communication between a neuron and a target cell: nerves, muscles, or glands.

Types of Synapses

• Electrical Synapses: Rare in vertebrates, involving tight contact between cell membranes for electrical coupling, enabling quick and reliable nerve impulse transmission.
  • Physical touching between two cells.
  • Faster and more synchronized than chemical synapses.
• Chemical Synapses: Feature a synaptic cleft, a gap between presynaptic and postsynaptic cells roughly of 10–15 times larger than electrical synapse, transmission occurs via neurotransmitter release from the presynaptic cell.
  • Allow control over the amount of chemical released.

Neurotransmitters

• Excitatory neurotransmitters excite the postsynaptic membrane, allowing positively-charged sodium ions to enter the cell, which makes the membrane potential less negative.
• This depolarization is known as an excitatory post-synaptic potential (EPSP), with its amplitude determined by the number of vesicles released.
• Reaching threshold initiates an action potential.
• If a neuron, the action potential travels along its fiber and if a muscle, it propagates and causes contraction.
• Inhibitory transmitters render the postsynaptic cell less excitable, often acting on receptors of chloride or potassium ions, hyperpolarizing the cell.
• Acetylcholine serves as an excitatory transmitter at nerve-skeletal muscle synapses, and glutamate is the primary excitatory transmitter in the CNS.
• Examples of excitatory neurotransmitters include Acetylcholine and glutamate.
• Examples of inhibitory neurotransmitters include glycine and Gamma aminobutyric acid (GABA).

Serotonin

• A presynaptic cell makes serotonin (5-hydroxytryptamine, 5HT) from the amino acid tryptophan, packaging it in vesicles within the end terminals.
  • Vitamin B6 aids this process.
  • Most of it is in your gut.
• An action potential travels down the presynaptic cell to its end terminals.
• The action potential stimulates serotonin-containing vesicles to fuse with the cell membrane, releasing serotonin into the synaptic cleft.
• Serotonin crosses the synaptic cleft, binds to receptors on the postsynaptic cell membrane, and depolarizes the postsynaptic cell.
  • If depolarization reaches threshold, a new action potential propagates in that cell.
• Remaining serotonin molecules in the cleft and those released by receptors are degraded by the enzyme monoamine oxidase (MAO).
• In the presynaptic cell, MAO destroys reabsorbed serotonin molecules, turning the nerve signal "off" and readying the synapse for another action potential.
• Catechol-o-methyl transferase (COMT): An enzyme similar to MAO targets catecholamines (dopamine, epinephrine, norepinephrine) instead of serotonin.
• MAOI (monoamine oxidase inhibitor) serves as an antidepressant.
• Serotonin can act as a modulator, which is longer-lasting and slower-acting.

Modulation

• 'Fast' neurotransmitters act briefly due to quick unbinding from receptors and rapid clearing from the synaptic cleft through breakdown or reuptake.
• The synaptic potential is also brief, with the membrane potential rapidly returning to its resting level.
• Modulators, like serotonin, dopamine, and noradrenaline act more slowly over a longer period.
• Their receptors activate messenger molecules inside the cell, initiating various responses, including gene switching.
• Nerve terminals can produce two or more transmitters and/or modulators beyond the traditional 'Dale's principle'.

Neurotransmitters

• Enkephalin (Opiate) (aka Endorphins):
  • Neuropeptide type with inhibitory postsynaptic effects, found in the brain and spinal cord.
  • It reduces stress, promotes calm, and acts as a natural painkiller.
  • Cold and exercise increases the release of endorphins.

Synapse Abuse

• Most drugs working on the brain, including abuse drugs, act on synapses.
  • Nicotine activates nicotinic acetylcholine receptors, causing dopamine release (euphoria).
  • Curare paralyzes prey by antagonistically blocking the acetylcholine receptor in the neuromuscular junction, preventing neuromuscular transmission (flaccid paralysis).
  • Morphine & Heroin act on opiate receptors.
  • Cannabis acts on cannabinoid receptors.
  • Cocaine blocks the dopamine reuptake system, prolonging dopamine presence in the synaptic cleft, resulting in stimulant effects.
  • Nerve gas (Sarin) blocks acetylcholine removal at nerve-muscle synapses, causing constant muscle contraction and spastic muscle paralysis.

Disorders of Synaptic Function

• Myasthenia Gravis: An inherited neuromuscular disorder.
  • The body produces antibodies that antagonize acetylcholine receptors on muscle fibers, reducing receptor numbers and compromising neurotransmission.
• Consequently, this causes easy fatigue.
• Graves Disease involves auto-antibodies agonistically bound to the thyroid gland, increasing thyroid hormone production.
• Epilepsy: Can be linked to decreased inhibitory transmission (GABA) efficiency in the brain, leading to neuron over-excitability.
• Depression & Schizophrenia: Psychiatric disorders involving synaptic disorders where serotonin and dopamine act as neurotransmitters respectively.
• Schizophrenia is linked to too much dopamine.
• Depression is linked to too little serotonin.

Neural Circuits

• Neurons organize into ensembles or circuits for specific information processing.
• Neural circuits arrangement depends on the intended function.
• Synaptic connections defining a circuit typically occur in the neuropil, a dense tangle of dendrites, axon terminals, and glial cell processes.
  • Few cell bodies are found here.
• Neuropil between nerve cell bodies is where most synaptic connectivity happens.
• Direction of information flow is crucial for understanding circuit function.
• Afferent neurons, efferent neurons, and interneurons are basic constituents of neural circuits.
• Afferent Neurons carries information toward the central nervous system.
• Efferent Neurons carries information away from the brain or spinal cord.
• Interneurons participate in local aspects of a circuit.
• The myotatic ("knee-jerk") spinal reflex serves as a simple example of a neural circuit.
• Sensory neurons of the dorsal root ganglion in the periphery form the afferent limb.
• Motor neurons in the ventral horn of the spinal cord with peripheral targets form the efferent limb.
• Flexor and extensor muscles in the limb are among the different peripheral targets.
• Interneurons in the ventral horn receive contracts from sensory afferent neurons and make synapses on the efferent motor neurons projecting to the flexor muscles.
• The sensory afferents and the extensor efferents share excitatory synaptic connections, causing extensor muscle contraction while interneurons activated are inhibitory, diminishing electrical activity in motor neurons, which results in flexor muscles relaxing.
• The complementary activation and inactivation of synergist and antagonist muscles control leg position.
• More complex circuits involve processes like addiction.

Neuronal Pools

• The human body has approximately 10 million sensory neurons, 20 billion interneurons, and one-half million motor neurons.
• Interneurons are organized into a smaller number of neuronal pools.
• Neuronal pools include interconnected neurons with specific functions and are defined on the basis of function.
• A neuronal pool may be diffuse, involving neurons in several regions of the brain, restrict to one specific location in the brain or spinal cord
• Actual estimates of the actual number of pools range between a few hundred and a few thousand
• Each pool has a limited number of input sources and output destinations, containing excitatory and inhibitory neurons with outputs that stimulate or depress other pools, control motor neurons, or peripheral effectors directly.
• The pattern of interaction provides clues to functional characteristics, referred to as a "wiring diagram" or a neural/electrical circuit of a house
• 5 circuit patterns exist.

5 Circuit Patterns:

• Divergence: Spreads information from one pool to multiple pools, enabling broad distribution of a specific input.
  • This pattern occurs when sensory neurons transmit information into the CNS, where distributes to various neuronal pools throughout the spinal cord and brain.
  • Visual info from the eyes reaches conscious awareness and distributing to brain areas controlling posture and balance.
• Convergence: Several neurons synapse on the same postsynaptic neuron, which enables several patterns of activity in the presynaptic neurons to have similar effects on it as the individual moves their diaphragm conscious and subconscious.
• Serial Processing: Relays information stepwise, from neuronal pool to the next.
  • Brains may send info from one hemisphere to the other in series.
• Parallel Processing: Several neurons or neuronal pools process the same information simultaneously after divergence.
  • Thanks to this processing, a response to stepping on a sharp object may include withdrawing foot shifting weight, moving arms feeling pay etc.
• Reverberation: Some circuits use positive or negative feedback.
• Collateral branches of axons somewhere along the sequence extend back toward the source of an impulse and further affect the presynaptic neuron.
• Reverberation involves a feedback loop for circuit activation, potentially stimulating itself or shutting itself off and can support consiousness, muscular coordination, and normal breathing through examples.

Sensation

• Sensation is a conscious or unconscious awareness of external or internal stimuli.
• The nature of sensation and the type of reaction vary depending on the destination of impulses in the CNS and the types of receptors stimulated.
• Sensory impulses relayed to the spinal cord may serve as input for spinal reflexes, such as the stretch reflex
• Sensory impulses reaching the lower brain stem can elicit reflexes such as changes in heart rate and breathing rate.
• Sensory impulses reaching the cerebral cortex can precisely locate and identify specific sensations such as touch, pain, hearing, or taste.

Sensation Vs. Perception

• Sensation - Any stimulus the body is aware of given that receptors are present.
• Heat, pain, touch, and smell are common awareness
• X-rays, ultra-high-frequency sound waves, and UV light do not trigger sensory perception, even when effects are there.
• Perception - Conscious awareness and interpretation of a sensation, involving localization, identification, and stored memories in the cortex.
• It is possible to sense something without perceiving it
• We are unaware of blood sugar

Sensory Modality

• Sensory modality differentiates sensations, such as touch, pain, temperature, vibration, hearing, and vision.
• A single receptor can only detect one type of stimuli, with exceptions in sensory modalities.
• General senses include somatic and visceral senses, providing information about conditions within internal organs.
• Tactile (touch, pressure, vibration, tickle, and itch), thermal, and pain sensations are types of somatic senses, alongside proprioceptive sensations for limb and body part positioning.
• Proprioceptive sensations are conscious and unconscious.
• Joint and muscle positions of limbs/body and head movement can be sensed, both static and moving.
• Information from within organs comes from visceral senses.
• The special senses cover smell, taste, vision, hearing, and equilibrium, which comes from the face and cranial nerves

The Process Of Sensation

• The process of sensation starts in specialized cells/dendrites of a sensory neuron receptor.
• Four typical events must occur; otherwise, sensations cease.

1. Stimulation: Appropriate receptor must be present in the area of stimulus.
2. Transduction: Energy from stimulus converts from a sensory receptor into a graded potential.

• Vary in amplitude and are not propagated.
• Molecule chemical energy converted into graded potential electricity

3. Impulses Generation: Graded potentials reach a potential threshold.

• Sensory neurons conduct from the PNS.
• Impulse propagated towards the CNS, via first order (1º).

4. Intergration of sensory input: CNS region receives the stimulus via sensory nerve, where they also integrate.

• Cerebral cortex integrate with perceptions/conscious.

Sensory Receptors

• Sensory Receptors have both simple or complex receptors.
• General Sensory Receptors fall into somatic examples that lack structural specializations in free nerve ending such as those that provide us with pain, tickle, itch, and temperatures.
• Some structural specializations can be found in receptors dealing with touch, pressure & vibration
• Vision, hearing, taste & equilibrium
• Structure is very complex with special sense receptors.

Classifying Sensory Receptors

• Can be done Structurally based
• Can be done by Type if stimuli detected to the type of response that happens if there is a stimulus
• Structural Classification involves

1. Free nerve endings, like basic bare dendrites, that lack a specific structure and give sensations like pain, temp, tickle, itch, and light touch.

• They are the "terminal branches" that spread through the dermis/epidermis, lacking myelin sheath.

2. Encapsulated nerve endings that have dendrites enclosed with/in a connective tissue capsule.

• Pressure, vibration & deep touch

3. Separate sensory cells responding in the different senses synapse with the first-order neuron receptors.

• Specialized/separate cells that respond to stimuli by synapsing with the first-order neurons
• Separate cells that aren't neurons will synapse onto a neuron
• Can be used structural to classify (vision, taste, earing, balance - special senses but excluding smell)

Stimuli Detected

1. Mechanoreceptors detect physical or mechanical stress touch, pressure, vibration, hearing, proprioception & equilibrium.

• Broadest category because receptors are physically moving.

2. Thermoreceptors detect increases or decreases in temperature.
3. Nociceptors detect/respond to intense mechanical deformation tissue damage & excessive heat or in response to chemical signals.
4. Chemicals are released due to tissue damage, stimulating stimulus.

• Impulse is sent prior to damage happening.

5. Chemoreceptors detect chemicals:
   • Taste & smell (arterial oxygen)

• Blood Glucose (blood CO2)
• Aorta and carotid both have chemoreceptors located.

5. Photoceptors detect visible light. Rods detect sensitivity but can't discern, where cones are low sensitivity but contains red, green and blue pigments within the sensory.
6. Ampullae of Lorenzini can act as salinity responders/electroreceptors reacting to salinity, electric fields and temperature.

• Baroreceptors - specialized receptors for pressure reacting, which are specialized mechanoreceptors.
• Electromagnetic Receptors are those that respond to electromagnetic waves.

Response to Stimuli

• Responses from Stimuli happen vary with stimulus intensity.

1. Generator potential is a type of graded potention.

• Can be seen in free nerve endings, encapsulated nerve endings and with receptors.
• Standard action potential are generated/amplified there due to these generator potentials.
• Receptor Potential: Is the term for a type of graded potential. ○ This one comes from Vision, hearing, equilibrium, and taste receptors. ○ They neurotransmitter (PSP) release molecules on the 1st order neuron, which triggers a nerve.

Location of Receptor

1. Exteroceptors near the body surface Receive external stimuli such as hearing, vision, smell ,taste, touch, pressure, pain, vibration & temperature
2. Interoceptors monitors internal environment (BV/viscera) Receive internal stimuli through conc., in blood & blood pressure etc.. Not a conscious response, except through press/pain.
3. Proprioceptors that exists in joint tendons/tissue capsules.

Adaptation

• Most sensory receptors exhibit adaptation: a tendency for the generator or receptor potential to decrease in amplitude during a maintained constant stimulus decrease in sensitivity .
• Tonic receptor: Receptor slows down its action towards the continuous long duration.
  • Convey information via that duration.
  • Tonic receptors always display activity and also indicates the baseline.
• Nociceptors and propriceoptors are examples.
• Phasic receptor: adapts to a given stimulis quickly.
  • Diminishes quickly.
• An example include Pacinian corpuscle.

Tactile Sensations

• All sensitivities that happens in the body is based on activations in a fingertip (tactiles). Includes is such as Touch, Pressure,Vibration, Itch & Tickle
• Sensation varies due to receptor changes that allow some overlap of the same stimuli.
• There a separate neural ways that are both crude or discrimitory.
• It occurs on multiple way to create a sense on multiple level

Touch

• Crude touch includes Ability to perceive something has touched the skin, even though its exact location, shape, size or texture cannot be determined. Something touched you in the area.
• Discriminative touch: Allows specific touch, and sensation about a location that is touching you at the exact moment and its texture
• Touch Receptors exist as a RAPIDLY adapting pair (Phasic receptor type)

1. Corpuscles of Touch (Meissner corpuscles) encapsulated

• Receptors are touch based and in the dermal papillae of the hairless skin.
• Each are located in tips, or in the hands and legs of the individual.

2. Hair Root Plexuses

• Found in hair, consisting free nerve endings.
• Free nerve endings Detect even minor disturbance of the shaft and trigger the impulses.
• SLOWLY adapting pair follows tonic receptor system

1. Type I Cutaneous Mechanoreceptors (Merkel Discs)

• Flattened endings that connect free with Merkel cells.
• Most is are touch, where the rest include general hairs and limbs.

2. Type II Cutaneous Mechanoreceptors (Ruffini Corpuscles)

• Can detect stretch and can detect pressure given its elongated.
• Most is are in hands, especially.

Pressure

• Pressure and Tactile Sensations happen to have an influence and correlation.

Vibration

• Vibration needs sensory inputs based from tactile signals.
• Each are: □ Meissner Corpuscles - Rapid, encapsulate to detect low frequency. □ Pacinian/Lamellar Corpuscles - More distributed, higher frequency. - This adapts quickly .

Itch

• Its mysterious, involving stimulus and is related to bradykinin and histamine.

Tickle

• Involves specific touch and stimulus.
• We currently don't know why this happens

Phantom Limb Sensation

• After an amputation, they feel they still may some kind of sensations.
• Cerebral cortex perceives the impulses as damaged.
• New evidence show that it is the neuronal activity and impulses is still there.

Thermal Sensations

• Is on the skin, about a 1 meter diameter across the skin where diameter field is on the surface.
• Cold Recptors are in the epidermis via myelin. - This is in temp between 10 to 35
• Warm Receptors are in dermis, diameter =c where 30-35.

Pain Sensations: Nociceptors

• Is on the skin, about a 1 meter diameter across the skin where diameter field is on the surface.
• Excessive activation leads to chemics/injury releases from the source.
• Chemicals such as: prostaglandins
  • This will make the pain persistent, leading to a lack of adaptation.
• Conditions in stimulus

Fast Pain (Acute)

• Time it took: .1 second.
• Short, pricking pain
  • No deep penetration of the stimulus.
  • A fibers due to myelin.

Slow Pain (Chronic)

• Takes a slow amount of time.
• Chronic aching and throbbing is possible.
• Skin and Tissue is affected along an internal organ
• The surface is known as "Somatic Pain".
• Visceral pain: is the skin that overlies.
• In surface area, the phenomenon is known as ""Referred Pain".

Referred Pain

• Stimulation happens at a different than where pain happens.
• Most in the spinal, in relation to heart attack.

Pain Threshold vs Tolerance

• Involves PNS
  • How much threshold is needed to elicit a pain response.

Proprioception

• Sensations Allow us to know location and movement of head and limbs.

Proprioceptors

• Has embedded muscles that tension amount joint in various parts of body.

Golgi Tendon Organ

• At the place where tendon and muscles meet.

Joint Kinesthetic Receptors

• Present to capsule joints as pacinian corpuscles.

Somatic Sensory Pathways

• To cortex and cerebellum
  • 1st order is spine, mouth and eye impulses travel to nerves and brainstem. -2nd is at the thalamus.
  • 3rd is to the primary motor area

Posterior Column

• Pressure from neck and trunk.
• It goes via discriminat touch stereognosis +proprioception +kinesthesia+ vibrations.
• 1ST order is trunk to spinal cord.
• Has nucleus in torso and arms
• 2nd: cross and go to the thalamus VPN.
• 3rd: is is out to the cortex

Spiniothalamic Pathways

• Temperature +ticklishness.
• Poor location but can sense vibrations.
• Go up to posterior and synapse with interneurons immediately
• Thalamus project into the prime area

Trigeminothalamic Pathway

• Sensory: face, nasal cavity and oral cavity ascend into the cerebral cortex(trigemio pathways).
• First area =sensory recpetors.

Spinocerebellar Pathways

• Proprioceptive tract
• Isipsilateral
• Brain is adjusted and motor are controlled by the Brain and Muscle as a result

Primary Somatosensory Area

• Left side of the body will travel t the right side of the hempshere and vice versa.
• It is based on relative region sizes.

Syphilis

• Bacteral from treponema Pallidum.
• This bacterial will degenerate. and cause symptoms such
• Loss of sensation.
• Walking impairment .

Somatic Motor pathways

• Central to muscles and spine will have a spinal nerve and send LMN to skeletal Muscles.
• Known ad final/summation output
• Frontal loves will initiate precise movement, that will integrate in basal ganglia and then coordinate the cerebellum.

Descending Somatic Motor Pathways:

• Spinal cord, through descending pathways (2 Types)
• Direct pathways (cortex).
• Indirect pathways (motor centers)
  • Damage causes spasms (UMN).

Direct Motor Pathways (Pyramidal Pathways)

• Pathway that goes to cerebral

Primary Motor Cortex

• Planning and execution of voluntary movements.
• Different muscles will vary on units, or amount of nerve.

Indirect Pathways

• All motor traits are There are the Tracts

1. Rubrospinal tracts.
2. Tectospinal Tracts.
3. Vestibulospinal Tracts.
4. Lateral Reticulospinal Tracts.
5. Medial Reticulospinal Tracts Descend is at different tracts(5) which will lower the stimulation to trigger an exciatto and inhibirtory.

Integratibe Functions

• There sleepland awakening.

Sleep and Wakefulness

• This system depends on the Reticular Activating System.
• The ARousa is a type of stimulation and that occurs on the cortex.

Sleep

A type of conciousness and that has different stimmuli. REM and NREM exist in the process

NREM

• 4 stages with EEG recordings
• Can have sleep walking.

REM

• Can be paralysis during stages.
• Oxygen increases with activity so does nerunal process occurs,
  • Totals reduce with amount of time and energy

Learning and Memory

• Skills learned.
• Storing and retrieving is based on time . Anterograde causes loss in the 1st memory while retrograde causes loss in past event.

This quiz focuses on serotonin's role in neurotransmission, the effects of enzyme inhibitors and vitamin deficiencies on serotonin levels. It also covers the roles of local circuit neurons, upper motor neurons, basal ganglia, and the cerebellum in motor control.