Chapter 11 Nervous system

• The nervous system is a mater controlling and communicating system of the body

The nervous system has three functions:

1. Sensory input : the process of gathering information from sensory receptors to monitor changes occurring both inside and outside the body.

2. Integration: process where system process and interprets sensory input and decides on an appropriate response.

3. Motor output : the nervous system activates the effector organs, such as muscles and glands, to produce a response based on the integrated sensory information.

Our nervous system is divided into two

1. CNS , central nerves system that consist of the brain and spinal cord, which occupy the dorsal body cavity and dictates motor output on reflex, current condition, and past experience.

2. PNS peripheral nervous system, consisting of mainly nerves that extend from the spinal cord and carry nerve impulses.

Peripheral Nervous system consist of two subdivisions :

1. Sensory or Afferent division: Responsible for transmitting sensory information from sensory receptors to the central nervous system.

• somatic sensory fibers carry impulses from skin, joints, and skeletal muscle

• Visceral sensory fibers transmit impluses from visceral organs

Central nervous system is informed by the sensory division from the inside and outside of the body.

• Motor or efferent division of the PNS carries impulses from the CNS to effector organs such as muscles and glands. This motor division cause muscles to contract and glands to secrete, the effect brings out a motor response.

Motor divison consist also of two parts:

• Somatic nervous system : from CNS which involves voluntary nervous system

• Auntonomic nervous system: we cannot control the action of smooth muscles, cardiac muscles, and glands, leading to involuntary responses that regulate bodily functions such as heart rate and digestion.

Nueroglia:

• supporting cells that wrap more delicate neurons , which are much smaller. Consist of six type.

Neuroglia in the CNS:

1. Astrocytes : most abundant glial cells. Support and anchor to their nutrient supply lines. Guid the migration of young neurons and formation of synapses. Also are important for mopping up leaked potassium ions and recycling neruotransmitters,

2. Microglia cells : The smallest glial cells, acting as the main immune defense of the central nervous system. They monitor the health of neurons and can transform into a type of macrophage to engulf and destroy pathogens or debris. Theri role is important due to the CNS having little access to the immune system

3. Ependymal cells : line the central cavities of the brain and spinal cord, helping to circulate cerebrospinal fluid (CSF) that cushions the brain and provides essential nutrients. They also can contribute to the formation of the blood-CSF barrier.

4. Oligodendrocytes: Line up on thicker nerve fibers in the CNS and produce a tight covering called a myelin sheath

Neuroglia in PNS:

1. Satellite cells : surround the neuron cell bodies and have same function as the astrocytes do in the CNS.

2. Schwann cells: form myelin sheaths around peripheral nerve fibers, facilitating rapid signal conduction and supporting nerve regeneration of damaged peripheral nerve fibers

Neurons: the structural unit of the nervous system.

• Neurons are amitotic which loose their ability to divide they cannot be replaced or destroyed.

• Neurons have hight metabolic rate and require oxygen and glucose.

Neuron Cell body : Contain a plasma membrane that is the receptive region that receives info from other neurons, located in the CNS protected by the vertebral column.

• Clusters of cell bodies called nuclei lie along PNS AKA Ganglia

• contains also mitochondria

• Rough ER known as chromatophilic substance

• Cytosyeletal elements: microtubles and neurofibrils which maintain the cell shape and integrity.

Neuron Processes:

• CNS consist of cell bodies and neuron process but the PNS only consist of neuron process.

• Dendrites of motor neurons are short , are the main receptors or input regions. They convay incoming messages algon the cell body and electrical signals are NOT Action Potential , but are known to be short graded potential.

• Axon: arise from cell body called axon hillock.

• Axon : known as nerve fibers

• Axon collaterals branch out at more or less right angles

• Axon in the CNS are called tracst

• Axon in PNS are called nerves

Characteristics of the Axon:

• Axon is the conducting region of the neruon , generates nerve impulses and transmits them, away from cell body along plasma membrane (axolemma)

• Anterogade movement: movement away from cell body

• Retrogade movement: toward body cell

Myelin Sheath:

• Protect and electrically stimulate fibers and increase transmission speed of nerve impulses.

• Myelinated fibers: conduct nerve impulses rapidly

• Nonmyelinated fibers: Conduct slowly

Myelination in the PNS :

• Formed by schwann cells that wrap around the axon, creating segments of myelin sheath that insulate the nerve fibers and enhance signal transmission.

• Plamsa membrane of myelinating cells contain much less protein than most cells. Myelin sheathes are good electrical stimulators.

• Myelin sheath. gaps occur in regular intervals along myelinated axons.

Myelination in the CNS:

• Contain both myelinated and nonmyelinated axons. The oligodendrocytes forms that from myelin sheath unlike the shwann cells, it can coil around since it has a flatter process

Classification of neurons:

• Multipolar neurons; contain three or more process and are the most common in human. Which are the main neurons in the CNS.

• Bipolar neurons: contain two process and are rare neurons found in retina of eye and olfactory mucosa.

• Unipolar neurons have single short process. Peripheral process is associated with sensory receptors and Cental process enters the CNS. These neurons originate from the bipolar neurons. These can be found in the ganglia in the PNS and function as sensory neurons. The central process of this cell is an axon because it conducts impulses away from cell body.

Functional Classification:

• Sensory receptor neurons transmit impulse from sensory receptors in the skin or internal organ INTO the CNS

• Motor Efferent neurons carry impulses AWAY from CNS to effector organs , Motor neurons are multipolar

• Interneurons are inbetween motor neurons and sensory and shuttle signals through CNS pathways making up 99% of the neurons in our body. Consisting of multipolar neurons.

Resting Membrane potential:

• Voltage : the measure of generated potential energy

• Current: the flow of electrical charge from one point to anothe r

• Ohm’s Law: gives relationship between voltage, current and resistance Current (i) = Voltage/ resistance , it states that the greater the voltage the greater the current.

Roles of membrane Ion Channels:

• Membrane channels are large proteins

• Leakage or (nongated channels) are always open

• “Gated” Channels change shape to open and close the channel in response to specific glands. There are three types of gated channels:

  1. Chemically gates channels AKA “ Lingand-gated channels” Open with the appropriate chemical.

  2. Voltage gated channels open and close in responds to changes in membrane potential.

  3. Mechanically gated channels open in response to a physical deformation of the receptor (sensory receptors for touch and pressure)

• Electrochemical gradient determins what direction an ion moves. Containing of two components.

• Concentration gradient when ions move along chemical concentration gradients from and are of HIGH concentration to an area of LOW concentration

• Electrical Gradient : Ions move toward and are opposite electrical charge

• These two gradients oppose each other

• Flowing ions create electrical current and voltage change across membrane V= Current (I) x Resistance (R)

Resting membrane potential :

• When the neuron is at rest, the resting membrane potential typically measures around -70 mV, minus sign indicates cytoplasmic side of the membrane is negative to the outside causing for it to be a Resting membrane potential which is polarized. Which can vary from -40mV to -90m.

Membrane Permeability:

• Membrane permeability is impremable to large anionic cytoplasmic proteins and slightly permeable to sodium, more permeable to Potassium and chloride, reflecting the properties of leakage ions channels in the membrane.

• Potassium diffuse out of the cell through a concentration gradient more easily then sodium entering. Potassium flowing out of the cell cause the cell to become more negative on the inside. For that reason a resting membrane potential is much greater ability for potassium to diffuse out of the cell than Na+ to diffuse in.

• The concentration gradient never runs down due tot he Sodium- Potassium Pumup: which first injects three NA+ from the cell and then transports two potassium out of the cell. this stabilizes the resting membrane potential

Changes in resting membrane potential:

• Can be produced by anything that alters ion concentrations on the two sides of the membrane or anythting that changes membrane permability.

• Changes in membrane potential can produce two types of signals:

  • Graded potentials : incoming signals operating over short distance that have graded strength

  • Action potentials: long distance signals of axons that always have same strength.

• Depolarization and Hyperpolarization describe changes in the mebrane potential

• Depolarization is a decrease in membrane potential. The inside of membrane becomes less negative (moves closer to zero) than the resting potential Example: -70mV to -65mv is a depolarization because it is closer to zero.

• Hyperpolarization is an increase in membrane potential: The inside of the membrane becomes more negative than resting potential. Ex: -70mV to -75mV.

Graded potentials are short lived , localized changed in the membrane potential. usually in dendrites or the cell body. Can be both depolarized or hyperpolarizations. The reason it is called graded is due to their magnification varies directly with stimulus. The stronger the stimuls the more voltage and further current flows.

• Graded potentials can change due to the neurons environment For instance : A receptor potential is produced when a sensory receptor is excited by its stimulus. A Postsynaptic potential is produced when stimulus is a neurotransmiiter released by another neuron.

Action Potentials (AP)

• The way neurons send signals over ling distances is by generating and Action potential. Only cells with excitable membranes can generate an action potential

• Action potential is a membrane’s potential with a total amplitue of 100mv , from -70mV to +30 mv.

• AP is also called a nerve impulse and is only generated in axons. Only creates an AP when adequentely stimulated.

• Voltage gated channels are only found on axons and critical for AP formation, no voltage gated channels, no AP.

• Voltage gated channels are activated by Graded potentials and spread along axon the dendritic and cell bodies

• In many neurons a local graded potential takes place in the inital segment of axon. It is generated by the peripheral process to the receptor region.

Generating an Action Potential:

1. All voltage gated channels are closed. Only leakage channels are open. Na+ (sodium) MUST have two gates a voltage sensitive activation gate that is closed at rest and responds to the to depolarization by opening and a inactivation gate that must be blocks channels once it opens. Both gates must be open for NA+ to enter but closing of either gate can close the channels. Potassium only needs one single voltage sensative gate and responds to depolarizations.

2. Depolarization: NA+ channels open : Voltage gated sodium channels open and Na+ goes into the cell where the influx causes the cells interior to become more negative by opening more Na+ channels to open.

   • When depolarization reaches a level between -55 and -50 mV it is known as the threshold. More Na+ channels open causing membrane potential to be less negative and then overshoots +30 mV, resulting in. the upward spike of AP.

   • Na+ permeability due to increases channels opening leads to greater depolarizarion.

3. Repolarizarion : Na+ channels are inactivating and voltage gated K+ channels open: Inactivation gates of Na+ start closing , permeability to Na+ declines to resting membrane , AP spike stops risinf and Na+ entry decline, allowing the Voltage gates K+ channels to open and come out of the cell following electrochemical gradient restoring the internal negativity.

4. Hyperpolarization: Caused due to K+ leaving the cell , Na+ channels have rest to original position. Repolarization restores resting elecrical conditions.

Threshold : membrane potential are which the outward current created by K+ movements is exactly equal to the inward current current created by Na+. Threshold is reached when membrane has been depoloarized by 15 to 20 mV. Local depolarization are graded potentials and their magnitude increase when stimulus become more intense

An action potential is an all or none, it either happens or doesn’t happen at all. An action potential must be propagated along the axon entire length. Depolarization move in forward directions which opens voltage gated channels and triggers action potentials, which repeats down the axon so that an AP is self propagating and continues along axon. Repolarization wave chase the depolarization wave down the length. This described the propagation process along a nonmyelinated axon.

Strong stimuli generate nerve impulse more frequently, allowing for the transmission of signals with greater intensity, which can impact the frequency and pattern of action potentials.

Refactory Periods : begins with the opening of Na+ channels and ends when Na+ channels being to rest to orginal states, ensures that each action potential is and all or none event and enforces one way transmission of AP

Relative refactor period comes after the absolute refractory period and is characterized by a reduced ability to generate another action potential, which occurs as the membrane potential returns to its resting state but is still not fully re-polarized.

The Degree of myelination increase the speed of propagation.

• Lightly myelinated conduct slower vs myelinated conduct faster

• Continuous conduction: AP continues to propagate along unmyelinated regions of the axon.

• Saltatory conduction AP is generated in mylinated fibers locals depolarization does not dissipate through adjacent membrane.

Multiple selerosis : automimmune diseas in result of immunes attach on myelin proteins and effects mainly young adults

Different group fibers:

• Group A fibers are mainly somatic sensory and serve skin, skeletal muscle and joints , and conduct impulses of 150 m/s containing think myelin sheaths

• Group B fibers are lightly myelinated and transmit fibers at much slower rate (15m/s)

• Group C fibers and non-myelinated and conduct at a even small pace (1 m/s)

• Fibers from B & C are typically responsible for transmitting sensory information from visceral organs and autonomic functions, which include pain.

Synapse : a junction that mediates information from one neuron to the next

• Persynaptic neuron : a neuron that conducts impulse toward the synapse.

• Postsynaptic neuron: neuron that sends signals away from the synapse.

Synapse contain two type

• Electrical synapse , much more less common , more abundant in the embryonic nervous tissue. Electrical synapse consist of mainly gap junctions found between adjacent neurons, allowing direct electrical communication and rapid transmission of signals. In adults these synapse are mainly found in the brain uses for jerky movements of the eye or the hippocampus , involves emotions

• Chemical synapse , more common. Specialized to allow release and reception of neurotransmitters .

• Chemical synapse is mainly made up of an axon terminal of the presynaptic neuron that contains neurotransmitters molecules is called the synaptic vesicles.

• The neurotransmitter receptor is mainly found in the postsynaptic neuron membrane, which is on a dendrite or cell body.

• The presynaptic and postsynaptic neuron are separated by a small fluid filled gap known as the synaptic cleft,

Chemical synapse process:

• AP arrives at axon terminal: Neurotransmission begins with the arrival of an AP. at presynaptic axon

• Voltage gated Ca2+open and Ca2+ enters axon terminal , depolarization of membrane opens Na+ and Ca2+ channels. Ca2+ floods down electrochemical gradient and from extracellular into terminal

• Ca2+ entry cause synaptic vesicles to release neurotransmitter by exocytosis:

• Neurotransmitter diffuses across synaptic cleft and binds to the synaptic receptor to the postsynaptic membrane

• This binding leads to the graded potential : neurotransmitter binds to receptor protein opens ion channels and creates graded potentials, depending on the receptor the postsynaptic may be either excited or inhibited.

• Neurontrasnmitter are terminated, or removed from the synaptic cleft through several mechanisms: reuptake by the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse, ensuring that the signaling is precise and transient. The neurotransmitter blocks reception of additional signals from presynaptic neruon.

• Synaptic delay is slow due to the diffusion of the neurotransmitter being released and diffused across synaptic cleft.

• Postsynaptic excitatory : short distance signaling spreads along axon hillock, and moves membrane toward threshold generating action potential . Na+ and K+ channles open and diffuse both at the same time

• Inhibitory presynaptic potentials (IPSPs) decrease the likelihood of an action potential occurring by hyperpolarizing the postsynaptic membrane, making it more negative and further from the threshold needed to trigger an action potential.

Neurotransmitters : chemical messengers released from neurons that transmit signals across synapses to other neurons or target cells, influencing excitatory or inhibitory responses.

Neurotransmitters are classified by the chemical structure:

ACH (Acetylocholine) released at neuromuscular junctions , released by all neurons that stimulate the skeletal muscle and ANS.

• When ACH receptor decrease in certain areas in Alzheimer’s disease.

Biogenic Amines

• Dopamine located in the substantia nigra of midbrain, hypothalamus, principle neruotransmitter of indirect motor pathways “feel good” neurotransmitter, increaes in schizophrenia, and deficient in parkinson’s disease.

• Serotonin: inhibitory , plays role in sleep, appetite, nausea, headache drugs that block its uptake relive anxiety and depression.

• Histamine, involved in wakefullness, appetite control, learning and memory

Amino Acids

• Glutamate: excitatory neurotransmitter, essential for synaptic plasticity, learning, and memory formation. excessive release of this can lead to blockage of blood vessels due to oxygen deprivation resulting in a stroke.

• GABA (gamma-aminobutyric acid): primary inhibitory neurotransmitter in the brain, crucial for regulating neuronal excitability and maintaining balance in the central nervous system. Binds with alcohol and modulates its effects, which can lead to increased sedation and impairment of cognitive functions.

• Glycine: another inhibitory neurotransmitter that plays a significant role in the spinal cord, helping to control motor functions and regulate sleep-wake cycles.

Peptides: short chains of amino acids that function as neurotransmitters or neuromodulators, playing pivotal roles in pain perception, reward processing, and stress response, often acting in conjunction with other neurotransmitters to modulate various physiological processes.

• Substance P is an important mediator for pain signals

• Endorphins, dynorphin and enkephalins , are all natural opiates that inhibit pain and mimicked by morphine, heroin, and methadone.

• Endorphins release enhances the body's ability to cope with pain and stress, promoting a sense of well-being and euphoria. “Runners high”

Purines : nigtogen-containing bases that make up DNA and RNA .

Channel linked receptors are ligandgated channels that mediate direct neurotransmitters actions , respond to GABA and gykcine and allow for CI- to pass which cause hyperpolarization.

The Nervous System Overview
The nervous system is a master controlling and communicating system of the body with three main functions:

1. Sensory Input: Gathering information from sensory receptors to monitor changes inside and outside the body.

2. Integration: Processing and interpreting sensory input to decide on an appropriate response.

3. Motor Output: Activating effector organs (muscles and glands) to produce responses based on integrated sensory information.

Divisions of the Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord, located in the dorsal body cavity, dictating motor output based on reflexes, current conditions, and past experiences.

• Peripheral Nervous System (PNS): Comprises nerves extending from the spinal cord, carrying nerve impulses.

Subdivisions of PNS:

1. Sensory (Afferent) Division: Transmits sensory information to the CNS; includes:

   • Somatic sensory fibers (from skin, joints, and skeletal muscles)

   • Visceral sensory fibers (from visceral organs)

2. Motor (Efferent) Division: Carries impulses from the CNS to effector organs; includes:

   • Somatic Nervous System (voluntary control)

   • Autonomic Nervous System (involuntary control)

Neuroglia: Supporting cells in the CNS and PNS that assist neurons.

• CNS Neuroglia Types:

  1. Astrocytes: Most abundant, support and anchor neurons, recycle neurotransmitters.

  2. Microglia: Immune defense, monitor neuron health, can engulf pathogens.

  3. Ependymal Cells: Line central cavities, circulation of cerebrospinal fluid (CSF).

  4. Oligodendrocytes: Form myelin sheath around CNS nerve fibers.

• PNS Neuroglia Types:

  1. Satellite Cells: Surround neuron cell bodies, similar function to astrocytes.

  2. Schwann Cells: Form myelin sheaths around peripheral nerve fibers.

Neurons: The structural unit of the nervous system, characterized by:

• Amitotic nature (cannot divide or be replaced)

• High metabolic rate requiring oxygen and glucose
  Neuron Anatomy:

• Cell Body: Contains plasma membrane, mytochondria, rough ER (chromatophilic substance), and cytoskeletal elements (microtubules, neurofibrils).

• Processes:

  • Dendrites: Short, main input regions conveying messages to the cell body.

  • Axon: Conducting region generating and transmitting impulses away from the cell body; can have collaterals and is called a nerve fiber. Axons are categorized differently in CNS (tracts) and PNS (nerves).

Myelin Sheath:

• Protects and electrically insulates fibers, increasing the transmission speed of nerve impulses.

• Formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

Classification of Neurons:

1. Multipolar Neurons: Most common, with three or more processes, primarily in CNS.

2. Bipolar Neurons: Rare, with two processes, found in retina and olfactory mucosa.

3. Unipolar Neurons: Single short process, mainly sensory neurons in PNS ganglia.

Functional Classification:

• Sensory Neurons: Transmit impulses from sensory receptors to CNS.

• Motor (Efferent) Neurons: Carry impulses away from CNS to effector organs (multipolar).

• Interneurons: Shuttle signals through CNS pathways, predominantly multipolar.

Resting Membrane Potential: Measures around -70 mV; it is polarized due to differing ion concentrations.

• Influenced by membrane permeability to potassium and sodium, with the sodium-potassium pump maintaining gradients.

Changes in Membrane Potential:

• Graded Potentials: Localized changes, can be depolarizations or hyperpolarizations.

• Action Potentials: Long-distance signals initiated by graded potentials, characterized by rapid depolarization and repolarization processes.

Propagation of Action Potentials:

• Continuous Conduction: Unmyelinated axons propagate AP along their length.

• Saltatory Conduction: Myelinated fibers skip along the axon, facilitating faster conduction.

• Refractory Periods: Ensure one-way transmission of APs with absolute and relative refractory periods.

Synapses: Connections between neurons, consisting of presynaptic and postsynaptic neurons.

• Electrical Synapses: Allow rapid transmission, found mainly in embryonic nervous tissue.

• Chemical Synapses: More common, involve neurotransmitter release and binding, synaptic cleft.

Neurotransmitters: Chemical messengers that influence various functions:

• Types Include:

  • ACh (Acetylcholine): Involved in muscular and autonomic functions.

  • Biogenic Amines: Dopamine, serotonin, histamine affecting mood, sleep, and motor control.

  • Amino Acids: Glutamate (excitatory), GABA (inhibitory), glycine (motor control).

  • Peptides: Endorphins, substance P, involved in pain and stress response.

  • Purines: Involved in energy transfer in cells.

The Nervous System Overview
The nervous system is a master controlling and communicating system of the body with three main functions:

1. Sensory Input: Gathering information from sensory receptors to monitor changes inside and outside the body.

2. Integration: Processing and interpreting sensory input to decide on an appropriate response.

3. Motor Output: Activating effector organs (muscles and glands) to produce responses based on integrated sensory information.

Divisions of the Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord, located in the dorsal body cavity, dictating motor output based on reflexes, current conditions, and past experiences.

• Peripheral Nervous System (PNS): Comprises nerves extending from the spinal cord, carrying nerve impulses.

Subdivisions of PNS:

1. Sensory (Afferent) Division: Transmits sensory information to the CNS; includes:

   • Somatic sensory fibers (from skin, joints, and skeletal muscles)

   • Visceral sensory fibers (from visceral organs)

2. Motor (Efferent) Division: Carries impulses from the CNS to effector organs; includes:

   • Somatic Nervous System (voluntary control)

   • Autonomic Nervous System (involuntary control)

Neuroglia: Supporting cells in the CNS and PNS that assist neurons.

• CNS Neuroglia Types:

  1. Astrocytes: Most abundant, support and anchor neurons, recycle neurotransmitters.

  2. Microglia: Immune defense, monitor neuron health, can engulf pathogens.

  3. Ependymal Cells: Line central cavities, circulation of cerebrospinal fluid (CSF).

  4. Oligodendrocytes: Form myelin sheath around CNS nerve fibers.

• PNS Neuroglia Types:

  1. Satellite Cells: Surround neuron cell bodies, similar function to astrocytes.

  2. Schwann Cells: Form myelin sheaths around peripheral nerve fibers.

Neurons: The structural unit of the nervous system, characterized by:

• Amitotic nature (cannot divide or be replaced)

• High metabolic rate requiring oxygen and glucose
  Neuron Anatomy:

• Cell Body: Contains plasma membrane, mytochondria, rough ER (chromatophilic substance), and cytoskeletal elements (microtubules, neurofibrils).

• Processes:

  • Dendrites: Short, main input regions conveying messages to the cell body.

  • Axon: Conducting region generating and transmitting impulses away from the cell body; can have collaterals and is called a nerve fiber. Axons are categorized differently in CNS (tracts) and PNS (nerves).

Myelin Sheath:

• Protects and electrically insulates fibers, increasing the transmission speed of nerve impulses.

• Formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

Classification of Neurons:

1. Multipolar Neurons: Most common, with three or more processes, primarily in CNS.

2. Bipolar Neurons: Rare, with two processes, found in retina and olfactory mucosa.

3. Unipolar Neurons: Single short process, mainly sensory neurons in PNS ganglia.

Functional Classification:

• Sensory Neurons: Transmit impulses from sensory receptors to CNS.

• Motor (Efferent) Neurons: Carry impulses away from CNS to effector organs (multipolar).

• Interneurons: Shuttle signals through CNS pathways, predominantly multipolar.

Resting Membrane Potential: Measures around -70 mV; it is polarized due to differing ion concentrations.

• Influenced by membrane permeability to potassium and sodium, with the sodium-potassium pump maintaining gradients.

Changes in Membrane Potential:

• Graded Potentials: Localized changes, can be depolarizations or hyperpolarizations.

• Action Potentials: Long-distance signals initiated by graded potentials, characterized by rapid depolarization and repolarization processes.

Propagation of Action Potentials:

• Continuous Conduction: Unmyelinated axons propagate AP along their length.

• Saltatory Conduction: Myelinated fibers skip along the axon, facilitating faster conduction.

• Refractory Periods: Ensure one-way transmission of APs with absolute and relative refractory periods.

Synapses: Connections between neurons, consisting of presynaptic and postsynaptic neurons.

• Electrical Synapses: Allow rapid transmission, found mainly in embryonic nervous tissue.

• Chemical Synapses: More common, involve neurotransmitter release and binding, synaptic cleft.

Neurotransmitters: Chemical messengers that influence various functions:

• Types Include:

  • ACh (Acetylcholine): Involved in muscular and autonomic functions.

  • Biogenic Amines: Dopamine, serotonin, histamine affecting mood, sleep, and motor control.

  • Amino Acids: Glutamate (excitatory), GABA (inhibitory), glycine (motor control).

  • Peptides: Endorphins, substance P, involved in pain and stress response.

  • Purines: Involved in energy transfer in cells.